Title,Question,Answer
Cells and organisms,Are all bacterias unicellular or just some?,"Most bacteria are unicellular. Some species of bacteria build up colonies in which many individual cells unite. Cells within those colonies can share tasks and even adopt different morphology (the way they look). In several cases it is very difficult to decide whether something is a colony of many cells, or one big multicellular organism. Scientists have been debating about this for long time now.

Learn more about it here:
https://www.jstor.org/stable/24989125
https://onlinelibrary.wiley.com/doi/epdf/10.1002/bies.20740
https://sfamjournals.onlinelibrary.wiley.com/doi/full/10.1111/j.1758-2229.2010.00215.x?casa_token=xG3l6_YtRx8AAAAA%3AV-6My7f896SeXRpQyshvIepvNNsJDnfpaEXcnFADjSpbqJ0B2nikZu-VvfKLXbD131QCjlI_ekm8UU8
https://royalsocietypublishing.org/doi/full/10.1098/rsif.2011.0102"
Cells and organisms,So I have 2 questions. 1 is last year we learned that atoms are the smallest things but this year we learned that cells are the smallest things so which is it. And number 2 if you have 2 unicellular things and they combine would that make it a multicellular,"The cell is the smallest unit of life, and the atom is the smallest unit of a chemical element. Cells are much bigger, and they’re made up of many, many atoms. 

Atoms aren’t even the smallest thing, though! They are made of tiny particles including protons, neutrons, and electrons. Protons and neutrons are made of even smaller things called quarks!

Two individual cells can be together to make something multicellular. If you take any two random cells, though, they won’t necessarily make a multicellular organism."
Cells and organisms,"How long do cells live? And if they do not live very long how are we alive? And if it is because they multiply, how do we die?","Cells in your body are constantly dying, but also constantly reproducing, so you live a much longer life than your cells. We die not when our cells die, but when they stop preforming the functions they are supposed to."
Cells and organisms,is a cell smaller than a atom or Atoms the smallest thing ever,"Cells are made up of many, many, many atoms, so they are definitely bigger than atoms. 

Atoms are very small (brooklyn.cuny.edu says “ a row of 10^8 (or 100,000,000) atoms would stretch a centimeter, about the size of your fingernail. ”). However, there are things even smaller than atoms! Atoms are actually made up of some combination of protons, neutrons, and electrons. The protons and neutrons make up the nucleus at the center. Just for scale, if the whole atom were the size of an American football stadium, the nucleus would be the size of a golf ball inside of it!

I hope this helps!"
Cells and organisms,Are eggs single cells?,"Yes, eggs, in a biological sense, are indeed single cells. Eggs in the common term (like chicken eggs) are basically containers that hold that cell (the yolk)."
Cells and organisms,What is that how small the cell?,i thought you were me for a second
Cells and organisms,what are cell divisions,"Cell divisions may sound like different groups, but it is a process of a cell splitting into two to make more cells"
Cells and organisms,What is that red blood cell,"this is a cell, which has protein called hemoglobin, that transports oxygen the lungs to the rest of the body.
imagine this, the hemoglobin is a car that transports the oxygen to and from somewhere, just like a taxi. then it drops the the oxygen off to its destination for example different types of organs."
Cells and organisms,what is made out of 1 cell?,some things that are teenie tiny like micro stuffs (i mean like the tiny bacteria in the ocean kind of stuffs)
Cells and organisms,If we got cells and our parents got cells and our grandparents got cells and our ancestors got cells where did the first cell come from?,"a smarter and shorter way to say it is:How did the first cell originate?

anyway to answer you qwestion, 
Enclosure of self-replicating RNA in a phospholipid membrane. The first cell is thought to have arisen by the enclosure of self-replicating RNA and associated molecules in a membrane composed of phospholipids.

i hoped this helped."
Sensory processing and the brain,why do we need to blink?,"It helps your eyes stay moist, and keeps some grime out of them."
Sensory processing and the brain,so what about the people that cant feel pain how does that work can they just not feel anything or is it just like a wired sensation or something and why do we feel pain what sense is that because it didn't explain that in the video?,"Pain is its own sense. The human body has pain receptors all over. Pain receptors send a signal to the brain through the neurons that tell the brain something is wrong. That message is what we perceive as pain. Some individuals have a different genetic trait that results in a different sensation of pain: it simply doesn't hurt. They feel something, but not the unpleasantries that everyone else feels."
Sensory processing and the brain,"so what happend to the blind poeple?
not being rude or anything",they became bilnd
Sensory processing and the brain,If your skin got ripped off would the nervous cells there die? Would you still feel pain if you pinch the scar left after? Or would the nervous system heal itself after?!,"If your skin were to be ripped off, the cells there would not die, but no, pinching the scar would not hurt just because you have been wounded there before. Your body would heal itself over time.

( but you should definitely go to the hospital to get some medical attention if this were to happen )"
Sensory processing and the brain,What happens if we don’t blink? Do we die?,"I don’t think it’s possible to not blink. When we blink, our eyelids protect us from dust and other things. Our eyes are also moistened by our tear glands each time we blink. That’s why staring contests are so hard! This is also why we blink when something unexpected comes toward our face. 

However, because snakes and fish don’t have eyelids, they can’t blink at all! So, never try to have a staring contest with a fish.😉

But to answer your question, no, I don’t think you would die if you never blinked, just that your eyes would get really irritated, and maybe even get damaged. But speaking seriously, I don’t think you could even keep your eyes open for that long! 

Hope that helped!"
Sensory processing and the brain,will i die if my lungs stop working?,"Yes,without being able to breath it's impossible to survive."
Sensory processing and the brain,"if someone is donating a kidney will they have to cut open their stomatch?
is it possible to donate a brain?","When someone donates a kidney, the process typically involves a surgical procedure called a nephrectomy. However, the surgeon does not need to cut open the stomach. Instead, they make small incisions in the side or abdomen to remove the kidney. This is known as laparoscopic surgery, which is minimally invasive and offers several benefits such as quicker recovery and minimal scarring.

As for donating a brain, currently, it is not possible to donate a brain while the donor is alive. The brain is a highly complex and vital organ that cannot be transplanted from one person to another. Brain activity and consciousness are intricately linked, making it challenging to transfer such functions between individuals. At present, brain donation for scientific research purposes typically occurs after a person's passing to study specific conditions or diseases."
Sensory processing and the brain,Why is stimuli related to sight called electromagnetic stimuli??,"What is the stimulus for the sense of sight?
Image result for Why is stimuli related to sight called electromagnetic stimuli??
Visual (seeing) Sight is processed through the 'Visual' sense. Visual stimuli is picked up by visual receptors located in the eye. Visual receptors are stimulated by light, colour and movement. I hope this answers your question."
Cell parts and functions,has there ever been anything that had both animal and plant cells?,"From what i searched i didn't see any organism that does but there is something called 
Euglena and it is  found in brackish water habitats."
Cell parts and functions,vote if you love your mom,my mom is ded
Cell parts and functions,"Hey quick question,

Do humans need mitochondria to survive or will they be okay without them?","Yes, humans (and all organisms with mitochondria) need them to survive. They break down sugars, giving our cells the energy they need to function."
Cell parts and functions,Am I the only one here from 2023?,No 2023 here as well.
Cell parts and functions,"When we cook vegetables sometimes they become floppy or mushy, does that mean that the cell wall is being broken down?","Great question, from logic and what I looked up, yes! It is breaking the cell walls. It makes it easier to eat and digest."
Cell parts and functions,"What are the differences between an animal cell and a plant cell? I know the differences between them, they are mitochondrion(animal cells) and chloroplast(plant cells). But what else?","Actually, you are partially wrong. Plant cells do indeed have chloroplasts while animal cells do not, but both types of cells have mitochondria.

Animal cells have structures called lysosomes (which are basically organelles containing an extremely acidic fluid to break down objects) and centrosomes (used in cell reproduction). Plant cells have neither of these.

Plant cells have cell walls that surround their cell membrane, and large central vacuoles that make the cell rigid. Animal cells have neither of these structures.

Additionally, animal cells usually have an irregular shape, while plant cells are more rectangular.

Does that answer your question?"
Cell parts and functions,How does the mitochondria and the chloroplast work together,"The chloroplast creates food for plants (sugars), and the mitochondria breaks them down for energy."
Cell parts and functions,"I have 2 questions! 
1: When we cook vegetables  sometimes they become floppy or mushy, does that mean that the cell wall is being broken down? 
2: Has there ever been a mutation where a animal cell contains something that only a plant cell has or vice versa?",It's probably being melted because of the heat for question 1
Cell parts and functions,i dont have a phone :(,me neither:(
Cell parts and functions,In which organelle does photosynthesis occur?,The Chloroplast.
Organization in the human body,Is an orange called an orange because the inside of an orange is orange or is an orage called an orange because the outside of an orange is orange??,the name of the fruit orange is older than the name of the color orange. orange was called "yellow-red" back then. Then they changed the name to orange because oranges were  orange.
Organization in the human body,can you sneeze into your organ?,i dont know
Organization in the human body,can foods cause our organs to fail?,Yes certain foods are not good for are organs if you eat to much of those certain food it can result in organ failure.
Organization in the human body,hi i think math is fun. Am i right?,Imma have to disagree
Organization in the human body,what happens if the tissues dont have cells anymore?,if tissues are made of cells if tissues don't have cells they simply just wont be tissues
Organization in the human body,"What happens when you have a heart attack? I know somewhat, your arteries get clogged and then your heart can't beat normally right?","During a heart attack, your arteries get clogged which can cause a lack of blood flow that causes the tissue in the heart muscle to die which can cause your heartbeat to slow down, and this can lead to death. Hope this helps!"
Organization in the human body,how many orgns are in the human body,"Altogether there are seventy-eight main organs within the human body. These organs work in coordination to give rise to several organ systems. Among these 78 organs, five organs are considered vital for survival. These include the heart, brain, kidneys, liver and lungs."
Organization in the human body,"if there are many tissue cells, can you count them all?","No because: 
1: Everyone has a different amount.
2: The amount constantly changes as cells die and are created again.
3: There are so many that it would take forever to count them."
Organization in the human body,"So, if the organ is made of tissues. Human cells are tissues too?","Actually, this is incorrect. If you go back and read the article, you will find that human cells are the smallest "unit", so to speak, of the organization of the human body. Tissues are made up of many cells. So human cells are not tissues; rather, tissues are groups of specialized human cells"
Sexual and asexual reproduction,Why does one parent make the offspring identical?,"If there is only one parent contributing genes, all of the genes from that parent are passed on, making the offspring genetically identical. If there are two parents, then half of the genes from one parent are contributed, and half the genes from the other parent. They mix and make offspring that aren't identical to either parent."
Sexual and asexual reproduction,"This sounds like a lame question, but if one type of bacteria always asexually produces, then would the genes of the very first kind of bacteria be the exact same as the newest bacteria just produced? Will there ever be a mistake in the genes or an addition of genes based on evolution and adaptation?","Well, bacteria are simple and therefore often lack mutation prevention systems that more complicated organisms have. They also reproduce a lot. Making mistakes are very rare, but they definitely do happen [Referense: today's biodiversity]. *Today's bactera are very different from the first bacteriums* because they've gone through _trillions_ of reproductions (assuming 1 thousand reproductions happen a year). And no, it's not a lame question."
Sexual and asexual reproduction,"If two parents make another and each give the offspring 1/2 of their DNA, why do some offspring look or act way more like one parent?","As for the appearance I am not sure, but behaviour is mostly based off of which parent influenced the child more after birth."
Sexual and asexual reproduction,What are the advantages and disadvantages of asexual and sexual?,"some advantages of a sexual, and asexual beings is that they both create life on earth, and somewhat do the same job!"
Sexual and asexual reproduction,```How does parents make twins and does that happen with cells?```,Twins happen when 2 egg cells get fertilized at the same time. Identical twins happen when a fertilized egg cell split into two.
Sexual and asexual reproduction,"What if a female dog and another female dog made out, would that make a puppy?",You need a male and a female to reproduce.
Sexual and asexual reproduction,What came first the chicken or the egg??,"The egg, because the first chicken was probably mutant."
Sexual and asexual reproduction,"So if parents give a birth to twins or triplets, does it mean that the children have each of their personality, looking, and stuff from the parents?","First, let’s make it clear that there are two kinds of twins/triplets: fraternal and identical. Fraternal twins happen when two eggs come out of the fallopian tubes, and both eggs are fertilized by the sperm. This means that two babies will grow inside their mother’s uterus, and the babies will not be the same.
However, identical twins happen when only one egg comes out of the fallopian tubes. After the egg is fertilized, it starts growing. An egg grows when it multiplies. This means that the egg splits into two parts, and each of those parts split into two parts, and so on. But since the egg splits so fast, sometimes it makes mistakes. Identical twins happen when the egg splits so quickly that it becomes two separate pieces, and then each of those pieces becomes its own baby. The egg comes from the mother and has her genes, and the sperm comes from the father and has his genes. Eggs are always female, or X. The sperm can be either X or Y, male. If an X sperm meets an egg, you get a baby girl. If a Y sperm meets an egg, you get a boy. But if you’re asking if twins are clones of their parents, then the answer is no. 

Hope that helps!"
Organism growth and the environment,Does a yellow dandilion turn into the white fluff version? Also if a dandilion grows some place that doesnt have a lot going on how do their seeds desperse? Do they just fall off? or do the seeds stay on until the plant dies?,"It depends what you mean, by nothing going on,if you mean no wind or animal dispersal, it wound most likely fall to the ground."
Organism growth and the environment,one time my dog ate a firefly and then she started foaming at the mouth... she was fine after a drink of water tho. Spicy bug?,"Also maybe because of the chemicals inside the firefly, as t=it uses those to create bioluminescence."
Organism growth and the environment,Does the average organism dwell better in hot or cold environments?,"Depends on its adaptations, but on average, I would say lean towards the hotter side as the air is more humid and since there tends to be more biodiversity in places like Costa Rica."
Organism growth and the environment,What if we interbred two species? Will the two different species provide their separate reproductive cells and fuse them into the offspring? Or is it something completely different?,"If you interbred a species,the offspring would have half of both of the parents genes.Search up interbred species images, and it will show you what happens when you interbreed any species."
Organism growth and the environment,I watched the video and I got really sad because my dog is really hurting right now and I feel really bad for him because he has been my best friend since the day that my dad brought him home. Anyways no more about me do you guys have any dogs?,"used to have the cutest hound mix puppy ever. dont have him anymore, couldnt buy his food anymore. he was so cute. i loved Buddy"
Organism growth and the environment,"what is the breed of the little dog?

-Elsie",Chihuaha
Organism growth and the environment,why are the dogs in the picture chained to each other?,"They aren't. The great Dane's leash is touching the ground, not attached to the chihuahua."
Animal behavior and offspring success,I went to a zoo once and a male peacock was showing off its feathers to a female peacock and the male peacock got rejected.,emotional damage
Animal behavior and offspring success,"Did you know?
Insects are more likely to asexually reproduce than animals?
FACTS.","Yes, some insects do reproduce asexually, but remember that insects are a type of animal, too!"
Animal behavior and offspring success,Do male birds always attract female birds like this or is there some other way?,"Not always.
When it comes to birds, the male usually attracts the female. This can be done through attractive looks, flying, fighting, and, of course, offerings."
Animal behavior and offspring success,how on earth does asexual reproduction work? is it for the organisms that don't require a mate to produce offspring?,"Yes, they don't require a mate, but it's kinda like cell division, to be honest."
Animal behavior and offspring success,Some behaviors increase the chance of producing offspring. These include displays that attract mates.,Correct.
Animal behavior and offspring success,"Why don't all species reproduce asexually? If they did, wouldn't it drive reproductive success? I'm asking this because if every animal reproduce asexually they wouldn't need to mate which would waste less time and energy.","Sexual reproduction actually contributes genetic diversity to populations. When the different animals have different traits, it’s more likely that some of them will have traits that let them survive in changing environments."
Animal behavior and offspring success,will there ever be a bird that can make a offpring by asexual,no. all birds have to have sex with a mate to make offspring
Animal behavior and offspring success,"I live on a farm, and I keep getting chased and KICKED by the rooster. Not only that but he chases the hens and tries get on their backs to mate with them. One of our hens hates it, and she runs away from him but sometimes gets caught. I hate that rooster. He hurts me ALL THE TIME by kicking me and chasing me around. 😭😭",Btw I have chickens too. And you just have to act calm around the rooster. also its normal for him to just want to mate 1 hen. though it crazy
Animal behavior and offspring success,does everything do offspring?,yes! every organism produces offspring in one way or another
Animal behavior and offspring success,can someone explain to me in the easiest way on what offspring reproduction means?,"The more babies (that actually survive birth and childhood),the higher the reproductive success."
Plant reproductive success,"I'm so glad I'm contributing to nature, by blowing my share of dandelions in exchange for the small small price of a wish:)","Actually, I have something else to say too. Dandelions actually spread it's children;) across the world using the wind. But since humans like blowing them so much, I predict that dandelions will start growing up near cities where more people live! Tell me if you see dandelions growing in a corner of your park!:-))))"
Plant reproductive success,"Bee's are cute, Who agrees?",There are people who agree or disagree with your question.
Plant reproductive success,be serious does anyone like Khan Academy?,yea its easy I'm not mad
Plant reproductive success,what happens if theres no more bees?,A drastic effect on the amount of pollinators likely causing a mass extinction. (That is if they die off very quickly).
Plant reproductive success,I don't understand this part. May I please receive an explanation for this part?,"Plants reproduce by pollinators and by seed despersal which means that bees,bats,and other pollinators carry pollen from plant to plant, this causes plants to create offspring (or plant children) then they do seed despersal which is where the plants seeds get sent far away. Normally the seeds get blown far away, the seeds are carried by birds, and even humans can cause seed despersal. Does this explanation help?"
Plant reproductive success,can insects help with pollination or seed dispersal,"Bees, wasps, butterflies, beetles, flies and moths can be pollinators. These aren't insects, but hummingbirds and bats can pollinate too. Pretty much any living creature that eats fruits with seeds in them can do seed dispersal as long as the seeds can survive going through their digestive system."
Plant reproductive success,What happens when one of the animals traveling the pollan get killed by another animal.,"Then the pollen would not get to a plant, making the pollen useless (unless some other thing carried the pollen to the plant after it fell)"
Plant reproductive success,What type of bee is that,that is timmy from south park
Activity: how can measuring cellular respiration help us reach a fitness goal?,"Is the person really climbing the stairs for exercise, or literally just to get into their house?",The person is probably doing neither and just posing for the camera
Activity: how can measuring cellular respiration help us reach a fitness goal?,why is the biology/science khan academy comment section not professional compared to the other subjects LMAO,Because we are goofy goobers.
Activity: how can measuring cellular respiration help us reach a fitness goal?,if all brains are made and look exactly the same then how do we have differing prefrences and ways of looking at things,Electric in brain go brrrrrrrrrrrrrrrrr
Activity: how can measuring cellular respiration help us reach a fitness goal?,what would happen if we became our fav animals for a week,"when we are human again, we will know what it feels like to be that animal."
Photosynthesis in organisms,"How do plants you buy at the store, stay alive in just water, and no dirt? Also, why are some plants supposed to get direct sun? Thanks!",the plants are already being put in mineral water. It isn't the dirt that helps the plant it is the minerals that help it grow.
Photosynthesis in organisms,"This says, "Photosynthesis is USUALLY carried out in chloroplasts." What are some examples of it being carried out in something else?","i have no idea at all, sure, call me dumb i probably am i think i am, i waste time,and i am a waste"
Photosynthesis in organisms,How the plants survive when they are in shops,These plants get the light they need either through a window or from a lamp that mimics the kind of light coming from the sun.
Photosynthesis in organisms,what else can plants live in instead of soil,"I have an air plant it is a specific kind of tropical plant that lives off of air moisture and a bit of water I give it. It has no roots, although it can develop feelers that allow it to latch onto branches."
Photosynthesis in organisms,Does a plant need soil to live?,"Plants don't require soil to live if you have access to water with the correct nutrients for plants in it. That's why lotuses live in mud/muddy water, it's because mud is full of nutrients that the lotus needs, so the lotus will do better in the muddy water as opposed to just water (without minerals, obviously)! Some plants need soil, however. They may be able to survive a period of time in water with their food, but succulents and cacti need to be transferred to soil after water propagation. Maybe you would find it interesting to research more into this? Anyways, hope this answers your question. Ask more if you need to, there's always somebody on Khan Academy that can help!"
Photosynthesis in organisms,How long can a plant survive without water?,"Depends on the plant. For example, some cacti can go two years, but some flowers can't go a week without it."
Photosynthesis in organisms,Can the plant also survive with out water for one day?,"Plants can go to a maximum of a week without water, right?"
Photosynthesis in organisms,how do plants stay alive,"The sunlight, water, and carbon dioxide make sugars which the plant consumes to stay alive."
Photosynthesis in organisms,what is chlorophyll,"Chlorophyll is a naturally-produced chemical that helps in the photosynthesis process by, in fact, absorbing the photons (sunlight) used to rearrange atoms, as said in the second point. It also is actually a pigment, giving plants their green color!"
Food and energy in organisms,if a dog eats a cat is the dog a herbivore,Herbivores eats only plants.
Food and energy in organisms,what do you get when you eat fish?,"Usually you get the protein, sugar, and energy from the food. It depends on what you put on the fish. You digest it, and bring all of the good molecules to the cells."
Food and energy in organisms,what if someone absorbs too many molecules or their stomach digest too much food?,Probably a stomach ache or vomiting.
Food and energy in organisms,Why is it that when you get older you usually get smaller?,"Your body stops working as hard as it did, your intake of food gets slower and slower, so you have less and less molecules entering your body, but you keep expelling them (via going to the bathroom, vomiting, etc) that is also a reason why we pass on at a similar age."
Food and energy in organisms,"So if i am what i eat, would i be 60% Pizza? or just bread, sauce,Cheese, and whatever topping i eat along with it?",Umm no.. that's not what they mean by "you are what you eat" they mean we have the same molecules as the food we eat not the same ingredients.
Food and energy in organisms,I do not think you should put sugar in bread; why it it classified as a 'sugar' ?,"You do put sugar in most breads, and it is a carbohydrate, which is a type of sugar."
Food and energy in organisms,Will you get sick if you absorb too much molecules?,"Yes! When you are finished with thanksgiving dinner, dont you feel stuffed? You feel sick to your stomach and just want to lay down for awhile. If you eat too much food, flavored water, etc, your body will have to do get rid of them somehow, (going to the bathroom or vomiting, in both you start to feel sick)"
Food and energy in organisms,how do they know what the things give off of ?,"There are a few ways you can check this:
1) With a microscope XD
2) If you don't have a microscope, you can submerge a plant completely underwater. Soon, you will see bubbles. Those bubbles are oxygen bubbles.
Of course, it is best to do both of these, for it proves both of the outputs."
Food and energy in organisms,what do sugar proteins and fats do for our body,"To put it simply, sugar and fats mainly give us energy. Proteins are also used for the same, but help the development and growth of muscles and hormones too."
Cellular respiration,I don’t understand how both animal and _plant cells_ release carbon dioxide during cellular respiration? I’m probably confusing it with photosynthesis but how are they different? They seem to serve the same function (i.e.: usable energy to grow and store.),"Photosynthesis uses energy (from the sun) to convert water and carbon dioxide into glucose and oxygen. Then the glucose can be stored for later use. Cellular respiration turns glucose and oxygen into water and carbon dioxide, releasing energy for the organism to use. 

Does that help?"
Cellular respiration,isn't respiration basically breathing?,"Technically speaking, breathing is the process of ventilating air in and out of your body, while respiration is the mitochondrial task of using the gases you breathe to create energy. Both processes work so closely together that the terms could be used interchangably in a broad sense, but there is a difference between the two."
Cellular respiration,does anyone else restart exercises whenever you get a question wrong?,I do.
Cellular respiration,How does your body turn glucose and oxygen into carbon dioxide and water,Chemistry. A chemical reaction occurs inside your mitochondria that results in the rearranging of the atoms in the inputs.
Cellular respiration,what does glucose mean,its a simple sugar and its your body's main source of energy
Cellular respiration,i did not understand anything bakaroo,Cellular respiration is a process that happens inside an organism’s cells. This process releases energy that can be used by the organism to live and grow.
Cellular respiration,What is mitochondria,"mitochondria are the organelles that convert sugars and oxygen into carbon dioxide, water, and energy."
"Populations, communities, and ecosystems","Make me get over 50 votes to get an earth badge so then i will get my nintendo switch back plzzzzzzz 

*edited :btw i got my switch back and didnt know im famous on this*",Why would they take it away anyway unless you were using it too much? Books are better anyway. Have you read _The Hiding Place_? It's SO good!
"Populations, communities, and ecosystems",what came first the egg or chicken?,A circle has no beginning.
"Populations, communities, and ecosystems",how is all the population stick together,because they are the same species.
"Populations, communities, and ecosystems",what is life and what should we live for?,i think that question leans into philosiphy more than biology
"Populations, communities, and ecosystems",this is not biology this is english why are they just feeding us definitions and saying its biology sure it may be slightly related to biology but this is literally just definitions,we invent concepts to not have to keep making sense of the same things over and over again
"Populations, communities, and ecosystems",is the programing lesson beginner friendly?,"Very much so. But please ask the question there, and not in the biology section."
"Populations, communities, and ecosystems",how many things can a ecostyem get befpre there is too many animals or objects in it?,"This is an interesting question...... I think it would depend on the ecosystem itself and how populated it was. For example, if there were a desert with a lot of animals in it then most of them wouldn't last long. There just wouldn't be enough food to go around."
"Populations, communities, and ecosystems",what if we lived ina ecosystem,We are living in an ecosystem
"Populations, communities, and ecosystems",why didn't the rock show up in the community part,because communities only include living things
Resources and population growth,what bird is that,"They are seagulls, look at the image caption"
Resources and population growth,what is the difference between a community and an ecosystem,"A *community* is a group of _different_ animals and organisms living in the same area while an *ecosystem* is _all_ of the organisms in an area plus every _nonliving_ part of the environment (sand, water, dirt, air etc.)."
Resources and population growth,"how do i  know whats an ecosystem, population, and community?",An ecosystem is everything that is alive and non living like water and soil along with the animals and plants. A population is a certain type of animal living together. A community is all the living things that are living close to each other. Does this help?
Resources and population growth,"But what will happen if the is water,food, air and space but too many animals and they start fighting and killing each other? Can that affect the growth and health of the animals?","yeah, they will fight with each other to get the limited amount of resources"
Resources and population growth,can we help ecosystem's,We can help ecosystems immensely in fact! Just look up videos of people helping and improving ecosystems to see for yourself.
Resources and population growth,"What if in a country there once was an abundant supply of water, then all of a sudden the water ran out?","A country with an abundant supply of water, like a river, would most likely rely on that river for agriculture, trade, and general housework. If that river dried up, they would depend on other sources of water from neighboring countries and whatnot."
Resources and population growth,can an ecosystem affect us humans?,yes a city with pigeons cats humans and buildings is an ecosytem dominated by humans (not counting microbes)
"Competitive, predatory, and mutualistic interactions","Is there a scientific term for when two organisms of the same species benefit off each other or work together? If so, what is it called?",mutualism
"Competitive, predatory, and mutualistic interactions",What _is_ the *green* thing in the image above?,"The green plant is a plant full of sweet honeydew. Aphids extract it, and the ants eat those aphids to keep that plant clean."
"Competitive, predatory, and mutualistic interactions",What kind of ant is that?,"well if you read the caption it will tell you but the answer is, Carpenter ants."
"Competitive, predatory, and mutualistic interactions",what are Carpenter Ants Noah G?,"Well I'm not Noah, (I know who you're talking about.) But Carpenter ants often carve into wood, and when they bite Humans they hurt. I think what the other person is referring to are Fire ants. Those are Exatally what he described! Hope this helps."
"Competitive, predatory, and mutualistic interactions",i think it is cool how the ants protect the aphids and they are friends i did not know  what and aphids is at all please help thank you,"Aphids are often considered pests, enough so that farmers sometimes go as far to release aphid-eating ladybugs on their fields to keep the aphid population under control. Hope this helps!"
Photosynthesis in ecosystems,"So how do photosynthesis break down things? You know, for CO2 to become separated, there needs to be a separation.","Right. Sugar has carbon (C) in its structure, so by reacting CO2 with H2O (carbon dioxide with water), they create sugar and release oxygen (O2) as a by-product."
Photosynthesis in ecosystems,what is the word biomass,"Mass that is made of cells-biomass, so like a burger patty is technically biomass"
Photosynthesis in ecosystems,Did you know that more than 50% of the world's oxygen actually comes from the ocean? And not trees?,I did not know that lol
Photosynthesis in ecosystems,wow how old are you gays i'm 11,"I'm not gay yet
maybe never"
Photosynthesis in ecosystems,what do it mean when it says it eats the soil,"My guy plants don't eat soil, they rely on water and the sun"
Activity: what happens when a food web is disturbed?,"How to u do the experiment? 

I don't even get what it's about...",you can simply follow the STUDENT GUIDE above or you can do it with your classmates
Matter and energy in food webs,"Lol what do you call an organism that eats decomposers? 

I mean the question",They are called scavengers.
Matter and energy in food webs,are there some poison clams,"Yes, there are two"
Matter and energy in food webs,"Ok random question. I know that humans are technically at the top of the food chain. Does that mean vegetarians are not "considered" human scientifically because they are not at the top of the food chain, since they don't eat meat?","No. Humans are not defined by their diet. Humans are defined by their genetic code. That's like saying if a snake were to starve, is he really a snake?"
Matter and energy in food webs,"In the first video, Sal described a bunny as a consumer, because it consumes a plant. But a bunny poops and poop is fertilizer for plants, this is a mutualistic environment, but wouldn't the bunny be a producer? Because the bunny produced the poop that acts like fertilizer for plants?","No producers are the ones that starts the food cycle because it can make its own food without consuming other organisms. Bunnies need to eat producers( plants ) in order to survive. Furthrmore, Plants dont need fertilizer to grow, they only need light and water to survive. Fertilizer(bunny poop) just encourages the plants to grow."
Matter and energy in food webs,"What do you call organisms that eat nearly anything (they eat primary consumers, producers, secondary consumers, decomposers, tertiary consumers, scavengers, and other types of consumers)?","Humans.
Let's be real here:
We have eaten literally almost every species on this planet!!
Not only that, but we live across the globe in all the biomes (except for the ocean)!
Hope this helps!"
Matter and energy in food webs,why dose the otter go back to the bacteria,"Because when the otter dies, the bacteria (a.k.a. the decomposers) decompose that body for energy.
Hope this helps!"
Matter and energy in food webs,"What is a "biomass"? lol I remember seeing it somewhere, just don't know where... :)","Biomass is the total mass of some population. You can also use biomass to compare the mass of other organisms. For example, 3,366 mice have about the same biomass as one human. Since it would take a really long time (and would be hard and boring) to count every living thing, we use biomass. Hope this helps 😋.

Sincerely, Straw Hat Pirates"
Matter and energy in food webs,what in a food wed?,A food web is a combination of all the different food chains in an ecosystem.
Matter and energy in food webs,In the article it states that consumers are organisms who eat other organisms would that make humans who eat meat consumers? Or do the other organisms have to be living?,"Humans count as consumers because they (even those who don’t eat animal products) get their energy from other organisms. These might be bean plants that made their energy from the sun, or they might be cows that ate grass that made energy from the sun. Either way, humans have to get their food from other organisms, so we’re consumers. 

Does that help?"
Biodiversity and ecosystem health,"To: Anyone that saw it,
   After reading this article, I felt that humans are having a serious environmental impact. Hence, I would like anyone that sees this post to be aware of pollution and global warming. I do not want to talk about all those really dull stuff in textbooks, so I REALLY want you guys to take action with me!
   Thanks!
Best wishes,
Moon_yl",Ok will do
Biodiversity and ecosystem health,"Key points:
Biodiversity is the variety of species in an ecosystem.
Biodiversity decreases when species go extinct, or die out. Extinction often happens when organisms can no longer survive because of changes to their ecosystems.
A decrease in biodiversity can be the result of human actions. For example, human actions are leading to habitat loss and climate change. These, in turn, are causing a decrease in Earth’s biodiversity.
When an ecosystem loses biodiversity, it doesn’t function as well. So, scientists often look at how complete an ecosystem’s biodiversity is in order to measure the ecosystem’s health.",sadness :(
Biodiversity and ecosystem health,"What happens if humans stop interacting with other species? Will the "safety net" break completely, or will there be a less major problem or even no problem?",it would most likely get better people have done lots of damage to lots of diferint ecosystems
Biodiversity and ecosystem health,"but there something i dont get. Lets say that the rabbit population is decreasing then the predetors eating rabbit start to decrease but when the predetors decrease, the rabbit population will increase meaning the it will go in a cycle over and over again. so if a prey population gets closer to extinction so do the predetors but then the prey get bigger again. So doesn't that mean that ecosystems/biodiversty can fix themselves?","But actually, the majority of extinction is caused by humans."
Biodiversity and ecosystem health,I am wondering how mosquitoes interact with the other species in the ecosystem. How??,"Great question! Mosquitos typically are prey for other insects, birds and spiders. This helps the spiders and other creatures that eat mosquitoes eat, but also keeps the mosquito population stable and prevents it from skyrocketing. Mosquitoes also feed on animal blood. As far as interactions go, the main interaction is a food source for other animals and insects while also sucking blood out of animals, hope this helps!"
Biodiversity and ecosystem health,How does biodiversity exist,"Simply because there are different species of living things on the planet.
Hope this helps!"
Biodiversity and ecosystem health,"If a species that is not native to the area suddenly arrives, can that harm the ecosystem? What are they (the new species) called?","Good question!

When a non-native species arrives, they are generally called an "exotic species". If they harm the environment (which they often do), they are called "invasive". They often disrupt food webs by over-eating a native species. Invasive species are generally fast reproducers, because they wouldn't survive long if they weren't. Because of this, they take up a lot of space meant for native species. They also might overrun an ecosystem.

Hope this helps!

Here are some KA articles & videos on this subject:
https://www.khanacademy.org/science/ap-biology/ecology-ap/disruptions-to-ecosystems/a/invasive-species

https://www.khanacademy.org/science/ap-biology/ecology-ap/disruptions-to-ecosystems/v/introduced-species-and-biodiversity

Have a good day!"
Biodiversity and ecosystem health,How will this help me?,This will help you understand what biodiversity is and give you a better understanding of ecosystems.
Humans and ecosystems,How do trees prevent erosions?,"The trees roots block off the area for erosion to happen, and it sucks up water so there is less chance for erosion."
Humans and ecosystems,what is the tallest mountain in the world,Mount Everest
Humans and ecosystems,what is erosion?,"Erosion, put simply, is when stone or dirt is weathered by wind, water, ice, or foot traffic, and particles of sediment are carried away. For example, a rock in a stream is slowly eroded by the water flow, and eventually becomes smooth. Trees and undergrowth help prevent the erosion of mountains and hillsides."
Humans and ecosystems,How can tree roots prevent erosion?,"Tree root systems help reduce erosion by holding soil in place. Even after being cut, the roots attached to the stump help stabilize soil for years. Reducing risk of landslides."
Ecosystem dynamics,What is this going to do for me in the real world?,We are living on a rock in the middle of this infinite black nothingness and we've no idea how we got here. All we can do is try to understand the world around us. There is value outside in understanding that extends beyond immediate benefit
Ecosystem dynamics,what came first the chicken or the egg?,"(Edit)"In practice, it is impossible to pinpoint the moment when this happened. But in theory, at some trace, two junglefowl bred along with offspring was genetically different enough from the species of its parents classified as chicken. This chicken would have developed within a junglefowl egg and only produced the very first chicken’s egg on reaching maturity. Looking at it this way, the chicken came first.""
Ecosystem dynamics,was orange named orange cause it's orange or was the color orange was named orange cause it's orange,Not sure if I'm correct but I'm pretty sure the color was called orange because it resembled the color of the fruit orange.
Ecosystem dynamics,what does disruptions mean,"Something that prevents something from occurring. E.g. if a trench is formed between a population, the populations on opposite sides are not able to reproduce/interact with each other."
Ecosystem dynamics,is it weird we have car but are car key have traveled more than our car,What does that have to do with anything?
Ecosystem dynamics,I have a pet bird and it helps my green onions grow by giving it fertilizer,Nice
Ecosystem dynamics,how did those types of animals end up their and how do they survive and reproduce,is the way life is
Ecosystem dynamics,"An area of forest burned by a fire. The changes caused by a forest fire affect populations in an ecosystem. Image credit: “Tinder Fire Burn Scar Area" by Coconino National Forest USDA, public domain.",sadness
"Genes, proteins, and traits",why do i have to do this?,"U know, I've been thinking of that myself... but ever since I started mowing the grass so that I can make some homemade water then at the end of the day woke up asleep tomorrow, I realized that it's because u need to learn🤔! That's so crazy, isn't it? Anyways hope this helps 😊."
"Genes, proteins, and traits",what is amino acids?,"_*Amino acids are molecules that combine to form proteins*. Amino acids and proteins are the building blocks of life. When proteins are digested or broken down, amino acids are left. The human body uses amino acids to make proteins to help the body: Break down food._"
"Genes, proteins, and traits",How many types of protein can there be?,"there can be about 10,000 different proteins."
"Genes, proteins, and traits",Are amino acids tiny proteins?,"Amino acids are small molecules that are the building blocks of proteins. Proteins serve as structural support inside the cell and they perform many vital chemical reactions. Each protein is a molecule made up of different combinations of 20 types of smaller, simpler amino acids. Hope this helps."
"Genes, proteins, and traits",y is there cells in grass :/,because the grass is a living thing. and cells are what make life possible.
"Genes, proteins, and traits",What are Amino Acids?,"Amino acids are molecules that are combined to form proteins. Basically when proteins are broken down/digested the amino acids still remain, it's used by the body to create proteins and to break down food."
"Genes, proteins, and traits",what are amino acids,"_*Amino acids are molecules that combine to form proteins*. Amino acids and proteins are the building blocks of life. When proteins are digested or broken down, amino acids are left. The human body uses amino acids to make proteins to help the body: Break down food._"
Genetics vocabulary and Punnett squares,what happens when there is two dominant alleles?,"Both will be expressed; both will blend.

The blending will also happen with two recessive alleles."
Genetics vocabulary and Punnett squares,what does genetic code mean?,Genetic codes are the 'instructions' that tell our cells how to reproduce.
Mutations,"So you can change the DNA in humans/animals but has it actually been done in humans before? I know its been done in animals, but has anyone changed human DNA?","He Jiankui affair 
You can try to google it, but shortly: Yes, it was successful experiment however the scientist was sentenced for that"
Mutations,"If I got bit by a radioactive spider and turned into a hero,,,,   Would that be a mutation?","Well, technicaly that would be less of a natural mutation and more of a forced rearrangement of your dna involving your pores in your limbs. Although radioactivity is know to cause mutations, this spider doubtabley had enough in it to cause a mutation."
Mutations,How easy would you say it could be to have a mutation\be born with one percent wise?,"I am not sure what the exact odds are, but a lot of mutations go largely unnoticed, so it could be that a lot of people have at least one mutation."
Mutations,Is there a specific limit to change the dna in human DNA?,"2%. Otherwise you would no longer be human.
Hope this helps!"
Mutations,"wait, so if you get a really good cell mutation, you might get something that maybe lowers your risk of getting cancer. Thats pretty cool and life saving","Yes, while that is possible, and a nice possibility, some forms
 of cancer are caused by mutations."
Mutations,what is a mutation?,"_From the article_

*Harmful mutations* have _negative_ effects on an organism’s health and survival. For example, some mutations cause inherited disorders such as sickle cell anemia and cystic fibrosis.
*Beneficial mutations* have _positive_ effects on an organism’s health and survival. For example, some people have mutations that lower their risk of developing type 2 diabetes.
*Neutral mutations* have _no observable effect_ on an organism’s traits. For example, some gene mutations do not lead to amino acid changes, and so do not affect protein function.

*Beneficial mutation example*: When humans were in their ape stage, they evolved over time; learning to use tools, create machines, and form a community. This is a beneficial mutation, as these skills are now very necessary to us these days. 
*Harmful mutation example*: Sometimes however, some mutations end up becoming harmful. Cancer is a example of this. The parents might have had some harmful genes that put them at risk of cancer. When they had a kid, the genes mutated and formed a higher risk of cancer for the kid, sometimes just giving him cancer. 
*Neutral mutation example*: Often times, these are small and unnoticed, because they don't really affect a human, or their DNA, or their biology. Different eye colors are an example of a neutral mutation.
Hope this helped :D"
Mutations,what is a gene protein,"Proteins are large, complex molecules that play many important roles in the body. They are critical to most of the work done by cells and are required for the structure, function and regulation of the body’s tissues and organs. A protein is made up of one or more long, folded chains of amino acids (each called a polypeptide), whose sequences are determined by the DNA sequence of the protein-encoding gene. 
Protein. Most familiar are proteins that make up structures, such as muscle and, very importantly, proteins that fold and form what are known as enzymes. These proteins help your body carry out all of the chemical reactions it needs to keep you alive. 

Did this help at all?"
Activity: why do some mutations cause genetic disorders?,Does vaping cause genetic disorders?,It does if you plan to give birth
Chromosomes and genes,Can people still be tall if they have short parents and family,"Technically, yes they can. If the parents are both short but have a dormant tall gene, that tall gene can be passed on to the child."
Chromosomes and genes,How many genes are in a cell?,"Around 50,000 genes. There are also 24 chromosomes (groups of genes) in every cell."
Chromosomes and genes,why do some kids look like there grandparerents?,"yeah like he said, you can look like just about any family member. genes get passed. even people back in the day that you were related to, just a small chance."
Chromosomes and genes,"I see many questions about genes and appearance, so I will try to explain some. Your gender (you being male or female), is decided by your mother and father's genes, whether you have XX chromosomes, which make you female, or XY chromosomes, which make you male.
Now, along with this, your father and mother's genes which are passed onto you, do a fun sort of dance while you are in your mother's womb, to create entirely new combinations to make an entirely new person, which is you!

Why do some people look like one parent or the other? One parent may have stronger genes then the other parent, so certain traits are more visible or apparent, which is why some people look very like the parent with stronger genes, but this does not mean you are like that parent in every way because genes decide much more then appearance, just because you look like, say, your dad, doesn't mean you act like him, or have the same health he does. Some people are a mix of their parents.

Sometimes, kids look like their grandparents, or a grandparent, in this case, it's likely that your grandparent's genes, which are carried their child, which is your parent, has been passed to you, and they just strongly show in you.","Thanks for sharing this. You might want to put each answer under its question, even though that could take more time. This post is technically in the wrong category, and I don’t want your post just taken down or anything. 

I was wondering about how you said parents’ genes “do a fun sort of dance while you are in your mother's womb, to create entirely new combinations.” It was my understanding that one parent’s genes combine with themselves during meiosis. Then both parents’ genes combine during fertilization, which is what makes you (the zygote). The genes don’t combine while you’re in utero, but they do eventually combine to _make_ you, right?"
Chromosomes and genes,if a cell can  multipluy and the genes are in the cell do the genes multipluy,"Yes, the genes do multiply, and the genes get cloned as part of the process. As people age, however, this process gets more difficult for the body, which is why when people get older they stop growing."
Chromosomes and genes,Why do some kids look like their dad more than there mom?,"According to a study published in Scientific American, babies tend to look more like their fathers than their mothers. This is because fathers are less certain that a baby is theirs and are more likely to invest whatever resources they have in their own offspring. However, there is no scientific evidence that supports this claim.

Another theory suggests that genetics cause people to look and behave more like their dads than their moms. This is because children inherit half of their genetic material from each parent, and some traits are determined by genes on the sex chromosomes (X and Y). Since males have only one X chromosome, they will pass on all of their X-linked genes to their daughters but none to their sons. On the other hand, females have two X chromosomes, so they will pass on one of their X chromosomes to both their sons and daughters.

It's important to note that while some children may resemble one parent more than the other, this does not mean that they are more related to one parent than the other. Children inherit half of their genetic material from each parent, so they are equally related to both parents."
Chromosomes and genes,can your DNA change through experiments,"Yes. DON'T try it, unless you're absolutely positively certain that you know what you're doing."
Chromosomes and genes,How is DNA formed?,"DNA, or deoxyribonucleic acid, is formed through a process called DNA replication. DNA replication occurs during the cell division process known as the S phase of the cell cycle. Here are the key steps involved:

1. Initiation: The DNA double helix unwinds and separates into two strands. An enzyme called DNA helicase breaks the hydrogen bonds between the base pairs, causing the DNA strands to separate and form a replication fork.

2. Primer Binding: Primers, which are short RNA sequences, are synthesized and bind to the DNA template strands. These primers provide a starting point for DNA synthesis.

3. Elongation: DNA polymerase, an enzyme, attaches to the primer and begins synthesizing new DNA strands. It reads the template strand and adds complementary nucleotides to each growing daughter strand. Adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G), maintaining the base pairing rules.

4. Leading and Lagging Strand Synthesis: DNA replication occurs in a semi-discontinuous manner due to the antiparallel nature of the DNA strands. The leading strand is synthesized continuously in the 5' to 3' direction, while the lagging strand is synthesized discontinuously in small fragments called Okazaki fragments. These fragments are later joined together.

5. Termination: Once the entire DNA molecule has been replicated, termination signals halt the replication process. The DNA strands are fully synthesized, and the new double-stranded DNA molecules are ready for further cellular processes.

DNA replication is a highly precise and complex process that ensures accurate transmission of genetic information from one generation of cells to the next. It plays a crucial role in the growth, development, and reproduction of organisms."
Chromosomes and genes,Can we change the genes of a person also after the birth?,"Gene therapy , or somatic gene editing, changes the DNA in cells of an adult or child to treat disease, or even to try to enhance that person in some way. The changes made in these somatic (or body) cells would be permanent but would only affect the person treated."
Chromosomes and genes,what's the difference between Adams and molecules,"I think you mean atoms :)

If you are talking about Adams, be informed that all things are made up of atoms, so all Adams are made up of atoms.

If you do mean atoms, the thing is, molecules are made up of atoms. For example, a molecule may contain 2 hydrogen atoms and 1 oxygen atom. This creates a water molecule."
Sexual reproduction and genetic variation,Can two black parents have a white child?,I believe it is _possible_ but very rare.
Sexual reproduction and genetic variation,why do they look like x?,"this is from what I looked up. "Chromosomes look like an x because there are two strands that are bonded together near the middle of the strand. Proteins are what holds these two strands together, which is called the centromere. When looking at a karyotype image of all 23 pairs, you can see how each strand look like an x because of that bond." so its basically saying that they're connected together by some strands of proteins."
Sexual reproduction and genetic variation,what are gametes,Gametes are the kinds of cells that are able to join together to make children.
Sexual reproduction and genetic variation,How does sexual reproduction relate to genetic variation?,"Sexual reproduction is related to genetic variation. I'll explain below.

During fertilization, each parent produce a gamete, as either an egg, (female), or sperm, (male), cells. These cells are haploid, meaning they each have one set of chromosomes, or 23 chromosomes. 

Since these chromosomes come from both of the parents, they contain DNA from both of the parents. This is because chromosomes are made up of DNA, which is made up of specific parts of DNA, or genes. These genes create proteins, based upon the nucleotides in the genes. These genes carry out different functions, which are based upon the nucleotides in the genes. These proteins can cause the offspring to have different traits.

The offspring of the parents has 46 chromosomes, (23 from each parent). Because the offspring gets a mixture of chromosomes from each parent, (which effects the offspring's traits), the offspring has different traits, some from each parent. 

There are so many different combinations of chromosomes that an offspring can have from its parents. This is why even siblings look different, even when coming from the same parents. 

These differences between a offspring and its parent, or two siblings, can all be called genetic variation.

I hope this helped describe the relationship between sexual reproduction and genetic variation."
Sexual reproduction and genetic variation,what are gametes,"A gamete is a reproductive cell of an animal or plant. In animals, female gametes are called ova or egg cells, and male gametes are called sperm. Ova and sperm are haploid cells, with each cell carrying only one copy of each chromosome."
Sexual reproduction and genetic variation,what happenings if none of the sperm makes it pass the uteri's,then no baby
Chromosome pairs,am i adopted because i dont have my parents hair color,"Your hair color doesn't necessarily come from your parents, it could be from your grandparents or great grandparents or so on"
Chromosome pairs,why do they get down syndrome.,If they have an extra chromosome 21 it causes down syndrome
Chromosome pairs,"Why do they have different alleles, or versions, of those genes?",""During meiosis, homologous chromosomes line up and recombination occurs between them. This results in gametes with unique combinations of alleles on each chromosome and therefore unique individuals.""
Chromosome pairs,how do homologous contain the same genes,"homologous chromosomes are 2 chromosomes that have the same genes, but those genes don't have to be the same versions.
like how I have hair and my friend has hair, but we have different versions or types of hair.
so let's take a pair of homologous chromosomes in my cell. 1 chromosome in this pair, let's call it chromosome "A", was given to me by my mum. she gave me a chromosome that was a mixture of her chromosomes (so it has some of her moms genes in it and some of her dads genes in it )
and the other chromosome in the pair was given to me by my dad, it has some of his dads genes in it and some of his moms genes in it)
now why did these two chromosomes pair u? well they paired up cuz they have the same sets of genes on them, like they have genes for hair colour, but they gene that will be active in my will be the more dominant one."
Chromosome pairs,Is it possible for human offspring to only get 10% of the genes from their parents?,"Yes... but only due to a HUUGE mutation.
Just a 2% differentiation in gene structure can create a whole new species.
Hope this helps."
Chromosome pairs,why are they green and red?,That's just how they look under an X-ray.
Earth's fossil record,Why do fossils take so long to decay.,"This is because they lived in the sea, where sand or mud could bury their remains quickly after they died. Once remains are buried under sediment, their decomposition slows down due to a lack of oxygen, giving enough time for fossilisation to occur."
Earth's fossil record,why do fossils take so long to decay,"This is because they lived in the sea, where sand or mud could bury their remains quickly after they died. Once remains are buried under sediment, their decomposition slows down due to a lack of oxygen, giving enough time for fossilisation to occur."
Earth's fossil record,what does the fossils tell us,"They can give us clues to what old species may have looked like or their bone structures and even more, we can even tell how old these fossils are by using radiology, which also tells us how old the extinct species are, there is many things!"
Earth's fossil record,why do mass extinction happen?,"Mass extinctions are caused by extreme changes. An example would be the asteroid that killed the dinosaurs. There have been 5 mass extinctions, some caused by extreme temperature changes, asteroid impacts that push so much ash into the atmosphere it blocks the sun for decades, and changes in atmospheric composition such as increases in CO2 and Oxygen."
Earth's fossil record,Can you tell how long they have been there?,yes using radiometric dating to see how much decay of certan things that were in the living organism sientists know how fast it happens so can tell how old they are
Earth's fossil record,How can fossils be preserved in sedimentary rock if it can break? what will happen?,"Well they stay in good condition because the rocks take very long to fully harden, because of this and the fact that they are buried under the ground, they are preserved and then can be dug up later by let’s say humans. Now if the rock was to break when people would try and get it out then simply the fossil would break. Breaking is unlikely to happen due to how big these rocks can be, I mean think about it, they are underground for many many MANY *MANY* Years. So the sediment forms together and makes a HUGE rock."
Earth's fossil record,Why do all fossil look different?,because fossil come from different animals
Earth's fossil record,Do things on land age differently than things in the water/sea?,"yes, think of it this way. an animal dies on land, it is in the woods and is on the ground. so the flesh decays by natural resources( ants, other animals, time and bugs) and only the bones are left, it gets dirt on it, which turns to mud and which then has bacteria and chemicals, it gets buried and starts to harden to a fossil, it does not take as long as they say it does. okay now water, so diff chemicals in dirt, rather than in water, helps or prevents the process of decaying. and silt on the bottom of the ocean floor might make it better or harder to fossilize organic matter."
Common ancestry and evolutionary trees,What would it look like if there is a common ancestor between A and B only?,"I think you are going to have to imagine that species C didn't even exist, just to see what it would look like with just A and B."
Common ancestry and evolutionary trees,how can they be close totgher,"When they are saying they are close together they don’t mean that they are the exact same species, what they mean is that they have common ancestors, so they may be more closely related than if they weren’t from common ancestors"
Common ancestry and evolutionary trees,"In the example of the branch points, who is the most closely related: A, B, or C?",B and C
Common ancestry and evolutionary trees,What can stop there from being another species?,"Several factors can prevent the emergence of a new species. One of the most significant factors is the availability of resources. If a particular area is already occupied by a well-adapted species, it may be difficult for a new species to establish itself and survive. Additionally, competition from other species can also pose a challenge to the emergence of a new species. Other factors such as environmental changes, genetic mutations, and natural disasters can also have an impact on the evolution of new species. Ultimately, the emergence of a new species is a complex and unpredictable process that is influenced by a variety of factors."
Common ancestry and evolutionary trees,I wonder if scientist made a evolutionarily tree for every thing that has existed in the world.,"Scientists have not made a evolutinary (or tree of life) that has every living thing in it. But there is a 'tree of life' that holds 2.3 million species in the world, sadly thats nowhere near the amount of animals in the world."
Common ancestry and evolutionary trees,Is there any diseases that can make other species,"From time to time viruses cross the host‐range barrier expanding their host range. However, in very rare cases cross‐species transfer is followed by the establishment and persistence of a virus in the new host species, which may result in disease."
Common ancestry and evolutionary trees,I'm still confused as to what a lineage is.,"It's the bloodline that includes you, your parents, your grandparents, and your future children."
Common ancestry and evolutionary trees,"At 5:20, it is getting harde to believe that chic me could be related to T. rex.","True, but remember, this Evolution happened over millions of years. So they had plenty of time to evolve into the tiny little birds we see today. 🐣🐥🦆🦅🦉🐤🐦🐧🐔 CHEEEEEP. Tell me if you don’t understand"
Fossils,What is a fossil record and Why do we have a fossil record?,A fossil record is a record of all the fossils and their dates found on the earth. We have it because it helps keep track of things that lived a long time ago.
Fossils,Is the moon cheese? and can i eat it,"no sadly not! we know this because astronauts have been to the moon and brought back rocks to study also surcumstantial evidence where is the milk from, who made it, why is it there, how could cheese be made in zero gravity, etc"
Fossils,what is the fossil record,"Fossil record, history of life as documented by fossils, the remains or imprints of organisms from earlier geological periods preserved in sedimentary rock."
Fossils,Why are scientists so interested in fossils,Scientists are interested in fossils because they are one of the only things that can tell us about prehistoric times.
Fossils,what is radiometric dating,"Radiometric dating is a method used to find the age of fossils. It uses very unstable radioactive isotopes. Over time, radioactive isotopes decay into smaller isotopes. Scientists can calculate the amount of decay in isotopes, calculate how long the isotopes have been there, and estimate the age of the fossils."
Fossils,can they ever bring back the species that long ago was in the world with fossil records?,maybe but that would take lots and lots of work
Fossils,What is the fossil records,"Fossil record, history of life as documented by fossils, the remains or imprints of organisms from earlier geological periods preserved in sedimentary rock."
Evolution,Is evolution intentinal? How do animals know how to evolve?,"Hmm, interesting question! I think it occurs naturally, as each species wants to survive.

The Snail Kite, a small predatory bird that lives in the Everglades, has a specially curved bill 'designed' to dig snails out of their shells. Around 2007, the island apple snail invaded the Everglades, wiping out smaller species of snails, for which the kite's bills were designed. 
At this point, something called 'natural selection' kicked in. The snail kites with bigger bills could eat the new snails more easily, and therefore survived better. This led to the reproduction of more big-billed snail kites. In just 10 years or so, the entirety of the species had evolved to have larger bills so they could eat the big snails.

So, I think it happens naturally, without much brains involved. The individuals with better traits survive more easily, and therefore change the species in good ways.

Hope this helped!"
Evolution,Is it just me or like the whole lesson all i could think about was Pokemon and the evolutions,Same honestly.
Evolution,is the evolution only in animals or is it in humans as well?,Evolution can happen in all living things. Not just humans and animals but also plants.
Evolution,Do all organisms have evolution.,no. In fact octopuses have no evolutionary ancestors
Evolution,what causes evolution,"A change in the environment around them, for example, maybe if a bird eats seeds but the shell starts to thicken, then they need stronger beaks."
Evolution,Why does evolution take millions of years to happen?,"It doesn't have to take millions of years. For example, rattle snakes have evolved during the past few decades so that the rattle they have on their tails don't give a sound. It was to avoid hunters and to protect themselves, and now they are known as one of the typical examples of an evolution through only a few decades."
Evolution,I dont have a question,"I don't have an answer
(upvote me if you like roast)"
Evidence of evolution: anatomy,is evolution really real,"Evolution is supported by evidence and observations of the physical world. Watching these videos in the “evidence of evolution” series can help explain how the theory is supported. Scientists constantly test evolution’s predictions, just like they do with other theories!"
Evidence of evolution: anatomy,so we basically evolved from birds?,"No, but humans and birds do have common ancestors. It’s a bit like asking if your sibling must be your parent because you look alike. Your sibling isn’t your parent, but you have some similar features because both of you descended from the same people (your parents).

Birds and humans are more like very, very distant cousins. In fact, our last common ancestor existed over 250 million years ago, according to the article “The Origin and Diversification of Birds” by Stephen L Brusatte and others, published in _Current Biology_ in 2015.

Does that help?"
Evidence of evolution: anatomy,How did we find out about evolution?,"That’s a good question! I think the simplest answer is that we have observed changes is species over time, and also have found fossils that clearly are different than what we are seeing today. Also we have observed generations of animals and have seen changes over time. It’s pretty exciting actually! That’s the simplest answer but also an answer with information. Hope this helps :)"
Evidence of evolution: anatomy,what if humans turn back in to monkeys,Thats quite unlikely to happen
Evidence of evolution: anatomy,If we were related to apes is that why I like bananas so much.,Humans are biologically a type of ape.
Evidence of evolution: anatomy,We are actually less than 50% human!,"Do you mean that, by mass, any human's body is less than 50% made up of human cells (as opposed to the microorganisms which live in us)?"
Evidence of evolution: anatomy,how did they make so much change how could it be possible to make a land creature to an amphibian,"*When an animal has _move from the environment they live in_, their species _adapts to the new way of life*_.
   
_For instance, the *first ancestor of whales* were *mesonychids*, which were *4 legged, long tailed furry mammals that lived on land*. They discovered it was *easier* and also *safer* to catch *fish* than it was to hunt on land_; eventually *evolving into whales*."
Evidence of evolution: anatomy,is evolution a thing that will always have to happen,"Evolution happens for all living things and viruses, as long as some individuals have a better chance of reproducing than others. 
Evolution does also happen to humans too, though we might not notice it on our time scales."
Evidence of evolution: embryology,So the embryo of a human can be viewed when doctor's view a child before it's born?,"A human embryo transitions to being a fetus at somewhere between 8 and 12 weeks of pregnancy. The human organism itself (as opposed to the gestational sac) may not be visible until somewhere between 6 and 10 weeks, so you may only see the human when they are a fetus instead of an embryo."
Evidence of evolution: embryology,This looks similar to babies in a human stomach. Do they actually have that many similarities?,"If you look at different mammals and birds when they are still embryos, you will find that they are quite similar. However, these similarities stop as the embryos keep developing. By the time a baby is born, it looks different from an embryo."
Evidence of evolution: embryology,so all humans and animals have an Embryo and which animals don't have one?,"I may be wrong but
All animals with a spine have embryos. Animals that don't have spines don't have embryos"
Evidence of evolution: embryology,So the embryo of a human can be viewed when doctors view a child before it's born?,"yep!! it can be an ultrasound, or a scan. and if the baby is before 8 weeks when the baby is first starting to form"
Evidence of evolution: embryology,I wonder why our "tail" falls off whenever we reach 8 weeks when we are a embryo,"They don't fall off, they just move position to make up the bottom of your spine, also called your tail bone."
Artificial selection,"I had durian another day and it tasted like jackfruit and cantoulupe mixed together. Do you think they mixed both fruits together to get durian. Also, whats your favorite fruit, mine are bananas 🍌","idk, i never tried durian but when i searched ur question up, it is an original fruit. also my favourite fruit is watermelon :)"
Artificial selection,Have you ever thought about how plants and vegetables grow. I f you think about it it's really crazy.,all of life is rlly crazy! its amazing how the world works
N/A,Why do animals have disadvantages and why cant they have just advantages,"Because as the environment shifts with time, a trait that was once disadvantageous will become advantageous once more. This can be seen with the peppered moths, the white ones became disadvantageous while the black ones became advantageous, but soon that shifted so the white became advantageous again."
N/A,i wonder how rare are black peppered moths now,Not rare at all according to google.
N/A,How can things turn in a colour? Why can't I turn blue or yellow?,"Technically speaking, you could turn blue and yellow. 

Take a bird for example: birds have evolved to have flashy/bright colors to attract a mate or to intimidate other bird competitors. 

Humans however, do not need blue or yellow skin. Humans have evolved to where we look more for personality and looks (and more) rather than bright, flashy colors."
N/A,what food do they eat,"Most adult peppered moths feed on flower nectars, fruit pulps and leaves. Some eat plant seeds."
N/A,Why are organisms with advantageous traits are more likely to reproduce?,"Organisms with advantageous traits are more likely to reproduce because they are more likely to survive long enough to have offspring and raise them. If a prey animal is less likely to be seen by predators, it is less likely to be eaten so it can breed, have offspring, and continue it's lineage."
N/A,If all the white animals were hunted by prey then how did they reproduce to bring them back?,not all of them were
N/A,if we put some in an enviroment with a more gray place would they survive?,"It depends on the shade of gray if they can camouflage in it, then they can still survive or they might need to change their fur color trait or move farther away."
N/A,If we put some in an environment with a more gray place would they survive?,"It depends, tan doesn't match with gray so it'd have to be a light brown color for the tan mice to survive long enough to reproduce."
Adaptation and environmental change,How long does it take for an organisms to adapt to its environment?,It varies with the creature and the change to the environment.
Adaptation and environmental change,What happens to the Dark brown beetles after environmental changes?,They become less common and less likely to reproduce.
Adaptation and environmental change,Is it possible for an animal not to adapt to an environment?,"Of course it is. However, in the process of natural selection, it is likely that animals will either adapt in some way or another or go extinct trying."
Adaptation and environmental change,What could've happened if the light brown beetle got extinct before the temperature change? Would there be any way that people might think the medium brown beetle was the light brown beetle?,I think that is a possibility because there must be more light brown beetles in their environment!
Adaptation and environmental change,"I assume that the color of the beetles mean something, so what do the different colors mean?","The different colors are the different colors of the actual beetles. The beetles have a better or worse chance of blending in depending on their color. Before the environmental chance, the dark brown beetles blended in the easiest,therefore helping them have more offspring. But after the change,the dark brown beetles couldn't blend in, so they got eaten by predators, so their population decreased."
Adaptation and environmental change,"If I were 2 move 2 someplace different after living somewhere for 12 years could that change the way I act, dress, and talk?",Maybe?
Adaptation and environmental change,"I have trouble staying focused, anyone have any tips to help?","Try Listening to music with or without words that helps me a lot, I also like to eat something before I do something that needs a lot of focus as it helps to"
Galaxies and gravity,What will happen when the galaxies collide?,"Because there is so much space between the stars in galaxies, it’s not very likely that any one star (or our solar system) would be significantly messed up from this happening. The galaxies would effectively pass through each other (imagine ghosts going through each other) while deforming a bit. Then the galaxies would gravitationally attract each other again and keep going back and forth a few times until they merged to form a new, bigger galaxy. You can actually look up pictures of spiral galaxies in various stages of merging to get an idea of what this might look like. 

Does that help?"
Galaxies and gravity,What will happen if you get suck in a milky way.,We are in the Milky Way.
Galaxies and gravity,How Big Is Sagittarius A*?,"Its radius is about 13.67 million miles, 46 million km, or 100 AU. Its mass is around 4 million times the mass of our sun."
Galaxies and gravity,What will happen when the Andromeda Galaxy and our Milky Way Galaxy collide? Will our galaxy survive the collision?,yes it will
Galaxies and gravity,how were the planits made,"Our solar system formed 4.6 billion years ago from a solar nebula, which is a cloud of gas and dust. A nearby supernova explosion caused a shock wave, which likely led to the collapse of the solar nebula. The Sun formed in the center with the planets in orbit around it. Moons also formed in orbit around several of the gas giants."
Galaxies and gravity,"These comments are cracking me up like crazy, man",Same dude.
Galaxies and gravity,If we didn't have Gravity and it rain would the rain stay up in air ?,we would probably be floating and i dont think the rain would even come down
Galaxies and gravity,"OK I'm just wondering, is the Sun pulling all the other planets towards itself or not?🟡",no it does not
Galaxies and gravity,Is the multiverse theory true,"While there is some evidence pointing to the possibility of a multiverse, it is all speculation. We cannot prove it, so it cannot be true. Interesting to think about, though."
Galaxies and gravity,What are some other galaxies in our local group other than the milky way and andromeda?,"The three big ones in our local group are the Milky Way, Andromeda, and Triangulum. There are many dwarf galaxies there, too, including: Tucana Dwarf, Phoenix Dwarf, Cetus Dwarf, and NGC 3109. EarthSky’s article “The Local Group is our galactic neighborhood” has a nice graphic with more names, if you want."
Earth’s place in the universe,what is retrograde motion an example of ?,"It's an example of the fact that we are orbiting the sun, that Mars, Jupiter, Saturn, Uranus and Neptune are orbiting further away from us and that the planets orbit the sun in ellipses rather than circles"
Earth’s place in the universe,why is the sun center of the solar system and not the unuverse,"The sun is the center of the solar system because its planets, asteroids, comets, and so on all orbit it. 

As Janice said, though, the solar system also orbits the center of our Milky Way galaxy, which is part of the Local group, which is part of the Virgo supercluster, and on to larger groups. 

Also, as far as we know now, there isn’t actually an absolute center of the universe. Space itself is expanding, so every point is expanding away from every other point. That means we can’t trace it all back to one “center” of the Big Bang or what the Big Bang expanded to become: the universe right now.

Does that help?"
Earth’s place in the universe,can new planets form in our universe? aslo can their be mini stars forming aslo because the moon slowly backs away from the earth  will a new moon form? :O,"No, new planets can NOT form in our universe. There was an era that allowed the materials that can be used to make new planets, but that was all used up long ago."
Earth’s place in the universe,"Have we ever tried studding black holes and what is past it? This is not really on topic but what if black holes were actually like a new "dimension" like a worm hole,but the power is to strong that nothing is able to handle the pressure that it gives.","The term black hole is potentially misleading. Calling it a hole makes you think that it is something that you can enter, pass through, and go to the other side. More accurately, they are massive objects with intense gravitational fields similar to stars. But, unlike stars they are so massive that light can't escape. If you think of them as dark stars, rather than holes, then you'll probably have a more realistic concept of what black holes actually are."
Earth’s place in the universe,When was the heliocentric model created?,1543 (source: google)
Earth’s place in the universe,why do we live on earth,It is the only planet we can find that gives us oxyegn and water. It is in the habital zone
Earth’s place in the universe,This article states that the sun is only the center of our solar system and not the entire universe so what is the center of the universe?,"Some people say that there's a black hole in the center of our universe, but I personally disagree with that because there is scientific evidence that the universe is speeding up. Here's a quote from an article that explains it "By carefully observing distant supernovae—stellar explosions that for a brief time shine as brightly as 10 billion suns— astronomers found that they were fainter than expected. The most plausible explanation for the discrepancy is that the light from the supernovae, which exploded billions of years ago, traveled a greater distance than theorists had predicted. And this explanation, in turn, led to the conclusion that the expansion of the universe is actually speeding up, not slowing down." Black holes tend to generally suck things into their grasp, if there was truly a gigantic one in the middle of the universe, we would be slowing down."
Earth’s place in the universe,what is an axsis or where is the axsis?,"They’re talking about the axis of rotation. This is an imaginary line that something spins around. If you roll a wheel, for example, its axis of rotation would be through its center. Earth’s axis passes through its poles, and it’s the imaginary line the planet spins around every day.

Does that help?"
Earth’s place in the universe,Can new stars or black hole come into the milky galaxy?,"Yes, new stars are constantly forming! Gravity pulls gas together, and the gas heats up. Eventually, once there's enough gas, gravity pulls on it so much that two smaller atoms can be forced together to make one bigger atom. This process is called fusion, and stars usually start by fusing hydrogen atoms to make helium atoms.

Black holes can also form in our galaxy. One common way to get a black hole happens when a large star "dies". Usually, the energy released during fusion keeps gravity from making a star collapse in on itself. Once big stars use up enough hydrogen, the reaction at the center of the star brings together the helium atoms to make even bigger atoms: carbon. The star keeps fusing bigger and bigger elements. Once the star's made iron atoms, though, it can't make any bigger atoms. Fusion doesn't work as much, then. That means the fusion loses the battle with gravity, and the star collapses in on itself. If the star is massive enough, gravity can make it collapse so much that its gravity pulls in even light. That's how a new black hole can form from an old star.

(There are also supermassive black holes, like the one at the center of our galaxy, that are much bigger than the black holes we see forming this way.)

Does that help?"
Earth’s place in the universe,Why do asteroids always hit the moon instead of Earth?,Asteroids hit the Moon more often than Earth because the Moon has no atmosphere to protect it from meteoroids
The solar system,Why are all of the biggest planets made up of gas and liquid?,"It is probably because the gas and liquid substances weren't able to be combined to create a planet nearby the sun, so they eventually moved outwards and became the gas giants we know."
The solar system,hi why do we do science?,so we can be big brain.
The solar system,I wonder who discoverd the solar system,"As Alex said, humans have known some things about the solar system since they started looking up. Copernicus popularized the fact that it’s a *solar* system, though: that the planets go around the sun instead of everything going around the earth.

Does that help?"
The solar system,"Jupiter (69,911 km / 43,441 miles) – 1,120% the size of Earth”.","very helpful thanks let me add on Jupiter Is Massive: ...
Jupiter Cannot Become A Star: ...
Jupiter Is The Fastest Spinning Planet In The Solar System: ...
The Clouds On Jupiter Are Only 50 km Thick: ...
The Great Red Spot Has Been Around For A Long Time: ...
Jupiter Has Rings: ...
Jupiter's Magnetic Field Is 14 Times Stronger Than Earth's: ...
Jupiter Has 67 Moons:"
The solar system,how are comets formed?,"According to NASA, "Comets are frozen leftovers from the formation of the solar system composed of dust, rock, and ices.""
The solar system,why does the comets have tails?,It's simply because it is the comet's particles being burnt as it moves near the sun.
The solar system,How *fast* can a Comet travel?,"A comet's top speed is 17,500 miles per hour, which in kilometers is 2816 kilometers per hour"
The solar system,How did the Solar system originate?,gravity pulled a cloud of gas so hared it became the sun and then the gravity from the sun made the solar system we now today🌌🪐🌍🌑🌞
The solar system,Which is the biggest planet?,"The biggest planet in our solar system is Jupiter. UniverseToday.com gives these measurements: “Jupiter (69,911 km / 43,441 miles) – 1,120% the size of Earth”.

I hope this helps! :)"
Seasons,if we came a few more miles closer to the sun than usual what would be the outcome,Earth is on an elliptical orbit so we get closer and further away all the time. If we got significantly closer we'd end up like Venus which is basically a death trap
Seasons,"Why does it start to get dark early in Winter and late in Summer? also, upvote me then i'll upvote you.","because of the tilt of our planet. When the north hemisphere is tilted with respect to the sun, it is summer and hence the sun's glow is felt more strongly. It is in adverse for winter. pls upvote this answer!
thanks.

and @kaia i upvoted yours."
Seasons,"How did the northern and southern hemisphere's get their names,and meaning's.","Their names are based on their position relative to the equator. So, the Northern Hemisphere is located north of the equator, and the Southern Hemisphere is located south of the equator."
Seasons,why is the earth tilled,"This is one of those tough questions which don't have a definite answer. One theory is that a mega asteroid from Jupiter (Who at the time was within range of Earth, and was flinging asteroids everywhere due to its strong gravitational pull) crashed into Earth during its primordial stage. This collision was so intense, that a massive chunk of the Earth flew off. However, the Earth's gravity slung it back into orbit, thus creating the Moon."
Seasons,how come the sun don't spin like the rest of the plants,the sun does spin but is spins slowly and on an axis so we can not feel it
Seasons,"how come even though fall and spring are getting a similar amount of sunlight, why is fall colder??","Remember that fall begins at an equinox (when we're getting an equal amount of daytime and nighttime) and ends at the winter solstice (the least amount of daylight. Spring begins on another equinox but ends on the summer solstice (when we're getting the most sunlight we get).

Does that help at all?"
Seasons,What if the sun spun incredibly fast? What would happen?,"It is kind of complicated, so I'll use an analogy here. The sun's rapid rotation would resemble that of a figure skater spinning while holding out their arms. The spin's force would spread the sun's material out like a figure skater's arms by pushing it away from the centre. As a result of the centrifugal force, the sun would become much larger becoming a red giant and growing significantly bigger and brighter. Because it would be more brighter and warmer, it would have a significant impact on the planets in the solar system and may make it difficult for life to survive. *After a few million years, Earth would be swallowed by the rapidly expanding sun*."
Seasons,Why do we have a sun?,Without the sun we wouldn’t be able to survive. Because the sun helps us grow our crops and keeps us warm.
Seasons,how does a eclipse happen,"A Solar Eclipse happens when the moon orbits just in front of the sun for a few moments every so often. There can be a total eclipse, where the moon completely covers the sun, causing it to turn black. There can also be a partial eclipse when the moon only covers a portion of the sun.

There can also be lunar eclipses! This happens when the sun, moon and earth are in near complete alignment, and you'll see the moon turn red and then disappear if it is total, or partially disappear if it is a partial eclipse, these happen every year around the world."
N/A,If u want to actually do it u have to PRINT IT 😭😭😭😡😡🤬,Or you could write it down separately.
The moon and its motions,My parents said not to look at the solar eclipse because it will have the same effect when you look at the sun too long. Is that true?,"Yes that is true, however looking at a lunar eclipse causes no problems"
The moon and its motions,why when the earth spin we don't fill dizzy,"Because even though we dont _feel_ it, we move along with it"
The moon and its motions,Why does the moon orbit the earth so much faster than we orbit the sun,"Because the moon is much closer to Earth, it will orbit faster. But the Earth is far from the sun so it will orbit longer. Hoped this helped!"
The moon and its motions,How can the full come every 30 and February has 28 or 29,"February is a strange month, but the cycle of the moon will continue unbothered, however every four years there is a 29th day in February, which is known as a leap year."
The moon and its motions,Why does a lunar eclipse make the moon orange if it is getting covered in the Earth's shadow? Wouldn't it just turn black like the new moon? I am confused.,"The body of Earth casts its shadow on the moon, but light hitting the atmosphere is bent around Earth and cast on the moon. The blue end of the light spectrum bends more than the red end of the spectrum. Most of the blue light is bent toward the surface of Earth or up into space, whereas the red light takes a straighter path and ends up on the surface of the moon.

The differential scattering of light that is responsible lunar eclipses looking red is the same physical phenomenon that causes the sky to be blue and sunsets to be red.

Total lunar eclipses aren't entirely red though. The moon will look red near the beginning and the end of the eclipse. But near the middle, when the moon is well within Earth's shadow, the moon looks quite black."
The moon and its motions,why the full only comes on 30?,"The full moon comes about every 29 and a half days. It comes that frequently because the moon orbits the earth about every 27 days, but the earth’s spinning, and it and the moon are also orbiting the sun. This all works out so that the moon repeats its phases every 29.5 days."
The moon and its motions,"If the earth spins about 1,000 mph, why don't we go to the other side of the earth when we jump? Thanks.","The earth's spinning speed doesn't affect the wind speed or the gravitational pull on earth. Think of it this way, when your in a car traveling on a road at 60 mph and you through an apple in the air it doesn't go and smash the back window out but if you open the front and back windows it will fly out the back of the car. So I'm also thinking that the atmosphere has a play in this to."
The moon and its motions,why does t only occur when the moon is fully coverd and why does luners eclipse only come durning ful moons,"The lunar eclipse is when the Earth blocks the sun's light from shining in the moon. For that to happen, the Earth must be between the sun and moon, which is also the position they are in when it is a full moon. There isn't a lunar eclipse every full moon because of the way the moon orbits Earth."
The moon and its motions,Why doesent gravity pull the moon closer and closer but it moves other objects like meteroids into our atmosphere.,"Because there are two vectors working on the Moon. There is the gravitational force vector pointing from the Moon to Earth and the Moon's velocity vector which is roughly perpendicular to that. Without Earth's gravity, the Moon would fly off into space. without the Moon's velocity, then the Moon would crash into Earth. The two combined have the Moon orbiting Earth. Gravity has the Moon constantly falling toward Earth but its velocity ensures that it always misses.

This interplay of gravity and velocity is the same reason why Earth doesn't collide with the Sun."
The moon and its motions,whys it callde the blood moon,"cuz, the moon is red."
Solar eclipses,is it going to be hot when a solar eclipse happens,It's actually a bit colder when a solar eclipse happens. It usually drops about 12-15 degrees
Solar eclipses,does a Solar eclipse happen in the middle of the day?,"Yes, it does, it gets in the way of the sun shining on earth."
Solar eclipses,is humming bird an AI?,What makes you say that?
Solar eclipses,"y is space one thing that people like to study when it is like plucking ants out of a ant bed
it is inprodictable",Because many things are interesting about space and a lot of earth's mysteries would not be solved.
Solar eclipses,How long does an average total solar eclipse last?,2 to 3 minutes
Solar eclipses,What is a solar eclipse like,"During a total solar eclipse: the temperature rapidly drops by about 10 degrees Fahrenheit, crickets and other insects start chirping because they are fooled into thinking it's night, and the sky gets dark enough for the Sun's corona to be visible. It's one of the most beautiful things that you can see in nature.

North America will get its next total solar eclipse on 8 April 2024. Don't miss it!"
Solar eclipses,how hot is it going to be during the solar eclips,"The temperature during a solar eclipse depends on a variety of factors, such as the time of day, the location, the season, and the local weather conditions. In general, the temperature may drop slightly during a total solar eclipse as the Moon blocks the Sun's direct radiation and casts a shadow on the Earth's surface.

During a total solar eclipse, the Moon completely blocks the Sun, causing the sky to darken and the temperature to drop by several degrees Fahrenheit (or Celsius) in the path of totality, which is the narrow region where the eclipse is visible in its totality. This temperature drop occurs because the Earth's surface is no longer receiving direct sunlight, which is the primary source of heating. However, the temperature change is usually temporary and returns to normal levels after the eclipse ends.

It is worth noting that during a partial solar eclipse, when the Moon only partially blocks the Sun, there may be little or no noticeable temperature change. Additionally, the temperature changes during an eclipse can be affected by local weather conditions, such as cloud cover and wind, which can impact the amount of sunlight that reaches the ground."
Solar eclipses,What is a lunar eclipse llike,"The moon either looks darker or red for some portion of the night. 

Does that help?"
Weather,Why does weather change,"First, you need to understand high and low-pressure systems. A low-pressure system brings heavy rain and thunderstorms. A high-pressure system is the opposite of that; it brings more pleasant weather, low-moderate amounts of rain, and warm temperatures. And both of them are all over the place. Places near the equator are hotter, moister, so they get more rain. There are sections of low and high-pressure systems around the world, and sometimes they mix around a bit. So in general, weather forms because of location, humidity, high/low pressures, and more. Hope it helps. ^v^"
Weather,How do the seasons change?,"As the Earth rotates around the sun, the Earth tilts on its axis. So one place might get the sunlight directly or not on an angle, which results in summer, and another place gets sunlight from an angle, resulting in winter, and fall and spring are kinda in the middle."
Weather,Why does clouds form at different heights in the atmosphere?,probaly so it never ends
Weather,why do clouds turn gray when its about to rain why not some other color,"Because water vapor doesn't absorb light. Clouds can appear white or gray by diffusing light, but into order to appear some other color then absorption would have to occur."
Weather,Cant we make an artificial storm with heavy high tech machinery?,"I think it would be possible if we made water vapor condense into a cloud with enough mass to start rain, and some electricity would probably create lightning."
Weather,how are lightning bolts made?,from a burst of energy coming from a storm.
Weather,"what are temperature fonts.
for example what is warm or cold font","A weather front is a boundary between two air masses. It can be thought of as the frontline in a battle, where the warm air represents one side and its 'enemy,' the cold air, the other side. Across a front, there can be significant variations in temperature, as warm air comes into contact with cooler air. This can cause the formation of clouds and even storms. 

I hope that helps! Let me know if you have other questions."
Weather,Is a rainbow a gas or a solid?🌈,rainbow is light reflecting off the water droplets creating a rainbow the light goes through all the droplets creating every color of the rainbow. so neither it is light from the sun reflecting of rain.
Weather,How bright can Lightning get?,"Lightning can be incredibly bright -- about equal to 100,000,000 light bulbs. (That may even blind you)"
The water cycle,So transpiration can happen to all plants?,"Transpiration in plants occurs in all living species with few exceptions, so whether you own an orchard or are growing a lawn, transpiration is an essential active process."
The water cycle,what happens if we cover the ocean,The vapor would go through it but if we use metal it would just keep all the vapor inside of the metal and when we take it off you will see a lot of vapor.I wonder if that would form new clouds live?
The water cycle,why do plants evaporate water?,"Plants have small holes in their leaves called stomata that water evaporates through. Evaporating water through the stomata creates a capillary action that draws new water into the plant through its roots. The capillary action is advantageous for two reasons. First, it allows the plant to pump water from the ground to its leaves without using energy. Second, cycling new water into the plant provides it with fresh nutrients."
The water cycle,Can you physically see the evaporation happening,"If you have a container of water that no water is being added to and you watch it closely, then you will eventually observe that there is less water in it than before."
The water cycle,is the sun the only thing that can make water evaporate?,"For water to evaporate, the environment must be heated. Air that is both warm and dry can give this heat. The evaporation of water inside a confined space serves as an illustration. As a result, sunshine is not required for water to evaporate. so it doesn't need to be direct sunlight to be evaporated.

Hopes it helps. :)"
The water cycle,Does water ever go away?,"No, water keeps changing forms but still remains unless something drinks it which im not too sure on what happens"
The water cycle,How does water form again if the cycle stops?,"Water does not _form again_. It is just in a different state of matter. The water cycle doesn't stop, it keeps on going."
The water cycle,what happens if there was no sun?,"If there was no sun, life on Earth would not be possible as we know it. The sun provides heat, light, and energy essential for sustaining life. Without the sun's energy, Earth would become extremely cold, and photosynthesis, which is the process by which plants convert sunlight into energy, would not occur. This would disrupt the food chain, leading to a loss of plant and animal life. Additionally, the sun's gravitational force helps to keep Earth in its orbit and maintains the stability of the solar system. Overall, the absence of the sun would have a catastrophic impact on Earth's climate, ecosystems, and the survival of living organisms."
The water cycle,HOW do we still have water if we keep drinking it like the dinosaurs did,"_because of the water cycle .... 
The water cycle recycles all the water again and again which tells us that the water is really , really old ._"
The water cycle,Does evaporation happen at night.,"Evaporation happens at night and during the day. Evaporation happens faster at higher temperatures and more slowly at lower temperatures. So, typically there is less evaporation at night."
Global winds and currents,When did scientists start studying currents?,Ocean currents were found in the mid 1700s. Then during 1872 - 1875 one of the first books were written
Global winds and currents,When was the Coriolis effect discovered?,The coriolis effect was didcovered in 1835 by Gustave-Gaspard de Coriolis
Global winds and currents,how does this help us in our day-to-day lives?,"Today, the majority of wind energy is utilized to produce electricity for use in buildings such as homes, offices, hospitals, schools, and industries. The wind is a renewable resource that doesn't contribute to pollution in any way. Strong turbines are used to capture wind energy.

Hopes it helps. :)"
Global winds and currents,Why do we have ocean currents?,"There are two main reasons why we have ocean currents:
Differences in water density, resulting from the variability of water temperature (thermo) and salinity (haline), also cause ocean currents. This process is known as thermohaline circulation.
Surface currents in the ocean are driven by global wind systems that are fueled by energy from the Sun. Patterns of surface currents are determined by wind direction, Coriolis forces from the Earth’s rotation, and the position of landforms that interact with the currents."
Global winds and currents,what of a warm and saltier water does it rise or fall,Warmer water rises and cooler water sinks.
Global winds and currents,I have one question. how does the water like sink and rise?. im rlly confused rn 🤣. pls helpp,"(saying what I know)
It is partially affected by water density. Water density is affected by temperature.
When the water temp is high, the molecules in the water have a lot of energy, (heat is one form of energy)the molecules can move more freely using the energy from the heat thus the molecules are more spread out, making the water less dense.
likewise, when the water temp is cold, the molecules don't have a lot of energy to move around with. making cold water denser. kinda like when you're sleepy. when something is less dense, it is lighter than something denser (warm water is less dense than cold water) which is why warm water rises and cold water sinks. 

How salinity affects water density, I don't think I will be able to say here, for it is a little too complicated to explain in detail,
 but the basic idea is that when salt (NaCl) dissolves in water, the water molecules will split the salt apart (NaCl to Na+ and Cl-) and hold the two ions apart in a cage of water molecules. depending on how much salt is dissolved, the water naturally becomes denser holding the weight of the salt(NaCl).note that dissolving and density depend on the solvent and solute
(solute is what you're dissolving, and solvent is what you're dissolving into)

hopefully this helps, Evan the chemist"
Global winds and currents,why are we learning this,to predict weather patterns and see if its going to rain tomorrow.
Global winds and currents,whats 9 plus 10,"What's"
Regional climates,"Underneath the photo of Greenland, It says that green land is the largest island in the world. I thought Australia was. 
(I live in Australia, so I'm not very happy that Australia is not the world's largest island)","The answer to this depends on what the definitions of “island” and “continent” are. Normally, I find discussions about the definitions of terms to be pedantic and boring, but we can use this one as a jumping off point to learn a bit of geology – namely the distinctions between continental and oceanic crust.

Using a simple definition, someone might say that an island is a landmass that is surrounded by water on all sides. Under that definition, Australia would be considered an island. But it wouldn’t be the biggest island on Earth. There are several other landmasses on Earth that are surrounded by water but are larger than Australia. Antarctica is a clear example.

I prefer a different definition, one that enables us to distinguish between continents and islands. The definition that I prefer doesn’t merely consider whether a landmass is surrounded by water, but also considers whether it is surrounded by continental or oceanic crust. 

The entire solid surface of Earth is covered by layers of rocks that we call the crust. Crust comes in two varieties: continental crust and oceanic crust. The main difference between the two is that continental crust and oceanic crust have different chemical compositions. The basement of continental crust is made of granitic rocks and oceanic crust is made of basalt/gabbro. 

Basalt/gabbro is denser than granitic rocks which causes oceanic crust to sit at a lower elevation than continental crust. Oceanic crust occupies the lowest elevations of earth, water flows downhill, and that’s why oceanic crust tends to have water on top of it. To be clear, oceanic crust does not begin where the ocean touches the beach and sometimes continental crust has water on top of it too. Continents are surrounded by what is called the continental shelf, which is an area of continental crust that is underwater.

Now that I’ve explained the difference between continental crust and oceanic crust, let’s get back to the question: is Australia an island or is it a continent? I’d call Australia a continent. That is because it is not merely a landmass that is surrounded by water, it’s surrounded by oceanic crust. If you go under the ocean in any direction and look at the rocks, you will encounter oceanic crust before you find another landmass.

Greenland is different. Although Greenland is surrounded by water on all sides, if you go under the water on a search for oceanic crust, you will encounter another landmass (Canada) before you find oceanic crust. Therefore, Greenland is an island that is attached to North America."
Regional climates,Where would you guys go for vacation?,The Bermuda Triangle
Regional climates,I like the earth,so do i (upvote this ans pls)
Regional climates,is there pizza in Australia?,yes there is
Regional climates,is there different climates in different regions?,"It depends on the region's distance from the equator, but climate usually is different in different regions."
Regional climates,Does time change throughout the different regions?,If you mean different regions of the world yes it could be 6:00 pm in America but 12:00 am in the UK if you do not mean that then I don’t know how to explain the Regions on the topic above.
Regional climates,what the meaning of regional climate ?,so you can learn about weather
Fossils and rock layers,"Are the different rock layers actually different colors? If not, how do geologists figure out the different rocks from different ages?","Rock layers are sometimes different colors and sometimes they are the same. When they are different colors, the layers are easy to distinguish. When they are the same color, then geologists have to take a closer look to tell them apart.

There is a lot that can be looked at to tell rocks apart. What is the rock made out of? Does it have big grains or small grains? Which minerals are present? What fossils can we find?

After examining the layers for those characteristics, a geologist might find that one layer is sandstone and the other is limestone. The geologist would then know that the layers are different rocks deposited at different times."
Fossils and rock layers,How do rocks get their shape?,"Rocks can be shaped based on erosion, how there'ye compressed into metamorphic rocks, or even what shape lava or magma cools. There are also other ways rocks can be shaped, but these were some of the main ones."
Fossils and rock layers,dose it heat up,It does.
Fossils and rock layers,can you tell the rocks apart,yea by shape and color
Fossils and rock layers,how do plants grow in rocks,"They don't grow inside of them, the rock forms around the plant. When sediment is compressed around the plant it turns into sedimentary rock."
Fossils and rock layers,what is the process of making sand from a rock?,Millions of years of erosion.
Fossils and rock layers,does it heat up?,"The further down you go in the earth's crust, the hotter it generally gets. This is because these deeper rocks are closer to earth's hot core and are under more pressure.

Does that answer your question?"
Weathering and erosion,Can acid rain dissolve human skin? I am curious,"Acid rain is about 100 times less acidic than Coca-Cola. Coca-Cola is not strong enough to dissolve skin. Therefore, acid rain is far too weak to negatively affect your skin in any way."
Weathering and erosion,"So basically if I added water to rock paper scissors, I would win each of them? Nice!","water can melt/dissolve/break down paper, water can erode rock, and water can also rust/mildly erode scissors(plus the fact that scissors can't cut water, and the fact that paper can't catch water either) so, I guess you could."
Weathering and erosion,Can erosion happen fast then others?,"Yes. with let's say a  small rock, sure it can take a while to break it down, but eventually the small rock will break but it won't take as long as it would for a big rock. because the big rock has more volume than the small rock, the water has more atoms to break down for the big rock to be broken."
Weathering and erosion,"if there is acid in rain, how come I'm not hurt when i get raindrops in my mouth?",and i dont think thats how it works it is just the rain water goes into the little crackes in the rock and it starts moveing to make more room for the water and starts braking and moveing into diffrent places for example a hevy storm comes and hits a rock that rock wants compane so it moves to make room and starts moveing and braking and gets swept around when it falls down
Introduction to plate tectonics,so will we every get to explore all the creature and find ones who are thought to be exstint animals under the sea bed kinda like the movie godzilla where there an whole other world,"We might, you never know what technology gets us to!"
Introduction to plate tectonics,Why do they move and why do they transform into different things.,"The tectonic plates move because the heat from radioactive processes within the planet’s interior causes the plates to move, sometimes toward and sometimes away from each other. This movement is called plate motion, or a tectonic shift."
Introduction to plate tectonics,"What will Earth look like 200 years from now? Will there be a part of a volcano somewhere, like by a Walmart?","That's a good question.. for your great great great (and so on, I'm not about to calculate how many greats' ) grandkids. As for if there will be a volcano next to a Walmart, I guess that's up to mother nature. ;)"
Introduction to plate tectonics,What does asthenosphere mean?,""Asthenosphere" literally translates to "weak sphere", so it makes sense that the asthenosphere is the less rigid part of the mantle. It's right under the lithosphere. The tectonic plates drift on currents in the asthenosphere.

Does that help?"
Introduction to plate tectonics,Does America get earthquakes because I have lived here all my life and never felt any vibrations,"America does get earthquakes. The most seismically active areas are: the west coast including Alaska, the areas of Tennessee, Kentucky, Illinois, Missouri, and Arkansas near the Mississippi river, the coast of South Carolina, the big island of Hawaii, and the area stretching from Salt Lake City to Yellowstone National Park. The likelihood of other parts of the country producing an earthquake strong enough for you to feel is quite low."
Introduction to plate tectonics,What does asthenosphere mean?,"There are different ways to divide the earth into layers. I'm sure you've heard of the crust, mantle, and core. Those layers are differentiated based on chemistry. Said differently, the crust, mantle, and core are distinct because they are made out of different stuff.

We can also divide the earth into layers based on physical and mechanical properties. Those layers are called the lithosphere and asthenosphere. The lithosphere is the outermost layer of earth (including the crust and upper mantle) where the rock is hard, rigid, and brittle. The asthenosphere is below that and is where the rock is hot, ductile, and slowly circulating. Circulating rock in the asthenosphere is the mechanism that drives plate tectonics."
Introduction to plate tectonics,I didn't understend about the tectonc plates on the image,"Think of tectonic plates as cookies overlapping, and when they get to their highest breaking point, they become a volcano"
Introduction to plate tectonics,how was all of this discovered?,"plate tectonics theorys started in 1915 when Alfred Wegener proposed his theory of the "continental drift" Wegener proposedthat the continents plowed through "crust of ocean basins" wich would explain why the outlines of many coastlines, like south america and africa look like they could fit together like a puzzle

Keypoints:

#1) 1596 recognition that the plates moved

#2) 1858 Correlating rock type and fossils across the ocean

#3) 1872 Mapping the atlantic Mid-ocean ridge

#4) 1896 Discovery of radioactivity

#5) 1897-1911 Delineating Earths layered interior

#6) 1915 Alfred Wegener nonsense (look at the top)"
Introduction to plate tectonics,why are the tectonic plates named?,So we can keep track of them easier
Introduction to plate tectonics,How Many Tectonic Platers are there in the world,7 major plates and 8 minor plates so 15 plates in total
The rock cycle,how did rocks get hard,"The chemical bonds that hold atoms together in these minerals are stronger in some than in others, and the atoms themselves determine which bonds are stronger than others. Stronger bonds make for stronger minerals and, thus, harder rocks."
The rock cycle,do fish get thirsty,"Saltwater fish must intentionally consume water to obtain enough into their systems, in addition to receiving water from osmosis. But, fish don't have to worry about becoming dehydrated because they can take in water via their skin and gills and live in water. Freshwater fish don't drink water because they have a greater blood-salt concentration than the water they are surrounded by, but seawater fish do so to prevent dehydration.

hopes it helps. :)"
The rock cycle,Why go through so much trouble to study how old a rock is?,It’s hard to answer the basic questions of geology without knowing the ages of rocks. People want to know how long life has existed on Earth and what the earliest lifeform was. We’ve answered those questions by dating rocks containing fossils. Life has existed at least as long as the oldest fossil. Wouldn’t you like to know when dinosaurs lived? We’ve answered that by dating the rocks that contain dinosaur fossils. We’ve determined the age of Earth by dating meteorites. We know when the moon formed by dating moon rocks. When did the Hawaiian Islands form? Which one of the islands is the oldest? Both questions were answered by dating rocks. We can also use our dating methods to answer questions about geologic hazards. When was the last eruption of the Yellowstone Supervolcano? How frequently has Yellowstone erupted? All of these questions have been answered through methods developed by geologists to determine the ages of rocks. They are powerful techniques that answer these questions and so many more.
The rock cycle,is sand sediment,"Sand is sediment. More specifically, sand is a size of sediment. Other common sediment sizes that you may have heard of are clay, silt, and gravel. Sand is larger than clay and silt, but smaller than gravel."
The rock cycle,i dont understand the magama and lava part,"Magma is lava when it is underground, when the magma gets shot out of a volcano, or when the magma comes out of the earth's surface, it becomes lava"
The rock cycle,why is the rock cycle important?,"It's important because it can help grant insight to the history of our planet, teaches us about how humans are impacted by natural disasters, and even provides resources that we use every day (such as salt and diamonds for drill-bits)."
The rock cycle,how Sedimentary rocks form into Igneous rocks,"If a sedimentary rock is subjected to intense heat it will melt. Once it rises up and cools down, it will form an igneous rock"
Plate tectonics and the ocean floor,why do waves in the ocean happen,"The common, constant waves that you see in the ocean are caused by wind. Storm surges, underwater earthquakes, and underwater landslides also generate waves, but those are relatively rare events."
Plate tectonics and the ocean floor,Will the people go and look in the trench for other animals that haven't been seen before.,yes they will so we don't face them in the near future
Plate tectonics and the ocean floor,"can people go in a trench, find megalodon DNA, and bring it back?","In simple words, yes."
Plate tectonics and the ocean floor,"1. how does the black hole is form. 
2. I am the biggest bird.","Im da biggest birb, muahhahaha!"
Plate tectonics and the ocean floor,"Is it safe for people to just go in the Mariana Trench ?
Like will we be safe and be able to get out of it safely ?
Is there any restriction for it ?","Look it up on Google, Safari, Microsoft Edge, etc."
Activity: how does weathering affect natural landscapes over time?,how is it possible for water to wear away rock?,Hydrogen bonds can slowly pull apart the atoms that make up rocks.
Activity: how does weathering affect natural landscapes over time?,why does it rain,Water in clouds get to heavy and comes down as rain.
Natural hazards,How far ahead of time can forecasters predict an earthquake?,"It depends on what you mean by predict. Seismologists are able to identify areas that have high probabilities of producing earthquakes within years or decades. But it is absolutely not possible to predict the time, location, and magnitude of an earthquake."
Natural hazards,how do i answer the percentage question? i'm not the best at math. i need help,"A percent is a part divided by the whole. I went into the natural hazards practice here and got a question asking "Approximately what percent of major natural disasters in 2020 were floods?". First I had to find the part, which was 193 floods. Then, the whole was the total number of natural disasters: 313. Then I divided 193 floods by 313 total natural disasters and got about 62% of 2020's natural disasters were floods. 

Make sure you multiply the decimal answer you get from a calculator (about 0.62 in my case) by 100 to get the percent.

Does that help?"
Natural hazards,Why do tornados form with warmness and heat?,"For a thunderstorm to produce a tornado requires warm humid air near the surface with cold dry air above. These conditions make the atmosphere very unstable, in the sense that once air near the ground is forced upward, it moves upward quickly and forms a storm.May 1, 2011"
Natural hazards,Do Lava-nadoes exist?,"lava is molten rock, making it very heavy. Even though tornadoes are strong, they aren't strong enough to lift molten rock into the air."
Natural hazards,"how can we predict some natural disasters but cant others, like how did we learn how to know when a tornado is coming yet we dont know the patters or the similarities that happen when a earthquake hits?",Small earthquakes always happen on earth so scientists can't predict when it is going to start causing damage. But some other stuff don't happen all the time.
Natural hazards,When is the next hurricane going to occur?,Depends on how Jesus feels. lol
Natural hazards,Are there really any signs that is earthquake is going to happen?,"foreshocks, ground tilting, water levels in wells, and the relative arrival times of P- and S-waves.

Hope this helps:)"
Natural hazards,what is a tornado in water called,"Waterspouts fall into two categories: fair weather waterspouts and tornadic waterspouts. Tornadic waterspouts are tornadoes that form over water, or move from land to water. They have the same characteristics as a land tornado.
  I got that from google hope it works!"
N/A,why cant we sometimes see the stars at night?,Because clouds cover them but it sometimes the way the earth is moving/facing
N/A,Why are clouds closer then we think they are,"The type of cloud that is formed will determine what level the cloud is in the atmosphere.
The various cloud types have different characteristics that are dictated by the elements available, including the amount of water vapor, the temperatures at that height, the wind, and the interplay of other air masses.
Colder clouds are higher in the atmosphere while warmer ones are closer to the surface. Also, warmer clouds can hold more water vapor than colder clouds, making it possible for clouds closer to the surface to become thicker and bigger than higher clouds."
N/A,what causes the clouds to become dark when it is about to rain?,Clouds get thicker and darker as their water content increases. It's more difficult for light to pass through a thick cloud that has lots of water in it and that causes the cloud to appear dark.
N/A,"While we need fossil fuels for somethings, it does not mean they are reliable. If we keep mining and have factories that produce these things, we are destroying the Earth. We need to take care of our Earth, because it is the only one we have.","I agree with you. Fossil fuels are a finite resource and their extraction and use have significant environmental impacts. The good news is that there are many alternatives to fossil fuels that are cleaner and more sustainable. Some of these alternatives include solar, wind, hydroelectric, geothermal, and biomass energy. Do you want me to look up more information on this topic?"
N/A,Why are clouds kinda close and not too high up ?,"The type of cloud that is formed will determine what level the cloud is in the atmosphere.
The various cloud types have different characteristics that are dictated by the elements available, including the amount of water vapor, the temperatures at that height, the wind, and the interplay of other air masses.
Colder clouds are higher in the atmosphere while warmer ones are closer to the surface. Also, warmer clouds can hold more water vapor than colder clouds, making it possible for clouds closer to the surface to become thicker and bigger than higher clouds."
N/A,"wait, but how does a dam decrease fresh water in a another region?","if the dam holds water from a stream, the water flowing out of the dam downstream from it could be a lot slower than if the dam weren't there, and that could decrease fresh water in another region"
N/A,what if stars are just holes poked in a container we live in?,"How would we test this idea against our observations of the natural world?

One possible prediction of stars being holes poked in a container is that stars would all be the same color: that of the light in the environment surrounding our container. Just with our eyes, we can observe that some stars are red or blue, for instance, so we know that isn't true. With more sophisticated equipment, we can tell from stars' light that they're different temperatures, too!

Does that answer your question at all?"
N/A,"Are things we set in space re-useable? B/c, everywhere i see its like markers or plastic. But can the materials engineers use to make space equipment be re-used? And if yes, where? Btw, i searched the whole net and i got weird answers. If that wasnt clear: Can can the equipment they use to make rockets/jets be re-used?","Not really. Before the Space Shuttle, all components of a rocket were dropped into the ocean or fell into micro-orbit. Nowadays, SpaceX is trying to create a rocket that can land and be reused."
N/A,If its day time here and its night time on the other side of the world then why can we see the moon around 3:00 sometimes,"The moon orbits the Earth, meaning that sometimes we're able to see it during the day."
Activity: how and why is Earth's climate changing?,"This is insane, the Earth is becoming more toasty and researchers want to make it colder, they should consider the reason why mammal population started growing rapidly during the cambrain explosion. And also, making the Earth colder will make us more vulnerable to viruses, we are only human after all.","False. Mammals and other land animals did not exist during the Cambrian Explosion. You are about 450 million years off. Also, the fact that you are more susceptible to a cold when it is colder outside is an urban myth. 

Global warming is something we should be serious about and take care of."
Human impacts on the environment,how did the water just suddenly dry up??...🧐,"Global warming is part of the problem but thats not all. Humans over use water for produce, livestock,and humans use water to wash and drink. Does this help?"
Human impacts on the environment,how many animals are there? and where the water??,4 and there is no water
Human impacts on the environment,Where is the water?,"What you are looking at is the aftermath of illegal logging in the Amazon rainforest. There is likely groundwater in the soil, but the now desolate area you see was once full of lush, exotic trees, plants and brush, all native to only the Amazon rainforest. With the trees, go the animals, either by force or of the animal's choice. This is a very saddening image, because they replace the beautiful tree's they've ripped out, with palm trees, which are not native to the area, nor beneficial to any of the wildlife in the area.

You can flip back to the Khan Academy videos on ecosystems, what has happened here, is human beings have destroyed part of an ecosystem. This is also why it is so important to have good conservation and protection efforts, because you are part of the ecosystem too."
Human impacts on the environment,Why does it have any grass,There is no grass because of global warming and human usage. All the water has either evaporated or has been used by humans.
Human impacts on the environment,how many animals are there?,approximately 8.7 million
Human impacts on the environment,"I know that smoke is hazardous to our health, but how can salt be unhealthy?",dehydration
Human impacts on the environment,is there water,yes. even when a place is completely dried up it usually still has nearby water. the world always has the same amount of water and water is always moving to new places it just isn't always spaced evenly.
Earth's changing climate,dang thats alot of smoke,It's gonna get worse
Earth's changing climate,Why human so ignorant and stupid?,Because sometimes we don't think about the climate like when I wasted food or throwed away paper. They just don't realize that they are causing harmful things to the environment.
Earth's changing climate,"I kinda wanna see what the earth would be like when global warming happens. Not that i WANT natural disasters or droughts to happen- i just think it would be really cool if the ocean rises because then people would ride boats everywhere and maybe have boat houses and since all most of the lights are way underwater or broken we could see the stars wayyyyyyy better and it would be like one of those space pictures from the internet that would be so cool!I know it would also be bad but people have been taking control of the earth and doing terrible things to the earth so i think it would be good for the earth to get higher oceans because people would stop burning as much stuff and using a ton of eleturicity and since valcano's would erupt i think in like maybe 100,000 - 10 million years the earth could get new continents, But i also know that it might be bad for the earth because it would mess up the animals habitats and animals wouldn't have enough food or they couldn't get the food they normally have and a ton of things would go into danger or extinction but i'm pretty sure the fish would be okay- but anyway whatever happens i'm gonna see it through >:O",but why not just use nohas ark
Earth's changing climate,"I don't get how climate change can cause more rain and storms. I understand that the poles will melt, but how does more water in the ocean correspond with more rain and thunderstorms?","there will be more water in the ocean there for more water for the sun to evaporate and turn in to clouds
more clouds = more chance of a thunder storm"
Earth's changing climate,The mean temperatures of planets in our solar system are: Mercury - 333°F (167°C) Venus - 867°F (464°C) Earth - 59°F (15°C),Huh?
Earth's changing climate,"These kinds of things make me afraid to have kids because i dont want them breathing dirty air and becoming sick, how do i reassure myself from this stressful situation and how do i as an individual reduce the CO2 in the air?","You can try to reduce the time you spend driving in your car, because cars run off of gas, which is basically fossil fuel, and when you drive your car releases co2 from the exhaust. You should try riding a bike or taking walks and/or jogs. You can also help reduce the amount of co2 by recycling."
Earth's changing climate,why not getrdof power plant,"If we got rid of every power plant all at once, millions who rely on that power to survive wouldn't have it any anymore! We wouldn't be able to survive. Also, there are several jobs that power plants provide. If they shut down immediately, a lot of people would be without work, and then the economy would be impacted too. There are just too many people relying on them for us to just get rid of them. It's better to switch to windmills and solar panels, but gradually, so that we humans can still survive, while at the same time slowly using less and less of these harmful power plants."
Forces and acceleration,How do we remember all this? I´m not kidding.,Practicing more has been shown to aid memory.
Forces and acceleration,Can a force be negative?,"Think of a magnet,when you put the two negative ends together do they attract or repel? They repel and that is a negative force."
Forces and acceleration,"But what if a massive rocket came and pushed an asteroid , so it was small vs big rocket? What would happen?","it would depend on how much force each rocket is outputting, if the bigger rocket is not efficient it could be giving a lot less force and the smaller rocket would win, and if the bigger rocket is efficient it would most likely work."
Forces and acceleration,can a force be negative,"Yes, forces can be negative. Forces have both a magnitude (how "big" of a force) and a direction. A force is negative if it's in the negative direction.

In Physics, we have to define which direction is negative, like putting an imaginary number line in space. We often define down and left as negative. If the force acts in the negative direction, you can say it's a negative force."
Forces and acceleration,"If an object was large and rolled down a hill, would it accelerate faster or just be slow?","It would accelerate faster, because the heavier the object is, the more gravity is acting on the object. If it is large, gravity pulls it more. That explains why a feather slowly drifts to the ground."
Forces and acceleration,Can a force be negative and postitive ?,"If a force is negative, it is just indicating the direction. A force can always be positive."
Forces and acceleration,How do we remember all this? I´m not kidding.,Copy this article and study it. That's what I am doing.
Forces and acceleration,how will this help me,"It will help you figure out what force, mass, and acceleration plus net force because you learn these things you can become a rocket scientist or something else with science."
Action and reaction forces,a equal force is when the force is balance and a opposite force is a force where if your playing tug a war and the other person is pulling the rope their way is that true,"Yes! If the person lets go of the rope, it will go shooting your way."
Action and reaction forces,I don't really get this concept. How does a box of something else push back on you when you push it?,"Whenever you push on a box, the box pushes back on you with an equal force in the opposite direction. This allows the box to maintain its position and prevents it from moving in the direction that you are pushing it. The strength of the force that the box exerts on you depends on the mass of the box and the amount of force that you apply to it. This is because of something called 'action and reaction'. When you push the object, it is the action, and the object pushing back is the reaction. So, the action and reaction are always equal but opposite in direction.

You might argue that you don't get pushed as far back as the that box
And that's because of friction and mass (which you'll learn later on)

Also, the force of the object pushing back is usually very small. For example, if you push a chair, the chair will push back on you with the same force, but since the chair is so much lighter than you, the force it applies on you will be too small for you to feel. However, if you push a wall, you will definitely feel the reaction force as the wall is much heavier and stronger than you, and since a wall probs wont move you'll be able to apply more force.

It’s alot to understand so don’t worry if you still don’t get it for now, you can always carry on in the course and it might make more sense, or you can ask me another question :)"
Action and reaction forces,what happens when you push something up a hill ?,the hill will be pushing back at you (search up newtons third law)
Action and reaction forces,"2+2= fish 
change my mind",yes because fish has four letters
Action and reaction forces,does gravitational force also have an opposite force ?,The ground pushes on the object being affected by the gravitational force.
Action and reaction forces,how do you do this?,*What do you mean?*
Action and reaction forces,so its like when you toss a ball at the wall this is the reason it bounces back?,"Yes! The ball bounces back because scientifically, it “reflects” off of the surface. Some other examples would be looking at yourself in a mirror or hearing an echo."
Action and reaction forces,how much jars of peanut butter to carry the empire state building,730 Million jars of peanut butter to equal the weight of the empire state building.
Action and reaction forces,How come 2 things don't cancel each other out if both are applying the same amount of force?,"Because they are on two different objects,
if both the forces are on the same object it dose cancel out. But not when the forces are on different
objects."
Representing motion,Could a person run faster than a car.,Maybe depending how fast the car is moving...
Representing motion,did you know that if the earth stopped spinning for just 1 millisecond everything on earth would be hurled forward at 1000 miles ph because that's how fast the earth spins?,i think the earth rotates at around 3560 kph maybe its just around 3000
Representing motion,Can a human run faster than a cat?,"Well you would need to know the speed of the cat compared to the human.. it is possible a human can run faster but a cat could run faster too. Not all cats and humans are the same, for example a cat could be fat and slow where as the human racing the cat could be very fit and fast. But it could also be the same way with the human being slow and the cat being fast."
Representing motion,why does the yellow truck think the blue car is going at 5mph if the blue car is ahead of them? the yellow truck should be much ahead of it if it's 5mph,"It's the *perceived* speed. The yellow truck can think of itself as stationary because its speed is constant and doesn't speed up or down, so to it all of the movement outside the window is the world itself moving around it.

Because the blue car is moving 5mph faster, the yellow truck that think itself stationary, will see the blue car is moving at 5mph only.

---

Here's more details if you're still confused:

The yellow truck will also see the trees on the sidewalk moving backwards at 40mph! But trees don't walk?! Yes, because this is the result of the truck seeing itself as stationary.

Someone on the sidewalk will see their "real" speeds at 40mph and 45mph. But also remember that's just another reference frame, Someone from space will see them both moving at a VERY fast speed because of earth's rotation!

This is what reference frames are all about: there's no "real" speed, it's all relative to your current reference frame. From the reference frame of the milky way galaxy, we are all moving at an extra speed of 828,000 km/hr! That's 515,000mph!

---

This is very relevant to real life btw, for centuries people thought that earth is stationary, and all the other planets are the ones doing all the movement. This led to a lot of messy math that couldn't account for all the planets movements correctly, because the earth IS moving relative to the other planets, and NOT at a perfectly constant velocity! It speeds up and slows down slightly as it orbits the sun, and so do the other planets.

So this is why it's important to choose your reference frames wisely, it's ok to assume earth is stationary when you're just working with cars on the road. But if you want to know how earth moves relative to other planets, you have to pick the sun as your stationary reference frame, even though you know its moving in the galaxy, it's not relevant here.

----

Edit for clarity, Speed VS. acceleration. Thanks @Crystal

Speed is relative, it depends on reference frame.
Acceleration (speeding up and down) is NOT relative, it's absolute.

Example: imagine you're in a windowless car moving at perfectly constant speed (no acceleration at all) on a frictionless road. Since you can't see outside, how can you tell if the car is moving? You can't, you could be stationary or you could be moving at super high speed, as long as it's constant speed, you can't tell the difference. 

Now imagine the car suddenly accelerates and speeds up, NOW you can tell that it IS moving, the acceleration will give it away, and if you had an accelerometer you can read the acceleration value. That's why acceleration is absolute while speed is not."
Representing motion,"If I jump out of a car window going 200 mph, and land on a trampoline. Will I die or will I go really high in the sky?","Both Cause if you can break your hand on the trampoline slow in perspective to 200 mph ,they you can die on the trampoline going very fast"
Representing motion,does the mass increase the speed,"Mass does not affect speed directly. If two objects with different masses move at the same speed, the object with more mass will not move faster. However, when an object is more massive it becomes harder to put into motion or stop when moving than a less massive object. Because more mass means more resistance. so to answer your question, more mass will not directly affect the speed of the massive object. But the more massive object will need more force to be at the same speed as a less massive object."
Representing motion,how do i walk on water,put water on the ground and step on the water boom
Representing motion,how fast is the earth moving relative to the sun,"It covers this route at a speed of nearly 30 kilometers per second, or 67,000 miles per hour."
Representing motion,what is quantum physics and what does it do and what are its uses?,"Quantum physics is the study of matter and energy at the most fundamental level. It aims to uncover the properties and behaviors of the very building blocks of nature. While many quantum experiments examine very small objects, such as electrons and photons, quantum phenomena are all around us, acting on every scale."
Representing motion,so practically it's not moving negative 5 mile per hour it's you're just subtracting five because the blue car is moving 45 and the other car is moving at 40 miles per hour,"The yellow truck is moving at 40 MPH, to the driver of the blue car, this looks like the truck is travelling at -5 MPH as the truck is slower then the car, trailing behind at a constant speed of -5 to the driver of the car. To the driver of the truck, the car is travelling at +5 MPH, the car is always in front of the truck. To a pedestrian on the side of the road, the car is travelling at 45 MPH and the truck is travelling at 40 MPH."
Electromagnetism,This is really interesting but also quite difficult to wrap your head around. Will we further delve into this topic in High School and College Physics?,Probably
Electromagnetism,Why does everything have energy,"Everything in the universe has energy because energy is a fundamental property of matter and particles. At the most basic level, all matter is made up of tiny particles called atoms, and these atoms contain energy. Fun fact, Energy is conserved, meaning it cannot be created or destroyed, but it can be converted from one form to another."
Electromagnetism,what if we never had eletromagnets,"electromagnets have a profound impact on our daily lives and are integral to numerous technological advancements. Without them, our ability to generate electricity, power devices, communicate, conduct medical diagnoses, and pursue scientific research would be severely limited, but humans could still live"
Electromagnetism,What can electromagnets be used for?,"Generators, motors, transformers, and a lot more."
Electromagnetism,How can sun get blocked by the moon if the sun is way bigger?,"The Sun is completely blocked in a solar eclipse because the Moon passes between Earth and the Sun. Even though the Moon is much smaller than the Sun, because it is just *the right distance* away from Earth, the Moon can fully blocks the Sun’s light from Earth’s perspective."
Electromagnetism,what can electromnets be use for,They are sometimes used in cranes.
Electromagnetism,why do we need electromagnets to help us with technology?,"Electromagnetism is an extremely important field. You use forms of electromagnetism everyday, from turning on a lamp, turning on a microwave, doing laundry. Motors in these devices are created with electric currents which are created from your power company using electromagnetism to produce electricity which travels through power lines into your home's power system, powering your house. So, by reading this, typing on your computer, you are using electromagnetism for your technology."
Electromagnetism,how doses the magnetic force transfor from the particals to the wire?,the particles are part of the wire basically what it's made out of. So the wire and the particles are both charged.
Electromagnetism,I thing I should copy that study work.,I think that is a good idea if you have a test on it
Electromagnetism,How can sun get blocked by the moon if the sun is way bigger?,The moon is much closer and appears to be larger in special scenarios such as the one you're talking about. It's all about the perspective.
Fields,"Wouldn't dark energy be classified in physics? It is a type of energy after all and the opposite of gravity, right? Actually, what specifically is dark energy? Give me a vote if you think this is interesting. And give it to :P. He also gets the credit for answering this question. Thank you :P!
P.S - Could someone please give me one more vote? That is all I need. Thank you very much.
P.S.S - I know all about your life!","Dark energy is a mysterious form of energy that is believed to make up a significant portion of the universe but is not directly observable through electromagnetic radiation (like light) or any other known means of detection. It was first proposed as a theoretical concept to explain the accelerated expansion of the universe.

Here are some key points about dark energy:

Accelerated Expansion: In the late 1990s, astronomers made a surprising discovery while studying distant supernovae (exploding stars). They found that the universe's expansion is accelerating rather than slowing down, as previously thought. This observation implied the presence of an unknown force pushing galaxies apart at an increasing rate.

Einstein's Cosmological Constant: The concept of dark energy is often associated with the cosmological constant, first introduced by Albert Einstein in his general theory of relativity. Einstein initially introduced the cosmological constant to keep the universe static, but later discarded it as unnecessary when the expansion of the universe was discovered. However, dark energy is now thought to be a possible explanation for the observed accelerated expansion and is sometimes referred to as Einstein's cosmological constant.

Properties and Nature: Dark energy is hypothesized to have negative pressure, meaning it counteracts gravity's attractive force, causing galaxies and galaxy clusters to move apart faster. Its exact nature remains one of the most significant unsolved mysteries in cosmology. Several theoretical models propose different candidates for dark energy, including the cosmological constant (associated with vacuum energy) and dynamic fields like quintessence.

Dominant Component of the Universe: According to current scientific understanding, dark energy is the dominant component of the universe, accounting for about 68% of its total energy content. Dark matter, another mysterious substance that does not emit light or energy, makes up around 27%, while ordinary matter, including stars, planets, and galaxies, accounts for only about 5% of the universe.

Despite significant progress in cosmology, much about dark energy remains unknown. It continues to be an active area of research and investigation, with scientists working to understand its properties, origins, and implications for the future evolution of the universe.

I hope this helps!"
Fields,"In the video, they said that the closer an object gets to another object's _field_ of *gravity*, then the object will feel a stronger _pull_ of *gravity*. Is that what happens inside black holes? Is that why even light cannot escape? I think it might be because of how much mass the black hole has right?","Yes, the black hole is very, very dense. This means its mass is very large. Because of this, it sucks in everything near it. Even light."
Fields,What makes the earth orbit around the sun,The gravity from the sun.
Fields,how can you tell where a gravatational force is?,Anywhere something has mass.
Fields,how do u know where a gravitational fields begins and ends,It depends on the force of it... maybe the farther the gravitational fields go it probably gets weaker and probably stops at a point at distance? This is just a hypothesis.
Fields,What makes the earth orbit around the sun?,Gravity
Fields,How do you know where a gravitational field is?,i guess theres one everywhere gravity works
Fields,Magnets have a magnetic field around them. But magnets also have mass. Does this mean that a magnet has both a magnetic field and a gravatational field?,*Yes*
Fields,If an object has enough mass could it collapse on itself? And could that object have a moon that would exert enough gravitational force on the object for it to prevent the object from collapsing on itself?,"Yes, when and object collapses in on itself, whoch is usually a star, it either goes supernova, and spreads the matter everywhere, sometimes making a nebula, collapses, becoming a black hole, or becomes a neutron star but I forgot how that one worked. And also I don't think a moon or planet or even other star could prevent a dying star from collapsing or exploding, as it would need to take away it's matter from it. A black hole could."
Activity: how do bees pick up pollen in flowers?,what flower is that in the pic?,Richardia grandiflora
Activity: how can a skydiver fall safely?,"Me: An activity ok...
+reads the first paragraph+
Me: ok
+jumps out of an airplane with a parachute on my back+
+parachute was actually a backpack+",What if your parachute won’t open?
Activity: how can a skydiver fall safely?,Is there a greater pull higher or lower from the ground.,"There is a greater pull lower to the ground, as gravity follows the inverse square law. If you are twice as far from the Earth as you were a little while ago, gravity is 1/4 as strong as it was."
Activity: how can a skydiver fall safely?,""It's not the fall that kills you, it's the sudden stop in the end."
So I guess, scientifically, skydiving should have a 100% mortality rate since opening a parachute causes you to stop suddenly","If a parachute caused you to stop suddenly, you would be stationary and hung in the air. This, obviously, does not happen. Parachutes suddenly slow you down, but they do not suddenly STOP you as the ground would."
N/A,Can magnets lose their magnetic field or power over time?,"Yes, they actually do decay over time."
N/A,how are magnets made? and how did they come up with the compound/mixture to make magnets! and how do they repel? is it a natural function?,"There are several processes for making magnets, but the most common method is called Powder Metallurgy. In this process, a suitable composition is pulverized into fine powder, compacted and heated to cause densification via “liquid phase sintering”. Therefore, these magnets are most often called sintered magnets.
Magnetism is the force exerted by magnets when they attract or repel each other. Magnetism is caused by the motion of electric charges."
N/A,I wonder if we can turn off the magnet? Arent this an infinite force?,Turn off is a little ambiguous. But demagnetization is possible. Demagnetisation is achieved by using the alternating magnetic field to move the evenly aligned elementary magnets into homogeneous disorder and to generate as fine a domain structure as possible.
N/A,How are the north and south poles of a magnet determined? Where do magnets get a north and south pole and does it have anything to do with our planet's north and south poles?,You can determine the north and south poles of a magnet by placing a magnet next to a compass and the compass will point toward the south pole of the magnet.
N/A,Why do opposite poles attract each other but not the same poles?,"Opposite poles attract each other but not the same poles because the density of the magnetic field lines is higher near the poles where the magnetic force is stronger. When two magnets are placed with their like poles facing each other, the lines of force are in opposite directions, and the like poles repel each other.

I hope this helps!"
N/A,Are magnets more attracted to some metals than others?,"Yes, for example, metal spoons and others are attracted to the magnet. but the electric water boiler's metal doesn't."
N/A,When people are making magnets how do they do what is the north pole and what is the south?,"You can hang the magnet on a line and make it sway. When the magnet stop moving. The side facing north is the north pole, the side facing south is the south pole."
N/A,When people are making magnets how do they do what is the north pole and what is the south?,A north pole will attract a south pole; the magnets pull on each other. But the two north poles will push each other away
Electric forces,We need some Minecraft education mode in Khan Academy,Yea we need Minecraft
Electric forces,why is it that when you slide down a slide or get out of a car and then touch something or someone you get shocked?how does this happen?,"it's called static electricity ,
static electricity is when your hand (or something else ) builds up electricity and all of it gets released at once when you touch something metal 
i hope this answers your question
i know this is a very cheesy ending but
have a nice day"
Electric forces,wait we have magnets that have positive and negative charges what would happen if they were both neutral would they stick together anymore if someone know that answer to this pls tell me this is facinating,don't confuse yourself between magnetic forces and electric forces. in magnets you can't make them neutral because the magnetic field of the magnet exerts the force. over here in electric forces its the force between charges. if you want you can remove the magnetic field of a few magnets by various methods but then it wont stick to anything.
Electric forces,Does a - and a - attract?,"nope. they repel
same charges repel"
Electric forces,Is the letter W and M attracted?,No because they are not objects that you can feel.
Electric forces,what would happen if the charges die,i feel like they wont if there magnets
Electric forces,how does this happen,"Electrical forces occur due to the interaction of charged particles, such as electrons and protons. These charged particles exert forces on each other based on their charges and the distance between them.

The fundamental property responsible for electrical forces is electric charge. Electric charge can be positive or negative. Like charges (positive-positive or negative-negative) repel each other, while opposite charges (positive-negative) attract each other.

The interaction between charged particles is mediated by the electric field. An electric field surrounds any charged particle and exerts a force on other charged particles within its influence. When a charged particle enters the electric field of another charged particle, it experiences a force due to the interaction of the electric fields.

According to Coulomb's law, the strength of the electrical force between two charged particles is directly proportional to the product of their charges and inversely proportional to the square of the distance between them. Mathematically, the electric force (F) between two charged particles can be expressed as F = k * (q1 * q2) / r^2, where q1 and q2 are the charges of the particles, r is the distance between them, and k is the electrostatic constant.

Electrical forces are responsible for various phenomena in our daily lives, such as the attraction or repulsion of magnets, the flow of electric current in wires, and the behavior of charged particles in electric fields. They play a crucial role in understanding and explaining the behavior of charged particles and the functioning of electrical devices."
Electric forces,how does this happen,"Electrical forces occur due to the interaction of charged particles, such as electrons and protons. These charged particles exert forces on each other based on their charges and the distance between them.

The fundamental property responsible for electrical forces is electric charge. Electric charge can be positive or negative. Like charges (positive-positive or negative-negative) repel each other, while opposite charges (positive-negative) attract each other.

The interaction between charged particles is mediated by the electric field. An electric field surrounds any charged particle and exerts a force on other charged particles within its influence. When a charged particle enters the electric field of another charged particle, it experiences a force due to the interaction of the electric fields.

According to Coulomb's law, the strength of the electrical force between two charged particles is directly proportional to the product of their charges and inversely proportional to the square of the distance between them. Mathematically, the electric force (F) between two charged particles can be expressed as F = k * (q1 * q2) / r^2, where q1 and q2 are the charges of the particles, r is the distance between them, and k is the electrostatic constant.

Electrical forces are responsible for various phenomena in our daily lives, such as the attraction or repulsion of magnets, the flow of electric current in wires, and the behavior of charged particles in electric fields. They play a crucial role in understanding and explaining the behavior of charged particles and the functioning of electrical devices."
Gravitational forces,Up vote my comment for a cookie🍪,where's my cookie
Gravitational forces,I wonder what happens if you stand very close to the Earth's core. (If you can't burn to the heat),huh good question I am wondering that too
Gravitational forces,_What is wrong with these comments?! XD_,the comments are weird but fun to read
Gravitational forces,I wonder what happens if 2 items with difference gravitational touches for ex. 2 magnets on opposite sides - and +,they would pull together
Gravitational forces,What if the sun was closer to the earth we would be burning up even more in the summer.,we are already being pulled by the suns gravitational force thats why the earth is revolving around the sun
Gravitational forces,What if I stay in space for 1 week I'll be dead?,you will die after the first 90 seconds and thne youll freeze as a whole unless youre next to a star then youll burn to a crisp peice of toast:)
Gravitational forces,what is the difference between gravity and gravitational force?,Gravity is the name of the phenomenon and gravitational force is how much power the gravity of an object has.
Gravitational forces,I wonder what would happen if I moved the Earth out of its orbit and into a straight line.,we'd die
Gravitational forces,what if you had a balloon? Why does it float not bang straight to the ground?,"Helium! It's less dense than air, and balloons that float are typically filled with helium, a gas that is less dense than the gasses in earth's atmosphere. That means a balloon-sized ball of helium weighs less than a balloon-sized ball of air. The difference in density is the key to a balloon`s floatation. 

I hope this helps!"
Changes in energy,why is there no video,"i don't know, but I guess this will have to do :/"
Changes in energy,Does velocity matter in transfer of energy,"Yep! There is a formula for Kinetic energy that says KE = half of your mass times your velocity squared (1/2 m v^2). So if two rocks both transfer all their energy somewhere, and both have the same mass, but one of them has a much greater velocity, then the one with the greater velocity will transfer more energy! This makes sense if you think about how much of a splash you can make in a pond by throwing a rock much harder (more velocity) or much softer, for example."
Changes in energy,"it says that if one object loses energy then another object gains that energy, so if you're sick and you lose some energy where does it go?","When energy is lost, it is usually converted into heat1. For example, when waste and dead matter are broken down by decomposers, the nutrients are recycled into the soil to be taken up again by plants, but most of the energy is changed to heat during this process1. However, the energy is still present in the system as kinetic energy. To bring the system to rest, the kinetic energy of the system must be transferred to some other part of the system1."
Changes in energy,If energy can’t be created how does it form,"It can't be formed, according to the Law of Conservation of Energy."
Changes in energy,"If water freezes and becomes ice, will it have the same weight as before? (i know that its different volume and mass, but how about weight) ?  pls explain","#Meow🤣, anyways *yes*, the water would have the *same mass* as the ice because no matter the form of anything it will always be the same mass or have the same mass. 

Sorry I'm *17 Days* late but Hope this helps! :)"
Potential energy,dose the mass of the object mater,"yes, so say there are two cars going the same speed, one is heavier than the other, you might think they have the same kinetic energy. But the larger car has more than the other because it has more mass. Just because mass doesn't matter as much, doesn't mean it doesn't matter at all.🙃"
Potential energy,"Wait, so when two positively charged objects get further away from each other, shouldn't their potential energy _increase_? After all, when they're further apart, you could move them closer, and make the electric energy stronger (because they're repelling each other more strongly as they get closer). So since the potential for the electric energy to increase increases (since the maximum would be when the objects are actually touching), shouldn't potential energy increase?","Potential energy is just the potential of kinetic energy in a given force. When two positively charged objects get further away from each other, the potential energy does not increase because the potential of the kinetic energy is not at its highest. In an electrical force, the potential of kinetic energy is highest when two objects are moving opposite the force direction. In other words, the potential kinetic charge will be highest when the two objects approach each other of equal net-charge. In gravitational force, it's a little different because the potential of the kinetic energy is highest when the objects are further away from each other. For example, when an apple falls from a very tall tree, the potential energy will be greater than if the apple falls from a small tree. Potential energy increases when an object (anything matter) moves opposite a force's pull."
Potential energy,What is the most common potential energy we use every day.,We mainly use gravitational potential energy every day.
Potential energy,what is the potential energy equation ?,"potential energy(P.E)
P.E=mgh
m=mass
g=gravitational acceleration
h=height"
Activity: why doesn't a basketball bounce forever?,"I have a theory... that I doubt is true but it makes sense. See, let's say when you were 3, you decided to drop a bouncy ball on the parking lot from a 5 story building. So, we know that as it bounces, the energy is slowly seeped into the ground until the ball has none. So, the energy has been transferred to the ground and according to the laws of physics energy is never created nor destroyed so is that energy from the ball, 10 years later, TECHNICALLY still in Earth roaming around and doing whatever energy does? Just curious ^^","More specifically...

Your theory is not far off from the truth! According to the Law of Conservation of Energy, energy cannot be created nor destroyed; it can only be transferred or converted from one form to another. So, when you dropped the bouncy ball from the 5-story building, the ball's kinetic energy was transferred to the ground upon impact, causing a small vibration in the ground. The vibration then dissipates into heat energy and sound energy as the ground returns to its original state. While the energy itself is not necessarily "roaming around," it has been absorbed by the surrounding environment and converted into different forms of energy, such as heat and sound. In other words, the energy that was once in the bouncy ball is now spread out among various forms in the environment."
Activity: why doesn't a basketball bounce forever?,Can something bounce without making a noice?,"Yes, something can bounce without making a sound. For example, if you drop a ball on a soft surface like a pillow or a foam mat, it will bounce without making much noise. However, if you drop the same ball on a hard surface like concrete or wood, it will make a sound when it bounces1.

I hope this helps!"
Activity: why doesn't a basketball bounce forever?,"When a basketball bounces (without being pushed down), it does not go all the way back up to its original height, as shown in Figure 2 below. This is because the basketball had an inelastic collision with the ground. After a few bounces, it stops bouncing completely. The energy has left the ball!",And?
Kinetic energy,how can we find the mass,It will usually be given in most exercises
Kinetic energy,"How would you get the mass of the object ? 
How would you get the weight of the object ?","Mass and weight are actually not the same thing in Physics, even though we sometimes use the words interchangeably in everyday life. Mass can be described as “how hard it is to move” something. Imagine you and an elephant are each on a skateboard. If we gave the same push to each of you, you would move a lot more than the elephant. That’s because you are less massive than an elephant.

Weight is the force of gravity acting on an object. Because gravity can be stronger or weaker depending on what planet (or other object) you’re near, your weight changes too! If you went to the Moon, the force of gravity on you would be about one-sixth what it is on Earth. That means that even though your mass is the same on the Earth or Moon, you’d weigh much less on the Moon!

We often measure an object’s mass by comparing how gravity (in the same location) acts on a known mass for comparison. If you see a balance-style scale, it’s measuring mass. 

Weight is measured like other forces. Many bathroom scales use springs to measure the force of gravity acting on the object on top of them. This means if you took a bathroom scale to the Moon, it would read one-sixth your weight on Earth. 

Does that help?"
Kinetic energy,How can we get the mass of an object,If the object is small enough to fit on a scale then we just weigh it.
Kinetic energy,I wonder who invented words. Because that person is smart,"It is difficult to attribute the invention of words to any one person or group. Scholars believed that all writing originated in ancient Sumer (in Mesopotamia) and spread over the world from there via a process of cultural diffusion. However, there have been many famous linguists and lexicographers throughout history who have made significant contributions to the development of language1.

For example, William Shakespeare appears as the first documented user of more words than any other writer, making it convenient to assume that he was the creator of all of those words. In reality, though, many of these words were probably part of everyday discourse in Elizabethan England2.

I hope that helps! Let me know if there is anything else I can help with."
Kinetic energy,what does mv stand for when you calculate kinetic energy,M is mass and v is velocity
Wave properties,Is there a certain name for the starting point of a wave?,"Yes, the origin"
Wave properties,What ocean has waves with the higest frequency?,not that type of wave bro
Wave properties,What gives the wave energy,"A wave is one way of how energy travels, so the wave is energy itself. How the energy travels as a wave, such as its velocity, depends on the type of energy however. A pulse of electromagnetic energy, for example, such as lighting, will travel at a higher frequency than that of sound energy."
Wave properties,can a wave length be measured,Yes. There are special devices to do so.
Wave properties,why does the wave go up and down?,Doesn't have to. Depends on how the energy is moving.
Wave properties,Why are hearing aids made of plastic (ignore this question)? Is it possible if we put aluminum in the form of a hearing aid in the ear that we will hear better?,Not to be an answer....
Wave properties,Frequency is how many crests (or how many troughs) pass a location per second not vaguely "in a certain amount of time" as per the official definition.,"The convention is per second, but in a certain amount of time is still valid. It is valid especially if the fraction is very ugly. People would rather say that the frequency is 1 "beat" per every 3 seconds rather than .3333333333333 beats per every 1 second."
Digital signals,""Digital signals are more reliable because interference or noise can be easily removed from the received signal. However, every change within an analog signal contains some information, so interference or noise can be almost impossible to remove." do you mean that interference can be removed from digital but not from analog?","Essentially. Digital values are exact, they leave little room for interpretation, but Analog has more room for error, but also, more room for interpretation. Depending on what Analog is being used for, this could be a good thing."
Digital signals,"I would like to know that what course should I take for physics subject after finished this middle school physics, please?","High School Physics
OR
High School Physics - NGSS"
Digital signals,"If waves have ups and downs depending on its volume, it can be that the starting of the wave is at 2, but it doesn't end at two, then how do you find its wavelength if you need to look at its identical points?","The wavelength of a wave is the distance between two identical points in the wave. To find the wavelength of a wave, you can use the equation: wavelength = speed of the wave / frequency of the wave. The speed of the wave is usually given in meters per second (m/s) and the frequency is given in hertz (Hz).12

So if you know the speed and frequency of a wave, you can easily calculate its wavelength using this equation. I hope that helps!"
Digital signals,Analogs tell us more details right?,Yes it does
Digital signals,this is very hard,i found it out now
Transmission and refraction,Why doesn’t the line stay straight?,Because the line is refracted.
Transmission and refraction,Why water?,"Because it's accessible and the situation is relatable, and water is indeed another medium."
Transmission and refraction,Why does the pencil go through the water though?,It goes through the water where it should go but because of the refraction it makes it look like the pencil is broken
Mechanical waves and light,what causes the color to move?,"The frequency of waves. Like how many waves a second. For example, low frequency would affect the color (blue, red, yellow). Like this wave: ~~~~. A more frequent wave is this: /\/\/\/\/\/\/\. That will affect the color a bit different."
Mechanical waves and light,What if you can eat color🤔,Eat an orange. You have completed your mission
Mechanical waves and light,why colors,idk maybe because colors are a relaxing thing to the human brain and when the colors brightness or exposure increases it is not a very relaxing thing to the human brain :)
Mechanical waves and light,what is a mechanical wave,"In physics, a mechanical wave is a wave that is an oscillation of matter, and therefore transferes energy through a medium.While waves can move over long distances, the movement of the medium of transmission—the material—is limited. Therefore, the oscillating material does not move far from its initial equilibrium position. Mechanical waves can be produced only in media which possess elasticity and inertia. There are three types of mechanical waves: transverse waves, longitudinal waves, and surface waves. Some of the most common examples of mechanical waves are water waves, sound waves, and seismic waves.

Like all waves, mechanical waves transport energy. This energy propagates in the same direction as the wave. A wave requires an initial energy input; once this initial energy is added, the wave travels through the medium until all its energy is transferred. In contrast, electromagnetic waves require no medium, but can still travel through one."
Absorption and reflection,"*Question*: What happens if the light hits right where the sand and water meet, _what would happen then?_ Would the surface reflect, absorb or both? Correct me if I am being dumb.","No, your question is not dumb. It's perfectly reasonable and means you were really thinking about the lesson :)
To answer you though:
No surface is completely reflective, so if you have a bowl of water in the sunlight some of the light hitting the surface some of the light will still be absorbed.
 At the point where the sand and water meet it will depend on how much they are mixed. If the sand is super saturated there is much more water than sand so the boundary is miniscule therefore it will reflect. (but like I said, nothing is perfectly reflective so much more light will be absorbed in this scenario)
Similarly, if there is more sand than water, the boundary is 'bigger'. So the light hitting it will be absorbed with little to no reflection. 
I hope this helped. Just remember, boundaries are just the stopping point of reflection.
 Stay inquisitive! :)"
Absorption and reflection,Absorption happens when a wave loses energy as it transmits into a material. This can happen in a medium or at a boundary between two materials. what is the meaning of "boundary"?,Consider a system made up of two media. Then the boundary in such a case would refer to the 'interface' where the wave leaves the first medium and enters the second medium as it travels.
Absorption and reflection,"A wave needs a medium to go through, but light from the sun doesn't go through a medium (because space is blank), so how does it happen? I know the Michelson-Morley experiment was conducted to find the supposed medium called aether, but I still don't fully understand it. Could you please answer and explain?","This is true for mechanical waves, but electromagnetical waves (like light) do not need a medium."
Absorption and reflection,Is there a material that could reflect all of the light that hits it?,"It would either have to be, like white beyond imagination, so like, vantablack(look it up) but white, or some kinda S U P E R  M I R R O R. TBH I don't know the awnser, there may be something like that idk about. Great question though. I encourage you to do your research."
Absorption and reflection,Wouldn't it lose energy when it is reflected,"Yes! Light loses energy as it is reflected. But it is in small amounts and also depends on the absorbency of the surface which it's being reflected off of.
:)"
Absorption and reflection,"so basically the more opaque an object is, the more light it absorbs?",Basically Yes
Absorption and reflection,How does a hat reflect light? It's not even a shiny surface so how?,"Not only shiny things reflect light. Everything around us that we can see is reflecting light to some degree, that's why we could see it. Darker colours just reflect less light than lighter colours, and shiny/smooth surfaces (like a mirror or countertop) do not scatter light like a rougher surface might (like your hat). When light hits your hat, it still bounces off into your eye, but the reflected light is all going in different directions because of the rough material.




_please someone fact check and confirm this-_"
Preparing to study biology,is it weird if a 9th grader takes this class in the middle of the summer for fun or is my life just sad,broooo..... SAME!! technically i'm going into 10th grade in fall though
Preparing to study biology,do we have the same genes as our ancestors,"mostly. You see all humans on earth have a 99.9% identical genitic makeup.The remaning .1% sperates you from the world. Usually your genetics are similar to your ancestors but not fully. Over time genes change and can mutate. If you can find some photos of your recent ancestors look at their face shape jawline bodybuild. Most likely it is similar to yours. In the end yes you do have the same genes as your ancestors, but only to an extent."
Preparing to study biology,bruhhhh science is sooo hard,You can learn anything.
Preparing to study biology,Why is the coronavirus going on in this world is it going to stop or keep on evolving than the first wave of this virus going on?,"The only virus humans have ever eradicated is smallpox (though two laboratories do still hold some). Given our track record, then, it doesn't seem terribly likely that covid will ever go away completely. Of course it's not completely impossible, so we'll see what happens.

Covid, like all viruses and living things, is always evolving. We tend to notice this when new variants like those from the UK, South Africa, and Brazil come into the spotlight largely because they likely affect the virus's behavior.

Did this help?"
Preparing to study biology,Can one study biology without these subjects/topics?,"Yes,as you go through the course it will probably explain the concepts that come from other fields."
Preparing to study biology,"I decided to take Geophysical Science in my High School Freshman year rather than Biology. I want to take Physics in my senior year, but cannot because of the course sequence. Is it recommended to double up in Chemistry and Biology?","Hey ThinkBright! Based on your school/district, it would more or less be recommended to double up in Chemistry and Biology. I would encourage you to contact your school/district to address your questions and concerns before your school starts instead of posting here on Khan Academy (there are many people who have different experiences that may not exactly relate to yours.) 

But at the same time, keep in mind that you will need to stick to your decision, whether or not you are going to end up taking one or two science classes. If you are leaning towards taking two science classes, know that it _is_ going to be a challenge (nothing is ever easy!) but you got this. 

Here's a quote that I hope helps you on your learning journey.

“When the going gets tough, put one foot in front of the other and just keep going. Don’t give up.”
― Roy T. Bennett, The Light in the Heart

Have a wonderful day (and school year!)"
Preparing to study biology,Why do we cry? I know how but why,"There are actually three types of tears. Each type is produced for different reasons, meaning that not all cries are alike.

1. Emotions. The most known reason as to why we cry. Some scientists propose that this is to relieve the body of chemicals that cause stress, as it has been noted that stress hormones are more present in emotional tears. 

2. A reflex. If something gets into your eye, your body wants it out as soon as possible to prevent infection or damage. You thus cry what are known as reflex tears. Have you ever got a dust particle or bug in your eye, or chopped an onion (releasing irritating fumes)? Your eyes watered, and you started to cry. You likely did not feel sad or happy, but you still cried. These tears have more water in them in order to flush the object out.

3. Moisturizing your eyes. Yes, your eyes are constantly producing tears, so you are technically crying all the time! However, these tears are there just to lubricate the eye and nourish the cornea. If you had dry eyes, your eyes would get irritated and your ability to see would be reduced.

Let me know if you need more help."
Controlled experiments,"In the case of environmental effects on children and how it affects their health, it being unethical to actually try an experiment, then from what I gather the best way to test a hypothesis would be to say, "When children are exposed to X, Y will happen." and then to collect data. Would legitimate studies only research this from children that are enrolled in such a study at birth with doctors/scientists/researchers taking blood samples or personally investigating the home environment for these factors? Or could this data be reported by parents? How would you account for people who are dishonest on their reports (as Gregory House states in nearly every episode, "Everybody lies.")? Is a retroactive study considered legitimate if children aren't entered into the study until they are older in age? Or if the researcher only relies on the parents' reporting data from birth to the current age that the child is involved in testing a hypothesis?","A lot of researches are done through surveys. Although it wouldn't be the most accurate, if having someone to check if children are exposed to X or if Y is happening is not possible due to financial, privacy, etc. reasons, survey would be the alternative method.

there is even a section on wikipedia of this:
https://en.wikipedia.org/wiki/Survey_(human_research)#Reported_behavior_versus_actual_behavior"
Controlled experiments,"when the coral reefs are bleached does that mean they have died, if not do they stay white forever or return to their original form?","When a coral is bleaching, it expels symbiotic algae (zooxanthellae), which supply food for the coral, get rid of metabolic byproducts, protect it from pathogens and also create its bright colors. Bleaching results in starvation, which is indicated by loss of color. This doesn't mean that they have died - if the corals find a different nutrient-supplying species, they can regenerate and stabilize again. If they don't find new symbionts and the factors which contribute to bleaching persist, then the coral might die of starvation or disease.
A colony of corals might regenerate if corals or their polyps from other colonies migrate and reproduce successfully elsewhere, where the conditions for growth are more favorable."
Controlled experiments,"So hypotheses are like conditional statements?

Thanks to anyone who answers,
Jack.",Yep! That's a great way of thinking about it. You could write your hypothesis as an if-then statement. :)
Controlled experiments,"How many times do you need to repeat an experiment in order to see if your  hypothesis is nearly true or not? 
Also how big does the sample size need to be to conduct the experiment? 10,20,100?","There are no official rules about how many times experiments should be repeated to be reliable. However, the replication level of your experiments will have an impact on the statistical tests you can perform on your dataset (parametric or non-parametric tests, which do not have the same power).

If the aim is to determine whether an event has occurred (for example, whether a pathogen is present in a colony of animals), the number of animals that need to be tested or produced is given by

Image p20007f55g177001.jpg
where β is the probability of committing a Type II error (usually 0.10 or 0.05) and p represents the proportion of the animals in the colony that are not infected.

*Sample size depends on type of experiment.*

Here is paper with formula:
https://www.ncbi.nlm.nih.gov/books/NBK43321/"
Controlled experiments,What is another example of an everyday use of controlled experiments?,"if you planted different types of seeds in each of the pots, trying to determine if soil type affected germination, you might find some types of seeds germinate faster than others."
Controlled experiments,"Isn't taking coral reefs from their environment unethical since corals are disappearing? Why not create an experiment that would remove co2 levels by adding plants that sequester carbon near the bleached corols? The corols in the water that do not have plants that sequester carbon would be the control group, while the others would be the experimental groups. The independent variables would either be the co2 or pH levels. The dependent variable would be the degree of bleaching from the corals. You would do a side-by-side comparison of each of the waters that have different co2 levels. Then, you could do large/repeated sample sizes by testing waters with high/medium/regular co2 levels that have corals in the water.","Adding plants would disrupt the ecosystem. It is much safer, and efficient, to study coral in a controlled environment."
Controlled experiments,why not test different acidity levels with different temperatures?,"If each one had different temperatures, then you have too many variables. Let's say you did the same experiment as the Australian researchers, but also had each sample at a different temperature. Let's say you get the following results:

Low acidity with cold temperature: 10% bleached

Medium acidity with mild temperature: 30% bleached

High acidity with hot temperature: 50% bleached

Now that you have your results, you know what causes bleaching in coral. But, do you? Is it temperature that causes it? Is it the acidity of the water? Is it the combination of both? How can you tell? This causes confusion and possibly false claims. If you want to know both, it is better to have two seperate tests. One for "Is Acidity Causing Coral Bleach" and another for "Is Temperature Causing Coral Bleach".

At the end, you will have two results, two claims, and zero variable confusion.

I hope this answers your question!

-Colin"
Controlled experiments,How do the sprouting seeds know to go up if they don't know which way the light is?,"Plants are PHOTOTROPIC I.e, they sense light and act accordingly. Some plants are negatively phototropic ( go against light) while others are positively phototropic (go towards light).

There is also GEOTROPISM, there plants that are negatively geotropic, go against gravity (upwards) while some others are positively geotropic ( the go towards the gravity). 

These phenomenons come under the topic TROPISM"
Controlled experiments,how come a prediction is not the same thing as a hypothesis? isn't a hypothesis what your predicting will happen?,"Yes, but the hypothesis has to be backed up by your experiment, and predicted outcome.

If you start frok predicted outcome and do nto know how to back it up: how to end upo getting those results and why presumably that happened, then it is not hypothesis.


You need scientific hypothesis to make a research proposal (this is an example)."
Controlled experiments,how do platns grow,"They grow by doing photosynthesis.(The taking in of carbon dioxide and water where the water is oxidised and when the carbon is reduced, causing a reaction where the carbon dioxide turns into glucose and the water turning into oxygen.)"
"pH, acids, and bases review","If the pH scale is 0-14, how can you have acids that are ranked at -6, -10, -18, -32, etc. pH?","Hi, the answer lies in the way the pH is calculated. Although this may seem a little advanced. The pH is calculated by taking the -log of the concentration of a certain ion in a solution. In scientific notation, for example, if the concentration of this ion is 1x10^-10 mol/L, then the pH would be 10! Therefore, you can work backwards to see that if an acid had a concentration of 1x10^2 mol/L, then its pH would be -2! so basically negative pH indicates that the acid is very strong.  (Just copy and pasted Aeshons comment so everyone could see.  This is not my original comment.  Aeshon gets all the credit)"
"pH, acids, and bases review",I thought that bleach was acidic because of the way it turns whatever it touches white?,I think that's the chemical reaction of the bleach when it reacts to clothing. Bleach is a base because it doesn't have anything that is acid.
"pH, acids, and bases review","Is there a reason alkaline batteries have the word "alkaline" in them? Because I saw on the scale battery acid is very acidic, but in the video it said alkaline was a term for basic solutions (1:25)",Maybe instead of having a acidic acid in the battery maybe it has a alkaline substance.
"pH, acids, and bases review",Just wondering. What will happen when you mix something very basic with something very acidic?,"Why don't you find out? 

Just kidding. ;) If you combine equal amounts of something extremely basic and something extremely acidic, you get a *neutralization reaction* where the two chemicals cancel each other out to create salt and water. When a neutralization reaction occurs, the pH will end up being 7, a neutral pH.

But, if the amounts of the acid and base are unequal, the result will be a solution that is slightly acidic, or slightly basic through a process called *hydrolysis*. I hope that answered your question, Harsh, and I hope you have a better understanding of what will happen in this specific scenario. Have a great day! :)"
"pH, acids, and bases review",is lemon juice more acidic than bleach,"since every number you go up the scale the baseity (?) gets 10 times stronger. So if lemon juice has a pH of 2 and bleach has a pH of 13 that means lemon juice is 100,000,000,000 times more acidic than bleach."
"pH, acids, and bases review",I have an interesting question: Do medicine pill or tablets even have a pH of acidic or basic?,"It would have to, I'm pretty sure all chemicals, liquids, foods, and medicines have a pH."
"pH, acids, and bases review","it was said that an Acidic solution is one with a higher concentration of hydrogen ion than pure water.
what does this mean?
does it mean that if the concentration of H ion in a solution is higher than the concentration of H ion in pure water then that substance is acidic?","Yes! The Hydrogen (or hydronium) ion concentration of pure water at 25 degrees Celsius is 10^-7 (if you're not sure where this came from, Khan Academy has some videos on it). If the Hydrogen concentration of a solution is higher than 10^-7, the solution is said to be acidic."
"pH, acids, and bases review",It is said above that " Most enzymes work best at a specific pH" Why is it so?,"It's because enzymes are sensitive to pH. For an enzyme to work and for a product, its active site must combine with the substrate to for an enzyme-substrate complex as in the induced fit model. However, in conditions that are not optimal, such as when an enzyme is placed in a solution with a pH value that's outside an enzyme's optimum, it can become denatured. In this, the enzyme loses its 3D shape and its ability to react with the substrate to form a product. This is why enzymes work best at a specific pH. Hope this helps."
"pH, acids, and bases review",Isn't bleach acidic because it turns everything white and burns to the touch?,Bases can be corrosive
"pH, acids, and bases review",Is chocolate syrup an acid or a base?,"This is because the chocolate syrup or powder used to make chocolate milk is usually quite acidic, with a pH of around 3.5. The pH range of most chocolate products ranges from 5.5 to 6.7, and their pH levels are near neutral."
N/A,So water is a covalent or ionic bond?,"Water has a polar covalent bond, in other words, it is covalent but oxygen is more electronegative than hydrogen so it pulls the electrons to it, giving oxygen a slight negative charge and hydrogen a slight positive charge. Good question!"
N/A,What is diffusion and give some examples,"Diffusion is a type of molecular movement that brings water particles from places of high concentration to low concentration. There really are 4 different types. Simple Diffusion, Osmosis, Facilitated Diffusion and Active transport."
N/A,I think water is a covelant bond,"Yes, it is a polar covalent bond. That means that while the atoms are "sharing" the electrons, the oxygen hogs them a bit closer, creating a partial negative charge on that side of the molecule, and a partial positive charge on the Hydrogen side"
N/A,why is O electronegative?,"To say that oxygen is electronegative fails to grasp the whole picture here. This is because ALL elements (except for the noble gases) are electronegative to some degree or other; ELECTRONEGATIVITY IS A PROPERTY OF THE ELEMENT which basically says "how strongly does it attract electrons?"

An element's electronegativity value is determined by a mixture of different factors, but the general rule is that it increases as you move right and upward across the periodic table. (Copy-&-paste this link for a visual: www.chemteacher.chemeddl.org/joomla/index.php?option=com_content&view=article&id=91)

So as for oxygen, (which was the subject of your question) it's electronegativity would indeed be one of the highest among all the elements because of where it is positioned in the periodic table (but more specifically because the factors that I alluded to earlier are manifest for oxygen in such a way as to make it such)."
N/A,"I still don't quite get the meaning of adhesion and cohesion, and the difference between them. Can somebody help me out?","adhesion is an attraction to unlike molecules, and cohesion is an attraction to like molecules."
N/A,which property allow solid ice to flot in liquid water,"One property of water is that it crystallizes when it freezes, that is it arranges itself in a particular formation whenever it freezes. This formation happens to be less dense than its structure when it is in liquid form. It is this property that allows ice to float. Hope this helped!"
N/A,"I'd like to know about the different types of bonds, like Sal mentioned Ionic Bonds, Covalent Bonds and Hydrogen Bonds, but what exactly are they?","A Covalent Bond is where atoms share eletrons, A ionic is an atom steals an eletron from another atom, giving it to the opposite charge, thus the atoms are attracted to each other. A Hydrogen Bond: A weak bond betweeen to molecules resulting from an electrostatic atrraction between a proton in one molecule and an electronegative atom in the other.   Hope this helps,"
N/A,"I have a question, what will happen if acids, fire and water combine together?","Its not as exciting as you think it would be. if you put something like lemon juice on a fire, it will most likely go out, same with water. I hope this helps."
N/A,what exactly is an ion,"an electrically charged atom or group of atoms formed by the loss or gain of one or more electrons, as a cation (positive ion), which is created by electron loss and is attracted to the cathode in electrolysis, or as an anion (negative ion), which is created by an electron gain and is attracted to the anode."
Biological macromolecules review,"After reading the key terms, I am a little bit confused.. to my understanding, monomers are the makeup of polymers... is that correct? If so, are the terms "polymer" and "biological macromolecules" synonymous?","Hello,
As I understand it, polymers are a subdivision of biological macromolecules. 'Polymer' is the branch of macromolecules that is made up of ONLY ONE monomer that repeats itself.

For example, a carbohydrate is a macromolecule that is classified as a polymer because it is made up of repeating monosaccharides, but a fat (lipid) is a macromolecule that cannot be further classified because if you look under the 'monomers' column, it is built up by more than one monomer.

Hope this helped!"
Biological macromolecules review,Isn't protein an energy molecule for muscles?,"Rather than providing energy for muscles, they are structural components, which means they build and repair muscles. Protein is only used as energy if carbohydrates and lipids aren't available for energy (side note: breaking down protein for energy is unhealthy and dangerous!). 
Hope this helps, - Layla"
Biological macromolecules review,Are phospholipids polymers?,There is considerable interest in the polymers bearing phospholipids in the main chains as the structures of these polymers are similar to biological tissues. Several polymers containing a phospholipid in the polymer backbone have been synthesized and characterized
Biological macromolecules review,how can lipids act as a chemical messenger?,"Some lipids such as steroid hormones serve as chemical messengers between cells, tissues, and organs, and others communicate signals between biochemical systems within a single cell."
Biological macromolecules review,"Are monomers and monosacchrides the same thing? Also, what is a polypeptide?","Monomers are the building blocks of the four basic macromolecules of life- monosaccharides are the monomers of carbohydrates, amino acids are the monomers of proteins, glycerol/fatty acids are the monomers of lipids, and nucleotides are the monomers of DNA.

Polypeptides consist of a bunch of amino acids bound together- so in a way it's a monomer of proteins!"
Biological macromolecules review,Why aren't minerals a macromolecule?,"What are the characteristics of a macromolecule?

Can you think of a mineral that meets all those criteria?

Does that help you to answer your question?"
Biological macromolecules review,why are vitamins not digested in the body,"Vitamins are not digested, whereas, they are absorbed.

Vitamins are organic compounds that are required for normal animal metabolism but are either not created in the body or are created in insufficient amounts and must be received through your diet. Almost all of vitamin absorption goes to the small intestine.

Vitamin absorption in the intestine is important for avoiding deficiency disorders, and it can be limited by a variety of factors, including intestinal disease, genetic abnormalities in transport molecules, excessive alcohol use, and drug interactions."
Biological macromolecules review,"which would be the differences between DNA and RNA were not very clear to me, they seem technically the same and I cannot differentiate them very well","If you are asking what the difference between the two is, here you go.

There are several differences. To start, DNA stands for deoxyribonucleic acid, while RNA stands for ribonucleic acid. These names describe the sugar that makes up their backbone--DNA = deoxyribose and RNA = ribose.

Second, while each has four nucleiotide bases, there is one difference. You probably know that DNA has guanine, cytosine, adenine, and thymine, and that guanine links to cytosine and adenine links to thymine. But RNA doesn't have thymine. Instead, it has uracil, a nucleiotide base with a slightly different chemical makeup. Thymine had the chemical formula C5H6N2O2 and uracil is C4H4N2O2. Uracil links to adenine in RNA just like thymine does in DNA

Finally, DNA is double-stranded and forms a double helix structure. RNA is single-stranded and is generally straight. DNA is a complete set of instructions needed for life (unless you're a virus, but that's a whole different story/debate) and RNA is used to copy DNA and to synthesize proteins. I know this is a lot to take in, but there are several videos and articles on Khan Academy to help. Here are a few.

https://www.khanacademy.org/science/high-school-biology/hs-molecular-genetics/hs-rna-and-protein-synthesis/v/molecular-structure-of-rna

https://www.khanacademy.org/science/high-school-biology/hs-molecular-genetics/hs-rna-and-protein-synthesis/v/rna-transcription-and-translation

https://www.khanacademy.org/science/high-school-biology/hs-molecular-genetics/hs-rna-and-protein-synthesis/a/hs-rna-and-protein-synthesis-review

Anyway, this is probably a lot, but I hope it helps!"
Biological macromolecules review,How should I remember all these terms?,You gain familiarity through repetition. Practice is key.
Biological macromolecules review,whats the main difference between saturated and unsaturated fats,"From a chemistry perspective, saturated fats have no double bonds between carbon atoms, while unsaturated fats have one or more double bonds. 

From a state of matter standpoint, saturated fats are solid at room temperature, while unsaturated fats are liquid or soft.

From a nutritionist's point of view, saturated fats can increase the risk for heart disease (because it stays as a solid at room temperature and can lead to atherosclerosis) and unsaturated fats can help maintain proper bodily functioning (because they stay as a liquid at room temperature and are less likely to clog your arteries.)

I know you asked for a main difference, but I included three because there are many differences between saturated and unsaturated fats. I hope you have a better understanding of saturated and unsaturated fats."
What is life?,do we have dna same as our parents?,"It's not exactly the same, we take roughly 50% from each. Also the expression of those genes can vary and some may be changed by factors such as DNA from viruses, or may not be expressed (shown) due to environmental factors."
What is life?,why are viruses hard to cure,"Because, most of the antibiotics, infect the bacteria through destroying their cell wall. Whereas Viruses insert their genetic material into a human cell's DNA in order to reproduce. Antibiotics cannot kill viruses because bacteria and viruses have different mechanisms and machinery to survive and replicate. The antibiotic has no “target” to attack in a virus"
What is life?,What are examples of Unicellular organisms?,"There are five groups of unicellular organisms:
bacteria, archaea, protozoa, unicellular algae, and unicellular fungi"
What is life?,"How does the ability to evolve define whether one living thing is alive?  Evolution only occurs because living things with less beneficial traits die.  Species evolve because they are alive; they are not alive because they evolve.  The individual organism itself does not evolve; it simply lives and dies.  Can anyone help explain why evolution is necessary for a species to be considered living?  As for right now, I would say that "evolution" shouldn't be on that list.","The qualities of living things are  synthesis, transport, excretion, regulation, nutrition, growth & development, respiration, and reproduction. I agree with you that evolution is not included in this, and Caleb has a point in saying that individuals that reproduce will evolve. Evolution is a result of life, not a cause."
What is life?,"In the "Is this the definitive list?" section, if the offspring of a female horse and a male donkey is a mule, what is the offspring of a stallion and female donkey?","Hinny is a stallion and a female donkey
Jenny is female horse and a male donkey"
What is life?,"If viruses are not considered alive organisms, how can they be so dangerous and reproduce them  so fast?","Viruses can hijack our cell's DNA to program it to make more copies of the virus. Though viruses themselves contain no DNA and are technically not alive, they can re-engineer our cells to help them proliferate."
What is life?,Do we know for sure that we are the only conscious organism?,"It is a matter of debate.

No, we are not the only species which could think, dream or feel, https://www.nationalgeographic.com/news/2015/07/150714-animal-dog-thinking-feelings-brain-science/
but we are the only species that are *self-aware*.

There are other conscious animal species as well, but human consciousness is different than animal consciousness.
Non-human primates are used for studies of the human model of consciousness.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3814086/

You can say that animals have consciousness:
' Human consciousness emerges on the interface between three components of animal behavior: communication, play, and the use of tools. These three components interact based on anticipatory behavioral control, which is common for all complex forms of animal life'

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5924785/

But humans have 'human awareness' - the ability to experience one's own “internal states” as intentional states. That's not something animals can do. 


You may find this interesting. Some Scientists theorize even Universe has consciousness.
https://bigthink.com/philip-perry/the-universe-may-be-conscious-prominent-scientists-state"
The scientific method,"I thought a hypothesis was an "if, then" statement, and not a prediction?","Well, you could consider it to be both.  If you say, "If I do X then Y will happen" you are predicting what will happen if you do something."
The scientific method,"a hypothesis is supported (likely correct), a theory has lots of evidence to support it. What then Makes a theory become a LAW. Such as the Law of Gravity? Only difference i see is a law has a mathematical proof. Is this a correct assumption? or what Constitutes a law?",Theories don't become laws. Here is a good resource for defining how these scientific concepts relate: http://ncse.com/evolution/education/definitions-fact-theory-law-scientific-work
The scientific method,What if one time an experiment works and the next it does not?,"Exactly, like others said if you do more experiments, then you will be sure to find out which info is credible. When I did experiments, my teacher asked us to write a summary about the results we got, so I tested out our hypothesis 3 times to find the average out of all of them, and I got pretty good info out of my experiment. I hope this helps you out!"
The scientific method,"I've been told that the proper way to compose a hypothesis is by using an if/then statement. But in the example above, it doesn't use an if/then statement. My question is, is there a proper way to write a hypothesis? If so, what is it? Thanks in advance:)","I think that there is no definite format to writing a hypothesis, but as you said, yes there is a 'proper' and appropriate way to writing a hypothesis. 

Like the article says, a hypothesis must be testable, meaning we can do experiments with it to see if it is supported or not. I think usually non-testable hypothesis are something that are not exactly 'measurable' or 'observable', such as "Many people may think that red apples are attractive". There is no accurate way of measuring if people think that red apples are attractive.

Yes, an if/then statement is a very safe way to write a hypothesis. One of the things that we must be careful when writing a hypothesis is that we should not make it a conclusion (an actual 'statement'!); for instance, "Red apples cause pimples." is a conclusion that could be obtained from an experiment, while "Red apples _may_ cause pimples" might be a hypothesis. 
However, yes the best way is to write an if/then statement, because it is formatting your prediction in a very testable way. You are saying 'IF I do this..' - which is  the experimental portion- that 'THEN this will happen'- which is the prediction or 'educated guess' portion."
The scientific method,"I am using a new account now, so I’ll ready my question.
I was looking at the last step, iteration. At my school, they have taught us an extra step, which would be conclusion and analyze/share data. Could someone specify the definition of the conclusion and analyze/share data? I get the analyze/share data part, but I always get stuck on conclusions, especially so when I have to write lab reports.","Why do you think you get stuck at conclusions? Are you afraid to say what you mean? Have you ever taken Logic classes?

I haven't but after quite a year it became habitual and 'easy' to conclude.

Maybe you lack the theoretical part or you are just scared of those lab reports (my personal opinion but I may be wrong).

Do not be afraid, and keep practicing.

If you read dozens of Scientific articles you may get an idea of what 'Conclusions' look like. Also, analyze and share means what it says. Analyze the best way you can do (don't be too hard on yourself) and share with others (peers, professors, online, scicomm, etc).


Good luck :D and keep asking questions :D"
The scientific method,Can a hypothesis be wrong.,"You can't be expected to come up with an accurate hypothesis every time, this is why you have to do observations and/or experiments to test the hypothsis."
The scientific method,Can a hypothesis always be right?,A hypothesis does not always have to be correct. The scientific method aims to prove or disprove the hypothesis and continue from there.
Biology and the scientific method review,if I want to know who would win in a fight: Batman or superman how would I experiment that? Do i pump one of my dogs with super powers and give the other kryptonite? please help I need to know by monday,"Well that's tricky since superman has superpowers while batman uses gadgets so it would be hard to make it a controlled experiment the best bet would be to make a clone of a baby and give either baby the skills, memories, powers, gadgets, and knowledge that the superheroes have and send them off into battle as soon as you do this."
Biology and the scientific method review,are y'all going to high school?,yess. 9th grade baby!
Biology and the scientific method review,"In the explanation for the term "placebo", what does it mean when it says it is 'used as a control'? Does it mean it is used as a treatment for the control group?","When for example you give someone a pill that has no therapeutic effect, that is, it has _no direct physiological effect_ on their body unlike real medications but the patient still thinks it does, the pill can still have a psychological effect on them since they _expect a positive effect_ on their body which itself may _trigger the intended effect_.

This phenomenon is called the *placebo effect* and needs to be taken into account when conducting certain experiments like testing the efficacy of new medications.

So when designing those experiments you intend to administer *placebos* (_effectless substance apart from the placebo effect_) to your control group to, so to speak, subtract the placebo effect from the results and only obtain data on the physiological effect of the drug."
Biology and the scientific method review,Why do electronics hurt people eyes?,Blue light is also another reason and glare from the screen but this can be avoided not fully but still partially by wearing anti-glare glasses or if your device has blue light filtering.
Biology and the scientific method review,""*Repeating experimental trials multiple times:* Errors may result from slight differences in test subjects, or mistakes in methodology or data collection. Repeating trials helps reduce those effects."

If there is a problem in the methodology, how does repeating experiments multiple times (I assume using the same methodology) correct the error if the error in its self is specific to the methodology?","Not the error in the chosen method, but in the procedure. there might be human error or computer error, that's why repeating is good."
Biology and the scientific method review,"If being able to reproduce is one of the factors of life, wouldnt that make infertile people slightly less alive than the rest of the population?","No, because they are apart of a species that can reproduce."
Intro to eukaryotic cells,Why are plant cells typically square (if they are) and why do they have a much larger vauole than animal cells?,"They are squarish because they have a stiff cell wall that forces them into that shape. If you meant vacuole, I think they have a larger vacuole because they have more need to store food than animals. In case of drought or famine, animals can move on to somewhere else if they need to get food or water, plants can't."
Intro to eukaryotic cells,In the above diagram the author gives us an example of what a plant cell looks like and I noticed that the cell has an abnormally thick cell wall. What is the reason for thick cell walls in plants?,"Cell walls not only provide structure, and protect from mechanical damage, they also prevent the cell from bursting as plant cells need to continually absorb water to survive."
Intro to eukaryotic cells,how come animal cells don't have a cell wall,"An animal cell needs to allow mobility for that animal so only has a cell membrane, a plant cell however has a cell wall to give the cell ridged structure and a plant doesn't move by itself so doesn't need mobility but rather it have protection."
Intro to eukaryotic cells,Why don't plant cells have lysosomes?,"Plant cells don't have lysosomes, because their cell walls are tough enough to keep out foreign substances that lysosomes would have to digest out of the cell."
Intro to eukaryotic cells,"The Endoplasmic Reticulum in a eukaryotic cell is the transport network of the cell and it extends from and connects the nuclear membrane to the plasma membrane of a cell. But then whenever we draw a diagram of a typical plant or animal cell, we never extend it to the plasma membrane- we always leave it somewhere in the cytoplasm. So, it should be extended, shoudn't it? And in that sense all our diagrams are theoretically wrong?","Well, from endoplasmic reticulum vesicles are formed and transport things to Golgi apparatus, where it may be modified somehow, sent back to ER or further to cell surface. So the whole network is: ER -> vesicle -> Golgi -> vesicle -> cell plasma membrane"
Intro to eukaryotic cells,Procaryotic cells lack vacuoles too then?,Yes. Only eukaryotes have vacuoles.
Intro to eukaryotic cells,Does the nucleus have a phospholipid bilayer?,Actually it is surrounded by a double membrane which has 2 phospholipid bilayers each.
Intro to eukaryotic cells,Why is there a nucleolus? Shouldn't the production of DNA just be spread evenly around the nucleus?,The nucleolus is a region from the nucleus where the different RNAs are found. It is also the site where ribosomes are joined. It´s important to mention that ribosomes are made 1/3 from proteins and 2/3 from RNA. Proteins for the ribosome are exported from the cytoplasm  to the nulcleus trough the nuclear pores.
Intro to eukaryotic cells,what is the function of a peroxisome?,"it is main function is to break down long chains of fatty acids and to detoxify substances, 

it produces H2O2 as a result, which can be harmful to the cell as a whole if not regulated, which is why it contains enzymes that is able to break down H2O2 into water and oxygen."
Intro to eukaryotic cells,"are there any unicellular eukaryotes? if there are, names ?","Yes, there are many unicellular eukaryotes. In fact, they have their own kingdom in the standard five kingdom classification scheme in biology called Kingdom Protista. Kingdom Protista is divided into subkingdoms of Protozoa and Algae. In Subkingdom protozoa, you have organisms like amoeba, euglena, volvox, paramecia, even plasmodia (the microorganisms that causes malaria), just to name a few. Most types of algae are also unicellular eukaryotes."
Prokaryotic cells,Are red blood cells considered to be prokaryotic since they don't have a nucleus?,They are considered Eukaryots. They loose the nucleus when they mature and many non-vertebrates have erythrocytes with a nucleus.
Prokaryotic cells,How do prokaryotes get rid of waste?,"Prokaryotes use the process of diffusion, to either take in (endo) or release (exo), materials through their semi-permeable plasma membrane. Now you might say, what about their cell wall, the cell wall must be stopping these materials. Well actually, the cell wall (made of peptidogylcan in bacteria) is fully permeable, as it's role is not to stop materials from going in or out. It's function is to give support to the cell, which is why it is rigid but fully permeable, thereby allowing exchange of materials. Hope this helps!"
Prokaryotic cells,Do humans have prokaryotic cells in their bodies,"Humans do have bacteria in their saliva and stomach that we use to break down things we need, but we can't make that ourselves. So technically there is some in our bodies, we just didn't make it."
Prokaryotic cells,What makes Trichodina different from all prokaryotes?,"Trichodina is considered Eukaryotic protozoa -meaning it has a nucleus.


That sets its apart from all Prokaryotes.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3750665/
https://elps.eastlongmeadowma.gov/files/9214/3525/7686/MCAS_review_packet_1.pdf"
Prokaryotic cells,"From paragraph 10 to 16, I still don't get idea of surface-area-to-volume.","If you're still confused, you can watch the video "cell size""
Prokaryotic cells,Why is the flagellum only in the prokaryotic cells and not in the eukaryotic cells?,Eukaryotic cells they do have flagella (only one: Sperm cells) but they have a different composition
Prokaryotic cells,are there are any multi celluler prokaryotic,"No, there are not known multicellular Prokaryotes. Distinguishing characteristic among Eukaryote and Prokaryote Domains is being unicellular or multicellular."
Prokaryotic cells,what cell is used by prokaryotic cells and some other single celled organisms for movement.,"Flagella:
 are whip-like structures that act as rotary motors to help bacteria move.
Pili:
Rod like structures
 Fimbriae :
are numerous, hair-like structures that are used for attachment to host cells and other surfaces."
Prokaryotic cells,How does the eukaryotic cell size impact the cell's ability to tranport materials into and out of the cell?,"Cell size does not have much impact on the transport - what really has impact is proximity to the next cell, the junctions between cells in the epithelial tissue and the shape of the cell (the more circular cell the greater surface vs volume ratio)."
Prokaryotic cells,Do I have to memorize all of this or just stick up with the -Prokaryotes and eukaryotes review-,"*You can do whatever you want to do when it comes to your learning*. If you want to study the major highlights of the unit, then go look at the Prokaryotes and Eukaryotes Review. If you want to have a better understanding of prokaryotes in a more detailed sense, then I guess "memorize all of this" in this article. Or if you want to understand prokaryotes a little bit more and then look at an overall review, then do it! 

But *please* don't make it about energy points. Even though the perks are nice (or was nice--I still miss backgrounds) and it's soo satisfying to see that blue check mark after you read a long article or watched a long video, that's a secondary priority. Your first priority on this website (I hope it's your first priority) is to learn.

I want you to know that *no one* is stopping you from *doing what you need to do* when learning. After all, learning all of this information on Khan Academy is for _your benefit_, not someone elses's. So learn however you want to, as long as you feel like _you're_ learning! I wish you *all the best* in your learning journey. :)"
Structure of the plasma membrane,what is between the phospholipid bilayer?,"Since the polor ends of the phospholipids face the outer/ inner surface of the cell. They are in contact with the inter/outer cellular fluid predominantly water, glycoproteins,glycolipids, However the hydrophobic tails inter twin with each other forming the enter space between the polor heads. The space between the polor heads would contain saturated and unsaturated fatty acids which forms these tails. This gives them a slight negative polarity. With these fatty acid tail ( bent or straight) we would find a mosaic of integral proteins, cholesterol,. and yes,  water molecules passing threw!"
Structure of the plasma membrane,"So with that example of the pinhead touching the fluid membrane (and the membrane flowing out of the way), I'm wondering how a person can bleed if all cell membranes do this. As in why don't sharp objects like pins and needles go straight through (I know it sounds silly) our skin without drawing blood?","Bleeding occurs when veins are torn out. When you pass a pin through your skin ,the pinhead is literally much bigger than the individual cell for the pinhead to pass through the said cell membrane.So you can guess the pin must torn out some small veins on its way into your skin,not into an individual cell.Moreover there is no blood inside a cell or cell membrane for it to come out.Hope this clears your doubt"
Structure of the plasma membrane,"What is meant by "Transmembrane proteins may cross the membrane just once, or may have as many as twelve different membrane-spanning sections." I don't understand the twelve different membrane-spanning sections part.",I think it looks like three-pass transmembrane protein (in the first picture about proteins) only having 12 sections instead of 3.
Structure of the plasma membrane,Why do we have proteins in the cell membrane?,http://www.sparknotes.com/biology/cellstructure/cellmembranes/section2.rhtml
Structure of the plasma membrane,Would I need all of this information for regular High School Bio?,Yes.
Structure of the plasma membrane,"What are lipid rafts, what are they made of and whats their function? and where in the plasma membrane are they located?
thank you!","Lipid rafts are regions within the plasma membrane that are more rigid than the surrounding membrane.  

They are made of the same components as the rest of the membrane, but in differing amounts — for example they contain much more cholesterol. 

AFAIK their function is not completely clear, but they may help concentrate certain membrane proteins in a way that makes some cell processes more efficient.

There is an extensive wikipedia article on this that you may find interesting:
https://en.wikipedia.org/wiki/Lipid_raft

This article might also be worth reading:
http://www.jlr.org/content/44/4/655.full"
Structure of the plasma membrane,fluid mosaic model is cell of ??,"That's not correct .... the fluid mosaic model is a model of the plasma membrane which is present in ALL cells, both eukaryotic and prokaryotic, single-celled and multi-cellular organisms."
Microscopy,"i was reading a question about where human samples come from,  and i was wondering why the cells die when they get into the vacuum.","Cells die upon entering a vacuum because a vacuum is a void.  This means that there is nothing there.  There is no air, just the absence of matter.  In the absence of matter, a cell cannot survive.  Plus, a cell in a multicellular organism cannot survive on its own for long, anyway."
Microscopy,When Was The Electron Microscope invented ?,"The electron microscope was invented in 1931 by  German physicist Ernst Ruska, and an electrical engineer, Max Knoll."
Microscopy,Why is an objective lens called that?,The lens closest to the object it is observing is called the objective lens. Get it? Object / Objective. It focuses light directly from the object to observe it.
Microscopy,what is a light microscope,"A light microscope is the typical microscope you would use at home: you simply observe something as it is using regular ilght. 
Other more specific and advanced microscopes might use electro-magnetic radiation that is not in the visible spectrum, such as electron microscope, but these images are not something you can detect by eye without proper machinery assistance."
Microscopy,"How many microscopes are made per year, both types of the electron microscopy. Who produces and, or make them with what foundation.","The production and distribution of microscopes, especially electron microscopes, can vary from year to year and depend on several factors. While I don't possess the exact figures for the current year, I can provide you with some general information.

Electron microscopes are typically produced by various manufacturers around the world. Some prominent companies known for manufacturing electron microscopes include JEOL, Thermo Fisher Scientific, Carl Zeiss AG, Hitachi High-Technologies Corporation, and FEI Company, among others.

These manufacturers often collaborate with various foundations, research institutions, and academic organizations to develop and manufacture electron microscopes. Additionally, there are government-funded initiatives and independent research institutes that contribute to the advancements in microscope technology and their wide availability.

It's important to note that the production numbers may vary significantly each year due to market demands, technological advancements, and research funding. To get specific figures for a particular year or detailed information about the production and distribution process, it would be best to consult industry reports, companies' annual reports, or contact the respective manufacturers directly."
Microscopy,which is the world's smallest cell?,"World smallest cell: SAR11 micro-organism (found in sea water). Length 1 micrometer.
while Mycoplasma gallisepticum has 10micrometers in diameter.

Human smallest cell: sperm cell.
While granular cells of cerebellum is 10micrometers (soma), sperm cell head is 5micrometers."
Microscopy,how much can the most powerful electron microscope magnify?,"A light microscope can only magnify up to 1000-2000 times, an electron microscope can magnify something up to 2 million times."
Microscopy,does time exist in perfect void?,"The void contains no space, no time, no mass, and no charge.

I see it kinda like this:

On Earth, one minute is 60 seconds. But on Mars, it is different. Same as all the other planets, because we tell the time via how we revolve around the sun, and how fast our planet is spinning. So if there were no sun and you weren't on a planet, there would be no time.

Time is a relative concept with no absolute, and is used as a guide to measure events in various ways. With gravity and possibly voids, all they do is slow the event down, not time.

So if you were an astronaut in space, you would only know how "old" you are if someone Earth were to tell you what the time is!"
Microscopy,Why is wave length the limiting factor?,"Correct me if I'm wrong, but according to the formula for resolution, the smaller the wavelength the better the resolution. That being said the shortest wavelength for visible light is blue at 450nm. Anything shorter our eye cannot capture."
Microscopy,can they still use the dead cells and can they get living cells from dead people?,"And for the second question, it would depend on how you classify a "dead" person. Some countries pronounce a person dead if their heart stops, whereas others have it as when there is no activity in the frontal lobe (of the brain). Any sample from a dead person would have to be taken very shortly after their "death", as the cells start to die (or are already dead) within minutes. You may, depending on the circumstance and whether they are "dead" when their heart ceases functioning, be restricted to what sample of living cells you can retrieve. If you somehow access the heart very soon after "death", you may stand a chance at getting a sample, although I do not recommend trying to do any of this as it is a: rather suspicious, and b: you may be required to commence cardiopulmonary resuscitation (CPR). This is all quite hypothetical, and don't try any of this, please."
Eukaryotic cell structures review,why does the Golgi body move,To deliver proteins to the other parts of the cell
Eukaryotic cell structures review,Can someone please explain the membrane bound organelles and the non membrane bound organelles. Just state the organelles.,"The membrane bound organelles are in the eukaryotic cell and the membrane helps the organelles maintain their shape. The non membrane bound organelles live in the prokaryotic cell and have no membrane, so they are more of a blob than anything."
Eukaryotic cell structures review,What cell structure is most likely responsible for whether or not a plant cell is flaccid or turgid?,"Vacuoles hold water. When there's a lot of water in the vacuole, it pushes the membrane against the cell wall."
Eukaryotic cell structures review,Why does mitochondrial DNA specifically come from the mother?,"That is an excellent question!

"One theory has to do with the fact that sperm must generate a lot of energy when competing to fertilize an egg. During this time, sperm mitochondria are overworked, which could possibly damage their DNA and lead to mutations." - The New York Times.

"In reproduction, mitochondria are normally inherited exclusively from the mother; the mitochondria in mammalian sperm (*The typical mammalian sperm midpiece contains approximately 50–75 mitochondria with one copy of mtDNA in each*) are usually destroyed by the egg cell after fertilization." - BYJU's

"While it is well-documented that almost all animals inherit mtDNA only from their mothers, the mechanism by which this occurs is still not understood." - thewire.in

In conclusion, we're not 100% sure just yet."
Eukaryotic cell structures review,"So much information at once 
I've already forgotten what he said at the start",Then rewatch.
Eukaryotic cell structures review,Which part is deals with photosynthesis again?,"Chloroplasts deal with photosynthesis. But keep in mind that chloroplasts are only present in plant cells. We don't perform photosynthesis, so as a result, we don't have chloroplasts."
Eukaryotic cell structures review,is the dna of mitochondria similar to the one in the nucleus ?,"No, it is completely different. You actually get all your Mitochondrial DNA from your mother. It is because of this that there is a theory Mitochondria were once their own organisms that were engulfed by our ancestor's cells and began to work together in harmony."
Eukaryotic cell structures review,"I have seen elsewhere a cell diagram with a part labelled 'lumen' I haven't seen that here, and with an internet search haven't been able to find info on it, or the same diagram. Any ideas what it could be? It was not within a chloroplast or any organelle, rather just by itself in the cytosol. Thanks",A lumen is a space enclosed by a membrane. The lumen in your cell diagram is likely referring to the space in the cell and not necessarily any of its organelles or the cytosol.
Plant vs animal cells review,which part of cell control the activities of the cell,"I think it is nucleus. The part is DNA, I think"
Plant vs animal cells review,What is a relationship between plant cell and animal cell?,"They are both examples of eukaryotic cells. In addition, eukaryotic cells also have protists and fungi."
Plant vs animal cells review,what size are the plant and animal cells? cell? Do non living things have cell?,"Size of an animal cell ranges from 10 to 30 micrometres while for plant cell it ranges from 10 to 100 micrometers. 1 micrometer is 1/1000 of a millimetre. And non-living things do not have a cell. They are not living and thus don't need any of our body systems. They just need a structure, no body systems, thus no cells. So non living things don't need cells. Hope that this answers your question."
Plant vs animal cells review,what is the shape of the plant and animal cell or it does not have a definite shape,"yes, cells do not have a definite shape, but plant cells do have a tendency to have shrp looking distinct edges."
Plant vs animal cells review,"If plants get all their energy from sunlight, then why do venus fly traps eat flies? Does sunlight not give them enough energy?","Carnivorous plants, like venus flytraps, are still photosynthetic, but rely on their prey to get nutrients (not energy) that may not be available in their habitat's soil."
Plant vs animal cells review,"Do plant cells contain lysosomes?
And if they don't what replaces its functions?","No, (most) plant cells don't contain lysosomes. Instead they have the cell wall. Because most plant cells have the cell wall to keep foreign particles away, it's not necessary to have lysosomes digest foreign substances that are not there."
Plant vs animal cells review,There was not a lot of information on the cell wall why do plants need it and animals don't?,"Think about it: animals are on the move. They need a heart that can pump blood. They need muscles that can flex and relax to move. They need a digestive system that can stretch to hold food. Plants, meanwhile, need to stay upright to photosynthesize. They need to support themselves and their organs; otherwise, they cannot grow.

Plants need the walls to support themselves. Animals, on the other hand, have skeletons, but they act as a frame for the other, flexible, fleshy organs that are required for movement.

Does this help?"
Plant vs animal cells review,isn't the membrane surrounds the cell wall. why not.,`nope cell wall protects membrane that's how it is`
The cell membrane review,"Does the phospholipid bilayer of the cell membrane, make the membrane "water resistant," due to inward hydrophobic tails and the outward hydrophilic heads?","Yes,  it does, even though water can still get through the bilayer into the cytoplasm via the integral proteins in the bilayer"
The cell membrane review,How can water pass through the phospholipid bilayer if it has aquaphobic tails? Won't the water molecules get repelled out?,"I think another article said that some water molecules can sneak past the hydrophobic tails because they are very small (the water molecules, that is)."
The cell membrane review,how many cells in my body,About 37 trillion cells
The cell membrane review,Do u like whoppers? How many cells are in one?,More than 1.
The cell membrane review,i have a question i do not understand the word phobia can anyone comment to explain a bit more thanks.,phobia is greek for fear >
The cell membrane review,"what does a skin cell membrane look like? they aren't semipermeable, are they?",Look anywhere in lesson 3 and you will find a cross picture of cell membrane. And they ARE semipermeable.
The cell membrane review,why is a cell membrane semipermeable?,"The cell is kinda like an exclusive concert. It can't let just anyone in.  There are all sorts of free radicals and harmful metals that could invade the cell, not to mention those bacteria and viruses that constantly try to attack the cell. The cell needs a membrane to protect itself - to some degree - and establish an environment where it can do its job. You wouldn't want some stranger to randomly pop into your house, and neither does the cell. It does need some things from the outside world, though. That is why it allows certain particles to pass through the membrane. Hope this helps!"
The cell membrane review,What is the big difference between plasma membrane and cell membrane.,"there is no big difference, it is the same thing. another name for a plasma membrane (or a cell membrane) is a fluid mosiac model. again there is no big difference between these names, they are the same thing."
The cell membrane review,how many cells in  my body,"It's an estimated answer, but scientists predict around 37.2 trillion cells."
The cell membrane review,"So, is the plasma membrane the same thing as the cell membrane?","Yes, the plasma membrane and cell membrane are the same things."
Mitochondria and chloroplasts,Would it be possible for a modern day cell or organism to capture one of these cells and start a new symbiotic relationship with the host cell?,"That is an intriguing question. The origin of mitochondria is thought to have been a very rare event. The mitochondria seem to have their origin from one particular family of bacteria (the alpha-proteobacterium ) which are related to some existing bacteria. There are people trying to build cells so I guess maybe someone could try to create a modern endosymbiosis event.

There are many theories as to how eukaryotes came about. If you want to know more; see this paper: Endosymbiotic theories for eukaryote origin http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4571569/"
Mitochondria and chloroplasts,It would be so cool if we could recreate endosymbiosis and incorporate chloroplasts in human cells so we could photosynthesize,"i hate to ruin your guys fun but i think we would die, if you put chlorophil into our bodies."
Mitochondria and chloroplasts,"1) Are there any animals that have chloroplasts? Or are they only in plants?

2) If they are only in plants, would it be possible for an animal to have chloroplasts, chemically speaking?","Well according to modern classification, the organisms which have chloroplasts in them and have an advanced nucleus are called plants. Those organisms which show both plant and animal features(like Euglena) are kept in Kingdom: Protista
As for your second question, as Biology is science of exceptions we cannot publish any definite law. So in future, due to evolution, there may be animals with chloroplasts."
Mitochondria and chloroplasts,is peroxisomes needed in a cell,"Before the ancestor of mitochondria entered the eukaryotic cells, Peroxisomes were asource of power to the cell. They used to break down H2O2(Hydrogen Peroxides) and would form water and and energy. But now, there only function is detoxification as the energy produced by mitochondria is much more than the energy produced by the peroxisome. So, peroxisomes are sort of vestigial organelles which had a major function in the past but aren't so useful in the present age.."
Mitochondria and chloroplasts,"If mitochondria and chloroplasts evolved from bacteria, what did the cells use for energy before?  Isn't this a case of you can't have the one without the other?  Wouldn't the cell/animal/plant die without the energy from the chloroplast or mitochondria?",Before mitochondria and chloroplasts became part of cells they had their own ways of producing energy from metabolizing food around them. These older methods of producing energy were lost along the way because the mitochondria and chloroplasts were better at it and it was a waste of resources to have the two ways of producing energy so the cells that eliminated the older way were more efficient and survived better that the ones that didn't.
Mitochondria and chloroplasts,"In the endosymbiotic theory, what was the factor that decided that the chloroplast wouldnt converge with the other cells present on earth, so that there would be two types of cells, 
1. plant cells
and 
2. animal cells","It just happened this way. Some phytoplankton probably merged with chloroplasts prokaryotic cells and absorbed them and formed a symbiotic relationship with them and also with mitochondria (they have both organelles), and some zooplankton probably got the short stick and managed to form symbiotic relationship only with mitochondria prokaryotic cells and from them out ancient common ancestor was created..."
Mitochondria and chloroplasts,"Most antibiotics inhibit bacterial ribosomes... so, would antibiotics have an effect on mitochondria when taken?","Some of them may, if the antibiotics manages to get all the way through all the membranes to the mitochondria itself (which is not an easy way). 
If they do get into mitochondria, it may not be a big deal since most of mitochondrial proteins are made by eucariotic cell and then transported into mitochondria, only few proteins are made by mitochondria itself.
Actually it seems that some antibiotics do harm mitochondria, so these usually aren't used as long as there is some harmless alternative."
Mitochondria and chloroplasts,Do stand-alone chloroplasts and/or mitochondria still exist in nature as prokaryotes (Outside of a eukaryotic cell)?,"Yes§, this is part of the evidence supporting the theory that these (and possible some other organelles) arose through endosymbiosis (aka symbiogenesis).

The group of bacteria from which mitochondria seem to have evolved are the Alphaproteobacteria.

Chloroplasts appear most closely related to the cyanobacteria.

You can read more about this here:
https://evolution.berkeley.edu/evolibrary/article/_0_0/endosymbiosis_01 _

You might also find these interesting:
https://biologos.org/blogs/dennis-venema-letters-to-the-duchess/evolution-basics-endosymbiosis-and-the-origins-of-mitochondria-and-chloroplasts
https://biology.stackexchange.com/questions/43372/origin-of-the-double-membrane-of-mitochondria-and-chloroplasts

§More correctly, there are other descendants of the progenitor of these organelles that have remained as free-living organisms."
Mitochondria and chloroplasts,"Does this mean that when you eat vegetables, you are you eating light energy?","Yes, pretty much. In fact you could say you're eating the energy produced in the fusion reactions occuring inside of the Sun's core."
Mitochondria and chloroplasts,"Have they proven endosymbiosis to be the reason why mitochondria and chloroplasts contain their own DNA and ribisomes? I am very blown by the idea that the mitochondria in our bodies were once bacteria and, if they really are bacteria before,we now have a gazillion of them.","Proof is an elusive concept in science, but this theory is now generally accepted as the best explanation for multiple observations.  

Another piece of evidence supporting the theory that these (and possible some other organelles) arose through endosymbiosis (aka symbiogenesis) is that if you make an evolutionary tree of the DNA within either of these organelles and bacteria, you find free-living bacteria that are closely related.

The group of bacteria from which mitochondria seem to have evolved are the Alphaproteobacteria — many of them are intracellular parasites, which suggests how they originally ended up inside the first eukaryotic cell.

Chloroplasts appear most closely related to the cyanobacteria.

You can read more about this theory here:
https://evolution.berkeley.edu/evolibrary/article/_0_0/endosymbiosis_01 _

You might also find these interesting:
•https://biologos.org/blogs/dennis-venema-letters-to-the-duchess/evolution-basics-endosymbiosis-and-the-origins-of-mitochondria-and-chloroplasts
•https://biology.stackexchange.com/questions/43372/origin-of-the-double-membrane-of-mitochondria-and-chloroplasts"
Introduction to cells review,What happens when we use live cells in an electron microscope ?,"electron microscopes produce electrons in an complete vacuum chamber, when live cells are placed in the chamber they would disintegrate due to vacuum"
Introduction to cells review,"They say that cells are the smallest living unit. However, they also say that viruses are smaller. Aren't viruses considered living units as well?","It depends who you ask. Generally the answer is that viruses are not living units, for two reasons: The first reason is just that we've decided a cell is the basic unit of life, and viruses don't intrinsically contain cells, therefore they are not life. The second reason is that viruses are more like parasites, and are dependent on cells to "reproduce", so they aren't really living on their own."
Introduction to cells review,Is there something called a micrometer ruler?,yes there is something called a micrometer ruler
Introduction to cells review,why does the cell have to be dead in order for the electron microscope to work?,"The reason for this is because the electrons destroy the living cells and when the cells are placed in the vacuum, there is no oxygen thus no life for the cells. Hope this helped clear any remaining doubts."
Introduction to cells review,how many cells does a human have,There is a estimation of more than 37 trillion
Introduction to cells review,¿En que año hicieron el primer microscopio ?,"El primer microscopio se inventó en 1590, pero no está claro quién lo inventó realmente. La primera vez que se utilizó un microscopio para observar células muertas fue por Robert Hooke a principios del siglo XVII, si eso ayuda. ¡Espero que esto ayude!"
Introduction to cells review,what would i use to examine the entercica cell,You could use an electron microscope if you want to see the enterica cell clearly or you can use a complex microscope if you just want to see the overall picture and it's parts. Hope this helped to answer your question.
Introduction to cells review,"In the introduction to cells review, three cell theories were given but in my biology textbook four cell theories were given which the last one is ( A cell contains information for its structural and functional development in its nucleic acid.This information is passed down from parent to offspring cells). so my question is how true is the fourth cell theory, should it be part of the cell theory or not?","Yes, I think so.  Sal probably forgot to mention it."
Introduction to cells review,"According to cell theory all cells must come from preexisting cells, but then how did the first cell come about, and more importantly, why can't that happen again?","We actually do not know this answer for sure. Some theories suggest that the primordial Earth was the perfect place for chemical reactions to occur, with molecules eventually coming together to form the first cellular mechanisms. One theory suggests that amino acid (protein building blocks) chains were able to survive in the hellish conditions on the early Earth, and that their composition and characteristics eventually gave way to cells. One other theory suggests that cells evolved from viruses. There are several guesses in the community, and without our very own primordial Earth or time machine, what lead to the first cells is unknown.

On Earth, if a primordial cell were to develop again, it would likely die, due to the millions of other, fully developed cells that exist (competition and natural selection). However, should there be life on other planets, then it could be safely said that the process did happen again.

Does this help?"
N/A,"I thought some prokaryotic organisms could be multicellular;such as blue green algae, isn't that a multicellular prokaryotic?",There are some cyanobacteria that form filaments with a differentiated cell type that fixes nitrogen and 'normal' photosynthesising cells. It's a form of symbiosis that could be classified as multicellular.
N/A,How can eukaryotes be multicellular? Aren't they cells on their own?,"A eukaryote is an organism with complex cells, or a single cell with a complex structures. In these cells the genetic material is organized into chromosomes in the cell nucleus. Animals, plants, algae and fungi are all eukaryotes. There are also eukaryotes amongst single-celled protists.  Unlike unicellular archaea and bacteria, eukaryotes may also be multicellular and include organisms consisting of many cell types forming different kinds of tissue. Prokaryotes are  singled cell organisms."
N/A,"I read on another article here on Khan Academy that prokaryotic cells can organize to form something that resembles a multicellular organism, and that it can be discussed if that's multicellular or not. So how can prokaryotes "always" be unicellular?

Source: https://www.khanacademy.org/science/high-school-biology/hs-cells/modal/a/prokaryotic-cells

"In general, prokaryotes are single-celled organisms. However, there's increasing evidence that some groups of prokaryotic cells can organize to form structures that resemble multicellular organisms. Whether this counts as "real" multicellularity is a question hotly debated by researchers today."","I believe that the debate is continued, so we should still agree to the previous answer that prokaryotes CANNOT be multicellular. Bacteria might be an interesting exception, but further research shows that the cells might work together, but they lack the organization that other multicellular beings have.

Hope this helps!"
N/A,"So chromosomes/chromatin can be floating around anywhere with DNA inside the cell and that it doesn't need to be around a nucleus? 
I'm sorry if I seem dumb I'm new to this.","No worries! We were all new to this at one time or another! To answer your question, yes, it doesn't need to be inside a membrane-bound nucleus in the case of prokaryotes

Hope this helps!"
N/A,are biofilms made with _prokaryotes_ or _Eukaryotes_ cells?,Biofilm Structure A microbial biofilm is made up of many prokaryotic organisms that combine to form a colony. The colony is adhered to a surface and coated with a polysaccharide layer (or slime layer).
N/A,do eukaryotes cells live longer than prokaryotes,"The answer really lies in whether or not the cells combine to form a multicellular mass or if they prefer living by themselves. Ones that form together tend to live longer.

Hope this helps!"
N/A,How Can a cell be multicellular?,It is not saying that a cell is multicellular. When it says eukaryotes can be multicellular it is referring to an organism made of eukaryotic cells.
Cellular respiration review,"Here u say that at the end of the Aerobic ( Cellular) respiration 38/36 ATP will be released. At the same time, in some books say 32/30 ATP will release in the Cellular respiration. Moreover, they gave the steps as well.

Total number of ATP molecules produced from one molecule of glucose, during aerobic respiration.
In glycolysis :
 As ATP                                   2ATP
From 2NADH                    5ATP (oxidation phosphorylation)
In pyruvate oxidation;
From 2NADH                     5ATP (oxidative phosphorylation)
In Citric acid cycle;
As ATP                                     ATP (substrate level phosphorylation)
From 6NADH                     15ATP (oxidative phosphyrlation)
From 2 FADH2                   3ATP
Total Number ATP =        32 ATP

I think here is a wrong. Pls help me to solve this doubt.","Depending on your teacher or textbook, the amount of ATP produced during aerobic respiration is either 30-32 or 36-38. Both are technically correct, but recent studies show that 30-32 is more accurate. While 36-38 ATP being produced is possible it only happens in the most ideal situations."
Cellular respiration review,I've read in a test prep text book that water is an input in the process of cellular respiration but I have not seen the same in this article or the accompanying video; is it true or false?,"Water is indeed used in cellular respiration. During Krebs cycle one molecule reacts with fumarate forming malate.
But it is also produced during ETC so basically (the net) water is product."
Cellular respiration review,Where does the water go after being produced as a byproduct? Is it sweat or urine or does it stay in the body? Thanks.,"it can become part of sweat or urine and leave the body, but it can also just join the multitude of water already in your body and go wherever the other water goes. it can even become water vapor and exit through your breath, just like the carbon dioxide."
Cellular respiration review,why is cellular respiration not the same as "breathing",Breathing has to do with taking in oxygen. Cellular respiration is where glucose is broken down into its chemical potential energy and stored as ATP (Adenosine triphosphate.
Cellular respiration review,I get that they also perform photosynthesis but how do carnivorous plants break down the animals they feed on into glucose?,"Venus flytraps use enzymes to break down their catch, and use it for nitrogen, since they are deprived, and produce glucose the same way, just not as much"
Cellular respiration review,Hi! May I know is fermentation part of cellular respiration? Or it is not cellular respiration because it is another pathway of obtaining ATP?,"Fermentation is the anaerobic process of producing ATP, so yes, it counts as cellular respiration. However, it is anaerobic, meaning it does not use oxygen to produce ATP.

In humans and other creatures, this process is usually much less effective than using oxygen and may have unwanted side effects. (For humans, it produces lactic acid, which causes muscle pain and fatigue.)

Hope this helps."
Activation energy,what is the defination of activation energy?,"The official definition of activation energy is a bit complicated and involves some calculus. But to simplify it:
 
Activation energy is the minimum energy required to cause a process (such as a chemical reaction) to occur."
Activation energy,"I thought an energy-releasing reaction was called an exothermic reaction and a reaction that takes in energy is endothermic. In the article, it defines them as exergonic and endergonic. Are they the same?",Exothermic and endothermic refer to specifically heat. Exergonic and endergonic refer to energy in general.
Activation energy,"When mentioning activation energy: energy must be an input in order to start the reaction, but is more energy released during the bonding of the atoms compared to the required activation energy? Can the energy be harnessed in an industrial setting?","In an exothermic reaction, the energy is released in the form of heat, and in an industrial setting, this may save on heating bills, though the effect for most reactions does not provide the right amount energy to heat the mixture to exactly the right temperature. Often the mixture will need to be either cooled or heated continuously to maintain the optimum temperature for that particular reaction. For endothermic reactions heat is absorbed from the environment and so the mixture will need heating to be maintained at the right temperature. By right temperature, I mean that which optimises both equilibrium position and resultant yield, which can sometimes be a compromise, in the case of endothermic reactions."
Activation energy,"I don't get this. If a molecule has more activation energy, shouldn't it be more likely to reach the high barrier required and complete the chemical reaction faster? If I have more energy when I wake up, it is easier to get out of bed and it takes me less time to do so. Shouldn't chemical reactions be the same?","yeah, like amathakbari said-activation energy is the amount of energy needed to activate the complex that ocurrs at the transition state. it isn't energy you have"
Activation energy,What is the activation energy of the reaction?,Activation energy is the amount of energy needed to initiate a reaction.
Activation energy,can a product go back to a reactant after going through activation energy hump? (sorry if my question makes no sense; I don't know a lot of chemistry),"Theoretically yes, but practically no.
So this concept can be visualized with combustion or fire. While wood does not spontaneously burst into flame, if you add additional energy, with a match for an example, to the pile of wood, it starts a fire. What happens is that the energy in the match pushes the wood over the activation energy hump and starts the fire. Afterwards, the fire is self-sustaining because the fire creates enough heat to activate the rest of the wood.

Chemically, wood is composed of mostly carbon, which reacts with the oxygen in the air when 'activated' to create carbon dioxide.
So, for this reaction, carbon is the reactant and carbon dioxide is the product, which can be converted back into carbon (like photosynthesis) but requires more energy to do so.

The bottom line is that while it is possible, it will (in general) require additional energy to go back from a product to a reactant"
Activation energy,"Is there a difference between the terms endothermic/exothermic reaction and endergonic/exergonic reaction?

I only learned endothermic and exothermic as a reaction that stores energy and a reaction that releases energy.","Endothermic and exothermic refers to sign of the enthalpy of a reaction. Whether the net enthalpy change is positive or negative respectively. Where enthalpy is equivalent to heat.

 Endergonic and exergonic refers to the sign of the Gibbs free energy of a reaction. Whether the net free energy change is positive or negative respectively. Free energy taking into consideration both the enthalpy and entropy change of a reaction. 

Hope that helps."
Active transport review,is sweating a form of active transport,I think that sweating is a form of passive transport as heat that is generated in the cells inside your skin is moving WITH the concentration gradient from hot (inside) to cold (outside). I think that's right. I haven't yet studied the videos on perspiration.
Active transport review,What is the difference between facilitated diffusion and active transport?,Facilitated diffusion is a type of passive transport and along the gradient. Think of a pipe connecting a full tank of water to an empty one. Active transport is against the gradient. Think of a pump moving water from a nearly empty tank to an almost full one.
Active transport review,Are the largest molecules moved by only active transport or also by passive?,"No, actually both facilitated diffusion and active transport occur. When the molecules moving from high to low conc. like Glucose is very large, then we need channel proteins to move them into the cell, and channel protein only because they have the shape and structure to do so, so that the movement is only unidirectional (into the cell). Active transport transports or moves materials against the concentration gradient, that is, from low to high, and the size doesn't matter here like facilitated diffusion, only the concentration."
Active transport review,What is importance of active transport ?,Active transport is important because it allows substances to move against the concentration gradient. This helps it maintain the appropriate balance of substances in the cell.
Active transport review,"How do carrier/channel proteins select which particles to pass through and when?
More specifically,
How do aquaporins only let water in? How can the cell control the amount of water that can diffuse through aquaporins? How come the channel protein will not bring in potassium ions when it needs to bring in sodium ions?","Hi ! The shapes of the channels is very specifically adapted to letting only one type of molecules through. For example, aquaporins are shaped in a way that only water can pass through (because water has a specific structure and charge). Sodium and potassium do not have the same size nor shape and therefore one cannot use the channel of the other as well. 
The cell can control the amount of water that it lets in or out, by controlling the amount of aquaporins in its membrane. This is done by exocytosis/endocytosis of aquaporins, that can be controlled for example by antidiuretic hormons (that tend to provoke endocytosis of aquaporins)."
Active transport review,"How does the carrier protein change shape? Can the protein somehow bend, or does it chemically change?",The protien changes shape by using ATP energy. And no it cannot bend
Active transport review,I don't understand active and passive transport i need help.,Active transport uses energy to transport molecules across the plasma membrane. This uses energy from ATP. They also use pumps to get molecules in or out of the cell. Passive Transport does NOT use energy to transport molecules across the membrane. This can also just be molecules diffusing across the permeable membrane or a direct channel which they can enter or exit.
Active transport review,"what actually makes particles move down the concentration gradient? as in, why are particles by random motion able to passively move into an area of low concentration?? how can random motion lead to an overall non-random outcome??","The movement of particles is random, but even with that randomness, particles have a high probability to move from the area with high concentration to an area of low concentration. 

A good example would be if you get some small objects and assign them into two groups (A and B for example). However, you add more objects to group A than you do to group B. Then, for each object flip a coin. If the coin comes up as heads, keep the object in its assigned group. If the flip is tails, move the object to the opposite group. Once you're done, no matter how many more objects you put in group A then B, you should have a roughly equal distribution in each. 

This isn't a non-random outcome, it's just how probability works. The chance of an object moving from group A to group B is greater only because there are more objects in group A and therefore more chances to move to the other group."
Active transport review,"What are the differences between a carrier and a channel protein? Also, what are some examples?","Channel proteins are proteins that create hydrophilic holes in cell membranes, facilitating the transport of molecules down the concentration gradient. Carrier proteins are integral proteins that transport chemicals across the membrane both down and up the concentration gradient
 Some examples of channel proteins include chloride, potassium, calcium, sodium ion channels, aquaporins, etc. Examples of carrier proteins are sodium-potassium pump, glucose-sodium cotransport, valinomycin, etc."
Active transport review,what is hydrophillic and hydrophobic? Please answer,"Hydrophilic means a molecule or part of a molecule is _attracted_ to water. Hydrophobic means the opposite, it _repels_ water."
Passive transport review,"Hi, what exactly is facilitated diffusion?",When the molecules pass through the membrane via protein. (passive/active transport) Usually large and charged molecules use facilitated diffusion.
Passive transport review,How can water pass through the hydrophobic part of the cell without breaking the cell membrane?,I think they have passage ways so the water doesn't touch the hydrophobic parts of the cell membrane.
Passive transport review,"so if I understand, channel proteins do not require ATP. Am I right?",Yes. Channel protein is passive transport and doesn't use energy.
Passive transport review,can cholesterol pass?,"Cholesterol is part of the phospholipid bilayer membrane, it doesn't pass through because it is part of the membrane"
Passive transport review,What direction in a gradient does passive transport go?,From higher concentration to the lower concentration.
Passive transport review,What are the differences between osmosis and diffusion? are osmosis a part of diffusion?,"Osmosis is a type of diffusion, but it is specifically the diffusion of water,H2O. Diffusion is a term for any movement along a gradient"
Passive transport review,what is osmosis and what are some examples for it?,"Osmosis is the flow of water or other fluids across a semi-permeable membrane to balance chemical concentrations on both sides of the membrane. Try these Khan Academy videos and articles for more information.

https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/mechanisms-of-transport-tonicity-and-osmoregulation/v/diffusion-and-osmosis

https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/mechanisms-of-transport-tonicity-and-osmoregulation/v/osmosis

https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/mechanisms-of-transport-tonicity-and-osmoregulation/a/osmosis

If you really want to understand osmosis, try this experiment. Take a normal egg. submerge it in vinegar for 24-48 hours, or until the shell has dissolved. Then, take your egg without a shell and submerge it in syrup for 24 hours. Observe. Then, take your egg and put it in distilled or bottled water for 24 hours. Observe again.

I know that this is a very vague answer, but I suggest going back and re-reading the article to try to understand why this is happening. I've found that sometimes knowledge gained by oneself when possible is better than getting an answer. Also, the practical application of osmosis in the experiment also helps understand it better."
Passive transport review,When water passes through the hydrophobic how does it get the water to go through the body and give it energy?,"Water passes through the membrane in a diffusion process called osmosis. During active transport, energy is expended to assist material movement across the membrane in a direction against their concentration gradient. Active transport may take place with the help of protein pumps or through the use of vesicles. hope that helps"
Passive transport review,Why does the hydrophobic center of a cell membrane prevent polar substances from diffusing through it?,Because they are to large to pass through without breaking it apart. (I think)
Overview of metabolism,"I'm curious about how ATP ended up being the energy currency for both plants and animals, why the same molecule? Is because of a common ancestor?
Is there any cell that doesn't use ATP as its "energy currency"?","Yes, it is because of the common ancestor. If there was a different, more efficient molecule then this would have been used instead. Keep in mind that in the long run only the most effective processes and molecules can transferred by generations."
Overview of metabolism,Why is it that ATP happens to resemble an adenine base in DNA? Are they related in any way beyond structure? Is the adenine base special? Is there another energy currency molecule like ATP? Can we artificially create another energy currency molecule?,"Both ATP and DNA are nucleic acids. All nucleic acids have 3 parts.
1. A pentose sugar(A sugar with 5 carbon molecules)
2. Phosphate group(s)
3. A nitrogen base. DNA and ATP have the same nitrogen base- Adenine, present.

ATP is specially called an energy currency because it has an easily breakable bond between 2 of its phosphate groups. There are several other triphosphate molecules present in cells like GTP and CTP that play various roles, but ATP is the main 'energy trading' molecule. 
Triphosphate molecules can be synthetically created under the right conditions, our cells will still rely on ATP."
Overview of metabolism,What is ADP (adenosine diphosphate)? How is it different from ATP?,"ADP is adenosine diphosphate 
and
ATP is adenosine triphosphate

In ADP there is 2 phosphate molecules
In ATP there is 3 phosphate molecules"
Overview of metabolism,"How can a molecule be "worn out"...? Does he mean they've outgrown their usefulness, or that they actually lose hydrogens or their groups come apart somehow over time?","Good question... they don't truly mean "worn out" as I think you are thinking... I think what they mean is that a molecule such as glucose gets broken down a few times to harvest some energy in the form of ATP... and then another molecule such as pyruvate, for instance, enters another metabolic process for recycling, harvesting both energy, and the use of the carbons for other purposes. See the citric acid cycle and this will start to make more sense ( https://www.khanacademy.org/science/biology/cellular-respiration-and-fermentation/pyruvate-oxidation-and-the-citric-acid-cycle/v/krebs-citric-acid-cycle )... but you are right... "worn-down" is confusing wording."
Overview of metabolism,"Does metabolism vary widely between people? I have heard that it does not, but it would seem that it would be highly dependent on the weight of an individual.","yes, it does, because you could have an illness and because of this illness one of your hormones gets produced more or less. And so your metabolism would be regulated as faster or slower."
Overview of metabolism,"Are ADP/ATP reusable? What I mean is, once ATP released its energy, does it transform back to ADP? If yes can this ADP be used again to form back ATP?","This is an essential cycle that never stops until you die: ADP gets phosphorylated in the mitochondria, storing energy in ATP, and the ATP gets used to perform cellular work, releasing its energy in coupled reactions, and transforming back to ADP."
Overview of metabolism,"So basically, Metabolism is the core of a cell. It's where all the work happens right?",Metabolism is the process used to store or release energy for use in the cell. It allows other essential chemical reactions to happen. it is the basis for all the work in cell. Try to think of it as a process not an area where reactions happen
Overview of metabolism,How energy is transfered from cellular respiration to the process that formats ATP. Is it in heat? If so doesnt it affect other molecules in the area? Thanks,"The majority of ATP is generated through ATP synthase at the end of the electron transport chain. In this process, a concentration gradient of protons (H+) is what is used to drive ATP synthase, not heat."
Overview of metabolism,Is the convergence of glucose to glycogen considered anabolism ?,"Yes - this is an anabolic process, promoted by the action of insulin on the hepatocyte or myocyte. The reverse - i.e. the hydrolysis of glycogen back into glucose-1-phosphate - is a catabolic process."
Osmosis and tonicity review,doesn't water move from high concentrated water to low concentrated water,"yes, so when the concentration of a solute is high, the concentration of water is lowered since there is more solute per water, less water per solute. Thus, when water moves from low concentrations of solute to high concentrations of solute, it moves from high concentrations of water to low concentrations of water."
Osmosis and tonicity review,"I am confused- how can Osmosis be a form of Passive Transport if water moves from areas where solutes are less concentrated to areas where they are more concentrated. I though passive transport is when molecules move from areas of high concentration to low concentration, so shouldn't Osmosis technically be classified as a form of active transport? I don't fully understand the explanation given here, since it looks a bit unclear.","Hi,

Active transport is a process that uses energy from respiration.

Diffusion and osmosis don't require the cell to expend any of its own energy, as they are passive processes. 

Diffusion is the spreading out of particles in a *gas or solution* resulting in the *net* movement of these particles from an area of *higher* concentration to an area of *lower* concentration  

Osmosis is the movement of *water* particles from a *dilute* solution to a *more* concentrated solution through a *selectively permeable membrane*

As we know both are passive processes and yet (in basic, short terms) diffusion is higher to lower and osmosis is lower to higher, so movement to concentration doesn't determine whether it is active or passive.

Hope this helps!
Franek Mierzejewski"
Osmosis and tonicity review,""In osmosis, water moves from areas of low concentration of solute to areas of high concentration of solute." 

Does this mean that in osmosis water ONLY moves from areas of low concentration of solute to areas of high concentration of solute? Or just that it can?
thanks in advance :)","So osmosis only occurs with a semipermeable membrane, and even with the membrane some water will move both sides. MORE water will move up the concentration gradient, thus there is a net flow up the gradient."
Osmosis and tonicity review,So dose Osmoses move in an area of Low to high concentaration?,"depends what you mean by concentration, if you are talking about solute, then yes. But remember, it is the movement of water particles/molecules. Also, most people tend to say that water molecules from an area of high water potential to an area of low water potential, but that is basically the same as you say... low concentration of solute (e.g. salt) to high"
Osmosis and tonicity review,Why does the water diffuse into the glucose cell that is semi-permeable? I thought it goes from a high concentration to a low concentration and doesn't glucose have a higher concentration than water?,You could think of it like there's a higher concentration of water outside the cell / more of the outside solution's made of water than the one with the glucose.
Osmosis and tonicity review,"In my notes, it says osmosis is from hypo to hyper and that diffusion is hyper to hypo.
But this video only looks at when water is moving. I am having a hard time understanding how these two situations play out","hi
Diffusion is the movement of molecules( of any kind )from a region of high concentration to a region of low concentration.On the other hand osmosis deals with water,purely.we could define osmosis as the movement of water molecules from a region of high water concentration to region of low water concentration,which is basically from hypo to hyper,because if there is more water/high water concentration the solution is hypotonic.I hope i have helped you in a way."
Osmosis and tonicity review,"I am confused- how can Osmosis be a form of Passive Transport if water moves from areas where solutes are less concentrated to areas where they are more concentrated. I though passive transport is when molecules move from areas of high concentration to low concentration, so shouldn't Osmosis technically be classified as a form of active transport? I don't fully understand the explanation given here, since it looks a bit unclear.","Hello! I hope this message find you well. Passive Transport is when a molecules moves from an area with a higher concentration of solvents to an area with a lower concentration of solvents. Think about this: If an area is 60% solutes, there are 40% solvents. If the other side of a membrane has 30% solutes and 70% solvents, the molecules would be moving from high to low solvent concentration, but low to high solute concentration (I believe). In this case, you can think of water as the solvent... (Does this help?)"
Photosynthesis review,"If you heavily breath on a plant, will it help growth considering it needs CO2, water, sunlight?","In an open environment, probably not by any noticeable amount. However, if you put the plant in a sealed container such as a greenhouse and sit in the greenhouse for a while then the CO2 concentration will rise. So in a sealed container the answer is yes but just a plant sitting in your house or outside breathing on it won't make a huge difference."
Photosynthesis review,how does the plant reléase the oxgen,through stomata on the back of it's leaves
Photosynthesis review,"Calvin Cycle: ATP is used to create sugars that the plant will use to grow and live.

My question is where does the ATP come from? Light-dependent reactions make ATP with the light energy, but the Calvin cycle seems to already have it so that it can convert into sugars... Does the Calvin cycle happen after the light-dependent reactions occurs or is the Calvin cycle independent? An example of my question:

Does photosynthesis happen like this?

LDR: Light energy + H2O = ATP + NADPH + O2 

And then after that:

Calvin Cycle: ATP + NADAPH + CO2 = sugar

? 
Sorry if I got some things wrong @~@","The Calvin cycle is dependent on the Light-dependent reactions, and almost in the same way Light-dependent reactions are dependent on "The Calvin Cycle".  The "light-dependent reactions" receive light, and provide energy for the Calvin cycle. After used by the Calvin cycle, the molecules go back to the thylakoids to be reenergized in a way. So it is almost like a constant cycle between the two areas. For clarity refer to the diagram given above."
Photosynthesis review,what is NADPH?,the electron carrier for photosynthesis. NADH(without the P for photosynthesis :) ) is used in cellular respiration. They carry electrons to and fro and are subsequently oxidized or reduced. They need to carry the electrons because electrons are high charge substances
Photosynthesis review,""Light energy is captured by chloroplasts and stored as ATP"
ATP is need to make sugar, BUT ATP is already compose of sugar. Where do this sugar come from?","ATP is not sugar, it is a nucleotide. The carbon atoms needed to build sugar molecules are taken from the CO2 that the plant absorbs. CO2 is converted into glucose during the Calvin cycle, which is an anabolic pathway and therefore needs ATP to actually build up the molecules."
Photosynthesis review,during what stage of photosynthesis are ATP and NADPH converted to ADP + Pi and NADP+,"During the Calvin Cycle, the ATP and NADPH are broken down into ADP, Pi, and NADP+ to provide energy for the cycle. Then, after passing through, the used-up molecules react to bind together into ATP and NADPH again."
Photosynthesis review,Why are *photosynthesis and cellular respiration* are not simply reversal of each other?,They are in a way. Photosynthesis uses carbon dioxide and water to make oxygen and high energy sugars like glucose. Respiration takes in oxygen and glucose and turns it back into carbon dioxide and water.
Photosynthesis review,""Light energy is captured by chloroplasts and stored as ATP" 
ATP is need to make sugar, BUT ATP is already compose of sugar. Where do this sugar come from?","ATP itself is not composed of sugar.

When light energy is captured by the chloroplast, it, along with carbon dioxide and water, gets converted to ATP, NADPH, and oxygen (light-dependent reactions). The ATP and NADPH then enter the Calvin cycle and fuel the synthesis of molecules that _eventually_ become sugar molecules. 

These sugar molecules can then be sent to the plant cell's mitochondrion to undergo cell respiration, which produces even more ATP that can be used to fuel the plant cell's many complex processes."
Photosynthesis review,How do trees survive when they lose their leaves in the winter? How can photosynthesis still occur without the chloroplasts in the leaves? Do they keep energy in storage to use during the season?,"Deciduous trees store energy and resources within their bark, which can be used during the winter months when they have no leaves. Additionally, their physiological process change and slow down, as to not consume as much energy compared to the warmer months. It's a bit like hibernation for trees, where they stock up on resources and decrease energy consumption to make it through the winter. 
Evergreen trees (like the firs you see during Christmas time) have special adaptations to the cold that negate the need for this period of dormancy.

Does this help?"
Introduction to metabolism review,"The more I know, I more I get confused with the concept of 'energy'. It seems to me that energy is very abstract, like an invisible force that pushes things around. So what exactly is energy?","Energy is what it takes to do work, mostly moving matter in the form of vibration/heat, rotation, and kinetic energy. Potential energy is the stored ability to do work. It is a name chosen for a specific unit."
Introduction to metabolism review,"I am a 11th grader and I am preparing to study medicine. Can anyone tell me if I have to know all the metabolic reactions such as glycolysis, glucogenesis... ?","Yes, you should know all of these metabolic reactions."
Introduction to metabolism review,This is hard and confusing (probably because i am a 6th grader),"9th grade now, is it any easier?"
Introduction to metabolism review,How does Cellular respiration work?,"hey mate, there are articles on cellular respiration in the next unit."
Introduction to metabolism review,Why is photosynthesis an anabolic process and why is cellular respiration a catabolic process?,"Anabolic processes are processes that build up compounds. That means higher energy bonds are created. Photosynthesis takes CO2 and H2O (quite low energy molecules), and then assembles them into glucose. Catabolism, which is the process of digestion and break down complex chemicals into simpler molecules."
Introduction to metabolism review,"If ATP has two high energy bonds, why only one of them is used? As in, we get from ATP to ADP, but why not further?","perhaps becuase if it splits off enough times it no longer preforms its job, also there may not be enough energy to split off again AND sustain itself. im honestly just making an educated guess tho"
Introduction to metabolism review,All of this is so confusing! can somebody please better explain?,"Metabolism is the process to either store or release energy, just like you live by spending money and saving it. Both are necessary. In our body, we're either building molecules or breaking them apart to give us what we need. Building molecules requires energy, which it gets from ATP. Building molecules is a process called anabolism: for a visual aid, just imagine your builder is called Anna. Taking molecules apart is catabolism: I imagine a cat coming in and breaking things down. Anna your builder needs energy to do her work of building molecules, so she takes what's called ATP. To remember ATP, just think "instead of an ATM that gives money, it's ATP." Anna the anabolic process cashes in her ATP money by converting it to a currency she likes more called ADP, which is done by tearing off a small part of her ATP bill. Cats (the catabolic), on the other hand, give money as an apology any time they destroy or break something apart. To be clear, no process is better than the other. So… just remember Anna the anabolic builder, cats the catabolic destroyer, and Anna who takes money and converts it to her currency (ATP to ADP) to build stuff, and cats giving money (energy/ATP) as an apology when they destroy stuff."
Enzymes review,Do enzymes in the human body have the same optimal peak rate?,"No, the optimal peak varies across enzymes and is dependent on the enzyme in question.
For example, pepsin typically functions optimally in the acidic conditions of the stomach while trypsin prefers the more alkaline conditions of the small intestine"
Enzymes review,"So, an actual field question! But this section got me wondering.

I take lactase to assist in the breakdown of the few milk products I consume because it appears I'm lactose intolerant. I'm instructed to take one (or two, if one doesn't seem to be enough over time) every time I consume dairy.

Why do I need to continue to take these over time? Enzymes are reusable, right? They're not reactants. They should stick around after managing my lactose intake. So why do I need to keep taking these things every time I consume dairy? Isn't there a point after prolonged use where there should be a sufficient buildup of lactase enzymes present in the gut to address this issue long term?

Is my immune system doing away with the lactase for some reason?  Do I have really garbage gut pH? What's going on here?","Take this with a pinch of salt, but I am pretty sure that enzymes do not last forever. They will eventually wear out, and will be broken down into amino acids for other proteins. The supplements may also have to fight through the acidity of the stomach, and if you are warmer than usual, it is more likely that the enzymes will denature. Because they will wear out or potentially get damaged, you would need to replenish these enzyme stores to ensure that your body can break down the lactose found in dairy.

Like diabetes, you would have to keep taking the supplements in order to manage the condition. Again, though, please take my answer with a pinch of salt."
Enzymes review,Can an enzyme have more than 2 active site?,"Yes they actually can-- Here's a bit I found on Reddit ( any search will bring up a number of more reliable sources saying the same thing however ;D)

Yes. Some enzymes will bind a substrate and then there will be a change in its quaternary structure that could open up another active site for a different type of substrate. Other enzymes have more then one of the same active site and they can bind multiples of the same substrate.

Hope that helps!"
Enzymes review,where are enzymes created? in the cell?,"Like all proteins they are produced by *ribosomes*, which are in the cytoplasm (the part of the cell that is outside the cell nucleus). After an enzyme is synthesized it may be modified in the Golgi apparatus or elsewhere in the cytoplasm."
Enzymes review,What is the pH?,"In chemistry, pH is a numeric scale used to specify the acidity or basicity (alkalinity) of an aqueous solution. It is roughly the negative of the logarithm to base 10 of the concentration, measured in units of moles per liter, of hydrogen ions. More precisely it is the negative of the logarithm to base 10 of the activity of the hydrogen ion.

You can also learn more about it here, on KA:https://www.khanacademy.org/science/high-school-biology/hs-biology-foundations/hs-ph-acids-and-bases/v/introduction-to-ph"
Enzymes review,What are the different types of enzymes and what are the differences?,"If you are asking the types of enzymes by *how* they break reactant, there are *7 types* (some websites say there are 6 because after 2018, one type was added (-_-)). 
Oxidoreductases, Transferases, Hydrolases, Lyases, Isomerase, Ligases, and Translocase. (Maybe you don't need to learn them at this point.)

If you are asking the types of enzymes by *what* reactant they break, there are...well there are many (it is said there are about 2000 kinds). 
I have never counted but maybe there will be 20 ~30 enzymes you will see learning biology. One third of them will be about plants and the rest will be about human body. Don't worry, you will learn them step by step.

As you can see the above, basically the difference is determined by  how they break or what they break."
Enzymes review,"In the last paragraph it mentions that an enzyme is not a reactant.
What is a reactant?",A reactant is a substance that changes in a chemical reaction.
Enzymes review,Why can enzymes work again after being inactivates but may not work after being denatured?,"When they are denatured, the shape of the protein is changed permanently, thus the active site is changed permanently as well. Therefore the enzyme cannot work like it used to. But an inactive enzyme is caused when the temperature is too low for example, the enzyme is fine because it is really cold, there are virtually no collisions/very less collision, meaning that no reaction is taking place. As there is nothing wrong with the enzyme, if you just merely increase the heat, the enzyme will work as it should because there will be collisions."
N/A,"So cells go under mitosis and meiosis. DNA is copied and split, but wouldn't that mean the other organelles in the cell have to copy too? It is never mentioned and I wonder if there is a reason or something.","There is a production of cellular organelles and proteins during the life of the cell prior to replication. And, in fact, some of the cellular organelles DO contain genetic material (for example, mitochondria and chloroplasts contain their own DNA specifying mitochondrial and chloroplastic proteins) which must be replicated during the process of organelle reproduction."
N/A,sperms have 1 sex determining chromosome x or y or it has 2 both x and y?,"Sperm cells contain either an x chromosome or a y chromosome, not both. They have only one sex determining chromosome, and that can be x or y."
N/A,"The general concept of mitosis is one cell splitting into two. But, the text does not discuss how any cell dies. It appears to me that the amount of cells in a certain organ would just keep increasing and increasing. It does not seem that the cells die to balance out the amount of cells, they just keep increasing by spitting into two. How does that work for the body?","In addition to what Aleksandr has said here, you may also wish to consider that mature organs contain many cells which no longer reproduce, but simply serve their function until they die and are replaced. These cells are said to be in "G-zero." You can think of them as done with reproduction and simply doing their job... like many humans at an advanced age!"
N/A,how does DNA get to the cells in the body?,"All cells start from the original fertilized zygote.   The two gametes (sperm and ovum) contain 23 chromosomes(n) each and when the sperm fertilizes the egg(ovum),  the zygote now has a total of 46 chromosomes and becomes diploid (2n).  This zygote then goes through many stages of the replication cycle to create more and more cells called somatic cells or body cells.  If your confused you should watch this video here: https://www.khanacademy.org/science/biology/cellular-molecular-biology/intro-to-cell-division/v/fertilization-haploid-diploid-gamete-zygote-homologous

So to try and sum up your question, the DNA does not enter into every new cell but is actually a genetic copy that was produced by its mother cell.  This process happens millions of times."
N/A,How many DNA are there in a chromosomes?,"A chromosome has many genes, a combination of genetic information that gives rise to characteristics, but it is only _one_ extremely super long DNA strand"
N/A,"In the first paragraph (DNA and Genomes), it says that _almost_ all cells in the human body have DNA. There are some cells without DNA?","Yes - red blood cells are enucleated to make more space for hemoglobin, the protein that binds to oxygen."
N/A,"what is the difference between chromatin, chromatid and chromosome ?","Chromosomes are the largest out of those 3, with an "X"  shape. Chromatids are each half of the Chromosome, if it was cut vertically. Finally, chromatin is the material that chromosomes and chromatids are made up of, containing DNA and proteins."
N/A,so a diploid cell is 2 homologous cells or 2 sister chromatids?,"Neither. A diploid cell has 2 homologous chromosomes. They have one set of chromosomes from each parent. Remember that homologous chromosomes do not have to be identical, they just need to have the same genes in the same location, but they can have different alleles."
N/A,"chroma means colored and soma means body. . . It means chromosomes are colored, right?",It actually comes from the fact that chromosomes can easy accept/take up dye. Heres a link I found:  https://www.vocabulary.com/dictionary/chromosome
N/A,"Can you explain me the basic understanding about mitosis and meiosis?

I am always getting confused between them.","Meiosis is for sex cells or gametes (these cells don't have the same genetic makeup as the original germ cell), and mitosis is to copy and reproduce new cells resulting in the same genetic makeup as the original somatic cell."
The cell cycle and mitosis review,"This might be a foolish question, but what if apoptosis happened to humans? Then "Survival of the Fittest" would be true, but the world population would decrease dramatically if that was a reality.","I think that apoptiosis does happen to human. As the cell grow old, (ex) skin cell) they will just kill itself. Also, some mutated cell will detect their own problem and perform apoptosis."
The cell cycle and mitosis review,what is the role of immune system in recognizing bad cells,So the immune cell will actively seek out dysfunctional cells and literally eat them.
The cell cycle and mitosis review,Is cytokinesis part of mitosis?,"I think it is not a part of mitosis itself, but is part of the mitotic phase which results in the two daughter cells. Mitosis deals only with the nucleus, while cytokinesis divides the cell after mitosis os finished."
The cell cycle and mitosis review,how long would apoptosis go on for,"Well, apoptosis is when a cell essentially says to itself, "Oh no, I have something wrong with me." and self-destructs itself. It basically commits suicide for the greater good of the colony to avoid spawning more defected cells. To make it simple, apoptosis cannot go on; it is a one-time thing. Hope this helps!"
The cell cycle and mitosis review,How long do these phases take? Can you give an example of a specific cell? Is it different for different types of cells?,"Yes it is different for different types of cells. A human cell ( I don’t know which) typically takes *about 24 hrs for a cell cycle* (most of the 23 hrs are interphase n’ the rest mitosis and cytokinesis), *in labs*. (Not in the human body). But most intestinal cell go through the phases  more quickly. 
Hope it helps.."
The cell cycle and mitosis review,What are the three parts of interphase?  What is the characteristic of each?,"In chronological order :
- G1, or first growth phase, is when the cell synthetises its proteins by translating its RNA through ribosomes
- S, or synthesis phase, is when the cell replicates its DNA in order to divide
- G2, or second growth phase, is when the last proteins for division are produced, and also organelles like mitochondria or chloroplasts divide"
Chromosome structure and numbers review,"what are the histones? and what do histones do? also, are the histones?","Histones are bobbin shaped, positively charged, eukaryotic proteins. Because the histones are positively charged, they attract negatively charged DNA which then wraps itself around the histones. This organizes and condenses the DNA, I believe this is for when the chromosomes duplicate. Histone also play a part in gene activity.

Hope that is helpful :)"
Chromosome structure and numbers review,What is a cohesin? What is its purpose?,"Cohesion or cohesive attraction or cohesive force is the action or property of like molecules sticking together, being mutually attractive. Wikipedia"
Chromosome structure and numbers review,"An organism has an "n" number of 15. In a diploid cell of this organism preparing to enter mitosis, there will be ____ chromosomes, which will contain ____ chromatids.","Basically 
2= diploid has two sets
n= the number of chromosomes in a set
30= number of chromosomes
Chromatids= 2*chromosomes (only of before mitosis)"
Chromosome structure and numbers review,"I believe there is an error to this lesson. Why does it say "DNA makes up genes, genes make up chromosomes" (at the very end). Shouldn't it be "Genes make up DNA, DNA makes up chromosomes"",DNA makes up genes because they are several DNA strands that come together and form a certain characteristic about an organism.
Chromosome structure and numbers review,how do we identify students misconception?,create scenarios that allow students to share their prior knowledge.
Fertilization and development review,"Human life begins with a single cell. Over the course of 9 months, this cell becomes trillions of cells. What process is responsible for this?","Mitosis, mainly. There's an article on Khan Academy showing this process:

https://www.khanacademy.org/science/ap-biology/cell-communication-and-cell-cycle/cell-cycle/a/phases-of-mitosis"
Fertilization and development review,when does the heart start beating?,It depends on the animal. For a human the hearts beating at 21-23 days in the fetus.
Fertilization and development review,So what happends differently in the fertilization cycle when a woman has twins?,"Two situations can happen :
- in the case of identical twins, the ovaries of the woman release one egg during ovulation, and once this egg gets fertilized it divides once too much, forms twice the amount of cells it was supposed to, and boom you've got two identical bundles of cells that will be the two children. Identical twins share the exact same genes as they come from the exact same egg fertilized by the exact same sperm cell. 
- in the case of non-identical twins : sometimes a woman's ovaries can release not one but two eggs during the same cycle. If those two eggs get fertilized by two different sperm cells at around the same time, then you've got two embryos that will be non-identical twins (not sharing the same genome because they come from two different eggs and two different sperm cells). 
Hope this helped !"
Fertilization and development review,does a female not undergo menstruation throughout the whole pregnancy,"Yes, because the part of menstruation that is "bleeding" is when a female sheds the lining of their uterus. So when the zygote, blastocyst, embryo, or fetus is inside the uterus. It relies on the uterus to develop a placenta and provide food, so it can not shed if that makes sense."
Fertilization and development review,How does sexual reproduction in plants differ from asexual reproduction in plants?,"It differs just like it would with animals or other organisms. In sexual reproduction, a male gamete fuses with a female gamete to form a zygote (requiring two parents, leading to more genetic variation, etc). In asexual reproduction, the organism essentially copies itself (one parent, very limited genetic variation). In plants, sexual reproduction looks like pollen, seeds, and plant ovules. An example of asexual reproduction would be where cuttings of plants form roots after being placed in water."
Fertilization and development review,What does the processes of fertilization not use?,"it uses everything, can you be more specific of exactly what you mean?"
Meiosis review,"In telophase 1 and telophase 2, I am confused about the use of the word "haploid." They are both labeled "haploid," but they do not look the same.","That is because in Telophase 1, the sister chromatids are still attached. Telophase 2 is basically splitting the 2 sisters apart, but, as each contains the same genetic info, it is still haploid.  Hope that answers your query!"
Meiosis review,"I am confused about the number of sister chromatids between mitosis and meiosis. For example, human. After replication, there are 46 chromosomes (92 sister chromatids in total) in a cell, right? 

During mitosis, they are split into 2 cells, each of which has 46 chromosomes (46 sister chromatids in total).

On the other side, during meiosis I, same as mitosis, they are split into 2 cells, each of which has 46 chromosomes (46 sister chromatids in total).

So, during meiosis II, these 2 cells was split again into 4 cells, each of which has 23 chromosomes (23 sister chromatids in total).

Am I right?","Your thought is correct but plz notice, after splitting 2 sister chromosomes in mitosis, each single one is no longer a sister chromatid but a chromosome. So you cannot say 46 chromatids in total in your second graph, it is only 46 chromosomes or 23 pairs of homologous chromosomes:)
Meanwhile, in meiosis1, after splitting into two cells, each one contains 46 sister chromatids but only 23 chromosomes (notice that two sister chromatids is a chromosome)."
Meiosis review,what is the difference between crossing over and synapsis?,"Synapsis is when the homologous chromosomes of the same size and length pair up. Crossing over is when bits of DNA are exchanged from each chromosome to produce genetically unique chromosomes. Though both happen in Prophase I, synapsis happens before the chromosomes can cross over. Hope that helps!"
Meiosis review,What does Homologous mean?,"In biology it means similar in position, structure, and evolutionary origin but not necessarily in function for organs, but for chromosomes it means similar in position, structure, and evolutionary origin but not necessarily in function. hope this helps:)"
Meiosis review,Is Meiosis a continues process or does it stop and begin whenever the body wants it to?,"Meiosis occurs in the testes in males and in the ovaries in females. In males, sperm production occurs in the testes almost continuously to replenish the supply. In females, egg cells are made from oocytes which are produce when the female is a fetus. Oocytes are cells arrested in meiosis I. Meiosis resumes when the oocyte is activated ready for ovulation and then arrests again in metaphase II. It is during fertilisation that the cell undergoes anaphase II so that the sister chromatids are finally separated"
Meiosis review,what happens to cells ( what is their fate or role) that have completed the mitosis cycle and the meiosis process??,"after mitosis, cells go back to the interphase stage of the cell cycle and carry on the cell cycle. for human somatic cells, mitosis can only occur about 20-50 times before it undergoes apoptosis, a number known as the Hayflick limit. scientifically, this is beneficial because of the accumulation of mutations that may potentially be dangerous. an exception is cancerous cells such as with the TP53 mutation, where mitosis keeps going on continuously even if there is insufficient energy/organelles available, often resulting in tumours. note that some cells are stuck in a phase of the cell cycle known as G_0, where they do not go through mitosis till reverted back to the G_1 stage.
as for meiosis, cells are usually nourished so that they grow. in humans, the sperm is nourished by the sertoli cells in the testes to ensure that they grow and mature. the ova are developed inside the follicles of the ovary and typically the one ovum that matures the most is released from its follicle during ovulation. their fate is either fertilization, in which case the sperm and ovum form an embryo that develops in the fallopian tubes and then in the uterus. in case that this does not occur, the ovum is shed off with the uterine lining in a process known as menstruation. as for the sperm, they are usually just left in the testes, and if not released through a process such as ejaculation they may start to die in the testes."
Meiosis review,so are the sister chromatids diploids?,"We say a cell is diploid or haploid or more,
Sister chromatids are just 'one-half' of the chromosome"
Meiosis review,"In the Starting Cell of Meiosis I, you say that it is the homologous chromosomes from mother and father that cross over... but how can this be if the cell has not been fertilized yet and Meiosis describes how a gamete cell is produced. Therefore, an egg  would only have the chromosomes from the mother and  a sperm would have only the chromosomes from the father.","You received homologous chromosomes from your mother and some from your father, that is your genetic make up.  I think the process of meiosis separates them so that the traits you pass on to your children can seem as if they are coming from grandparents or from you.  I think it why I have blue like my dad and not brown ones like my mom.  My maternal grandmother had blue eyes so she gave my mom the blue eyed chromosome.  I was the one child of 4 with blue eyes.  My eye color chromosomes from both my parents were different than for my siblings.  I think meiosis has a role in that."
Meiosis review,meiosis 2 is similar to mitosis because?,"Meiosis 2 is similar to mitosis because it separates the chromosomes to have sister chromatids in each cell. In both processes, you are separating the chromosome and dividing the cell to make 2 cells out of 1 (the only difference is that in meiosis, you're doing that for 2 cells to get 4). These are called daughter cells."
Types of reproduction review,Where do babies come from?,they come from huge birds
Types of reproduction review,How do yeast cells reproduce? Is that budding?,"When cells divide, they make new cells. A single cell divides to make two cells and these two cells then divide to make four cells, and so on."
Types of reproduction review,"parthenogenesis occurs in some invertebrates, as well as in some fish, amphibians, reptiles. is it related to them being cold blooded?","What causes parthenogenesis to occur in a species?
In certain insects, salamanders, and flatworms, the presence of sperm serves to trigger parthenogenesis. Sperm cells launch the process by penetrating the egg, but the sperm later degenerates, leaving only the maternal chromosomes. In this case, sperm only sparks an egg's development––it makes no genetic contribution."
Types of reproduction review,what is a sperm,"Sperm is a male gamete(sex cells of an organism). It has three parts- a head, a middle piece and a tail. Head contains all the cytoplasm, cell membrane and nucleus. The middle piece contains mitochondria which contains ATP. The tail is for locomotion."
Types of reproduction review,How is yeast different from bacteria?,yeast is a uni-cellular(kingdom) Fungus  while bacteria are bacteria mean they belong to Kingdom Monera.
Types of reproduction review,Does asexual reproduction require DNA similar to how sexual reproduction requires it?,"Yes, both require DNA. While there are some viruses which only have RNA, they're still not living. A big part of the reason they don't count as alive is because in order to replicate themselves, they need a host (so this doesn't count as reproduction)."
Types of reproduction review,so would a beluga whale reproduce sexually?,"Yes it does because beluga whale is mammal and their reproduction process includes the fusion of the male gamate (sperm) and female gamate (egg), which is according to the definition of sexual reproduction."
Types of reproduction review,what are parthenogenesis,"reproduction from an ovum without fertilization, especially as a normal process in some invertebrates and lower plants."
Types of reproduction review,Can humans reproduce through *Parthenogenesis*.,"Yes and no. It usually results in tumors called teratomas and abnormal fertilized eggs called hydatidiform moles. It happens in females from what I know, I haven't seen any males. In the sense of true parthenogenesis- no."
The law of independent assortment,"I understand this, but I still get confused on the Mendelian laws.
Here is what I think I know:
The law of segregation states that the two alleles of a single trait will separate randomly, meaning that there is a 50% either allele will end up in either gamete. This has to do with 1 gene.
The law of independent assortment states that the allele of one gene separates independently of an allele of another gene. This has has to do with 2 genes.
Is my understanding of these laws correct?","That is correct. But as an addition, there is also the concept of *linkage*, where the allele of one gene is very close to an allele of another gene in the same DNA strand, that it is very unlikely for the two allele to separate independently (in other words, they are inherited as one unit). This has to do with 2 genes. This concept is essentially independent assortment, but deals with *unit of multiple alleles*, rather than *just an allele*."
The law of independent assortment,Why is science soooo complicated??😩,Because Adults
The law of independent assortment,What is the difference between segregation and independent assortment? :),"Segregation means that the chromosomes or any gene present on chromosome did not lose its identity or get mixed up with other genes. During gametogenesis it keeps its identity. 
While independent assortment means that the chromosomes whether dominant or recessive after gametogenesis goes into any of the gametes i.e in simple language the movement of chromosomes is not affected by movement of other chromosomes"
The law of independent assortment,For the experiment of F1 generation how did Mendel know for sure that the tall parent's genotype is (TT) ?,"The pea plants he used self-fertilized, meaning that each parent ends up having the same set of genes as the offspring. (This is _before_ he crossed them.) This means that there were pure lines of descent from the original pea plants without variation. The genotypic variation of the offspring (heterozygotes) was introduced by Mendel, who crossed 2 plants of different traits."
The law of independent assortment,"The phenotypes are a 9:3:3:1 ratio, but what are the possible genotypes?","there are 9 different genotypes in a F1 dihybrid cross and the ratio is
1:2:1 :2:4:2: 1:2:1

in a monohybrid cross the phenotype ratio is 3:1 which gets compounded when doing a dihybrid cross into 9:3:3:1

the genotype ratio in a monohybrid is 1:2:1
and gets compounded to my answer in a dihybrid cross. I show the work below.

F1 generation is heterozygote for both traits: AaBb or Aa and Bb 
  A  a
A AA Aa
a Aa aa
and 
  B  b
B BB Bb
b Bb bb

here are the possible genotypes and ratios made from the squares above:
AABB(1) AABb(2) AAbb(1) AaBB(2) AaBb(4)Aabb(2)aaBB(1) aaBb(2) aabb(1)

this is nothing more than a 1:2:1 compounded to two characters."
The law of independent assortment,"Does this mean that any living organism (Pea plant, dogs etc.)
will show phenotypic ratio of 9:3:3:1 ? Where 9 plants have all dominant alleles and 1 plant has all recessive alleles ?",Just know that a 9:3:3:1 ratio happens when you cross TWO Heteroygous pairs. Also....Look over what a Dihybrid cross is. Dihybrid cross is when your crossingg 2 different types of Genes. So you should get an out come out of 16...
The law of independent assortment,"Can you explain to me what is the difference between linked and not linked. Also, how to identify if an allele is not linked.","Linkage or whether 2 genes are linked or not depends upon the distance between them. If the distance between 2 genes are small or if they are next to each other in a chromosome, most probably when meiosis occur these genes remain together. So genes that remain together and almost never segregate are called linked genes.  
Hope this helps."
The law of independent assortment,Does the law of independent assortment apply to two genes on different chromosomes or two alleles on different chromosomes?,"Law of independent assortment applies to two genes of different chromosomes _and_ two alleles of same genes.


What does it mean_ It means that alleles are inherited independently and do not affect alleles from _other_ genes."
The law of independent assortment,"If the genes are the same, then why is it that many people look different form their parents?
That's just if they were the same though.","In each of your parents, there are genes coding for their appearence, i.e bone structure, hair color, eye collar, that are shown. However, there are also genes that aren't expressed by your parent that they have, such as something different. Considering there are billions of genes that code for even one thing, there is an extremely high liklihood of you expressing a gene that wasn't expressed in your parents, (but was still there)"
The law of segregation,Who came up with  the punnet squares,"As the name suggests, a Mr./Ms. Punnett, Mr. Reginald Punnett to be exact."
The law of segregation,explain why is it possible for browned eye parents to have a blue eyed child ?which law does it indicate??,"This demonstrates recession and dominance.  Brown eyes are dominant; blue eyes are recessive.  The phenotype is what the appearance is - mother and father have brown eyes.  The genotype, is what the genes they have code for - in order for mother and father to have a blue eyed child, they must have a genotype that includes both brown and blue.  If father and mother each give their individual blue eye gene to their child, the child will have two blue eye genes and no brown eye genes, so eyes will be blue."
The law of segregation,what is epistasis,"It is when one gene affects the expression of another gene. For example, mice have a color gene and can have an allele for black (B) fur color and an allele for brown (b) fur color (black being dominant), BUT they also have a gene that determines pigmentation; one allele C produces pigment (fur color shows) and the other allele c does not (fur color is white/mouse is albino).
So, the possible genotypes would be:
- CCBB, CCBb, CcBB, CcBb (phenotype: black)
- CCbb, Ccbb (penotype: brown)
- ccBB, ccBb, ccbb (phenotype: white, pigment is not produced and therefore fur color cannot be expressed)
I hope this example clarifies things a bit! (:"
The law of segregation,Why does both Geno and phenotype influence from the environment??Are they  talking about the environment that the Gene's are placed or just mean the environment in general? Question No.2,"Genes mainly influence phenotype. However, the environment also influences gene expression.

Phenotype relies on the grade of gene expression."
The law of segregation,Doesn't the crossover between the homologous chromosomes mix up the alleles?,I'm not sure what you mean by "mix up" the alleles — a major benefit of crossovers is that it can create new combinations of alleles (and sometime even new alleles if the crossover happens within a gene).
The law of segregation,How did Mendel derive his law of segregation from this monohybrid experiment? (It is not clear to me in the article).,"If gamete can pass down both alleles, the possibility will be 1/16. The fact that the possibility of 1/4 exists, suggests that only 1 of the 2 alleles is passed down by the gamete."
The law of segregation,"when it says self fertilization, I think I understand the concept of how one of a plant's sperm fertilizes the same plant's seed/ but I also know that usually in human life when like 500 years ago, the kings used to marry his sister to keep the royalty in the same family and when they would have kids, those kids would have serious problems like internal bleeding and many disabilities. so my question is, do the pea plants that come out of self-fertilization have any sort of problem or are they perfectly healthy?","I think they're healthy. Many kinds of plants are able to self-fertilize without any issues, and since these pea plants did it, I assume their offspring is healthy."
The law of segregation,if your parents are one brown and blue eyed and the child is brown eyed. in the future can the child's child be able to have blue eyed if he/she marries brown eyed person?,"The child's child would only be able to get blue eyes (25% of the time, like Okapi said) if both parents were Bb.  Zero chance if either, or both were BB."
The law of segregation,what are homologous genes,"i don't think the other posted answer is right. The question was "what are homoLOgous genes", but the answer seemed more lined up for "homoZYgous" genes. I am still learning this stuff, but my understanding is
- Homologous means genes controlling the same inherited character - may have different versions of same gene. For example - flower colour, may be purple, or white, but still homologous because it's flower colour.
- Homozygous means the genes carry two identical alleles, PP or pp.
- Heterozygous means the genes carry two different alleles, Pp."
X-linked inheritance,"In the second paragraph of the section titled "Sex Chromosomes in Humans", do Chromosomally female (XX) embreyos that develope into males make them have a more girlish appearance? Do Chromosomally male (XY) embreyos that develope into females make them have a more boyish appearance? Some boys might look a lot like girls or vice versa.","Hi Tanya, my understanding is that XX individuals with an SRY translocation (who develop as male-bodied) may need hormone supplementation at puberty to develop some male secondary sex characteristics (e.g., facial hair). However, they generally have what their cultures recognize as a male appearance. You can learn more in the Genetics Home Reference entry about SRY translocation: https://ghr.nlm.nih.gov/condition/46xx-testicular-disorder-of-sex-development."
X-linked inheritance,""SRY is found on the Y chromosome and encodes a protein that *turns on other genes* required for male development.
 
If an SRY-bearing X chromosome fertilizes a normal egg, it will produce a chromosomally female (XX) embryo that develops as a male."
So, the SRY induces other genes to produce male character.
 Does that mean that the X chromosome also contains *other genes* that are required for male development?(genes that would be dormant in the absence of SRY)","I'm not an expert on this, but my understanding is that SRY† is (usually) sufficient for embryonic testis formation and that the hormonal effects of having testis are (usually) sufficient for male primary and some secondary sexual traits§.  One way of looking at this is that male and female sexual anatomy aren't as different as they appear, they just have different structures emphasized and elaborated with a few small changes in "plumbing".

UPDATE:
†Note: SRY encodes TDF (testis determining factor) a transcription factor that enhances expression of genes needed for testis development and possibly suppresses expression of genes that promote ovary development.  This is an active area of research and there is evidence that SRY is not always necessary for male development and also may not always be sufficient for male development. 
If you want to learn more about this, here is a good (and freely available) review article:
https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1001899

§Note: Some other genes on the Y chromosome are necessary for sperm production, but they don't appear to be needed for "maleness"."
X-linked inheritance,What is Gene-linkage? How is it different from the Sex-Linkage?,"Sex linkage referes to a gene being linked to (or "on") a sex chromosome. Gene linkage refers to two genes that are on the same chromosome, and are thus "linked" (inherited/transferred together). :)"
X-linked inheritance,"It says in the 2nd paragraph of 'sex chromosomes in humans' that the X chromosome has 800-900 protein-coding genes while the Y chromosome has only 60-70, half of which are responsible for roughly the same task or processes in the same area. How does the male genome make up for that lack of proteins? Are they just not needed or are they found somewhere else? Surely the second X chromosome in females carries something which would be important in males too.","Any time you have dominant and recessive alleles of a gene it is only the dominant allele that gets expressed. There doesn't have to be a second allele for the trait to be present.  

A male having a single X chromosome any genes that are on the X that are not present on the Y chromosome become by default dominant."
X-linked inheritance,all the x linked alleles a man has come from his mother,"Yes all the x-linked alleles a male has comes from his mother. As you may know, a male is XY while a female is XX. For a male to be a male, he has to get the Y allele from his dad. This makes it 100% certain that the male gets his X allele from his mother."
X-linked inheritance,"If the father is colorblind, but the mother is not, then their children can't be colorblind. The males would get their dad's Y and the non-colorblind X. Thus, they would not be colorblind. The females would have a colorblind X, but it would not be expressed, because it is recessive. Is this correct? Am I understanding this correctly?","Yes, that is correct."
X-linked inheritance,Is it impossible to have parents with twelve kids that pass on an infected trait to 6 of the males and 1 female. I was given this problem on another site and got it wrong when I said no. Help!,"The question didn't mention that it is X-linked or Y-linked, so you cannot assume it is sex linked. (Or perhaps it did, but as you didn't mention, then I'd assume the question didn't)

The only way for a pair of unaffected parents to have affected offspring is for the allele for the disease to be recessive, both parents must have a dominant allele and parents must be heterozygous so they have a dominant allele. To have a heterozygous male, the allele cannot be on the non-homologous portion of the X chromosome. (Note that this doesn't mean it cannot be on the X chromosome.)
*Also I want to mention that as the question asks whether it is possible to have 6 affected males and 1 affected female, but does not state that there are that number of affected males and females. Therefore @Anson Chan you cannot prove the allele is recessive by that. And it did not mention how many female and male offspring they have in total, and this is not important. It is sometimes fatal to assume something the question has not said, even though in this case, there isn't much difference.
**Idk if I sound harsh, bu no offence. I am just trying to share my experience

Back to the question, in the case I just mentioned (heterozygous parents for the disease caused by recessive alleles) it is possible for 6 males and 1 female to have the disease if they inherit both recessive alleles from both parents.

As the aforementioned case suits the situation of the question completely, the answer is yes.
------------
Now I have finished explaining this question, let's go for something extra.

So this situation can happen when the locus of this allele is on a pair of autosomes.

Now let's assume there are six boys and six girls among the offspring. (You cannot assume this when solving the question because it's not mentioned, but as a case study, we'll assume this. And don't worry, it is a possible case)

Now the rate of the male offspring getting the disease is 100% while that of female offspring is just 16.7%. Why the great difference? One possibility is that the allele is on the homologous portion of the sex chromosomes. The allele from the father is on his Y chromosome. Therefore the rate of male offspring getting the disease is much larger. Then why does one girl get the disease? That's because crossing over may occur and the allele causing the disease shifted to the X chromosome of the sperm that.

Anyway, this whole case isn't very likely because for the male offspring, even if they all receive the defective chromosome from the father, there is still half the chance they receive a dominant good allele from their mother.

Happy learning to all of you!"
Polygenic inheritance and environmental effects,how environment causes pku?,"The environment doesn't actually cause the PKU -- that is genetic. But the environment can cause it to express in the phenotype -- create symptoms -- based on the environment. The PKU gene simply causes a person to be unable to properly process phenylalanine (they lack an adequate amount of the necessary enzymes). If that person eats foods that are high in it, they can begin to express symptoms of that genetic mutation. If they limit or eliminate those foods, they often will have no symptoms."
Polygenic inheritance and environmental effects,"What's the difference between polygenic and epistasis?
It sounds like in both of them, multiple genes affect one trait.","While a polygenic phenotype can occur without epistasis, if you have epistasis you must be dealing with a polygenic phenotype.

Polygenic just means that there are multiple genes involved in a phenotype.  
Epistasis refers to situations where one allele masks the phenotypic effect of one or more alleles of another gene."
Polygenic inheritance and environmental effects,how are we able to walk on the earth,"Gravity. I personally wouldn't ask this question in the genetics unit, though."
Polygenic inheritance and environmental effects,Does anyone know anything about syndactyly and its genetic inheritance?,"Syndactyly is a mendellian dominant trait, so it is inherited much like any other gene."
Polygenic inheritance and environmental effects,"Can a disaster, natural or man-made, affect human traits?","Quite interesting question!

I can think of radiation which causes *mutations*.

Definitely causes of mutations can affect human traits and phenotype, but not in the form that it will _favor_ survival. Nonetheless, future generations may be less adaptable and degenerated (recall Chernobyl nuclear plant disaster or Minamata disease in Japan (caused by excessive mercury due to chemical industry).


My answer is *definitely yes*. *Negative impact*."
Polygenic inheritance and environmental effects,"So I am very short for my age , yet my mom and dad are both tall but my mom is a little shorter than my dad . Why is that? Do i have a disease or something that affects my growth ?","A short stature can be caused by a variety of causes. It could be genetic, a hormone known as growth hormone could be low in the body, or, in more serious cases, an underlying disease or condition may have contributed to your stature (I.E: tumors, malnutrition, mitochondrial disease). If you are otherwise healthy, it is most likely either genetic or hormonal.

Does this help?"
Pedigrees review,How can you tell if someone is a carrier?,"For Autosomal dominant and X-linked dominant, there is no question of a carrier since the affected allele will be dominant.
For *X-linked recessive*, the carrier will always be the mother/female. Since she has 2 X-chromosomes, one can compensate for the function of the other non-functional chromosome. The father/male can never be the carrier because he has only one X-chromosome, which, if affected, will be indicated on the pedigree chart.
For *Autosomal recessive* cases, it is a little tough to figure out the carrier without sufficient information. We can only know that the affected individual will be homozygous recessive, but we have no way to know if the unaffected individual is a dominant homozygote or a heterozygote (carrier). The only exception to this will be when one parent is homozygous recessive (affected). Then we can say that the offspring will definitely be carriers of the condition.
Hope that is helpful!"
Pedigrees review,"If a recessive trait shows up in all the generations, how can we figure out that the trait is recessive?","For autosomal recessive where there is no skipped generation, the other parent must be heterozygous for the trait, which would mean the children have a chance of having the recessive trait through inheriting the recessive chromosome from the carrier parent.
For X-linked recessive, the same is true, with one parent being a carrier. Ways to prove X-linked recessive are that if the trait is recessive, there will be mother-son and/or daughter-father links. This means that if the mother is affected, the son must be as he must inherit one of her affected X chromosomes. The same is true with daughter-father links. If the daughter is affected then the father must also be as she will inherit one of her X chromosomes from him.

Hope this helps someone."
Pedigrees review,how dow we know if it is autosomal?,Equal number of males and females affected i think
Pedigrees review,"So if a parent is a carrier but doesn't show, it has to be female as a male would have to express it. 
Am I correct?  
thank you for correcting me if it is required.","for sex-linked genetic disorders/diseases, you are correct. This is because the alleles expressing the disorder/disease are usually only present in the x chromosome, although some (few) genes are expressed in both x and y chromosome. This is due to the fact that the y chromosome is smaller.
If you are female, you have xx chromosomes, while you have xy chromosomes if you are a male. 
As mentioned earlier, genetic disorders/diseases are usually found only in the x chromosome. Hence, if the allele for the disorder/disease is recessive, to be a carrier, the person must be heterozygous. 
Because females have two x chromosomes, they can either get the disease (homozygous recessive), be a carrier (heterozygous), or just not have it at all (homozygous dominant). 
But for men, as they only have one x chromosome, only one chromosome can express it, so they can either have it (one recessive allele), or not have it at all (one dominant allele)."
Pedigrees review,whats the difference between x-linked and sex linked?,"Genes that are carried by either sex chromosomes are said to be sex linked.
Men usually have a combination of X and Y sex chromosome, while women have two X’s. since men inherit Y chromosomes, they are the only ones to inherit Y-linked traits.
Hope that helped 👍"
Pedigrees review,Can you have a male who is a carrier of an x linked recessive trait but doesn't express it?,"No that is not possible. Since males only get one x, it is impossible for them to be only carriers of a trait and not express them. Females, on the other hand, have two x chromosomes, which means they can be a carrier for an x-linked trait.




Hope this helps!"
Pedigrees review,how to understand whether a trait going within a pedigree chart is recessive or dominant,"If both parents do not have the trait and the child does, it is recessive. If one parent has the trait and the child does or does not, it is dominant."
Pedigrees review,"On a pedigree chart, how do you show that a person is a heterozygous carrier for a particular recessive allele that is not expressed in the phenotype? For example, how do you visually show that someone is an UNAFFECTED carrier for a genetic disorder?","I've seen carriers denoted by squares or circles that are half shaded, sort of like a full moon. 

Edit: What? Not a full moon, a half moon"
Sex linkage review,is Aneuploidy the same as chromosomal abnormalities ?,"I know this might be late, but Aneuploidy is essentially the same as chromosomal abnormalities."
Sex linkage review,Why does the cat have both tan and black if one of the is inactivated? thats really confusing. whats the point of inactivation?,"The inactivation occurs at random in every cell. One cell over here may inactivate the tan and only show the color black, while in a different cell it may do the complete opposite. This gives the cat a patchy pattern of both colors."
Sex linkage review,how many X chromosomes are in in a females body?,"There are normally two X chromosomes in a human female's body. However, one gene is inactivated and is known as the Barr body."
Probabilities in genetics,What is the probability of having 5 boys in a roll,"Probability for sex ratio is always 1/2, but since we are speaking of having 5 boys in a row, probability changes.

1/2 x 1/2 x 1/2 x 1/2 x 1/2 = 1/32"
Probabilities in genetics,"If monohybrid crossing is something like this Aa x Aa and dihybrid  crossing is something like this AaBb x AaBb, then is this AaBbCc x  AaBbCc called trihybrid crossing and this AaBbCcDd x AaBbCcDd called tetrahybrid crossing? 
Or is there a specific word for crossings that involve more than one pair of alleles?
Perhaps polihybrid crossing?","Not really, but I agree. We need a word to group all these together."
Probabilities in genetics,Why do possible outcomes change? Why can you not guarantee the total outcome in a punnett square?,"There's still chance involved. It's like if you tossed two coins. Each has a 50% chance of landing heads side up, but you can't say that there will definitely be one that lands heads up and one that lands tails up. 

The same goes for genetic probabilities. In the article's example with the dogs' fur color, there might be a litter of eight puppies in which five puppies have the lighter color. Even though each puppy only has a 1/4 probability that it would have light fur, it's not like the genes are sorting themselves out and saying "Well we already have two puppies with light fur, so we have to stop allowing those genotypes to happen now." Each is an independent event.

Hope this helps!"
Probabilities in genetics,I'm still a little confused about the whole probability thing could somebody explain it in a more understandable way please?,"basically, you use the punnets squares to determine all the different possible combinations u have. u line them up and cross them to tell the combos. and then u look and see: how many times does, lets say, AA occur? u look and it occurs 2/4 times in the box, so u know there is a 50% chance of the cross producing an AA set. do u understand the whole punnett square thing, or...?"
Probabilities in genetics,What's an example of an "or" situation (either Event X or event Y) that is NOT mutually exclusive?,"If two events are not mutually exclusive, it would be the same as "and" situation."
Probabilities in genetics,"If I am given 50% of AD and 30% of BC and 30% of AC and 10% of AB, (not precise percentages). How can I figure out the alleles of the "parents" that have ABCD combinations? Or work the math backwards?","If both parents had ABCD alleles, then it would be equal percent for all combinations, which is not given by this task.


Also, I see no CD combination.

Since there is no CD, my projection is it is 0% that both parents have ABCD alleles."
Probabilities in genetics,"If the baby came from the mom , would we have more of the moms genes?","No, as the genes are formed from a 50% contribution from the genes of both male and female gamete."
Probabilities in genetics,what is the reason for the 9/16 probability,"Because, 3/4*3/4=9/16. You get multiply these due to the probability rule of multiplication."
Probabilities in genetics,how do solve all recessive traits?,"It 0% since in every possibility of getting CC and Cc, there will be a dominant trait.  If you multiply that by anything, the answer will still be 0%.

If you want to know for any case that does not come out to be 0%, then you would make a punnet square for each trait separately and multiply the probabilities. For example, if you have AaBb and aabb, you would make a punnet square for Aa and aa and another punnet square for Bb and bb. Then you calculate the probability of a recessive trait coming up and multiply them. In this case, there is a 2/4 chance for a recessive trait for the first one and a 2/4 chance for a recessive trait for the second one. 

2/4 * 2/4 = 4/16 = 1/4 

In this case, there is a 1/4 chance for all recessive traits."
N/A,What is multiple allele is one sentence that is easy to understand?,Multiple Alleles are three or more possible alleles for one individual trait.
N/A,isnt codominance the same as incomplete dominance in that case if both alleles can be expressed?,"Not really.
In codominance, both alleles are completely expressed.  If you crossed a red flower with a white one and the alleles were codominant, you might get flowers that are red and white in patches.  If the alleles were incompletely dominant, the flowers would be pink because the traits blend."
N/A,"I'm confused on why there are some "exponents" on the alleles. For ex, c^ch c^ch
what does that exactly mean?","It's to distinguish the alleles in an easier way, once you have to deal with different traits it will be useful since the base could specify the trait while the exponent specify the allele for that trait.

For example, if you were talking about the traits color and height with the alleles red and blue, and tall and short, respectively, you could express genotype as:
C -> Color
H -> Height 
R -> Red 
B -> Blue
T -> Tall
S -> Short

* C^R C^B H^T H^S (This would be heterozygous in both traits)
* C^R C^R H^T H^T (This would be homozygous for red color and tall height)

You can also use lower case to denote that an allele is recessive (although this is arbitrary)."
N/A,in case of pea plant tall is the dominant gene and dwarf is the recessive gene. does that hold good for other organisms as well? is dwarf always recessive gene and cant it be dominant in the presence of tall gene?,"What's dominant and recessive can change between organisms because species tend not to be able to breed with other species, so the gene pool for a species tends to be isolated to just that species."
N/A,Is multiple allelism the same as polymorphism?,"Not exactly — what is true is that genetic polymorphisms are responsible for the existence of (most) alleles.

Polymorphism (literally "many forms") means different things in different contexts, but in a genetic context it really just means that there are differences in the sequences. 

For example SNPs (pronounced "snips" — stands for single nucleotide polymorphisms) are a very common type of sequence polymorphism.

Having multiple alleles is (usually§) a consequence of multiple different sequence variants for a gene (i.e. genetic polymorphisms) being present in a population.  However, any two alleles are likely to have multiple polymorphisms (i.e. sequence differences) that separate them.  Furthermore, two alleles that appear to the same at a phenotypic level may have different sequences.  A good example of this is the ABO blood groups — traditionally we have identified three alleles Iᴬ, Iᴮ, and i, but it turns out that are multiple sequences that correspond to each of those alleles!
For more on this see:
https://en.wikipedia.org/wiki/ABO_blood_group_system#Subgroups

§Note: Sometimes alleles result from epigenetic changes (heritable changes that don't alter the sequence) — these can be referred to as epialleles and appear to be less common than alleles based on sequence polymorphisms."
N/A,Is the rabbit example also an example of epistasis?,"Epistasis occurs when the phenotypes associated with alleles of one gene are affected by what alleles are present for a *different* gene.

How many genes are involved in the rabbit example?

Does this help you to answer your question?"
N/A,"Where multiple alleles exist for a trait, anyone individual will have more than two alleles for that trait?","No, they will only have 2 alleles (unless something is wrong). Multiple alleles just means that more than 2 exist. For example, there are 3 alleles for blood type in existence, but healthy individuals will only inherit 2."
N/A,what is codominance i dont unerstand,codominance is when both parents are both homozygous dominant  and both traits show in the offspring like if a homozygous dominant yellow flower and a homozygous dominant red flower made a new flower the flower would have both red and yellow petals
Non-Mendelian inheritance review,"If codominance is possible, are corecessive traits possible as well?","Good question, there seems to be a lot of discussion about this. The answer is no, there's nothing called co-recessive. In reality, being dominant or recessive is _relative_. An allele may be recessive to one allele but dominant to another. Which means if one particular locus can hold three alleles, say K k1 and k2, where K is dominant to both k1 and k2. Suppose a person has alleles k1 and k2, they can show co-dominance, incomplete dominance or complete dominance. It depends on the extent of dominance against each other. As this person only has k1 and k2, we are comparing which one is more dominant, rather that comparing them against K."
Non-Mendelian inheritance review,"Will recessive traits eventually disappear from the population, or at least become less common?","I think it would depend on whether or not the recessive traits jeopardized an organism's safety. For example, if a recessive trait for a rabbit was bright white fur compared to a muted brown, and the rabbit's habitat was in a jungle or swamp, than the rabbit's with the recessive traits would be easier to target by predators, and therefore the recessive trait would be less likely to be passed on through each generation. The recessive trait would be very hard to get out of a large population compared to a smaller one, and it depends on if the recessive trait effects the animal's ability to adapt and avoid danger. For this reason, most recessive traits in humans will not eventually disappear, because even though the recessive trait is harder to pass down; there are so many humans (around 7.8 billion) that humans with common recessive traits will never be fully extinct. And since humans are the ultimate (apex) predator, people with common recessive traits face no real danger because of the recessive trait they may have. An only exception is if the recessive trait causes some kind of cancer, or other highly dangerous medical condition. It is possible for recessive traits to become less common, but with the human population growing so much, it is hard to predict the trend that recessive traits will take. However; like I noted before, most animals face a different playing field in their natural habitat than humans. So it is possible that recessive traits would become less common to the point of extinction in smaller animal populations."
Non-Mendelian inheritance review,"In this article, I noticed that certain alleles were expressed with a superscript. When is a superscript used? Is it when there are multiple alleles?","Yes, I believe a subscript is used when there are multiple types of alleles at play. They are to distinguish the types of alleles that are being passed down through a generation."
Non-Mendelian inheritance review,the whole rabbit thing does not make sense to me like what does Cch mean?,Cch stands for a syndrome called Congenital central hypoventilation
502 Bad Gateway,what is difference between geneotype and phenotype,"genotype = genetic code 
phenotype = physical appearance/properties/expression of the gene"
502 Bad Gateway,what does it mean when it says that it "self fertilizes"?,Self fertilizing is when the pollen from one plant is put on the stigma of the same flower or another flower that is growing on the same plant.
502 Bad Gateway,why the ratio  is always roughly 3:1 not exactly?,"It is correct that it won't be exactly half ,because as Alexander said, there would be slight imperfections (nothing is absolute ,I mean).
But , for this pea plant experiment ,I think it would be that tall and short are compound traits ,like they are made up from a combination of small traits."
502 Bad Gateway,"What determines what gamete is chosen to move on? Or is it just random, and each gamete has an equal chance at being passed on to the offspring?","Does garden pea, Pisum sativum has a discontinue character on height, colour...? mostly those characters are continuous, they are controlled by many genes."
502 Bad Gateway,How can we identify that after breeding multiple times we have got a homozygotic offspring and does multiple breeding results in a homozygote  offspring ?,"When 2 parents breed, they each have a genotype, let's say one is AA, the other is aa. Both are purebred and homozygous. In its offspring, they create a new genotype, one letter from each of the parent's genotype. This creates many outcomes, including the heterozygous, Aa."
502 Bad Gateway,"why did he use pea plants, why not any other flower?",because pea was an annual plant and its was a self fertilizing plant and its easy to manually fertilize it
502 Bad Gateway,what is difference between geneotype and phenotype,Genotype is the specific gene alleles where as the phenotype is the physical expression of the alleles.
502 Bad Gateway,How it can be explained if Gregor Mendal studied eight character?,"Who knows, really depends on what 8 character was. What really important is that those traits are not linked (on the same chromosome) and that those traits are comparable (for example tall and short) and easily distinguishable.


All 3 Mendelian Laws would probably stay the same."
502 Bad Gateway,"If a tall plant and a short plant bred together, how would all of the plants end up being tall? Wouldn't 75% become tall and 25% become short based on the 3:1 ratio?","All plants would end up being tall if the parents are homozygous for the traits controlling each character. 75% would be tall if and only if the p generation is heterozygous for the character while 25% would be short, which conforms to the 3:1 ratio."
502 Bad Gateway,What does F1 generation mean? It doesn`t make sense.,"The F stands for filial, which comes from the Latin word _filius_, meaning son.  F1 means the first generation of children (or baby pea plants)."
N/A,"If the extra copy of X chromosome is inactivated by Barr bodies, why does XXX or XXY show an abnormal phenotype? Is the inactivation not perfect (i.e leaky)?","Excellent question. X inactivation happens in XXY males, as well as normal XX females. However, in XXY males, a few genes located in the pseudoautosomal regions of their X chromosomes have corresponding genes on their Y chromosome and are capable of being expressed. This means even though the extra X is deactivated, during recombination in Meiosis 1 there may be exchange of genes between X and Y and would result in expression of these traits."
N/A,"And about that, how will the inactivated X chromosome be when it undergoes meiosis to produce gametes?","@Junsang is right, the compact X chromosome winds open during meiosis undergoes gamete production normally."
N/A,"Given the explanations above, how does Swyer syndrome occur? (a person who is typically raised as female and has female external genitalia but also has a Y chromosome) I noticed this in the 2016 Olympics, as it was hotly debated with track and field.",hmm.. perhaps the Y chromosome is missing an SRY gene? would love to hear from an expert
N/A,"In Turner's syndrome, the individual has 45 chromosomes of the karyotype XO (only one X chromosome), and displays mental retardation and physical abnormalities, among other symptoms,while a zygote with two X chromosomes would develop as a normal female.Why is that? Wouldn't one of the X chromosomes be inactivated anyway?","Great question!

At least one factor that contributes to this is that the X (and Y) chromosomes have what are called pseudoautosomal regions (PARs).

The PARs allow crossing over between the X and Y — this allows for meiotic pairing, crossing over, and disjunction of the X and Y in males.

The PARs are not X-inactivated and so are thought to contribute to the defects associated with sex-chromosome aneuploidy including Turner's syndrome.

For example Turner's syndrome patients are usually short and one PAR gene, _SHOX_, is a transcription factor that promotes skeletal development particularly bone growth in the arms and legs."
N/A,"Can a malfunction happen in which both X chromosomes stay active somehow, and would that be lethal? Could that ever happen?","Good question. From what I've found so far:

The mechanism of inactivation is still not very well understood, but there are some theories.
In mice, there are 2 events of inactivation. It is known that inactivation happens in females and also in males and cases which have an extra X chromosome.
In the fisrt, the event of inactivation fraternal X (Xp) is inactivated, and in the late blastocyst, second inactivation event happens. This time fraternal Xp reactivates and now _random_ inactivation happens.

Meaning that it never catches _both_ X chromosomes.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2630377/

I guess mutations can happen. However, it is _hardly possible_ that in every single cell of the female body both X chromosomes are inactivated. If that happens I suppose it would be lethal and cause severe bodily malfunctions.

If both X chromosomes are inactivated in some cells, that female is a chimera.

Also, bear that:  X chromosome inactivation is not an all-or-none phenomenon. Of the 2000 or so X-linked genes on the X chromosome, about 10% are not inactivated by X inactivation of the chromosome on which they lie. Thus, these genes maintain two actives, transcribed and translated copies in individuals with two X chromosomes.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2885450/

May this photo help:
https://dev.biologists.org/content/develop/139/12/2085/F1.large.jpg?width=800&height=600&carousel=1"
N/A,"It's stated that the extra X chromosome in people with Klinefelter syndrome will be inactivated. Since it's been inactivated, by right, it'd virtually be the same as normal people, isn't it? But why is it people with Klinefelter syndrome still have abnormalities? Thank you.","As stated by Dr. Barry Starr, "the problem comes from the fact that X inactivation is not complete. X inactivation starts at the middle of the chromosome and spreads towards the ends. Apparently it peters out before it makes it all the way. The genes at the ends that are still on lead to Klinefelter's syndrome. In fact, many of the symptoms of Klinefelter's are really those of a feminized male."  Link to the full article: http://genetics.thetech.org/ask/ask141"
N/A,But my question is that some X. Linked dominant disorder like alpart syndrome etc if the defective allele come in heterozygous can cause problems what's about the other normal allele (recessive)??,"Well, normal allele cannot do much in that case since it is _recessive_.

What you ask is, what if X on which dominant allele is, gets inactivated? In that case, it is not heterozygous and the normal allele is only expressed.

But, there is a tricky part. What if during crossing over, dominant allele got onto X which will stay active? In that case, the syndrome will manifest."
N/A,"(Under Sex chromosome aneuploidies topic)
What about Just Y chromosome in male (relative to the non dis-junction of sex chromosome)? Will it result in fetal death as there's no X chromosome at all?","only Y will be spontaneous abortion, at least one X required to be viable. because X has more expressed genes than Y."
N/A,"Is there Y inactivation as well for when the genotypes are mutated into XYY, XYYY, etc.? If so, does it work the same way as X inactivation?",I don't think there is a y inactivation since there are usually just one y chromosome
Pleiotropy and lethal alleles,Are there also genetic disorders that are Y-linked?,Yes there are genetic disorders that are Y-linked. Y-linked genetic disorder means the the disorder of gene of the Y chromosome. As males have only Y chromosomes. Genetic disorders are likely to pass from the father to son.(so all girls....you guys are safe)
Pleiotropy and lethal alleles,"Hi! If the color of the flower correlates to the seed coat and the axil color, then How do we know that gene coding for seed cover nor axil color are pleiotropic? I mean, can't one argue that the gene coding for the axil color is what affects the flower color?","The control of purple color in flowers, axils, and seed covers is all from the same gene – the most noticeable phenotype is the flower color, so that is how people generally talk about the gene.  However, the gene is actually what is known as a transcription factor and is needed for expression of proteins that make a purple pigment (anthocyanin).
https://www.sciencelearn.org.nz/resources/2001-identifying-mendel-s-pea-genes

Naming of genes is actually quite chaotic and sometimes very confusing - for example a gene that does the same thing in different organisms will often have a different name."
Pleiotropy and lethal alleles,Does it means that dominant lethal alleles are more harmful than recessive lethal alleles?,"Yeah, if you have recesive lethal allele, you can live a happy life as long as you are heterozygous (= you have good dominant allele) , but if you have dominant lethal allele, you will die (no matter what other alleles are). Dominant alleles are rare tho, since carriers often die before they can pass it to next generation."
Pleiotropy and lethal alleles,what is achondroplasia?,"Achondroplasia is a genetic disorder with an autosomal dominant pattern of inheritance whose primary feature is dwarfism. In those with the condition, the arms and legs are short, while the torso is typically of normal length. Those affected have an average adult height of 131 centimetres (4 ft 4 in) for males and 123 centimetres (4 ft) for females. Other features can include an enlarged head and prominent forehead. Complications can include sleep apnea or recurrent ear infections. Achondroplasia includes short-limb skeletal dysplasia with severe combined immunodeficiency.

Achondroplasia is caused by a mutation in the fibroblast growth factor receptor 3 (FGFR3) gene that results in its protein being overactive. Achondroplasia results in impaired endochondral bone growth (bone growth within cartilage). The disorder has an autosomal dominant mode of inheritance, meaning only one mutated copy of the gene is required for the condition to occur. About 80% of cases occur in children of parents of average stature and result from a new mutation, which most commonly originates as a spontaneous change during spermatogenesis. The rest are inherited from a parent with the condition. The risk of a new mutation increases with the age of the father. In families with two affected parents, children who inherit both affected genes typically die before birth or in early infancy from breathing difficulties.The condition is generally diagnosed based on the clinical features but may be confirmed by genetic testing.

Treatments may include support groups and growth hormone therapy. Efforts to treat or prevent complications such as obesity, hydrocephalus, obstructive sleep apnea, middle ear infections or spinal stenosis may be required. Achondroplasia is the most common cause of dwarfism and affects about 1 in 27,500 people."
Pleiotropy and lethal alleles,can the alleles that cause sickle cell be seen as lethal alleles in this case.,"Yes, sickle cell is when a mutation happens in red blood cells where the amino acid glutamic acid is misplaced by the amino acid valine. This prevents the hemoglobin to form correctly: form crescent instead of the normal disc-shaped. We know that shape determines function, so without having the correct shape, hemoglobin can no longer function. Homozygous recessive will be lethal. However, in some areas where malaria is common, heterozygous will benefit because it helps resist malaria.
If you want to dive deeper, use this link: https://www.sciencedirect.com/topics/medicine-and-dentistry/heterozygote-advantage"
Pleiotropy and lethal alleles,"Still didn't get the names.
Recessive lethality is when homozygous dominant dies. why is it called recessive then?","It is so called because the lethality caused by that gene is recessive as we can see that a heterozygote survived.
Recessive lethality whether it be a dominant or recessive gene it causes lethality only in homozygous condition."
Pleiotropy and lethal alleles,"What does it mean to breed true, as mentioned in the yellow mice section?",it means it would be homozygous for the yellow allele.
Pleiotropy and lethal alleles,what if the mouse caring both trait of AA will it have a birth defect?,"It will die as an embryo. So technically no, the mouse caring AA will not have a chance to survive to actually carry a birth defect, since, in order to have birth defects, one must be birth first, right? :D"
Introduction to heredity review,"How does the dominant allele mask the recessive one at a molecular level? Does the recessive allele not code for proteins? (If, so how does the cell know which genes to code for and which not to code for?)","There isn't a DNA sequence that tells us why or how the dominant allele masks the recessive allele.  When we say that a gene is "expressed" and "not expressed" we really mean that it is not seen in the organism's phenotype. Recessive alleles apparently are expressed. However, the proteins which result from the expression would technically "not work," meaning that it would not have a direct effect on the organism's phenotype. For example, let's say that there is a allele A that produces some sort of red pigment in, well, I don't know, alligators. The recessive allele to the allele A would be a, which, let's say, produces green pigment. In fact, both of these alleles get expressed. However, a heterozygous alligator with the genotype Aa would be observed to have "red" scales, because the allele A was expressed. The proteins from the recessive allele a did not function as effectively, and thus did not produce green pigment in the alligator's scales.
However, if the alligator had both recessive alleles for green pigment, the scales would, well, be *green*, thus "recessive inheritance." The alleles produced proteins that are functional, which therefore contribute to the scale's color in alligators(The alligator example I used is made up; this is just to show how it works.)
In brief, the recessive allele is expressed, but it does not have effective gene products. This is seen in molecular analysis :)"
Introduction to heredity review,how do you know when to use a lower case letter ?,"An upper case letter is usually used in reference to an allele of a gene that is dominant and the lower case letter is used for an allele of a gene that is recessive. Therefore if a person is homozygous dominant he may have something like BB, a person who is homozygous recessive would have something like bb and a heterozygote would have both dominant and recessive which is Bb."
Introduction to heredity review,Why does the capital letter always have to be the dominate trait?,"It's the other way around, dominant trait is represted with caps"
Introduction to heredity review,Can two parents with dominant characters produce an offspring with a recessive character?,"If their alleles are something like Aa and Bb, then they have a 25% chance of producing offspring with recessive genes (ab). Aa and BB or AA and Bb have two homozygous dominant genes and two heterozygous dominant genes. If it's something like AA and BB, then no."
Introduction to heredity review,Can you destroy the genetic genes in our bodies?,"You can't make them completely disappear. But there's lots of stuff you can do to harm them (if you really want to). You can eat the destroying angel (_amanita bisporigera_), a type of mushroom. You can also undergo radiation poisoning. But I wouldn't recommend either of them. The effects aren't pleasant."
DNA sequencing,"This might be a bit off topic, but I am a chemistry student and I want to get a tattoo of my father DNA. Now I know the human DNA contains too many basepairs to fit as a tattoo. But if a small segment of the sequence is used, how likely is it that that sequence also belongs to a different person?","Technically speaking, you could use the sequence from DNA fingerprinting (the method used to identify a person), but it would be still a lot of material for a tattoo, it's typically thirteen sequences of varying length... I think it would be pretty big tattoo.
Another option would be getting a tattoo of "DNA ladder" (the DNA fingerprinting pattern seen on electrophoresis), this is also unique for a person and DNA related. And add only two or three nice, detailed basepairs next to it."
DNA sequencing,"Why can't the die molecule be attached to a regular nucleotide, and then the entire DNA chain could be read as a single item?","you cannot read the entire dna chain as a single item, even if each base pair were to be dyed since you would be getting the four colours at once due to the small size of the molecule. you use ddntp to stop the synthesis for a strand and get fragments of all possible lengths that move in ascending order of length. this lets you to exactly know which base comes at what point."
DNA sequencing,How do we know the specific primer if we already don’t know the DNA fragment sequence ?,"If we want to amplify a fragment of DNA, but don't know the sequence a technique known as "Ligation-mediated PCR" can be used.  This technique starts by adding (ligating) the primer sequences to the ends of the DNA fragment."
DNA sequencing,"Are there two systems to sequencing?
one with light (laser) and the second with electric field?","In traditional (Sanger) sequencing, both electric fields and lasers are required for slightly different, but interdependent, purposes. The electric field is applied to the DNA in the capillary tube, and it pulls the DNA pieces through in order from shortest to longest. As the pieces pass the laser (moving through because of the electric field), they are excited and detected by the detector.

Some next-generation sequencing does not use lasers at all. Instead, it uses H+ ion fluxes to determine whether bases have been added. I'm not super familiar with this technique, but you can read more in this Wikipedia article: https://en.wikipedia.org/wiki/Ion_semiconductor_sequencing.

Hope one of those answers addresses your question!"
DNA sequencing,in a chromatogram why are the peaks of different heights?,The height of each peak is in proportion to the amount of the particular component present in the sample mixture injected into the chromatograph.
DNA sequencing,Does a 2000bp or a 500bp migrate faster throgh this agarose gell,"In other words, the 500bp would migrate faster."
DNA sequencing,Why do the nucleotides used here have 3 phosphate groups instead of 1?,"It's to provide it with energy. The regular DNA replication also uses 3phosphate groups because by removal of each one of them, it gets enough energy to bind to the previous nucleotide."
The genetic code,"One of the stop codons, UGA, codes for the 21st amino acid, selenocysteine. But how does the tRNA know whether to add selenocysteine (and continue translating) or to stop?","It depends on the overall structure of the mRNA product. If the mRNA product contains a so-called selenocysteine insertion sequence (SECIS) element, that signals for the translation machinery to read the UGA codon to code for a selenocysteine rather than a stop codon. Proteins that have a selenocysteine in their active site must thus also have this SECIS element in their mRNA product, while "normal" proteins that don't require a selenocysteine simply use this UGA as a stop codon.

There are lots of ifs and buts in biology, and few things are ever hard rules. This is one of many examples of how biological context causes different results from what we would expect based on the information provided here and in textbooks."
The genetic code,How do you remember all of this?,"One of the best ways to memorize difficult information and vocabulary words is to make up silly stories about them that are easy to remember! It can be completely unrelated to the subject, as long as it sticks in your head better. 

Example: To remember the difference between translation and transcription.

There is a full-time translator that works in the ribosome department, who is sick of having RNA patients coming in late at night to have themselves translated into amino acids. He is jealous of the 'transcriber' who works in the nucleus-HQ as a scribe, copying the DNA and getting much more money!"
Biotechnology review,How many clones can be made off of a small amount of DNA?,"Infinite, I guess, as when you cloning something, you are copying their DNA. Thus in the end, you will end up of more of that DNA, and you can just keep on making more clones"
Biotechnology review,Is hybridisation an example of recombinant DNA biotechnology ?,"Not really, because recombinant DNA technology is taking DNA from a different organism and inserting it into another species' DNA strand. Hybridization is where you cross-breed two different but similar species."
DNA proofreading and repair,why would cells ever apply non-homologous end joining if there is a cleaner and safer alternative? Do they only do that when there's no undamaged template available?,"In the absense of homologous chromosome (when DNA hasn't undegone replication yet) 
non homologous end joining is done."
DNA proofreading and repair,"Is there potential, during any of the above proofreading methods to "correct" the template DNA rather than the newly-formed strand?","By potential, do you mean that is mistakenly correcting the template strand possible? If so, then yes it is. The mechanism to determine which is the newly-formed and the template strand isn't perfect and relies on methylation and other epigenetic markers. These can fail. If the damage includes these markers, or the damage/defective piece is extensive so as to avoid these markers from being introduced, or if the damage doesn't allow the DNA repair machinery to sense these markers, it is very much possible the correction is faulty. Some repair machineries are anyway strand non-specific, and some are even sequence non-specific (see Non Homologous End Joining, which is the last resort at DNA stability)."
DNA proofreading and repair,Why is thymine in DNA and uracil in RNA?,Thymine is the nucleotide that DNA uses. RNA is not the same thing as DNA so it seems very natural that the two of them would have some differences. Uracil is one of them.
DNA proofreading and repair,"what happen if DNA have uracil instead of uracil ? how can DNA repair it ?
and what are the reasons that DNA contain thymine not uracil","In your question – "what happen if DNA have uracil instead of uracil ?"  — I am assuming your second "uracil" was supposed to be "thymine" ...

I'm not sure what you really want to know — as it says in the article, uracil in DNA is usually recognized as a mistake and removed by the `Base Excision Repair` pathway ...


There are a number of proposed reasons why thymine is used in DNA.

1) Cytosine residues in DNA undergo a spontaneous change that converts them into uracil.  There are enzymes that specifically recognize and remove uracil (but not thymine) from DNA and this helps suppress what would otherwise be a major contributor to the rate mutations.  

2) Thymine is chemically more stable (though slightly more expensive to make), so this again probably helps reduce the mutation rate.

An interesting and detailed discussion of these factors and more can be found here:
http://www.scienceinschool.org/2011/issue18/uracil

If you have further questions please leave a comment."
DNA proofreading and repair,"What occurs in cancerous cells when going through mismatch repair? Is the issue ignored? Or is it because the cancerous cell had gone through mismatch repair, then became cancerous?","In cancer cells, the mismatch repair has not happened. This leads to mutations. This is a classic example: https://en.wikipedia.org/wiki/Xeroderma_pigmentosum Without the nucleotide excision repair system, the individual develops melanoma and/or carcinoma at a very young age. Also recall that skin cancer metastasizes to the lungs, so this is a very bad prognosis indeed."
DNA proofreading and repair,How the proteins involved in DNA repair detect the fault?,"It depends on what is wrong. For example, some damage distorts the shape of the DNA helix, and there are proteins scanning the genome for this. Sometimes damage is detected when an RNA polymerase stalls. In mismatch repair, there are proteins involved that detect the mismatch, and proteins that detect which is the old and which is the newly synthesised DNA strand."
DNA proofreading and repair,Why is thymine in DNA and uracil in RNA?,"Uracil is the cheapest to produce energetically, and is therefore favored at the RNA level where fidelity is not as important and large quantities are produced."
N/A,"What is the difference between:
Replication fork
Replication complex
Replication unit
Origin of replication 
Replication bubble","The replication fork is the branched (forked) DNA at either end of the replication bubble.

The replication complex is the group of proteins that help synthesize the new DNA strands.

A replication unit is any chunk of DNA that is capable of being replicated — e.g. a plasmid with an origin of replication (ORI) is a replication unit.  Alternatively, this can also mean a region of DNA that is replicated together.

An ORI is a DNA sequence at which replication is initiated.  ORIs are recognized by the replication machinery — specifically the pre-replication complex.

A replication bubble is the region of DNA where new strands of DNA have been or are being synthesized.  A replication fork is found at each end of a replication bubble.

You can find more details and (many) of these terms in this free online book chapter:
https://www.ncbi.nlm.nih.gov/books/NBK26826/


This seems like a reasonable source for quick definitions of terms:
http://dictionary.sensagent.com/"
N/A,What does it mean to have a 3' end as opposed to a 5' end?,"5' ends with the phosphate, and 3' ends with the deoxyribose sugar."
N/A,"1-Unwinding the (origin of replication) is done when certain proteins are attached to the site (which is AT rich) , I mean not by Helicase , right?


2-who removers the primers in the lagging strand?
Is it the same DNA pol ?

3-Why does polymerization rate in prokaryotes is faster than in eukaryotes?","1) My understanding is that many proteins are involved in unwinding the origin of replication including at least one helicase.  
Note that helicase is a type of activity, not a single protein — for examples and more details see:
https://en.wikipedia.org/wiki/Helicase

2) The primer is removed by an endonuclease that recognizes RNA:DNA hybrids (RNase H) and then exonucleases that remove the RNA nucleotides.  In _E. coli_ this exonuclease activity is performed by DNA polymerase I.

3) Eukaryotic DNA is generally much longer, more complex (typically multiple linear chromosomes with ends vs. usually circular DNA), and is highly packaged into nucleosomes (and higher order structures).  All of these factors mean that it takes longer to replicate eukaryotic DNA.


References and further reading:
https://www.ncbi.nlm.nih.gov/books/NBK9940/

https://sydney.edu.au/science/molecular_bioscience/PHAR2811/PHARlectures/PHARlecture5/PHARlecture5notes.pdf"
N/A,which enzyme breaks the h bonds?,"As enzymes breaks the hydrogen bonds that hold the double helix together,so the two strands unwind and separate and that enzymes is helicase"
N/A,is there any case in which primer exist in DNA after replication,"Usually, there is not because DNA Polymerase always replaces the RNA nucleotides with the DNA nucleotides. Unless for some reason, the DNA Polymerase fails to function, it may happen but proofreading should catch it. Otherwise, there should not be any errors."
N/A,lagging strand how to memorize it,"leading strand synthesized continually whereas lagging strand is synthesized in fragments(Okazaki fragments)
Memorize it this way: Lagging strand lags behind and does his homework(replicating dna) in bursts when he feels like it. Leading strand leads the way and is a good model. lol"
N/A,"I may be understanding this wrong, but when DNA separates, a new strand forms that is identical to the one it separated from. So, wouldn't those double helices of DNA be identical to each other?","When DNA separates to replicate, DNA polymerase (and the other enzymes) attach new bases to each strand, and those new bases are each complementary to the template strand, matching the other original strand that the template strand just broke off from. The end result of this is two completely identical DNA molecules, each having one strand from the original DNA and one strand of new DNA made from surrounding materials, put together by DNA polymerase and other enzymes."
N/A,isnt the leading and lagging strand different because when unzipping the DNA the halfs are pointing in oppisite directions of one another?,yes the leading strand goes towards the replication fork and the lagging strand goes away from the replication fork in okazaki fragments
Discovery of the structure of DNA,What is a codon and how does it relate to a DNA function and structure ?,"A codon is the name for a group of three subsequent nucleotides in RNA. Since RNA is transcribed from DNA, the DNA sequence will determine the sequence of RNA, the codons, and ultimately what amino acids come together to form a protein. If a DNA sequence  (template strand) goes CTTAGG, the corresponding RNA will read GAAUCC. In this sequence there are two codons: GAA followed by UCC, which will code for amino acids."
Discovery of the structure of DNA,"well I have 2 doubts:
1) in the second para under the topic 'right hand helix'  i couldn't understand as to why DNA is a right handed helix
2) in the second para under the topic 'base pairing' how exactly is the bigger size of purines and small size of pyramidines affecting the bond length?","As far as the 2nd question is concerned , it is because the double helix should have a uniform diameter all throughout otherwise there might be problems during the supercoiling . Now if , purine is bonded to purine , both being bigger , would end up in a diameter that would be larger than that formed by the 2 pyrimidines and thus the diameter would be uneven . The fact that A will pair T and G with C was found experimentally ."
Discovery of the structure of DNA,"Am I understanding this correctly? The amount of the total bases in a cell's DNA is always the same in each organism in a species, but the amount of each type of base (A,T,G, and C) in a cell's DNA can vary between organisms in the same species.

And is the double-helix form of DNA its condensed or decondensed form? 

Thanks!","Not exactly.

The amount of each type of base in a cell's DNA is the _same in all cells in the whole organism_. Genetic code is the same, but gene expression is different.

What is different is proprotion of AG to CT for each species and defined as a different number (CHargaff's rule).


The condensed form is *chromosomes*. The double helix is always double helix, regardless of being part of Euchromatin or Heterochromatin.

So, in metaphase, you can only see the condensed form of chromosomes. But you can isolate DNA (extract) by various methods and see t by the naked eye as well.


Hope this helps :D"
Discovery of the structure of DNA,"I want to make sure I have these ideas true! 
It may have nothing to do with the article but I found it relevant.
Starting from zero:
We all have 2 copies of chromosomes; one from the mother and the second from the father.
Each chromosome is formed of DNA and proteins ( basically histamin) .
DNA is a double helix; 2 strands, each one has coding  areas ( which are 2% and maybe less) and non-coding areas . Within the gene itself there are non-coding sequences which their name is “ introns “. 
The non-coding area (outside the gene) of DNA strand has different types of sequences ; satellites and repeated sequencing . 
Is that true for now?","Seems mostly correct.

The one mistake I notice is that I think the word you were looking for was histones (not histamin).  
Chromatin is composed of DNA plus associated proteins and RNAs.  These other molecules organize, fold, protect, and control the DNA. 
A major component of chromatin are nucleosomes — a twist of DNA wrapped around an octamer of histones.

Note that the non-coding DNA between genes is *very* diverse and much of it is composed of many different families of repeated sequences including multiple types of transposons and inserted retroviral genomes."
Discovery of the structure of DNA,Why is adenine a purine base?,"I'm not sure it is the NH2 group which accepts protons most readily to make it a base. I think it could be the nitrogens in the rings, which I think also have lone pairs of electrons that could accept a H+. I think on the other hand the NH2 nitrogens the lone pair electrons are delocaslised so wouldn't make it very basic."
Discovery of the structure of DNA,How can you tell the helix is right handed?,"You can tell if if the helix is right handed or left handed based on the way it twists. Here's a link to an image that shows the difference between a right and a left. Hope this was helpful!  

https://www.google.com/imgres?imgurl=http://1.bp.blogspot.com/-a9mozeRTQ3M/VQ7VbFXcLfI/AAAAAAAAXpc/FLsA3yb63nU/s1600/right%252Bvs%252Bleftt%252Bhanded%252BDNA.jpg&imgrefurl=http://sandwalk.blogspot.com/2015/03/on-handedness-of-dna.html&h=357&w=222&tbnid=4six7X82OnMXYM:&tbnh=160&tbnw=99&usg=__3ts8S2DUkv-GCt810cHksqyLH48=&vet=10ahUKEwjiubHonbbTAhXkzIMKHXmRDe0Q9QEIJTAA..i&docid=bxjwHpzOd_V1PM&sa=X&ved=0ahUKEwjiubHonbbTAhXkzIMKHXmRDe0Q9QEIJTAA"
Discovery of the structure of DNA,What are the four different kinds of nitrogen bases?,"The four nitrogenous bases are as follows: Adenine, Thymine, Guanine, and Cytosine.
Cytosine and Thymine are pyrimidines
Adenine and Guanine are purines. 
Adenine and Thymine are a complementary pair.
Cytosine and Guanine are a complementary pair.
Hope that helps!"
Discovery of the structure of DNA,What is the order of the nitrogenous bases of the DNA if I have to put up a 3d model?,"There isn't a single order — all combinations along a strand are possible.  The only thing that is fixed in DNA is that A pairs with T, and G pairs with C.

The sequence of bases is a very complex code that we are still working to understand.  You can think of DNA as being the instructions for building, operating, and maintaining a cell.  The order of the letters is used to encode how, when, and where proteins and RNAs are made.  This affects every process within that cell and often in neighboring cells as well.

So, for a structural model of DNA the order doesn't actually matter, but if you could pick the sequence associated with something well known like the restriction enzyme _EcoRI_ ...

Does that help?"
Discovery of the structure of DNA,What is the difference between DNA and RNA,"I will answer you the way I have answered this question before with other users. I hope it is adequate.

There are several differences. To start, DNA stands for deoxyribonucleic acid, while RNA stands for ribonucleic acid. These names describe the sugar that makes up their backbone--DNA = deoxyribose and RNA = ribose.

Second, while each has four nucleiotide bases, there is one difference. You probably know that DNA has guanine, cytosine, adenine, and thymine, and that guanine links to cytosine and adenine links to thymine. But RNA doesn't have thymine. Instead, it has uracil, a nucleiotide base with a slightly different chemical makeup. Thymine had the chemical formula C5H6N2O2 and uracil is C4H4N2O2. Uracil links to adenine in RNA just like thymine does in DNA

Finally, DNA is double-stranded and forms a double helix structure. RNA is single-stranded and is generally straight. DNA is a complete set of instructions needed for life (unless you're a virus, but that's a whole different story/debate) and RNA is used to copy DNA and to synthesize proteins. I know this is a lot to take in, but there are several videos and articles on Khan Academy to help. Here are a few.

https://www.khanacademy.org/science/high-school-biology/hs-molecular-genetics/hs-rna-and-protein-synthesis/v/molecular-structure-of-rna

https://www.khanacademy.org/science/high-school-biology/hs-molecular-genetics/hs-rna-and-protein-synthesis/v/rna-transcription-and-translation

https://www.khanacademy.org/science/high-school-biology/hs-molecular-genetics/hs-rna-and-protein-synthesis/a/hs-rna-and-protein-synthesis-review

Anyway, this is probably a lot, but I hope it helps!"
RNA and protein synthesis review,If amino acids are not made during protein synthesis then how and where are they made?,*Amino acid synthesis* is the set of biochemical processes by which the amino acids are produced.
RNA and protein synthesis review,Why is protein synthesis a two-part process,"The two parts consist of transcription and translation.
Transcription is the step where the genetic information from DNA is copied onto mRNA and sent out of the nucleus.

Translation is when the the mRNA ticks to a ribosome and tRNA joins mRNA to form an amino acid chain and eventually a polypeptide"
RNA and protein synthesis review,why do changes in DNA lead to mutations but changes in the RNA code do not lead to mutations?,RNA is dependent on DNA. So a change in DNA results in a change in RNA. Hope this helps!
RNA and protein synthesis review,where does transcription and translation take place?,"In eukaryotic cells, transcription occurs in the nucleus, and translation occurs at the ribosomes in the cytoplasm.

In prokaryotic cells and bacterium, both transcription and translation happen in the cytoplasm, because these types of cells don't have nucleuses. Does this help?"
N/A,Why there are 61 codons? Why not 64??,3 of them are stop-codons which terminates translation (61+3=64).
N/A,what  happens to the mRNA after translation process i.e after proteins are produced?,"Hi Srinidhi,

After mRNA is translated, is either stored for later translation or is degraded. The eventual fate for every mRNA molecule is to be degraded. The process of degrading mRNA molecules happens at a relatively fixed rate.

Hope this helps!

Jonathan Myung"
N/A,"I'm still confused on two things. One, what is a TATA box? ANd two, what are the poly-a tails and 5' caps?",The TATA box tells where a gene begins so that it can be transcribed.  The Poly-A tail is a string of (mostly) adenines on the 3' end of the mRNA that gets eaten away by hydrolytic enzymes.  It is there so that the coding section of the mRNA doesn't get eaten.   (The hydrolytic enzymes themselves are there to protect from viruses.)   It is also recognized by the nuclear pore and allows the mRNA to leave the nucleus.  The 5' cap tells the ribosome where to begin translating.
N/A,What happens if a mRNA breaks? Will part of the protein be produced from the broken piece?,"Yes, most likely. If the context of the mRNA fits with the translational machinery (applicable  for the part of mRNA with the initiation codon only. The part without the initiation codon would not be translated), it might produce a truncated protein where the N-terminal part would be present but the C-terminal part (wrt to the original full length protein) would not be there.  However, most of these truncated proteins are recognized by the cellular repair machinery as abnormal and they are recycled. Sometimes though, such proteins can linger and may even participate in cellular functions (in a positive or detrimental way). Most likely source of truncated proteins is DNA rearrangement though, and mRNA breakage would not likely have a major effect (it might, depending upon the need of the original protein) as there would be other full-length mRNAs that would be translated into the protein of interest. Hope this helps."
N/A,Can a DNA end in 3' and the last molecule in this end is a phosphate? Why not??,"Phosphate is always attached to 5' end, and OH group to 3' end, because of the chemical structure of DNA."
N/A,It is essential that we need RNApolymerase for transcription. But to synthesize this enzyme we need transcription to happen .  So either RNApolymerase has to be present from the start or there should be another mechanism by which polymerisation of RNA happen. So how is it done for the First Time ??   How is it possible ?,"Some proteins and other molecules come from the previous cell, so the new cell can start its own production. Another thing is that some RNA can act as an enzyme and catalyzes reactions, though it occurs much less often."
N/A,Why do the number of A's on the poly-A tail vary?,"Each time a mRNA is read, an ''A'' of the poly-A tail is cut off, when there's no more ''A'' in the tail, the mRNA can be degraded. A mRNA (let's call it mRNA 1) can have more ''A'' in its tail than another mRNA (mRNA 2) depending on how much the cell needs that product  (1 instead of product 2)."
N/A,"It is mentioned in The Genetic Code, that,
One codon is a "start" codon that indicates where to start translation. The start codon specifies the amino acid methionine, so *most* polypeptides begin with this amino acid.

AUG codes for methionine, which contains sulfur. In the Hershey-Chase experiment, they made use of the fact that all proteins contain sulfur (because of the presence of methionine, I guess)
Are there proteins which do not begin with methionine?","There are, but this is (usually) due to removal or modification of the amino-terminal (start) methionine.  For example enzymes called "methionine amino-peptidases" cut off this amino acid from the beginning of some proteins — this is an example of what is known as a "post-translational modification".

It is also quite common for the first part of a protein (including the starting methionine) to be removed during processing — an example is secreted proteins that have their signal sequences removed during secretion or membrane insertion. 

Methionines can also be oxidized to form chemically related residues."
N/A,Why is amino acid sequence not directly read from a template DNA strand? Why do we need an intermediary mRNA ?,"This is an interesting question to think about, but "why" questions in biology are often very difficult to answer in a meaningful way.  

Below I've listed one possible evolutionary reason for the use of mRNA as an intermediary and then some advantages to this system.


One strongly supported hypothesis is that RNA actually came first — this known as the "RNA world hypothesis"§.  

This means that we use RNA because "life" has always used RNA and getting rid of it by evolutionary processes would be essentially impossible.  (You'd have to redesign life from scratch!)


Making mRNA also allows efficient production of proteins from a single gene.  

This is because many mRNAs can be transcribed from a gene and then each mRNA can be translated independently (and multiple times).


There are also multiple levels of regulation that can control how much mRNA is present, what parts of the mRNA get kept‡, and how frequently the mRNAs get translated.  

This allows cells to be much more responsive to changing conditions.


In addition, in eukaryotes DNA is kept in the nucleus, while translation happens on ribosomes (found in the cytoplasm).  

Having an RNA intermediate allows the information in DNA to travel from the nucleus to the cytoplasm.


There are probably more advantages that I haven't thought of — I encourage you to keep thinking about your question as you learn more about how cells work!


Does that help?



§Note: For more information see:
https://en.wikipedia.org/wiki/RNA_world


‡Note: For example alternative splicing in eukaryotes — to learn more see:
https://www.khanacademy.org/science/biology/gene-expression-central-dogma/transcription-of-dna-into-rna/a/eukaryotic-pre-mrna-processing"
N/A,What happens in a mutation where the Stop Codon is removed/altered? What does the cell do then? does it perform apoptosis?,"There are repair mechanisms. That one is called *Non stop Decay* that mechanism is able to detect mRNA which cannot be degraded because there is no STOP codon. It has to detach mRNA from the ribosome so it can translate the next mRNA sequence.

Nonstop decay is the mechanism of identifying and disposing aberrant transcripts that lack in-frame stop codons. It is hypothesized that these transcripts are identified during translation when the ribosome arrives at the 3′ end of the mRNA and stalls. Presumably the ribosome stalling recruits additional cofactors, Ski7 and the exosome complex. The exosome degrades the transcript using either one of is ribonucleolytic activities and the ribosome and the peptide are both released. Additional precautionary measures by the nonstop decay pathway may include translational repression of the nonstop transcript after translation, and proteolysis of the released peptide by the proteasome.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3638749/"
Evolution and natural selection review,What is the difference between natural and artificial selection,"The difference between the two is that natural selection happens naturally, but selective breeding only occurs when humans intervene. For this reason, selective breeding is sometimes called artificial selection."
Evolution and natural selection review,"Hi, I'm not sure whether I'm correct or not.
This page gives the meaning of natural selection as an *"Evolutionary mechanism in which individuals that are better suited to their environment survive and reproduce most successfully".*

So in this case, doesn't it mean that natural selection doesn't have to lead to evolution. For example, people (in a population) living in a harsh condition should exercise to be stronger in order to fit the environment. However, their strength can not be inherited (their offsprings don't descend from them).

Therefore, in my opinion, the definition of natural selection and evolution should involve genetic matters. Otherwise, it is not reasonable to say that natural selection is the cause of evolution.","For your specific case, natural selection can still be genetic. Yes, you can't always pass down behaviors. However, there still are genes that influence muscle function and how easy it is to exercise. For instance, ALS, the disease that rendered Stephen Hawking unable to move much of his body, is hypothesized to be partially genetic. Plus, there are genes that influence muscle strength, and "strongman" genes do exist. Even if behaviors will not be passed down, those with  genes that promote muscle strength will survive and would be more likely to pass them down. They will build more strength faster, and will thus be more fit. There are so many genes in just a single organism alone, and only now are scientists discovering what all of them do. Thus, for a characteristic, it is likely that it may be genetically inherited (what degree the gene influences the characteristic, though, is still up for debate).

However, you are somewhat correct on your statement regarding natural selection being the cause of evolution: it is not the sole cause of it. There is also genetic drift and random mutations, which do not relate to the survival of the fittest.

Does this help?"
Evolution and natural selection review,Is evolution why humans are the apex predators in every enviorment or is it that we have the most advanced brain?,"yeah, and we have more function because of hands and like thinking we arent the strongest creature by far but we innovate,"
Evolution and natural selection review,How does natural variation affect evolution?,"Natural variation in a species affects evolution because when there is only one type of variation of a species, natural selection would be more difficult. If there was no natural variation, and some of the organisms survive and reproduce, since they have the same characteristics and no different variation in DNA the offspring would have the same characteristics as the parents.

So, in order for a species to evolve, only those that are stronger and better than the others can survive.
In conclusion, natural variation affects evolution because the more variation there is in a species, the more results in future generations. Sometimes, it does not matter though. Even if an organism had the same DNA as another, the better one (the one who gets the food, survives from predators, and gets enough necessities) will pass its "strength" to their offspring."
Evolution and natural selection review,What is the difference between evolution and adaptation?,"Evolution evolves a population and usually happens on accident rather than on purpose, however, adaptation adapts members of a species to sudden changes in their environment."
Phylogenetic trees,"Can a phylogenetic tree show which organism is more evolved, if they evolved at the same nod?","Look at (or make) a tree showing your family going back at least to your grandparents.

First question: What does this tell you about people in your family?

Phylogenetic trees are really very similar, but for species rather than individuals within a family.

Second question: What do you mean by "more evolved"?

Does this help?"
Phylogenetic trees,how to represent an extinct specie in a tree diagram,Ending a line before present day shows that a species is extinct
Phylogenetic trees,What phylogenetic trees can and can’t tell us,"One example that comes to mind is that a phylogenetic tree determines where two organisms diverged from their common ancestors but not specifically when. These diagrams are not chronological in a direct way, more so a before and after situation. (Hope I helped, correct me if I am wrong)"
Phylogenetic trees,how did a common whale evolve from a common ancestor?,"I'm not sure what you mean by a "common whale".

The following has information on whale evolution:
https://evolution.berkeley.edu/evolibrary/article/evograms_03

If that doesn't help, can you please clarify your question?"
Phylogenetic trees,how does phylogenetic classification related to phenetic  classification?,"Phenetic speciation means classification of species by appearance alone. For example if two frogs look similar they are called a species even if they cannot mate.
Phylogenetic classification does consider appearance and phenotype, but it also goes much further in terms of looking at functionality, and comparison of genomes. Phylogentics explains an organisms evolutionary history. This is a more rigorous system than phenetics."
Phylogenetic trees,What are the characters used to determine the most accurate evolutionary trees?,The most accurate phylogenetic tree will have the fewest nodes. It's something called parsimony which means that the best tree is the simplest.
Phylogenetic trees,Can someone explain to me the process when a new species will emerge on the tree? Thank you,"Speciation is a huge topic and still being researched — I recommend starting with the following material on KhanAcademy:
https://www.khanacademy.org/science/biology/her/tree-of-life/v/allopatric-and-sympatric-speciation
https://www.khanacademy.org/science/biology/her/tree-of-life/a/species-speciation

You can also browse through the KhanAcademy material on evolution to learn more:
https://www.khanacademy.org/tag/evolution"
Phylogenetic trees,"The fact that branches can be rotated and still remain true indicates that branching order (the order in which species are listed) doesn't matter. If that's the case, I don't understand the purpose of polytomy. This article says it's because we don't know the branching order, but why does that matter?","I think you may have misunderstood what branching order means — confusingly it doesn't mean the order of the branches!  

Rotation doesn't change the branching order — it rearranges the order of the branch tips, which we all agree isn't significant.

Branching order is being used to describe the sequence in which species split from each other.

Thus, a polytomy is a way of acknowledging that there is not yet enough information to say which of the species split off from the common ancestor first.

Take the example PQR polytomy — we know that the ancestral population ("PQR") probably first split into one of the following: 
P + "QR"
Q + "PR"
R + "PQ"

And then the second population split again.

This is what the article means by branching order.

Does that help?"
Phylogenetic trees,"In the phylogenetic tree containing A,B,C,D,E, what is the closest relative to E?","E's closest relative is whatever species is at the first node (the first 2 branches that extend from the root, or trunk)"
Phylogenetic trees,How would you draw a phylogenetic tree given simple DNA sequences between species?,"It is a difficult task. What you are asking is phylogenetic reconstruction from genomic sequence analysis. There are some ways to do this. One obvious way is to consider two species closest if they match at more base pairs. But what is difficult is to decide if one arose from the other or if they are at the same level, arising from a different common ancestor. 

All of this is very difficult and many algorithms are available, especially since genomic data itself is large, complex (different kinds of genomic data is available - RNA, DNA, Methylated DNA etc) and also based on what we know of the function of the genes (difference in functional gene is a more significant difference than the difference in non-functional genes).

If you are interested, look up maximum-parsimony methods of phylogenetic tree reconstructions."
Evidence of evolution review,when did whales have hands?,"The 'hand' is the whale's flipper. The image above shows how they are similar in bone structures, but their function is different depending upon the environment."
Evidence of evolution review,why the animals can change?,"Animals have changed over thousands and millions of years and this has been adapted to the environment in which they live. Therefore, many genetic changes and deviations have occurred over the ages with different traits in individuals, whether of the same species or of different kinds, I hope to be able to help you and answer your question :-) ."
Evidence of evolution review,are we descendants of whales,"Humans and whales likely have a common ancestor, but I don't think all mammals just came from whales that went on land because I remember seeing that whales actually evolved from land dwelling wolf-like mammals."
Phylogeny review,"pls, let me know the basic knowledge of the phylogenetic floristic region. And also if there is some tutorial or some example to build the phylogenetic tree with data, I want to learn how to set up these trees from basic to advance. because I don't have too much knowledge about the phylogenetic tree and I have no idea where from the start it. Thanks, I look forward to yours kind response.","Sal drew a line and at the bottom of the line is their common ancestor they are all related to. He started from the least related based on the fact that they have the least number of commonalities with other animals in the group put that at the bottom, then he went up to the next least related and branched that off at another point, he repeated the same thing for the subsequent animals in the group.
You can watch Sal make a phylogenetic tree here: 

https://www.khanacademy.org/science/high-school-biology/hs-evolution/hs-phylogeny/v/understanding-and-building-phylogenetic-trees-or-cladograms

Hope it helps!"
The musculoskeletal system review,"If there are only voluntary and involuntary muscles, then what would your diaphragm be? You don't have to think about it contracting to breathe, but you can also stop yourself from breathing.","I believe that the diaphragm would be a mixture of both involuntary smooth muscles and voluntary skeletal muscles. Because you can exhale and inhale without thinking, that indicates the involuntary portion of the diaphragm. But when you take deep breaths, such as when you're meditating, you're conscious and aware of breathing and therefore voluntarily controlling your breaths, which leads to the skeletal muscle portion. Side note, I don't think there would be any cardiac involuntary muscles as that is just located in the heart. Hope that made sense."
The musculoskeletal system review,what connects the skeletal system to the muscular system?,"muscles are connected to bones thru tendon so the answer can be taken as tendon

[its been 2 yrs but hopefully if others have the same q it might be helpful]"
The musculoskeletal system review,how does the skeletal and muscular system work together to contract and extend?,"The bones of the skeletal system serve to protect the body's organs, support the weight of the body, and give the body shape. The muscles of the muscular system attach to these bones, pulling on them to allow for movement of the body."
The musculoskeletal system review,Is all the muscles discovered in the body?,"I'm fairly certain that they have. _However_ it's also impossible to know. If certain muscles exist in the body that haven't been discovered, then we don't know that they exist in order to determine that they're undiscovered. Idk if that actually makes sense, sorry"
The musculoskeletal system review,how do your lungs work,"The diaphragm, an involuntary muscle, pushes up and down to help the lungs move"
The musculoskeletal system review,"Kinda stupid question, but are the muscles in your butt involuntary or voluntary? The article states that voluntary muscles can be contracted voluntarily and involuntary muscles move on their own autonomously. But your butt muscles don't move at all... is there a special name for them?","The muscles in the glutes are voluntary. Aside from the famous Gluteus Maximus, you also have the Gluteus Minimus, the Gluteus Medius, the Piriformis, the Superior Gemellus, and many more. While you might not notice them, these muscles play a role in moving and rotating the leg at the hip.

Does this help?"
The musculoskeletal system review,How strong are your bones?,it depends on which one. you femur is about three times the strength of concrete but it takes only 25 pounds to break the weakest.
The musculoskeletal system review,"How exactly *does* the brain send messages to the muscles to contract? I tried searching for what connects them, but i can't find out what is it.","Single nerve cells in the spinal cord, called motor neurons, are the only way the brain connects to muscles. When a motor neuron inside the spinal cord fires, an impulse goes out from it to the muscles on a long, very thin extension of that single cell called an axon. When the impulse travels down the axon to the muscle, a chemical is released at its ending. Muscles are made of long fibers connected to each other longways by a ratchet mechanism, the kind of mechanism that allows the two parts of an extension ladder to slide past each other and then lock in a certain position. When the chemical impulse from the motor neuron hits the muscle, it causes to muscle fibers to rachet past each other, overlapping each other more, so that the muscle gets shorter and fatter. When the impulses from the nerves stop, the muscle fibers slide back to their original positions.
Each motor neuron connects to just one muscle, say the bicep on the front of your upper arm that lifts your forearm, or to the triceps, the one on the back that extends your forearm. But when you move, you never think, “I’d like to contract my bicep two inches and relax my tricep two inches” — instead you think, “I’d like to put this cake in my mouth!” How does the brain translate from the general idea to lift something to your mouth to specific commands to muscles? It does it in stages. In the cerebral cortex, the commands in the neurons there represent coordinated movements – like pick up the cake, hit the ball, salute. The cortex then connects to a sort of console in the spinal cord that overlays the motor neurons. This console lays out arm position in space, up-down, left-right. Each desired arm position then is read out as a collection of specific commands to each motor neuron and muscle.

www.ccmr.cornell.edu/faqs/how-does-your-body-move-does-the-brain-send-it-messages/"
"Tissues, organs, & organ systems",Are glial cells part of nervous tissue?,"Yes. Glial cells are the neuron's "helper". They provide neurons with support, insulation, and protection."
"Tissues, organs, & organ systems",Which hormones are made in the brain,"One of the more well-known hormones that are made in the brain is the *Growth Hormone*, which is produced by the pituitary gland. It is a small gland that sits in the sella turcica (‘Turkish saddle’), a bony hollow in the base of the skull, underneath the brain and behind the bridge of the nose.

Apart from the growth hormone, other hormones produced in the brain included follicle stimulating hormone, also known as gonadotrophins. They act on the ovaries or testes to stimulate sex hormone production, and egg and sperm maturity. Apart from that, the brain also produces the prolactin, which stimulates milk production, and the thyroid stimulating hormone, which stimulates the thyroid gland to secrete thyroid hormones -- which are hormones that can affect energy levels, mood, even weight. They can also be factors in depression."
"Tissues, organs, & organ systems","Do you think that increasing the complexity of the organ systems and/or tissues, lead to a better survival of an organism/ species or do you think that would be a disadvantage?","I would say it depends on the organism and how it functions! For example, we are quite complex (organ-wise) and are obviously quite successful animals. But there are also sponges in the oceans (Porifera) that are some of the oldest animals, and they have continued to survive and thrive, with systems that aren't nearly as complex as ours! This was a very good question"
"Tissues, organs, & organ systems",what tissues are in the cardiovascular system?,Arteries have an outer tube of connective tissue for structural support. And smooth muscle tissue makes next layer.  Smooth muscle tissue layer allows to change the diameter of the arteries.
"Tissues, organs, & organ systems",how  does connective tissue repair injured parts of the body?,"Cells of connective tissue work in synergy. 
They provide matrix (as some form of a skeleton) which is 'invaded' with mobile or fixed cells of connective tissue. Also, it's mobility helps. By signaling from other cells they get 'orders' to come closer and work together until they seal wounds and form a *fibrous patch*. 

However, that *fibrous patch* may _reduce_ the lifespan and decrease the quality of the organ (for example after _cardiac arrest_ fibrous tissue starts to form on your heart. You know that the heart is myokard, heart muscle, which has the function of conducting an electrical signal and contracting. In the case of fibrous scar, fibrous tissue cannot conduct electricity or contract. It is _just a physical barrier to open wound but nothing else_.)"
"Tissues, organs, & organ systems",What primary tissue would be heavily involved in coordinating functions of different organs in an organ system?,"Every tissue has its role in an organ!
Epithelial gives protection, skeletal gives support, muscle helps locomotion and neural conducting signals!


If you say primary, it depends which organ system and which organ.

E.g. in the heart you can find cardiac muscle as the most abundant and primary tissue."
"Tissues, organs, & organ systems",Why don't you have anything about the arteries,"They do — arteries are a type of blood vessel (i.e. an element of the cardiovascular system), which is mentioned in this article.

In the future, for questions like this I encourage you to search on the Khan Academy website — for example, doing this for "arteries" would lead you to this material:
https://www.khanacademy.org/search?page_search_query=arteries

For example, you can start to learn more about arteries and the cardiovascular system on Khan Academy — here:
https://www.khanacademy.org/science/health-and-medicine/circulatory-system-diseases/blood-vessel-diseases/v/arteries-vs-veins-what-s-the-difference

Does that help?"
Homeostasis,Can someone explain what is negative feedback?  I didn't understand the concept from the article....,"From what I understood, negative feedbacks is your body's response to keep things normal or stable, whereas positive feedbacks exacerbate certain effects on the body by repeating functions deliberately.  In essence, negative feedbacks preserve your body's original or 'set' condition and positive feedbacks do the opposite and change you body more by constantly pushing certain types of growth or development in the same direction until something has been accomplished. The example they used was a fetus's head constantly putting more and more pressure on the cervix until birth. Since this is very necessary and important, a positive feedback loops is run: the substance that  pushes the fetus' head towards the cervix, oxytocin, is released as a cause of contractions from the uterus, which are themselves a cause of pressure from the fetus' head on the cervix. So the pressure essentially causes contractions in the uterus which stimulate nerve impulses in the brain to release more oxytocin, which further increase the pressure of the fetus' head. Clearly the goal isn't to maintain the fetus' current state but rather push it to the point where it is primed for birth."
Homeostasis,"Is the system that regulates pH, homeostasis?","To be precise, homeostasis is a process/phenomenon not a system.

Homeostasis is actually the process of maintaining a stable internal environment despite changes in the external environment. 

There are mechanisms in organisms that regulate pH and this regulation is an example of homeostasis.  For example, if you have learned about buffers, then it may help to know that essentially all organisms use buffers (and other mechanisms) to maintain control over the pH — for example the different organelles within eukaryotic cells will consistently have different pHs:
http://book.bionumbers.org/what-is-the-ph-of-a-cell/

Does that help?"
Homeostasis,what is pH guys and how does it relate to homeostasis.,"pH is a measure of how acidic or basic a solution is. More specifically, pH=-log[H+], which essentially means that the more positively charged hydrogen ions you have in a volume of solution, the lower the pH is and the more acidic the solution is. You can also check out this video (if you haven’t already seen it): https://www.khanacademy.org/science/high-school-biology/hs-biology-foundations/hs-ph-acids-and-bases/v/introduction-to-ph

pH matters for homeostasis because it’s part of the chemical environment in which biochemical reactions have to take place. For example, enzymes (which help speed up chemical reactions in living things) have ranges of pH where they work best. Because these molecules’ proper functioning is necessary, pH is very important for maintaining homeostasis. 

Hope this helps!"
Homeostasis,what is the control center in temperature homeostasis hot?,The control center for temperature is the hypothalamus.
Homeostasis,How can very low temperatures be fatal?,"Low temperatures would mean that the enzymes would be inactive or they may not be able to catalyse as much. This slows down reactions in the body (lowers metabolism), meaning that you may be deprived of essential things such as energy etc, which can eventually lead to complications such as death."
Homeostasis,How does Blood clot relate to Homeostasis?,"Blood clotting is considered part of the Positive Feedback (PF) Loop. This is defined as an effector that will AMPLIFY the effect of the Negative Feedback (NF) Loop. For instance, when there is a hemorrhage (loss of blood), it will cause a sequential activation of clotting factors. Here, a single clotting factor results in the activation of many more clotting factors. This is also known as a PF cascade. This overall process will give the completion of the NF Loop because blood loss was prevented with the clotting factors, resulting in Homeostasis."
Homeostasis,How can blood vessels dilate result in heat loss？,"This is because the dilation of blood vessels increases their surface area making it easier for the blood to interact and transfer heat with cooler parts of the body, generally the more surface area, the more heat loss."
Homeostasis,can someone please tell me which organ in the body controls homeostasis?,"Homeostasis is mainly controlled by the organs in the central nervous system and the endocrine system (hormones). Organs in the two systems send commands to other organs in other systems to allow them to carry out certain functions. 

Example for the nervous system: You have stepped outside into some snowy weather. It is cold outside, and your body temperature is dropping. The nervous system sends signals to the muscles that tell them to shake. The shaking of the muscles generates heat, keeping you warm.

Example for the endocrine system: Unfortunately, your have not eaten anything for hours. This results in a low blood sugar level. To maintain homeostasis, cells from the pancreas release a hormone known as glucagon, which raises your blood sugar by decreasing the storage of sugar in body cells.

Does this help you?"
Homeostasis,What system controls homeostasis?,"There are *many* different systems that organisms use to maintain homeostasis.  

For example, the processes used for thermoregulation in mammals and birds are very different from the methods used to keep pH relatively constant."
Homeostasis,"I understand how homeostasis happens in our bodies, but why does it occur? Furthermore, why do we need it? Why do we try to control the internal functions of our bodies rather than the external stimuli that cause them? Why are there not more uses of positive feedback loops?","1. It occurs so our body can function.
2. (See number one)
3. It is much easier to control our bodily functions than the weather and climate.
4. What do you mean?"
The circulatory system review,how long does it take to do a full rotation through the full body,"For the blood to circulate throughout the body and back to the heart, it takes about one minute."
The circulatory system review,What kinds of diseases can the circulatory system get?,"Hypertension
Heart Attacks
Strokes
Heart murmurs
There are many more and you can learn about them through this link:

https://www.khanacademy.org/science/health-and-medicine/circulatory-system-diseases 

I hope this helps."
The circulatory system review,blood on the right side vs. blood on the left side of the heart,Blood on the right is deoxygenated (on its way to the lungs through the pulmonary artery) whereas blood on the left is oxygenated (on its way to the rest of the body through the aorta).
The circulatory system review,Why does oxygenated blood go to the heart and deoxygenated blood go away?,"Blood in need of oxygen enters heart called deoxygenated passes from the right atrium to the right ventricle then send it to the lungs through the  pulmonary valve into the pulmonary artery,Fresh blood full of oxygen leaves the lungs and comes back to the heart in the pulmonary veins. This oxygen-rich blood enters the left atrium — the top left chamber of the heart blood passes from left atrium to left ventricle
The left ventricle relaxes and fills up with blood before squeezing and pumping the oxygen-rich blood through the aortic valve into the aorta — the main artery that carries blood to your body. The muscle wall of the left ventricle is very thick because it has to pump blood around the whole body.


in short : 
1/ the oxygenated blood enter the heart to pump through the aortic valve into the aorta to the rest of your body 
2/ the deoxygenated blood need oxygen to get "pump" in the heart so the heart push it to the lungs to "oxygenate"."
The circulatory system review,"If even the de-oxygenated blood isn't blue, why does our face turn blue/purple when we are chocked (in movie)? 
Some people just say it is lacking oxygens","Blood that is well-oxygenated tends to appear bright red because oxygen binds to hemoglobin, changing its molecular structure and causing it to reflect light in a way that appears red. Deoxygenated blood, on the other hand, has a darker, bluish-red appearance due to the different way light interacts with the altered hemoglobin molecule. For the most part, whenever you see a face turning blue or purple is because of a condition called cyanosis. It is caused by a lack of oxygen reaching the body's tissues."
The circulatory system review,how fast is the heart blood flow,"The heart can shoot blood from the heart down to the foot about (on average) 3-4 MPH, or about walking speed."
The circulatory system review,What is a heart attack and what does it have to do with the circulatory system?,"If oxygenated blood doesn't reach the heart due to blocks or clots in arteries, then the muscle cells of the heart weaken which leads to what we call the heart attack. Since it is in the circulatory system where the blockage takes place, it is linked to the causes for a heart attack."
The circulatory system review,"If deoxygenated blood is not blue, than why do my science books show that? Is it just their artificial color so that you can see them, like they do for x-rays?","They mostly just picture deoxygenated blood as blue to make it easier to tell from the stuff that's oxygenated. If you can see veins (carrying deoxygenated blood) under your skin they _look_ blue, though that's an illusion, but it's probably partially why they chose blue."
Intro to viruses,Can viruses be considered a separate kingdom from the main five kingdoms of living  organisms?,"No, because they are not living things. Good question, though."
Intro to viruses,Will science/medicine ever find a way to make us immune to every virus and bacteria?,"Another aspect is that we are constantly running into new viruses. Why? Viruses can be divided into two groups: one group of viruses spreads only between humans, and the other group mainly spreads between animals and may spread to humans. Drastic population increase and worldwide drought led to widespread deforestation, in order to acquire more farming land and wood. Naturally, many animals lost their habitats and were forced to move into lands where humans lived. Viruses that were originally spread only between these animals were able to spread to humans as well. So if the status quo continues, humanity is going to come across much more diverse viruses than ever before. It can be assumed that it won't be easy to find a cure for all these new viruses."
Intro to viruses,How did Viruses develop in the first place? Did they just evolve or something......,"This is an excellent question and is the subject of current scientific research!

Short answer — we don't know and the answer may be different for different viruses.

For a longer (more satisfying) answer I recommend this:
https://www.nature.com/scitable/topicpage/the-origins-of-viruses-14398218"
Intro to viruses,"If a surface, e.g., a table, is  contaminated with a virus, e.g., COVID 19, is the virus unit attached to some carrier unit such as inside a water vapor droplet or attached to dust, etc. or is it a separate chemical unit free to be moved about like a stone laying on the ground that can be kicked around?","I think "chemical unit" is the wrong phrase to use here. A simple stone or pebble at a microscopic scale can be compared to a rough mountain range on earth. At that scale, it's basically the same as any other similar surface. A small pebble or a giant boulder is the same at that level.

On all surfaces, there are a lot of places for germs to hang out, but it depends on the germ and the surface whether you can actually find anything there.

Usually, the answer is both. 
Viruses can most definitely stick around, even on smooth, dry surfaces for hours or even days, and water vapor and dust are great examples of where to find pathogens.

But again, it depends on the surface and the virus."
Intro to viruses,"Could there be a way to attract viruses to certain areas? Because it was noted in the article that a virus binds to receptors such as proteins.
Is it possible to get the virus out of the host cell without causing harm to the host cell?
Can some host cells be immune to viruses or unaffected by even the worst of viruses?","It would be possible, but not practical. Having free roaming proteins in your body to attract viruses is like having pools of acid in the ocean to digest plastic.
It works, but not particularly well and causes more harm than good.

Also it's worth noting once a virus is inside a cell, its not coming out until thousands of copies of itself are ready to burst out.

And as far as we know, a virus-immune cell isn't quite biologically possible.


Hope this helps"
Intro to viruses,"I know you told us about the life cycle of a virus in the above lesson. But I was wondering about the life cycle of a virus with growth (development) and death. 
Do viruses die? 
Do they grow/develop - along with reproducing?","No, viruses do *not* have that trait of living organisms - growth and development. 

Viruses only reproduce - if they find host (cell).

Do viruses die? No. They just don't reproduce in case they do not find a suitable host (meaning wasted proteins and nucleic acids.

Moreover, prions (just proteins) may cause a ruckus if in human body (thought to lead to Alzheimer disease).


Think of viruses rather as *machinery* not living organism."
Intro to viruses,can a virus be killed by freezing it,No the scientific community is split on whether a virus is alive or not but freezing a sample will actually preserve it. Researchers have found and analyzed ancient samples of viruses taken from glacial deposits. Hope this was helpful. :)
Intro to viruses,How is a viral infection treated?,"Viral infections are hard to treat because viruses live inside your body's cells. They are "protected" from medicines, which usually move through your bloodstream. Antibiotics do not work for viral infections. There are a few antiviral medicines available so far.
Hope this helps!"
Intro to viruses,Why are viruses smaller than their host?,So they can attach to the host as stealthily as possible. Too large of a pathogen could alert the immune system to a threat before the virus even gets anywhere.
Intro to viruses,"If a virus meets a hydrogen peroxide molecule, what happens?","From What I can gather, according to this:https://www.ncbi.nlm.nih.gov/pubmed/203115, Hydrogen peroxide can make viruses inactive."
The reproductive system review,"I have certain doubt regarding female reproductive system
(1) There are two ovaries in female reproductive system and in video lecture sir said there is only one egg is produced in female so which ovary produce egg?
(2) There are two fallopian tubes in which one ferilization occure?
(3)how the sperm  reaches from the vagina to fallopian tube in the female reproductive system diagram it is not clear
kindly help me","1)it depends on the readiness of each ovary to release the egg so when one ovary is still building the egg the other ovary releases the egg 
2)any (depending on what direction sperm cells swim)
3)the sperm enters through the the cervix through the mucus and swims up the uterus till it meets the egg and till it fertilizes"
The reproductive system review,Why is the regulation of the temperature of sperms important?,it is important because if the temperature is above 22degree c it will kill the sperms
The reproductive system review,What gets clipped during a vasectomy?,"The vas deferans (hence VASectomy), which is the tube that takes sperm from the testes to the seminal vesicle and through the prostate gland to the urethra. This prevents any sperm from exiting the body."
The reproductive system review,Fertilization starts at what point,it starts in the fallopian tube where the sperm after ejaculation meets the egg to fertilize
The reproductive system review,what is the ovarian cycle,"ovarian cycle (28 days) is the cyclic changes which take place in the ovary of the fertile female every mounth , under the effect of the hormones of the pitutary gland (FSH and LH) . 
this cycle has 3 phases :
1. follicular phase 
2. ovulation
3. luteal phase"
The reproductive system review,"Is it dangerous if, hypothetically, you ejaculate at the same time as urination? It is confusing since they are sent through two different tubes yet they still come out the same area.","This is from a website GoAskAlice:
"The male body has a system that keeps it from being able to ejaculate and urinate at the same time. During sexual arousal, muscles at the base of the bladder contract in order to close off the passageway from the bladder into the urethra, the tube through which urine and semen leave the body. This makes it impossible for urine to be released during ejaculation.""
The reproductive system review,the sperm enters through the the cervix through the mucus and swims up the uterus till it meets the egg and till it fertilizes,"That's true. After it swims up to the uterus, however, it goes into one of the two fallopian tubes, where it fertilises."
The digestive and excretory systems review,What path does water take to get from the mouth to the kidneys?,"Water is absorbed into the body via the large intestine, at which point it enters the bloodstream. Blood is then filtered through the kidneys."
The digestive and excretory systems review,How do cll affect the kidneys in the long run,"Cancer starts when cells start to grow out of control. Cells in nearly any part of the body can become cancer and can spread to other parts of the body . Chronic lymphocytic leukemia (CLL) is the most common leukemia in adults. It's a type of cancer that starts in cells that become certain white blood cells (called lymphocytes) in the bone marrow. The cancer (leukemia) cells start in the bone marrow but then go into the blood.In CLL, the leukemia cells often build up slowly. Many people don't have any symptoms for at least a few years. But over time, the cells grow and spread to other parts of the body, including the lymph nodes, liver,kidneys, and spleen. i wish it can help"
The digestive and excretory systems review,what causes a person to need dialysis,"The waste component of urine is called Urea.  If your kidneys stop working then that urea will build up and cause your body to stop functioning.  It is toxic if not excreted through the kidneys. Therefore, the person needs dialysis to filter this urea (toxin) out of their body. The machine is doing the function of their kidneys.  Person's can live on dialysis for years if they take care of their body through diet, exercise etc."
The digestive and excretory systems review,will you die if the urter doesn't work,"your ureter is one of the most important things in the urinary system. It is a tube that transports urine from your kidneys to the bladder. If your ureter doesn't work, then you will not be able to pee. There are artificial ureters that can be put in your body if your ureter does not work."
The digestive and excretory systems review,Will you die if you get your two kidneys donated?,"You cannot live without having at least one kidney. 
Here's why....
So as the daughter of a man who worked with dialysis patients (kidney failure patients) your chances of survival without your kidneys is low. You will either need a kidney transplant or you will need dialysis. Dialysis won't prevent you from dying it will just allow you to live a little longer than having no kidneys at all.
Hope you find this answer helpful. :>"
The digestive and excretory systems review,what happens when the mucus secretion in stomach becomes abnormal ?,If there's no mucus in the stomach then an ulcer develops.
The digestive and excretory systems review,So are stomach don't  make urine,"No, your kidneys do. The stomach does extract water from the food though. That water enters the blood and is used by cells, then extracted out of blood along with excess nitrogen in the kidneys.

So it kind of depends on what you mean by "make urine." The energy in urine was created at the big bang. The elements were created in stars and supernovas. The water was mostly extracted in the stomach, and the nitrogen waste was produced in cells all over the body. However, the thing only becomes actual urine in the kidneys, so we say the kidneys make urine."
The digestive and excretory systems review,what is oral cavity,"The oral cavity represents the first part of the digestive tube. Its primary function is to serve as the entrance of the alimentary tract (gastrointestinal tract) and to initiate the digestive process by salivation (through the salivary glands) and propulsion (through peristalsis) of the chewed up food into the pharynx. This is done with aid from the teeth, salivary glands, tongue, and lips. Basically, it's your mouth."
N/A,Where exactly is the glial cell ? And how does it help in protecting.,"Glial cells surround neurons. For example, Schwann cells are wrapped around the axon. They insulate the axon, allowing more efficient transmission of the electrical impulse. I assume that other glial cells can surround the neuron in different places; in the picture of types of neuroglia, the satellite cells appear to be surrounding the surface of the soma (cell body). Hope that helps you!"
N/A,I want to know how the enzyme activated (:,"its a lock and key structure. The substrate which binds with enzyme is key and enzyme is the lock and it has a special site called active site, whats where  the substrate binds to it and activates it. the specific substrate attaches with specific active site."
N/A,What would happen if the nervous system stopped working with the endocrine system?,"I believe if that were the case, then our nervous system will work just fine while the endocrine system will not. We would receive signals thanks to our receptors and the signals would travel via our neurones to reach our brain, but if the nervous system stopped working with the endocrine system, then glands won't be triggered. So the endocrine system is essentially dormant, thus you would only see the effects of your nervous system.
This would be detrimental to the body as hormones help with homeostasis as they help to regulate metabolic rates (TRH, TSH, Thyroxine) and regulate water levels (ADH) etc. Without hormones, our bodies will spiral out of control, resulting in complications such as death"
N/A,what is so important about Testosterone and Estrogen?,"Testosterone is the male sex hormone.It helps in development of male features(facial hair etc.) and the male reproductive system.

Estrogen is  the female sex hormone.It helps in development of feminine features and the female reproductive system."
N/A,What would happen if any of the systems were to not function?,Well since the endocrine is basically a stimulus system   and this is just at the top of my mind. For instance if the thyroid gland stopped producing thyroid hormone it would lead to a gradual gain in weight because this affects your metabolism
N/A,please explain the types of neuroglia briefly,"*Astrocytes* - Wound tightly around blood vessels, and regulate the exchange of substances between brain neurons and capillaries 
*Microglia* - Motile, undergoes phagocytic action, which is that they destroy impaired or foreign cells through specialised immune defence
*Oligodendrocytes* - Their cell bodies insulate a section of the axon, lowers its resistance. (The myelin sheath of the brain)
*Ependymal cells* - Line ventricles, and create, secrete and circulate cerebral spinal fluid to cushion organs"
N/A,"Hi, does anyone know the interrelationship between the nervous and the endocrine systems?
Please help","This might help you:

The endocrine system is linked to the nervous system by effects of the hypothalamus on the pituitary gland, as seen in the adjacent image. 
The pituitary gland is known as the ‘master gland’ because its secretions control the activity of other endocrine glands.  The activity of the pituitary gland is however controlled by the hypothalamus which as well as being an endocrine gland, is also part of the nervous system.
Along with the nervous system, the endocrine system coordinates the body’s functions to maintain homeostasis during rest and exercise.  The nervous and endocrine systems also work together to initiate and control movement, and all the physiological processes movement involves. 
Where the nervous system acts quickly (virtually instantly) delivering messages by nerve impulses, the endocrine system has a slower but longer lasting response which compliments the nervous system.  The endocrine system regulates growth, development and reproduction and augments the body’s capacity for handling physical and psychological stress.


Source:
https://www.iptaustralia.com.au/fitness-articles/endocrine-system/system-overview"
The immune system review,What are the 5 steps of the lytic cycle?,https://www.quora.com/What-is-the-lytic-cycle-What-are-the-steps .. Refer this
The immune system review,list four other barriers of the body,"i. Physical barrier: mechanic shredding/washing off the pathogen; eg. shower
ii. Chemical barrier: skin pH.
iii. Biological barrier: mucus production.
that's all I got."
The immune system review,I don't understand. I thought only living organisms had DNA/RNA. How come virus would be classified as "non-living" yet have DNA/RNA?,"The distinction between living and non-living things is not totally clear. Generally viruses are classified as non-living, even though they have DNA/RNA. They might be able to go either way, but they do not have a cell structure, and cells are supposed to be the basic unit of life."
The immune system review,"does anyone listen to music while they read the articles and if so, what music are you listening to?",city girl/ joakim karud
The immune system review,What disease 🦠 can kill the immune system,aids
The immune system review,what are the major structures of the immune system?,"The immune system is not like other systems (say, the digestive system) structurally, as many of the reactions occurring are at around the cellular level. However, there are quite a few body parts that assist in keeping you healthy.

One system that your body has is the lymphatic system, where its main function is to rid your body of toxins and waste by producing white blood cells, another major part. Other organs, such as the spleen, tonsils, and thymus gland also play a role in the immune system. When looking at it on the cellular level, the thymus and the bone marrow are extremely important, as the bone marrow produces B-cells and the thymus produces T-cells."
The respiratory system review,"Related, are our bodies only using the oxygen? or do they use the other gases as well?",They use the oxygen and other gases like nitrogen to create protein and other vitamins from the air and food we eat.
The respiratory system review,Why right bronchus is wider and shorter than the left one?,"The right lung is larger as it does not need to make space for the heart .the left lung,needs to make space for the heart as the heart is located slightly to the left."
The respiratory system review,What's asthma and how is it caused ?,"*Asthma* is when a person's airways becomes inflamed, narrows and swells, and produces an overabundant amount of mucus. Asthma happens when an irritant or allergen gets into the lungs."
The respiratory system review,What do our bodies do with the 71% nitrogen that we breathe?,"This nitrogen helps in protein synthesis, amino acids that influence growth, hormones, brain functions and the immune system."
The respiratory system review,How dose the lungs look when you have asmath,"Asthma is what is known as an acute obstructive disease. In other words a condition that can come on suddenly and make it difficult to exhale air. The changes you would see if you could see inside the airways during an attack which contribute to this difficulty breathing out include constriction of the smooth muscle in the airway, making it narrower, increase mucus production and swelling in the lining (odema) which all reduce the diameter of the airways. The lungs themselves can become hyper inflated (think of the alveoli as overinflated balloons) as the patient is still breathing in air (often rapidly) but is unable to expel the trapped air passed narrow airways."
The respiratory system review,how is respiration necessary,"Respiration is necessary to live. It is one of the 8 main life processes common to most living beings. Living beings need respiration to get energy from food to convert it for daily activities- movement, growth, chemical reactions, active transport, cell metabolism, nerve impulses etc. 
Respiration: the process of taking in oxygen to breakdown glucose to release the stored chemical energy it contains"
The respiratory system review,Does Brain cells need oxygen?,"What do brain cells do? 
The create nerve impulses. What are nerve impulses?
They are (technically) energy. Where do they get this energy from? 
From respiration. Where does respiration occur? 
In mitochondria. What does mitchondria produce and what does it need?
It produces energy along with water and carbon-dioxide molecules. It needs OXYGEN and glucose to do so.

Fun Fact: Brain cells have lots of mitochondria!"
The respiratory system review,what will happen if the food go down the wrong pipe,"There is a flap-like structure present at the site of forking of the pharynx into larynx and (o)esophagus, known as the epiglottis. This flap prevents the food and water ingested from entering the larynx or trachea. When we try inhaling and swallowing at the same time, such a disturbance of food entering the wrong pipe can occur, which could result in chocking. That is even why it is highly advised not to talk while eating."
The respiratory system review,can People die if the food go down in to the wrong pipe?,"Yes, if food goes down a person’s trachea instead of the esophagus, that person can choke and die because of the lack of oxygen."
The respiratory system review,why it is advisable to not breath through mouth,mouth has no hair and mucous lining like nose . therefore it is not advised to breathe through mouth. As air coming from mouth is not filtered as it is from nose
N/A,At what levels of organization does the body need to maintain homeostasis?,"All. Homeostasis is maintained at all levels of organizations, from organisms to cells. Cells undergo homeostasis by diffusing different ions and molecules to maintain their balance and organisms have multiple systems working together to maintain homeostasis (e.g. vasodilation (cardiovascular system) and sweating (integumentary system) to give off heat, which affects the body as a whole)."
N/A,What are common cause for you body to leave homeostasis and what are way to come back to that state.,"Your body's homeostasis balance can be thrown off as easily as getting too hot from an exercise or drinking too much water. 

Example 1: If you're in hyperthermia (>38C or >100.4), the body will act accordingly to cool itself down and maintain homeostasis. This includes vasodilation and sweating. 

Example 2: If you're *not* dehydrated and you drink multiple glasses of water, your body will filter the excess water out of the body via the kidneys and the urinary system. If the over-intake of water is rapid (i.e. water intoxication), the excess water will enter your cells. Sometimes, the body's reflexes will trigger you into vomiting."
N/A,what does hypocalmcemia mean,Hypocalmcemia is the deficiency of glucose in the bloodstream.
N/A,What are the effects of hypoglycemia?,"Hypoglycemia--Low (hypo-) blood (-emia) sugar (-glyc-, refers to glucose)

Glucose is the main source of energy in the body. If a patient does not get enough, either from diet or an underlying condition like diabetes, they will suffer from a myriad of symptoms. There are physical effects like hunger, tiredness and shakiness, and there are also mental effects like anxiety, confusion, and nervousness. If severe, a patient can become unaware or even die.

Does this help?"
"Population size, density, & dispersal","How can i measure the density of grass? I mean, in grass is hard recognizing an individual of another one.","setting up quadrats up staking out an area with sticks and string or by using a wood,plastic or metal place on the ground"
"Population size, density, & dispersal",What are patterns of distribution and density.,Patterns of distribution are how individuals in a population are distributed in space at a given time
"Population size, density, & dispersal",so whats exactly the diffrence between population density and size ?,"Population size means the total number of organismns in a given area like number of oak trees in a forest. 
Population density means number of organisms living per unit area like number of oak trees in say 1 sq km of the forest."
"Population size, density, & dispersal",I don't unederstand the mark-recapture method,"The Mark-recapture method is a method used by ecologists to estimate populations that are too difficult to count manually. For example, imagine yourself and two others manually trying to count all the people in New York. Impossible, right? 
The mark-recapture method has two parts: marking a group of animals, say deer, and recapturing a group of deer at a later date, say three months (the two groups of deer have nothing in common except they're captured in the same area and I assume are the same species). For an example with numbers, say we marked 20 deer and released them into the wild, then three months later we return to the same area and capture 50 deer, 5 of them marked. Since 1/10 or 10% of the deer were marked, we can assume that 10% of the deer are the deer we marked previously, or 20 deer. We then multiply 20 by 10 (to get 100%), and so we have an estimate of 200 deer.
This method is fallible though, as deer might be voluntary  captured to receive food (example)which would result in a underestimate, or that the marked deer might be more shrewd the next time the experimenters come along and escape quicker than the rest, resulting in an overestimate."
Ecological relationships review,What does a community ecologist examine?,Study of the interactions between species in communities on many spatial and temporal scales.
Ecological relationships review,what is it called if you only eat bacteria or fungi?,"Fungivore is an organism that consumes fungi. (fungivory or mycophagy) 
Bacterivore is an organism (usually microscopic organism) that consumes bacteria. (bactivory)"
Ecological relationships review,what is the primary source of energy used by producers during photosynthesis?,The sun?
Ecological relationships review,what does a community ecologist helps us learn.?,Helps us learn about the interactions between species on scales.
Biogeochemical cycles review,What is ecological niche,ecological niche and niche are the same things. There are 2 very important terms concerning ecology - habitat and niche. Niche is defined as the natural area where an organism lives AND interacts with. The thing that differentiates niche from habitat is that organisms interact with the environment rather than just livin' in it.
Biogeochemical cycles review,I thought all living species can only breath oxygen not a little of nitrogen.,"We can breath Nitrogen, we just can't use it in our body."
Biogeochemical cycles review,is carbon dioxide drinkable,"No. Carbon dioxide is gaseous at room temperature, so liquid carbon dioxide would be freezing and poisonous."
Biogeochemical cycles review,"What is the most important "sphere"? As in like atmosphere, geosphere, etc.","earth's environment includes atmosphere, hydrosphere, lithosphere and biosphere. individual spheres have their unique essentiality and each sphere linked to one another. so, every sphere is equally important in general aspect."
Ecological interactions,Would overfishing affect other ecosystems than that of the fish themselves?,"Probably. Ecosystems are connected. While scientists do break the world down to study it in smaller pieces because we can't comprehend the ecosystem of the whole world at one time, the whole world is one big ecosystem. Some parts of it are more directly connected to others, and some parts are less directly connected. If something catastrophic happened in one ecosystem, it would affect other ecosystems. But also remember that the bigger the network, the less any one species affects it. Because there are so many species in the world, the world is a HUGE ecosystem. The affect would be somewhat absorbed by the vastness of the ecosystem. However, if the extinction of one species (such as fish) has a large impact on one ecosystem, it's impact on surrounding ecosystems might be noticed. When you look at the world as a whole, it's not the extinction of any one species that is very, very dangerous but the extinction of many species. If enough species (like the fish) died in "separate" ecosystems, eventually the ecosystem of the whole would be affected."
Ecological interactions,can someone give an example of parasitism in which the human being is not the definitive host?,"Of course yes. The protozoan of the genus plasmodium, which is the etiological agent that causes malaria in humans, has as its definitive host the anopheles mosquito within which it reproduces."
Ecological interactions,what does an ecosystem means,An *ecosystem* means *all the biotic factors* (organisms/living things) + *all abiotic factors* (nonliving factors) *interacting in a specific area*. I hope this explains it to you! :)
Ecological interactions,"By reading this article, I understand that there an ecosystem is made up of consumers, producers, etc. But what types of interactions happen or don't happen in an ecosystem when an organism is eliminated? What impact would this have on the interactions within an ecosystem?","When you say 'eliminated' it depends on what you mean by that.

If you artificially remove one individual o even species you create ruckus in an ecosystem and the system is crashing down.

While when an individual dies (this is not elimination until all matter is removed by detritivores) it acts as a source of food."
Ecological interactions,"If we took more than what we need from an ecosystem, would that upset the balance of nature? Or would everything stay the same?","It would upset it because since you are taking away, whatever needed that doesn't have enough now."
Ecological interactions,Would speciation reduce intraspecific competition?,"In one sense yes because then the two organisms would not even be the same species anymore! However, this would likely increase interspecies competition as even after speciation the organism may still compete for the same resources and occupy a particular niche."
Ecological interactions,"In an ecosystem, material is constantly doing what from one location to another","In an ecosystem, *matter and energy are constantly being transferred* from one location to another. For more info, watch this video: https://www.khanacademy.org/science/biology/ecology/intro-to-ecosystems/v/flow-of-energy-and-matter-through-ecosystems. I hope you find this useful! :)"
Population ecology review,"How isn't population growing when people are having babies and, what is a negative growth rate","Human populations are growing as long as the death rate doesn't surpass the birth rate. In case it does, we're speaking of a *negative growth rate*.

Hope this helps!"
Population ecology review,If people have babies shouldn't the population increase .?,it is increasing and the only way it would stop is if the death rate surpassed the birth rate
Population ecology review,How might a population capacity change in an environment; what's an example?,"If a population is at capacity due to predators, and then some of those predators die due to a virus. The population then doesn’t have as many predators holding it back and the population is able to increase."
Population ecology review,Did  ever find a solution to what happened in Australia?,I heard about a time when Napoleon was hunting and was swarmed by so many bunnies he had to retreat. Haha!
Community structure,"Is it possible for there to be more than one keystone species in an area, as well as foundation species?","Yes, there can be more than one keystones species and foundation species in an area. The densities will be similar for the species but one species can have reduced biomass than the other."
Community structure,Explain why we would expect low species diversity when disturbance/predation occur with a high frequency.,If a lot of the spices are being eaten by predators and disturbances are stopping the species from surviving and reproducing then the species will die off and it will lead to low diversity
Community structure,"Can you explain how, for example, an area with only 7 types of species and a total 27 individuals has greater biodiversity than an area with 10 different species and a total 48 individuals?","Because in the first case there is a smaller number of individuals.

7/27 = 0.25
10/48 = 0.20

Biodiversity is greater in the first case."
Community structure,How does climate shape a biological community?,"Climate is one of the abiotic factors that can introduce variation. According to the videos on niches and competition, no two species can coexist indefinitely if they use the same survival strategy. For example, both wolves and foxes may hunt rabbits, but wolves can run faster so they will eventually outcompete the foxes, driving them to extinction and reducing overall biodiversity. With temperature variation, the foxes' strategy might actually prove better in some years. For example, foxes might have better vision and find it easier to spot rabbits against snow, so they would do better in years with more snow, while wolves will do better in years with less snow. The constant change of climate allows both species to find a niche in otherwise identical conditions and therefore coexist. 

Another example would be tree populations - taller trees grow better because they get more sunlight, so if a single tree was to grow much taller than all the others and grow in an umbrella shape, blocking out sunlight and killing all the trees around it, giving other tress 0 chance of survival. If a tree would be much taller that all other trees, it would be more susceptible to breaking due to wind as it would have to take all the wind resistance by itself. A forest full of trees roughly the same height help each other break wind thus climate (wind intensity or lightning bolts) prevent one tree from pushing out all the others."
Community structure,what are the factors that affect species diversity in an ecosystem,"Several notable factors are listed in the article. I have copied/paraphrased them here.
- Climate of the community's location.
- Geography of the community's location. 
- Heterogeneity (patchiness) of the environment
- Frequency of disturbances, or disruptive events.
- Interactions between organisms
Hope this helps!"
Community structure,what are Dominant species?,"Generally, the predatory species, or species that have a greater amount of members end up being dominant. Hope that helps!"
N/A,Why doesn't the government do anything like reducing oil mines or cutting down trees.,"It's not really that simple. We need trees for coal and oil mines for well, oil. Without coal and oil, we can't create materials like, well, the device you wrote this comment on. We need to find a better alternative because we can't just stop. As long as people will be buying things, trees will be cut down."
N/A,What are the positive human impacts on ecosystems?,There are many positive things happening in ecosystems around the US.  There are many conservation agencies and organizations focused on improving water quality and biodiversity that have shown positive impacts on protecting watersheds and other key conservation targets.  Look at groups like your local Soil and Water Conservation District or The Nature Conservancy in your state to find a few positive examples.
N/A,How many new born animals die each day ?,30 million newborns will die within the first 28 days of life between 2017 and 2030. That's sad Dx
N/A,Is anything even being done about climate change and why is nothing be said.,"So much is being done!
The problem is that the focus is rarely on what is being done to fix climate change problems and is more on the negative. Many people, like you! have tried to put these issues in the spotlight through little things. So, it is incorrect to think that nothing is being said against these problems or is being done. Look into some of the many ways that are today!"
Ecological levels: from individuals to ecosystems,""An individual is one organism and is also one type of organism(species)"

If two species mated and some infertile hybrid was made that could not pass on its genes, would that infertile hybrid technically NOT be an individual because it doesn't belong to a species, being the only member?","Good question! The definition of what a species is--and to some extent, what an individual is--does not have a clear consensus among taxonomists. I will illustrate this with a genetic definition, a biological definition, and an evolutionary definition of species.

Being a genetically distinct species, regardless of fertility or species population, is sometimes enough for taxonomists to classify different organisms as separate species. Take Lonesome George for instance: he was widely considered to be the last individual of the species _Chelonoidis abingdonii_. However, he was still genetically distinct from the other Galápagos tortoises. George would therefore be considered a separate species by genetic standards. The same principle can be used for hybrids, who have a different genetic makeup than their parents (I.E: The mule).

However, some may use different definitions of species to draw the line between different organisms. Some use what is called the Biological Species Concept, which involves the ability to interbreed with other individuals. If two species cannot breed with each other, they are distinct. This definition breaks down with hybrids; with hybrids, you can have two genetically separate species with two different niches be considered the same species because of hybrid production. Applying this concept here, your infertile hybrid would be the same species as its parents.

If you look at the Evolutionary Species Concept, though, you'd be right. This concept is like the Biological Species Concept, but the offspring maintain their characteristics over time. For instance, look at Pakicetus, what is known as the most basal whale. Its remains suggested an aquatic lifestyle, and it also had an inner ear structure found in modern Cetaceans. All of these characteristics remained as the species evolved. Because the hybrid is infertile, it would not be able to maintain its characteristics, meaning that it is not a species under this concept.

I encourage you to explore more of these species concepts, as this question does not have a clear answer. Depending on your definition, the answer would be a yes or a no.

Did this help?"
Ecological levels: from individuals to ecosystems,How are niches related to these levels in ecology?,"Niche is the *role* an organism has in an ecosystem. For more info, click https://www.khanacademy.org/science/biology/ecology/community-ecosystem-ecology/v/niche-bozeman (video) or https://www.khanacademy.org/science/biology/ecology/community-ecosystem-ecology/a/niches-competition (article). I think the study of niche should be in *community*, because it is the *role* it has that impacts other populations. I hope you find this helpful! :)"
Ecological levels: from individuals to ecosystems,Can an ecosystem consist of two communities,"Yes, an Ecosystem can have two communities."
Ecological levels: from individuals to ecosystems,What are some of the "many definitions" of species?,A biological species is a group of organisms that can reproduce with one another in nature and produce fertile offsprings.
Ecological levels: from individuals to ecosystems,What would happen if there were no ecosystems/ if all the ecosystems died? Is there a theory for what would happen to all the living things?,Probably the whole Biosphere and Life would collapse. But I do not see shortly :D
Ecological levels: from individuals to ecosystems,"Could a community of animals slowly start collapsing on its self. For example they start to eat each other slowly, slowly eating there population away until they no longer exist. Basically eating each other to extinction.",Every population that experiences a spike eventually exhausts their food source and collapses. They don't usually resort to canibalism but it does happen sometimes. This usually causes a chain reaction across the food web that can increase and decrease other organisms in the community.
Ecological levels: from individuals to ecosystems,why is population bigger than ecosystem,It does not make sense. The ecosystem is a category above the population of individual species. An ecosystem comprises of many populations...
Ecological levels: from individuals to ecosystems,"In the second paragraph, individual and species are the same thing or different? Kinda need more information","Individuals and Species are different.. Look at it this way - 
Definition of Individual - A single organism, of a specific species. 
Definition of Population - All of that particular species in a given area.
So, species in this example,  is just an additional way to specify the  ecological levels. 
Hope that helps!"
Ecological levels: from individuals to ecosystems,Can an ecosystem consist of two communities?,"Yes, an Ecosystem can consist of two communities. :D"
N/A,What is a climax community?,"Community which has reached a steady state after ecological succession" the terms are on the top of the page.
N/A,Are invasive species danger for a habitat?,"Yes and no, because they might help soil and vegetation but, they might kill off species."
Trophic levels review,Does that mean that the decomposers dont have a trophic level?,Because death occurs at all trophic levels decomposers work on all trophic levels.
Trophic levels review,What level would humans be classified in on a trophic level,"Depending on what. If a human eats a lettuce, he is considered a primary consumer. If a human eats a cow, it's considered a secondary consumer."
Trophic levels review,At which trophic level would you expect to find only 10% of the energy that was initially stored in the food chain?,"You would find 10% of the mass at the next trophic level up. For example, 10% of a primary producer's biomass is transferred to the primary consumer, and 10% of that primary consumer's biomass is transferred to the secondary consumer and so on. That means that the secondary consumer contains 1% of the initial primary producer's biomass."
Introduction to ecology review,"Would climate change be considered an abiotic or biotic factor? I can see the point of view for it being biotic, but isn't it abiotic because human air pollution?","abiotic. its concerning the environment.
If its easier think about the links to abiotic and biotic factors with the environment/ecosystem:)
which fits in which? and the differences between the two:)"
Introduction to ecology review,how can abiotic factors affect the ecosystems?,"A rock in the enviroment could be home to an insect or two. Water is not considered biotic, yet there are loads of species that live in it. There are many ways abiotic factors affect the enviroment."
Introduction to ecology review,So is a tree biotic or abiotic? Thank you :),"a tree is biotic
anything living is biotic anything nonliving is abiotic"
Introduction to ecology review,Would climate change be considered an abiotic or biotic factor?,"Ecologists know that changes in abiotic conditions, in biotic interactions, and in direct human impacts can all impact populations. However, some of these changes may be more impactful than others.

Hope this helps! 
:D"
Introduction to ecology review,"Are dead organisms abiotic or biotic?? I feel like it'd be abiotic because it's non living, but it was once living","biotic, living or once living"
N/A,Why is it that only 10% is transferred and not more?,"The consumer doesn't consume all of the producer, the producer uses some of the energy, some of the energy is put off in poop, and some of the energy escapes as heat."
N/A,"In the energy flow diagram with numbers about the Silver Springs ecosystem, the tertiary consumers end up with only 21 kcal/m^2/yr, which seems like only 21 kcal flow through their trophic level every year. This seems utterly unreasonable as the article mentions snakes and large fish among that level, and I don't think they could all survive on 21 kcal/ yr, let alone one of them. 
Am I looking at these numbers the wrong way?
Thanks in advance.","Never mind, it's about the rates, not the solid amounts."
N/A,Why does only a certain percentage of the energy get transferred but not all of it ?,Because nature is not perfectly efficient and that would probably take more energy than would be gained.
Food chains & food webs,how does decomposition work in a dessert.,"In the desert, the dead thing just rots away or is eaten by a scavenger (most the time)."
Food chains & food webs,why are their a food web and a food chain in life,"In short, because without them life would not, could not, exist. Each level of consumer needs a lower level of consumer or a producer to get them energy it needs to live. The only way there could not be a food chain, is if we were all autotrophs. However, if this were to occur, there would be such a large build up, it seems, of waste from the natural death of organisms that living organisms would eventually become extinct. 
The world is made perfectly to run itself, so that large changes like the removal of all heterotrophs could be catastrophic. Think what an intelligent mind must created such a perfect utopia that a bunch of atoms could make up the beautiful and stable world which you and I live in today!"
Food chains & food webs,I noticed that the producers were referred to as Primary Producers. Are there such thing as secondary consumers?,"Yes, there is because they come right after the primary consumers."
Food chains & food webs,Then what are the onivores what is their part,they can be found everywhere in the food web they just eat different things.
Flow of energy and cycling of matter in ecosystems,Where would we be on the food chain and web,"The very very top because we, the humans of this world, kill everything"
Flow of energy and cycling of matter in ecosystems,"tertiary consumers count as vultures (vultures are decomposers) therefore, decomposers are tertiary consumers",Some tertiary consumers are decomposers.
Flow of energy and cycling of matter in ecosystems,I still don't understand this food web so can somebody hear explain it to me,so the food web consists of producers which are plants like grass which then get eaten by primary consumers like a mouse then there is a heterotrophic animal such as a snake that eats the mouse and the at the top of the food web there is an apex predator that eats the stuff in the food web but doesn't get eaten by anything in the food web such as a hawk. And while the animals are eating each other only roughly 10 percent of the energy goes to the next animal because there is more of that animal in the ecosystem to an example would be the mouse eating the grass the mouse would get about 10 percent of the energy because there is way more grass out in the ecosystem
The carbon cycle,What is carbon fixation,"Carbon Fixation is the process where inorganic forms of Carbon, like CO2, are converted or "fixed" by photosynthetic organisms into organic and biologically accessible molecules"
The carbon cycle,"hey 
Anyone, please answer my question.

THANKYOU",You can take whichever. The NGSS is just the updated version or something like that. I’m taking the NGSS first and then the normal one.
The carbon cycle,"hello everyone
I have recently joined the Khan Academy. I'm confused between HS BIOLOGY AND HS BIOLOGY NGSS. Which one should I take?. Can anyone please help me with that?
THANKYOU","The lessons in NGSS are going to be aligned to certain learning standards that may or may not be used at your school, whereas the other one is going to be more general. Both are certainly useful! I would recommend looking through some of the lessons on each to decide which one aligns more closely with what you are looking for."
The carbon cycle,what's the carbon cycle,see above article and previous video
The carbon cycle,How does carbon form shells?,"when carbon enters the oceans, it becomes carbonate. Calcium carbonate is what shells are made of."
The carbon cycle,whats CO2,"carbon dioxide. 1 carbon atom, and 2 oxygen atoms."
Population growth and carrying capacity,human activity or natural disaster For example if a fire destorys many trees in a forest ecosystem the forest's carryng capacity for tree -nesting birds will decrease,Either. It's not important for this example whether the fire was the result of human activity or natural disaster. All that matters is the end result of the fire destroying many trees.
Population growth and carrying capacity,Can carrying capacity can change,"Yes, carrying capacity can change, usually due to the amount of available resources in the environment. For example, if the environment had a lot of resources, more organisms would be able to survive, opposed to if there were less resources."
Human impacts on ecosystems,Why do we use hard chemicals while knowing they're bad for the environment.,Because the people in charge are old men who don't want to change their ways because this gives them money. Any other questions? /gen
Human impacts on ecosystems,What is the impact of air pollution for human health?,"Air pollution mainly affects the human lungs. Instead of clean oxygen, they get chemicals that clog the lungs and make it harder for the lungs to do their jobs.

Prolonged periods of air pollution may damage the lungs even more, and could cause cancer."
Human impacts on ecosystems,What are negative impacts that humans do to the enviroment,Polution
Ecosystem resilience and change,who are volcanos,""A volcano is an opening in the earth's crust through which lava, volcanic ash, and gases escape. " got it from https://chis.nrcan.gc.ca/volcano-volcan/volcano-volcan-en.php"
Ecosystem resilience and change,what does ecosystem mean,The definition of ecosystem is: a biological community of interacting organisms and their physical environment
Creative thinking in science: exploring biodiversity,what is something that you wouldnt allow to happen,The extinction of animals
Creative thinking in science: human impacts on biodiversity,Through the years will humans be more responsible about the ecosystem and animals and how to keep caring for them and others.,"Some humans may be more responsible, by making electric cars instead of gasoline cars. Or reducing the amount of fossil fuels. But some people don't care and some ways of helping CO2 might make other things harder or worst. We just need to keep solving the problems with small solutions, until we can get everything resolved probably in the next 100 or so years. It already took some people many centuries to realize what's going on, so let it be you who takes the first step to helping the earth by solving the problems with small solutions. The smallest thing can make the greatest difference.
Let me know if this helps!"
Humans and biodiversity,"we need to find a new energy source, one that doesn't destroy the world. electricity won't work because we use fossil fuels to get  it. Anyone have an idea?",We could maybe eventually use solar energy for power if we could develop efficient enough stations for collecting it.
Humans and biodiversity,How about sticking to electric cars instead of the fuel ones?,because of the energy the batteries take to make (also the child labor going into the production) is just as high. batteries don't last long at all and are 100% non recyclable. also there not really that affordable...
Humans and biodiversity,"Is  there such a thing as making a planet out of scratch? because if there is, then why not make one so the Earth will be clean,while the other one will be for trash?","I don't think there is a such thing as making a planet out of scratch. All of the planets we have is what we have, and as been there for many years. But making something to help keep the Earth clean is a very good idea, Violet. If there was a way to send the trash to a "trash planet", then we could solve that problem."
Humans and biodiversity,"if you ever seen those giant garbage piles,why not just send and army of recycling people so they can pick all of the recycable trash?","That would help us keep the environment cleaner by doing that. But not many people want to do that. But if you can get like your neighborhood, friends, or family to help out I bet your plan would work very well! Using small solutions, can help with big things."
Humans and biodiversity,"OOH OOH! I know! how about planting a gajillion trees? trees can take up carbon dioxide,right?",Yep! As long as you make sure to plant a balance of native trees.
Instantaneous velocity and speed from graphs review,How do you you find the Instantaneous velocity speed from graphs review?,"The slope of a given point is the instantaneous velocity. For example if you had a position vs. time graph, then if you were to find the instantaneous velocity of a moment, point P, then the slope of point P is the instantaneous velocity. Was this helpful?"
Instantaneous velocity and speed from graphs review,Can someone tell me why the area under the slope is the displacement?,"Displacement is basically the vector form of distance, and we know distance is speed x time. So displacement is velocity (vector form of speed) x time, which is what’s plotted on the graph. The area under the graph will thus be velocity x time, giving you the displacement."
Instantaneous velocity and speed from graphs review,What does it mean when it says that instantaneous speed is the magnitude of instantaneous velocity?,"It's the quantity without the sign. So if the instantaneous velocity is, for example, -2m/s, the instantaneous speed is 2m/s."
Instantaneous velocity and speed from graphs review,"can any one please explain to me the part, 

At what time does the penguin have the same position as 
t=0s?
 
why we need to calculate the two triangles and cancel them out then find the rest displacement ? can anyone help and thank you guys.","The first triangle has an area of 5 from the line.
The second triangle has an area of -2.5 from the line.
That means you need to find at what point past 3 seconds will remove another 2.5.
The answer is 3.5.
That's because at 3.5 seconds a rectangle from the -2.5 triangle to the end of 3.5 is formed.
It's area is -2.5 because 5 * 0.5 = 2.5, and it's under the line so negative."
Instantaneous velocity and speed from graphs review,"I don't really get the concept of displacement.
What is the easiest way to figure out displacement problems?","say you walk 1 meter right, away from your house, then you walk 1 meter back to your house. you travelled 2 meters, so your distance is 2, but you ended up 0 meters from your house, so your displacement is 0.
If walk 1 meter to the left of your house, your distance is 1 meter and your displacement is either 1 or -1, depending on what you arbitrarily designate as forward (positive) or backward (negative) (the convention is to use right as forwards).
On a graph, a line going forwards is like you walking to the right, and a line going down is like going to the left. if the y is positive, you are to the right of your house, if it is negative, you are at the left of your house."
Instantaneous velocity and speed from graphs review,I dont understand the concept of area found by the displacement on graph,"On a Velocity-Time graph, you can find the displacement of a time interval by finding the area under the curve.  Usually this involves triangles and rectrangles."
Preparing to study physics,"What is Quantum Physics, and what is its difference to Quantum Mechanics?","Quantum Physics can be used synonimically to Quantum Mechanics and even Quantum Theory.

Quantum Physics is theory which try to explain why Classical Mechanics doesn't work in cases for example very small particles or also explains some "more visible" phenomenon like superconducting. There is the series of videos in Khan Academy, so if you are interested you can learn from them a lot :)"
Preparing to study physics,"I don't know if it even makes sense but consider this, if I hit my head against let's say a table with some force and then hit my head against a wall with the same force, it hurts more in the second case. If the reaction force is same for both cases, why dont i get hurt in both cases the same way?",Is it possible that the table moved after hitting it which slightly reduced the impact while the wall did not move at all so the unlucky person got the full brunt of the blow?
Preparing to study physics,"It all sounds very interesting, though I have a question, Since even light can't escape from a black hole, so until it (as in black hole) explodes the light just sits there?","There could be something behind a black hole like an infinite randomness.
Because according to Stephen Hawking universe originates in white holes and ends in black holes.
So the laws of universe may not apply there."
Preparing to study physics,I'm 13 years old i have not studied trigonometry or algebra yet but I have a very open mind and I am very eager to learn about physics.What should I do?,"Study trigonometry and algebra.  The more math you know, the better at physics you will be.  Physics is essentially applied math."
Preparing to study physics,what is physics,"Physics is the study of the different laws of the universe, and how they affect our lives. This facet of science provides the foundation for other sciences, such as chemistry and biology."
Preparing to study physics,"Hi, whats the difference between HS Physics and HS Physics NGSS?","NGSS is a program of newer education. They have more concise lessons, and they have cut out certain information that might not be needed as much. The best way to know if you should use it is (1) what state you are in and (2) what you're using the course for. NGSS has only been implemented in the following states' education: Arkansas, California, Connecticut, Delaware, Hawaii, Illinois, Iowa, Kansas, Kentucky, Maine, Maryland, Michigan, Nevada, New Hampshire, New Jersey, New Mexico, Oregon, Rhode Island, Vermont, and Washington, which is 20 out of the fifty states in the US. If you live in a state not listed (like mine, I live in Texas), then your state does not use it in their curriculum. If you are taking the course on your own and not taking a credit by exam or taking it for your school or university, then you can choose whichever you prefer. If you are taking it for school, then I would recommend using whichever one is used according to your state/country. (I'm not sure if Khan Academy teaches for out of the US or not)"
Preparing to study physics,What is  Pythagorean theorem,"If we have a right triangle whose hypotenuse has a length of C and the other two sides have lengths of A and B, then A^2 + B^2 = C^2."
What are velocity vs. time graphs?,How would you calculate the average speed on a velocity/time graph?,"On a position vs time graph, the average velocity is found by dividing the total displacement by the total time. In other words, (position at final point - position at initial point) / (time at final point - time at initial point)."
What are velocity vs. time graphs?,"In the last graph, to find the area of the area under the graph couldn't we use the formula of a trapezoid?","Yeah, you can use the formula of a trapezoid 
Area of a trapezoid = 1/2 * sum of the parallel sides * the distance between them 
Area of the trapezoid = displacement
= 1/2 * (7 + 3) * 6
=30
thus, the displacement = 30m"
What are velocity vs. time graphs?,"If a curve represents the motion(velocity) of a body, then when the curve slopes downwards, is it just slowing down compared to the previous velocity or is it the fact that it immediately decelerates or else is it the case as if it moves too another direction as indicated by the y-axis?","When (on a Position time-graph), the line (which represents velocity) is sloping downwards, it means that the object is moving in the opposite direction and has nothing to do with acceleration or deceleration.

Acceleration and deceleration can be determined by the slope, if the velocity is decreasing, the it is decelerating and and if the speed is increasing, there is acceleration."
What are velocity vs. time graphs?,Is acceleration both for speed and velocity? Cuz' now I'm getting confused,"When a position vs time graph is concave up, the acceleration is increasing. When a position vs time graph is concave down, the acceleration is decreasing."
What are velocity vs. time graphs?,"Can speed decrease over time, but acceleration increase over time? If yes, how is it possible?",If you had a ball traveling to the right at a speed and then you applied a force impeding that movement that becomes bigger in magnitude. the speed of the object would decrease because of the force acting opposite its direction of motion however the acceleration of the ball would increase because of the increasing force acting upon it. This is how you can achieve the situation you described.
What are velocity vs. time graphs?,So you can only use average velocity to find displacement when the acceleration is constant? Which you could still do on this breaking it up where the acceleration is zero and where its 3/2 per second,"You can always use average velocity to find displacement.
Calculating the average becomes more difficult if acceleration is not constant."
What are velocity vs. time graphs?,"If the triangle is stated to be between t=3s and t=7s, why was t=4 used in the Triangle Formula?","Bcuz you're trying to find the base, the base being 4 (the distance between 3 and 7)."
What are velocity vs. time graphs?,if I have a problem like justin drives west at 20M per S then slows down to stop at a red light  and there is a graph that shows his velocity over time where westword is negative and asks for the acceleration what doesthe diretions have to do with this i mean what ireally want is the slope and if it is constant or not and the velocity on the y axis so there is really no use from knowing thedirections ofhis motion,The direction tells you if his change in velocity is negative or positive.
What are velocity vs. time graphs?,"When distance (r) between two objects is zero i.e they are touching each other, the the G force between them must be
F = g X m1Xm2/r2
   =gXm1Xm2/0 square
    = infinite
That means the force by which they both attract each other is infinite, so they cannot be separated at all. How is this possible?","It's very important to understand that the distance r "between objects" is not the distance between their surfaces, but the *distance between their centers*.  So when a person is standing on the earth, and we want to use that formula to find the force between them, we don't say "r = 0 because they are touching", we say "r = 6400 km, the distance between the the center of the earth and the center of the person"."
What are velocity vs. time graphs?,Is negative acceleration still considered "high acceleration" if the graph is curving downwards steeply?,High acceleration usually refers to a large magnitude of acceleration so it doesn't matter if it is positive or negative.
Freefall review,"An astronaut holds a rock at 100m above the surface of Planet X. The rock is thrown upward with a speed of 15m/s. The rock reaches the ground 10s after it is thrown. The atmosphere of Planet X has a negligible effect on the rock when it is in free fall. 
Based on my calculations, I found that the acceleration due to gravity of the rock when it is on Planet X is -1.5m/s^2. How does the speed of the rock when it reaches the ground vd compare to the speed of the rock when it is thrown upward vu?
____vd > vu____vd = vu____vd < vu","*note: the _ symbol refers to a subscript. So, v_f refers to the final velocity.

Sorry, but I believe the acceleration is -5m/(s^2).
x_f = x_i + v_i(t) + 0.5at^2
0m = 100m + (15m/s)(10s) + 0.5a(10s)^2
-100m = 150m + 50s^2a
-250m = 50(s^2)a
a = -5m/s^2

Now to the answer. The velocity as the rock reaches the ground will be greater than the initial velocity. Just try substituting values to test this out.

v_f = v_i + at
v_f = 15m/s - 5m/s^2(10s)
v_f = 15m/s - 50m/s
v_f = -35m/s
speed_f = |v_f|
speed_f = |-35m/s|
speed_f = 35m/s
Therefore, speed_f > speed_i."
Freefall review,What is the difference between Terminal Velocity and Constant Speed?,"CONSTANT VELOCITY =>If you say that velocity is constant, is just a way to say that the velocity does not change with time...;) 


TERMINAL VELOCITY => When an object which is falling under the influence of gravity which increases with velocity, it will ultimately reach a maximum velocity where the drag force equals the driving force. This final, constant velocity of motion is called a "terminal velocity", a terminology made popular by skydivers..:) 

HOPE U GET IT ;)"
Freefall review,Can an object be in free fall if it is moving upwards?,Yes.
Freefall review,How do you determine whether the acceleration (due to gravity) is positive or negative.,"If you dont mind me answering, we know that acceleration due to gravity is positive or negative when the question we are doing tells us that either upwards is positive or negative. For example if they tell us that upwards is positive that means downwards is negative and acceleration due to gravity is always downwards (in this context of 1d motion ofcourse) So the positive or negative sign is determined by the convention of the question.

I hope that helped. anyone in the forum please correct me if i am wrong.
thx"
Freefall review,"A ball is thrown straight upwards with an initial velocity of 10 meters per second. Acceleration due to gravity is 9.81 meters per second squared downward. Does the ball come to rest in mid-air? If so, why? How many seconds after release does the ball come to rest? How high is the ball above the initial position when it comes to rest?","Yes actually! When you throw a object vertically in the air, there is a brief moment where the ball is stationary. You can find the rest using kinematic equations using -9.81 for a and 10 for v0."
Freefall review,"When we drop an object vertically downward from a certain height, then can we say that its *Initial Velocity* is *Zero*","Yes, when dropping objects we make that assumption that for a brief instant, the object is stationary."
N/A,What would the displacement be when going around a circle?,"Imagine or get two thumbtacks.  Stick thumbtack 1 in while making thumbtack 2 go in a circle starting from thumbtack 1. Stop thumbtack 2 wherever you want in the circle you're creating, and stick it in.  Then tie a string from thumbtack 1 to thumbtack 2. THAT STRING IS YOUR DISPLACEMENT AND THE PATH YOU TRAVELED IS YOUR DISTANCE:
Visit link for example:
https://www.google.com/url?sa=i&source=images&cd=&cad=rja&uact=8&ved=2ahUKEwiN0-HA3drgAhU6JTQIHdnXDhEQjRx6BAgBEAU&url=https%3A%2F%2Fwww.quora.com%2FA-body-is-moving-along-a-circular-path-of-radius-r-What-will-be-the-distance-and-displacement-of-the-body-when-it-completes-half-a-revolution&psig=AOvVaw2ahScm9ik2ti3H8hx2vSLS&ust=1551316231398291"
N/A,"I've worked in the aerospace industry for 40 years. In all that time I've never once come across negative velocity. If I told my colleagues about this concept, they've wouldn't believe it.","My guy, if you are 40 years old and are an engineer, why are you on a khan academy page for high school physics 💀"
N/A,"My question is...when someone reached to his car and then go back to his home because he forgot something, the average speed cannot be 0 because he has walked at least few meters. So, how am I suppose to calculate the average velocity?","Well the average velocity is displacement divided by time, so If Jonny walks to his truck from his house and realizes he forgot his wallet and then goes back to the house where he started over 68 seconds, his average velocity would be zero. The reason for that is because his displacement would be none, displacement is how far the object is from its original position, not the total distance traveled. Hope this helps!"
N/A,"How would you calculate the displacement if for example, an object moved north (vertical) and then east (horizontal)? Im struggling to find the Avg. Velocity for this question: "A truck traveled 400 meters north in 80 seconds, and then it traveled 300 meters east in 70 seconds. The magnitude of the average velocity of the truck was most nearly (answer)." My professor said the answer was 6.6 m/s. But how?","By the way I found the answer was 3.3m/s, where you don't divide 150 seconds by 2. 
http://msgrantsphysics.weebly.com/uploads/2/1/3/3/21339258/ap_physics-1d_linear_motion_exam_review.pdf"
N/A,if they ask us to round of to 2 significant values do we round of the greater or lower digit for ex 3.344 should be rounded off to 3.35 or 3.34,"Rounding 3.344 to two significant digits would be 3.3. (in your example, rounding to 3.34 would be rounding to two decimal places)"
Acceleration review,"How can an object accelerate by changing direction?? Can you explain more clearly "If the speed of an object remains the same but it changes direction, then the object is accelerating"?","Remember, velocity and acceleration are vector quantities, which have both magnitude and direction (+/-). 

For example you are running east with an acceleration rate of k m/s^2. For every second you run, your speed/velocity increases by k. After a period of time, you then turn around 180 degree (we're talking about one dimensional motion) and head west instead. Now even though your speed stays the same, the next second you run, the acceleration is going to be -k as you are heading towards the opposite direction. Hope that helps."
Acceleration review,"What's SI?
Standard Integration?
Super Integer?","It's Systemme Internationale, French word for International System. Hope that helps!"
Acceleration review,"I have difficulty understanding this too.

"People forget that an object can accelerate by changing direction. Velocity and acceleration are vector quantities, so they have both magnitude and direction. If the speed of an object remains the same but it changes direction, then the object is accelerating."

If an object was traveling at a certain velocity and zero acceleration, then switched direction 180 degrees and continued in that direction at the same magnitude of velocity, how does that give acceleration?","when you say same magnitude of velocity, that basically is speed. Instead of 180 degrees, lets say you turn 90 degrees and you continue at the same speed, same idea but easier to explain. 
Initially, before turning, you are going straight at 5 m/s for example. But then you suddenly turn right 90 degrees and continue at 5 m/s. Here speed has remained constant while velocity has changed. 
Velocity takes direction into account as well. So after turning right, as we were initially taking forwards as the direction, velocity is 0. This is because you are not going forwards anymore, you turning left. This results in a change in velocity, hence causing acceleration.
Here is an analogy which may help.
You are in a 100m race, and the track is straight. Let's say you travel 50m in 5 seconds. That is 10m/s. But for some reason, you turn right and run at 10 m/s. But because you are going right, you are not surpassing 50m in the race. You are in the same place as someone standing still at the 50m mark. Therefore your velocity is now 0m/s. The change from 10m/s to 0m/s is acceleration. (deceleration to be more precise)"
Acceleration review,what is the acceleration for the pointer movement on your computer??,"The computer screen cursor has no acceleration nor even movement. The computer checks how you have moved the computer mouse and redraws the cursor in the appropriate location on the screen. This happens so quickly that it gives the appearance that the cursor is moving, though in reality, it is simply appearing in a new location without movement."
Acceleration review,""People sometimes forget that acceleration and velocity aren’t always in the same direction. When velocity and acceleration vectors point in opposite directions, the object is slowing down."

I don't really understand this. Please could someone explain it, possibly with an example?","Sure! Lets say you are in a car and you are traveling east and you encounter a red light. As you brake, your velocity is still eastward but its just getting smaller while your acceleration is westward since that is the direction the net force on you points. Thus, the velocity and acceleration are in opposite directions, causing the object to slow. Hope this helps!"
Acceleration review,How are acceleration and velocity different?,"*Velocity* measures an object's change in position over time. The units for velocity are _meters / seconds_ (meters per second) and therefore give the rate of an object's displacement.

*Acceleration* instead measures the change in an object's velocity. The units for acceleration are _meters / seconds^2_ (meters per second squared). This means that acceleration tells you how much the velocity changes every second. 

For example, an object can have a velocity of *8 m/s*, which means it will travel 8 meters in 1 second. However, if it also has an acceleration of *2 m/s^2*, it will speed up from 8 m/s to 10 m/s in 1 second."
Acceleration review,How would you find instantaneous acceleration without a graph?,"That would require another mean to describe the acceleration; that is, a formula. With that, you could graph the formula, or use calculus."
Motion with constant acceleration review,Is there a trick to memorize these formulas?,"*You only need to memorize the 1st and 2nd formulas*.
The 3rd and 4th can be made from those two by using some algebra. Specifically isolating "a" in the first equation, plugging it into the second, and simplifying gives you the forth equation while doing the same with "t" gives you the third equation."
Motion with constant acceleration review,Do all the kinematic equations apply for constant acceleration only?,Yes because kinematics only requires algebra. To solve problems with changing acceleration you need Calculus( Langrarian mechanics or EOM's)
Motion with constant acceleration review,I dont know how these equations even work. I am so confused and not sure what to do,"First, memorise the formulas
Usually, I’ll memorise an acronym SUVAT where S stands for displacement, U stands for initial velocity, V stands for final velocity, A stands for acceleration and T stands for time taken. 

Thus, I’ll memorise the formula like this:
1. v=u + at
2. s=ut + 1/2at^2
3. v^2=u^2 + 2as

Secondly, practice. 
Tip: try drawing out the scenario to help you better understand the question. 
Tip: before attempting the question, list out the values for the different variables in SUVAT. This will help you identify which variables are presented/not presented in the question so that you can identify which formula to use given the variables, instead of trying to picture the whole scenario inside your mind. Moreover, you should also strive to indicate the direction (e.g. if a car is moving right to left, indicate it so that you would know if the velocity/acceleration/displacement is positive or negative) or (e.g. a stone dropping from the sky, indicate stone, top to bottom (vertical), then you would know if you are dealing with positive or negative vectors. ). 

Third, keep trying even if you don’t manage to get the answer immediately. Practice makes perfect. 

All the best. Hope this helps."
Motion with constant acceleration review,How do I know when to use the quadratic formula for the second kinematic equation?,When trying to calculate time you need to use the quadratic formula (or completing the square) because there is a "t^2" term and a "t" term.
Motion with constant acceleration review,"Do all of the kinematic formulas have initial velocity? All of the other variables are missing from one equation, but it looks like initial velocity is in all of them. If that's the case, how would you solve an equation where initial velocity is the variable that you are not given and not asked to find?","Most of the time, you won't find a situation where you don't know the initial velocity (you normally know it's at least at rest, so 0m/s, or it's initial velocity). If you find that you do need such an equation, you might want to look back on the problem or your work. 
In the off chance you do need it, the equation is x= v*t - 1/2*a*t^2 (shown in here https://www.khanacademy.org/science/physics/one-dimensional-motion/kinematic-formulas/a/what-are-the-kinematic-formulas)."
Motion with constant acceleration review,why do the equations listed here include an x0? This is not shown in the videos.,"The equations here include the term "x0" because that is part of delta x, which is used in some cases to help solve for some kinematic problems, and sometimes we are solving for x final. The reason it might of not been shown in videos is because they didn't need to solve for a "x" value, therefore leaving it out. An example:

v=v0+at

In conclusion, they include "x0" because it is the initial position for x, and is needed to find the final position, and is part of the 5 variables used in kinematic equations."
Distance and displacement review,what is the difference between distance time graphs and position time graphs?,"The gradient of a distance-time graph represents the speed of an object. The velocity of an object is its speed in a particular direction.Note that a motion described as a changing, positive velocity results in a line of changing and positive slope when plotted as a position-time graph."
Distance and displacement review,Can someone Please simplify this I still do not understand,"Distance is the length of the path taken by an object whereas displacement is the simply the distance between where the object started and where it ended up. For example, lets say you drive a car. You drive it 5 miles east and then 3 miles west. The distance travelled is 8 miles, but the displacement is 2 miles because you end up 2 miles from where you started. Hope this helps!"
Distance and displacement review,Δx is a vector quantity. Shouldn't the x have a arrow above it?,"It can have the arrow above it, but if it doesn't have one it is still generally understood to be a vector."
Distance and displacement review,"When solving for direction and displacement on a position-time graph, how do you know when the values for each will have the same absolute value (or in other words, despite the displacement possibly being negative)?",It depends whether or not the direction changes. For the position-time graph you can think of change in direction as crossing the x-axis. If direction does not change then distance and displacement will be the same (distance will not have a sign in front of the value). If the direction does change then the two will vary.
Distance and displacement review,"How can an Armadillo start at 6m at 0s? What is the question actually meaning? Because when i measure an animal running or moving. i pick 0m and 0s to be right where the animal is currently standing. I just dont randomly decide to say that the origin of my graph is, lets say, 6m behind it haha","I'd posit that an armadillo doesn't care where the origin of your graph is - you have a nice field laid out in a grid pattern with 0 as the center of the field, but this armadillo with a devil-may-care attitude and a roguish charm just rolls all up in your field, and moves ONLY in one axis because it's apparently 2D cartoon armadillo ;) You get over your shock at seeing a live action cartoon armadillo and finally start measuring its movement, which is at 0 seconds, and the armadillo does whatever armadillo wants, you're just observing at this point.

... hypothetical fictional animals behave very oddly scientific rather than organic, especially in K-12..."
Distance and displacement review,"am unable to solve distance from the position graph , but i can solve displacement , can you please explain this in simpler and clean manner :)",Finding the distance is not that much harder than finding the displacement. If the line goes up 15m in the first 5 seconds and then down the same 15m in the second 5 seconds the distance is 30m and the displacement is 0. The distance is just the total movement (vertical movement) of the line no matter up or down. Does this help?
Distance and displacement review,"Even if the object might be moving vertically, can I still the one-dimensional number line to figure out the displacement or the distance, because it worked for me on some of the practice problems.","I believe that you could consider the negative numbers to be "down" and the positive numbers to be "up". However, I think you would have to label or caption somewhere near the number line indicating that negatives and positives are up and down. Hope this helped!"
Distance and displacement review,why is eurth born,first think why you born 😏
What is weight?,"Why do we say "I am 70 kilograms" then if weight has units of Newton and mass has units of kg? If i am 70 kg, is my mass 7,14?","The kilogram is not actually a unit of weight, although people use it as such. It is actually a measure of mass, measurable only because we rarely need to have a force of gravity other than Earth's. The Newton is the real measure of weight, although it is used almost never. So 70 kg is your mass, not your weight.
I hope this helps."
What is weight?,"this article says that astronauts in the int'l space station experience weightlessness because they are in a free fall orbit around earth. if it's free fall, then why are they remaining in orbit and not falling to the ground where gravity is pulling it? thanks! :)","It's not contadictory. The object is still falling. Just because it never reaches ground doesn't mean it isn't falling toward that ground.
Essentially, an object in orbit means that object is constantly falling toward another object (an object in orbit around Earth constantly falls toward Earth), but because it is also moving sideways (and not just straight down, imagine throwing a ball how it moves 2 directions: down and in the direction you threw it) then it never actually hits the ground. If you could throw a baseball fast enough, it would circle the earth because the farther the ball goes forward the further down "ground" is since the earth is curved, if you would move in a straight line the ground would eventually recede beneath you. (If you are having trouble seeing this just imagine the horizon and how ships can go 'over' it. It's because the earth curves that the ships will drop below a point where they can be seen.)
That's what makes science and math so great is that it explains why things like this, that initially sound counterintuitive, are actually correct."
What is weight?,"How do we define how much is a kilogram, or a pound, etc?","An excellent question.
This video provides an excellent answer.
https://www.youtube.com/watch?v=ZMByI4s-D-Y"
What is weight?,Whats the point of the 6700 N force of the thrusters and 4300 N of the air resistance have to do with problem 1? Are they just there to confuse us? Thanks for your help!,They're given as additional information to test whether the student understands the concept of weight which remains a constant or gets befuddled by the presence of extra forces.
What is weight?,"In example 1, the thruster force of the airplane as well as the air resistance is given. But why we are not taking them into consideration while solving the problem??","You can calculate the vertical and horizontal components of forces separately. 
The extra numbers are "red herrings" meant to trip up students who have some idea of what to do but not a solid foundation. This sort of tactic is used on tests a lot."
What is weight?,"Normally, even when filling up medical records, how much you weigh is called weight, not mass. But when you step down on a weighing scale, the downward pull of gravity gives you the weight you're seeing in the scale as lbs or kgs which are units of mass, not weight. Are you saying that we've been perceiving weight and mass incorrectly all this time? I mean you explain all these stuff about weight vs. mass to other people and they'd just give you a big "huh?" and might even laugh at you and think you're being ridiculous.","Since the conversion between mass and weight is fairly constant for every day activities they have been used fairly interchangeably. When you are dealing with science you usually have to be more precise about the terms you use because you can be dealing with conditions that are not as simple as you standing on a stationary scale in a doctors office where.  

For pounds it is considered a unit of mass and can be used as force, also referred to as the pound-force, but that causes confusion with formula like F = m * a for example if you have a 1 pound (mass) object accelerated by gravity at 32 ft/s^2 you have a force of 32 pounds (force) but a 1 pound mass produces a 1 pound-force force under standard gravity.  Because of this there is a unit called a slug that is used for mass where a 1 slug mass will accelerate at 1 ft/s^2 when a 1 pound force is applied and using this a 1 slug mass will produce 32 pound-force under standard gravity.  If you don't use slug & pounds you need to modify F = m * a to be something like F = k * m * a where k is a unitless scaling constant equal to 1/32 to adjust the result so that 1 pound mass under standard gravity produces 1 pound-force."
What is weight?,The text says that the Earth still exercises a gravitational force at the height at which the ISS orbits. Would an astronaut who jumps out of the ISS fall down to earth? And do the pods that bring astronauts back from ISS missions need an engine for acceleration?,"yes they wuld fall eventually, but they are travelling in a circular path, very quickly. In fact they need some way to slow them down so they can fall towards the Earth..."
What is weight?,what is the difference bw gravity and gravitational force,"The terms *Gravity* and *Gravitational Force* are mostly used interchangeably, and it is more or less permissible to do so. However, the difference between these two terms is considered prominent in some studies. 

Gravitational Force *describes the attraction force between any two masses*. Gravity specifically *describes the resultant force with which a mass is attracted towards the Earth*.

Gravitational Force means the force of attraction between *any two masses*. Weight is the Gravitational force with which the Earth attracts the masses towards its center.

Gravity is related to the resultant force with which a mass is attracted to Earth. So, this happens *only between Earth and a mass*, unlike gravitational force which occurs between any two masses.

Hope this helps."
What is weight?,"'The astronauts in the International Space Station experience weightlessness not because there is no force of gravity, but since they are in a free fall orbit around the Earth.' What do you mean by ' a free fall orbit' ?","Yes, they are falling all the time toward the earth. Hard to understand till you see an example. Put a dot on a piece of paper and draw a Circle around the dot with a 10 cm radius. Now, put another dote 15 cm directly above from the center dot (it should be 5cm above the surface of the circle). Have your dot go 15 cm to the right and 15 cm down the paper. You should still be 5cm from the circle (same as before) even though your dot fell for 15 cm; that's because it's moving forward in a way that keeps it getting any closer to the surface. If you repeat (15 cm down, plus 15 cm back to to the left now) you should still be 5cm from the middle circle; even though your dot 'fell' toward the circle another 15cm. Once you see it, it makes sense."
What is weight?,What is the difference between Weight and Gravitational Force? My textbook doesn't clarify this.,Weight is the gravitational force from large celestial objects like the earth.  The gravitational force between you and your computer is not considered to be weight.
Newton's third law review,"Did not understand this:  "they do not because they act on different systems. If the swimmer is the system, then F,wall on feet is an external force on this system and the swimmer moves in the direction of F, wall on feet."","The swimmer is pushing on the wall and the wall is pushing on the swimmer. Therefore, the forces are balanced but not acting on the same object so the net force will not be zero and the objects could move depending on their mass"
Newton's third law review,What and how were Neton's laws made?,"The three laws of motion were first compiled by Isaac Newton in his Philosophiæ Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy), first published in 1687. Newton used them to explain and investigate the motion of many physical objects and systems. (Source: http://gravitee.tripod.com/axioms.htm)"
Newton's third law review,"How is it possible to have unbalanced forces given Newton's 3rd law? If I push down on a table and the table breaks, where's the reaction coming from?","There is a reaction. When you push on the table, the table is pushing back on you. The table breaks because it is unable to withstand the force you put on it. The fact that the table breaks is irrelevant to the notion that the table exerts a force back on you.

As for your other question: This is a very common misconception. Think about it, Newton's third law deals with an interaction between two objects. This two objects will both experience a force of equal magnitude. But now if you focus on only one object and ignore the other. You will notice that there is only one force acting on that object. Therefore, it will accelerate. Hope this helps!"
Newton's third law review,Why doesn't the wall move?,"The force acting on the person and the wall might be the same, but remember that a=f/m. The swimmer has little enough mass that the acceleration is still a lot, but the wall is so massive that the acceleration is not noticeable. If the swimmer were to push off a very thin wall with nothing behind it, that wall would probably move too."
Newton's third law review,"Isn’t “the force exerted on an object” and “the force experienced by the object” the same thing? The definition of action-reaction pair in this article says that the former is the action and the latter is the reaction, but I thought the action would be the force exerted _by_ the object.","I think the concept of which force is the action and which is the reaction just depends on the perspective that you view it from. If object X exerts a force on object Y, then Y reacts by exerting a force that is equal in magnitude on object X. But since the forces pretty much act at the same time, you could also say that Y exerts a force and X reacts to it.
I also thought the action was considered to be the force exerted by the object :) , but I guess the distinction between action/reaction doesn't matter too much in most cases."
Newton's third law review,"If Newtons law is true, then wouldn't the water exert a force on the swimmer as well? How is she able to move?","Oooh! Good question! Umm... I would just say that the movement of the swimmers arms and even other actions can override the force of the water. Also, in the image in the overview, it shows how she is starting of with a leading force by pushing against the wall. Therefore, I infered that these could be the reasons."
N/A,"The videos on Newton Second Law of Motion only showed things in their current state; how would you show something moving, for example, accelerating North at 20 Newtons and slowing down by a Southern moving force of 15 Newtons. How would that be shown in an illustration like the ones in the video?","If you wanted to illustrate the object in a free body diagram, you would just draw the forces acting on it, as in the example you gave with 20N north and 15N south (similarly to how the objects were shown in the video). The object's velocity and acceleration are not included as part of a free body diagram, but I usually notate those as arrows on the side for visual convenience."
N/A,Is a light particle/wave at equilibrium: acceleration =zero?,"technically , yes
that's why we regard the speed of light as a constant"
N/A,The videos and this article cover the method for 2 and 3 dimensions but what happens in higher dimensions. Are Newton's laws applicable?,"No. Being that higher dimension's have more things impacting an object, such as time, Newton's equations don't work."
N/A,Hi! I'm wondering why the velocity could be non-zero when the forces are at equilibrium (F_net=0) and when the acceleration is also 0. Shouldn't velocity only be 0 (according to Newton's First Law) because the forces are balanced and acceleration doesn't exist?,"Okay, I'm going to remind you of some things you already know: acceleration can be defined as the change in velocity over time, and if a force is being applied to something it should accelerate unless an equal and opposite force is being applied. (An equal force is being applied in the direction opposite of the original force)
If an object is moving, and there are no forces being applied to is (no friction, gravity, or any work whatsoever) then it is not accelerating, as a force is necessary for acceleration to be observed, and at the same time there are no forces, so F_net=0.
Okay, you say, but what if there are forces?
The same principle- as you know F_net=F_1+F_2+...+F_n, so if I were pushing a box along a plane with friction, applying a force of 10 N, and the friction on the box was 10 N in the opposite direction, we would say that the net force is zero, F_net=0, which means there is _ALSO_ no acceleration, even though the box is moving, which means there is a velocity."
N/A,"hello, please I would like to know when is the acceleration considered to be negative?","When your velocity starts to decrease, for example when a car is coming to a halt just before a traffic light (Retardation)."
N/A,"What are real-life examples of unbalanced forces, and why does unbalanced force not affect speed","An example of unbalanced force could be, a rather unfair game of tugs-of-war, where there are 5 strong people on one side(A), contrasted to a lanky person(B) on the other. In this case, the rope will get pulled towards (A)- which seems intuitively apt as well- and poses a great example of unbalanced forces because the net force on side (A) is more than side (B)- which makes the rope veer towards side (A). 

Unbalanced forces do affect speed- An unbalanced force acting on an object results in the object's motion changing. The object may change its speed (speed up or slow down), or it may change its direction. Friction is a force that resists the motion or the tendency toward motion between two objects in contact with each other."
N/A,how do you know if a number is to be subtracted,"If the force is in the opposite direction, then you subtract it!

Just keep in mind which directions are positive. Then all you need to do is add the forces in the positive direction while subtracting those in the opposite direction. Of course, keep in mind that you can't add or subtract vectors that are perpendicular to each other (i.e. forces in x-direction and y-direction)."
N/A,What is the difference between inertia and equilibrium?,"equilibrium is when there is a net force of zero, so the forces acting upon the object equal zero but the velocity is still constant and non-zero. If velocity were zero then it would be static equilibrium. Inertia is a force that acts as a guidline to objects, it keeps them in uniform motion or rest, what makes this different from equilibrium is that when an object is acted upon by an outside force an object still has inertia because objects always have a resistence to change their motion."
N/A,"I don't understand exactly how an object with constant velocity that isn't at rest has a resultant force of zero, is there always some kind of opposing force? But what if there isn't a force such as friction or air resistance? I'm confused","Acceleration implies force. If we have constant velocity that means that we don't have acceleration. If we don't have an acceleration, that means that there's no force involved. 

In real life, yes. If we only focus on classical mechanics and not the physics behind it that explains more profoundly why it works like that, I can't think of any force that doesn't have an opposing force. Every material has an associate coefficient of friction. If there's no force such as friction or air resistance, objects would experience a constant acceleration, meaning they would be speeding up until reaching the speed of light all the time. Because if we are at a rest (0 velocity) and want to change our velocity we need a force. And that force wouldn't had a counterpart. We would be constantly accelerating, making life pretty difficult. If not, not viable."
Introduction to forces and free body diagrams review,"In the problem with the block of cheese sliding up an incline, I understand Fg, Ff, and Fn, But it seems like there should be a force causing the uphill slide. Even if the block isn't accelerating, it is overcoming the acceleration of mgsinΘ as well as Ff, isn't it? 
It seems like that would require force. Maybe I'm wrong.","The force up the incline might no longer be acting on the cheese. If you look at a thrown ball in mid air your throwing force is no longer acting on it. It is being carried forward by sheer momentum and the only forces acting on it are gravity and air resistance. 

The same is the case with this cheese. Imagine that someone has given it a velocity and then let go (like a curling stone) it will keep moving forward up the incline, but there is no longer any force acting on it to propel it, so given enough time the friction force will make it stop. 

Remember that the diagram we look at is a snapshot at a particular time. There might have been a force in the past that is no longer being applied, with only the movement remaining."
Introduction to forces and free body diagrams review,"Hey!
Here's what I don't understand: in a system, in which there are two objects, and those objects  are stacked (i.e. lie one on top of another) - why would the inferior object's free-body-diagram would include the normal force of the superior object, *pointing down*, rather than the weight of that very same body? Isn't it always the same? Isn't the normal force suppose to point up, counter-reacting the force exerted by the superior body?","The normal force doesn't always have to counteract Force due to gravity or weight. Touch a wall, push, Normal force is exerted on your hand (equal mag.).
It arises due to contact, more specifically cuz of the repulsion of atoms between surfaces(you can't touch anything, it's just you feeling the repulsion)
Hence Normal force along with the weight of the above object is exerted on the inferior object. 
and, in a free-body dia, forces acting ON a body are expressed to keep things simple."
Introduction to forces and free body diagrams review,"If an elevator is accelerating downwards and is coming to a stop, in which direction would the acceleration be pointing?",The acceleration vector would be pointing upwards since its change in velocity is increasing from a negative value towards zero. Negative velocity would be downward in this case.
Introduction to forces and free body diagrams review,"In a pivoted body, the force that should act upon it will be rotational force. How do I draw o free body diagram for such an object?",That is a discussion of toqu
Introduction to forces and free body diagrams review,"If I put a mug on the table right to the wall, so the mug is on the table and in the same time it touches the wall, will there be a normal force between the mug and the wall?","Yes. There will be one normal force between the table and the mug (in the vertical direction), and another normal force between the mug and the wall (in the horizontal direction).

Each physical contact between the mug and another object will produce a normal force."
Introduction to forces and free body diagrams review,can we calculate acceleration of the body by its Free Body Diagram,"yes we can
f vector = m * a vector (now dont tell me what are f,a?? )
so here a = f/m or net force by mass of the system
ok bhai?"
Introduction to forces and free body diagrams review,how do you know the direction of force without arrows?,"Think of it intuitively. For example, if a box is being pushed to the right, then the force is to the right."
Introduction to forces and free body diagrams review,what is projectile motion?,pl reply because i have a big doub in that
Introduction to forces and free body diagrams review,can you eat gravel?,Yeah try it out
Inclined planes review,Is there a video or a question that explains how friction is applied to an object in motion on an incline? Say if you wish to find the force applied to an object being pushed up an incline.,"I believe it would be in the friction unit, the 2nd video isn't specific to incline planes but I think it can be pretty easily aplied"
Inclined planes review,Can a non contact force like mg be ever considered to be a contact force?,"Gravity is a non-contact force that can act on objects within the gravitational field of the exerting body, whereas in the case of contact forces the exerting body has to be in direct contact with the object the force is applied on. So it is a non contact force."
Inclined planes review,is this in radians or degrees,It doesn't matter. Just make sure your calculator is set in degree mode if you're given angles in degrees.
Inclined planes review,why does the perpendicular axis has no acceleration?,"Because the normal force is counteracting the perpendicular component of gravity. If the perpendicular axis had acceleration, the object would either be flying away from the ramp or going into it."
Horizontally launched projectile review,"a plane is travelling with twice the horizontal velocity that is, with a velocity 230 m/s. if all other factors remain the same, determine the time required for the package to hit the ground.","it's going be the same time for the package to hit the ground, but the horizontal displacement is twice as before"
Horizontally launched projectile review,how does increasing/decreasing the height of a horizontal projectile impact the time and horizontal displacement?,"If you increase the initial height of the projectile, it will take longer to fall to the ground, so the impact time will be larger. If the projectile is in the air longer, it will have more time to travel horizontally. So, the horizontal displacement will be larger."
Horizontally launched projectile review,how will this affect the trout population?,It depends on how tough they are.
Friction review,is there a video for calculating the net force on an inclined plane with the components of friction included in the problem?,"Yes, please let us know if there is a video regarding this. It would be very helpful. Thank you!"
Friction review,is it possible for an applied force to have a magnitude less than the magnitude of the kinetic friction?,"No, because in order to move an object, you have to overpower the maximum static friction. And since kinetic friction is always less than the maximum static friction, it would mean that the force can never be less than the kinetic friction"
Friction review,""Suppose two children push horizontally, but in exactly opposite directions, on a third child in a wagon. The first child exerts a force of 75.0 N, the second a force of 90.0 N, friction is 12.0 N, and the mass of the third child plus wagon is 23.0 kg." in this situation since there is two people pushing in opposite direction is there going to also be two frictions in opposite directions and are they both 12n or 6n each?","This kind of problems are tricky. Since there are two forces in opposite directions with friction, which way should the frictional force point? The way I like to think of this kind of thing is to take it in steps. First, find the net force if there was no friction. The frictional force will be in the opposite direction of this net force. From there, it is kind of self-explanatory. Hope this helps!"
Analyzing vectors using trigonometry review,"Two vectors A and B of magnitudes A = 30 units and B = 60 units respectively
are inclined to each other at angle of 60 degrees. Find the resultant vector.","First, draw the vectors on any piece of paper. One way to approach this problem is to draw one vector that has an angle of elevation of 0 degrees, which just means that's parallel to the x-axis, and draw the other vector with an angle of elevation of 60 degrees. Let's assume that vector A is horizontal, and vector B is elevated at an angle of 60 degrees. Just connect both vectors with one vector being elevated 60 degrees above the other. If you were to draw the missing side of the triangle, you would see it's not a right triangle and therefore we can't use our basic SOH CAH TOA identities. Fortunately, we can use our beloved Law of Cosines because we know the length of two of the sides and the angle between them.  I assume you know how to use it and therefore I will not explain it here, however, if this sounds unfamiliar to you, here is the URL link to the playlist of the Law of Sines and the Law of Cosines https://www.khanacademy.org/math/trigonometry/trig-with-general-triangles
Nevertheless, if we were to use the Law of Cosines to solve for the magnitude of the resultant, the answer should be (30)*(3^1/3) or 30 times the square root of 3.
;)"
Analyzing vectors using trigonometry review,Why kicking a ball with 45 degree will travel further horizontally than 60 degree,the horizontal distance is called the range. and R=(u^2sin(2thetha))/g. and since the largest value of sine is 1. and that only happens if thetha is 45.that means 2thetha would be 90 and the sine of 90 gives u one
Analyzing vectors using trigonometry review,how do I know when to use the inverse of tan?,"When you have both sides ( opposite and adjacent) but no angle. 
Normally you’re looking for a side or both given an angle. So you’d write it out as Sin 45 = opposite/3 (opposite/hypothenuse). But when you’re give two sides and looking for and angle you’d write it out — > tan 0= 4/3(opposite/adjacent). To solve that you’d write the inverse of tan (tan-1) 
Which is tan-1(1.33) *divide before using inverse tan or else you’ll get a different answer. 
You know to use the inverse of tan when given two sides and need to find the angle."
Analyzing vectors using trigonometry review,"should I have studied trigonometry before starting this course? Because I didn't, and I'm kind of confused now.",Definitly. Trig is an integral part of this course.
Analyzing vectors using trigonometry review,why θ=tan^−1 ?I didn't catch :c,"Nice question!
First off -1 is not the exponent of tan there. tan is a function, a lot of functions have inverses. tan^-1 denotes the tan inverse function or the _arctan_ function.
E.g. If we have tan(y)=x
Now if we apply the tan inverse function on both sides,
tan^-1(tan(y))=tan^-1(x)     This gives:

y=tan^-1(x)

Hope that helps!
And that is a really good question, and its always nice to ask questions!
If anything was unclear or needs more explaining feel free to ask a follow up!
Cheers!"
Projectile motion graphs review,"why does the horizontal motion not affect the vertical motion? If the object is dropping faster doesn't the horizontal motion decrease because it isn't traveling any further, rather downwards.","For this case, no, because they are assuming there is no air resistance."
Projectile motion graphs review,"Does vertical motion really have a constant acceleration?  plz correct me if i am wrong, but since Acceleration is a vector quantity because it has both magnitude and direction. i.e. When an object has a negative acceleration (it's slowing down), the acceleration occurs in the opposite direction as the movement of the object--> this is the case from start till max height then acceleration will be in the same direction as the movement of the object and becomes positive. so i think we better say vertical motion has a constant "absolute" acceleration or "vertical motion has an acceleration of constant magnitude.  plz correct me if i am wrong","On Earth, we use the constant g = -9.8 m/s^2 to represent the constant acceleration due to gravity that pulls us to Earth's center of mass. Whether you use +g or -g depends on how you define your system; some people like to use +g and switch all their variables around. However, g always represents motion towards the center of Earth. The direction of g depends on how you define the system."
Projectile motion graphs review,What is "projectile motion"? Are there other types of motion?,"Projectile motion is the movement of an object through the air while only considering gravity. Other types of motion get more complicated and can consider, for example, both gravity and air resistance. Hope this helps!"
Projectile motion graphs review,how does the trajectory and velocity vectors actually effect the projectile?,"Trajectory and velocity vectors actually don't affect the projectile, they describe its comportament"
Projectile motion graphs review,I do not understand why does the blue scenario have vertical velocity? he is moving in horizontal direction only!,"No, a drop only has vertical motion. vertical is up and down."
Projectile motion graphs review,Why does the horizontal motion move at a constant velocity? Is this common sense?,"The velocity of an object remains constant until it is acted on by an accelerating force.  Gravity is a vertical force.   So if you say that air resistance is negligible, the horizontal velocity will not change.. At least not until it impacts the ground."
Angled forces review,"This question rose to my mind because of an answer I had to someone else's: If an object is free-falling isn't there technically normal force with all of the air particles, or is the normal force of these air particles considered air resistance?","There is no normal force acting upon an object if it is in the air. Also, there is no air resistance in free fall, the only force acting on the object has to be gravitational force."
Angled forces review,If you are trying to find the acceleration of an object and the force is being applied at an angle do you substitute the total force for f in the a=f.m formuala or only the horizontal force that you find using cosine?,You would only substitute in the horizontal component of the force because the components of the force are independent from each other.
Angled forces review,"I was told to use -9.8 as the force of gravity but these videos say that I should use the opposite of the normal force or the weight.

Also how do I factor in mass when calculating these problems?","-9.8 m/s^2 is not the force of gravity, it is the free fall acceleration due to gravity on Earth. According to Newton's second law, F = ma. Which means that Weight = mass * gravitational acceleration = m * 9.8 m/s^2. Now, you put in the mass of the object in kilograms to get the weight of the object in Newtons. Hope this helps!"
Angled forces review,is a_y the same as F_g?,"Not necessarily. For objects in freefall, the answer is yes, because gravity (F_g) is the only force acting upon the object. However, if there is a vertical or angled force other than gravity acting upon the object, a_y will not equal F_g. 

To visualize this- think of a cup sitting on a table. F_g is acting upon the object, but so is the normal force that the table exerts on the object. Since the normal force (F_n) is equal to F_g, the block has no vertical acceleration, so a_y=0. Hope this helps!"
Angled forces review,"This is too hard for me to understand :c,
is there a simplified answer?","Sure! Think the an angled force as a right triangle, shown above in Figure 2. In trigonometry, you learned these two formulas:

`sinθ = Opposite/Hypotenuse
cosθ = Adjacent/Hypotenuse`

Where Opposite is our vertical upward force, and our Adjacent is our horizontal rightward force.

Looking back at the triangle, we can see the Hypotenuse is our Force variable F, so we can replace Hypotenuse with F.

`sinθ = Opposite/F
cosθ = Adjacent/F`

Multiply both sides of the equation by F to solve for the Opposite or Adjacent:

`Opposite = Fsinθ
Adjacent = Fcosθ`

As you can see, our upwards force has a value of `Fsinθ` and our rightwards force has a value of `Fcosθ`. Now we just have to group the two forces with their respective directions. 

For horizontal forces, since there is no friction, then there is no other horizontal forces, so our horizontal force would just be `Fcosθ`.

For vertical forces, we have the force of gravity and normal force, so we can just add them together with our newly found upwards force.

`Fsinθ + Normal Force + Force of Gravity
Fsinθ + FN + (-Fg)
Fsinθ + FN - Fg`

All Horizontal Forces: `Fcosθ`
All Vertical Forces: `Fsinθ + FN - Fg`"
N/A,Why is this in science?,This is in the AP Physics 1 class. Physics is a type of science.
Projectiles launched at an angle review,Why is 45 degrees the angle at which horizontal displacement is greatest? Wouldn't a horizontal launch have the greatest displacement since the object will be traveling in a straight path?,"45 degrees optimizes the horizontal distance hypothetically. On Earth, this value is closer to 42 degrees. To echo what Prince Grey said, a horizontally launched projectile would be immediately pulled to the ground by gravity. (This assumes you are on a planet with gravity like Earth.)"
Projectiles launched at an angle review,what would be a good equation for solving range(x) if I only have angle that the projectile was launched?,"You would have to create a system of equations:

v0 sin(theta) - 9.8t = 0     (In this equation t is the time to max height).
2(-9.8)t^2 + 2*v0*t sin (theta) = 0 (In this equation t is also the time to max height)

Note: These equations come straight from the kinematic equations and 2*t is only the total time in the air if the projectile lands at the same level from which it is launched. Hope this helps!"
Projectiles launched at an angle review,How do you find the maximum height?,"to find the H max, or the highest height
u^2 sin^2(theta)
_______________
2g"
Projectiles launched at an angle review,_"The only acceleration of a projectile is the downwards acceleration due to gravity"._ Is there no acceleration as the projectile is being launched forward or does that count as velocity?,"When the object is in flight, the only acceleration (while neglecting air resistance) points straight down, this is the force of gravity."
Projectiles launched at an angle review,"in all these cases, is it only if the object was in a väcuum?","Yes, this is assuming that the object is in a vacuum. Otherwise, the force of air friction would impede the projectile's horizontal motion, thus causing it to decelerate. In projectile motion, the horizontal acceleration is 0."
N/A,"When an object is thrown straight up, its velocity decreases, and at its maximum height the velocity reduces to zero and then it falls back down. My question is, exactly how long does the object stays in the air at zero velocity, and does it (time) varies from place to place due to different gravity?","The object will stay at 0 velocity for an infintensimally small time period (it doesn't last long). To visualize this, let's say for example, the object reaches zero velocity 6 seconds when it is thrown. This means that at 5.9999999999999999 seconds, the object still has some velocity. Only at exactly 6 seconds the ball has 0 m/s. At 6.000000000000000000000000001 seconds, the object has velocity (which is really really really close to zero but not exactly zero). This means that only at that small point of time, exactly at 6 seconds (to infinite precision of digits), it will have exactly 0 m/s. 

To answer your other question, the time does vary from place to place due to different gravity. For instance, if you would try this same experiment on the Moon, it would take longer for it to fall back since the acceleration due to gravity is slower. (It would also go higher which would mean more distance).

If you are talking about Earth, there are some places where the acceleration due to gravity is different, but that is only due to abnormal events (Earth's buldge, mountains, etc.)"
Centripetal acceleration review,"This might be silly, but this is one thing that I can't get sorted:
In this unit, the videos taught that anything travelling with uniform speed has a constant acceleration, or change in velocity _because the *direction* is changing_, and that the formula is A(c)=v^2/r.
But if the speed is constant, only direction is changing, why would it have any acceleration magnitude? And what units would it be measured in?","Note that *only* the speed is constant. If we are moving in a circle at a constant _speed_ then our velocity is obviously changing.

So our acceleration is changing, which causes our velocity to change, but even so our speed can remain constant if we apply the force correctly.

Note that there are two accelerations to consider here:
1) Centripetal acceleration.
2) Regular acceleration.

Regular acceleration is what you are thinking of (I believe), and it has the standard units that it always has, aka m/s^2.

Hope this helps!
- Convenient Colleague"
Centripetal acceleration review,What is the difference between centripetal acceleration and angular acceleration?,"Centripetal acceleration points towards the center of a circular path and is due to a centripetal force causing the circular motion. Angular acceleration on the other hand is the change in the angular velocity with respect to time. This describes how an object rotates faster and faster or slower and slower. This is the difference, hope this helps!"
Centripetal forces review,"In the roller coaster example, because more forces are added onto the centrifugal force, that means that the centrifugal force gets larger, correct?","Yes.  Remember that the centripetal force is not a type of force in itself (like forces of gravity, tension, or the normal force), but instead just a name we give to any force causing the object to undergo circular motion."
Power review,"A car weight 2500 N operating at the rate of 130 kW develops a maximum speed of 31 m/s on a level, horizontal road. Assuming that the external force (due to friction and air resistance ) remains constant,What is the car’s maximum speed on an incline of 1 in 20 ( i.e if θ is the angle of the incline with the horizontal, sin θ  = 1/20 ) ?","I can let you know the strategy for solving this problem. 

First you need to find the force applied to the car when it is traveling on a level road. Use the power formula to find this. P=Fv From this formula you can see that using 130000W and 31m/s we can find the force to be 4193N. Since the car was on a level road and traveling at a constant velocity then that means the friction force by air resistance and drag must also be 4193N.

We now move on to the second phase of the problem. The problem said to assume the resistance force is equal. So in this case the resistance force as it travels up the incline is also 4193N. At this point you need to draw a free-body diagram(FBD) of the forces involved acting on the car as it travels up the incline. I can not do that for you here so you will need to do that yourself. After analyzing the FBD you should discover that the Force acting on the car from the ground is
 ```F = 4193 + 2500*sin(_theta_) = 4193 + 2500(1/20) = 4318N```

You now have the force applied to the car by the ground. This is just the third law pair of the force the car applied to the ground. So the car output a force of 4318N on the incline. But you also know the power output of the car to be 130000W. So using the power formula again we can discover the velocity of the car on the incline. 

```v = P/F = 130000W/4318N = *30.1m/s*```

So the maximum speed of the car on the incline is *30.1m/s*. This is only slightly slower than  the original 31m/s on the level road and that is reasonable since the incline is very small, 2.87 degrees."
Power review,How can I create an equation for the time from this formula,"You can create an equation for the time from the power formula by using some algebraic manipulation.

*P = ▲E /▲T*  (Given)

*P · ▲T = ▲E*  (Multiplying by ▲*T* on both sides)

▲*T = P /▲E*  (Dividing by *P* on both sides)

We have now isolated ▲*T* (*time*) so that it can be written in terms of *P* (*power*) and ▲*E* (*energy*)."
Wheel,how can a jack wheel lift a car,"Physically, the center of gravity for a car is right in the middle, but the jack has strong suspenders/ leverage that is can lift a car off the ground, moving the center of gravity not too much, but still sustainable to not break down, so you can lift the car! (Well, maybe only 1 side, but ok)."
Introduction to work review,"Hi! The work = change in energy equation here is confusing me. Is that work energy theorem? Does work equal change in total energy, or only change in kinetic energy? I've also seen something about how work done by the non-conservative forces is change in energy? Are these all correct, and just reiterations of the same principle? What is the relationship between them? It's different everywhere I look and one source never seems to address the equation given in the other sources. Thanks!","The Work Energy theorem states, work equals the change in kinetic energy. Also, from the Conservation of Energy equation, Ki+Ui+Wext=Kf+Uf, if you rearrange it, you get Wext=ΔE (total)."
Introduction to work review,"In the Common Mistakes section, should it be cos90 = 0 ?",Yes you can write as cos 90=0 by rounding. But it is preferably used as -1. The exact value is equal to -0.44807361612.
Introduction to work review,why does negative sign means that it is giving energy to its surrounding? is the sign not for our ease only?..(i mean we assume that object moving toward left is negative and toward right is positive.),"When work is negative, the force on the object is the opposite direction of the direction it is moving, so we can assume the object is slowing down. This kinetic energy must be going somewhere. So it is possible the energy is going to the object's surroundings, but it could also be going to potential energy.

Work is not a vector. It can be positive or negative the way temperature can be positive or negative. It is not an arbitrary convention."
N/A,I don't understand what net work means. It says in the article that kinetic energy can be equal to the net work done on a system. What does net work mean?,Net-work just means the _total work_ done by the system. And the value of *net work* = change in kinetic energy.
N/A,"in the exercise 2 , how is the total chemical potential energy stored in the propellant is (Energy density) x (mass of hydrazine)??","By definition, "energy density" tells you energy per mass for the propellant. In other words, energy density is equal to the amount of energy contained in each kilogram of propellant. Multiplying by the number of kilograms of propellant will thus give you the total energy."
N/A,"Why is kinetic energy related to the square of the velocity, as opposed to momentum which varies linearly with velocity? How do I know when I'm dealing with a momentum problem or a kinetic energy problem?","The simplest derivation is this..... Work W=Fx sort of definition.
Then putting F=ma and x=(1/2)at^2 in above gives 
W=(1/2)m(a^2)(t^2) 
    =(1/2)m v^2 
This is called the kinetic energy, KE.
If you realise it doesn't matter how one arrives at the given speed v then this result must be quite general."
N/A,"For exercise 2, I want to know the units of factors used in the last step to calculate the V value. When I calculated the velocity with Ed = 1.6MJ/kg, Mp = 1000kg, and Mr = 100kg, I got 5.657. It looks like 1000 was multiplied to the value, but why? Is it because of the MJ to J? But isn't 1megajoule = 1000000J?","Yes, you should convert MJ to J. The reason that your answer must me multiplied by 1000 since sqrt(10^6)=10^3=1000"
N/A,"if the propellant is contained by rocket then the K.E of rocket shouldn't be => K.E= 0.5(mr+mp)(v)^2
i know it's incorrect but can't figure out .... please clarify , its confusing me
plus , how can the K.E of rocket equal to the CHEM P.E of hydrazine?","The propellant is used up as the rocket gains speed, right? When the propellant is all gone, the rocket's KE has to be equal to whatever energy was produced by the propellant as it burned (actually the propellant leaves as gas and that gas has KE, too, so it' really the sum of that KE plus the KE of the rocket that has to add up)"
N/A,Can you say that kinetic energy is the source of sound energy? Can you say that kinetic energy and sound energy exist together?,Sound energy is a type of kinetic energy.
N/A,prove that K.E = 1/2 mv2?,"You are asking a question, which is answered very well in the current topic :( However, here is somewhat a different proof based on the same idea, although I tried to increase the understanding. Hope this helps.
```
To prove that Kinetic Energy is ½ mv^2
```
We already know that _Energy w = f x s_ that is *force x displacement*.
So, ```
ΔK = W = FΔs = maΔs
```
From the *third equation of motion* that is _v^2 - u^2 = 2aΔs_ (-1) 
where ```
v = final velocity, u = initial velocity, a = acceleration, and Δs denotes change in displacement
```
ΔK = maΔs, so from equation (1)
```
 ΔK = m(v^2 - u^2) / 2
=> ½ mv^2 - ½ mu^2
```
 _but If kinetic energy is the energy of motion then, naturally, the kinetic energy of an object at rest should be zero. Therefore, we don't need the second term and an object's kinetic energy is just_
```
½ mv^2
```"
N/A,"If you see in first paragraph,how will object move with a constant speed if I apply 
energy only once?     It will stop after a certain interval of time","If it stops, that means someone or something else was "applying energy".  In physics we call that "doing work".  Friction does work to stop the object after you did work to get it moving.  If you did it in outer space the object wouldn't stop"
Work-energy theorem review,"If we're lifting an object up, wouldn't the net work be equal to the change in kinetic energy PLUS the change in potential energy? (total change in mechanical energy?)","The work done by your force would be positive, and the total work done would be mgh, assuming the change in height to be h meters. So, according to the work-energy theorem, the final kinetic energy is mgh. Therefore, the square of final velocity should be 2gh. So, use the equations of motion to find out the final velocity. There is no need to find the initial velocity, assuming it started from rest.

From the 3rd equation of motion, v^2 - u^2 = 2as, we find that v^2 = 2gh.

Hence proved.
Cheers!"
Work-energy theorem review,how to find of an objects mass from force vs position graph?,"First we need to find out the area under the force vs position graph which will give us the net work done and then we will set the 
net work = change in kinetic energy
       (Work-energy theorm) 
then we will be able to find the objects mass using the given data."
Work-energy theorem review,How do you find the initial kinetic energy?,initial kinetic energy is equal to 1/2*(mass of body)*(initial velocity of body)^2
Work-energy theorem review,"since work is a vector, do we have work both on the y-axis and x-axis? for instance, if the force is made to a degree from the horizontal axis?",Work is not a vector. It is simply a quantity. If work is positive that means work is being done ON a system and if work is negative then that means that work is being done against the system. Hope this helps!
Work-energy theorem review,How do we know when to use cosine 180?,"you can use the cos(x) when a certain degree of an angle is given, or if they want you to find the degree of an angle using a given/explained equation using the kinetic energy equation"
Spring potential energy and Hooke's law review,Why in the Spring Potential Energy equation is x^2 and not just x?,Because elastic potential energy is Average force multiplied by the extension so (1/2kx)(x)=1/2kx^2
Spring potential energy and Hooke's law review,"hi, does anyone know the difference between a potential energy and force? I  would rlly appreciate it if anyone would help me out!","Hi there! Potential energy is stored energy in an object due to its situation/position that can be converted into other kinds of energy, such as kinetic energy, while a force is a type of influence on an object that can cause/change the motion of the object."
Spring potential energy and Hooke's law review,F=-Kx Then work should be = -Kx^2 why is it 1/2-Kx^2,"Work is force times distance, yes. But, the work done by stretching (compressing) a spring is not constant, since more force is required as the displacement increases. So, a better way to look at it is "Work from x1 to x2 = F * (x2 - x1)". Or, Delta W = F * Delta x. The total work done by stretching from x0 to xn is Sum(Delta W) = Sum(F* Delta x), and as Delta x -> 0, this becomes W = the integral of F dx, from x=x0 to x=xn. The integral of F = kx is (1/2) k x^2."
Spring potential energy and Hooke's law review,What is K as an approximate value?,"`k` is the spring constant for a specific spring and differs for different springs (as a value for its stiffness); therefore, there is no specific value for it."
Spring potential energy and Hooke's law review,Why is the sring potential energy is x^2,"spring potential energy is area under the graph 
(the shape observed is a triangle)
Area of a triangle = 1/2 * base* height 
=1/2*F*x     (here F is the Force of the spring and x is the displacement)
=1/2*kx*x     (because F=kx)
=1/2*kx^2
I hope that helps"
N/A,how do you solve K=1/2mv^2,"If you are solving for "m" you would use the following formula.
m = (2(K))/(v^2)
If you are solving for "v" you would use this formula.
v = sqrt((2(K))/(m))"
N/A,Is energy scalar or vector?,"It can only be a scalar because it doesn`t matter the direction it`s going, just the speed."
N/A,What is rotational kinetic energy?,"consider watching this Khan video for the answer:
https://www.khanacademy.org/science/ap-physics-1/ap-torque-angular-momentum/rotational-kinetic-energy-ap/v/rotational-kinetic-energy"
Gravitational potential energy and conservative forces review,"Does anyone know why the value of gravity in the exercises is sometimes used as positive 9.8 and others are -9.8?​ Isn't gravity's constant, always -9.8.",we've learned that we must always use positive 9.81 while doing exercises but the change can normally occur while doing force changes as in the change of height h2 can be shorter than h1 and it leads to a negative gravity value
Gravitational potential energy and conservative forces review,How is the work done by the force independent when there has to be some type of force exerted on an object?,"Its a late reply, but I think I understand what you are asking.  A conservative force (like gravity) only cares about the objects starting position and its ending position.  So when they say its independent they mean that it does not rely on -how- you arrive at your final location. 

Displacement is your final minus your initial.  (X - Xo) for example.  If Fgrav = mg, and W = F*d, then you can see that how you arrive at your location doesn't matter.  If you start at 0 then go 30m east, then 20m west then 40m east, and finally 30m west. 30-20+40-30 = 20m  So your displacement from 0 is 20m.  (20-0) = (X - Xo).

Notice that if you plug this information into W = F*d, the path had no affect on the d value, and if you had just gone from 0 to 20m without going back and forth, you would arrive at the same Work done.  Thus, conservative forces are independent of the path you take."
Gravitational potential energy and conservative forces review,"When is g -9.8m/s^2, and when is it +?","It depends on how we choose to define the positive and negative directions when working on a problem. We can arbitrarily say that g is positive or negative as long as we are consistent with our signs throughout the problem. Note that if a problem is given to you, it may already define which directions are positive and negative."
Conservation of energy review,can someone upload a video explains this a little more with detail and examples?,"The intial amount of energy in a closed system is equal to the final amount of energy. Energy can't be created nor destroyed, its always transferred."
Conservation of energy review,"Can someone explain the difference between the formulas 
K0 + U0 + Wnc = K + U
and K0 + U0 = K + U?",The formula K0 + U0 = K + U is a simplification of the formula K0 + U0 + Wnc = K + U. The first formula is used when there are only conservative forces present (such as elastic and gravitational potential) whereas the other formula is used when there are also non-conservative forces present such as friction. In this formula: (K0 + U0 = K + U) Wnc is equal to 0 and is therefore omitted from the equation
Conservation of energy review,are non-conservative forces on the side with initial mechanical energy or the side with final mechanical energy?,"Usually, non-conservative forces like friction or air resistance are on the side of the final energy, as they normally are taking away some energy from the system."
N/A,"Technically there are only three simple machines, right?","No, there are 6 distinct simple machines. Pulley Screw, Wheel, Lever, Wedge, and Inclined plane.  I really liked the explanations given at http://iqa.evergreenps.org/science/phy_science/ma.html
Mathematically a Wedge and  Inclined plane are similar, but as far as application they are very different tools for different purposes.  I'm also not sure which of the other 3 you think are the same but I can assure you there are 5 types of simple machines."
N/A,what's the point of a fixed pulley if there's no mechanical advantage?,They can change the direction of a force not the actual speed.
N/A,"Whoo, first question ok! So looking at the figure in 2:28 in the Simple Machines video specifically, I'm intuitively confused about how we "lost" 50N of force/ only have to exert 50N to pull a 100N block? What happened to the other 50N? Who's pulling that part? Also, if we assume that both pulleys are massless, what is the force on the "bar" holding the fixed pulley, and the force (tension) and direction of force on string 1 and 2?","The 50N of force are not lost. When you pull with a 50N force to move a 100N block, it moves 1/2 the distance. The energy is conserved."
N/A,"This is really col but i don't know if I have all the stuff to make this,isn't there an easier way to make it.",why not take a tube like object (a desk lamps adjustable neck) that is suspended in mid air. take a string and tie it round a eraser and then put the string over the top. that way when you pull the non eraser end the eraser will rise up. just like a pulley! YAY!
N/A,"Please review, and correct my thoughts:

Video 1:
Q1. no mechanical advantage.
Q2. Can use this, so that instead of lifting something above your head (against gravity), you can push something else down and work with gravity.

Video 2:
Q1. No idea, but I can see the effects i.e. A heavy gondola on the right can easily be raised. A force downward on the left, causes a much larger upward force on the right.
Q2. The right gondola moves approximately half the distance of the one on the left.
Q3. Since the right gondola moves half the distance, it implies that it also requires double the force. Therefore, a force on the left applies about double that force to the right, indicating a mechanical advantage to the right gondola.

Video 3:
Q1. So that the left can apply a large force over a small distance causing the right to travel a large distance with a minimal force applied.
Q2. The gondola on the left travels much less distance, approximately 1/4 the distance travelled by the right gondola.
Q3. The gondola on the left requires more force, therefore, it has the mechanical advantage.

Motorized Pulley Video:
Q1. Didn't quite understand what was done to even it out.. I had my own idea, but it wasn't the technique used. My idea: Add an identical second motor and wheels on the right side, which would cause the weight to tilt to the right. Thus, the same force is applied on either side. 
Q2. I need to understand question 1 first! - But thoughts: The pulley wheel on the right requires the most amount of force, therefore, it has the mechanical advantage?","Motorized Pulley Video:
The video's way was to connect the end of the string on the right side to the original motor so it reeled in the load from both ends, making it level.
The second question wasn't asking which pulley has mechanical advantage, but rather what the mechanical advantage was in terms of numbers. The "Simple Machines" video shows you how to calculate that."
N/A,what is better for lifting heavy objects a pulley or a lever,"Pulley pros:
1. Easy to transport (if you attatch a pulley system to a crane, for example)
2. Able to lift the object much higher

Cons:
1. Non-efficient for small tasks
2. Time-consuming to make 

Lever pros:
1. Easy to make.
2. Object easily slides off the lever to destination

Cons:
1. It's almost impossible to push a lever and an object at the same time so it's not really great for transport.
2. Cannot lift objects straight (it will tilt to one side) so if you were carrying, say, a big basket of some sort with items inside, the items inside the basket could fall out due to the tilting.
3. Not great for lifting things off into the sky.

So to answer your question, it depends on what the situation is. Hope this helps!"
N/A,How is the mechanical advantage equal to the number of strings?,The tension in the string is the same throughout the pulley system.  If you look at the the tension on the strings  that are doing the lifting you will see that if there is 1 string there is 1 times the tension lifting but if you have 2 string you have twice the tension lifting so the lifting force it is directly proportional string tension times the number of strings.
Lever,How is simple machine useful in lifting thing,"Simple machines increase force, increase distance, and change direction"
Lever,Is there a relationship between the distance the load force moves and the distance the effort force moves?,"Absolutely! He explains this in the mechanical advantage videos but more easily you can think of it like a wrench turning a stuck bolt. Just using the wrench doesn't work but if you put a pipe on the handle of the wrench to extend the handle, the bolt easily breaks loose. Why? Because the force you apply times the distance of the handle creates what we call a "moment" (a turning force) on the bolt. Mathematically expressed" F * d = P (where P is the moment)"
Lever,What materials do you use for this demonstration so that we can try a hands-on as well? Thanks!,"Hi! You could use a ruler and a slim pencil rubber. The advantage of using a ruler is that you can literally measure the distances as you change the mechanism! And the rubber won't let the ruler slide apart, but remeber that it has to be slim, otherwise it won't represent a fulcrum. As for the weight, some coins will do the job. Hope you can do it yourself! Thank you!"
Lever,in the middle of the video how did he know to put on the coins,it was probably part of an experiment he had to demonstrate.
Lever,"in a lever just like the fulcrum was moved to different positions to equalise the position of load and effort... does situation comes where the load has to be moved towards the fulcrum to balance the lever arrangement,, if so can load be moved by keeping fulcrum intact?",yes in the 2nd class lever the load is near the fulcrum eg luggage bag
N/A,What exactly causes objects to stick together after a perfectly inelastic collision?,"Hi,

Actually, having a perfectly inelastic collision is kinda requires the two objects stick together by definition. 

Below is some math to prove it. If you want to skip the math, go to "Skip to here!" 

(warning: solid algebra with bad formatting):
Let object A have mass M, initial velocity VI, final velocity VF; let object B have mass m, initial velocity vi, final velocity vf.
By the equation of kinetic energy, in the system of A and B,
ΔKE=0.5M(VF^2-VI^2)+0.5m(vf^2-vi^2).
       =0.5(M·VF^2+m·vf^2)+C.
(C=0.5(M·VI^2+m·vi^2), which is a constant)
By the conservation of momentum, M·VF+m·vf=M·VI+m·vi=K.
(K is another constant)
Therefore VF=(K-m·vf)/M. Substituting in ΔKE gives:
ΔKE=0.5((K-m·vf)^2/M+m·vf^2)+C.
Simplifying:
0.5/M·(K^2-2Km·vf+m^2·vf^2+m·vf^2)+C.

(Skip to here!)
Because a perfectly inelastic collision means a maximum loss in kinetic energy, we are looking for a min in ΔKE (note that ΔKE is negative, so a smaller value means a larger change in magnitude).
Using vertex of a parabola (precal..?) or minimum of a function (calc) gives us vf=K/(M+m), plugging vf into VF=(K-m·vf)/M gives us that:
vf=VF=M·VI+m·vi/(M+m).

Since the final velocity of the objects is the same, they stick together."
N/A,Is mechanical energy conserved during an explosion?,"Yes, energy is conserved. In a bomb there are special chemicals that react to cause an explosion. This means that there is chemical potential energy stored in the chemical bonds. After the explosion, some of that initial potential energy turns into the kinetic energy of shrapnel, some into heat, some into light, and some into sound. Thus, energy is conserved."
Linear momentum review,"It's written that the "bigger the change in momentum, the more force you need to apply to get that change in momentum," but couldn't the time the force is acting for be decreased too to make a bigger change in momentum?","Yes! If you use a certain net force and time to obtain impulse, then if you increase the net force and proportionately decrease the time or vice versa, you will obtain the same impulse (change in momentum)."
N/A,"Why,(if a boat and a man are an isolated system), when the man walks away from the shore, does the boat move towards the shore? I don't see this in the video.","Lets say a man is standing on a boat which is floating and is at rest. If the man walks to one end of the boat, the boat will move in the opposite direction in order to conserve momentum. Due to this effect, the center of mass of the man-boat system will stay stationary. Hope this helps!"
N/A,how does the c.m of planets revolving be calculated.the double planet revolution and also the planet revolving around their star,"here, the two stars together form a system on which there is an external force due to the star. Hence the motion of the CM of the two planets would be same as if the net force is acting on the CM"
What is conservation of momentum?,"In the exercise 2b when we calculate the force, why is it the mass of the ball in the equation? Shouldn't it be the mass of the golf club?","This is rather confusing... If they are imputing the acceleration and mass of the ball, you find its force. Right. But, if instead of using the mass of the ball, we take the mass of the golf club, the resulting force will be a lot biger (!) Which is not compatible with Newton's third law because the force exerted on the ball by the club will be larger than the force exerted on the club by the ball. Can someone comment on this?"
What is conservation of momentum?,"Hello. I believe in 2b acceleration is negative because the final velocity of the club minus the initial velocity is 32-40=-8, which would make the force negative, thus the answer to 2b should be -4kN.  Which make sense since the ball applies an impulse force opposite to the swing of the club (Newton's 3rd).","Also, the club is losing force since some of it transferred to the ball.  So, in the question the force obtained should be negative."
What is conservation of momentum?,what's smaller than miliseconds?,"Microsecond, nanosecond, picosecond and etc."
What is conservation of momentum?,Why did we not subtract 20m/s from 25m/s in exercise 3?,"In the problem the ball is thrown from person A to person B at 25 m/s then the ball is thrown from person B to person A at 20 m/s.  

The direction from A to B is the opposite direction than B to A so if you consider the velocity of the ball from A to B to be positive then the velocity from B to A is negative giving you Vi = 25 m/s and Vf = -20 m/s.  

When you  put them into the Vi - Vf part of the equation you have (25 m/s) - (-20 m/s) = 25 m/s + 20 m/s = 45 m/s."
What is conservation of momentum?,Is conservation of momentum only applied for two objects that are in motion and are colliding? Is there a conservation of momentum for a ball hitting a wall? How is conservation of momentum differ from Newton's third law of motion?,"Conservation of momentum is separate from Newton's third law and it is applicable in any isolated system.  So a ball hitting a wall is subject to conservation of momentum.  

Even when you have a system that seems to violate conservation of momentum you can almost always increase the system to include enough to have momentum conserved."
What is conservation of momentum?,"In the facts about conservation of momentum in third point you said KE is likely not conserved, can you please explain that in detail and state some examples where KE  cannot be conserved","Here is a video of an experiment where KE is not conserved but momentum is: https://www.youtube.com/watch?v=N8HrMZB6_dU

The KE and momentum of the two bullets should equivalent to each other.  The two blocks travel to the same height because of the conservation of liner momentum but the KE of the bullet gets split between heat, sound, block and bullet deformation as well as rotation in one of the blocks..  

Since both blocks attain the same height  so the KE from vertical motion but the block that was shot off center also has KE from rotation so it has retained more the the bullets KE as KE.  In the block that is shot in the center there is more of the KE transferred to heat, sound, block and bullet deformation than in the one shot off center."
N/A,"Wouldn't the legitimate formula be v2-v1 instead? In this formula, if the frame of reference is moving faster, the object in front appears to have a positive velocity? It seems as though this may be written incorrectly.","I don't understand very well what you mean. Actually that last formula is derived from the equation of conservation of kinetic energy. KA has two videos, one showing the very long way and shorter way. If you use that formula, your equations will be much less tedious and doing a system of equations with the momentum one will give you the result you are searching for this type of problems where momentum and energy is conserved (ellastic collision). The frame of reference doesn't move... I just think it's poorly worded. If you can please be more clear, if I'm capable, I would be happy to help. What drove you into that conclusion? You seem to have upvotes and so maybe I'm the only one who doesn't understand the question..."
N/A,"Im confused about relative velocity, I can see how the principle would work with objects of equal mass, but not different mass.",Well first of all velocity doesn't depend on the mass which is insane. Could you develop more your question? If you plug in the equations is going to give you the desired result. Remeber that we are talking about ellastic collisions where both kinetic energy and momentum are conserved.
N/A,What is the difference between impulse and momentum?,Impulse is defined as the change in momentum. Hope this helps!
Impulse review,"In the practice problems using a force v time graph to find change in momentum, when a negative impulse was applied, a negative final velocity results, and the 'correct' answer states velocity decreases. But velocity increasing in the negative direction is not the same as a decrease velocity. In fact velocity can be increasing in the negative direction, and a negative impulse can result in an increase in velocity. If an object starts from rest and accelerates in the negative direction, would you say its velocity decreases??","You gotta be careful with the terms "velocity" and "speed". Speed is the absolute value of the velocity. In the questions, the velocity is decreasing, it is getting negative, but the speed is increasing (in the negative direction)."
Impulse review,"`During a safety test, a car hits a wall and stops in 0.55,
The net force on the car is 6500 N during the collision.

What is the magnitude of the change in momentum of the car?`

Shouldn't the answer be divided by two?
If the net force during the collision is 6500 N, and the car stops after 0.55 s, doesn't that mean the force goes from 6,500 N to 0 in 0.55 s, and the area under the force time graph (the impulse) is a triangle?","No, the force does not change. The force is constant during those 0.55 seconds. The force is equal to the change in momentum over the change in time. You know the force, you know the time, so you can solve for the change in momentum:
Net force = (∆p)/(∆t)

6500 N = (∆p)/(0.55 s)

∆p = 3575 kg m/s. Hope this helps!"
Impulse review,"the article says"When the force is not constant, we use the average force to find the impulse."but in previous article was written that"For a constant force over time, the net external force is the same as the average external force over the time period."!",""When the force is not constant"
"For a constant force"
reread that please"
Torque and equilibrium review,why is a counter clockwise positive and clockwise negative torque?,"That is an arbitrary convention that we follow. Questions should normally give you the direction that is considered positive though, like how it was given here."
Torque and equilibrium review,"Which mass is the mass used in the equation T = F x r?
Is force acceleration times the *mass of the person pushing* or is it the *mass of the object being pushed*?","The mass of the object being pushed, because it is the object that is being focused on within the system. The weight of the person pushing the object is irrelevant"
Torque and equilibrium review,so im stuck home because of c-19. and studying applied physics for my 3rd trimester is this what i start with to study it.,I would think probably not. Im currently in AP Physics 1 and I would say it would be a good idea to start with 2d kinematics
Torque and equilibrium review,"This was great and helpful, but quick question regarding equilibrium and torque. So the equilibrium here seemed to be of an object with a pivot point but what about examples like a hanging sign... I find this incredibly difficult to think about because let's say you have a hanging sign that sticks out from a wall via a rod both with respective masses and a cable from a building holding it. You are trying to calculate the tension in the cable. 

You have to find the tension of this static equilibrium case -- I know that you have to balance the torques though they add up to 0, but I guess I am just confused about how to find the tension Force from the torques.","Think about it this way (I am going to assume that we know where the cable is attached to the sign): 

Both the rod and sign have mass. So that means that they both have weight. This weight is a force that acts on their centers of mass. This means there is a torque on the sign because of gravity. There are two torques on the sign through gravity due to the rod's weight and the sign's weight, treat these like two different torques and add them together to get the total torque due to gravity. Now, since you know that the system is in equilibrium, this means that force of tension must exert a torque equal in magnitude to the total torque due to gravity. You can create an equation from this:

Tension * lever arm = Torque due to gravity.

Now just divide by the lever arm and you have your tension.

Note: In this example I assumed that the cable is perpendicular to the sign, if the cable is not perpendicular, you have to find the component of the tension force that is perpendicular to the sign using some trigonometry and replace the tension in the equation with this. Hope this helps!"
Angular momentum and angular impulse review,"The equation for angular momentum is given as: 
L = Iw (where "w" is omega)
The unit for I or rotational inertia is "kg.m^2". 
The unit for omega is "rad/sec"
The unit for angular momentum L is "kg.m^2/sec"
When we multiply I with w (omega) what happens to the radians?",Radians have no units and act as a placeholder. In the case you specified we can simply remove them.
Conservation of angular momentum review,How would you show the graph of angular momentum vs. time of a collision of a ball and stick that rotates at around its end?,"I think it depends on what system you are graphing. If you are graphing just the rod alone, then you would show that its angular momentum is initially zero until the moment of collision where its angular momentum equals the angular momentum of the ball prior to the collision; this is only if the ball stopped and transferred all its angular momentum into the rod. However, if your showing a graph of the angular momentum of the ball-rod system, then by conservation of angular momentum, the total angular momentum would be the same prior and after the collision."
Rotational kinetic energy review,Are the units of linear kinetic energy the same as rotational kinetic energy?,"Yes, they are the same, they are both in units of Joules which is newtons times meters since it is the amount of energy needed to exert a force a meter. Any measurement of energy are in units of Joules."
Rotational kinetic energy review,"If I have three identical disks (same m and r), one on top of the other, rotating about a central axis, will the Inertia of the system be the 3 * the Inertia of one of the disks?","Yes it will. The inertia of a system is equal to the sum of the individual inertias. So, if all three disks have identical inertias, then the inertia of the system has to be three times the inertia of one disk."
Rotational kinetic energy review,"For rotational Kinetic energy, it's says were using Joules which is J. Why would we use Joules when the equations doesn't say anything about using Joules",Because the units used to measure Kinetic Energy are in Joules (J)
Introduction to rotational motion review,Are rotational motion and angular motion are same thing ? Or are they two different things ?,I think they're the same thing. The actual name is angular velocity and angular acceleration.
Introduction to rotational motion review,"The author of this article made a mistake, v should be defined as speed of object.","v (aka speed) is also known as the linear velocity (or tangential velocity), as it is the instantaneous velocity of the object at that point in the rotational motion"
Angular kinematics review,I do not understand that why our speed or acceleration is negative when the object is moving clockwise or virce versa,"Its also due to the fact that the speed(velocity to be precise) and acceleration are vectors and hence the direction in which they are applied matters to us. Since we are working in a rotating system, clockwise being negative and counter-clockwise being positive is analogous to moving forward being positive and moving backward being negative in a translational system"
Angular kinematics review,A fan is rotating at 90rpm. It is then switched off. It stops after 21 revolutions.Calculate the time taken by it to stop assuming that the friction torque is constant.....why is time 2x theta in the solution,Use equation 4.  "w" is zero because the final velocity of the fan is zero. And "theta0" is zero because the initial position can be defined as zero.  So it reduces to theta = 1/2 * omega0 * time.
Gravitational potential energy at large distances review,Why does the gravitational potential energy increases as r increases if the equation states that they are inversely proportional?,"Think about it, the formula gmh applies for small distances. But for ridiculously large distances, it makes sense that the further away an object gets, the smaller the gravitational potential energy it has. The further away the object gets, the less influence it will feel gravitationally. Hope this helps!"
Rotational inertia and angular second law review,"given that the formula for the angular acceleration is:
alpha = torque/mr^2.
Under the assumption that the force is applied in a 90 degree angle it can be simplified to:
F*r/mr^2 which leads to: alpha = F/mr.
Why is it that in order to get the highest angular acceleration the force must applied at the largest distance from the pivot point when the acceleration is inversely proportional to the distance.

thanks in advance.","Your argument is okay when you deal with a mass attached to a massless rope, but when you are dealing with objects like discs, hoops or cylinders they have an specific moment of inertia that is given by their mass and their geometrical characteristics. I.e if we deal with the same disc its moment of inertia is a constant because its mass an its geometrical characteristics doesn't change independently the place we apply the force.
Moment of inertia of different objects: 
http://hyperphysics.phy-astr.gsu.edu/hbase/imgmec/mic.png"
Rotational inertia and angular second law review,"so I took the practice: Angular acceleration and angular second law, and I kept failing. The correction was "Applying the force farther from the axis of rotation increases the angular acceleration, so we should decrease the distance instead." Meanwhile, in the video, David said that an increase in r, results in a decrease in angular acceleration. Why the different school of thoughts?","No, an increase in r makes a larger angular acceleration because increasing r means that you are increasing the torque. The more torque you exert, the more angular acceleration you will have. Hope this helps!"
Rotational inertia and angular second law review,"It is false that "if the net force on an object with fixed pivot is zero,then its net torque is also zero.

What is the reason?","The statement is true.
If the net force is zero, the object is at rest because there is no unbalanced force acting upon it. Torque is force times distance (or radius). If the force is zero, the torque is also zero because they are directly proportional to each other."
Introduction to simple harmonic motion review,Why we are interested in finding HM?,"in my perspective, the mathematical model used in analyzing simple harmonic motion is fairly common,you can google the equation of simple harmonic motion and you will find that it's actually a solution of differential eqaution of SHM ( which is also described by Sal). this kind of modeling can also be used in predicting the kinematics of basketball bouncing and in my research case- violin bowing technques, where restoring forces are responsible for similar motions. I guess it's just a way of analyzing the diverse kinematics of nature"
Introduction to simple harmonic motion review,"can the displacement, velocity, and acceleration be at their greatest magnitudes at the same time?","Nope. Because the velocity is always greatest when the displacement is 0, and when the displacement is 0, acceleration must also be 0."
Introduction to simple harmonic motion review,What happens at equilibrium in SHM?,"At the point of equilibrium, the spring does not exert any force on the block. At this point, the block is traveling at its maximum velocity because all the elastic potential energy stored in the spring is converted into the block's kinetic energy and the acceleration is zero at this point."
Introduction to simple harmonic motion review,"Can you explain the velocity vs. time paragraph for figure 1? I get why it starts at zero, but shouldn't it go from negative to positive, so that the first loop is below the x-axis, instead of positive to negative, like it is?","the oscillator starts going in the -x direction, so naturally even the velocity will be negative, since from the start, the displacement is negative"
Introduction to simple harmonic motion review,"If the velocity on the position-time graph is zero, what would the force be? Would it also be zero?","No it need not to be zero.
Just take the example of a ball at its highest point in the projectile motion. The gravitation force is not zero but velocity is zero."
Simple pendulum review,Hi! I don't really know why you're using Pi 2 in the equation. What does pi have to do with that? I really want to know. Although im 13 i still love physics and math. Greetings from Armin.,"The reason Pi is used is because if you think about the shape a pendulum makes as it swings back and forth, it makes a shape similar to a circular arc. When dealing with circles, you mainly deal with the value of Pi, as what my physics teacher explained to my class."
Simple pendulum review,"In the equation for the period of the pendulum, is the value g always constant or can it change","g can change if you're on a different planet. Otherwise, it's going to be a constant 9.8 m/s^2."
Simple pendulum review,"In figure 1 isn't there a y-component to gravity as well? Which's responsible to balance tension out, which actually  is added over by centrifugal force as well?","First of all, centrifugal force is not a thing. It is just an illusion that is due to the objects inertia. It is not an actual force. Second of all, the diagram is a free-body diagram. So, the solid lines show the forces but not the component of the forces. The dotted line shows the component of gravity that causes the motion. The thing is that, the force of tension is not balanced out. If it were, the ball would not travel in a circular path, it would just go in a straight line. The tension force is larger than the component of gravity that goes in the same direction, thus there is a net centripetal force causing circular motion. Hope this helps!"
Simple pendulum review,"Hello. I don't understand why
this equation "F≈−mgθF" makes simple pendulums to be simple harmonic oscillators","The *approximation* is

F ≈ −m g θ,

not what you wrote. This makes it a simple harmonic oscillator because there is a restoring force (here: F) that is (approximately) _proportional_ to the (magnitude of the) displacement (here: θ). (As explained in the video.)"
Energy of simple harmonic oscillator review,"how do you calculate Kmax and Us, max","Hi!

Us, max is 1/2kA^2, where A is the Amplitude and k is the spring constant.

Kmax is 1/2m(v,max)^2 where m is mass"
N/A,"Say we have a horizontal SHM frictionless spring-mass system. If I take another mass and drop it on top of the mass in oscillation, will it change the amplitude? I did a specific example and solved for the new amplitude with the new velocity after the mass was added and got the same amplitude. Am I correct to get the same amplitude?","you actually are correct because by adding more mass you are simply increasing the force and hence the acceleration of mass moving through the distance in the same amount of time. the distance ( amplitude ) doesn't change because more mass was added, cause mass has no effect on it.
more mass means more force= more acceleration moving through a greater distance in the same amount of time."
N/A,would changing the mass (and nothing else) of an object change the graph of simple harmonic motion?,Yes-changing the mass would change the time taken to complete one full cycle (the period) and therefore would change the graph.
N/A,"A 0.5 kg mass hangs on a spring, find it’s period
of oscillation","For a mass attached to a spring, the period of oscillation is equal to 2π √(m/k). Plug in 0.5 for m and if you know what the spring constant k is you can solve."
N/A,A 125 N object vibrates with a period of 3.56s when hanging from a spring. What is the spring constant of the spring?,"F=ma, (a=g=9.8 m/s/s)
find m, substitute in 
k=m*4*pi^2/T^2
voila, you get ur answer,
k = 39.735 N/m"
Transverse and longitudinal waves review,Is there an easy way (an acrostic or something) to remember what wave is bunched together and which has up and down movement?,I find that the 'long' in longitudinal reminds me a bit of 'along'. As in along the medium. While the 'trans' out of transverse is more readily used in various fields and comes from Latin and translates to 'the other side of'. So it travels from one side to the other side. Hope it helps.
Transverse and longitudinal waves review,here its written "Sometimes people forget wave speed isn't the same as the speed of the particles in the medium" but wont the increase in particle speed increase wave speed,"Nope, increasing particle speed does not increase the wave speed. They are separate. Actually it elaborated right after the sentence you quoted. 'The wave speed is how quickly the disturbance travels through a medium. The particle speed is how quickly a particle moves about its equilibrium position.' An increase in particle speed will increase the energy the wave carries but will not affect the wave speed at all."
Transverse and longitudinal waves review,"So if you move the slinky forwards and backwards, then the slinky with get bunched up in some places, like how the air was in the sound wave from the video, creating a longitudinal wave? But if you move it up and down, then the slinky with go up and down until you stop, like the string in the video, creating a transverse wave?","Yes. Imagine ripples in water is a longitudinal wave, and transverse waves are those waves like when you shake a string and the curve continues along the string."
Transverse and longitudinal waves review,how does waves move through a medium?,"If you are talking about physical waves, such as sound waves and vibrations, here is the answer. As the wave passes through a material, the particles at the wave are moving a very small distance. As they move, they bump into other particles and impart their momentum onto these new particles. These new particles in turn move and bump into other particles, repeating the cycle of movement and imparting momentum, thus allowing the wave to move through the medium."
Transverse and longitudinal waves review,is there an easy way to memorize waves,Transverse waves are up and down and Longitudinal waves are right and left.
Standing waves review,does a standing wave have a period?,"Yes. All waves have a time period. A wave is the propagation of energy. So although the wave might appear to be stationary, there is energy being propagated, at a constant rate (for standing waves)."
Standing waves review,Is antinode the same as amplitude,"`Antinodes` are not the same thing as the `amplitude`, but they are very closely related. The `amplitude` is the `distance` from the `rest position` of the wave to the `antinode`. The `antinode` is just a point along the wave that has the greatest maximum velocity in the `y-direction`."
N/A,"Is the wave energy proportional to the amplitude? In the practice problem, when two periods of different amplitude but same frequency, the energy of the higher amplitude period is higher. In another problem, two waves of same amplitude and of different frequency have the same energy. By Planck constant, shouldn't the one with higher frequency have more energy?","I too am confused by the question of how frequency of the wave impacts energy. 

Consider this thought experiment: 

Person A moves a rope up and down causing a wave to propagate on that rope. 

Person B vibrates the rope made of the same material but at twice the rate. This means that the waves will have double the frequency. 

Who is expending more energy? 

Obviously it is Person B (If in doubt, look to the folks in the gyms who work out with battle ropes. Doing it faster makes you sweat more.) 

And by the law of conservation of energy, that energy has to move somewhere. In this case, it moves down the rope. 

Therefore , frequency has an impact on the energy. 

Can somebody please point out the flaw in this argument?"
N/A,Why does changing the frequency does not affect the energy of the wave,"In the classical wave theory, energy of a wave doesn't depend on the frequency of the wave. However, the energy of individual photons in a beam is determined by the frequency of the beam. Wave's energy is directly proportional to the square of its amplitude"
N/A,"_"Changing the frequency or amplitude of the waves will not change the wave speed, since those are not changes to the properties of the medium."_ But the equation is for velocity (speed) is *v= λf*, which means that *the higher the frequency and the larger the amplitude, the higher the  speed (velocity)*, right? Maybe i am misinterpreting the definition of velocity and speed...","v=λf is (speed of wave)=(wavelength)(frequency).
Frequency is the number of cycles per second. If you increase the number of cycles in a second, the wavelength of each cycle must decrease.

If you increase frequency, the wavelength must decrease by the same factor. If you decrease the frequency, the wavelength must increase by the same factor."
N/A,"how to calculate lambda,whats the formula?","Just rearrange the formula given to you to find wavespeed. If you know wavespeed is wavelength x frequency, then rearranging the formula will allow you to find out the wavelength."
Wave interference review,is pulse and superposition same?,"No, a pulse is a single disturbance in a wave. Superposition, however, is when two pulses cancel out each other. A pulse's amplitude may be 50m at one point in time, but if there is a pulse which has an amplitude of -50m at the same time, they will cancel out and nothing will be heard, that is how noise-cancelling headphones work."
Beats and interference of sound waves review,"On the previous practice, I am confused about the pressure graphs. From what I am understanding from the practice, it is saying that when there is more pressure, there is more displacement and thus a larger amplitude/volume, but when I look it up, I find the opposite. Can someone please help me understand what I am missing here?","https://bit.ly/2OdXTXZ

You may be mixing up the terms *loudness* and *pitch* (see image above).

If not, post the link that says higher amplitude = quieter sound."
Introduction to sound review,We watched all the videos and are confused because the summary basically says exactly the opposite of the teaching videos where the drawings of nodes and antinodes are concerned. THe videos say that in an open tube the node would be directly in the middle with the antinodes at either end "dancing around wildly." But the diagram in the summary shows the opposite. The teaching video states that a closed tube has one node at the closed end of the tube with the antinode being on the open end. The summary says the node in a closed tube would be at the open or closed end with the antinode being in the middle- I'm confused.,"Hi Karen!
I think you are confused between the two different diagrams given for each open and closed tubes. The first diagram for each is of the displacement of air molecules which is we use to calculate the wavelength. On the other hand, the second diagram for each represents the air pressure variation around the tubes (which we needn't be concerned for any calculation purpose!).
   Consider the fig 2 i.e for air pressure variation in open tubes. At the ends air pressure is equal to the atmospheric pressure. Since air molecules can’t oscillate at displacement nodes (in the middle) to equalize pressure, displacement nodes have maximum pressure variations. So is the graph shown. Please read the whole text carefully. Cheers!"
Doppler effect review,Why is the doppler effect an "effect" if the frequency and the wavelenght are actually different comparing the waves that are in front of the source and the ones that are left behind?,"I would say that the Doppler effect is the effect the relative velocity of an object has on its generated sound waves' perceived frequency and wavelength, if that makes sense."
Doppler effect review,What happens if the source and Observer are both moving?,The manifestation of Doppler effect will depend on the relative velocities of the source and the observer.
Doppler effect review,What if the source of the sound is moving faster or slower (acceleration) relative to the observer?,"Think of an ambulance blaring its siren while you're riding your bike down the street. It is safe to assume that the ambulance is accelerating faster than your riding (if both you and the ambulance are moving toward the same end of the street). The ambulance’s faster acceleration relative to your riding acceleration will cause an increase in the observed frequency because the ambulance will eventually catch up to you (the observer). After all, the wave fronts are still being compressed in front of the ambulance (the source) as it approaches you (the observer).

On the other hand, if you're a criminal (I hope you're not) that is driving faster than the cops after a bank robbery, your observed frequency of the police siren will decrease because you're driving farther away from the source, which is similar to the source driving away from the observer in the above image from the text.

I hope this helps."
Doppler effect review,"Is the frequency that an observer would hear the same everywhere to the direct right of the source? Would it change if the observer was also moving and if so, how?","Yes, as the observer moves, there is an increase or decrease in the relative velocity that cause an increase or decrease in the perceived frequency"
Doppler effect review,"is it always the case, when we are talking about doppler effects we are mostly reffering to sound only?","The Doppler effect can occur with a variety of types of waves, including electromagnetic (light) waves."
Doppler effect review,bhgjhb ihbj i hbhj,yes because yes
N/A,a neutral object has positive and neagtive charges both. so when a postively charged object comes close to neutral one why electrons from neutral gets transferred because if there is attraction between opposite charges it must be within neutral object also so electrons of neutral object must be attracted to protons of same object. what is so special about the positive charge on other object,"Your question is really an interesting one and actually you came up with a valid point. The first thing which you have to keep in mind that 'Electron Transfer' only happens with metals. In insulators and semiconductors, the scenario which takes place is called 'Electron Localisation'. The electrons which are transferred or localised are called 'Valence Electrons' which means the electrons residing on the last orbit in an atom. The valence electrons are loosely bound in all the atoms may it be of a conductor or of an insulator. 'Loosely Bound' means that if we can apply enough force which supercedes the attraction force between the nucleus and the electrons, the electrons will be transferred to a positively charged atom(for conductors) or be localised at a side of an atom(for insulators).

If we take a positively charged atom to a neutral one, the electrostatic force occurring between the positive charge and the valence electrons of the atom(because of Coulomb's Law) is more than the force between the valence electrons and the protons of its own atom. So, the electrons will be transferred to the positively charged atom as those will have enough energy to get 'free'. That is why they are called 'Free Electrons'.

For insulators and semiconductors, almost the same incident happens; but the electrons can't be transferred, instead, they get localised at a side of the atom. The reason is that to get free, the electrons have to be in 'Conduction Band'(kind of an energy state), but here they are in 'Valence Band' which is a lower energy state. Though they don't have enough energy to get free, they localise at a side of the atom.

If you want to know more about 'Electron Bands', you can google a bit and I hope you'll find some YouTube videos which might clear some of your clouds in mind.

And remember, all the 'electrons' I used to explain are 'Valence Electrons'."
N/A,What happens when the net charge of the two objects is an odd multiple of e?,The material with more protons get the extra electron
N/A,Could someone please explain me what happened in the 2nd pratice question of Applying conservaton of charge ? I did not quite grab it. Thank You.,"It is a particle that decays into two smaller particles. But charge must be conserved, therefore the sum of the charges of the two smaller particles must add up to the total charge that you started out with."
N/A,How do I find the Electric field if the charge is not given but distance is?,"The farthest you could get is to:
Fe =(9*10^9 |q1*q2|)/(whatever your distance is)^2"
N/A,What are the laws of attraction?,"Like forces repel one another, and opposites attract. Positive repels positive but attracts negative, and negative repels negative but attracts positive. Its almost kind of like a positive person being the most picked on in school. The negative bullies are using this positive person as a platform, and the positive person always wants to help the negative people "BECOME" positive. 
Hope this helps!"
N/A,Will an object with more charge have a greater force than the object with a smaller charge?,"An object with greater charge will exert a greater force on an object than an object with smaller charge would. However, if you consider two charges that exert a force on each other, regardless of the magnitude of charge, both charges will exert an equal force on each other because of Newton's third law."
N/A,Is there any derivation of relation needed for comparision of Gravtitational and Electrostatic Energy,"Often in exams, comparison b/w electrostatic and gravitational forces between electron and proton are asked. In that case the ratio b/w Fe and Fg is approx 10^40."
N/A,"is r measured in cm? if not, what unit?",in "CGS" system [centi;gram;second] r is measured in centimeters but in "MKS" system [meter;kilo;second] r is measured in meters
N/A,"If both q1 and q2 are positive or negative, how would the equation represent that they are repulsing? Since it takes the absolute value it would always end up as positive, which is attraction. Right?","it's just for the magnitude of the force, if you want the proper direction then use the vector form of coulomb's law"
N/A,"What is the direction of force between a proton and an electron?
*Please explain your answer*","*If there are two charges that are ALIKE, they REPEL.
If there are two charges that are DIFFERENT, they attract*.

So, a proton and an electron would attract, because they are different.

A proton with another proton would repel because they have the same charge.

An electron with another electron would also repel, because they have the same charge.

It's like a magnet's south and north poles, but with protons and electrons."
Electric charge review,How come quarks have fractional charges?,The idea of electrons/protons having an "elementary" (lowest level) charge was developed and set in stone before physicists realized that there were sub-sub-atomic particles (quarks) that had charges smaller than the previous elementary charge.
Electric charge review,"Quantization of charge does not work at the macroscopic level, Why?",It works. But we ignore it. suppose a body has a charge of 250C then adding an electron would mean we are adding 0.0000000....016 C to it. thus we can ignore it and assume that charge is continuously added .
Electric charge review,what mean is by integer multiple of e,"e= 1.6 x 10 to the power of -19. So essentially multiples of e will be 1.6, 3.2, 4.8 and so on which are e, 2e, 3e,.. respectively.  This are integer multiples of e."
Electric charge review,""deficiency of electrons results in positive charge on body, while excess of electrons means body have negative charge. we do not use proton excess or deficiency terminologies because protons are way more heavier than electrons and do not move when we charge a body either negative or positive. it is electrons that just move and decides positive and negative charge on body".

just like when an neutral atom of Na(sodium) become positive charge ion because it has deficiency of 1e- but its proton remains fix on place. a case of deficiency of electrons.
                Na  ----------> Na+ +1e-

if you imaginize it other way around neutral Cl(chlorine) atom become negative charge ion for its accept a electron but its proton do not go anywhere. a case of excess of electrons.
               Cl + e-  ------------> Cl-

and i think the case is same when we say something is negative charge( have predominant electrons) or positive charge( have fewer electrons).

am i right? all about the charge.","You're partially correct, let me explain why so, only electron can transferred and not proton not because of electron is light and proton is heavy in weight, it is because energy required to pluck an electron from a neutral atom is way more less that that of proton. Energy required to pluck the Proton is very high because Protons reside inside the nucleus. And that of electrons they revolve around the nucleus in orbits(path), hence electrons are easy to be removed from atom. We need to give very very high energy to remove a proton from nucleus. Therefore electrons are used to deal the transfer of charge"
Electric charge review,"Bit of a dumb question, but how exactly do you read this: -2e or 2e? Is it something like, "2 negatively charged protons" and "2 positively charged protons" or some other way? Apologies if this has been asked somewhere already","Nope, your question isn't dumb at all! 
I believe you would call it "charge of negative two" for the first one and "charge of two". You can omit the "protons" portion as one unit of charge is already defined as the charge of one proton/electron.
Of course, you can say it slightly differently for each situation, like "the beryllium atom has a charge of two."

Cheers!"
Electric charge review,what is quantization of charge,"Charge only comes in countable numbers. The smallest amount of charge that has ever been observed is the charge on the electron and/or the charge on the proton (both the same amount, but opposite type). Hence the term "quantization of charge." Quantum or "quantized" means that it is numbered or integer-countable (can come in -1, 0, 1, 2, 3, etc. but not 1.5 or pi, etc), and a quantum is essentially one of those quantized objects. The total charge on a charged object is therefore the number of individual charges, all of which are either electrons or protons, multiplied by the charge on one of them. This explains the existence of the following equation:

Q=n*e"
Electric charge review,what happens if an object has less protons than electrons? What does it means when the charge is quantizise on an object?,"if an object have less proton the electron then object is negatively charge it means that the object has more no of multiple of e
Because Quantization(q) = n x e
               where e is 1.6 x 10^-19
               And n is integer value"
Resistors in series and parallel review,"Why in a circuit with several branches the voltage drop across each of the branches is the same? 
Why doesn't it also split up as the current?","Hi,

Here's an analogy that might help you understand:

Imagine there is a bakery, and it produces 5 slices of bread/min and there's 60g of carbo per slice of bread. 
If you own the production for yourself, you get 5 bread/min, and 60g carbo/bread.
If you are sharing with 4 other friends and you are dividing the bread evenly, you are getting only 1 bread/min, but still 60g carbo/bread.

In this analogy, 
the bakery=battery
You and your friends=//resistors
Bread production=flow of electrons
Bread=electrons' charge, measured in C.
Carbo=energy, measured in J.
Time is, well, time. 
Therefore carbo/bread=J/C, which is the voltage; 
bread/min=C/s, which is the current.

Here we can see that the voltage doesn't drop with //resistors, but the current does.

(This is not a proof, but only a way to understand)"
Resistors in series and parallel review,"It is given that the resistor with the biggest resistance has the greatest voltage. We know that electric current is directly proportional to the potential difference across a circuit. So, this statement now means that the biggest resistance allows the largest amount of current to flow through it. Isn't this fact contradictory to what we have learnt? (Current is inversely proportional to resistance)","V=IR can be rearranged to I=V/R therefore while the resistance increases the current decreases.  In series, the current is the same throughout the circuit.  So, a  larger resistor will have a larger voltage drop.

If I have a larger resistor in parallel with a smaller resistor and they both have the same voltage applied since they are in parallel, which one do you think has more current flowing through?"
Resistors in series and parallel review,what if there are 2 resistors in series that are parallel to 1 other resistor?,"In these types of cases it is best to simplify parts of the circuit and then find out the net resultant. In your example let each of the resistors individually have a value of resistance R. Then: 
The equivalent resistance of the resistors in series
Req1= R + R = 2R
Now as you mentioned, these two in series, are in parallel to one other resistor R.
Finding Req1 basically gives us that a single resistor of 2R would perform the same function(in this case) as the 2 resistors R in series. 

So we can instead, now consider, a resistor with resistance Req1 to be in parallel combination to a resistor with resistance R. And we know how to do this:
1/ReqFinal= 1/Req1 + 1/R
Now, as Req1=2R, we get:
1/ReqFinal= 1/2R + 1/R = 3/2R
i.e: ReqFinal=2R/3
Which is the equivalent resistance of the whole combination!
You can extend this to more complex circuits as well, simplify parts of it and keep going!
Cheers!"
Resistors in series and parallel review,"I need help in understanding Series-Parallel circuits, where there are both circuits in series and parallel in one individual circuit.","It would help to just solve the resistance for the parallels first and then add it to the total resisters.

for example if you had a 5 ohm resistor in series with parrallel resistors (8 and 8 ohms)
then you could do the parrallel resistors first and once you get the resistors value (4 ohms)
you could add it to the 5 ohm resistor (9 ohms)

Think of parrallel resistors as if they are combined to make one resistor"
Electric potential difference and Ohm's law review,"I was stuck in this place, where is says the electrons move to the positive terminal because the potential is lower.

" The boulder will naturally fall toward the ground where potential energy is lower. The electron at the negative terminal of a battery will naturally flow toward the positive terminal, where the electric potential is lower."

But a few paragraphs up it says the opposite..?

" The short side is the negative end, with a lower electric potential, and the long side is the positive end, with a higher electric potential."","The reason for this is that electrons are negatively charged. They are in a state of high potential when at the negative end and low potential at the positive end.
Before physicists knew that electrons moved, they assumed that positive charges were doing the moving. For this reason, conventional circuits state positive (+) to be high potential and negative (-) to be low potential."
Electric potential difference and Ohm's law review,I couldn’t understand how non-ohmic devices work. How do non ohmic devices work if they do not follow a directly/indirect proportion to the electric potential difference and resistance?,"Resistance not only depends on length, area and type of the conductor, it also changes with temperature for some devices. So in a light bulb, because the temperature increases when it is illuminated, its resistance changes...we then have three variables and the relation between the current and the potential difference no longer gives a straight line (since its gradient, the resistance, is no longer a constant).
Devices whose temperature changes affect the resistance are called non-ohmic devices."
Electric potential difference and Ohm's law review,I understand the equation for Ohms law and how electric potential is directly proportional to current and resistance. But conceptionally electric potential increasing when resistance increases doesn’t make sense. How does this relationship make sense conceptually? Wouldn’t voltage decrease if there is more resistance added?,Electric potential would increase when resistance increases given a *constant current*. Voltage would have to be higher to maintain the same current when resistance is higher.
DC Circuit and electrical power review,Why doesn't some of the current flow through resistor R2 in Figure 10B?,"Actually, there are charges flowing through R2; it's just that the path of least resistance will be preferred and so will have a considerably larger current compared to the path with the resistor."
DC Circuit and electrical power review,why does the voltage remains constant in a parallel combination circuit,"This is because there are only two sets of electrically common points in a parallel circuit, and the voltage measured between sets of common points must always be the same at any given time."
DC Circuit and electrical power review,is power equal to thermal energy released by the resistor in joules per second,"In case the circuit only contains the resistor, the total power is indeed equal to the thermal energy released by the resistor. (J/s)"
"Current, resistance, and resistivity review",Can there be a resistance in a vacuum even if the liquid hits that walls or other objects within the vacuum?,"It's important to remember that water through a tube is only an analogy.  A tool to help describe physical interactions. Our senses were not designed to observe "subatomic particle-wave electron thingys" but by connecting them to real life phenom we're familiar with we can better learn about the universe... Hopefully you keep that in mind. In terms of your question, yes, if there is a pressure difference and a tube connecting the ends, water will flow; if your tube is filled of stone there will be more "resistance"."
"Current, resistance, and resistivity review","If the electrons are the ones who move in a current,then wouldn't the atoms become unstable? I mean as we know that the electrons move in orbital shells around the positively charged atomic nucleus then how are they able to seperate from the atom and move freely in a current....please help me to have a clearer image of this....( sorry if my question was found to be inappropriate but I just had to polish my basics).","Only the valence electrons in a conductor metal atom usually are involved in the flow of current(1 to 3 out of the many electrons a metal atom has. Copper has 29). These valence electrons too are loosely bound to the nucleus and can be used for current flow easily, this is because on losing a certain amount of electrons these metal atoms actually gain stability in some ways.
Also even when they participate in current flow the electrons are still there near every metal atom(a bit like water flowing in a pipe).
So as a combination of all these factors it doesn't lead to unstability. But yes, if you tried to extract say 10, or even 5 electrons from Copper atom got them away then the copper atom would be quite unstable.
Feel free to ask a follow up!
Hope that helps!"
DC Ammeters and voltmeters review,is there any instrument made to measure resistance,"Yes, a multimeter can measure voltage, current, and resistance."
DC Ammeters and voltmeters review,Ideally the internal resistance of a voltmeter should be infinite and that of an ammeter should be zero. Why is it so?,"Hello, 

In a voltmeter you are measuring in paralell. You do not want to be involved in the circuit essentially, only measure it. So you want nothing to go through the voltmeter and electricity takes the path of least resistance, so it will not go through the voltmeter if it has lots and lots of resistance. In an ammeter, you are measuring current, the electricity is going through the meter. You do not want your measurement to affect the current, and you do that by having lots of resistance. Hope this helps. 

AP Physics Student"
What is conservation of momentum?,"In the exercise 2b when we calculate the force, why is it the mass of the ball in the equation? Shouldn't it be the mass of the golf club?","This is rather confusing... If they are imputing the acceleration and mass of the ball, you find its force. Right. But, if instead of using the mass of the ball, we take the mass of the golf club, the resulting force will be a lot biger (!) Which is not compatible with Newton's third law because the force exerted on the ball by the club will be larger than the force exerted on the club by the ball. Can someone comment on this?"
What is conservation of momentum?,"Hello. I believe in 2b acceleration is negative because the final velocity of the club minus the initial velocity is 32-40=-8, which would make the force negative, thus the answer to 2b should be -4kN.  Which make sense since the ball applies an impulse force opposite to the swing of the club (Newton's 3rd).","Also, the club is losing force since some of it transferred to the ball.  So, in the question the force obtained should be negative."
What is conservation of momentum?,what's smaller than miliseconds?,"Microsecond, nanosecond, picosecond and etc."
What is conservation of momentum?,Why did we not subtract 20m/s from 25m/s in exercise 3?,"In the problem the ball is thrown from person A to person B at 25 m/s then the ball is thrown from person B to person A at 20 m/s.  

The direction from A to B is the opposite direction than B to A so if you consider the velocity of the ball from A to B to be positive then the velocity from B to A is negative giving you Vi = 25 m/s and Vf = -20 m/s.  

When you  put them into the Vi - Vf part of the equation you have (25 m/s) - (-20 m/s) = 25 m/s + 20 m/s = 45 m/s."
What is conservation of momentum?,Is conservation of momentum only applied for two objects that are in motion and are colliding? Is there a conservation of momentum for a ball hitting a wall? How is conservation of momentum differ from Newton's third law of motion?,"Conservation of momentum is separate from Newton's third law and it is applicable in any isolated system.  So a ball hitting a wall is subject to conservation of momentum.  

Even when you have a system that seems to violate conservation of momentum you can almost always increase the system to include enough to have momentum conserved."
What is conservation of momentum?,"In the facts about conservation of momentum in third point you said KE is likely not conserved, can you please explain that in detail and state some examples where KE  cannot be conserved","Here is a video of an experiment where KE is not conserved but momentum is: https://www.youtube.com/watch?v=N8HrMZB6_dU

The KE and momentum of the two bullets should equivalent to each other.  The two blocks travel to the same height because of the conservation of liner momentum but the KE of the bullet gets split between heat, sound, block and bullet deformation as well as rotation in one of the blocks..  

Since both blocks attain the same height  so the KE from vertical motion but the block that was shot off center also has KE from rotation so it has retained more the the bullets KE as KE.  In the block that is shot in the center there is more of the KE transferred to heat, sound, block and bullet deformation than in the one shot off center."
Newton's second law review,"The videos on Newton Second Law of Motion only showed things in their current state; how would you show something moving, for example, accelerating North at 20 Newtons and slowing down by a Southern moving force of 15 Newtons. How would that be shown in an illustration like the ones in the video?","If you wanted to illustrate the object in a free body diagram, you would just draw the forces acting on it, as in the example you gave with 20N north and 15N south (similarly to how the objects were shown in the video). The object's velocity and acceleration are not included as part of a free body diagram, but I usually notate those as arrows on the side for visual convenience."
Newton's second law review,Is a light particle/wave at equilibrium: acceleration =zero?,"technically , yes
that's why we regard the speed of light as a constant"
Newton's second law review,The videos and this article cover the method for 2 and 3 dimensions but what happens in higher dimensions. Are Newton's laws applicable?,"No. Being that higher dimension's have more things impacting an object, such as time, Newton's equations don't work."
Newton's second law review,Hi! I'm wondering why the velocity could be non-zero when the forces are at equilibrium (F_net=0) and when the acceleration is also 0. Shouldn't velocity only be 0 (according to Newton's First Law) because the forces are balanced and acceleration doesn't exist?,"Okay, I'm going to remind you of some things you already know: acceleration can be defined as the change in velocity over time, and if a force is being applied to something it should accelerate unless an equal and opposite force is being applied. (An equal force is being applied in the direction opposite of the original force)
If an object is moving, and there are no forces being applied to is (no friction, gravity, or any work whatsoever) then it is not accelerating, as a force is necessary for acceleration to be observed, and at the same time there are no forces, so F_net=0.
Okay, you say, but what if there are forces?
The same principle- as you know F_net=F_1+F_2+...+F_n, so if I were pushing a box along a plane with friction, applying a force of 10 N, and the friction on the box was 10 N in the opposite direction, we would say that the net force is zero, F_net=0, which means there is _ALSO_ no acceleration, even though the box is moving, which means there is a velocity."
Newton's second law review,"hello, please I would like to know when is the acceleration considered to be negative?","When your velocity starts to decrease, for example when a car is coming to a halt just before a traffic light (Retardation)."
Newton's second law review,"What are real-life examples of unbalanced forces, and why does unbalanced force not affect speed","An example of unbalanced force could be, a rather unfair game of tugs-of-war, where there are 5 strong people on one side(A), contrasted to a lanky person(B) on the other. In this case, the rope will get pulled towards (A)- which seems intuitively apt as well- and poses a great example of unbalanced forces because the net force on side (A) is more than side (B)- which makes the rope veer towards side (A). 

Unbalanced forces do affect speed- An unbalanced force acting on an object results in the object's motion changing. The object may change its speed (speed up or slow down), or it may change its direction. Friction is a force that resists the motion or the tendency toward motion between two objects in contact with each other."
Newton's second law review,how do you know if a number is to be subtracted,"If the force is in the opposite direction, then you subtract it!

Just keep in mind which directions are positive. Then all you need to do is add the forces in the positive direction while subtracting those in the opposite direction. Of course, keep in mind that you can't add or subtract vectors that are perpendicular to each other (i.e. forces in x-direction and y-direction)."
Newton's second law review,What is the difference between inertia and equilibrium?,"equilibrium is when there is a net force of zero, so the forces acting upon the object equal zero but the velocity is still constant and non-zero. If velocity were zero then it would be static equilibrium. Inertia is a force that acts as a guidline to objects, it keeps them in uniform motion or rest, what makes this different from equilibrium is that when an object is acted upon by an outside force an object still has inertia because objects always have a resistence to change their motion."
Newton's second law review,"I don't understand exactly how an object with constant velocity that isn't at rest has a resultant force of zero, is there always some kind of opposing force? But what if there isn't a force such as friction or air resistance? I'm confused","Acceleration implies force. If we have constant velocity that means that we don't have acceleration. If we don't have an acceleration, that means that there's no force involved. 

In real life, yes. If we only focus on classical mechanics and not the physics behind it that explains more profoundly why it works like that, I can't think of any force that doesn't have an opposing force. Every material has an associate coefficient of friction. If there's no force such as friction or air resistance, objects would experience a constant acceleration, meaning they would be speeding up until reaching the speed of light all the time. Because if we are at a rest (0 velocity) and want to change our velocity we need a force. And that force wouldn't had a counterpart. We would be constantly accelerating, making life pretty difficult. If not, not viable."
Conservation of momentum,So I get the problem when you have the mass of the object and the velocity of the object. I just don't understand it when you have just kg*m/s,"I don't know what you are trying to get (if it is momentum, then just do kg*m/s) 

Yes, kg*m/s is enough to solve for momentum

Kg is the unit for mass
M/S is the unit for velocity"
Conservation of momentum,"so if I get this right, Momentum and force are correlated?
since by my understanding saying 40 Netowns is the same as saying 40 kg * m/s^2 momentum.

fun fact: a force of 40Newtons is around 4KG of weight force.
          1 meter / second is 3.60km/h",Force would be the rate of change of momentum.
Conservation of momentum,how is 40 N equivalent to 40kg * m/s2,"I just posted this in the comment section that follows, so well, I hope u can understand why kg m/s^2 is the unit for force. 

Well, we humans are too lazy to write the whole thing, that is, 'kg m/s^2' every time we talk about force and its units. So, we decided to keep another unit, N, that is , Newton. 

Consider this, when we are given a math problem of this type , " **insert name** has 5 apples which amount to 25 (unit currency). Now, the person wishes to buy 3 more apples from the same shop. Calculate the extra money he needs to pay." We simply divide 25 by 5 to get the cost of one apple, and then multiply it by three. Well, this is not so lengthy at this stage for most of us, but it does cause quite some silly calc errors. It would have been way easier if we just had the cost of one apple from the beginning, right?  

Similarly, in force, what we do is this:

We consider a case where an acceleration of 1 m/s^2 is produced for a mass of 1 kg when a certain force is applied. And, according to the formula, we get the answer as 1 kg m/s^2 . This 1 kg m/s^2 is given the name Newton and the symbol 'N'. 
Thus, in your case, when we say 40N, we say _40 x 1 N_ that is _40 x 1 kg m/s^2_ . This is why they're equal.

Hope this helps, and sorry for such a lengthy explanation. I seem incapable of explaining in short."
Introduction to momentum,Is the equation in the introductory paragraph right? Shouldn't it be P(total) = p1 + p2 instead of P(total) = v1 + v2?,Yes I think the equation in the introductory paragraph is incorrect.
Introduction to momentum,"probably a stupid question to ask:- 

why is momentum p?","Some interpret the reason for keeping P as the symbol for momentum as the letter being derived from Latin word Petere which means ‘to go and seek’. This meaning is also related to the word ‘impetus’ which is the earlier term used for ‘momentum’. The word ‘impetus’ gives the meaning as to go and rush upon which was explained by the term Petere. Hence, momentum is represented by the letter P."
Introduction to momentum,"why momentum is multiple of mass and velocity,

i mean we have feel that momentum should increase when either mass or velocity increase, so there can't be subtraction or division.

we could add both mass and velocity and the result will increase in that case too,

what decided that they should be multiple instead of other increasing operations like square or something,

or is this one of the special case of more bigger picture?","That's because this is in fact a concept, just as in length there is no absolute "one", so what ever is the unit is just defined by the scientists. Through experiments they have determined that momentum is proportional to the mass of the object and its velocity, and proportion indicates that the relationship is multiplication instead of addition. You can also add a factor k, but in this case since this concept is quite isolated and does not need to be merged with other unit systems, simply multiplying is enough."
Introduction to momentum,How is velocity a vector?,"A vector in physics is defined as something that has magnitude and direction.

Velocity has both. For instance, a car is traveling at 60 miles per hour in a southward direction.

60 mph is the magnitude
south is the direction.

thus, it is a vector.

speed just has magnitude, so if you say a car is traveling 60 mph, that is just speed."
Introduction to momentum,whats the difference between -v and +v,"The + and - signs denote the direction part of the velocity _vector_, where in most cases, + indicates to the right and - indicates to the left. Of course, you can make your own system and call + to the left and - to the right, but it should be consistent throughout your calculations."
Coulomb's law and electric force review,How do I find the Electric field if the charge is not given but distance is?,"The farthest you could get is to:
Fe =(9*10^9 |q1*q2|)/(whatever your distance is)^2"
Coulomb's law and electric force review,What are the laws of attraction?,"Like forces repel one another, and opposites attract. Positive repels positive but attracts negative, and negative repels negative but attracts positive. Its almost kind of like a positive person being the most picked on in school. The negative bullies are using this positive person as a platform, and the positive person always wants to help the negative people "BECOME" positive. 
Hope this helps!"
Coulomb's law and electric force review,Will an object with more charge have a greater force than the object with a smaller charge?,"An object with greater charge will exert a greater force on an object than an object with smaller charge would. However, if you consider two charges that exert a force on each other, regardless of the magnitude of charge, both charges will exert an equal force on each other because of Newton's third law."
Coulomb's law and electric force review,Is there any derivation of relation needed for comparision of Gravtitational and Electrostatic Energy,"Often in exams, comparison b/w electrostatic and gravitational forces between electron and proton are asked. In that case the ratio b/w Fe and Fg is approx 10^40."
Coulomb's law and electric force review,"is r measured in cm? if not, what unit?",in "CGS" system [centi;gram;second] r is measured in centimeters but in "MKS" system [meter;kilo;second] r is measured in meters
Coulomb's law and electric force review,"If both q1 and q2 are positive or negative, how would the equation represent that they are repulsing? Since it takes the absolute value it would always end up as positive, which is attraction. Right?","it's just for the magnitude of the force, if you want the proper direction then use the vector form of coulomb's law"
Coulomb's law and electric force review,"What is the direction of force between a proton and an electron?
*Please explain your answer*","*If there are two charges that are ALIKE, they REPEL.
If there are two charges that are DIFFERENT, they attract*.

So, a proton and an electron would attract, because they are different.

A proton with another proton would repel because they have the same charge.

An electron with another electron would also repel, because they have the same charge.

It's like a magnet's south and north poles, but with protons and electrons."
Newton’s law of universal gravitation,I'm confused about calculating all numbers like this "6.67 x 10^-11 m^3/kg*s^2". I know that is gravitational constant but how to solve that kind of number?,"Remember that 10² is 100. 10³ is 1,000. So 10^10 is a one followed by ten zeros, or ten billion. 10^-10 is going backwards: a decimal point followed by nine zeros and then a one. Whatever this is then multiplies the number in front, and at the end are just a bunch of units. For example, 2.345*10^-6 m²/kgs is the same thing as 0.000001*2.345 meters squared / kilogram seconds, which is 0.000002345 of the same thing."
Newton’s law of universal gravitation,How do I calculate after I input the numbers in the formula? What does N stand for?,"N stands for Newtons, which is a unit of force. Could you clarify what you mean about inputting the numbers in the formula?"
Newton’s law of universal gravitation,Is the "little g" just a gravitational field? And is it specifically Earth's gravitational field?,"Little g is the numerical value of Earth's gravitational field's pull at the Earth's surface.

Another planet would have a different value for its own gravitational pull."
Newton’s law of universal gravitation,Will `G` always be  6.67 x 10^-11 m^3/kg*s^2?,"Yes. By definition, G is a constant."
Newton’s law of universal gravitation,"Wait, so, I'm kind of confused. If g = G*(m1/r^2), then does that mean that the mass of m2 does not affect the gravitational effect that m1 has on it?","It does, but it is mostly not obvious. Everything has a gravitational pull, but it is not noticeable except for some exceptions; your dog, for instance, won't fly up to you the moment you get 2 feet close to it, but the Moon circles the Earth because of the gravitational pull. To put it simply, the mass of the objects still have a pull on each other, but many times it is small, so it can be ignored, except if you want to be super specific or have huge objects, like Jupiter's moons.

Hope this helps!"
N/A,Does the earth have a magnet inside?,earth as a whole is a magnet
N/A,why do moving charges cause an magnetic field?,"beacause the electric and magnetic force are tightly related and form togheter the *ELECTROMAGNETIC FORCE*  which is defined by Maxwell's equations, a set of 4 equations (not all developed by Maxwell), Faraday's Law, Ampere's Law (with Maxwell's additions), Gauss's Law (not the math one) and Gauss's Law for magnetism"
N/A,Can a planet move?,yeah
Spring potential energy and Hooke's law review,Why in the Spring Potential Energy equation is x^2 and not just x?,Because elastic potential energy is Average force multiplied by the extension so (1/2kx)(x)=1/2kx^2
Spring potential energy and Hooke's law review,"hi, does anyone know the difference between a potential energy and force? I  would rlly appreciate it if anyone would help me out!","Hi there! Potential energy is stored energy in an object due to its situation/position that can be converted into other kinds of energy, such as kinetic energy, while a force is a type of influence on an object that can cause/change the motion of the object."
Spring potential energy and Hooke's law review,F=-Kx Then work should be = -Kx^2 why is it 1/2-Kx^2,"Work is force times distance, yes. But, the work done by stretching (compressing) a spring is not constant, since more force is required as the displacement increases. So, a better way to look at it is "Work from x1 to x2 = F * (x2 - x1)". Or, Delta W = F * Delta x. The total work done by stretching from x0 to xn is Sum(Delta W) = Sum(F* Delta x), and as Delta x -> 0, this becomes W = the integral of F dx, from x=x0 to x=xn. The integral of F = kx is (1/2) k x^2."
Spring potential energy and Hooke's law review,What is K as an approximate value?,"`k` is the spring constant for a specific spring and differs for different springs (as a value for its stiffness); therefore, there is no specific value for it."
Spring potential energy and Hooke's law review,Why is the sring potential energy is x^2,"spring potential energy is area under the graph 
(the shape observed is a triangle)
Area of a triangle = 1/2 * base* height 
=1/2*F*x     (here F is the Force of the spring and x is the displacement)
=1/2*kx*x     (because F=kx)
=1/2*kx^2
I hope that helps"
N/A,How do people actually look and measure the angles of bonds if we haven't actually seen an atom?,"I think it's just maths, based on the knowledge we already have. If a molecule has 4 hydrogens and 1 carbon (methane, as in the example above), and we know that electrons repel each other, then there's only one set of angles that allow those electrons to all be as far apart from one another as possible. The lower the number of electrons, the greater the angle, presumably."
N/A,"is there a program in which a person can mix and match different elements together and see what compounds they come up with, what compounds they form. then when the compound is formed the program gives a backstory o how that compound is used throughout life",Check out materialsproject.org they have so much info on different elements and compounds.
N/A,Why is oxygen electronegative?,"Oxygen is electronegative because it only needs 2 electrons to complete it's valence shell. Instead of losing an electron (like sodium, in sodium chlorine), it simply attracts to those 2 electrons. The more a atom wants an electron, the more electronegative it is and visa versa. 

To imagine whats more electronegative, simply look at the periodic table. At the far bottom left  to the top right is the scale for how electronegative an atom is. The closer to the bottom left, the less an atom is electronegative. Closer to the top right, the more electronegative the atom is.

Hope this helps ;)~"
N/A,Is it possible to artificially create diamond using huge hydraulic presses with super hot base plates such that all conditions to create diamond are fulfilled ?,"While I'm not sure if it's possible through the means at which you said, I know that it is possible to artificially create diamonds.  Some pet owners have made their pets into diamonds because all earth life is based off of carbon."
N/A,"If the bonds in methane are repelled to each other, then wouldn't the bonds be too far apart that it would break the bonds?","The force that repels the pairs of electrons in the bonds in not as strong as the force that attract the electron to the protons of the carbon and hydrogen atoms. Thus, the best the electron bonds can do to stay away from each other is to form a tetrahedron. :)"
N/A,"Here it says that carbon can bond with 4 other atoms because it has 4 electrons on its outermost shell, while oxygen can bond with only 2 but yhe outermost shell has 6 electrons why can't it bond with 6 atoms.","The octet rule means that atoms tend to prefer having eight electrons in the outside valence shell. Since carbon has 4 valence electrons, it can bond with 4 hydrogen atoms (that have 1 valence electron) to reach the preferred 8 valence electrons. Since oxygen has 6 valence electrons, it only needs to bond with 2 hydrogen atoms in order to reach the preferred 8 valence electrons."
N/A,How do people die?,"People can die from various causes, and the scientific study of death is known as thanatology. Some common scientific explanations for death include:

1. Cardiovascular events: Heart attacks, strokes, or other conditions that disrupt blood flow to vital organs can lead to death.

2. Respiratory failure: Illnesses such as pneumonia, chronic obstructive pulmonary disease (COPD), or severe asthma can result in the inability to breathe properly, leading to death.

3. Infections: Bacterial, viral, or fungal infections can overwhelm the body's immune system, causing organ failure and ultimately leading to death.

4. Trauma: Severe injuries, including those from accidents, falls, or violence, can damage vital organs and cause death.

5. Cancer: Uncontrolled growth of abnormal cells can invade and destroy healthy tissue, impairing essential bodily functions and eventually leading to death if left untreated.

6. Neurological disorders: Conditions like Alzheimer's disease, Parkinson's disease, or amyotrophic lateral sclerosis (ALS) can progressively affect the brain and nervous system, leading to death.

7. Organ failure: When one or more vital organs, such as the heart, liver, kidneys, or lungs, stop functioning properly, it can result in death if not treated or replaced through transplantation.

8. Metabolic disorders: Conditions like diabetes, kidney failure, or liver disease can disrupt the body's normal metabolic processes, leading to complications that can be fatal.

It is important to note that this list is not exhaustive, and each case of death is unique. Scientists and healthcare professionals continually study different aspects of death to better understand its causes and find ways to prevent or treat the underlying conditions."
N/A,What is a carbon monoxide and what does it do?,"Carbon Monoxide (CO) consists of one carbon atom and one oxygen atom. It is often formed through combustion reactions, and is a toxic compound. This is why you may see carbon monoxide detectors."
N/A,what is a Hydrocarbons and what does it do?,"Hydrocarbons are organic molecules composed solely of hydrogen and carbon, hence the name. There's a number of uses for hydrocarbons, but the main purpose of them in human society is a source of energy through their combustion, or burning them for energy.

Hope that helps."
Biological macromolecules review,"After reading the key terms, I am a little bit confused.. to my understanding, monomers are the makeup of polymers... is that correct? If so, are the terms "polymer" and "biological macromolecules" synonymous?","Hello,
As I understand it, polymers are a subdivision of biological macromolecules. 'Polymer' is the branch of macromolecules that is made up of ONLY ONE monomer that repeats itself.

For example, a carbohydrate is a macromolecule that is classified as a polymer because it is made up of repeating monosaccharides, but a fat (lipid) is a macromolecule that cannot be further classified because if you look under the 'monomers' column, it is built up by more than one monomer.

Hope this helped!"
Biological macromolecules review,Isn't protein an energy molecule for muscles?,"Rather than providing energy for muscles, they are structural components, which means they build and repair muscles. Protein is only used as energy if carbohydrates and lipids aren't available for energy (side note: breaking down protein for energy is unhealthy and dangerous!). 
Hope this helps, - Layla"
Biological macromolecules review,Are phospholipids polymers?,There is considerable interest in the polymers bearing phospholipids in the main chains as the structures of these polymers are similar to biological tissues. Several polymers containing a phospholipid in the polymer backbone have been synthesized and characterized
Biological macromolecules review,how can lipids act as a chemical messenger?,"Some lipids such as steroid hormones serve as chemical messengers between cells, tissues, and organs, and others communicate signals between biochemical systems within a single cell."
Biological macromolecules review,"Are monomers and monosacchrides the same thing? Also, what is a polypeptide?","Monomers are the building blocks of the four basic macromolecules of life- monosaccharides are the monomers of carbohydrates, amino acids are the monomers of proteins, glycerol/fatty acids are the monomers of lipids, and nucleotides are the monomers of DNA.

Polypeptides consist of a bunch of amino acids bound together- so in a way it's a monomer of proteins!"
Biological macromolecules review,Why aren't minerals a macromolecule?,"What are the characteristics of a macromolecule?

Can you think of a mineral that meets all those criteria?

Does that help you to answer your question?"
Biological macromolecules review,why are vitamins not digested in the body,"Vitamins are not digested, whereas, they are absorbed.

Vitamins are organic compounds that are required for normal animal metabolism but are either not created in the body or are created in insufficient amounts and must be received through your diet. Almost all of vitamin absorption goes to the small intestine.

Vitamin absorption in the intestine is important for avoiding deficiency disorders, and it can be limited by a variety of factors, including intestinal disease, genetic abnormalities in transport molecules, excessive alcohol use, and drug interactions."
Biological macromolecules review,"which would be the differences between DNA and RNA were not very clear to me, they seem technically the same and I cannot differentiate them very well","If you are asking what the difference between the two is, here you go.

There are several differences. To start, DNA stands for deoxyribonucleic acid, while RNA stands for ribonucleic acid. These names describe the sugar that makes up their backbone--DNA = deoxyribose and RNA = ribose.

Second, while each has four nucleiotide bases, there is one difference. You probably know that DNA has guanine, cytosine, adenine, and thymine, and that guanine links to cytosine and adenine links to thymine. But RNA doesn't have thymine. Instead, it has uracil, a nucleiotide base with a slightly different chemical makeup. Thymine had the chemical formula C5H6N2O2 and uracil is C4H4N2O2. Uracil links to adenine in RNA just like thymine does in DNA

Finally, DNA is double-stranded and forms a double helix structure. RNA is single-stranded and is generally straight. DNA is a complete set of instructions needed for life (unless you're a virus, but that's a whole different story/debate) and RNA is used to copy DNA and to synthesize proteins. I know this is a lot to take in, but there are several videos and articles on Khan Academy to help. Here are a few.

https://www.khanacademy.org/science/high-school-biology/hs-molecular-genetics/hs-rna-and-protein-synthesis/v/molecular-structure-of-rna

https://www.khanacademy.org/science/high-school-biology/hs-molecular-genetics/hs-rna-and-protein-synthesis/v/rna-transcription-and-translation

https://www.khanacademy.org/science/high-school-biology/hs-molecular-genetics/hs-rna-and-protein-synthesis/a/hs-rna-and-protein-synthesis-review

Anyway, this is probably a lot, but I hope it helps!"
Biological macromolecules review,How should I remember all these terms?,You gain familiarity through repetition. Practice is key.
Biological macromolecules review,whats the main difference between saturated and unsaturated fats,"From a chemistry perspective, saturated fats have no double bonds between carbon atoms, while unsaturated fats have one or more double bonds. 

From a state of matter standpoint, saturated fats are solid at room temperature, while unsaturated fats are liquid or soft.

From a nutritionist's point of view, saturated fats can increase the risk for heart disease (because it stays as a solid at room temperature and can lead to atherosclerosis) and unsaturated fats can help maintain proper bodily functioning (because they stay as a liquid at room temperature and are less likely to clog your arteries.)

I know you asked for a main difference, but I included three because there are many differences between saturated and unsaturated fats. I hope you have a better understanding of saturated and unsaturated fats."
Carbohydrates,"Why are galactose and glucose isomers, when the hydroxyl group that is "flipped" is linked to the chain by single bonds only? I thought only double+triple bonds forced atoms to stay where they are. According to the previous lesson about ethene/ethane, galactose and glucose should be the same thing because the flip happens around single bonds.","Well, single bonds allow the actual atom/molecule to rotate. However, in this case, when the article is talking about "flipped" molecules, the molecules are not able to rotate, they are just upside-down in relation to the neighboring molecules."
Carbohydrates,"Confused about differences between beta-glycosidic and alpha glycosidic linkages. Are beta-glycosidic linkages inherently stronger due to some chemical property, or is it just that humans lack the enzymes to digest it? Whatever the answer, this is not to be confused with the reason cellulose is so strong (which is due to the hydrogen bonds acting between different polymers of glucose, forming thin fibrils), am I correct?","Well from what I learned beta-glycosidic linkages are stronger due to the way bonds criss-cross between every alternate glucose molecule such as cellulose making it both physically and chemically stable. 

These beta-glycosidic linkages can be broken down by enzymes stored by the bacteria stored in a cow's gut for example which why cow's can ingest complex carbohydrates like cellulose and as you suggested humans cannot digest such carbohydrates as we do not have the enzymes that can specifically break beta-glycosidic linkages."
Carbohydrates,"How can you identify a carbohydrate? Are all molecules with a carbonyl group (C=O) and hydroxyl group (OH) carbohydrates? Or is it so that ONLY carbohydrates have one carbon (C) atom to one H2O? If the latter is true, why is deoxyribose a carbohydrate with a formula C5H10O4?","Unfortunately there isn't a universally accepted definition for what makes up a carbohydrate.

A very restrictive definition is as follows:
Carbohydrates consist of carbon, hydrogen, and oxygen — with the hydrogen and oxygen occurring in a 2:1 ratio.  There also must be at least three carbons.
In other words, these are organic molecules that incorporate multiple water molecules and have at least three carbons.


However, derivatives of molecules that meet the above definition are still generally thought of as carbohydrates.  
(In addition, some molecules that fit these parameters aren't generally thought of as carbohydrates.)

For example: deoxyribose is a sugar (carbohydrate) found in DNA that has had an oxygen removed.

Other modifications including addition of groups containing nitrogen and sulfur are also commonly found.


I recommend the wikipedia article on this subject:
https://en.wikipedia.org/wiki/Carbohydrate


Does that help?"
Carbohydrates,"With the glucose and galactose isomers, can't glucose's 3rd carbon spin around if it  doesn't have a double bond? Then it would be exactly like galactose. Does this happen or is there a reason why it can't?","Because it requires breaking off the bonds.

If you want to turn H, and OH into one another, you will have to break bonds and reattach them. This does not happen spontaneously in water. 

You _cannot_ turn one into another through mere rotations of a bond. :)"
Carbohydrates,"What is the advantage of polysaccharides, storage wise?","To add to the excellent reply from Okapi, another reason why glucose is stored as glycogen is that if it were stored as free glucose, this would cause osmotic pressure to increase such that cell membranes would rupture.  Even the elevated glucose level (hyperglycemia) seen in uncontrolled diabetes cause changes in osmotic pressure that are responsible for some of the symptoms, such as increased urination and excessive thirst."
Carbohydrates,Is fructose sugar healthier than glucose sugar?,It depends on the context of how its used.
Carbohydrates,What is the difference between a monomer and a monosaccharide?,"A monomer is the smallest unit of a polymer.
A polysaccharide (carbohydrate) is a polymer. A monosaccharide is the monomer that makes up a polysaccharide.
In short- Monomer is a general term, while monosaccharide is a specific term for the monomer that makes up a carbohydrate.
A monosaccharide is a single sugar molecule. This includes glucose, fructose, and galactose.
Disaccharides are double sugars, such as sucrose (table sugar).
Polysaccharides are long chains, such as plant and animal starches."
Carbohydrates,if single bonds can rotate freely do the stereoisomers become each other interchangeably ?,"No, single bonds stereoisomers such as some enatiomers are not interchangeably because they are stuck in the three dimension world"
Nucleic acids,How do mRNA and tRNA communicate with eachother during the formation of the proteins?,"mRNA is like a recipe from a cookbook; a list of ingredients to make a protein. mRNA is a chain of nucleotides (A, U, C, and G, not T since this is RNA). A group of three nucleotides is called a codon. A codon matches with three nucleotides, called an anticodon, on a single tRNA molecule while in a ribosome. The tRNA carries an amino acid, our ingredient to make the protein.
So mRNA is the recipe, tRNA matches to the recipe bringing an ingredient, and the line of ingredients become a protein."
Nucleic acids,"If A-T bonds have 2 hydrogen bonds and G-C bonds have 3... Would it be true that longer periods of A-T bonds in DNA (so like: AATAATTATTTTAATTAAAA) are less stable parts of the DNA helix than parts that have more (or only) G-C bonds in them? And if this is true, are these parts (AT only parts) more prone to mutations?","The first part is true, T-A bonds are less stable and more likely to come apart. The A-T bond strands also signal where DNA needs to separate for commonly transcribed genes, such as the TATA Box commonly found just before the beginning of gene sequences.

I'm not sure if they are more prone to mutations though."
Nucleic acids,"DNA is common to all organisms, all organisms use the same 4 nitrogenous bases, A T, C G

is that right?","Entirely true. Also, AT/GC are found in DNA while RNA is made from AU/GC. Just keep in mind that, even though all life forms have DNA, not everything that has DNA is alive: viruses can have DNA but are not living."
Nucleic acids,"Why do some nitrogenous bases have two fused carbon rings while other have one? Would it be possible for there to be nitrogenous bases with more than two fused carbon rings? Could there ever be an instance where there are more than just five kinds of nitrogenous bases (Adenine, Thymine, Guanine, Cytocine and Uracil)? If it could be possible how would DNA and RNA have to rearrange themselves? Would it be possible for DNA and RNA to use other sugars aside from Deoxyribose and Ribose? If so, like what? If not, why?","https://www.khanacademy.org/science/organic-chemistry/aromatic-compounds/aromatic-stability/v/aromatic-heterocycles-i

https://en.wikipedia.org/wiki/Heterocyclic_compound

https://en.wikipedia.org/wiki/Abiogenesis

https://en.wikipedia.org/wiki/Nucleic_acid_analogues

Hope this helps!"
Nucleic acids,Are the functions of nucleic acids guided only by molecular forces and just appear to have intention or are there other forces at work that I'm not aware of? How do these macromolecules "know" what to do?,"A creationist would say that this is part of the intelligent design. An evolutionist would say it's all down to chance. Two spanners to consider - 1) one molecule of hormone, once recognised by the cell, leads to prduction of thousands of times more molecules, and types of molecules, than a mere chemical would suggest, and such secretions can be brought about by tiny changes in brain activity. 2) DNA is just for storage. It is a molecularly inert form for the passing on of genes without having a massive effect upon the rest of the body - and so the active form is the sticky stuff of RNA and these determine how the proteins are folded together."
Nucleic acids,"When transcription takes place and the DNA is broken into two, and then mRNA is formed with one of the DNA strands or for BOTH the DNA strands?","Within a gene *usually* only one strand is transcribed, but there are many examples where transcription happens from the both strands. This is especially common in viruses.

Also, the strand that is transcribed for one gene may not be the same as the strand being transcribed for a neighboring gene.

Finally, the whole DNA double helix is not separated - just a small bubble is opened around each RNA polymerase as it works its way along the DNA."
Nucleic acids,"In the first paragraph of the section "Regulatory RNA (miRNAs and siRNAs)" it says "They bind to specific mRNA molecules (with partly or fully complementary sequences) and reduce their stability or interfere with their translation, providing a way for the cell to decrease or fine-tune levels of these mRNAs."

Does this mean that the purpose of microRNAs (miRNAs) and small interfering RNAs (siRNAs) it to make sure that there are not too many mRNA molecules producing proteins? They are regulating the amount of protein produced by the cell? Am I understanding this correctly?

Please help! Thanks. :)","Yes, miRNA regulates protein synthesis in a way it binds to mRNA transcript and 'silence' it."
Nucleic acids,how are DNA and RNA different and alike to each other?,"As stated in the summary at the end of the article, DNA and RNA have different functions. While DNA stores genetic information, RNA is involved in protein synthesis and gene regulation, as well as storing genetic information in some viruses. DNA and RNA also have different structures; DNA's phosphate-sugar backbone contains deoxyribose, while RNA's contains ribose. While DNA is double-stranded and has the nitrogenous bases adenine, thymine, cytosine, and guanine, RNA is usually single-stranded and contains uracil instead of thymine.

As for the similarities between DNA and RNA, they are both important biological polymers and contain four bases and a phosphate-sugar backbone."
Functional groups,"There are many more functional groups,any tips for remembering there names?",You could try active recall where you watch a video or read and then you close it and try and write down as many things as you can remeber. (This works because it is more difficult at first telling your brain that it needs to focus on it creating connections between your brains nerves)
Functional groups,"In the table, what is the difference between a functional group being polar and being charged?",A charged group is either positive or negative (gains or loses an electron) and a polar group contains atoms that have a difference in electronegativity.
Functional groups,"Can someone please elaborate on what makes a molecule or atom,      polar/non-polar or acidic/basic?","Sure thing! An atom is the smallest building block of life, it cannot be broken down further (like Carbon). A molecule is a group of atoms chemically bonded in a fixed proportion (like CO2), which can be further broken down. An atom is polar molecularly if it is asymmetrical (in terms of bonding, it is polar when its electronegativity difference is >0.6). An atom is nonpolar molecularly if it is symmetrical (in terms of bonding, it's EN difference is <0.6). An atom is acidic when there are more positively charged hydroniums than negatively charged hydroxyls (same vise-versa)."
Functional groups,How can you tell if a functional group is acidic or basic just by looking at the functional group?,well determining by its ability to loose or gain a proton
Functional groups,"Are aldehydes and ketones (carbonyls) significantly soluble in water like alcohols and carboxylic acids? If not, why not?","The short molecules are soluble in polar substances like water because they are relatively polar. The longer the carbon chain is however, the greater the non-polar tail is, and the less soluble aldehydes and ketones become."
Functional groups,"In what year in school do we learn this? I am home schooled and i want to learn 11th grade, but i am not sure if this is near grade 11 or is it for 9th graders or for collage. What grade do you learn this?",this would be basic chemistry so you could learn this is 9th or 10th or even 11th grade if you take biology or chem
Functional groups,"is it normal that in the video, it written. that an Amino group is N-H-H,  while here its R-N-H-H","Well first thing is that we don’t write condensed structural formulas like that. The formula is written in a specific order so we know what is bonded to what. So if you write N-H-H or R-N-H-H, it looks as if nitrogen is bonded to only one hydrogen and that there’s a bridging hydrogen joining the nitrogen to the other hydrogen. If we have multiple atoms bonds to the same central atom, we use subscripts. 

If it’s an amine, we need that ‘R’ part of the formula to show that the nitrogen is bonded to a larger organic molecule. Otherwise it looks like a lone nitrogen molecule, like ammonia. So it’s properly written as R-NH2 (where the 2 is a subscript). 

Another thing to point out that we can have slightly different types of amines depending on how many carbon atoms are bonded to it from the rest of the organic molecule. An amine is essentially an ammonia molecule where a hydrogen has been replaced by a carbon atom. But since ammonia has a formula of NH3, we have the possibility of replacing all three hydrogen atoms with carbon atoms. 

An amine with only one carbon atom is called a primary amine (symbolized 1°) with a formula of R-NH2.
An amine with two carbon atoms is called a secondary amine (2°) with a formula of R2-NH.
An amine with three carbon atoms is called a tertiary amine (3°) with a formula of R3-N.

Hope that helps."
Functional groups,how alkanes are less reactive. why?,"Alkanes are less reactive than alkenes.
This is because alkenes have double bonds (C=C).

It is easy to break just one of these bonds in the double bond and make a reaction happen, but breaking the C-C single bond in an alkane is difficult"
Functional groups,Does anybody know whether there is a difference between O-H and OH?,There is no difference. OH has an imaginary bond between them (seen in O-H). We assume it is there. It is a common group so we do not have to draw the bond every time.
Functional groups,is phosphate group polar or non-polar?,"The phosphate group is non-polar, it is made up of a polar head but three non-polar tails, making the overall charge, non-polar"
Chemical bonds,"In the third paragraph under "Ionic Bonds", it says that there is no such thing as a single NaCl molecule. Why can't you have a single molecule of NaCl?","This is because sodium chloride ionic compounds form a gigantic lattice structure due to the electrostatic attractions between the individual ions. In this case, each sodium ion is surrounded by 4 chloride ions and each chloride ion is surrounded by 4 sodium ions and so on and so on, so that the result is a massive crystal. This particular ratio of Na ions to Cl ions is due to the ratio of electrons interchanged between the 2 atoms."
Chemical bonds,"Regarding London dispersion forces, shouldn't a "dispersion" force be causing molecules to disperse, not attract?",dispersion is the seperation of electrons
Chemical bonds,"What is the typical period of time a London dispersion force will last between two molecules? 
To me it seems it last far shorter than a second. If so, has it got time to do anything productive with the molecules? Do this London dispersion forces come in bursts? Electrons rapidly moving back and forth between two atoms in a molecule creating many London dispersion forces so fast it acts like a long-lasting bond between molecules?",The London dispersion forces occur so often and for little of a time period so they do make somewhat of a difference. In my biology book they said an example of van der Waals interactions is the ability for a gecko to walk up a wall. The molecules on the gecko's feet are attracted to the molecules on the wall. You could think of it as a balloon that sticks to a wall after you rub if on your head due to the transfer of electrons. The bond is not long-lasting however since it is easy to break.
Chemical bonds,"If enough energy is applied to mollecular bonds, they break (as demonstrated in the video discussing heat changing liquids to gasses).  Usually, do intermolecular or intramolecular bonds break first?  Is there ever an instance where both the intermolecular bonds and intramolecular bonds break simultaneously?","Intermolecular bonds break easier, but that does not mean first. Statistically, intermolecular bonds will break more often than covalent or ionic bonds. Yes, they can both break at the same time, it is just a matter of probability. Water, for example is always evaporating, even if not boiling. But, then, why no hydrogen or oxygen is observed as a product of pure water? Because water decomposes into H+ and OH- when the covalent bond breaks. The concentration of each of these ions in pure water, at 25°C, and pressure of 1atm, is 1.0×10e−7mol/L... that is: covalent bonds are breaking all the time (self-ionization), just like intermolecular bonds (evaporation). By the way, that is what makes both pH and pOH of water equal 7.

Note that even though H+ and OH- are naturally produced in water, they also recombine back into H2O. The speed of bonds breaking and the speed of recombination "fight" one another, until they are in chemical equilibrium, that is when both speeds are the same. See https://en.wikipedia.org/wiki/Chemical_equilibrium

For instance, this kind of "fight" also happens with evaporation inside a closed recipient. The equilibrium is reached when the number of molecules escaping from the liquid phase is the same as the number of molecules entering it."
Chemical bonds,what determines a molecule's electronegativity?,"The electronegativity of an atom depends on its effective nuclear charge (the positive charge experienced by an electron in the atom's outermost shell) and the distance between the outermost shell and the nucleus. Elements with a high effective nuclear charge and a small atomic radius tend to have high electronegativities. Fluorine, which has the highest electronegativity value of 4.0 on the Pauling scale, has a small atomic radius and a high effective nuclear charge."
Chemical bonds,Are hydrogen bonds exclusive to hydrogen?,"A hydrogen-bond is a specific type of strong intermolecular dipole-dipole interaction between a partially positively-charged hydrogen atom and a partially negatively-charged atom that is highly electronegative, namely N, O, and F, the 3 most electronegative elements in the periodic table."
Chemical bonds,"In the section about nonpolar bonding, the article says carbon-hydrogen bonds are relatively nonpolar, even though the same element is not being bonded to another atom of the same element. 

How is one supposed to know which bonds are nonpolar if the same atom isn't being bonded to the same atom (e.g. O2)","Look at electronegativities, and the difference will tell you."
Chemical bonds,what are metalic bonding,"Metallic bonding occurs between metal atoms. In this type of bond, the metal atoms each contribute their valence electrons to a big, shared, cloud of electrons. Because the electrons can move freely in the collective cloud, metals are able to have their well-known metallic properties, such as malleability, conductivity, and shininess."
Cohesion and adhesion of water,"So, in the case of the water strider, the strider is more dense than the water but stays afloat because of surface tension. Is this in any way the same as saying that the insect is less dense than the "film" on the surface of the water?","I would not go as far as to say that the 'film' is denser than the water strider; seeing as this is a problem that more involves pressure and resistence, a better solution would be to form an equation to determine the pressures at the point of contact between the water strider and the 'film'. And Paul Tatman is completely justified in stating that the water strider would likely sink if all of its body weight were to be concentrated on one leg, or all four legs right next to one another (increasing the pressure), as opposed to it being spread out over four widly splayed legs (a greater area), if there are four legs in the above image that is."
Cohesion and adhesion of water,I was wondering if adhesion is affected by the temperature of a fluid,"Yes. Cold water will adhere to a glass container more than hot water, because I think the water molecules are moving around more slowly when they're cold and are therefore more able to stick to the glass than the faster moving hot ones. (Note: I actually tested this with some hot water and cold water. Try it!)"
Cohesion and adhesion of water,"I just had my blood donated and we are learning this in my Ap biology class, I was just wondering, does adhesion and/or cohesion take place when someone is donating their blood? I mean through the tube, or is it some other biophysics term?","Yes. Adhesion happens because the water prefers to stick to the tube, causing capillary action. That then goes up the tube, because blood prefer sticking to the tube."
Cohesion and adhesion of water,will water eventually fill and  the capillary tube and go out,"No, because the water can only rise as long as the adhesive forces are stronger than the force of gravity. Once the force of gravity is equal to the adhesive forces (which vary from substance to another, according to the degree of polarity) between the water molecules and the substance's, the water will cease to rise. This is why the water rises to different heights in capillary tubes made of different materials (substances).
Hope this helps! :)"
Cohesion and adhesion of water,"ok, so does capillary action contribute to why bubbles work? just curious","That's correct. Cohesive forces cause the water molecules to stick together with a lot of elasticity, allowing the water to function very much like a rubber balloon so that when it is filled with air it doesn't break and simply forms a blanket over the air pocket."
Cohesion and adhesion of water,"If the surface of water when it is in a glass tube is called a concave meniscus, is there a term for the dome shape caused by surface tension from an overflowing glass like in the first paragraph? Would it be right to call it a convex meniscus?",Yes!
Cohesion and adhesion of water,"If cohesion is the cause of water moving to the tops of trees, (I'm guessing this is a also a capillary action) what is water adhering to in the tree that overcomes the cohesion in the water? (If this sounds like nonsense, apologies, I am trying to grasp the concepts in this article).","Cohesion is when water sticks to things simply because it is water and has polar bonds which can create some polar interaction. Capillary action is precisely what drives water up to the branches and leaves at the top. I don't think water is "overcoming" anything (misuse of the word?). Water is transported through a tube-like system called Xylem, and it might simply stick to the walls here."
Cohesion and adhesion of water,"Do all liquids have these properties, even non-polar ones?","nope. water is just so so special🤣but think about it. even oils and alcohols have different cohesive and adhesive properties. and if the sea was oil instead of water, when it froze over, life under it would die cuz the density would be higher frozen"
Cohesion and adhesion of water,"When the water strider ‘walks’ on the water, does that mean it is lighter than the water?",it means that they are not heavy enough to break the hydrogen bonds between the water molecules
Cohesion and adhesion of water,Is an example of Adhesion when you drink a glass of water and there is still water droplets still stuck to the inside of the glass?,"If the cup is polished to the perfection then the droplet should roll all the way down to the bottom of the cup. This should happen because an isolated droplet stuck to the wall of the cup is surrounded by glass in all directions, so, not only the glass over the droplet is attracting it, but also glass under the droplet. The fact is that cups that we use to drink are not perfect. They have grooves, bumps and notches caused by production itself, or by washing it, or by entering in contact with other tableware, whatever... these imperfections plus adhesion are what makes the droplets that we see possible."
"Specific heat, heat of vaporization, and density of water","In this paragraph of heat of vaporization I got a bit confused by these numbers: "Water’s heat of vaporization depends on the temperature: it's around 540 cal/g at 100 °C (water's boiling point) and around 580 cal/g at 25 °C (room temperature)." 
So in room temperature it needs only (?) 40 calories more to heat up 1C as it takes in the boiling point?  How come there is such a tiny difference, or is it actually a huge difference?","Yes, that part is not very clear. How come only 40 calories can increase the water temperature by 75 degrees to its boiling point, if the specific heat property tells us that 40 calories can only increase it by 40 degrees?

The relationship is non-linear. Remember that when you apply energy to water, some of it will increase the avg kinetic energy of the molecules (related to the temperature) and some will be spent to break off all hydrogen bonding and send the molecules flying away (related to heat of vaporization at a GIVEN temperature). 

You don't need to wait until 100 degrees for vaporization to begin. It occurs more and more as you near towards it. And as more molecules fly off, less energy is needed to break off the remaining bonds. That's why the difference between heat of vaporization at 25C (energy required to break all H-bonds between 1 gram of initially slow moving molecules) and at 100C (energy to break all H-bonds of 1 gram of fast molecules) is LESS then the energy required to make all of those 1 gram of molecules faster."
"Specific heat, heat of vaporization, and density of water","In the last paragraph it says: "In lakes and ponds, a layer of ice forms on top of the liquid water, creating an insulating barrier..."

How does ice provide an insulating barrier?","Awesome question. Part of the answer is that less dense materials conduct less heat, and thus slow down heat transfer. If you think about using a metal vs wooden spoon in a hot pan of water, it's the metal one that will burn you, because it is more dense and a better conductor of heat. So the transfer of heat from water to air is slowed down by the layer of ice. Another part of the answer is the ice prevents evaporative cooling, the liquid water molecules become physically trapped and so the ones with the highest kinetic energy can't escape, which would reduce the overall average kinetic energy and thus temperature of the water (see Sal's video on evaporative cooling). Because this doesn't happen with the layer of ice in the way, water can stay warmer for longer."
"Specific heat, heat of vaporization, and density of water","But why is the distance between molecules in ice bigger than in water? They are still, but why not close enough to each other to make a dense body?","This is because when water goes lower than 4 degrees celsius it expands. Meaning the molecules are further apart. So when water reaches 0 degrees celsius it is frozen at an expanded state. And since it is frozen at an expanded state with molecules further apart, it is less dense than water which has it's molecules closer together."
"Specific heat, heat of vaporization, and density of water",Why do the fastest-moving molecules leave the liquid?,"The higher the speed, the greater the movement, the larger the likelihood that the particle will ricochet off the container or another particle in just the right way to escape."
"Specific heat, heat of vaporization, and density of water",What if you drop a solid into a liquid and they both have the same density. Will the solid float or sink?,The solid would be suspended in the middle of the liquid without moving.
"Specific heat, heat of vaporization, and density of water",what is the difference between heat and temperature?,Heat is how fast the molecules are moving in a given object. Temperature is the way we measure heat.
"Specific heat, heat of vaporization, and density of water",Why is water’s high heat of vaporization important?,"Water's high heat of vaporization is important because it helps to moderate the temperature of the ecosystem. When water goes through the water cycle (evaporation, condensation, precipitation), at the stage of precipitation, heat is released, and rain falls."
"Specific heat, heat of vaporization, and density of water","At the surface of a liquid, why do some molecules evaporate but others do not?","The layer which is most closer to the air, interacts with air molecules.


Rest of molecules cannot eadily evaporate because cohesion forces are *stronger* than cohesion forces."
"Specific heat, heat of vaporization, and density of water",do these relate to adhesion?,it would be cohesion as its talking about water molecules only and not an external body like glass.
N/A,"The first sentence of the section "The structure of an atom" reads: "An atom is the smallest unit of matter that retains all of the chemical properties of an element. For example, one gold atom has all of the properties of gold and is still a solid metal at room temperature."

My question is, how can just one atom be a liquid or sold or gas, etc? won't it still look and act the exact same no matter what state it's in? It still has electrons and a nucleus. What would the change look like on the atomic level in these different states?","Thanks very much to everyone who noticed this problem and upvoted or commented on it. You're absolutely right that there is no meaningful way to classify an individual atom as a solid, liquid, or gas, as these terms are based on interactions between atoms or molecules.

I've corrected that paragraph to reflect that the gold atom is still considered gold because it has the same chemical properties as a larger quantity of gold (thanks to having the set of subatomic particles, specifically protons, that define gold at the atomic level). The correction should be live on the site later today.

If that section is still unclear, or if you have any other comments or suggestions, please don't hesitate to ask here (or to report issues with the "Report a mistake" button).

Thanks again for noticing this!"
N/A,"In the fourth paragraph, it says "There are 118 elements, but only 92 occur naturally. The remaining elements have only been made in laboratories and are unstable." Why are the elements made in laboratories unstable?","There are several forces at work inside the nuclei of atoms. The electromagnetic force of the protons wants to push them away from each other. Fusion allows these protons to get close enough together for the stronger, yet short ranged, nuclear force to overpower the electromagnetic force. Neutrons will help add to this nuclear force, but they tend to become unstable when they get into too great of concentration and the weak force will cause them to decay into protons. 

With all of that to consider, as you get larger and larger nuclei with more protons, the electromagnetic forces increase, as well as the distances in the nuclei, putting more strain on the nuclear forces holding it all together. The ratio of neutrons to protons gradually increases to try to compensate, but this results in the neutrons getting more unstable themselves, resulting in more opportunity for weak forces to destabilize them. Hence, larger atoms become more unstable. 

There are believed to be certain numbers/ratios that are inherently more stable. These are called magic numbers. It's thought that another one of these magic numbers lies just beyond the range of currently known elements, which means we could potentially discover some new elements that are relatively stable and extremely massive."
N/A,What is the specific difference between atoms and molecules?,Molecules are made up of two or more atoms.
N/A,The last paragraph said that the electrons will repel each other if they get too close and resulting in our perception of solidity...what does that mean..can someone explain to me thx a lot,"Since electrons have like charges,they repel each other (much like a magnet).This results in our idea of solidity."
N/A,"The only thing that has always confused me about atoms, is, how can nonliving atoms make up living things? If you look at the world at the subatomic viewpoint, does that mean nothing is alive? I mean, I get how living things are living and the defining properties of a living organism make sense to me, but if you talk about atoms, doesn't that mean we are living, but only to a point?",How can atoms form a computer or an Egyptian pyramid or a novel? These are examples of what is known as an emergent property -- a property possessed by a group that is not present in any individual making up that group. Life is an emergent property.
N/A,I'm very interested in the whole idea of our perception of solidity (last sentence).  Does this mean that the reason I cannot punch through a wall is because the atoms making up the elements of matter in the wall are repelling the atoms making up my body (more specifically my fist)?,"Exactly! It sounds surprising (I couldn't believe it when I first learned about it), but it's true."
N/A,What do you mean by perception of solidity  and explain with an example?,"Imagine a stack of books, the atoms of the books aren't able to pass through each other because of the electron clouds that surround their nucleus. The electron clouds repel each other because the forces aren't attracted to one another.

Since they don't pass through each other, this gives us our perception of solidity, and why solid objects won't pass through each other."
N/A,So water is a main element in our body right?,"Water is not an element but a molecule but it is the most common molecule in our bodies. 
Oxygen is the most common element _by mass_ (43% of all weight; carbon is 16% and hydrogen is 10%) in the body. The most common element _by number_ is hydrogen (62% of all atoms; water is only 24% and carbon is 12%)."
N/A,What's smaller: A proton or a neutron?,"Proton, by very little, is smaller."
Hydrogen bonds in water,what is used to break hydrogen bonds in water?,"In addition to heating water, you can use an electric current. Check out splitting water experiments online."
Hydrogen bonds in water,What is a partial positive or partial negative charge ?,"When one atom "shares" an electron with another atom to form a molecule, the atom with higher electronegativety (electron-greedy) will keep the shared electrons closer to itself than to the partner-atom. Since one atom gained an electron and keeps it near itself, the atom receives a "partial negative charge." It isn't fully charged because the molecule is neutral due to its balance of negative and positive regions. 
p.s. More electrons = negative charge, fewer electrons = positive charge."
Hydrogen bonds in water,"Could someone explain what a polar molecule and bond are? I'm not great at science in general, so I don't understand what a polar molecule is and why water is a polar covalent bond is.","a bond is when 2 or more elements combine chemically and create a molecule. Elements bond either by sharing or transferring electrons. When a bond is formed by sharing electrons, it's called a covalent bond. sometimes the electrons in a covalent bond are shared unequally which causes some parts of the molecule to be partially positive and other parts to be partially negative. When this happens, its called a polar molecule. In water, the oxygen atom gets the electrons more frequently than the two hydrogens because of unequal sharing. This causes the side of the molecule with the oxygen to be partially negative and the side with the hydrogens to be partially positive, making water a polar covalent molecule. hopefully that helps  :)"
Hydrogen bonds in water,Is every hydrophilic molecule polar?,"That is generally a safe assumption, but should not be regarded as a "law".  

An example that doesn't fit this rule perfectly is `CO₂`, which is non-polar, but still somewhat soluble in water — this is in part because it reacts with water, but also because of weak effects due to the presence of polar bonds within this non-polar molecule.

Also, note that hydrophilicity and polarity are both continua, so there are many molecules that are in the middle of both of these scales.

There are also many polyatomic ions (not formally molecules since they have charges) that are very hydrophilic, but also completely non-polar because they are symmetrical.  Examples include: ammonium (NH₄⁺),  sulfate (SO₄²¯), carbonate (CO₃²¯), and oxalate (C₂O₄²¯).

It is also worth remembering that single atom ions (e.g.s `Na⁺`, `Cl¯`, `Mg²⁺`) are hydrophilic but not polar."
Hydrogen bonds in water,what is the reason to bond,"Polar molecules, such as water molecules, have a weak, partial negative charge at one region of the molecule (the oxygen atom in water) and a partial positive charge elsewhere -(the hydrogen atoms in water). Thus, when water molecules are close together, their positive and negative regions are attracted to the oppositely-charged regions of nearby molecules which makes it bond! and even the answer- to become neutral is also correct! for more information visit-http://www.biology-pages.info/H/HydrogenBonds.html"
Hydrogen bonds in water,Every Organism is 60 to 70 percent water . Then Why am I not fluid? Why my bones Are Solid?,"Most of your cells are filled with cytosol, which is water. Your bones are made from cells called osteoblast, they arent cells, but a type of cement made by these cells. Your epidermis (skin) holds all the water in you together. Your blood cells have water, your muscles have water, your neurons have, water. Most of you is water. I hope that makes sense and helps :)"
Hydrogen bonds in water,how does water come around  the cycle,"The water cycle, in the simplest form, is evaporation, condensation, and precipitation. 
Evaporation: When the temperature raises high enough, the water particles begin to move faster and gain more kinetic energy. As they move faster, the particles spread out in all directions. This spreading converts the water into a gas, or water vapor.
Condensation: The temperature slowly or slightly drops to where the water vapor's particles begin to slow. The decrease in speed makes the particles come closer together, making small droplets.
Precipitation: When the droplet or cloud gets full with water, the density makes the water fall, making it rain. If the temperature is cold enough, the rain droplets will freeze as the particles slow, making snow.

I hope that helps!"
Hydrogen bonds in water,How many Hydrogen bonds can water theoretically form at one time and why?,"Have a look at the Lewis structure for a water molecule — in how many places do you think a hydrogen bond could form?

It may help to remember that hydrogen bonds typically form between a hydrogen atom that is covalently bonded to F, O, or N and a lone-pair of electrons on an electronegative atom.  

For details see this free online book chapter:
https://en.wikibooks.org/wiki/Structural_Biochemistry/Chemical_Bonding/Hydrogen_bonds

Does that allow you to answer your question?"
Hydrogen bonds in water,am confused why is oil hydrophobic?,"Oil is hydrophobic, because it is a nonpolar molecule. Thus, they will not have the same attraction, as a polar molecule."
Lesson summary: Water and life,So water is a covalent or ionic bond?,"Water has a polar covalent bond, in other words, it is covalent but oxygen is more electronegative than hydrogen so it pulls the electrons to it, giving oxygen a slight negative charge and hydrogen a slight positive charge. Good question!"
Lesson summary: Water and life,What is diffusion and give some examples,"Diffusion is a type of molecular movement that brings water particles from places of high concentration to low concentration. There really are 4 different types. Simple Diffusion, Osmosis, Facilitated Diffusion and Active transport."
Lesson summary: Water and life,I think water is a covelant bond,"Yes, it is a polar covalent bond. That means that while the atoms are "sharing" the electrons, the oxygen hogs them a bit closer, creating a partial negative charge on that side of the molecule, and a partial positive charge on the Hydrogen side"
Lesson summary: Water and life,why is O electronegative?,"To say that oxygen is electronegative fails to grasp the whole picture here. This is because ALL elements (except for the noble gases) are electronegative to some degree or other; ELECTRONEGATIVITY IS A PROPERTY OF THE ELEMENT which basically says "how strongly does it attract electrons?"

An element's electronegativity value is determined by a mixture of different factors, but the general rule is that it increases as you move right and upward across the periodic table. (Copy-&-paste this link for a visual: www.chemteacher.chemeddl.org/joomla/index.php?option=com_content&view=article&id=91)

So as for oxygen, (which was the subject of your question) it's electronegativity would indeed be one of the highest among all the elements because of where it is positioned in the periodic table (but more specifically because the factors that I alluded to earlier are manifest for oxygen in such a way as to make it such)."
Lesson summary: Water and life,"I still don't quite get the meaning of adhesion and cohesion, and the difference between them. Can somebody help me out?","adhesion is an attraction to unlike molecules, and cohesion is an attraction to like molecules."
Lesson summary: Water and life,which property allow solid ice to flot in liquid water,"One property of water is that it crystallizes when it freezes, that is it arranges itself in a particular formation whenever it freezes. This formation happens to be less dense than its structure when it is in liquid form. It is this property that allows ice to float. Hope this helped!"
Lesson summary: Water and life,"I'd like to know about the different types of bonds, like Sal mentioned Ionic Bonds, Covalent Bonds and Hydrogen Bonds, but what exactly are they?","A Covalent Bond is where atoms share eletrons, A ionic is an atom steals an eletron from another atom, giving it to the opposite charge, thus the atoms are attracted to each other. A Hydrogen Bond: A weak bond betweeen to molecules resulting from an electrostatic atrraction between a proton in one molecule and an electronegative atom in the other.   Hope this helps,"
Lesson summary: Water and life,"I have a question, what will happen if acids, fire and water combine together?","Its not as exciting as you think it would be. if you put something like lemon juice on a fire, it will most likely go out, same with water. I hope this helps."
Lesson summary: Water and life,what exactly is an ion,"an electrically charged atom or group of atoms formed by the loss or gain of one or more electrons, as a cation (positive ion), which is created by electron loss and is attracted to the cathode in electrolysis, or as an anion (negative ion), which is created by an electron gain and is attracted to the anode."
Introduction to macromolecules,Can you have a polymer made of different macro molecules? Like a carbohydrate bonded to a protein?,"You mean like a _glycoprotein_? Yes, but then it is just one (even larger) macromolecule"
Introduction to macromolecules,Don't you just love biology?,Yes! It's wonderful and fascinating!
Introduction to macromolecules,Why are lipids polynomials,Do you mean polymers?
Introduction to macromolecules,Are glycogen molecules stored in every cell of the body or only in liver cells or other cells specialized for storing it? If it is only stored in certain parts of the body then is it broken down into glucose before it is transported to other cells for use?,"Glycogen is also stored in skeletal muscle cells for use by those cells. Muscle cells can break down glycogen but lack glucose-6-phosphatase, the enzyme that is needed if glucose is to enter the blood stream to be used by other cells.

Glycogen is also stored by other tissues in amounts smaller than in muscle."
Introduction to macromolecules,How are Hydrocarbons related to Macromolecules? Are they considered to be macromolecules or are they closely related?,"A hydrocarbon is a type of macromolecule. Basically a macromolecule is a "big molecule". Hydrocarbons are just a chain of carbon atoms with hydrogens bonded to all the carbons (hence, hydro-carbon). So, a big chain of carbons and hydrogens is a type of macromolecule. There are other types of macromolecules, but since most are organic (consisting of mostly carbon), hydrocarbons are used as an example."
Introduction to macromolecules,"The article states that "Dehydration synthesis reactions... generally require energy, while hydrolysis reactions... generally release energy." However, in chemistry we were drilled that breaking bonds requires energy and creating bonds releases energy; how would these guidelines mesh?","The breaking of bonds does require an input of energy, while the formation of bonds results in a release of energy. This is true for all reactions. But then we also have to concern ourselves with the magnitude of these energy inputs and outputs. It’s possible for a reaction to release more energy in bond formation than was put into it for bond breaking, and vis versa. 

We formalize this phenomenon in chemistry with the idea of enthalpy, or specifically the change in enthalpy. Reactions which release more energy than they take in are referred to as exothermic, and reactions which release less energy then they take in are referred to as endothermic. 

Hope that helps."
Introduction to macromolecules,what are macromolecules?,"There are four classes of macromolecules that constitute all living matter: carbohydrates, lipids, proteins, and nucleic acids. While they have different structures and functions, they are all composed of long complex chains of molecules (polymers) made up of simpler, smaller subunits (monomers). They are joined together in a process known as dehydration synthesis, in which a covalent bond is formed between two monomers by releasing a water molecule."
Introduction to macromolecules,"are there any other macromolecules apart from carbs ,fats,protiens and nucleotides","To some extent that depends on how you choose to define macromolecule, but those are (representatives of) the four groups that are usually considered to be biological macromolecules.

The second group is actually lipids, which includes compounds like steroids that are not fats.

The last group is nucleic acids — nucleotides are the monomers that make up nucleic acids.


Other than these there are many biological macromolecules that contain parts from two (or more) of these types.  Some examples are:
• glycoproteins — proteins with attached carbohydrate chains
• lipoproteins —  proteins with attached lipids
• lipopolysaccharides — carbohydrates with attached lipids


There are also many (usually) synthetic (i.e. artificial or "man made") macromolecules such as plastics, and allotropes§ of carbon (e.g. graphene and carbon nanotubes).

§Note: see — https://en.wikipedia.org/wiki/Allotropes_of_carbon"
Introduction to macromolecules,So lipids are macromolecules but not polymers? Is that even possible?,"Yes, macromolecules are large molecules that are formed by the joining of smaller units. Lipids fit that description, but they aren't polymers because they are made up of smaller units of different kinds (like glycerol and fatty acids) rather than monomers that repeat themselves."
Introduction to macromolecules,What are the four macro-molecules in living things?,"Proteins, lipids, carbohydrates, and nucleic acids."
Active transport,"Questions:
1. How is the energy from the sodium ions transferred to the sodium/glucose symporter?

2. Does the energy from the sodium ions increase the affinity of the symporter to actively collect glucose? or does the symporter simply wait for a glucose to fall into place in its own time?

3. Can the symporter be activated by two sodiums without a glucose present? if not, does the symporter store energy from sodium ions until a glucose arrives? or do the sodium ions and glucose need to interact with the symporter simultaneously?","1) The "sodium/glucose symporter", known as SGLT (sodium glucose linked transporter), receives the energy needed to perform its transport from the electrochemical gradient established by the sodium/potassium pump. Because of the difference in sodium concentration (between the inside and outside of the cell) and due to the electrical potential difference (between the inside and outside of the cell), the SGLT is able to perform its function.

2) The affinity of the symporter to collect glucose is not dependent on the sodium concentration, but rather the concentration of glucose (you can imagine there would be a higher probability of glucose being able to cross the system if more glucose was near the system). The purpose of the sodium ions is to establish the electrochemical gradient which provides the energy for the SGLT to perform its function.

3) The exact mechanism for the transporter is not fully understood - the diagram, which indicates 2 sodium ions and 1 glucose ion, is meant for gaining a conceptual understanding of the system. If you're curious about the topic, I have linked an article and a video below. SGLT is typically seen in action in the intestines and kidneys.

http://physrev.physiology.org/content/91/2/733
https://www.youtube.com/watch?v=jCdJyUHqJhM"
Active transport,"how does the antiporter provide energy for molecules to go in the "opposite" direction? in a symporter it makes sense that the flow of one ion should cause other molecules to go along with it, however in an antiporter, what causes the other molecule to move up its conc. gradient?","In an antiporter it uses the energy of the ions flowing down their concentration gradient. Imagine this just like a hydroelectric power station uses the energy of water flowing down the waterfall to create electricity. This electricity can do work.
In case of the cell the energy is used directly to move the other molecule out of the cell against it´s concentration gradient."
Active transport,"if there are more Potassium ions in a cell, how is the cell negatively charged? shouldn't it be positively charged? this is in relation to the electrochemical gradient section. thank you","There are certainly more numbers of potassium ions in the cells, but remember that there are greater numbers of sodium ions outside the cell (since for every three sodium ions moved out of the cells, two potassium ions enter the cell), therefore, resulting in a net positive charge outside the cell and net negative charge inside the cell."
Active transport,"Hi, I'm just a little curious, why can't 3 potassium ions be pumped out and 2 sodium ions pumped in(the other way around)? Can't that serve the same role?","No, because the potassium is highly concentrated in the cell, and so that's where the molecules must go(based on active transport going low concentration to high concentration). And sodium is highly concentrated outside of the cell, so that's where it goes during active transport considering it is low to high concentration.
Hope this helped:)"
Active transport,"why wouldnt cells use atp for primary active transport of glucose directly, why go through a second step?","Because it is faster to utilize already available ATP through the electrochemical gradient. Also, it is spatially more available than in the case of ATP."
Active transport,i dont quite understand the secondary active transport. how does the carrier protein "harness" energy from another molecules concentration gradient? does the glucose molecule just randomly attach itself to the protein when it's about to transport a sodium ion to the other side?,"If for example there are alot of sodium ions outside, their positive charges will repel and like atoms don't like being near eachother so they flow to the other side if there's a way to. Active transport works by using a phosphate group from ATP to change the shape of the protein and thus do work."
Active transport,"what is the main difference between active transport using a carrier protein, and passive transport using facilitated diffusion?","Main difference: In facilitated diffusion, the solute moves down the concentration gradient, from regions of higher to lower concentration, relying on the specificity of the protein carrier to pass through the membrane. This process does not require energy. Conversely, in active transport, the solute moves against the concentration gradient, from regions of lower to higher concentration. This process requires some form of chemical energy."
Active transport,why do cells need membrane potential?,"Hi, your question is about to be answered after 2 years.
Cells need electrochemical gradient because that's what powers secondary active transporters, such as symporters or antiporters.
I hope you're still on Khan academy, because the key to success is to never stop learning ;)"
Active transport,what's the difference between the primary and secondary active transport?,Primary active transport uses energy that comes directly from ATP hydrolysis. Secondary active transport uses the energy from another chemical gradient that was itself created through active transport and ATP hydrolysis.
Active transport,can I be lost?,"I don't understand what you mean. I mean, yes, you could be lost if you wander off on your own in a mall or museum or so forth, but I'm pretty sure that's not what you mean."
Active transport review,is sweating a form of active transport,I think that sweating is a form of passive transport as heat that is generated in the cells inside your skin is moving WITH the concentration gradient from hot (inside) to cold (outside). I think that's right. I haven't yet studied the videos on perspiration.
Active transport review,What is the difference between facilitated diffusion and active transport?,Facilitated diffusion is a type of passive transport and along the gradient. Think of a pipe connecting a full tank of water to an empty one. Active transport is against the gradient. Think of a pump moving water from a nearly empty tank to an almost full one.
Active transport review,Are the largest molecules moved by only active transport or also by passive?,"No, actually both facilitated diffusion and active transport occur. When the molecules moving from high to low conc. like Glucose is very large, then we need channel proteins to move them into the cell, and channel protein only because they have the shape and structure to do so, so that the movement is only unidirectional (into the cell). Active transport transports or moves materials against the concentration gradient, that is, from low to high, and the size doesn't matter here like facilitated diffusion, only the concentration."
Active transport review,What is importance of active transport ?,Active transport is important because it allows substances to move against the concentration gradient. This helps it maintain the appropriate balance of substances in the cell.
Active transport review,"How do carrier/channel proteins select which particles to pass through and when?
More specifically,
How do aquaporins only let water in? How can the cell control the amount of water that can diffuse through aquaporins? How come the channel protein will not bring in potassium ions when it needs to bring in sodium ions?","Hi ! The shapes of the channels is very specifically adapted to letting only one type of molecules through. For example, aquaporins are shaped in a way that only water can pass through (because water has a specific structure and charge). Sodium and potassium do not have the same size nor shape and therefore one cannot use the channel of the other as well. 
The cell can control the amount of water that it lets in or out, by controlling the amount of aquaporins in its membrane. This is done by exocytosis/endocytosis of aquaporins, that can be controlled for example by antidiuretic hormons (that tend to provoke endocytosis of aquaporins)."
Active transport review,"How does the carrier protein change shape? Can the protein somehow bend, or does it chemically change?",The protien changes shape by using ATP energy. And no it cannot bend
Active transport review,I don't understand active and passive transport i need help.,Active transport uses energy to transport molecules across the plasma membrane. This uses energy from ATP. They also use pumps to get molecules in or out of the cell. Passive Transport does NOT use energy to transport molecules across the membrane. This can also just be molecules diffusing across the permeable membrane or a direct channel which they can enter or exit.
Active transport review,"what actually makes particles move down the concentration gradient? as in, why are particles by random motion able to passively move into an area of low concentration?? how can random motion lead to an overall non-random outcome??","The movement of particles is random, but even with that randomness, particles have a high probability to move from the area with high concentration to an area of low concentration. 

A good example would be if you get some small objects and assign them into two groups (A and B for example). However, you add more objects to group A than you do to group B. Then, for each object flip a coin. If the coin comes up as heads, keep the object in its assigned group. If the flip is tails, move the object to the opposite group. Once you're done, no matter how many more objects you put in group A then B, you should have a roughly equal distribution in each. 

This isn't a non-random outcome, it's just how probability works. The chance of an object moving from group A to group B is greater only because there are more objects in group A and therefore more chances to move to the other group."
Active transport review,"What are the differences between a carrier and a channel protein? Also, what are some examples?","Channel proteins are proteins that create hydrophilic holes in cell membranes, facilitating the transport of molecules down the concentration gradient. Carrier proteins are integral proteins that transport chemicals across the membrane both down and up the concentration gradient
 Some examples of channel proteins include chloride, potassium, calcium, sodium ion channels, aquaporins, etc. Examples of carrier proteins are sodium-potassium pump, glucose-sodium cotransport, valinomycin, etc."
Active transport review,what is hydrophillic and hydrophobic? Please answer,"Hydrophilic means a molecule or part of a molecule is _attracted_ to water. Hydrophobic means the opposite, it _repels_ water."
Diffusion and passive transport,Why no energy is spent on switching the carrier proteins?,"These carrier proteins are gated trans-membrane proteins and do not require ATP (adenosine triphosphate) to function. The gate is activated due to the concentration gradient of its target molecule. The target molecule binds to the gated carrier protein and, in response, the carrier protein opens up - this allows the target molecule to enter. The carrier protein then changes shape and releases the target molecule into the cell. It waits in its closed position, once again, until it is activated by the binding of its target molecule (outside of the cell). Therefore, no energy is spent switching shapes. The shape change only occurs due to the binding of the carrier protein's target molecule, in accordance with a concentration gradient."
Diffusion and passive transport,What is the difference between simple diffusion and facilitated diffusion?,Simple diffusion is the movement of molecules through a cell membrane without using the channels formed by integral membrane protein. Facilitated diffusion is the movement of molecules through those channels.
Diffusion and passive transport,"Can carrier proteins move molecules from the inside to the outside? Also, is it possible to replace carrier proteins with channel proteins that are specific to the same molecules? Channel proteins is faster, and you can still precisely modulate how much goes in and out by gating.","Yes and it depends but generally yes
the big thing to keep in mind is that many of these gates are evolving randomly. So getting the most efficient solution while inevitable is not going to happen quickly so if it works it works. Also keep in mind that for larger molecules (think an enzyme or a long carbon chain) the channel would have to be very large meaning that a lot of things could flow out on accident due purely to the size of the pipe. So using a gate instead keeps internal pressure while also heavily regulating the release of the molecules."
Diffusion and passive transport,"I noticed that according to the quiz (Practice: Passive transport) sodium, potassium, and calcium can't move through the channel proteins. In this article mentioned nerve and muscle cells in which channels can pass sodium, potassium, and calcium. Maybe it was about active transport, but this article about passive transport. It is strange, I had some troubles in the quiz because of it. Can somebody explain this stuff?","Yes , i also think that question is wrong. There are channel proteins in the body for transport of those ions.
Sodium : Voltage gated Channel Proteins in Neurons for propagation of nerve Impulse.
Potassium : There are Leaky Channels inside nerve cells ...refer Nerve trnsmission videos of Khan Academy itself.
Calcium : In smooth muscles of the Body...there are Voltage Gated Calcium Channels Present."
Diffusion and passive transport,the topic states above that "a concentration gradient itself is a form of stored (potential) energy" please explain this?,"A concentration gradient will cause movement of molecules from high concentration to low concentration. Therefore, it is a driving force for the movement and thus can be considered as energy."
Diffusion and passive transport,"If a molecule wanted to diffuse across the plasma membrane, but wasn't able to make it all the way through,  what would happen to it? Would it eventually work its way in, or would it get stuck in the membrane?","Interesting question, I don't know if anyone has looked into whether membranes might get "gummed up" by material getting stuck part way through.  

One interesting example I was able to find are the persistent organic pollutants known as PCBs (polychlorinated biphenyls) — these bioaccumulate and at least in some cases are known to disrupt membranes:
https://academic.oup.com/toxsci/article/80/1/54/1674897

Membranes are incredibly dynamic.  Vesicles are constantly leaving and joining each membrane.  In addition, membrane molecules (e.g. phospholipids) move between the two layers§ — for example the lipid composition of the inner and outer layer of the plasma membrane is quite different on most cells .  This very tight control of membrane composition suggests to me that there are probably mechanisms for clearing out bad/contaminated sections of membrane.

If this sort of thing interests you, you might want to consider going to grad school :-)

§Note: This is done by enzymes called flippases and floppases, just in case you were wondering if biologists had a sense of humor!"
Diffusion and passive transport,"What is faster, a simple diffusion (of oxygen, for example), or a facilitated one (of water through aquaporines)?","I don't think there is a general rule (leaning toward facilitated but I have counter examples too).
However, you cannot use passive diffusion to move things from low concentration to high concentration but you can do this with facilitated/active. Depending on the difference in concentration, the simple/passive diffusion will vary while facilitated diffusion can move against concentration gradients and if affected by other conditions too."
Diffusion and passive transport,What is osmosis,The movement of water across a concentration gradient.
Diffusion and passive transport,if particles moves from low concentration to higher concentration can we call it the concentration gradient of that substance as the concentration changes?,"Careful: it moves from HIGH to LOW, not the other way around.
That said, this is also the definition of a _gradient_: it changes as you move from high to low. 
Using a real life example of gradient: lets say you are in a dark room and then you turn on one lightbulb. The light will have a gradient too because the closer to are to the lightbulb, the brighter it becomes (high concentration of light) and the further you move away, the less light there is (low concentration of light). The differences in light intensity is a gradient."
Diffusion and passive transport,Which of these cells can help to move and transport blood,"Blood is a cell, not a particle. That means that it could not be diffused. It actually gets transported by blood vessels, which are long chains of muscle cells."
Mitochondria and chloroplasts,Would it be possible for a modern day cell or organism to capture one of these cells and start a new symbiotic relationship with the host cell?,"That is an intriguing question. The origin of mitochondria is thought to have been a very rare event. The mitochondria seem to have their origin from one particular family of bacteria (the alpha-proteobacterium ) which are related to some existing bacteria. There are people trying to build cells so I guess maybe someone could try to create a modern endosymbiosis event.

There are many theories as to how eukaryotes came about. If you want to know more; see this paper: Endosymbiotic theories for eukaryote origin http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4571569/"
Mitochondria and chloroplasts,It would be so cool if we could recreate endosymbiosis and incorporate chloroplasts in human cells so we could photosynthesize,"i hate to ruin your guys fun but i think we would die, if you put chlorophil into our bodies."
Mitochondria and chloroplasts,"1) Are there any animals that have chloroplasts? Or are they only in plants?

2) If they are only in plants, would it be possible for an animal to have chloroplasts, chemically speaking?","Well according to modern classification, the organisms which have chloroplasts in them and have an advanced nucleus are called plants. Those organisms which show both plant and animal features(like Euglena) are kept in Kingdom: Protista
As for your second question, as Biology is science of exceptions we cannot publish any definite law. So in future, due to evolution, there may be animals with chloroplasts."
Mitochondria and chloroplasts,is peroxisomes needed in a cell,"Before the ancestor of mitochondria entered the eukaryotic cells, Peroxisomes were asource of power to the cell. They used to break down H2O2(Hydrogen Peroxides) and would form water and and energy. But now, there only function is detoxification as the energy produced by mitochondria is much more than the energy produced by the peroxisome. So, peroxisomes are sort of vestigial organelles which had a major function in the past but aren't so useful in the present age.."
Mitochondria and chloroplasts,"If mitochondria and chloroplasts evolved from bacteria, what did the cells use for energy before?  Isn't this a case of you can't have the one without the other?  Wouldn't the cell/animal/plant die without the energy from the chloroplast or mitochondria?",Before mitochondria and chloroplasts became part of cells they had their own ways of producing energy from metabolizing food around them. These older methods of producing energy were lost along the way because the mitochondria and chloroplasts were better at it and it was a waste of resources to have the two ways of producing energy so the cells that eliminated the older way were more efficient and survived better that the ones that didn't.
Mitochondria and chloroplasts,"In the endosymbiotic theory, what was the factor that decided that the chloroplast wouldnt converge with the other cells present on earth, so that there would be two types of cells, 
1. plant cells
and 
2. animal cells","It just happened this way. Some phytoplankton probably merged with chloroplasts prokaryotic cells and absorbed them and formed a symbiotic relationship with them and also with mitochondria (they have both organelles), and some zooplankton probably got the short stick and managed to form symbiotic relationship only with mitochondria prokaryotic cells and from them out ancient common ancestor was created..."
Mitochondria and chloroplasts,"Most antibiotics inhibit bacterial ribosomes... so, would antibiotics have an effect on mitochondria when taken?","Some of them may, if the antibiotics manages to get all the way through all the membranes to the mitochondria itself (which is not an easy way). 
If they do get into mitochondria, it may not be a big deal since most of mitochondrial proteins are made by eucariotic cell and then transported into mitochondria, only few proteins are made by mitochondria itself.
Actually it seems that some antibiotics do harm mitochondria, so these usually aren't used as long as there is some harmless alternative."
Mitochondria and chloroplasts,Do stand-alone chloroplasts and/or mitochondria still exist in nature as prokaryotes (Outside of a eukaryotic cell)?,"Yes§, this is part of the evidence supporting the theory that these (and possible some other organelles) arose through endosymbiosis (aka symbiogenesis).

The group of bacteria from which mitochondria seem to have evolved are the Alphaproteobacteria.

Chloroplasts appear most closely related to the cyanobacteria.

You can read more about this here:
https://evolution.berkeley.edu/evolibrary/article/_0_0/endosymbiosis_01 _

You might also find these interesting:
https://biologos.org/blogs/dennis-venema-letters-to-the-duchess/evolution-basics-endosymbiosis-and-the-origins-of-mitochondria-and-chloroplasts
https://biology.stackexchange.com/questions/43372/origin-of-the-double-membrane-of-mitochondria-and-chloroplasts

§More correctly, there are other descendants of the progenitor of these organelles that have remained as free-living organisms."
Mitochondria and chloroplasts,"Does this mean that when you eat vegetables, you are you eating light energy?","Yes, pretty much. In fact you could say you're eating the energy produced in the fusion reactions occuring inside of the Sun's core."
Mitochondria and chloroplasts,"Have they proven endosymbiosis to be the reason why mitochondria and chloroplasts contain their own DNA and ribisomes? I am very blown by the idea that the mitochondria in our bodies were once bacteria and, if they really are bacteria before,we now have a gazillion of them.","Proof is an elusive concept in science, but this theory is now generally accepted as the best explanation for multiple observations.  

Another piece of evidence supporting the theory that these (and possible some other organelles) arose through endosymbiosis (aka symbiogenesis) is that if you make an evolutionary tree of the DNA within either of these organelles and bacteria, you find free-living bacteria that are closely related.

The group of bacteria from which mitochondria seem to have evolved are the Alphaproteobacteria — many of them are intracellular parasites, which suggests how they originally ended up inside the first eukaryotic cell.

Chloroplasts appear most closely related to the cyanobacteria.

You can read more about this theory here:
https://evolution.berkeley.edu/evolibrary/article/_0_0/endosymbiosis_01 _

You might also find these interesting:
•https://biologos.org/blogs/dennis-venema-letters-to-the-duchess/evolution-basics-endosymbiosis-and-the-origins-of-mitochondria-and-chloroplasts
•https://biology.stackexchange.com/questions/43372/origin-of-the-double-membrane-of-mitochondria-and-chloroplasts"
Bulk transport,"excuse me, can you tell me an example for pinocytosis ?",Cells in the kidney can use pinocytosis to separate nutrients and fluids from the urine that will be expelled from the body.Hope this helps!
Bulk transport,Amino acids are monomers of proteins and proteins such as receptor proteins are involved. Does that mean that individual amino acids can enter a cell through receptor-mediated endocytosis?,"I am not fully sure, but I believe Receptor Mediated endocytosis means that the proteins act like an enzyme, meaning that only a specific macromolecule can fit into the receptor. An individual amino acid means that it cannot bind to the receptor because it does not fully meet the qualifications of the specific receptor. Imagine a password that scans your body to verify your entry. If you come one day without an arm(missing some amino acids), then the scan won't recognize, thus you won't enter. Similarly, receptor mediated endocytosis works this way. Hope this helps"
Bulk transport,"in the first paragraph, a white blood cell's "work" is described. What happens when there are not enough white blood cells?","The body wouldn't be able to fight of infections and diseases, mainly because the white blood cells are the main line of immune defense. Thus causing illness disorders and in some cases death."
Bulk transport,what is a real life example of endocytosis?,"Let me give you a biological example of endocytosis :
1.   Absorption of nutrients in the intestine.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1353524/
http://www.ncbi.nlm.nih.gov/pubmed/7226201
These two pubmed articles might give some insight.
Just check the abstract ."
Bulk transport,How exactly do pathogens use receptor mediated endocytosis to enter the cell?,"The specifics are different for each pathogen, but in general a pathogen will have surface molecules that interact with the host cell receptors and "trick" the cell into initiating endocytosis.  Once the pathogen is inside a vesicle within the host cell it will sometime be able to break out of the vesicle§ and enter the cytoplasm where it can begin exploiting the host cell.

§ for example, enveloped viruses like the influenza viruses can fuse with the vesicle membrane to escape.

*References and further reading*:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4107984/ — very technical, but the figures give a decent overview

_Viruses:_
http://jcb.rupress.org/content/195/7/1071
https://www.nature.com/scitable/topicpage/how-viruses-hijack-endocytic-machinery-14364991

_Bacteria:_
https://www.frontiersin.org/articles/10.3389/fcell.2018.00001/full"
Bulk transport,Are all the vesicles used in all bulk transport all coated in clathrin (or clathrin coated) or is it only in receptor-mediated endocytosis?,"The formation of the clathrin-coating is vital in vesicle formation, clathrin causes the vesicle to form while SNARE proteins make sure that the vesicle will arrive in the right place. 

Vesicle formation without the clathrin mechanism seems possible (I found a paper discussing the possibilities from 1994: ''Endocytosis without clathrin'' by Sandvig and Deurs, you'll hit a paywall if you can't use a university proxy).

That said however, clathrin does play a vital role and will be involved in (almost) all bulk transport."
Bulk transport,What is a transmembrane protein?,"A transmembrane protein goes across the cell membrane, from the cytoplasm to the outside of the cell."
Bulk transport,Can a plant cell undergo endocytosis?,"Off course! Think of roots. How can they absorb nutrients from the ground, if not through endocytosis?"
Bulk transport,"If macrophages devour pathogens, how do they make sure that they win the fight? What if they themselves get infected by the virus since penetration seems to be so easy?","Macrophages are a type of immune cell that plays a crucial role in the body's defense against pathogens, including viruses. While it is true that macrophages can be susceptible to infection by certain pathogens, they have developed several mechanisms to minimize the risk and maximize their effectiveness in fighting off invaders. Here are some key aspects:

Recognition and Phagocytosis: Macrophages have surface receptors that can recognize specific molecules present on pathogens, such as viruses. Once a pathogen is detected, the macrophage engulfs it through a process called phagocytosis. This allows the macrophage to physically encapsulate and internalize the pathogen.

Degradation: Once inside the macrophage, the pathogen is targeted for destruction. Macrophages have specialized compartments called lysosomes that contain enzymes capable of breaking down the internalized pathogens. This helps to neutralize and eliminate the infectious agents.

Activation of Immune Response: Macrophages are capable of presenting antigens—fragments of the pathogens—to other immune cells, such as T cells. This presentation activates a more specific and potent immune response, coordinating the elimination of the pathogens.

Antiviral Defense Mechanisms: Macrophages can release antiviral molecules, such as interferons, which can inhibit viral replication and spread. They also produce reactive oxygen species and nitric oxide, which have antimicrobial properties.

While macrophages have these defense mechanisms, some highly adapted viruses can still evade or manipulate these responses, leading to macrophage infection. However, the immune system as a whole has multiple layers of defense. Other immune cells, such as T cells and natural killer cells, work together to eliminate infected macrophages and control the infection.

Additionally, macrophages can activate a process called apoptosis, which is programmed cell death. If a macrophage detects that it is heavily infected and unable to eliminate the pathogen, it may undergo apoptosis to prevent the further spread of the infection.

It's important to note that the immune response is a complex and dynamic process. The outcome of the fight between macrophages and pathogens depends on various factors, including the specific pathogen, the virulence of the infection, the overall immune status of the individual, and the coordination of the immune response.

Hope that helped!"
Prokaryotes and eukaryotes review,"I thought some prokaryotic organisms could be multicellular;such as blue green algae, isn't that a multicellular prokaryotic?",There are some cyanobacteria that form filaments with a differentiated cell type that fixes nitrogen and 'normal' photosynthesising cells. It's a form of symbiosis that could be classified as multicellular.
Prokaryotes and eukaryotes review,How can eukaryotes be multicellular? Aren't they cells on their own?,"A eukaryote is an organism with complex cells, or a single cell with a complex structures. In these cells the genetic material is organized into chromosomes in the cell nucleus. Animals, plants, algae and fungi are all eukaryotes. There are also eukaryotes amongst single-celled protists.  Unlike unicellular archaea and bacteria, eukaryotes may also be multicellular and include organisms consisting of many cell types forming different kinds of tissue. Prokaryotes are  singled cell organisms."
Prokaryotes and eukaryotes review,"I read on another article here on Khan Academy that prokaryotic cells can organize to form something that resembles a multicellular organism, and that it can be discussed if that's multicellular or not. So how can prokaryotes "always" be unicellular?

Source: https://www.khanacademy.org/science/high-school-biology/hs-cells/modal/a/prokaryotic-cells

"In general, prokaryotes are single-celled organisms. However, there's increasing evidence that some groups of prokaryotic cells can organize to form structures that resemble multicellular organisms. Whether this counts as "real" multicellularity is a question hotly debated by researchers today."","I believe that the debate is continued, so we should still agree to the previous answer that prokaryotes CANNOT be multicellular. Bacteria might be an interesting exception, but further research shows that the cells might work together, but they lack the organization that other multicellular beings have.

Hope this helps!"
Prokaryotes and eukaryotes review,"So chromosomes/chromatin can be floating around anywhere with DNA inside the cell and that it doesn't need to be around a nucleus? 
I'm sorry if I seem dumb I'm new to this.","No worries! We were all new to this at one time or another! To answer your question, yes, it doesn't need to be inside a membrane-bound nucleus in the case of prokaryotes

Hope this helps!"
Prokaryotes and eukaryotes review,are biofilms made with _prokaryotes_ or _Eukaryotes_ cells?,Biofilm Structure A microbial biofilm is made up of many prokaryotic organisms that combine to form a colony. The colony is adhered to a surface and coated with a polysaccharide layer (or slime layer).
Prokaryotes and eukaryotes review,do eukaryotes cells live longer than prokaryotes,"The answer really lies in whether or not the cells combine to form a multicellular mass or if they prefer living by themselves. Ones that form together tend to live longer.

Hope this helps!"
Prokaryotes and eukaryotes review,How Can a cell be multicellular?,It is not saying that a cell is multicellular. When it says eukaryotes can be multicellular it is referring to an organism made of eukaryotic cells.
Fluid mosaic model: cell membranes article,"The article says the cell membrane has 2 types of proteins but it's missing the lipid bound protein (in-between the two phospholipid leaflets) mentioned in the "cell membrane proteins" video.

The article says there are 5 types of molecules but only 4 are listed.

The article says "The kinked shape of cis-unsaturated fats make it more difficult to pack tightly." What about trans-unsaturated fats?","I think lipid bound proteins are excluded because they do not play a role in transport or signaling.

In part 4 of the 5 types of molecules, there are two different categories lumped into one: large, polar; and ions.

Trans-unsaturated fats can pack more tightly than cis-unsaturated fats but less tightly than saturated fats."
Fluid mosaic model: cell membranes article,"How does phospholipid movement (flipping, flopping, scrambling) in the bilayer contribute to the survival of a cell?","This is actually a super cool question, never thought of it. I can think of several possible answers:
1) Signaling: though these videos don't mention it much, there are many different kinds of phospholipids and they can be useful for signaling and telling other cells what type of cell this is.  e.g. some phospholipid types are only on the outside membrane. One type of phospholipid, phosphatidylserine, is usually present more on the outside than inside. We know from observation that if it's present in equal numbers on the outer and inner leaflets, the cell is dying. So there might be some signaling going on.
2) To remove potentially dangerous molecules. Sometimes atoms or molecules generate radicals which are highly reactive. Maybe switching a radical from the outer to inner leaflet allows for safe removal or modification of the radical by the cell. It's better to contain a danger inside a cell so the cell can just die instead of losing the cell (in cases that the cell can be regenerated like in skin).
3) To increase the size of the membrane. Maybe phospholipids are produced inside the cell and they need to be flipped to the outer membrane to increase its size. The opposite could also be true, moving phospholipids into the inner leaflet to decrease the overall size of the outer membrane."
Fluid mosaic model: cell membranes article,"The article asks what makes a cell membrane fluid and then talks about three points that influence the fluidity of the cell, one of them being cholesterol.  Towards the end of the paragraph it says that without cholesterol, the phospholipids get closer together, then a sentence or two later it says that without cholesterol phospholipids get farther apart.  Is this a typo, or will phospholipids do both depending on the environment and condition they are in?","The key is temperature. Without cholesterol, the phospholipids will get closer together in a cold environment. The cholesterol acts as a kind of spacer to prevent them from getting too close. Conversely, in hot temperature, the phopholipids spread too far apart without cholesterol. The phospholipids want to be near the cholesterol molecules, causing them to be closer together."
Fluid mosaic model: cell membranes article,How might a phospholipid bilayer's tail become unsaturated?,"The unsaturation of the phospholipid bilayer's tail refers to the presence of double bonds in the fatty acid chains that make up the tails of phospholipids. These double bonds create kinks or bends in the fatty acid chains, affecting the overall fluidity and properties of the membrane.

The unsaturation of phospholipid tails can occur through two primary mechanisms:

Biosynthesis: Phospholipids are synthesized by cells through various enzymatic reactions. During the biosynthesis of fatty acids, the cell may introduce double bonds into the fatty acid chains through an enzyme called desaturase. Desaturase enzymes catalyze the insertion of double bonds between specific carbon atoms in the fatty acid chain, resulting in unsaturated fatty acids. The extent of unsaturation depends on the specific desaturase enzymes present in the cell.

Dietary intake: In certain cases, the degree of unsaturation in the phospholipid bilayer can be influenced by the dietary intake of unsaturated fatty acids. When organisms consume foods containing unsaturated fats, these fats can be incorporated into newly synthesized phospholipids, increasing the level of unsaturation in the membrane.

Hope that helped!"
Fluid mosaic model: cell membranes article,are all membranes made of phospholipid bilayers,"Mostly yes, but some archaea that live at high temperatures us a monolayer, basically the lipid tails go through the whole membrane and are attached to head groups on either side. If you google it, some diagrams will make it clear.
Maybe other exceptions also exist, but that is the only one that comes to mind."
Fluid mosaic model: cell membranes article,Is cell membrane different than plasma membrane? If so what are the differences and the similarities between cell membrane and plasma membrane?,"No difference, they are different terms for the same thing."
Fluid mosaic model: cell membranes article,How can you master this topic if you have trouble with it?,"Repetition and practice. Something else that may help is using different sources. Here's a link to the Amoeba sister's youtube video on the subject:https://www.youtube.com/watch?v=qBCVVszQQNs
But there is also crash course:https://www.youtube.com/watch?v=dPKvHrD1eS4 and the organic chemistry tutor.
Try looking for resources that work best for you, these all helped me and I hope they help you too :) :D"
Fluid mosaic model: cell membranes article,Can someone tell me the nitty gritty bits of the role cholesterol has on the membrane?,"Cholesterol is important because it controls the fluidity of the membrane.

*At low temperatures*: due to the limited movement, the membrane would become less fluid without cholesterol. However, because cholesterol is there, it does not. Why? I like to think of it as cholesterol "gets in the way" of the phospholipids packing together, since it is hydrogen bonded to them. 

*At high temperatures*: Without cholesterol, the membrane could become too fluid. However, cholesterol raisings its melting point, thus preventing this.

Cholesterol has these properties because it is a special type of lipid known as a *steroid*.Therefore, it has a rigid 4-ring structure. These rigid rings interact with the phospholipids around them and limit their movement due to their rigidity, thus preventing the membrane from undergoing any exxtreme changes in fluidity.

Hope this helps! :)"
Fluid mosaic model: cell membranes article,Can anyone also please provide some info about the saturated and unsaturated tails? Thanks.,"Saturated means that the tail does not have double bonds (the carbons are *saturated* with hydrogens) while unsaturated means that there are some double bonds and the carbons are not fully saturated with hydrogens. There are varying levels of unsaturation depending on the amount of double bonds present in the tail. Double bonds in the tail introduce bends and kinks that prevent the lipid tails from stacking as closely together and as such will increase the fluidity of the membrane. Conversely, a membrane with mostly saturated lipids will have lower fluidity because the tails stack closer together."
Passive transport review,"Hi, what exactly is facilitated diffusion?",When the molecules pass through the membrane via protein. (passive/active transport) Usually large and charged molecules use facilitated diffusion.
Passive transport review,How can water pass through the hydrophobic part of the cell without breaking the cell membrane?,I think they have passage ways so the water doesn't touch the hydrophobic parts of the cell membrane.
Passive transport review,"so if I understand, channel proteins do not require ATP. Am I right?",Yes. Channel protein is passive transport and doesn't use energy.
Passive transport review,can cholesterol pass?,"Cholesterol is part of the phospholipid bilayer membrane, it doesn't pass through because it is part of the membrane"
Passive transport review,What direction in a gradient does passive transport go?,From higher concentration to the lower concentration.
Passive transport review,What are the differences between osmosis and diffusion? are osmosis a part of diffusion?,"Osmosis is a type of diffusion, but it is specifically the diffusion of water,H2O. Diffusion is a term for any movement along a gradient"
Passive transport review,what is osmosis and what are some examples for it?,"Osmosis is the flow of water or other fluids across a semi-permeable membrane to balance chemical concentrations on both sides of the membrane. Try these Khan Academy videos and articles for more information.

https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/mechanisms-of-transport-tonicity-and-osmoregulation/v/diffusion-and-osmosis

https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/mechanisms-of-transport-tonicity-and-osmoregulation/v/osmosis

https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/mechanisms-of-transport-tonicity-and-osmoregulation/a/osmosis

If you really want to understand osmosis, try this experiment. Take a normal egg. submerge it in vinegar for 24-48 hours, or until the shell has dissolved. Then, take your egg without a shell and submerge it in syrup for 24 hours. Observe. Then, take your egg and put it in distilled or bottled water for 24 hours. Observe again.

I know that this is a very vague answer, but I suggest going back and re-reading the article to try to understand why this is happening. I've found that sometimes knowledge gained by oneself when possible is better than getting an answer. Also, the practical application of osmosis in the experiment also helps understand it better."
Passive transport review,When water passes through the hydrophobic how does it get the water to go through the body and give it energy?,"Water passes through the membrane in a diffusion process called osmosis. During active transport, energy is expended to assist material movement across the membrane in a direction against their concentration gradient. Active transport may take place with the help of protein pumps or through the use of vesicles. hope that helps"
Passive transport review,Why does the hydrophobic center of a cell membrane prevent polar substances from diffusing through it?,Because they are to large to pass through without breaking it apart. (I think)
Osmosis and tonicity,"Why doesn't the pressure of the cell (even a red blood cell that isn't rigid), balance out the net inflow in a hypotonic solution? The net inflow doesn't work with energy, but because their is room to slide around!?",I think this is the case with a plant cell that has a rigid cell wall thus in a fixed volume hydrostatic pressure will increase until osmotic pressure is opposed. But with an RBC the volume is not fixed (due to lack of cell wall) so osmotic pressure increases unopposed until the cell lyses.
Osmosis and tonicity,What could be an example of solute in a plant cell?,"eg of solute in a plant cell - Mineral nutrients like Na , K , Ca ."
Osmosis and tonicity,what is ion and molecule? and how do elements become positive / negative charged?,"An Ion is basically a charged atom. The atom can be either positively charged (by losing one electron) or negatively charged ( by gaining one electron).
Molecules are groups of electrically neutral atom/s which are chemically bonded.
Charge is due to loss or gain of an electron in an atom."
Osmosis and tonicity,"My group and I are making lab project by estimating the osmolarity in tissues by bathing the blood samples from the 3 members of my group with hypotonic and hypertonic solutions and observing it by using our microscope. Since we are done with observations, we are assigned to do a group lab report, and my individual task is to basically do the data analysis. However, I do not know which type of graph should I create regarding the observation and its results of the osmolarity of the blood samples in all three solutions. Should it be line graph, bar graph, pie graph, or, etc.?",I might recommend using a line graph because it will clearly show the difference between the three blood samples.
Osmosis and tonicity,What are some factors that affect Osmosis?,great question
Osmosis and tonicity,Why does the cells of stomata becomes flaccid instead of shrinking when they loss water from them?,"First cells become flaccid. If enough water is lost they will plasmolyse, which is where they shrink away."
Osmosis and tonicity,so essentially the cell is trying to keep the ratio of solute to solution the same both inside & outside of the cell? is that why water moves out?,"Yes, you got it exactly right!"
Osmosis and tonicity,I keep on getting hypertonic and hypotonic mixed up any suggestions?,"Maybe you could think of the *e* as standing for excess, while the *o* stands for low?"
The endomembrane system,What's the difference between a vesicle and a vacuole?,vesicles function is to transport proteins etc. while vacuoles store things
The endomembrane system,What's the difference between a lipid and a phospholipid? And why are proteins so important?,"A lipid is composed of glycerol and three fatty acid chains. A phospholipid has a phosphate group attached to it. 

And proteins are so important because they do all the key activities to make a functioning human. When an embryo is growing, it is because of proteins. When the muscles send and receive signals from the brain,  it is because of proteins. When cuts heal, it is because of proteins. When we digest food, it is because of proteins. You get the idea. They essentially do everything to make you able to live."
The endomembrane system,"i know there are vacuoles in plants and animals cells, are there any major differences between the two other than the size? location maybe. like characteristics or different functions? both vacuoles in each type of cell store energy.","The central vacuole of a plant has a crucial role. As mentioned above, the water  there pushes the cytoplasm outward against the cell wall. This creates  hydrostatic pressure - turgor. The mechanism keeps the plant from wilting and plays a key role in the water balance. Generally this central vacuole has a lower pH, witch help digesting substances; it can also be used as a storage room  - citruses have their juice in these vacuoles; it also  keeps the cell wall rigid and thus keeps the plant in upright position and so on. It also pushes every other cell organelle against the wall and to the surface of the cell. This a very clever way to push the chloroplasts closer to light and ''promote'' photosynthesis. Animal cells do not have a cell wall (they can have a similar thing , called a cell cortex). So the vacuoles here play a more subordinate role - they still help with endo- and exocytosis. Also the are quite smaller than plant vacuoles and greater in number. And of course, there are some animal cells with no vacuoles at all. Hope that helps :)"
The endomembrane system,""single-celled eukaryotes"?
isn't that wrong ?","No, that is not wrong. While most eukaryotic organisms are multicellular, there are some unicellular eukaryotes as well, though not many."
The endomembrane system,Why is the inner membrane of the lysosome not affected by the enzymes present inside it?,"The inner membrane of a lysosome is made up of proteins with an 'unusually' large number of carbohydrate groups attached to them. This prevents the breaking down of the proteinaceous membrane, ergo protecting them from the hydrolytic action of the enzymes."
The endomembrane system,"Why are mitochondria, choloroplasts, and peroxisomes not included in the endomembrane system?",I believe that they are not included into the endomembrane system because none of them receive anything from the Golgi apparatus. Hope this will help you:)
The endomembrane system,"Hey, everyone!
I'm having a rather hard time grasping some of the concepts in this article; specifically, how are the "shipments" between organelles (I.E. the ER and the Golgi) made? What structure connects them? Or do they just sort of float over?
I would appreciate some help on this. Thanks!","I'm reasonably sure the cytoplasm moves them. It's kind of flowing, and catches the "shipments" in its "current" and floats it over. I think the ER prepares them to flow through the cytoplasm to the next organelle,."
The endomembrane system,"If plant has no lysosomes, than how do they defend themselves from bacteria? Or bacteria simply do not attack plants?","Yes, bacteria do attack plants but plant cells have a different defense mechanism.

They have proteins which defend the plant from being infected. If a pathogen attacks a plant cell, then the proteins first try to prevent the pathogen from entering the plant cell. If that strategy fails and the pathogen manages to enter the cell, then the cell(or cells) have to sacrifice themselves, i.e, they die and prevent the pathogen from spreading further into the plant."
The endomembrane system,Do plant cell contain lysosomes?,Both plant and animal cells contain lysosomes.
Structure of the plasma membrane,what is between the phospholipid bilayer?,"Since the polor ends of the phospholipids face the outer/ inner surface of the cell. They are in contact with the inter/outer cellular fluid predominantly water, glycoproteins,glycolipids, However the hydrophobic tails inter twin with each other forming the enter space between the polor heads. The space between the polor heads would contain saturated and unsaturated fatty acids which forms these tails. This gives them a slight negative polarity. With these fatty acid tail ( bent or straight) we would find a mosaic of integral proteins, cholesterol,. and yes,  water molecules passing threw!"
Structure of the plasma membrane,"So with that example of the pinhead touching the fluid membrane (and the membrane flowing out of the way), I'm wondering how a person can bleed if all cell membranes do this. As in why don't sharp objects like pins and needles go straight through (I know it sounds silly) our skin without drawing blood?","Bleeding occurs when veins are torn out. When you pass a pin through your skin ,the pinhead is literally much bigger than the individual cell for the pinhead to pass through the said cell membrane.So you can guess the pin must torn out some small veins on its way into your skin,not into an individual cell.Moreover there is no blood inside a cell or cell membrane for it to come out.Hope this clears your doubt"
Structure of the plasma membrane,"What is meant by "Transmembrane proteins may cross the membrane just once, or may have as many as twelve different membrane-spanning sections." I don't understand the twelve different membrane-spanning sections part.",I think it looks like three-pass transmembrane protein (in the first picture about proteins) only having 12 sections instead of 3.
Structure of the plasma membrane,Why do we have proteins in the cell membrane?,http://www.sparknotes.com/biology/cellstructure/cellmembranes/section2.rhtml
Structure of the plasma membrane,Would I need all of this information for regular High School Bio?,Yes.
Structure of the plasma membrane,"What are lipid rafts, what are they made of and whats their function? and where in the plasma membrane are they located?
thank you!","Lipid rafts are regions within the plasma membrane that are more rigid than the surrounding membrane.  

They are made of the same components as the rest of the membrane, but in differing amounts — for example they contain much more cholesterol. 

AFAIK their function is not completely clear, but they may help concentrate certain membrane proteins in a way that makes some cell processes more efficient.

There is an extensive wikipedia article on this that you may find interesting:
https://en.wikipedia.org/wiki/Lipid_raft

This article might also be worth reading:
http://www.jlr.org/content/44/4/655.full"
Structure of the plasma membrane,fluid mosaic model is cell of ??,"That's not correct .... the fluid mosaic model is a model of the plasma membrane which is present in ALL cells, both eukaryotic and prokaryotic, single-celled and multi-cellular organisms."
The endomembrane system,What's the difference between a vesicle and a vacuole?,vesicles function is to transport proteins etc. while vacuoles store things
The endomembrane system,What's the difference between a lipid and a phospholipid? And why are proteins so important?,"A lipid is composed of glycerol and three fatty acid chains. A phospholipid has a phosphate group attached to it. 

And proteins are so important because they do all the key activities to make a functioning human. When an embryo is growing, it is because of proteins. When the muscles send and receive signals from the brain,  it is because of proteins. When cuts heal, it is because of proteins. When we digest food, it is because of proteins. You get the idea. They essentially do everything to make you able to live."
The endomembrane system,"i know there are vacuoles in plants and animals cells, are there any major differences between the two other than the size? location maybe. like characteristics or different functions? both vacuoles in each type of cell store energy.","The central vacuole of a plant has a crucial role. As mentioned above, the water  there pushes the cytoplasm outward against the cell wall. This creates  hydrostatic pressure - turgor. The mechanism keeps the plant from wilting and plays a key role in the water balance. Generally this central vacuole has a lower pH, witch help digesting substances; it can also be used as a storage room  - citruses have their juice in these vacuoles; it also  keeps the cell wall rigid and thus keeps the plant in upright position and so on. It also pushes every other cell organelle against the wall and to the surface of the cell. This a very clever way to push the chloroplasts closer to light and ''promote'' photosynthesis. Animal cells do not have a cell wall (they can have a similar thing , called a cell cortex). So the vacuoles here play a more subordinate role - they still help with endo- and exocytosis. Also the are quite smaller than plant vacuoles and greater in number. And of course, there are some animal cells with no vacuoles at all. Hope that helps :)"
The endomembrane system,""single-celled eukaryotes"?
isn't that wrong ?","No, that is not wrong. While most eukaryotic organisms are multicellular, there are some unicellular eukaryotes as well, though not many."
The endomembrane system,Why is the inner membrane of the lysosome not affected by the enzymes present inside it?,"The inner membrane of a lysosome is made up of proteins with an 'unusually' large number of carbohydrate groups attached to them. This prevents the breaking down of the proteinaceous membrane, ergo protecting them from the hydrolytic action of the enzymes."
The endomembrane system,"Why are mitochondria, choloroplasts, and peroxisomes not included in the endomembrane system?",I believe that they are not included into the endomembrane system because none of them receive anything from the Golgi apparatus. Hope this will help you:)
The endomembrane system,"Hey, everyone!
I'm having a rather hard time grasping some of the concepts in this article; specifically, how are the "shipments" between organelles (I.E. the ER and the Golgi) made? What structure connects them? Or do they just sort of float over?
I would appreciate some help on this. Thanks!","I'm reasonably sure the cytoplasm moves them. It's kind of flowing, and catches the "shipments" in its "current" and floats it over. I think the ER prepares them to flow through the cytoplasm to the next organelle,."
The endomembrane system,"If plant has no lysosomes, than how do they defend themselves from bacteria? Or bacteria simply do not attack plants?","Yes, bacteria do attack plants but plant cells have a different defense mechanism.

They have proteins which defend the plant from being infected. If a pathogen attacks a plant cell, then the proteins first try to prevent the pathogen from entering the plant cell. If that strategy fails and the pathogen manages to enter the cell, then the cell(or cells) have to sacrifice themselves, i.e, they die and prevent the pathogen from spreading further into the plant."
The endomembrane system,Do plant cell contain lysosomes?,Both plant and animal cells contain lysosomes.
Intro to eukaryotic cells,Why are plant cells typically square (if they are) and why do they have a much larger vauole than animal cells?,"They are squarish because they have a stiff cell wall that forces them into that shape. If you meant vacuole, I think they have a larger vacuole because they have more need to store food than animals. In case of drought or famine, animals can move on to somewhere else if they need to get food or water, plants can't."
Intro to eukaryotic cells,In the above diagram the author gives us an example of what a plant cell looks like and I noticed that the cell has an abnormally thick cell wall. What is the reason for thick cell walls in plants?,"Cell walls not only provide structure, and protect from mechanical damage, they also prevent the cell from bursting as plant cells need to continually absorb water to survive."
Intro to eukaryotic cells,how come animal cells don't have a cell wall,"An animal cell needs to allow mobility for that animal so only has a cell membrane, a plant cell however has a cell wall to give the cell ridged structure and a plant doesn't move by itself so doesn't need mobility but rather it have protection."
Intro to eukaryotic cells,Why don't plant cells have lysosomes?,"Plant cells don't have lysosomes, because their cell walls are tough enough to keep out foreign substances that lysosomes would have to digest out of the cell."
Intro to eukaryotic cells,"The Endoplasmic Reticulum in a eukaryotic cell is the transport network of the cell and it extends from and connects the nuclear membrane to the plasma membrane of a cell. But then whenever we draw a diagram of a typical plant or animal cell, we never extend it to the plasma membrane- we always leave it somewhere in the cytoplasm. So, it should be extended, shoudn't it? And in that sense all our diagrams are theoretically wrong?","Well, from endoplasmic reticulum vesicles are formed and transport things to Golgi apparatus, where it may be modified somehow, sent back to ER or further to cell surface. So the whole network is: ER -> vesicle -> Golgi -> vesicle -> cell plasma membrane"
Intro to eukaryotic cells,Procaryotic cells lack vacuoles too then?,Yes. Only eukaryotes have vacuoles.
Intro to eukaryotic cells,Does the nucleus have a phospholipid bilayer?,Actually it is surrounded by a double membrane which has 2 phospholipid bilayers each.
Intro to eukaryotic cells,Why is there a nucleolus? Shouldn't the production of DNA just be spread evenly around the nucleus?,The nucleolus is a region from the nucleus where the different RNAs are found. It is also the site where ribosomes are joined. It´s important to mention that ribosomes are made 1/3 from proteins and 2/3 from RNA. Proteins for the ribosome are exported from the cytoplasm  to the nulcleus trough the nuclear pores.
Intro to eukaryotic cells,what is the function of a peroxisome?,"it is main function is to break down long chains of fatty acids and to detoxify substances, 

it produces H2O2 as a result, which can be harmful to the cell as a whole if not regulated, which is why it contains enzymes that is able to break down H2O2 into water and oxygen."
Intro to eukaryotic cells,"are there any unicellular eukaryotes? if there are, names ?","Yes, there are many unicellular eukaryotes. In fact, they have their own kingdom in the standard five kingdom classification scheme in biology called Kingdom Protista. Kingdom Protista is divided into subkingdoms of Protozoa and Algae. In Subkingdom protozoa, you have organisms like amoeba, euglena, volvox, paramecia, even plasmodia (the microorganisms that causes malaria), just to name a few. Most types of algae are also unicellular eukaryotes."
The cell membrane review,"Does the phospholipid bilayer of the cell membrane, make the membrane "water resistant," due to inward hydrophobic tails and the outward hydrophilic heads?","Yes,  it does, even though water can still get through the bilayer into the cytoplasm via the integral proteins in the bilayer"
The cell membrane review,How can water pass through the phospholipid bilayer if it has aquaphobic tails? Won't the water molecules get repelled out?,"I think another article said that some water molecules can sneak past the hydrophobic tails because they are very small (the water molecules, that is)."
The cell membrane review,how many cells in my body,About 37 trillion cells
The cell membrane review,Do u like whoppers? How many cells are in one?,More than 1.
The cell membrane review,i have a question i do not understand the word phobia can anyone comment to explain a bit more thanks.,phobia is greek for fear >
The cell membrane review,"what does a skin cell membrane look like? they aren't semipermeable, are they?",Look anywhere in lesson 3 and you will find a cross picture of cell membrane. And they ARE semipermeable.
The cell membrane review,why is a cell membrane semipermeable?,"The cell is kinda like an exclusive concert. It can't let just anyone in.  There are all sorts of free radicals and harmful metals that could invade the cell, not to mention those bacteria and viruses that constantly try to attack the cell. The cell needs a membrane to protect itself - to some degree - and establish an environment where it can do its job. You wouldn't want some stranger to randomly pop into your house, and neither does the cell. It does need some things from the outside world, though. That is why it allows certain particles to pass through the membrane. Hope this helps!"
The cell membrane review,What is the big difference between plasma membrane and cell membrane.,"there is no big difference, it is the same thing. another name for a plasma membrane (or a cell membrane) is a fluid mosiac model. again there is no big difference between these names, they are the same thing."
The cell membrane review,how many cells in  my body,"It's an estimated answer, but scientists predict around 37.2 trillion cells."
The cell membrane review,"So, is the plasma membrane the same thing as the cell membrane?","Yes, the plasma membrane and cell membrane are the same things."
The extracellular matrix and cell wall,How is this related to cell signaling? Does the extracellular matrix act as receptors?,"The integrins, which connect the ECM to the cytoskeleton, act as receptors in the sense that they receive signals from the ECM and modulate the cell signaling pathways."
The extracellular matrix and cell wall,The ECM and cell wall are used for support. Then what are cytoskeleton for?,ECM is outsideof cell Cytoplasm-like material and cytoskeleton isinside of cells structural material
The extracellular matrix and cell wall,Where are collagen synthesised and how does it reach its destination,"Proteins that get exported are (typically) synthesized by ribosomes bound to the ER (i.e. in the rough ER) and this is true of collagen.

The collagen precursor polypeptide then gets processed in the ER and Golgi before being exported via. exocytosis (vesicles bud off from the Golgi and then fuse with the plasma membrane).

Once outside the cell, collagen undergoes further modification by enzymes that are also secreted by cells.


To start learning more about the ER, Golgi apparatus, and exocytosis on Khan Academy:
•https://www.khanacademy.org/science/biology/structure-of-a-cell/tour-of-organelles/v/endoplasmic-reticulum-and-golgi-bodies
•https://www.khanacademy.org/science/biology/membranes-and-transport/bulk-transport/v/exocytosis
(You can also find other material on this by searching for various keywords such as "rough ER", "Golgi", or "exocytosis".)


Wikipedia also has an article on collagen that describes these steps in more detail:
https://en.wikipedia.org/wiki/Collagen#Synthesis


Does that help?"
The extracellular matrix and cell wall,"What is a polysaccharide? Is this the sticky goo that bacteria produce and nestle in, when a biofilm forms on a surface? What makes a molecule sticky? Sorry - 3 questions.",1) Multi sugar/carbohydrate molecule. 2) Bacteria usually lives in colonies and sometimes due to overpopulation can kill itself with their own waste byproducts. 3) It usually depends on the type of molecules. Polarity matters as well. Polar wise molecules ( such as water) will attract same affinity molecules. Fats are non polar molecules and attract similar affinity molecules. Thisis also why soap has both polar and non polar sides so it will attach to both fats and water so it can remove fats when rinsed with water...
The extracellular matrix and cell wall,why animals have extracellular matrix not a cell wall ?,This allows us to bend and be flexible! With a cell wall our skin would be rigid and we might break if we bend our arm for example!
The extracellular matrix and cell wall,"What is the difference between Proteoglycan and Glycocalyx?
Many thanks!",Glycocalyx is what surrounds a bacteria cell while Proteoglycan is what surround animal cell
Mitochondria and chloroplasts,Would it be possible for a modern day cell or organism to capture one of these cells and start a new symbiotic relationship with the host cell?,"That is an intriguing question. The origin of mitochondria is thought to have been a very rare event. The mitochondria seem to have their origin from one particular family of bacteria (the alpha-proteobacterium ) which are related to some existing bacteria. There are people trying to build cells so I guess maybe someone could try to create a modern endosymbiosis event.

There are many theories as to how eukaryotes came about. If you want to know more; see this paper: Endosymbiotic theories for eukaryote origin http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4571569/"
Mitochondria and chloroplasts,It would be so cool if we could recreate endosymbiosis and incorporate chloroplasts in human cells so we could photosynthesize,"i hate to ruin your guys fun but i think we would die, if you put chlorophil into our bodies."
Mitochondria and chloroplasts,"1) Are there any animals that have chloroplasts? Or are they only in plants?

2) If they are only in plants, would it be possible for an animal to have chloroplasts, chemically speaking?","Well according to modern classification, the organisms which have chloroplasts in them and have an advanced nucleus are called plants. Those organisms which show both plant and animal features(like Euglena) are kept in Kingdom: Protista
As for your second question, as Biology is science of exceptions we cannot publish any definite law. So in future, due to evolution, there may be animals with chloroplasts."
Mitochondria and chloroplasts,is peroxisomes needed in a cell,"Before the ancestor of mitochondria entered the eukaryotic cells, Peroxisomes were asource of power to the cell. They used to break down H2O2(Hydrogen Peroxides) and would form water and and energy. But now, there only function is detoxification as the energy produced by mitochondria is much more than the energy produced by the peroxisome. So, peroxisomes are sort of vestigial organelles which had a major function in the past but aren't so useful in the present age.."
Mitochondria and chloroplasts,"If mitochondria and chloroplasts evolved from bacteria, what did the cells use for energy before?  Isn't this a case of you can't have the one without the other?  Wouldn't the cell/animal/plant die without the energy from the chloroplast or mitochondria?",Before mitochondria and chloroplasts became part of cells they had their own ways of producing energy from metabolizing food around them. These older methods of producing energy were lost along the way because the mitochondria and chloroplasts were better at it and it was a waste of resources to have the two ways of producing energy so the cells that eliminated the older way were more efficient and survived better that the ones that didn't.
Mitochondria and chloroplasts,"In the endosymbiotic theory, what was the factor that decided that the chloroplast wouldnt converge with the other cells present on earth, so that there would be two types of cells, 
1. plant cells
and 
2. animal cells","It just happened this way. Some phytoplankton probably merged with chloroplasts prokaryotic cells and absorbed them and formed a symbiotic relationship with them and also with mitochondria (they have both organelles), and some zooplankton probably got the short stick and managed to form symbiotic relationship only with mitochondria prokaryotic cells and from them out ancient common ancestor was created..."
Mitochondria and chloroplasts,"Most antibiotics inhibit bacterial ribosomes... so, would antibiotics have an effect on mitochondria when taken?","Some of them may, if the antibiotics manages to get all the way through all the membranes to the mitochondria itself (which is not an easy way). 
If they do get into mitochondria, it may not be a big deal since most of mitochondrial proteins are made by eucariotic cell and then transported into mitochondria, only few proteins are made by mitochondria itself.
Actually it seems that some antibiotics do harm mitochondria, so these usually aren't used as long as there is some harmless alternative."
Mitochondria and chloroplasts,Do stand-alone chloroplasts and/or mitochondria still exist in nature as prokaryotes (Outside of a eukaryotic cell)?,"Yes§, this is part of the evidence supporting the theory that these (and possible some other organelles) arose through endosymbiosis (aka symbiogenesis).

The group of bacteria from which mitochondria seem to have evolved are the Alphaproteobacteria.

Chloroplasts appear most closely related to the cyanobacteria.

You can read more about this here:
https://evolution.berkeley.edu/evolibrary/article/_0_0/endosymbiosis_01 _

You might also find these interesting:
https://biologos.org/blogs/dennis-venema-letters-to-the-duchess/evolution-basics-endosymbiosis-and-the-origins-of-mitochondria-and-chloroplasts
https://biology.stackexchange.com/questions/43372/origin-of-the-double-membrane-of-mitochondria-and-chloroplasts

§More correctly, there are other descendants of the progenitor of these organelles that have remained as free-living organisms."
Mitochondria and chloroplasts,"Does this mean that when you eat vegetables, you are you eating light energy?","Yes, pretty much. In fact you could say you're eating the energy produced in the fusion reactions occuring inside of the Sun's core."
Mitochondria and chloroplasts,"Have they proven endosymbiosis to be the reason why mitochondria and chloroplasts contain their own DNA and ribisomes? I am very blown by the idea that the mitochondria in our bodies were once bacteria and, if they really are bacteria before,we now have a gazillion of them.","Proof is an elusive concept in science, but this theory is now generally accepted as the best explanation for multiple observations.  

Another piece of evidence supporting the theory that these (and possible some other organelles) arose through endosymbiosis (aka symbiogenesis) is that if you make an evolutionary tree of the DNA within either of these organelles and bacteria, you find free-living bacteria that are closely related.

The group of bacteria from which mitochondria seem to have evolved are the Alphaproteobacteria — many of them are intracellular parasites, which suggests how they originally ended up inside the first eukaryotic cell.

Chloroplasts appear most closely related to the cyanobacteria.

You can read more about this theory here:
https://evolution.berkeley.edu/evolibrary/article/_0_0/endosymbiosis_01 _

You might also find these interesting:
•https://biologos.org/blogs/dennis-venema-letters-to-the-duchess/evolution-basics-endosymbiosis-and-the-origins-of-mitochondria-and-chloroplasts
•https://biology.stackexchange.com/questions/43372/origin-of-the-double-membrane-of-mitochondria-and-chloroplasts"
Intro to eukaryotic cells,Why are plant cells typically square (if they are) and why do they have a much larger vauole than animal cells?,"They are squarish because they have a stiff cell wall that forces them into that shape. If you meant vacuole, I think they have a larger vacuole because they have more need to store food than animals. In case of drought or famine, animals can move on to somewhere else if they need to get food or water, plants can't."
Intro to eukaryotic cells,In the above diagram the author gives us an example of what a plant cell looks like and I noticed that the cell has an abnormally thick cell wall. What is the reason for thick cell walls in plants?,"Cell walls not only provide structure, and protect from mechanical damage, they also prevent the cell from bursting as plant cells need to continually absorb water to survive."
Intro to eukaryotic cells,how come animal cells don't have a cell wall,"An animal cell needs to allow mobility for that animal so only has a cell membrane, a plant cell however has a cell wall to give the cell ridged structure and a plant doesn't move by itself so doesn't need mobility but rather it have protection."
Intro to eukaryotic cells,Why don't plant cells have lysosomes?,"Plant cells don't have lysosomes, because their cell walls are tough enough to keep out foreign substances that lysosomes would have to digest out of the cell."
Intro to eukaryotic cells,"The Endoplasmic Reticulum in a eukaryotic cell is the transport network of the cell and it extends from and connects the nuclear membrane to the plasma membrane of a cell. But then whenever we draw a diagram of a typical plant or animal cell, we never extend it to the plasma membrane- we always leave it somewhere in the cytoplasm. So, it should be extended, shoudn't it? And in that sense all our diagrams are theoretically wrong?","Well, from endoplasmic reticulum vesicles are formed and transport things to Golgi apparatus, where it may be modified somehow, sent back to ER or further to cell surface. So the whole network is: ER -> vesicle -> Golgi -> vesicle -> cell plasma membrane"
Intro to eukaryotic cells,Procaryotic cells lack vacuoles too then?,Yes. Only eukaryotes have vacuoles.
Intro to eukaryotic cells,Does the nucleus have a phospholipid bilayer?,Actually it is surrounded by a double membrane which has 2 phospholipid bilayers each.
Intro to eukaryotic cells,Why is there a nucleolus? Shouldn't the production of DNA just be spread evenly around the nucleus?,The nucleolus is a region from the nucleus where the different RNAs are found. It is also the site where ribosomes are joined. It´s important to mention that ribosomes are made 1/3 from proteins and 2/3 from RNA. Proteins for the ribosome are exported from the cytoplasm  to the nulcleus trough the nuclear pores.
Intro to eukaryotic cells,what is the function of a peroxisome?,"it is main function is to break down long chains of fatty acids and to detoxify substances, 

it produces H2O2 as a result, which can be harmful to the cell as a whole if not regulated, which is why it contains enzymes that is able to break down H2O2 into water and oxygen."
Intro to eukaryotic cells,"are there any unicellular eukaryotes? if there are, names ?","Yes, there are many unicellular eukaryotes. In fact, they have their own kingdom in the standard five kingdom classification scheme in biology called Kingdom Protista. Kingdom Protista is divided into subkingdoms of Protozoa and Algae. In Subkingdom protozoa, you have organisms like amoeba, euglena, volvox, paramecia, even plasmodia (the microorganisms that causes malaria), just to name a few. Most types of algae are also unicellular eukaryotes."
Active transport review,is sweating a form of active transport,I think that sweating is a form of passive transport as heat that is generated in the cells inside your skin is moving WITH the concentration gradient from hot (inside) to cold (outside). I think that's right. I haven't yet studied the videos on perspiration.
Active transport review,What is the difference between facilitated diffusion and active transport?,Facilitated diffusion is a type of passive transport and along the gradient. Think of a pipe connecting a full tank of water to an empty one. Active transport is against the gradient. Think of a pump moving water from a nearly empty tank to an almost full one.
Active transport review,Are the largest molecules moved by only active transport or also by passive?,"No, actually both facilitated diffusion and active transport occur. When the molecules moving from high to low conc. like Glucose is very large, then we need channel proteins to move them into the cell, and channel protein only because they have the shape and structure to do so, so that the movement is only unidirectional (into the cell). Active transport transports or moves materials against the concentration gradient, that is, from low to high, and the size doesn't matter here like facilitated diffusion, only the concentration."
Active transport review,What is importance of active transport ?,Active transport is important because it allows substances to move against the concentration gradient. This helps it maintain the appropriate balance of substances in the cell.
Active transport review,"How do carrier/channel proteins select which particles to pass through and when?
More specifically,
How do aquaporins only let water in? How can the cell control the amount of water that can diffuse through aquaporins? How come the channel protein will not bring in potassium ions when it needs to bring in sodium ions?","Hi ! The shapes of the channels is very specifically adapted to letting only one type of molecules through. For example, aquaporins are shaped in a way that only water can pass through (because water has a specific structure and charge). Sodium and potassium do not have the same size nor shape and therefore one cannot use the channel of the other as well. 
The cell can control the amount of water that it lets in or out, by controlling the amount of aquaporins in its membrane. This is done by exocytosis/endocytosis of aquaporins, that can be controlled for example by antidiuretic hormons (that tend to provoke endocytosis of aquaporins)."
Active transport review,"How does the carrier protein change shape? Can the protein somehow bend, or does it chemically change?",The protien changes shape by using ATP energy. And no it cannot bend
Active transport review,I don't understand active and passive transport i need help.,Active transport uses energy to transport molecules across the plasma membrane. This uses energy from ATP. They also use pumps to get molecules in or out of the cell. Passive Transport does NOT use energy to transport molecules across the membrane. This can also just be molecules diffusing across the permeable membrane or a direct channel which they can enter or exit.
Active transport review,"what actually makes particles move down the concentration gradient? as in, why are particles by random motion able to passively move into an area of low concentration?? how can random motion lead to an overall non-random outcome??","The movement of particles is random, but even with that randomness, particles have a high probability to move from the area with high concentration to an area of low concentration. 

A good example would be if you get some small objects and assign them into two groups (A and B for example). However, you add more objects to group A than you do to group B. Then, for each object flip a coin. If the coin comes up as heads, keep the object in its assigned group. If the flip is tails, move the object to the opposite group. Once you're done, no matter how many more objects you put in group A then B, you should have a roughly equal distribution in each. 

This isn't a non-random outcome, it's just how probability works. The chance of an object moving from group A to group B is greater only because there are more objects in group A and therefore more chances to move to the other group."
Active transport review,"What are the differences between a carrier and a channel protein? Also, what are some examples?","Channel proteins are proteins that create hydrophilic holes in cell membranes, facilitating the transport of molecules down the concentration gradient. Carrier proteins are integral proteins that transport chemicals across the membrane both down and up the concentration gradient
 Some examples of channel proteins include chloride, potassium, calcium, sodium ion channels, aquaporins, etc. Examples of carrier proteins are sodium-potassium pump, glucose-sodium cotransport, valinomycin, etc."
Active transport review,what is hydrophillic and hydrophobic? Please answer,"Hydrophilic means a molecule or part of a molecule is _attracted_ to water. Hydrophobic means the opposite, it _repels_ water."
Intro to photosynthesis,"Okay, if the light dependent reactions can create the ATP itself, then why not just transport that ATP everywhere instead of forming Glucose then spending a lot of other time in transforming back that Glucose into ATP?","Excellent question.

The major reasons that I know of:
1) The high energy bonds in ATP are (by definition) unstable, so for long term storage of energy ATP is not a good choice.
2) In many situations phosphate is a limiting nutrient, so needing to make more ATP could severely limit the plants ability to store energy.
3) Fixed carbon (e.g. glucose) can be converted into other molecules the plant needs including:
• cellulose for structure
• lipids for long term energy storage, cell membranes, etc.
• proteins for structure, catalysis, etc."
Intro to photosynthesis,what is hydrolysis,"When you add water, you can separate a compound into two. For example in hydrolysis of an ester,  when you add water you get alcohol and carboxylic acid."
Intro to photosynthesis,Why is the first photosystem depicted in photosynthesis diagrams called "photosystem II" and the second photosystem called "photosystem I"? Are the names arbitrary or do they tell us something about the nature of how the photosystems work?,"The reason for this is simply because Photosystem I was discovered first, and Photosystem II was discovered second.  You're right, it is confusing because the Photosystem II process occurs first, followed by Photosystem I."
Intro to photosynthesis,"The reactions occur without any dependence on light...so can it run during night time?...if so,in night time, the guard cells of the stomata close, so how can it take in carbon-dioxide to continue the cycle?...","Both reactions, the light-depended reaction and the Calvin's cycle OCCURS ONLY in the light (and out of color spectrum, mainly blue and red colors are used thus green reflected into your eye).  
1. Light-depended reaction gives you the NADPH
2. You need NADPH in Calvin's cycle 
And you don't get the NADPH without light.
EDIT after a comment brought up by Safwan: to be exact, The Calvin cycle needs light to start, but can continue for a while even without the light."
Intro to photosynthesis,"You, along with the rest of the human population, owe your existence to plants and other organisms that capture light: FALSE!",Do you care to give some supporting information for that statement?
Intro to photosynthesis,What happens after the plants form glucose and oxygen? What happens to the oxygen when it is released?,"Glucose is utilised in respiration and excess glucose is stored  in the form of starch....
The o2 released might be utilised by humans etc"
Intro to photosynthesis,What does the Pi stand for in the pictures describing light reactions and the Calvin cycle?,"Pi stands for inorganic Phosphate... It is described in chemistry as the phosphoryl group, i.e. PO3 with a 2- charge.... This phosphate bonds with the adenosine group to form AMP, ADP, ATP, and the like. Hope this helps"
Intro to photosynthesis,Why would you consider photosynthesis important ?,"Photosynthesis is extremely important! It is the process in plants that allows it to harness energy from sunlight and convert it into chemical energy that can be used by plants and other organisms. In fact all the energy we get from food is derived from the energy we get directly from plants or indirectly from animals that ate plants. Hence without the sun or plant's ability to carry out photosynthesis, there would be no energy to sustain most of the life on earth."
Intro to photosynthesis,"Wait, so:ATP=Three Phosphates. ADP=Two Phosphates. What if there is only one Phosphate?
What would it be called? And what would happen if there was only one phosphate?","ATP is Adenosine TriPhosphate, with three phosphates, and lots of energy stored in bonds.
ADP is Adenosine DiPhosphate, with two phosphates, and some energy stored in bonds.
AMP is Adenosine MonoPhosphate, with a single phosphate group. These do not have energy stored in the bonds between phosphates, as there is only one.
Biological processes add/subtract phosphates, changing these into each other.
A related molecule, cAMP (cyclic AMP), has a cyclic structure, and rather than an energy storage role, it functions as a messenger in cell signaling pathways."
Steps of cellular respiration,if glycolysis requires ATP to start how did the first glycolysis in history happen?,"You must remeber that life on this planet has been evolving for billions of years, it is highly unlikely that the originating system resembles the current system. The development of celluar respiration began as a simple inefficient system progressing to it's current incarnation."
Steps of cellular respiration,What is the role of NAD+ in cellular respiration. Why is the role NAD+ plays so important in our ability to use the energy we take in?,"Hello Breanna! 
NAD+ is an electron transport molecule inside the cristae of a cell's mitochondria. In glycolysis, the beginning process of all types of cellular respiration, two molecules of ATP are used to attach 2 phosphate groups to a glucose molecule, which is broken down into 2 separate 3-carbon PGAL molecules. PGAL releases electrons and hydrogen ions to the electron carrier molecule NADP+. Each PGAL molecule has a phosphate group added to it, forming a new 3-carbon compound. These phosphate groups and the phosphate groups from the first step are then added to adenosine diphosphate or ADP, forming 4 ATP molecules. This also produces 2 molecules of pyruvic acid."
Steps of cellular respiration,"When it states in "4. Oxidative phosphorylation" that the NADH and the FADH2 return to their "empty" forms NAD+ FADH2, the author meant FAD when referring to the "empty" forms, right?","the empty state of FADH2 is FADH, after oxidation it loses 1 h+ ion and elctron."
Steps of cellular respiration,I have a question... Which part of the body will most likely use the cellular respiration? Is it lungs?,"Cellular Respiration happens in your cells and you entire body is made up of cells, it goes on all throughout your body including your lungs and brain."
Steps of cellular respiration,"When the electron carriers NAD+ and FAD gain electrons, why are 2 hydrogen ions also being added?","The free energy from the electron transfer causes 4 protons to move into the mitochondrial matrix. 


In other words, electrons provide energy for hydrogen atoms. Electrons fuel movement of protons. :)"
Steps of cellular respiration,Does the glycolysis require energy to run the reaction?,Yes glycolysis requires energy to run the reaction. 2 ATPs  are used up by glycolysis this then begins the oxidative process of glycolysis.
Steps of cellular respiration,Aren't internal and cellular respiration the same thing?,"Cellular respiration is oxidative metabolism of glucose which takes place in mitochondria and in the cell. 

Internal repsiration is gas exchange between blood and tissues.


https://med.libretexts.org/Bookshelves/Anatomy_and_Physiology/Book%3A_Anatomy_and_Physiology_(Boundless)/21%3A_Respiratory_System/21.9%3A_Gas_Exchange/21.9B%3A_Internal_Respiration"
Steps of cellular respiration,"In the Citric Acid Cycle (Krebs Cycle),  would the four-carbon molecule that combines with Acetyl CoA be Oxaloacetic acid?",Yes. Acetyl CoA and Oxaloacetic Acid combine to form a six-carbon molecule called Citric Acid (Citrate).
Steps of cellular respiration,"I was taught that it was Glycolysis, Pyruvate Oxidation, Krebs cycle, Electron Transport, and then Chemiosmosis. Which is correct? or is it saying the same thing in different terms?","It is the latter...the same thing is being said in different terms.
- Glycolysis and pyruvate oxidation are directly mentioned.
- Citric Acid cycle is also known as Kreb's cycle (Discovered by Hans Kreb).
- The Oxidative Phosphorylation step as mentioned above can be broken into these two steps: 
a. Electron Transport Chain helps in creating a proton gradient i.e. as the electron travels through the electron transport chain, its energy is used up to transport hydrogen ions into the intermembrane space.
b. Chemiosmosis: As a proton gradient is achieved, the hydrogen ions pass into the mitochondrial matrix through the ATPase (FoF1 complex) embedded in the mitochondrial membrane, and ATP is produced. these two steps together are known as oxidative phosphorylation since the energy and electrons are obtained by oxidizing (taking electrons from) NADH and FADH2."
Steps of cellular respiration,"After oxidative phosphorylation, the ATP created is in the mitochondrial matrix, right? If so, how does it get out of the mitochondrion to go be used as energy?","Just like the cell membrane, the mitochondrion membranes have transport proteins imbedded in them that bring in and push out materials."
Photosynthesis review,"If you heavily breath on a plant, will it help growth considering it needs CO2, water, sunlight?","In an open environment, probably not by any noticeable amount. However, if you put the plant in a sealed container such as a greenhouse and sit in the greenhouse for a while then the CO2 concentration will rise. So in a sealed container the answer is yes but just a plant sitting in your house or outside breathing on it won't make a huge difference."
Photosynthesis review,how does the plant reléase the oxgen,through stomata on the back of it's leaves
Photosynthesis review,"Calvin Cycle: ATP is used to create sugars that the plant will use to grow and live.

My question is where does the ATP come from? Light-dependent reactions make ATP with the light energy, but the Calvin cycle seems to already have it so that it can convert into sugars... Does the Calvin cycle happen after the light-dependent reactions occurs or is the Calvin cycle independent? An example of my question:

Does photosynthesis happen like this?

LDR: Light energy + H2O = ATP + NADPH + O2 

And then after that:

Calvin Cycle: ATP + NADAPH + CO2 = sugar

? 
Sorry if I got some things wrong @~@","The Calvin cycle is dependent on the Light-dependent reactions, and almost in the same way Light-dependent reactions are dependent on "The Calvin Cycle".  The "light-dependent reactions" receive light, and provide energy for the Calvin cycle. After used by the Calvin cycle, the molecules go back to the thylakoids to be reenergized in a way. So it is almost like a constant cycle between the two areas. For clarity refer to the diagram given above."
Photosynthesis review,what is NADPH?,the electron carrier for photosynthesis. NADH(without the P for photosynthesis :) ) is used in cellular respiration. They carry electrons to and fro and are subsequently oxidized or reduced. They need to carry the electrons because electrons are high charge substances
Photosynthesis review,""Light energy is captured by chloroplasts and stored as ATP"
ATP is need to make sugar, BUT ATP is already compose of sugar. Where do this sugar come from?","ATP is not sugar, it is a nucleotide. The carbon atoms needed to build sugar molecules are taken from the CO2 that the plant absorbs. CO2 is converted into glucose during the Calvin cycle, which is an anabolic pathway and therefore needs ATP to actually build up the molecules."
Photosynthesis review,during what stage of photosynthesis are ATP and NADPH converted to ADP + Pi and NADP+,"During the Calvin Cycle, the ATP and NADPH are broken down into ADP, Pi, and NADP+ to provide energy for the cycle. Then, after passing through, the used-up molecules react to bind together into ATP and NADPH again."
Photosynthesis review,Why are *photosynthesis and cellular respiration* are not simply reversal of each other?,They are in a way. Photosynthesis uses carbon dioxide and water to make oxygen and high energy sugars like glucose. Respiration takes in oxygen and glucose and turns it back into carbon dioxide and water.
Photosynthesis review,""Light energy is captured by chloroplasts and stored as ATP" 
ATP is need to make sugar, BUT ATP is already compose of sugar. Where do this sugar come from?","ATP itself is not composed of sugar.

When light energy is captured by the chloroplast, it, along with carbon dioxide and water, gets converted to ATP, NADPH, and oxygen (light-dependent reactions). The ATP and NADPH then enter the Calvin cycle and fuel the synthesis of molecules that _eventually_ become sugar molecules. 

These sugar molecules can then be sent to the plant cell's mitochondrion to undergo cell respiration, which produces even more ATP that can be used to fuel the plant cell's many complex processes."
Photosynthesis review,How do trees survive when they lose their leaves in the winter? How can photosynthesis still occur without the chloroplasts in the leaves? Do they keep energy in storage to use during the season?,"Deciduous trees store energy and resources within their bark, which can be used during the winter months when they have no leaves. Additionally, their physiological process change and slow down, as to not consume as much energy compared to the warmer months. It's a bit like hibernation for trees, where they stock up on resources and decrease energy consumption to make it through the winter. 
Evergreen trees (like the firs you see during Christmas time) have special adaptations to the cold that negate the need for this period of dormancy.

Does this help?"
Overview of metabolism,"I'm curious about how ATP ended up being the energy currency for both plants and animals, why the same molecule? Is because of a common ancestor?
Is there any cell that doesn't use ATP as its "energy currency"?","Yes, it is because of the common ancestor. If there was a different, more efficient molecule then this would have been used instead. Keep in mind that in the long run only the most effective processes and molecules can transferred by generations."
Overview of metabolism,Why is it that ATP happens to resemble an adenine base in DNA? Are they related in any way beyond structure? Is the adenine base special? Is there another energy currency molecule like ATP? Can we artificially create another energy currency molecule?,"Both ATP and DNA are nucleic acids. All nucleic acids have 3 parts.
1. A pentose sugar(A sugar with 5 carbon molecules)
2. Phosphate group(s)
3. A nitrogen base. DNA and ATP have the same nitrogen base- Adenine, present.

ATP is specially called an energy currency because it has an easily breakable bond between 2 of its phosphate groups. There are several other triphosphate molecules present in cells like GTP and CTP that play various roles, but ATP is the main 'energy trading' molecule. 
Triphosphate molecules can be synthetically created under the right conditions, our cells will still rely on ATP."
Overview of metabolism,What is ADP (adenosine diphosphate)? How is it different from ATP?,"ADP is adenosine diphosphate 
and
ATP is adenosine triphosphate

In ADP there is 2 phosphate molecules
In ATP there is 3 phosphate molecules"
Overview of metabolism,"How can a molecule be "worn out"...? Does he mean they've outgrown their usefulness, or that they actually lose hydrogens or their groups come apart somehow over time?","Good question... they don't truly mean "worn out" as I think you are thinking... I think what they mean is that a molecule such as glucose gets broken down a few times to harvest some energy in the form of ATP... and then another molecule such as pyruvate, for instance, enters another metabolic process for recycling, harvesting both energy, and the use of the carbons for other purposes. See the citric acid cycle and this will start to make more sense ( https://www.khanacademy.org/science/biology/cellular-respiration-and-fermentation/pyruvate-oxidation-and-the-citric-acid-cycle/v/krebs-citric-acid-cycle )... but you are right... "worn-down" is confusing wording."
Overview of metabolism,"Does metabolism vary widely between people? I have heard that it does not, but it would seem that it would be highly dependent on the weight of an individual.","yes, it does, because you could have an illness and because of this illness one of your hormones gets produced more or less. And so your metabolism would be regulated as faster or slower."
Overview of metabolism,"Are ADP/ATP reusable? What I mean is, once ATP released its energy, does it transform back to ADP? If yes can this ADP be used again to form back ATP?","This is an essential cycle that never stops until you die: ADP gets phosphorylated in the mitochondria, storing energy in ATP, and the ATP gets used to perform cellular work, releasing its energy in coupled reactions, and transforming back to ADP."
Overview of metabolism,"So basically, Metabolism is the core of a cell. It's where all the work happens right?",Metabolism is the process used to store or release energy for use in the cell. It allows other essential chemical reactions to happen. it is the basis for all the work in cell. Try to think of it as a process not an area where reactions happen
Overview of metabolism,How energy is transfered from cellular respiration to the process that formats ATP. Is it in heat? If so doesnt it affect other molecules in the area? Thanks,"The majority of ATP is generated through ATP synthase at the end of the electron transport chain. In this process, a concentration gradient of protons (H+) is what is used to drive ATP synthase, not heat."
Overview of metabolism,Is the convergence of glucose to glycogen considered anabolism ?,"Yes - this is an anabolic process, promoted by the action of insulin on the hepatocyte or myocyte. The reverse - i.e. the hydrolysis of glycogen back into glucose-1-phosphate - is a catabolic process."
Activation energy,what is the defination of activation energy?,"The official definition of activation energy is a bit complicated and involves some calculus. But to simplify it:
 
Activation energy is the minimum energy required to cause a process (such as a chemical reaction) to occur."
Activation energy,"I thought an energy-releasing reaction was called an exothermic reaction and a reaction that takes in energy is endothermic. In the article, it defines them as exergonic and endergonic. Are they the same?",Exothermic and endothermic refer to specifically heat. Exergonic and endergonic refer to energy in general.
Activation energy,"When mentioning activation energy: energy must be an input in order to start the reaction, but is more energy released during the bonding of the atoms compared to the required activation energy? Can the energy be harnessed in an industrial setting?","In an exothermic reaction, the energy is released in the form of heat, and in an industrial setting, this may save on heating bills, though the effect for most reactions does not provide the right amount energy to heat the mixture to exactly the right temperature. Often the mixture will need to be either cooled or heated continuously to maintain the optimum temperature for that particular reaction. For endothermic reactions heat is absorbed from the environment and so the mixture will need heating to be maintained at the right temperature. By right temperature, I mean that which optimises both equilibrium position and resultant yield, which can sometimes be a compromise, in the case of endothermic reactions."
Activation energy,"I don't get this. If a molecule has more activation energy, shouldn't it be more likely to reach the high barrier required and complete the chemical reaction faster? If I have more energy when I wake up, it is easier to get out of bed and it takes me less time to do so. Shouldn't chemical reactions be the same?","yeah, like amathakbari said-activation energy is the amount of energy needed to activate the complex that ocurrs at the transition state. it isn't energy you have"
Activation energy,What is the activation energy of the reaction?,Activation energy is the amount of energy needed to initiate a reaction.
Activation energy,can a product go back to a reactant after going through activation energy hump? (sorry if my question makes no sense; I don't know a lot of chemistry),"Theoretically yes, but practically no.
So this concept can be visualized with combustion or fire. While wood does not spontaneously burst into flame, if you add additional energy, with a match for an example, to the pile of wood, it starts a fire. What happens is that the energy in the match pushes the wood over the activation energy hump and starts the fire. Afterwards, the fire is self-sustaining because the fire creates enough heat to activate the rest of the wood.

Chemically, wood is composed of mostly carbon, which reacts with the oxygen in the air when 'activated' to create carbon dioxide.
So, for this reaction, carbon is the reactant and carbon dioxide is the product, which can be converted back into carbon (like photosynthesis) but requires more energy to do so.

The bottom line is that while it is possible, it will (in general) require additional energy to go back from a product to a reactant"
Activation energy,"Is there a difference between the terms endothermic/exothermic reaction and endergonic/exergonic reaction?

I only learned endothermic and exothermic as a reaction that stores energy and a reaction that releases energy.","Endothermic and exothermic refers to sign of the enthalpy of a reaction. Whether the net enthalpy change is positive or negative respectively. Where enthalpy is equivalent to heat.

 Endergonic and exergonic refers to the sign of the Gibbs free energy of a reaction. Whether the net free energy change is positive or negative respectively. Free energy taking into consideration both the enthalpy and entropy change of a reaction. 

Hope that helps."
Enzyme regulation,Allosteric regulation confuses me a lot. I don't really get it even after I watched the video on Khan Academy (MCAT) . Can anyone explain it to me briefly?,"I'll try an analogy — let me know if this helps.

Imagine that an enzyme is like tiny sculpture made from a wire twisted into a very complicated, but somewhat loose structure.  
The substrate is another much smaller sculpture that fits into a gap in the first sculpture — let's say it fits perfectly.
 Now think of hanging a weight off another part of the sculpture — the whole structure shifts a bit under the strain and now the substrate sculpture doesn't fit!   In this situation the weight would be analogous to an allosteric inhibitor. 

You could also imagine a similar scenario, but with the substrate fitting poorly until you added a weight — in this case the weight would be analogous to an allosteric activator."
Enzyme regulation,whats the difference between non competitive inhibition and allosteric regulation(involving inhibitor)? .its all so confusing,"Allosteric regulation and noncompetitive inhibitor bind to site other than active site but allosteric regulation change the conformation of enzyme and making the reaction less effective while the noncompetitive inhibitor, like mention in the reading just poison the enzyme so reaction does not take place at all."
Enzyme regulation,"In school, we conducted an experiment where a small piece of paper dipped in a liver solution was dropped into a test tube filled with hydrogen peroxide. After a few seconds, the liver juice coated paper rose to the the top. Why did it act in that way?","This is because the liver cells contain enzymes called catalase which speed up the breaking down of hydrogen peroxide into water and oxygen. When the reaction happens, oxygen is released and it pushes the piece of paper up to the surface along with it. This reaction happens faster or slower depending on the concentration of the liver juice you soaked the paper with."
Enzyme regulation,"if a allosteric inhibitor casues distortion of the enzyme's shape so that it cannot function, is it non-competitive or competitive?
(i looked up many resources ,such as princeton review AP bio,Barrons, internet, but they all weren't clear)","Being *allosteric* lets you know that the inhibitor binds somewhere other than the *active site*, where the substrate binds. The location that the allosteric inhibitor binds is called the *allosteric site*.

Because it isn't "competing" for the same binding site as the substrate, you can tell that it is non-competitive as the substrate will still be able to bond at the active site."
Enzyme regulation,what would happen if our bodies do not have inhibitors?,"*Good question*

Than uncontrolled cell divisions, uncontrolled sugar breakdowns, uncontrolled and unlimited phosphorylations (until the moment of using up all resources) and ultimately leading to energy depletion and death.

It may cause a ruckus in the body and high dysregulation which would end up fatal."
Enzyme regulation,What is an allosteric activator?,"A molecule that attaches to the enzyme at a site (not the active site), changing the configuration of the enzyme, which allows the substrate to attach to the active site easier."
Enzyme regulation,"Life is a process regulated by enzymes. What might be the sources of these enzymes? If particular enzyme is not available in person's cells, what sequence of events might result to produce it?","Enzymes are encoded as genes in the DNA — these genes are then transcribed to produce RNA and (for most enzymes§) then translated† to make a protein that has a catalytic activity (i.e. is an enzyme).

Typically enzymes found within a cell are encoded by the DNA of that cell.  However, multicellular organisms are colonized by many different microbes (these may be prokaryotes or other eukaryotes such as fungi) — these microbes often supply enzyme activities that aid the organism.  The digestive system of animals is one example of this.  In fact, most multicellular organisms depend on their microbiota for survival!

The process of regulating gene expression is highly complex, but there is KhanAcademy material on this is several places — I recommend starting here:
https://www.khanacademy.org/science/biology/gene-regulation

§Note: Some enzymes are make of RNA and these RNAs do not get translated.

†Note: Many proteins undergo post-translational modifications that are essential for them to function."
Enzyme regulation,"The information about noncompetitive inhibitors contradicts what Sal said in his videos: "Competitive Inhibition" and "Noncompetitive Inhibition"

What is described here as noncompetitive inhibition, Sal explains as allosteric. Sal has an entirely new definition for noncompetitive inhibition, describing it as a phenomena where the inhibitor and substrate can both bind.

I'm confused, someone please clear this up for me.","I think Sal is right about Competitive Allosteric Inhibition. In CAI, the inhibitor binds to an allosteric site (somewhere on the enzyme that is not an active site) and PREVENTS the substrate from binding in the first place. In non-competitive inhibition, the binding of the inhibitor still allows the binding of the substrate - the catalysis just doesn't work. 
The short answer is: CAI is competitive because only one thing, be it substrate or inhibitor, can bind to the enzyme.Non-competitive inhibition lets two things bind to the enzyme.
(I think Sal didn't write this article.)"
Enzyme regulation,How do you determine whether an enzyme's activity is enhanced or inhibited by regulatory cell binding?,"You follow up with the next steps. If reactions proceeds - it was activation, otherwise it must be some kind of inhibitor. :D"
N/A,I still can't understand why heat is considered unusable energy? Why cant heat which is the kinetic energy of particles be transformed to another type of enegry that can be used?,"There is a device called a thermocouple which converts heat to electricity. However, you do have to have one end of the thermocouple in something colder than the heat source."
N/A,Friction leads to entropy?,Yes. This generates heat (thermal energy) that in turn leads to a increase in entropy.
N/A,"When it is said that some o the energy converts to unusable energy, it means unusable right know due to limited tecnology? or is it never going to be usable? (I'm not sure why molecular kinnetic energy could no be used)","That heat(that is no more in a closed system) is not usable because it can not be converted to other form of energy, and this is because it can not be ''captured/collected''.
  The heat is not kinnetic energy itself, Its what causes kinnetic energy (the movement)."
N/A,"This might sound a bit gruesome, but do dead organisms also increase entropy of the universe?","Yes, actually. There’s a related thermodynamic concept known as equilibrium which all reactions, including biological reactions in organisms, try to reach. Going to equilibrium means a reaction is trying to maximize the increase in entropy to the universe. Organisms spend their whole lives trying to fight this equilibrium since maximizing entropy runs counter to a functioning complex living thing. 

It is possible for an organism to decrease the entropy in itself by using an input of energy because it corresponds to an increase in the entropy of the environment and a net change is an increase of the universe’s entropy. That’s really the main thermodynamic reason all organisms have to eat and consume energy, to obstruct all the life sustaining reactions from going to equilibrium. Once an organism dies, it can no longer resist equilibrium and all of the matter and energy of the once living organism disperses which causes an increase to the entropy of the universe. 

Hope that helps."
N/A,"Everything posted has been very helpful and I thank you all . Since energy cannot be created or destroyed and it can only change form or be transferred from one object to another, can we not consider the sun as the "factory" of energy and if not where does the sun receive his energy from?","Nuclear fusion, the forces in the nucleus are transformed into energy. https://www.euro-fusion.org/faq/how-is-it-that-both-fission-and-fusion-produce-power-if-splitting-a-large-atom-into-two-smaller-atoms-releases-energy-it-seems-that-combining-two-smaller-atoms-into-one-larger-atom-would-require-ene/"
N/A,Is there a formula or unit of measurement for entropy? Can we measure it in Joules or Kelvin/unit area?,"joules per kelvin
and it can get really tricky bc im pretty sure enthalpy is kilojoules/kelvin :)"
N/A,Is computer considered as a closed system?,"No, a computer gives off heat. Think of it this way: when the computer whirrs, that means the fan is going. If you put your hand near the fan, you can feel the heat. Therefore, the computer is giving off heat. Not to mention it's gaining electrical energy from the outlet or whatever the computer is plugged into."
N/A,"Regarding Entropy, do we know what is order is and where it comes from, or is it like Energy (we know what it does but as Feynman says that no one knows what energy is)?","I'm assuming you're asking about the opposite of entropy.  Technically, order can be measured as negentrophy (literally _negative entropy_), but it essentially just the reverse measurement of the entropy of a system and is of limited use.
   In regard to the origin of order, it can be assumed that since entropy increases as you follow the arrow of time, it must decrease as you follow it in the opposite direction. Since the universe is believed to have begun with a "big bang" resulting in a massive amount of entropy, it could hypothetically be assumed that the closest the universe has ever come to "order" was at same point before that. However, that is purely hypothetical. Assuming the currently popular model of a random universe, we would not expect order anyway, presumably negating the need for a real measurement of it. 

Hope that helped!"
N/A,Can heat be turned back into usable energy?,Heat can be used to produce energy if there is a lower temperature system to transfer that energy to.
Enzymes review,Do enzymes in the human body have the same optimal peak rate?,"No, the optimal peak varies across enzymes and is dependent on the enzyme in question.
For example, pepsin typically functions optimally in the acidic conditions of the stomach while trypsin prefers the more alkaline conditions of the small intestine"
Enzymes review,"So, an actual field question! But this section got me wondering.

I take lactase to assist in the breakdown of the few milk products I consume because it appears I'm lactose intolerant. I'm instructed to take one (or two, if one doesn't seem to be enough over time) every time I consume dairy.

Why do I need to continue to take these over time? Enzymes are reusable, right? They're not reactants. They should stick around after managing my lactose intake. So why do I need to keep taking these things every time I consume dairy? Isn't there a point after prolonged use where there should be a sufficient buildup of lactase enzymes present in the gut to address this issue long term?

Is my immune system doing away with the lactase for some reason?  Do I have really garbage gut pH? What's going on here?","Take this with a pinch of salt, but I am pretty sure that enzymes do not last forever. They will eventually wear out, and will be broken down into amino acids for other proteins. The supplements may also have to fight through the acidity of the stomach, and if you are warmer than usual, it is more likely that the enzymes will denature. Because they will wear out or potentially get damaged, you would need to replenish these enzyme stores to ensure that your body can break down the lactose found in dairy.

Like diabetes, you would have to keep taking the supplements in order to manage the condition. Again, though, please take my answer with a pinch of salt."
Enzymes review,Can an enzyme have more than 2 active site?,"Yes they actually can-- Here's a bit I found on Reddit ( any search will bring up a number of more reliable sources saying the same thing however ;D)

Yes. Some enzymes will bind a substrate and then there will be a change in its quaternary structure that could open up another active site for a different type of substrate. Other enzymes have more then one of the same active site and they can bind multiples of the same substrate.

Hope that helps!"
Enzymes review,where are enzymes created? in the cell?,"Like all proteins they are produced by *ribosomes*, which are in the cytoplasm (the part of the cell that is outside the cell nucleus). After an enzyme is synthesized it may be modified in the Golgi apparatus or elsewhere in the cytoplasm."
Enzymes review,What is the pH?,"In chemistry, pH is a numeric scale used to specify the acidity or basicity (alkalinity) of an aqueous solution. It is roughly the negative of the logarithm to base 10 of the concentration, measured in units of moles per liter, of hydrogen ions. More precisely it is the negative of the logarithm to base 10 of the activity of the hydrogen ion.

You can also learn more about it here, on KA:https://www.khanacademy.org/science/high-school-biology/hs-biology-foundations/hs-ph-acids-and-bases/v/introduction-to-ph"
Enzymes review,What are the different types of enzymes and what are the differences?,"If you are asking the types of enzymes by *how* they break reactant, there are *7 types* (some websites say there are 6 because after 2018, one type was added (-_-)). 
Oxidoreductases, Transferases, Hydrolases, Lyases, Isomerase, Ligases, and Translocase. (Maybe you don't need to learn them at this point.)

If you are asking the types of enzymes by *what* reactant they break, there are...well there are many (it is said there are about 2000 kinds). 
I have never counted but maybe there will be 20 ~30 enzymes you will see learning biology. One third of them will be about plants and the rest will be about human body. Don't worry, you will learn them step by step.

As you can see the above, basically the difference is determined by  how they break or what they break."
Enzymes review,"In the last paragraph it mentions that an enzyme is not a reactant.
What is a reactant?",A reactant is a substance that changes in a chemical reaction.
Enzymes review,Why can enzymes work again after being inactivates but may not work after being denatured?,"When they are denatured, the shape of the protein is changed permanently, thus the active site is changed permanently as well. Therefore the enzyme cannot work like it used to. But an inactive enzyme is caused when the temperature is too low for example, the enzyme is fine because it is really cold, there are virtually no collisions/very less collision, meaning that no reaction is taking place. As there is nothing wrong with the enzyme, if you just merely increase the heat, the enzyme will work as it should because there will be collisions."
Enzymes and the active site,What would happen if the shape of the enzyme's active site were changed?,"If the active site were changed, possibly by a large change in temperature or pH, the enzyme would most likely not be able to catalyze the same reactions. This is because temperature and pH can denature (or change) and enzyme's shape and therefore make it unable to bind with the same specifically shaped substrates as before."
Enzymes and the active site,Which type of bond exists between enzyme and the substrate in enzyme substrate complex?,"Generally, they are ionic bonds or van der Waals forces (hydrogen bonds, London dispersion forces, and dipole-dipole interactions). They can occasionally be covalent bonds."
Enzymes and the active site,"Hi, I think there's a mistake in the text. Or perhaps I don't understand it. There's written "Instead, enzymes lower the energy of the transition state, an unstable state that products must pass through in order to become reactants". Products become reactants? Isn't it supposed to be the other way around? That reactants become products. I don't know.",yeah its probably a typo
Enzymes and the active site,what exactly are activated co enzymes,"(Activated) Coenzymes are small molecules. They cannot by themselves catalyze a reaction but they can help enzymes to do so. Enzymes are biological catalyst that do not react themselves but instead speed up a reaction.
So, a coenzyme activates the enzyme to speed up a (biological) reaction."
Enzymes and the active site,How does RNA catalyze a reaction?,"RNA molecules that can function as enzymes are known as ribozymes. RNA can have 3 dimensional structure because it can hydrogen-bond with itself and form loops. Some of the bases in the RNA have special functional groups which can add specificity to the shape. The RNA can also hydrogen-bond with other nucleic acids to create an even more specific shape.
 
One example ribosomal RNA, which can catalyze the translation of mRNA in ribosomes. In ribosomes, rRNA and proteins come together and form a space for messenger RNA to be read and for transfer RNA to bond to the ribosome and attach the correct amino acid. The specific shape of the rRNA allow the mRNA to be translated properly."
Enzymes and the active site,"Can you give me an example of a catalyst that is not an enzyme?
Many thanks!","Metals like rhodium and platinum are used as catalysts in catalytic converters, which lower dangerous emissions from cars. In the presence of these catalysts, nitrogen oxide, a dangerous substance, is broken into nitrogen and oxygen, both harmless."
Enzymes and the active site,enzymes have an active site that does all the actual work. but what is the function of the rest of the molecule? why it still exists? what is the evolutionary role of it?,"In general terms, the rest of the enzyme molecule is there to ensure that the active site contains the right amino acids in exactly the right orientation relative to one another.

Let's say that the active site needs three specific amino acids lined up in a very defined way. The rest of the molecule provides a framework (scaffolding, if you like) that ensures the active site is properly set up. Without this framework there would be no way of fixing the key amino acids into the correct positions.

Also, the critical amino acids may be a long way apart from one another in the primary sequence of the protein and are only brought together through the secondary and tertiary structuring of the protein.

What's more, with the induced fit model, the rest of the molecule can be involved in changing the confirmation of the enzyme. Related to this is enzyme regulation where modification of an amino acid remote from the active site can control the activity of the enzyme. Furthermore, in some enzymes there is a second binding site and when something, such as an inhibitor, binds to that site it changes the shape of the active site, also controlling the enzyme."
Enzymes and the active site,How do enzymes enable chemical reaction to take place rapidly ?,"They offer an alternative reaction pathway that has a lower activation energy i.e. less energy is required for the reaction to occur. Therefore, more particles will have the required energy, and more particles can react at the same time, thus increasing the reaction speed."
Enzymes and the active site,How do inhibitors stop enzyme activities?,"There are four different kinds of inhibitors; *competitive inhibitors, noncompetitive inhibitors (allosteric inhibitors), irreversible inhibitors*, and *feedback inhibitors*. 

*Competitive inhibitors* compete with the _substrates_ of an enzyme at its _active site_. When they bind to the active site of the enzyme, they prevent the enzyme from breaking or creating molecules. 

*Noncompetitive inhibitors*, also known as *allosteric inhibitors*, do not compete with substrates for the active site. Rather they bind to a different area on the enzyme. This area is known as the _allosteric site_. When the inhibitor binds to the allosteric site, it causes a _conformational shape change_, preventing the enzyme's substrates from attaching to it. Thus preventing the breakdown or formation of a molecule.

*Irreversible inhibitors* have two forms; *irreversible competitive inhibitors* or *irreversible noncompetitive inhibitors*. These inhibitors either bind to the _active_ or _allosteric site_ of an enzyme. 

*Feedback inhibitors* are the end products of reactions. They interfere with the enzyme that helped produce them. They bind to the _allosteric site_ of the enzyme changing the shape of the enzyme. They usually help in _regulating_ and _coordinating the products_ of an enzyme."
Enzymes and the active site,Rather than the environmental pH. Does the pH of the substrate also causes a change in it's active site?,"Okay, so pH is actually defined based on the concentration of H+ in a given volume. So the substrate doesn't have a pH. Many molecules of the substrate dissolved in water do have a pH, but an individual molecule? Nah. The substrate does have different polarities (positive and negative charged areas) but the enzyme is built to handle that. These differently charged regions help the substrate lock in place."
Introduction to cellular respiration and redox,What is the difference between nadph and nadH,"It is just one extra phosphate group in NADPH, the rest of the molecule is identical. Both act as proton donors although for different sets of biochemical reactions."
Introduction to cellular respiration and redox,What is the difference between NADPH and NADH,NADH is used in cellular respiration whereas NADPH is used in photosynthesis; NADPH has an extra phosphate group.
Introduction to cellular respiration and redox,Is NAD+/NADH primarily involved with glucose (entering ETC via complex1) & FAD/FADH2 primarily (exclusively?) involved with fats & amino acids (entering ETC via complex2)?,"Not that I know of. They are both carriers for hydrogen ions (H+) and their purpose is to get those electrons/ions to the ETC where they can be used to make ATP. Since the NADHs are dropped at the first protein complex, the hydrogen ions that it brings in go through active transport in 3 proteins, making 3 ATP for every NADH. The FADH dropps off the H+s at the second protein complex, and since the H+s it brings in only go through 2 proteins, it only makes 2 ATP for every FADH molecule.

So to answer your question, where the molecules enters, to my knowledge, has nothing to do with whether it is involved with glucose or amino acids. Could you possibly be getting it confused with something else?"
Introduction to cellular respiration and redox,"I still can't comprehend the notion of electrons' energy levels. I thought that it had to do with which orbital the electron was in, being the furthest away from the nucleus the ones with higher energy levels. But then, why are electrons at a higher energy level when associated with a hidrogen than when associated with an oxygen?","Yes, further apart orbitals are associated with higher energy levels.

Look, if an element is more electronegative than it attracts other atoms and makes electrons scroll down to the lower energy states. More electronegative element hogs electrons stronger than a less electronegative element."
Introduction to cellular respiration and redox,What is the purpose of Cellular Respiration??,"Cellular respiration is an absolutely essential process for any cell because it's how it produces energy. 

Cells need energy for all kinds of things: moving things around, producing substances, getting nutrients, etc.

For cells, this energy typically comes in the form of a molecule called ATP. Cellular respiration is a series of steps by which fuel molecules (such as glucose from your food) can be used to produce ATP that the cell can use. 

Does that help?"
Introduction to cellular respiration and redox,"Do all catabolic processes occur under anaerobic conditions, while anabolic process occur under aerobic conditions, or is that just a coincidence?","Did you mean the opposite of what you wrote?

In any case, things are not nearly that simple.


Catabolism (the breakdown of complex molecules to simpler components) can be anaerobic or aerobic.  In fact both types happen in our bodies all the time — in most tissues we typically use oxidative respiration (an aerobic process) to maximize the amount of energy we extract from food.  However, during vigorous exercise our muscles run out of oxygen and switch to an anaerobic process called lactic acid fermentation.  This is also the process that powers our red blood cells.

You will learn more about some forms of anaerobic respiration later in this section:
https://www.khanacademy.org/science/biology/cellular-respiration-and-fermentation#variations-on-cellular-respiration


Anabolism (building complex molecules from simpler components) in most cases isn't directly influenced by oxygen availability, but since it requires energy it will be hampered by anaerobic conditions (at least in aerobic organisms like us).

However, there is at least one hugely important anabolic process that is poisoned by oxygen — nitrogen fixation.
(For more information on this see:
https://www.nature.com/scitable/knowledge/library/biological-nitrogen-fixation-23570419)"
Introduction to cellular respiration and redox,Why is it that O is more electronegative but when a carbon based molecule loses O it becomes reduced?,Because it gains an electron.
Introduction to cellular respiration and redox,i still cant understand the concept of oxidation and reduction in term of NAD+ and FAD.. when NAD+ oxidise or reduce to NADH? why ?,"NAD+ --> NADH is reduction (because it's gaining a hydrogen). It's being reduced because NAD+ is made up of carbon, hydrogen, nitrogen, oxygen and phosophorus atoms and all of these are very electronegative except for hydrogen. When the NAD+ bonds with a hydrogen the electrons are hogged by the very negative atoms like when Sal was talking about glucose. This is the same for FAD I think because it's made up primarily of those electronegative atoms. Hope that helps :)"
Introduction to cellular respiration and redox,Is the action/movement of ATP synthase passive or active?,Overall functioning of ATP synthase is 'passive'. It requires a proton gradient in order to work. it does not require dephosphorization of another ATP molecules.
Introduction to cellular respiration and redox,Can you explain how 36 ATP is forned in cellular respiration in eukaryotes?,"Actually, the amount of ATP produced in cellular respiration actually varies. It depends on the cell's efficiency and therefore fluctuates in the maximum production of ATP. So it can be any whole number of ATPs, probably 34, 36, or 38 ATPs in a eukaryotic cell. Usually, that number varies in the oxidative phosphorylation step, depending on the amount of NADH and FADH2 available for the process. NADH produces 3 ATP while FADH2 produces 2 ATP via chemiosmosis. Glycolysis produces 2 ATP and 2 NADH, Krebs Cycle produces 2 ATP, 6 NADH, and 2 FADH2. Then, you have a net total of 36 ATP. Sal explains this much better than I could :P."
The light-dependent reactions,"Ok so from what I am understanding from this article is that the electrons for the electron transport chain come from the splitting of water, but I am having trouble grasping that? Specifically, are the electrons moving on up and down the chain by themselves...without protons and neutrons?","You are correct. When we split the H2O, our 2 protons in the hydrogen (the h+ ions, basically just a proton floating around), the waste product of oxygen, and then our 4 electrons. Since we have these 4 electrons removed, they allow the hydrogen to be positively charged, as the hydrogen now only has a positive charge in it. 

A simpler way to think of it is to relate this to a circuit - only electrons flow through circuitry of say, a light bulb, not entire atoms."
The light-dependent reactions,How does ATP release energy?,"ATP consists of adenosine - itself composed of an adenine ring and a ribose sugar - and three phosphate groups (triphosphate). The phosphoryl groups, starting with the group closest to the ribose, are referred to as the alpha (α), beta (β), and gamma (γ) phosphates. The system of ATP and water under standard conditions and concentrations is extremely rich in chemical energy; the bond between the second and third phosphate groups is loosely said to be particularly high in energy. Strictly speaking, the bond itself is not high in energy (like all chemical bonds it requires energy to break), but energy is produced when the bond is broken and water is allowed to react with the two products. Thus, energy is produced from the new bonds formed between ADP and water, and between phosphate and water. 
The net change in energy at Standard Temperature and Pressure of the decomposition of ATP into hydrated ADP and hydrated inorganic phosphate is -12 kcal / mole in vivo (inside of a living cell) and -7.3 kcal / mole in vitro (in laboratory conditions). This large release in energy makes the decomposition of ATP in water extremely exergonic, and hence useful as a means for chemically storing energy. Again, the energy is actually released as hydrolysis of the phosphate-phosphate bonds is carried out. 
This energy can be used by a variety of enzymes, motor proteins, and transport proteins to carry out the work of the cell. Also, the hydrolysis yields free inorganic Pi and ADP, which can be broken down further to another Pi and AMP.
I Hope This Helps."
The light-dependent reactions,"May I ask about the source of hydrogen ions for reduction of NADP+? I am reading some articles that say that the hydrogen ions derived from the photolysis of water are used to reduce NADP, but in my understanding, photolysis and NADP reduction occur on opposite sides of the thylakoid membrane, photolysis contributes to the proton gradient, and that the uptake of hydrogen ions to form NADPH occurs in the stroma (and thus also indirectly contributes to the size of the proton gradient through consumption of stromal hydrogen ions). Can you make this any clearer for me? Thanks!","Remember that all aqueous solutions contain a small amount of hydronium (H₃O⁺) and hydroxide (OH¯) due to autoionization§. 

This means that processes in cells can use water to get rid of or grab "protons" (H⁺) as needed.

Does that help?


§Note: If you are not familiar with this concept, I suggest watching:
https://www.khanacademy.org/science/chemistry/acids-and-bases-topic/acids-and-bases/v/autoionization-water
and then reading the article following that video for details."
The light-dependent reactions,I am still confused whether the hydrogen ions are pumped from lumen to stroma or from stroma to lumen or both?,"at first hydrogen ions are pushed into lumen, but as the concentration increases inside the lumen , it is going to activate the ATP synthase enzyme which synthesis ATP by pulling 2 hydrogen ions out to the stroma"
The light-dependent reactions,"i just thought of this, would it be possible to genetically engineer a plant that can use light in the infared wavelengths (heat) for photosynthesis?","Quite interesting question!

I do not think it would be possible.

Plant cells are not designed to accept/tolerate infrared or UV light (which is destructive to plants).
BUT

there are some speculations about engineering plants to harvest infrared light to perform photosynthesis more effectively and produce more sugar.

Since there are algae which can do photosynthesis in low light conditions, why wouldn't it be possible for plants too?

We have to be patient and see where this is going. :)


https://undark.org/article/can-better-photosynthesis-help-feed/"
The light-dependent reactions,"photosynthesis involves the 
a. oxidizing of carbohydrates
b produces all the earth oxygen gas
c reduction of carbohydrates
d. oxidation of carbohydrates",？？i am so screwed for AP bio
The light-dependent reactions,"My textbook says that ATP is made as electrons move along the electron transport chain. It this referring to the contribution of pumping protons across the membrane for chemiosmosis, or is there another method of synthesising ATP entirely?","Electrons move down the transport chain, which creates a proton gradient, and then that gradient is used to make ATP"
The light-dependent reactions,"In paragraph 13 you say that the ATP and NADPH produced from the light dependent part of photosynthesis are used to fuel the Calvin Cycle. I'm wondering if ALL of the ATP and NADPH get used this way, or if some are used as fuel for other immediate cellular processes. Thanks!","Some must get used within the chloroplast for other metabolic processes, but my understanding is that most gets used to fix carbon — this uses a lot of ATP, which is part of why cyclic photophosphorylation exists.   Chloroplasts even have a mechanism for exchanging ADP for ATP to support their basal metabolic processes in the dark.

In particular ATP isn't very stable, so it makes sense to use it to make sugars (and other macromolecules) before exporting the "energy".

You might also find this discussion interesting:
https://biology.stackexchange.com/questions/42888/why-is-atp-produced-in-photosynthesis-used-to-synthesize-glucose"
ATP and reaction coupling,Is it possible to run out of ATP?,"The cell also has in place mechanisms to stop this from happening. Like the enzyme phosphofructokinase (crazy name, I know) which is involved in the beginnings of glycolysis. Glycolysis is one of the early stages of making ATP from ADP. So, when there's more ADP around phosphofructokinase will work harder (which allows to the whole cycle to go faster, regenerating more ATP).  When there's a lot of ATP, though, phosphofructokinase (and other enzymes like it) will slow down. So basically, the cell has things set up carefully so that the right amount of ATP will be available (unless, as Laurent said, the cell is dying)."
ATP and reaction coupling,What happens with those -3kJ/mol from the formation of sucrose? Does it transform on heat?,"Yes, this 3 kJ/mol is released as heat that dissipates in the environment."
ATP and reaction coupling,"Where does the energy come from to synthesis ATP from ADP and P ?
is it when you couple the reaction that turns it back into ATP",It comes from oxidative phosphorylation at the end of the electron transport chain.
ATP and reaction coupling,"Why just ATP though? Why not TTP, CTP, or GTP as well? If it is possible with one nucleotide, why not the others?","All eukaryotic proteins use ATP for their respective energy requirements not TTP, CTP, or GTP. Also because ATP donates a phosphoryl group."
ATP and reaction coupling,Why do energy released by ATP under standard conditions at 25 °C is important if human body temperature is 36.5–37.5 °C ?,"It is used for standardization, 25°C is called "room temperature" and is used for lab experiments in test tubes rather then inside of your body."
ATP and reaction coupling,"Wouldn't ATP be more stable when the middle phosphates' charged oxygen was located above the phosphates, so the charges are further apart?","Single bonds rotate along their axis, so any drawing you might see of a molecule is, by all means, NOT set in stone. Yes, like charges move away from each other, when permitted, but we usually don't draw it like that, for the sake of consistency."
ATP and reaction coupling,"When it is said "ATP releases energy", I would imagine something imaginary (kinda like a wave) travelling to help in creating another bond.

Energy is not created nor destroyed. At the end of the reaction above:
3K. energy transferred as heat.

The reaction glucose + fructose requires 27K.
As I said I used to imagine some imaginary wave, instead I'm thinking now that when ATP gives this 27K. it does this by creating instability, and we classify it as giving energy. Is this true?

If true, then theoretically can't phosphate, without being part of ATP, just 'run' around the cell and just keep creating instability (sounds like unlimited free energy). Why does it have to be reattached to ADP to form ATP again? Is it because inorganic phosphate is not unstable enough?

If not true then what is this 27K. energy represented by?","It is not ATP itself that releases energy, and also not the bond to the final phosphate bond being broken. If you think about it, you actually need energy to break any bonds, including that one (otherwise it would fall appart and not be a bond that keeps atoms together!). The energy is actually from _hydrolyising_ ATP, ie breaking that bond, but also forming new ones. The products ADP and inorganic phosphate are lower in (potential) energy than ATP. (This has several reasons, and isn't as simple as counting bonds and expecting them to have the same energies as in other molecules, but also that having a solvated inorganic phosphate is more entropically favourable). So, the ATP reaction wants to move in the ADP+ Pi direction. But you can't just do that and hope it magically drives another reaction in reverse/uphill. What often happens, is that ATP will react with the reactants of the other reaction, some steps occur converting reactant to product, and in the end ADP and Pi are released. Each step turns out energetically favourable, driven forward by a loss in free energy, and by the end you have converted reactants to products in a reaction that would not normally go forwards on its own by allowing ATP to drop from a high energy to low energy. Does this help explain?"
ATP and reaction coupling,"Could someone explain what "ΔG" is? I know it means something like "free energy", but I can't find any good articles about what it really is.","Delta G is really Gibb's Free Energy. If Delta G is less than 0, the reaction is spontaneous. If not, the reaction is not spontaneous. I encourage you to watch https://www.khanacademy.org/science/biology/energy-and-enzymes/free-energy-tutorial/v/gibbs-free-energy-and-spontaneous-reactions"
Enzymes review,Do enzymes in the human body have the same optimal peak rate?,"No, the optimal peak varies across enzymes and is dependent on the enzyme in question.
For example, pepsin typically functions optimally in the acidic conditions of the stomach while trypsin prefers the more alkaline conditions of the small intestine"
Enzymes review,"So, an actual field question! But this section got me wondering.

I take lactase to assist in the breakdown of the few milk products I consume because it appears I'm lactose intolerant. I'm instructed to take one (or two, if one doesn't seem to be enough over time) every time I consume dairy.

Why do I need to continue to take these over time? Enzymes are reusable, right? They're not reactants. They should stick around after managing my lactose intake. So why do I need to keep taking these things every time I consume dairy? Isn't there a point after prolonged use where there should be a sufficient buildup of lactase enzymes present in the gut to address this issue long term?

Is my immune system doing away with the lactase for some reason?  Do I have really garbage gut pH? What's going on here?","Take this with a pinch of salt, but I am pretty sure that enzymes do not last forever. They will eventually wear out, and will be broken down into amino acids for other proteins. The supplements may also have to fight through the acidity of the stomach, and if you are warmer than usual, it is more likely that the enzymes will denature. Because they will wear out or potentially get damaged, you would need to replenish these enzyme stores to ensure that your body can break down the lactose found in dairy.

Like diabetes, you would have to keep taking the supplements in order to manage the condition. Again, though, please take my answer with a pinch of salt."
Enzymes review,Can an enzyme have more than 2 active site?,"Yes they actually can-- Here's a bit I found on Reddit ( any search will bring up a number of more reliable sources saying the same thing however ;D)

Yes. Some enzymes will bind a substrate and then there will be a change in its quaternary structure that could open up another active site for a different type of substrate. Other enzymes have more then one of the same active site and they can bind multiples of the same substrate.

Hope that helps!"
Enzymes review,where are enzymes created? in the cell?,"Like all proteins they are produced by *ribosomes*, which are in the cytoplasm (the part of the cell that is outside the cell nucleus). After an enzyme is synthesized it may be modified in the Golgi apparatus or elsewhere in the cytoplasm."
Enzymes review,What is the pH?,"In chemistry, pH is a numeric scale used to specify the acidity or basicity (alkalinity) of an aqueous solution. It is roughly the negative of the logarithm to base 10 of the concentration, measured in units of moles per liter, of hydrogen ions. More precisely it is the negative of the logarithm to base 10 of the activity of the hydrogen ion.

You can also learn more about it here, on KA:https://www.khanacademy.org/science/high-school-biology/hs-biology-foundations/hs-ph-acids-and-bases/v/introduction-to-ph"
Enzymes review,What are the different types of enzymes and what are the differences?,"If you are asking the types of enzymes by *how* they break reactant, there are *7 types* (some websites say there are 6 because after 2018, one type was added (-_-)). 
Oxidoreductases, Transferases, Hydrolases, Lyases, Isomerase, Ligases, and Translocase. (Maybe you don't need to learn them at this point.)

If you are asking the types of enzymes by *what* reactant they break, there are...well there are many (it is said there are about 2000 kinds). 
I have never counted but maybe there will be 20 ~30 enzymes you will see learning biology. One third of them will be about plants and the rest will be about human body. Don't worry, you will learn them step by step.

As you can see the above, basically the difference is determined by  how they break or what they break."
Enzymes review,"In the last paragraph it mentions that an enzyme is not a reactant.
What is a reactant?",A reactant is a substance that changes in a chemical reaction.
Enzymes review,Why can enzymes work again after being inactivates but may not work after being denatured?,"When they are denatured, the shape of the protein is changed permanently, thus the active site is changed permanently as well. Therefore the enzyme cannot work like it used to. But an inactive enzyme is caused when the temperature is too low for example, the enzyme is fine because it is really cold, there are virtually no collisions/very less collision, meaning that no reaction is taking place. As there is nothing wrong with the enzyme, if you just merely increase the heat, the enzyme will work as it should because there will be collisions."
Fermentation and anaerobic respiration,Is there a reason why Flourine can't be used in place of oxygen as the final acceptor in the electron transport chain? Wouldn't it produce more ATP due to its higher electronegativity?,"There are a few reasons that spring to mind. The first is simply to do with availability. Oxygen makes up 21% of our atmosphere and is stable in both air and water whereas fluorine is much rarer. In addition fluorine is very reactive so would not exist by itself for very long. Also if fluorine were used as the terminal electron acceptor it would form HF, hydrofluoric acid in solution which is hard for the cells to deal with and would affect pH in the cytosol affecting enzyme function whereas oxygen just forms water. Finally fluoride is known to be damaging to the body above certain concentrations affecting things like the nervous system and hormone secretion as well as protein synthesis.
Please bear in mind these are just my thoughts.

P.S remember oxygen is not producing the ATP itself it is merely keeping the transport chain unblocked so the electrons keep flowing. A more electronegative element wouldn't necessarily have any effect on the rate of electron flow down the ETC and therefore wouldn't affect the rate of ATP production."
Fermentation and anaerobic respiration,Would Balsamic Vinegar be an example of lactic acid fermentation since the grape bypasses the alcohol?,"To make vinegar, grapes are first made into wine via fermentation. The next step in the process is the introduction of an Acetobacter bacteria strain. Acetobacter in the presence of oxygen will feed upon ethanol and release acetic acid (vinegar) as a byproduct."
Fermentation and anaerobic respiration,"In the diagrams there write, "NADH regeneration," wouldn't it be more accurate to say "NAD+ regeneration?"",its kind of like regenerating nad+ so that they can accept electrons to *become nadh again*
Fermentation and anaerobic respiration,"Okay, this is actually really interesting... if the lactate isn't what's causing the soreness of muscles after exercising, then what is it?","It is associated with damage to the muscle fibers, but the details don't appear to be well studied.

This article seems to be the source for much of the information currently available on the internet:
https://www.ncbi.nlm.nih.gov/pubmed/7830383"
Fermentation and anaerobic respiration,Where is the electron transport chain in an anaerobic respiration found?,"The electron chain is not found in anaerobic respiration. Anaerobic means "without oxygen". The electron transport chain requires oxygen, therefore it cannot be present in anaerobic respiration.

I hope this helped! Comment if you have any questions; I'll answer to the best of my ability."
Fermentation and anaerobic respiration,Why can't human undergo ethanol fermentation? is there an enzyme that is required which we don't have?,"Exactly.

We lack alcohol pyrivate dehydrogenase.

Also, it would be lethal for humans to produce ethanol. Ethanol is very toxic, causing: drowsiness, cognitive impairment, liver failure, liver cirrhosis, and eventually death."
Oxidative phosphorylation,how does the nadh from glycolisys gets into the matrix so its electron could be used?,"It says above that NADH can't't cross the mitochondrial membrane, so there is some sort of shuttle protein."
Oxidative phosphorylation,"if the volume of the intermembrane space  was increased, what effect would this have on the function of a mitochondrion?","Hm.... A cell stays small to allow easier transport of molecules and charged particles from organelles. If the intermembrane space of the mitochondria was increased, I would think that respiration would be less efficient, because now the electrons have to cross a larger space and lose much more energy. So.... That's my guess and it would probably be wrong,"
Oxidative phosphorylation,What does substrate level phosphorylation means?,"Substrate level is the 'direct' formation of ATP in glycolysis and the Krebs cycle, basically any ATP not formed during the electron transport chain."
Oxidative phosphorylation,"Where did all the hydrogen ions come from? If NADH becomes NAD+, it releases H+ and if FADH2 becomes FAD and would release 2H+. So are the hydrogen ions released by those electron carriers are going to be used for the gradient and also for the water formation? Or are the Hydrogen ions that just came back through the ATP synthase going to be used for forming H2O??","The individual reactions can't know where a particular "proton" came from.  

Remember that all aqueous solutions contain a small amount of hydronium (H₃O⁺) and hydroxide (OH¯) due to autoionization.  

This means that processes in cells can use water to get rid of or grab "protons" (H⁺) as needed.  

This does have a small local effect on the pH, but forming that NADH or FADH₂ used protons so it all balances out in the end."
Oxidative phosphorylation,"I don't quite understand why oxygen is essential in this process. I get that oxygen serves as an electron acceptor at the end of the electron transport chain, but why is having this electron acceptor so important? Why would ATP not be able to be produced without this acceptor (oxygen)?","It is sort of like a pipeline. If you block the exit, the flow through the entire pipeline stalls and nothing moves. Oxygen is what allows the chain to continue and keep producing ATP."
Oxidative phosphorylation,"Where do the hydrogens go? I mean in glycolysis, one glucose is oxidised into two pyruvic acid and two NADHs. But technically there should be net two protons left in cytosol and that's where I am puzzled. Are the protons tansported into mitochondria matix and later pumped out by ETC or intermembrane space to form electrochemical gradient, or are they left in cytosol? According to the amont of water molecules generated in chemiosmosis, all the hydrogen from the glucose should be used to  form water, so do protons go into the mitochondria or mitochondria has extra protons itself?","Remember that all aqueous solutions contain a small amount of hydronium (H₃O⁺) and hydroxide (OH¯) due to autoionization.  

This means that processes in cells can use water to get rid of or grab "protons" (H⁺) as needed.  

This could have a small local effect on the pH, but cells are well buffered.  Also, in the end the various processes that create and use H⁺ end up balancing each other out.

The only situations where we really need to keep an account of H⁺ are processes involving membranes (e.g. oxidative phosphorylation) where H⁺ gradients are created and used."
Oxidative phosphorylation,How much H2O is produced is the electron transport chain?,"`C6H12O6 + 6O2 → 6CO2 + 6H2O + energy`


6 molecules of water :D


This is the overall formula for cell respiration, however, you ask how many water molecules are produced _specifically_ during electron transport chain?

Knowing that in the end, you get 6 molecules of water from *one* glucose molecule.
In the electron transport chain, hydrogen atoms are being added to available oxygen in order to produce water.


So you are confused about 6Co2, too? well, you know that after glycolysis, you get 3C molecules and bot undergoes Krebs cycle. Now, what you get from one Krebs cycle and proceeding ETC is doubled.

While it is true that via Krebs cycle we get 2 CO2 (giving 4 in total), do not forget decarboxylation prior to entering Krebs cycle (in between Glycolysis and Krebs cycle) there are is 1CO2. 1x2 = 2, 2+4 = 6

only 2NADH are reduced during ETC, giving a total number of 2, and also one FADH2 giving 1. It is 3x2 =6

*as for Oxygen*, it comes from the red blood cells which carry oxygen to absolutely every cell. Once in the cell, it enters mitochondria and acts as final acceptor of electrons. if not, water would not be produced.


http://www.dbriers.com/tutorials/2012/04/the-electron-transport-chain-simplified/"
Basics of enzyme kinetics graphs,""Conversely, for a competitive inhibitor, the reaction gets never reaches its normal V{max}" it's noncompetitve right?","Yes, you are absolutely right, I just fixed that and it should be reflected on the site soon. Thanks for your good eye!

Also, if you find other errors in the future, please don't hesitate to report them through the "report a mistake" button.

Thanks again!"
Basics of enzyme kinetics graphs,""An uncompetitive inhibitor reduces Vmax, but increases the apparent Km"... doesn't the uncompetitive inhibitor bind to the enzyme and enhancing its binding to the  substrate (higher affinity means lower Km)?","You're right, and it should be changed in the article. The apparent Km decreases in uncompetitive inhibition because by binding to the enzyme-substrate complex, uncompetitive inhibitors are "pulling" that complex out from the reactions. This removal of substrate decreases its concentration, and allows the remaining enzyme to work better. In general, a lower Km indicates better enzyme-substrate binding."
Basics of enzyme kinetics graphs,"Can someone please clarify why Km is always the same?  If i were to add more enzyme Vmax would increase and since Km is just 1/2 of Vmax, wouldn't Km increase as well?","Km is not 1/2 Vmax!

Km is the substrate concentration at which the initial reaction rate is equal to 1/2 Vmax.

One way to avoid this type of confusion is to note that the units are completely different."
Basics of enzyme kinetics graphs,"Super helpful article!!
Why does the Vmax occur at the same determined time interval each time in a reaction?","Because every enzyme has its kinetics and speed it can operate with.

Cars also take always the same time to reach Vmax if starting from zero speed (start)."
Basics of enzyme kinetics graphs,"I don´t understand the graphs.   What the curves show is a minimum rate of reaction   at minimum  substrate concentration ,  and maximum rate at higher concentrations, which is the opposite of the theory. If I want to plot rate vs concentration the curve should be a  kind of decreasing exponential function, with 0 rate at maximum concentrations. Im I wrong?","If I'm understanding you correctly I think you've got things backwards ...

You seem to be saying that according to theory the maximum reaction rate would occur when there was no substrate.  
Does that really make sense?"
Basics of enzyme kinetics graphs,"An irreversible inhibitor, wouldn't the number of enzymes available decrease, thus making it a noncompetitive inhibitor?","Yes, I believe you're right about that. I didn't think about that before!"
The Calvin cycle,Do  plants move,"Yes, they can. For example, morning glories and Venus flytraps move. Some other plants also have reflexive movement, as in a response to being touched."
The Calvin cycle,if a plant is in drought conditions i.e. wilting does chloroplast activity slow down?,"Yes. Because the plant can no longer absorb more H2O through its root structure, the plant will use what water it has stored. The wilting occurs because it is undergoing plasmolysis which reduces the turgor pressure on the plant's cell wall."
The Calvin cycle,Why is the O2 not counted in the calvin cycle? In light reaction plant takes H2O and uses the H but releases the O. In calvin cycle plant takes CO2 and uses the carbon but my gues is that the O2 is not lost. Is it also released to the atmosphere?,It gets added to the glucose molecule( C.6 H.12 O.6 )
The Calvin cycle,"Where did the Oxygen removed from 1st Carbon in 3PGA  went? 
In the reduction process 3PGA(Carboxylic acid)--> G3P(aldehyde), 1 O is missing? Where did it went?","actually the O is in between of  C-1 and P. when 2H are added by NADPH2 , the bond between C and P  breaks. 1H is used to reduce C. other H togather with O combines with P forming phosphate group.          hope you understand"
The Calvin cycle,"To clarify, one cycle of the Calvin Cycle would produce 1/6 of a glucose molecule, hypothetically speaking?","Not quite. It is true that you need to fix six CO2 molecules for each glucose molecule you produce, and you need 6 ribulose-1,5-bisphosphate to do so, however the reactions need 3 of each to produce phosphoglyceraldehyde. ie. the cycle does not produce 1/6th of a glucose molecule 6 times and join the units together. Instead, it takes 3 of each reactant to produce PGAL, which happens *two times* to lead to production of 1 glucose molecule. This is why it takes *2* cycles to produce one glucose molecule."
The Calvin cycle,Where does the sugar go after being produced from the compounds leaving the Calvin Cycle?,"Sugar goes into plastids to be stored or being actively utilized for plant growth, flowering and seeds."
The Calvin cycle,Does calvin cycle produces oxygen as a by product too?,"No it does not.

All the oxygen released comes from "splitting" of water by photosystem II during the light-dependent reactions.  

The "extra" oxygen in CO₂ gets used during the hydrolysis of ATP during the Calvin Cycle."
The Calvin cycle,Why does it take 6 turns of the Calvin Cycle to form 1 molecule of glucose?,"because three carbons bond with 3 RuBp to make 3 molecules. This splits into 6PG or 6 phosphoglycerate. 6 phosphoglycerate is changed into 6 biphsophoglycerate, which is changed to 6G3P. 5 of those goes back into the cycle to make RuBp so that it can do it all over again, and one is put aside to make glucose. But you need 6 of these to make glucose, so it will take you 6 turns. Hope this helps!"
The Calvin cycle,in the last line why does it say that it takes 6 cycles to make one molecule of glucose? is only one CO2 and one RuBP used in each cycle?,"One cycle takes in one CO2. Three cycles, after many smaller steps, creates six G3P (three-carbon); here, five goes back into the cycle, and only one is used for glucose. Glucose is a six-carbon molecule, so two G3P are needed. The math, then, is 3X2=6."
The Calvin cycle,What's the formula of the calvin cycle?,"3 CO2 + 6 NADPH + 6 H+ + 9 ATP + 5 H2O → glyceraldehyde-3-phosphate (G3P) + 6 NADP+ + 9 ADP + 8 Pi   (Pi = inorganic phosphate)
Taken from wikipedia article on it"
Introduction to cell signaling,"Wait, so then whats the feature of a target cell that makes it receptive to a particular signalling molecule? Would this be the shape of the receptor? Was that the second part spoken about in the overview video?","Yes, the shape of the receptor is due to its function.  A specific ligand will only fit into a specific shape of receptor protein."
Introduction to cell signaling,"Could someone give an example of a ```
gaseous plant hormone
```","The plant hormone ethylene promotes ripening, as seen in the ripening of dates. Ethylene is widely used in agriculture. Commercial fruit growers control the timing of fruit ripening with application of the gas."
Introduction to cell signaling,Can a ligand have more than one receptor?,"Yes, and a receptor can have more than one ligand.

You can read more about this here:
https://www.khanacademy.org/science/biology/cell-signaling/mechanisms-of-cell-signaling/a/signal-perception"
Introduction to cell signaling,How do these types of cell communications apply to the immune system?,"Cell signaling is essential for the functioning of the immune system.


The first line of defense, the humoral immune system relies on signaling. Leukocytes are being attracted with chemoattractants to come to the place of infection and pass blood barrier via diapedesis.


Later, when the second line of defense kicks in - B and T lymphocytes, again is influenced by signaling molecules.

B plasma cells recognize receptors on the surface of the cells of antigens so antibodies can bind to them and neutralize/kill them.

T killer cells need also receptor recognition in order to work properly and kill the pathogen, not a cell of host."
Introduction to cell signaling,"How autocrine signaling is important in cancer, I mean what's the mechanism?","That is way more advanced than can be covered in this introductory material and definitely not something I'm familiar with.

You might however find this section of the wikipedia article on autocrine signaling a useful place to start learning more:
https://en.wikipedia.org/wiki/Autocrine_signaling#Cancer"
Introduction to cell signaling,"Is there a distinction between Paracrine signaling and Synaptic signaling?
Some sources suggest the two are different, kindly clarify for me on that point.","Yes, they are different since *synaptic signalling* is more precise and _specified_ form of paracrine signalling.


So to clear out, both are types of paracrine signalling. But paracrine signalling is just broader term, while synaptic is specuiifc for synapses and neuronal tissue.


Paracrine signalling is any type of signalling where  signals bind to receptors and stimulate nearby cells. But in synaptic, those nearby cells involve synapses."
Introduction to cell signaling,what is the difference between cell signaling and signal transduction??,"Cell signaling is the broad multiple sets of pathways involved in how cells communicate. Signal transduction is one of those pathways. When a cell receives a signal, signal transduction is the multiple sets of processes that happen within the cell for that signal to reach its intended target and to then illicit a response."
Introduction to cell signaling,I don't understand the last sentence of synaptic signaling. Can someone please explain?,The signaling cell reabsorbs the neurotransmitters so that it can release it again later.
Introduction to cell signaling,"If a cell wants to signal itself by autocrine signaling, why does it release the substance to the surroundings? Wouldn’t it be better if the signaling molecule stayed inside the cell and affected the intracellular pathways directly. What are the advantages of releasing a signaling molecule to the surroundings compared to making it signal directly inside the cell?","Autocrine signaling unlike intracellular signaling occurs outside of the cell. They bind to receptors on the outside of the cell, to initiate a response that is quick. Intracellular signaling, on the other hand, binds to receptors inside the cell to initiate responses that take a long time. An example of such a response is the transcription of DNA which leads to other processes that later produce a protein. So, it is much better for cells to send autocrine signaling outside especially if the response is needed quickly."
Chromosomes,"So cells go under mitosis and meiosis. DNA is copied and split, but wouldn't that mean the other organelles in the cell have to copy too? It is never mentioned and I wonder if there is a reason or something.","There is a production of cellular organelles and proteins during the life of the cell prior to replication. And, in fact, some of the cellular organelles DO contain genetic material (for example, mitochondria and chloroplasts contain their own DNA specifying mitochondrial and chloroplastic proteins) which must be replicated during the process of organelle reproduction."
Chromosomes,sperms have 1 sex determining chromosome x or y or it has 2 both x and y?,"Sperm cells contain either an x chromosome or a y chromosome, not both. They have only one sex determining chromosome, and that can be x or y."
Chromosomes,"The general concept of mitosis is one cell splitting into two. But, the text does not discuss how any cell dies. It appears to me that the amount of cells in a certain organ would just keep increasing and increasing. It does not seem that the cells die to balance out the amount of cells, they just keep increasing by spitting into two. How does that work for the body?","In addition to what Aleksandr has said here, you may also wish to consider that mature organs contain many cells which no longer reproduce, but simply serve their function until they die and are replaced. These cells are said to be in "G-zero." You can think of them as done with reproduction and simply doing their job... like many humans at an advanced age!"
Chromosomes,how does DNA get to the cells in the body?,"All cells start from the original fertilized zygote.   The two gametes (sperm and ovum) contain 23 chromosomes(n) each and when the sperm fertilizes the egg(ovum),  the zygote now has a total of 46 chromosomes and becomes diploid (2n).  This zygote then goes through many stages of the replication cycle to create more and more cells called somatic cells or body cells.  If your confused you should watch this video here: https://www.khanacademy.org/science/biology/cellular-molecular-biology/intro-to-cell-division/v/fertilization-haploid-diploid-gamete-zygote-homologous

So to try and sum up your question, the DNA does not enter into every new cell but is actually a genetic copy that was produced by its mother cell.  This process happens millions of times."
Chromosomes,How many DNA are there in a chromosomes?,"A chromosome has many genes, a combination of genetic information that gives rise to characteristics, but it is only _one_ extremely super long DNA strand"
Chromosomes,"In the first paragraph (DNA and Genomes), it says that _almost_ all cells in the human body have DNA. There are some cells without DNA?","Yes - red blood cells are enucleated to make more space for hemoglobin, the protein that binds to oxygen."
Chromosomes,"what is the difference between chromatin, chromatid and chromosome ?","Chromosomes are the largest out of those 3, with an "X"  shape. Chromatids are each half of the Chromosome, if it was cut vertically. Finally, chromatin is the material that chromosomes and chromatids are made up of, containing DNA and proteins."
Chromosomes,so a diploid cell is 2 homologous cells or 2 sister chromatids?,"Neither. A diploid cell has 2 homologous chromosomes. They have one set of chromosomes from each parent. Remember that homologous chromosomes do not have to be identical, they just need to have the same genes in the same location, but they can have different alleles."
Chromosomes,"chroma means colored and soma means body. . . It means chromosomes are colored, right?",It actually comes from the fact that chromosomes can easy accept/take up dye. Heres a link I found:  https://www.vocabulary.com/dictionary/chromosome
Chromosomes,"Can you explain me the basic understanding about mitosis and meiosis?

I am always getting confused between them.","Meiosis is for sex cells or gametes (these cells don't have the same genetic makeup as the original germ cell), and mitosis is to copy and reproduce new cells resulting in the same genetic makeup as the original somatic cell."
Signal relay pathways,What regulates the distribution of fluid between interstitial and intracellular compartments?,"I was under the impression that this is due to osmotic pressure, so differences in solute concentration"
Signal relay pathways,What mechanism ampfily the signal ? and why they have to do that ?,"Many if not all of the steps described in this article can amplify a signal.  

For example each step in the section titled *Phosphorylation example: MAPK signaling cascade* involves a kinase phosphorylating downstream molecules.  For instance, if each time a RAF molecule gets activated it phosphorylates 20 molecules of MEK, then you've amplified the signal by 20 times.

Why questions are typically difficult in biology, but I'll give a slightly hypothetical example of why this is important.  One response a cell needs to divide is an increased rate of protein synthesis, so maybe at the end of the pathway ERK needs to phosphorylate the (up to) 10 million ribosomes to increase their activity.  This would take a very long time if only a few ERK molecules were activated!  In addition, there are 244 known direct targets identified for ERK in humans§, so even if you only had a few of each of those molecules amplification would still be needed to get a timely response!  
(Note: Those targets often need to modified in multiple locations — for example at least two ribosomal proteins are targets of ERK, one on two different amino acids.)

§Reference:
http://sys-bio.net/erk_targets/targets_all.html

Does that help?"
Signal relay pathways,How exactly does the cell signalling reverse?,"This differs per pathway. For pathways that release Ca2+ for example, the Ca2+ pumps pump the Ca2+ back into the ER, so there will be less and less Ca2+ in the cytosol. 
Also, in these messenger cascades, often at the end of the cascade a phosphatase is activated, which will deactivate the kinases. If only a very short, small signal is needed, the phosphatases will be activated earlier on in the cascade (depends on the pathway).
For the ligand/receptor interactions: a ligand often binds it's receptor for a short while, but not very long, so the initial signal won't be active for long.
Hope this helps you out a bit!"
Signal relay pathways,Do all signaling pathways simply turn on or turn off enzymes?,"No, they can also regulate the transcription of genes, the translation of proteins, the behavior of structural proteins, vesicle transport within cells, inhibitors of enzymes, and countless other processes.  You can probably assume that most processes in a cell are affected in some way by at least one signaling pathway!"
Signal relay pathways,"How does cAMP activate protein kinase A? If it's through phosphorylation, does the cAMP disappear after it has done its job (because it loses its only phosphate)?","No, not through phosphorylation. Note that the text says that it "activates" PKA and *the latter* then establishes a phosphorylation cascade. 
 
PKA is composed of 4 subunits - 2 Regulatory (R) and 2 Catalytic (C) subunits; and as the name suggests only the 2 C subunits have a further signaling role. The R-subunits feature _cAMP_-binding sites.

In the resting state when _cAMP_ levels are low, the C-subunits are in a deactivated state due to the R-subunits. What _cAMP_ does is that when it binds at the R sites, it causes a dissociation of the C subunits from this protein ("conformational change") making them now "activated" and thus eliciting downstream responses. 

And yes the _cAMP_ does "disappear" after it has done its job but not quite by losing its phosphate. The enzyme _phosphodiesterase_ converts _cyclic-AMP_ to _AMP_ (by hydrolyzing the _3'C-Phosphate_ bond) marking the termination of the pathway.


https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3504441/"
Signal relay pathways,can someone explain how this works with insulin and glucose? Along with GLUT2 and GLUT4 and their function in all of this? Is GLUT4 relevant for all body cells or just muscle and adipose? So confusing...,"*GLUT4* is an insulin-responsive glucose transporter that is found in the heart, skeletal muscle, adipose tissue, and brain.


*GLUT2* is expressed mainly in beta cells of the pancreas, liver, and kidney.

There are many more receptors:
Class I facilitative glucose transporters are represented by GLUT1 to GLUT4,
Class II has four members, namely, GLUT5, GLUT7, GLUT9, and GLUT11.
 Class III glucose facilitative transporters, namely, GLUT6, GLUT8, GLUT10, GLUT12 and GLUT13 (HMIT).

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5425736/"
Signal relay pathways,What does it mean to be a proto-oncogene? I have been having a hard time grasping what oncogenes are.,"Thank you for this question. I've recorded a video on this topic and will give you a link once I upload it.

So *protooncogene* is signalling molecule which acts as *green light* to form a tumour. It is switched on for tumour. If it is activated (or even mutated) tumour arise.

You may ask, how comes I am not having cancer? 

Because proto-oncogene has its antidote - *tumour suppressor gene*.
Tumour suppressor gene acts as a brake for cell cycle and sits between G0 and G1 phase of the cell cycle.

No matter that you have proto-oncogenes, as long as you have an unmutated version of tumour suppressor genes, proto-oncogenes won't harm you.


You can think of them both as antigen and antibody."
Signal relay pathways,Do signal transduction pathways require a source of energy? Might proteins involved have to be altered or modified?,There's usually an activation of some sort in the signal transduction pathway to incite a response. So for example the proteins involved might be enzymes that receive substrate from the previous protein/step and are thus activated to function. Hope this helps!
Signal relay pathways,How does the signal transduction mechanism works underlying mitosis?,"I'm not exactly sure what you are asking but I'll do my best to answer. When a cell receives the appropriate growth factor, a kinase is activated. For example, in the article above, MAP Kinase is eventually activated, which phosphorylates different proteins in the cytosol and nucleus. These proteins, once phosphorylated, begin causing reactions that cause the cell to enter the S phase of the cell cycle, where DNA is replicated. Once the cell enters from G1 to S phase, it will inevitably complete the cell cycle through G2 and M, or mitosis, phase."
Phases of the cell cycle,When are mutations more likely to occur in the cell cycle? Is there a specific stage in mitosis  or phase that leaves the DNA extremely susceptible or vulnerable to mutations? Or can mutations occur at any given moment? When is the DNA most vulnerable to external factors that could create mutations in the genetic code?,"Interesting question!

I'm not sure how well studied this is, but the consensus seems to be that mutations mostly happen during DNA synthesis — i.e. S phase.  A major reason for this is that DNA synthesis introduces many errors — some of which are not corrected."
Phases of the cell cycle,what is the difference between DNA & RNA?,"to be more specific, there are 3 main RNA types: mRNA (matrix) - is copied from DNA, to later copy proteins off it, rRNA (ribosomal) - is what ribosomes are made of, and it makes proteins, using mRNA, tRNA (transport) - holds amino acids, which are later brought to rRNA with mRNA to make proteins.
To sum up, DNA holds information on how to make all proteins, and all the RNA work to make them."
Phases of the cell cycle,Why do cells divide than grow,"I think they grow to accommodate for the doubling of new organelles and the split of DNA in later stages. After that, then they split. I hope it helps :-)"
Phases of the cell cycle,"in other words, you go from a     cell to a    cell.","Not necessarily. You go from a cell to two cells, or even four during meiosis."
Phases of the cell cycle,What is the DNA inside a cell called? genetic material or chromosome?,"DNA is genetic material, and the way it is physically present in our nuclei is by being condensed into chromosomes."
Phases of the cell cycle,"How long does it take for a cell to fully grow? Days, weeks?","It really depends from cell to cell. Division and growth of cells take 24 hours for many human cells, but liver cells take more than a year and neuronal cells take many years and once they fully develop they never re-enter the cell cycle.

For example, sex cells, spermatozoids take 74 days to fully finish the cycle, while oocyte sometimes takes 40 years. (meiosis starts when the female embryo is in mom's uterus and stops until puberty, then that same oocyte may not be 'unlocked' until the age of 40+)."
Phases of the cell cycle,"In my textbook, it says the chromatin fibres condense into chromosomes in prophase. However, here it says the chromosomes already existed in interphase, but in the form of chromatins. Which one is correct?","Right after the cell is born, the DNA is in the form of chromosomes, but in early G1 phase, the chromosomes break apart into chromatids and are only reformed as chromosomes in early prophase, in preparation for division. Pretty much once the  nuclease is formed in the young cell, the chromosomes are free to break apart into the thinner strands called chromatins. But once prophase starts, the DNA has to be collected and organized for division so they regroup/bundle up as chromosomes."
Phases of the cell cycle,How does a cell copy its DNA?,"Hi Thandeka, 

The way a cell copies its DNA is actually a pretty complex (but very interesting!) process. There are quite a few steps to this, but the main process that copies the DNA of a cell is called transcription. Khan Academy has some fantastic videos about transcription, you can watch one using the following link: 

https://www.khanacademy.org/science/biology/gene-expression-central-dogma/central-dogma-transcription/v/rna-transcription-and-translation

Happy learning!"
Phases of the cell cycle,"About the mitosis. Why does a cell have to divide? Is it because our body needs more cells because others die? For example if you make a cut onto your finger. If that's the case, what about the inner cells, say, cells of liver or heart?","Many cells have a limited life span, so mitosis needs to occur so that healthy, living cells can be maximized."
Phases of the cell cycle,Can you give a short summary of mitosis using the steps??,"The cell goes through 4 steps (prophase, metaphase, anaphase, and telophase.) The cells at the end of the process also have the same amount of chromosomes as the parent cell. At the end, 2 cells are produced. Mitosis is used to make body cells, and occurs in the body."
Phases of mitosis,So is mitosis the same as asexual reproduction?,"Asexual reproduction = formation of one or multiple genetically identical individuals from one parent. Mitosis = duplication of the cell's chromosomes, after which two identical cells are formed, so not whole individuals. ... Asexual reproduction involves only one parent. All the offspring are identical to the parent"
Phases of mitosis,"In the last paragraph, it's said that you end up with 2 "new" cells, but wouldn't one of those new cells be the parent cells? The diagram could be read like that too.","The 'original' cell, before it divides, is called the parent cell. Both new cells are called daughter cells. (The 'parent' cell ceases to exist after mitosis.)"
Phases of mitosis,"In plant cells the "celll wall" separates the cell into two daughters at the end of mitosis right? then they split into two or they remain together?
(sorry if there's a mistake my native language is not english)","In plant cells, the first part of mitosis is the same as in animal cells. (Interphase, Prophase, Metaphase, Anaphase, Telophase). Then, where an animal cell would go through cytokineses, a plant cell simply creates a new cell plate in the middle, creating two new cells. The cell plate later changes to a cell wall once the division is complete."
Phases of mitosis,why does nucleolus disappear during cell division and then reappear again?,"The nucleolus is a region in the nucleus where the genes encoding rRNA (for ribosomes) are found. In fact, the structure of the nucleolus relies on transcription of these genes. The rRNA genes are found on several chromosomes. During mitosis, the chromosomes each condense and separate, so clearly the nucleolus can't stay around the whole time during mitosis. I would guess that there is more control to its disassembly though than just the surrounding DNA being pulled away during condensation."
Phases of mitosis,Is actin in cytokineses also the same protein as the actin which plays a role in our muscle fibers and their contractions.,"Yes, it is, you are exactly right! Actin is an important part of the cell's "skeleton" and is used in many different cellular processes that need strong fibers."
Phases of mitosis,Are motor proteins found in all living creatures? Do they all serve a similar function or can they have many varied or specific roles? Examples?,"Yes motor proteins are essential proteins for all organisms - they have lots of important roles such as muscle contraction, transporting cargo around the cell and cell motility (e.g. enabling sperm to swim!). Nice question. https://en.wikipedia.org/wiki/Motor_protein"
Phases of mitosis,How does the cell "know " to carry out Mitosis ? Is it directed by its DNA ?,"The details of what causes this or that to happen is probably still being studied. Whereas we know how proteins are made from genes, many questions remain in other areas like mitosis. Like, how does the mitotic spindle system know that all chromosomes have been connected?"
Phases of mitosis,What would happen in anaphase if one or more of the chromosomes didn't pull apart?,"Good question!

Under normal circumstances this is relatively rare, but if the sister chromatids from a chromosome fail to separate during anaphase they will typically both end up in one daughter cell.  

This mistake is known as mitotic _nondisjunction_ and results in the daughter cells being aneuploid (having an incorrect set of chromosomes).  

Aneuploidy is often associated with severe developmental defects, cancer, or death.

You can start learning more about nondisjunction and aneuploidy here:
https://www.khanacademy.org/science/biology/classical-genetics/sex-linkage-non-nuclear-chromosomal-mutations/a/aneuploidy-and-chromosomal-rearrangements"
Phases of mitosis,What is the purpose of mitosis?,Mitosis allows organisms to grow and it repairs damaged cells. This is because it creates more identical cells.
Cell cycle regulators,In the first section you mention a graph of cyclin levels over the expression cycle throughout mitosis. Why is G1 Cyclin required throughout the entire cyclin expression cycle of mitosis?,"G1 cyclins levels are _not_ required throughout mitosis. In fact, the concentration of G1 cyclin drops during mitosis. 

Don't confuse the cyclin expression cycle with mitosis. The cyclin expression cycle refers to the levels of cyclins throughout the eukaryotic cell cycle, which includes interphase (G1, S, and G2) and mitosis (M phase). 

I think the question you meant to ask is: "why do G1 cyclin concentrations span the entirety of the cyclin expression cycle?"

Short answer: Mitogens 

Long answer:  Most eukaryotic cells only divide in the presence of _mitogens_.  Mitogens stimulate cell division by increasing the amount of _G1 cyclins_, which trigger cells to enter _Start_ (i.e., the point in G1 which cells commit to divide). 

G1 cyclins regulate entry into _Start_ by turning on expression of G1/S and S cyclins. Thus, G1 cyclin concentrations are elevated during the phases that require G1/S and S cyclins. This explains why the levels of G1 cyclin span a large portion of the cyclin expression cycle. 


At what point in the cell cycle would cells no longer require mitogens for division?

As mentioned above, at  _start_, cyclin G1/S is activated by G1 cyclin and through a positive feedback loop, G1/S cyclin is able to maintain its own activity and G1 cyclin and mitogens are no longer needed to drive the cell cycle. This explains why the levels of G1 begin to plateau. 


Yet, G1 cyclin is still needed for S cyclin activation, so G1 cyclin concentrations does not rapidly fall after the activation of G1/S cyclin.  
 

Sources: Yale School of Medicine
http://medcell.med.yale.edu/lectures/cell_growth_control.php"
Cell cycle regulators,Do cyclins and cdks have a role in meiosis too or just mitosis?,"Good question!

Yes, recent research has shown that regulation of meiosis is similar to that of mitosis (though somewhat more complicated).

References and further reading:
https://www.sciencedirect.com/science/article/pii/S153458070800172X

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4411289/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4080918/

http://rstb.royalsocietypublishing.org/content/365/1546/1653"
Cell cycle regulators,"G1/S cyclins move the cell from G1 phase to S phase, so what does the G1 cyclin (relatively abundant throughout the cell processes in the diagram) do?",G1/S is activated by G1 cyclin. Look at the answer above. It is positive feedback loop.
Cell cycle regulators,How do the presence/absence of Cdk inhibitors affect (or result in the formation of) cancer cells?,"CDK inhibitor inhibits binding of cyclin to Cdk. 
If that is prevented, the cell cycle stall.


However, in the absence of *inhibitors* cell cycle is continually proceeding and happening (circulus vicious) ending up in cancerous growth."
Cell cycle regulators,Why are cyclin/cyclin-dependent kinases important for our understanding of the biology of cancer?,Cyclin/Cyclin-dependent kinases (CDK) prevent the cell from moving on to the next phase until everything is checked and is confirmed to be working properly. Cancer is when the cyclin/CDK is unable to do its job so the cells divide rapidly
Cell cycle regulators,I tutor AP biology students and a teacher has asked students to find the size of Cdk vs cyclin. The students and I have not been able to locate this specific information.  Your drawings indicate that Cdk is larger which is what I would presume but do you know this from some reference source?,"Size in what units§ and of the individual polypeptides or of the complex? 
(For example CDKs typically make a dimer and are often found in a complex that includes regulatory subunits and a cyclin)?  
(Note that the answer will also change for the many different forms within and across species ...)

Thus there is no one "size" — possibly the intention is to get a feeling for relative sizes?

§Note: This could be molecular weight, length in amino acids, or dimensions in angstroms (Å). 

Two resources for answering this type of question are Uniprot (for protein information) and PDB (for structural information including 3D visualizations) — e.g. for Cdk1s:
https://www.uniprot.org/uniprot/?query=cdk1&sort=score
http://www.rcsb.org/pdb/results/results.do?tabtoshow=Current&qrid=1D52EF2E

Links for a specific (yeast) Cdk1 protein, which is known as Cdc28p:
https://www.uniprot.org/uniprot/P00546
https://www.rcsb.org/structure/3LJ1"
Cell cycle regulators,How does p21 regulate p53? How does the thresh hold level of p53 work?,"p21 is a cyclin-dependent kinase inhibitor. 

p21 induces cell-cycle arrest by binding and inhibiting CDK4 and CDK6/cyclin D complexes, resulting in de-phosphorylation and activation of the retinoblastoma (RB) pocket proteins that function together with E2F transcription factors to repress the transcription of cell cycle-related genes.

 p53-mediated repression has also been implicated through activation of its direct transcriptional target, p21.

p21 expression is necessary for the downregulation of p53-repression targets.



https://www.nature.com/articles/onc2013378"
Cell cycle regulators,Is the protein APC/C destroys that holds the sister chromatids together the synaptonemal complex mentioned in meiosis?,"Exactly!

In mouse oocytes, APC/CCdh1 mediated degradation of substrates appears to be required for maintaining prophase I arrest and preventing entry into meiotic divisions.


https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4070676/"
N/A,What regulates the distribution of fluid between interstitial and intracellular compartments?,"I was under the impression that this is due to osmotic pressure, so differences in solute concentration"
N/A,What mechanism ampfily the signal ? and why they have to do that ?,"Many if not all of the steps described in this article can amplify a signal.  

For example each step in the section titled *Phosphorylation example: MAPK signaling cascade* involves a kinase phosphorylating downstream molecules.  For instance, if each time a RAF molecule gets activated it phosphorylates 20 molecules of MEK, then you've amplified the signal by 20 times.

Why questions are typically difficult in biology, but I'll give a slightly hypothetical example of why this is important.  One response a cell needs to divide is an increased rate of protein synthesis, so maybe at the end of the pathway ERK needs to phosphorylate the (up to) 10 million ribosomes to increase their activity.  This would take a very long time if only a few ERK molecules were activated!  In addition, there are 244 known direct targets identified for ERK in humans§, so even if you only had a few of each of those molecules amplification would still be needed to get a timely response!  
(Note: Those targets often need to modified in multiple locations — for example at least two ribosomal proteins are targets of ERK, one on two different amino acids.)

§Reference:
http://sys-bio.net/erk_targets/targets_all.html

Does that help?"
N/A,How exactly does the cell signalling reverse?,"This differs per pathway. For pathways that release Ca2+ for example, the Ca2+ pumps pump the Ca2+ back into the ER, so there will be less and less Ca2+ in the cytosol. 
Also, in these messenger cascades, often at the end of the cascade a phosphatase is activated, which will deactivate the kinases. If only a very short, small signal is needed, the phosphatases will be activated earlier on in the cascade (depends on the pathway).
For the ligand/receptor interactions: a ligand often binds it's receptor for a short while, but not very long, so the initial signal won't be active for long.
Hope this helps you out a bit!"
N/A,Do all signaling pathways simply turn on or turn off enzymes?,"No, they can also regulate the transcription of genes, the translation of proteins, the behavior of structural proteins, vesicle transport within cells, inhibitors of enzymes, and countless other processes.  You can probably assume that most processes in a cell are affected in some way by at least one signaling pathway!"
N/A,"How does cAMP activate protein kinase A? If it's through phosphorylation, does the cAMP disappear after it has done its job (because it loses its only phosphate)?","No, not through phosphorylation. Note that the text says that it "activates" PKA and *the latter* then establishes a phosphorylation cascade. 
 
PKA is composed of 4 subunits - 2 Regulatory (R) and 2 Catalytic (C) subunits; and as the name suggests only the 2 C subunits have a further signaling role. The R-subunits feature _cAMP_-binding sites.

In the resting state when _cAMP_ levels are low, the C-subunits are in a deactivated state due to the R-subunits. What _cAMP_ does is that when it binds at the R sites, it causes a dissociation of the C subunits from this protein ("conformational change") making them now "activated" and thus eliciting downstream responses. 

And yes the _cAMP_ does "disappear" after it has done its job but not quite by losing its phosphate. The enzyme _phosphodiesterase_ converts _cyclic-AMP_ to _AMP_ (by hydrolyzing the _3'C-Phosphate_ bond) marking the termination of the pathway.


https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3504441/"
N/A,can someone explain how this works with insulin and glucose? Along with GLUT2 and GLUT4 and their function in all of this? Is GLUT4 relevant for all body cells or just muscle and adipose? So confusing...,"*GLUT4* is an insulin-responsive glucose transporter that is found in the heart, skeletal muscle, adipose tissue, and brain.


*GLUT2* is expressed mainly in beta cells of the pancreas, liver, and kidney.

There are many more receptors:
Class I facilitative glucose transporters are represented by GLUT1 to GLUT4,
Class II has four members, namely, GLUT5, GLUT7, GLUT9, and GLUT11.
 Class III glucose facilitative transporters, namely, GLUT6, GLUT8, GLUT10, GLUT12 and GLUT13 (HMIT).

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5425736/"
N/A,What does it mean to be a proto-oncogene? I have been having a hard time grasping what oncogenes are.,"Thank you for this question. I've recorded a video on this topic and will give you a link once I upload it.

So *protooncogene* is signalling molecule which acts as *green light* to form a tumour. It is switched on for tumour. If it is activated (or even mutated) tumour arise.

You may ask, how comes I am not having cancer? 

Because proto-oncogene has its antidote - *tumour suppressor gene*.
Tumour suppressor gene acts as a brake for cell cycle and sits between G0 and G1 phase of the cell cycle.

No matter that you have proto-oncogenes, as long as you have an unmutated version of tumour suppressor genes, proto-oncogenes won't harm you.


You can think of them both as antigen and antibody."
N/A,Do signal transduction pathways require a source of energy? Might proteins involved have to be altered or modified?,There's usually an activation of some sort in the signal transduction pathway to incite a response. So for example the proteins involved might be enzymes that receive substrate from the previous protein/step and are thus activated to function. Hope this helps!
N/A,How does the signal transduction mechanism works underlying mitosis?,"I'm not exactly sure what you are asking but I'll do my best to answer. When a cell receives the appropriate growth factor, a kinase is activated. For example, in the article above, MAP Kinase is eventually activated, which phosphorylates different proteins in the cytosol and nucleus. These proteins, once phosphorylated, begin causing reactions that cause the cell to enter the S phase of the cell cycle, where DNA is replicated. Once the cell enters from G1 to S phase, it will inevitably complete the cell cycle through G2 and M, or mitosis, phase."
Cell-cell signaling in unicellular organisms,Are there any medical applications of quorum sensing yet?,"This video probably won't anwser your question, but you should definitely check it out!
https://www.youtube.com/watch?v=KXWurAmtf78"
Cell-cell signaling in unicellular organisms,Are bio films also involved in brain neurons since they are all connected?,"No. Biofilms are aggregates of microorganisms.

There is no place in neurons nor in blood for microorganisms."
Cell-cell signaling in unicellular organisms,Can someone explain the positive feedback loop? What does that have to do with the transcription factor of the gene for the enzyme that makes AHL? Says it amplifies the response for a positive feedback loop. Not sure what that means.,A positive feedback loop amplifies the response. Here is a link to the article on homeostasis.        https://www.khanacademy.org/science/biology/principles-of-physiology/body-structure-and-homeostasis/a/homeostasis
Cell-cell signaling in unicellular organisms,If AHL is hydrophobic doesn't it have to transport in some vacuole?,"Not a vacuole, I think you mean vesicle. I also don't think so. Water can't pass through, and it has to be polar to bond to water, so it's likely nonpolar, meaning it should be able to pass through the membrane unless it's too big."
Homeostasis,Can someone explain what is negative feedback?  I didn't understand the concept from the article....,"From what I understood, negative feedbacks is your body's response to keep things normal or stable, whereas positive feedbacks exacerbate certain effects on the body by repeating functions deliberately.  In essence, negative feedbacks preserve your body's original or 'set' condition and positive feedbacks do the opposite and change you body more by constantly pushing certain types of growth or development in the same direction until something has been accomplished. The example they used was a fetus's head constantly putting more and more pressure on the cervix until birth. Since this is very necessary and important, a positive feedback loops is run: the substance that  pushes the fetus' head towards the cervix, oxytocin, is released as a cause of contractions from the uterus, which are themselves a cause of pressure from the fetus' head on the cervix. So the pressure essentially causes contractions in the uterus which stimulate nerve impulses in the brain to release more oxytocin, which further increase the pressure of the fetus' head. Clearly the goal isn't to maintain the fetus' current state but rather push it to the point where it is primed for birth."
Homeostasis,"Is the system that regulates pH, homeostasis?","To be precise, homeostasis is a process/phenomenon not a system.

Homeostasis is actually the process of maintaining a stable internal environment despite changes in the external environment. 

There are mechanisms in organisms that regulate pH and this regulation is an example of homeostasis.  For example, if you have learned about buffers, then it may help to know that essentially all organisms use buffers (and other mechanisms) to maintain control over the pH — for example the different organelles within eukaryotic cells will consistently have different pHs:
http://book.bionumbers.org/what-is-the-ph-of-a-cell/

Does that help?"
Homeostasis,what is pH guys and how does it relate to homeostasis.,"pH is a measure of how acidic or basic a solution is. More specifically, pH=-log[H+], which essentially means that the more positively charged hydrogen ions you have in a volume of solution, the lower the pH is and the more acidic the solution is. You can also check out this video (if you haven’t already seen it): https://www.khanacademy.org/science/high-school-biology/hs-biology-foundations/hs-ph-acids-and-bases/v/introduction-to-ph

pH matters for homeostasis because it’s part of the chemical environment in which biochemical reactions have to take place. For example, enzymes (which help speed up chemical reactions in living things) have ranges of pH where they work best. Because these molecules’ proper functioning is necessary, pH is very important for maintaining homeostasis. 

Hope this helps!"
Homeostasis,what is the control center in temperature homeostasis hot?,The control center for temperature is the hypothalamus.
Homeostasis,How can very low temperatures be fatal?,"Low temperatures would mean that the enzymes would be inactive or they may not be able to catalyse as much. This slows down reactions in the body (lowers metabolism), meaning that you may be deprived of essential things such as energy etc, which can eventually lead to complications such as death."
Homeostasis,How does Blood clot relate to Homeostasis?,"Blood clotting is considered part of the Positive Feedback (PF) Loop. This is defined as an effector that will AMPLIFY the effect of the Negative Feedback (NF) Loop. For instance, when there is a hemorrhage (loss of blood), it will cause a sequential activation of clotting factors. Here, a single clotting factor results in the activation of many more clotting factors. This is also known as a PF cascade. This overall process will give the completion of the NF Loop because blood loss was prevented with the clotting factors, resulting in Homeostasis."
Homeostasis,How can blood vessels dilate result in heat loss？,"This is because the dilation of blood vessels increases their surface area making it easier for the blood to interact and transfer heat with cooler parts of the body, generally the more surface area, the more heat loss."
Homeostasis,can someone please tell me which organ in the body controls homeostasis?,"Homeostasis is mainly controlled by the organs in the central nervous system and the endocrine system (hormones). Organs in the two systems send commands to other organs in other systems to allow them to carry out certain functions. 

Example for the nervous system: You have stepped outside into some snowy weather. It is cold outside, and your body temperature is dropping. The nervous system sends signals to the muscles that tell them to shake. The shaking of the muscles generates heat, keeping you warm.

Example for the endocrine system: Unfortunately, your have not eaten anything for hours. This results in a low blood sugar level. To maintain homeostasis, cells from the pancreas release a hormone known as glucagon, which raises your blood sugar by decreasing the storage of sugar in body cells.

Does this help you?"
Homeostasis,What system controls homeostasis?,"There are *many* different systems that organisms use to maintain homeostasis.  

For example, the processes used for thermoregulation in mammals and birds are very different from the methods used to keep pH relatively constant."
Homeostasis,"I understand how homeostasis happens in our bodies, but why does it occur? Furthermore, why do we need it? Why do we try to control the internal functions of our bodies rather than the external stimuli that cause them? Why are there not more uses of positive feedback loops?","1. It occurs so our body can function.
2. (See number one)
3. It is much easier to control our bodily functions than the weather and climate.
4. What do you mean?"
Response to a signal,"(Third paragraph in Example: Growth factor signaling)
What do you mean saying that MNK1 help to translate folded mRNA? Can it translate even hairpins?
Thank you :)","Yes, you've got it right! MNK1 helps to translate certain mRNAs which form, hairpins.


However, the accent is on the _certain_ meaning that it cannot help _every_ singular hairpin,l but _some_ hairpins. :)"
Response to a signal,"About Gene Expression, do the transcription alterations of factors such as c-Myc pass on the daughter cells of future generations? or is there a reversion mechanic before the cell goes into mitosis? Thank you.
P.S: in the last paragraph of "cellular metabolism" you wrote "moelcules"","Alterations to the genetic sequences that code for transcriptional regulators such as c-Myc may be inherited from a parent cell, assuming it isnt imprinted(genomic imprinting). The ability of a daughter cell to retain a memory of the gene expression patterns that were present in the parent cell is an example of epigenetic inheritance: a heritable alteration in a cell or organism's phenotype that does not result from changes in the nucleotide sequence of DNA."
Response to a signal,What are two examples of a response (or end result) of a cell signalling pathway?,"Let's say you are bleeding and lost lots of blood. And then you immediately stand up. Ending result of a signaling pathway is falling unconsciousness (blood pressure drop).

You just finished oyur meal. Your stomach is full and stretching receptors. The ghrelin hormone suddenly drops in its concentration in your blood. Why? Because Ghrelin is the hunger hormone and you do nto need it anymore. You are not hungry.


I can tell you anything happening in your body and nature is cell signaling influencing physiology."
Response to a signal,"Biochemically, what triggers the adrenalin gland to pump a high number of adrenalin signals?","Adrenaline is released mainly through the activation of nerves connected to the adrenal glands, which trigger the secretion of adrenaline and thus increase the levels of adrenaline in the blood. This process happens relatively quickly, within 2 to 3 minutes of the stressful event being encountered. When the stressful situation ends, the nerve impulses to the adrenal glands are lowered, meaning that the adrenal glands stop producing adrenaline.

 http://www.yourhormones.info/hormones/adrenaline/


Meaning that biochemically, the electrical signal from nerves activates the release of adrenaline. 
High level of stress also activates the release of ACTH which stimulates the release of cortisol."
Response to a signal,"I'm confused about something, Is EPGFR  a tyrosine kinase receptor while RAS is a G protein?","Nice observation!
Ras is a subfamily of G-proteins while EPGFR is tyrosine kinase receptor.

https://www.ncbi.nlm.nih.gov/pubmed/11129168
http://pathwaymaps.com/maps/398"
Response to a signal,How could activating a transcription factor cause long-term cellular changes?,"Activating factor activated transcription of certain DNA. Usually RNA transcript is unstable and that's how transcription is controlled. Where transcription factor takes place, that mRNA is 'preserved'. That way certain genes are 'turned on'."
Response to a signal,how are things possible i mean like how will people know this type of stuff what if scientist don't know about these things ?,"Could you clarify, I am sorry I don't fully understand the last part of your sentence?"
Response to a signal,Why do different cells respond differently to the same signal?,"In many cases, the same signal molecule binds to identical receptor proteins yet produces very different responses in different types of target cells, reflecting differences in the internal machinery to which the receptors are coupled.


Meaning that based on the architecture and organisation fo the cell (not just the receptor per se, the response depends on).


https://www.ncbi.nlm.nih.gov/books/NBK26813/"
Cancer and the cell cycle,How does DNA get damaged in the first place?,"A number of factors, radiation, carcinogens, mutagens, and oxidative stress all contribute."
Cancer and the cell cycle,"Could you make a cancer-like cell, or rather a cell that has a mutation that makes it and its offspring grow into a neoplasm, and have their mutation be GOOD? The article says that cancer cells are known to be immortal, so if that's the case, could you use "good" neoplasms to fight cancerous ones that would later form tumors? Thanks to anyone who can understand my question :-)","It is feasible, however the main issue is you don't want to introduce some foreign type of human mutated and immortal cancer without the full ability to knock it out and rein it in. Probably there will be treatments that revolve around this whether is be putting drug producing genes in cells that surround a cancer, although it wouldn't exactly be wise to use a cancer cell to fight a cancer cell by definition, since there are better cell options out there. However if such a cell was discovered tomorrow that didn't grow very fast, only grew near tumors, somehow produced weapons to fight it, no doubt it would become a very popular therapy, however a non-cancerous cell may do the trick better without the risk of it turning into actual cancer."
Cancer and the cell cycle,"Why not engineer a retrovirus to insert an extra copy of the P53 gene? First as a treatment for people with a dangerous cancer, then try it on people who have only one working copy of P53?",I think there are several reasons why this isn't a treatment (yet). I'm sure there's a lot you have to figure out before you can get a virus to successfully insert a copy of the gene. There may be some epigenetic factors that would make this technique not work very well and nobody has figured out how to get around that yet.
Cancer and the cell cycle,"It might not be directly related to this topic, but I have a question. Can cancer be inherited? or does it just depends on your normal habits?","Some people are born with a gene mutation that they inherited from their mother or father. This damaged gene puts them at higher risk for cancer than most people. When cancer occurs because of an inherited gene mutation, it is referred to as "hereditary cancer."
Although this is often referred to as inherited cancer, what is inherited is the abnormal gene that can lead to cancer, not the cancer itself."
Cancer and the cell cycle,"So, I was wondering what could happen if P53 is introduced to cancer cells, once they have mutated. May be, introducing a functional P53 to cancer cells before they progress so far, could prevent them. Is it possible ? What do you say? Please answer","I was thinking the same thing! except maybe giving immunization shots to fix the DNA in earlier stages like when you are just born. But it would definitely be interesting to see if it worked after the patient had cancer. I think it could possibly work afterwards, but the only problem is, if the cancer is already affected large parts of the body, and the P53 activates the apoptosis, then you could kill of a large amount of cells in your body, too much to live. Other than that, I think this would completely work."
Cancer and the cell cycle,"Besides chemo and radiation, what other cures are there for cancer?","here is a website that can show you more examples and what they mean
http://www.cancer.org/treatment/treatmentsandsideeffects/treatmenttypes/treatment-types-landing"
Cancer and the cell cycle,"So, how long does cancer cell cycle take compared to normal cell?","That depends if it is a benign tumor (not to bad) or a bad tumor (I cannot spell its name). If the tumor is benign the cells it contains will split only slightly faster than a normal cell.  If it is a dangerous cancerous tumor, then the cells in it will split much faster and more uncontrollably than a normal cell would.  

If a normal cell takes a second to divide and then waits a week and divides again (this is just an example, this is not accurate information) a bad cancer cell might take a second to divide and then wait an hour. If this is the case you will have two good cells from one good cell and 168 bad ones from the cancerous cell. NOTE: this is just an example I made up, real cells divide much quicker and can wait much shorter or longer amounts of time before dividing again, some cells never even divide again."
Cancer and the cell cycle,""In general, human cells can go through only about 40-60 rounds of division before they lose the capacity to divide, "grow old," and eventually die" what factor defines which cell is the old one, and which on is this the new one when the cell divides? if one cell was not younger compared to the original cells, wouldn't all the cells just die at the same time?","There are A Caps (long strings of adenosine nucleotides) at the end of chromosomes, and as the cell keeps replicating, it starts to wear off. These are what the checkpoints in previous articles talk about. If there is not enough A cap to safely replicate the DNA without it wearing off, then the more important DNA could be damaged irrevocably and could be damaged and the cell would permanently go into G0 stage or apoptosis."
Cancer and the cell cycle,Can cancer become so cancerous that kills itself? Could so many mutations accumulate that it would not be able to divide anymore?,"_Interesting question!_

Definitely, yes. But do not rely on that. Once there are too many mutations accumulated it is too late and it will affect healthy cells as well. You mean, mutations which trigger apoptosis, right? In that case, cancer would resemble an auto-immune disease.


Other than that it is not possible for cancer to just 'kill itself', moreover it thrives really well and always finds a way to grow and spread."
Cancer and the cell cycle,"Is it possible to completely reverse the damage done by cancer cells to the host's DNA? Few form of cancers, which occur due to mutation in DNA, leading to uncontrollable growth of cells, may be treatable by gene therapy by targeting the mutated gene.","That sounds like a nice idea but in reality, many mutations cause cancer. Plus there is that variability among cancer cells. What do I mean by that?


I mean that even within cancerous tissue not all of them are clones. there are genetic variants among them.

If you prepare gene therapy, how do you know which one to traget? Let's suppose you know which one, - cell variant A. Then you are left off B, C, D.
If there is left the only one of let's say D, that's enough to regrow and reoccur - several years later. Without you even knowing you left that one cell."
Cell-cell junctions,What sorts of cells does the blood/brain barrier consist of? I believe chemotherapy molecules are often too big to get through to treat the brain.,Each nerve cell in the brain must be fed by blood or the cells will quickly die of oxygen deprivation.  I believe you are perhaps reffering to a cappilary system that sustain these cells in a way that compartmentalise them as much as possible. It is also possible because of the late hour that my mind makes me write b.s. and I'm sorry if the answer is misleading or not helping...
Cell-cell junctions,Could someone thoroughly explain to me what desmosomes are?,"A desmosome, also known as a *macula adhaerens*, is type of cell-to-cell adhesion.

Desmosomes resemble plasmodesmata in plant cells because they also provide little space through which membranes of to adjacent epithelial cells are connected. Hiwever, in the case of desmosomes, intermediate filaments of cytoskeleton are connected. How?


First, desmosomes, have its connecting proteins (just liek the other types of cell-to-cell connections in animal cells). Their proteins are called _cadherins_.

Cadherins are attached to both cells and they protrude the cell enterior and anchor on intermediate filaments (cytoskeleton). Precisely, they attach to cytoplasmic plaque, which connects to intermediate filaments.

Is it clearer now? :)"
Cell-cell junctions,Do desmosomes and cadherins depend on one another?,"Yes, the cadherins are a big part of the desmosomes"
Cell-cell junctions,Can bacteria form junctions with each other in order to exchange genetic material?,"Bacteria can form junctions with each other to exchange genetic material. This is known as conjugation. Genetic material is exchanged between bacteria through conjugation tubes or sex pilus. One bacterium usually donates its DNA while the other receives it.
For more information check out this link:
https://www.quora.com/Does-hydrogen-atom-prefer-to-lose-or-gain-an-electron"
Cell-cell junctions,What is the difference between desmosomes and tight junctions?,"Like aria said in the comments, desmosomes allow stretching and are in more complex organisms. This is because with desmosomes, cells link up together, and the intermediate filaments have a connection in between. This allows for strength, tightness, and flexibility in the tissue. Tight junctions prevent water from leaking out of the cell and are present in the bladder."
Cell-cell junctions,"What are the functions of Cadherin ? Can you help me to answer this question by writing in points, not descriptive pattern? Thanks!","cadherins are basically proteins attatched to the cytoplasmic plaque of animal cells. They act as a sort of tie that prevents cells from seperating under pressure. 
This is probably a really dark way of putting things but think of it as two scenarios like this:
1) you bind two people together by their wrists or bodies with a rope.
2) you bind two people by skeletons. 
its harder to seperate the two bound by their skeletons no matter how far away they stretch, ryt?. its something like that. it connects two cells, say cardiac cells, by their adjacent cytoplasmic plaques which are in turn connected to the cells' cytoskeleton, which holds them together as they stretch.
Hope you got an idea:)"
Cell-cell junctions,What is cytoplasmic plaque and what are intermediate filaments and how exactly do they work with the cadherins to anchor the junction between epithelial cells?,"Cytoplasmic protein plaque is protrusion of cytoplasma which from luminal side binds intermediate filaments (ctoskeleton) and from the other sides binds cadherin. Cadherin binds to another cadherin which holds cytoplasmic plaque and binds to another intermediate filament in lumen of second cell adhering to the first cell.


Cytoplasmic plaque plays scaffolding role.


https://www.histology.leeds.ac.uk/cell/assets/desmosome_diag.gif"
Cell-cell junctions,"Is the "junction" between the nuclear membrane and the E.R. considered a junction?
If yes, what kind of junction is it?
If no, it is not a junction, what is it?
Many thanks!","I don't think there is _any_ junction since endoplasmic reticulum membrane is _continuous_ with the external nuclear envelope. When something is continuous means it is attached directly, we are speaking of one bigger entity."
Ligands & receptors,"Why don't hydrophobic ligands get stuck in the membrane? If they're passing through the membrane, then they encounter the hydrophobic space that is the inside of the membrane. If they are also hydrophobic, why do they leave that to continue on into the cell?","I think one reason is diffusion due to the ligand's concentration gradient.  Typically more than one signaling molecule gets released into the environment. If they make it to the hydrophobic portion of the membrane, the next lowest area of concentration would likely be the inside of the cell."
Ligands & receptors,took me 1000 yrs to read,🤣 i tried just putting the face and it said it was too brief
Ligands & receptors,wouldn't lipid ligands generally be hydrophobic??,"You are correct in the notion that only hydrophobic molecules can ''touch'' eachother for interaction; in a cellular environment however, you usually deal with proteins that contain both hydrophylic and hydrophobic patches due to the characteristics of the amino-acids constituting the protein in question. These patches, together with 3D-structural constraints usually determine possible interactions.

An interesting fact is that the hydrophobic/hydrophylic patches of proteins can be influenced by pH changes (protonation of amino-acids in low pH environments and de-protonation in high pH-environments); this can play an important role in experiments."
Ligands & receptors,"So do hydrophobic ligands only bind to intracellular receptors or do they also bind to trans-membrane receptors even though they can diffuse passively across the membrane? Same question for hydrophilic ligands, do they only bind to trans-membrane receptors or do they also bind to intracellular receptors?","Good question — there are few absolute rules in biology!

For hydrophobic ligands I'll give you examples for steroid hormones — many steroid hormone receptors are found in the cytoplasm and then move into the nucleus once bound by their steroid, while others are always found in the nucleus.

However, recent research has revealed that there are also steroid hormone receptors in the plasma membrane.

I recommend this wikipedia article as a place to start learning more:
https://en.wikipedia.org/wiki/Steroid_hormone_receptor


While uncommon, there are some hydrophilic ligands that bind to intracellular receptors.  One example is the neurotransmitter epinephrine, which also acts as a hormone.

You may find this free online textbook chapter helpful in learning more:
https://www.ncbi.nlm.nih.gov/books/NBK9924/"
Ligands & receptors,"What happens to the ligands after they are received? Do they dissolve and become energy, are released back into the extracellular fluid, or something else entirely?","Usually they can be re-absorbed and used again. In the case of Calcium, it is reabsorbed.

Nothing in our body is wasted. It either binds reversibly< or become converted to metabolic intermediate."
Ligands & receptors,what are considered kinases: an RTK receptor or an RTK's specialized ligand?,You find the kinase activity in the receptor itself. But you need a ligand to trigger the dimerization (2 receptors molecules share one ligand) of 2 receptors which only the can act as a proper kinase on each other
Ligands & receptors,"since water-soluble messengers bind to receptors situated on the outside of the cell membrane, is it possible for these messengers to influence gene transcription in the cell nucleus","Yes, it is, by activation of for example MAPK pathways. Cell signaling always includes some cascade and rarely ends up on just one action step.

:)"
Ligands & receptors,"In this, it says 'They [hormones] must bind to carrier proteins in order to travel through the (watery) bloodstream.' The fact that they must bind to carrier proteins implies that otherwise they would repel water. However, hydrophobic molecules are just nonpolar and should still be able to go through water. Why do they [hormones] need to bind to carrier proteins?","Hydrophobic molecules will most likely precipitate in the watery bloodstream. This way they will accumulate in, obstruct bloodvessels or accumulate in fatty tissues. They also won't be transported as efficiëntly and thus have little to no effect. By binding to carrier proteins they won't precipitate or accumulate in specific places and can do their thing in cells where they are supposed to do their thing.
Hope this helps!

PS. I am not sure if you understand the polar-apolar principle, so here it is in short: polar molecules dissolve in other polar molecules. apolar molecules dissolve in other apolar molecules, but polar molecules generally don't dissolve (or in very, VERY tiny amounts) in apolar molecules (same for apolar in polar)."
Ligands & receptors,what would happen if it was nonpolar ligand that was binding?,"What do you mean by *nonpolar* ligand?

Here we are not talking about polar and nonpolar substances and covalent bonds."
Cell-cell signaling in unicellular organisms,Are there any medical applications of quorum sensing yet?,"This video probably won't anwser your question, but you should definitely check it out!
https://www.youtube.com/watch?v=KXWurAmtf78"
Cell-cell signaling in unicellular organisms,Are bio films also involved in brain neurons since they are all connected?,"No. Biofilms are aggregates of microorganisms.

There is no place in neurons nor in blood for microorganisms."
Cell-cell signaling in unicellular organisms,Can someone explain the positive feedback loop? What does that have to do with the transcription factor of the gene for the enzyme that makes AHL? Says it amplifies the response for a positive feedback loop. Not sure what that means.,A positive feedback loop amplifies the response. Here is a link to the article on homeostasis.        https://www.khanacademy.org/science/biology/principles-of-physiology/body-structure-and-homeostasis/a/homeostasis
Cell-cell signaling in unicellular organisms,If AHL is hydrophobic doesn't it have to transport in some vacuole?,"Not a vacuole, I think you mean vesicle. I also don't think so. Water can't pass through, and it has to be polar to bond to water, so it's likely nonpolar, meaning it should be able to pass through the membrane unless it's too big."
N/A,what is difference between geneotype and phenotype,"genotype = genetic code 
phenotype = physical appearance/properties/expression of the gene"
N/A,what does it mean when it says that it "self fertilizes"?,Self fertilizing is when the pollen from one plant is put on the stigma of the same flower or another flower that is growing on the same plant.
N/A,why the ratio  is always roughly 3:1 not exactly?,"It is correct that it won't be exactly half ,because as Alexander said, there would be slight imperfections (nothing is absolute ,I mean).
But , for this pea plant experiment ,I think it would be that tall and short are compound traits ,like they are made up from a combination of small traits."
N/A,"What determines what gamete is chosen to move on? Or is it just random, and each gamete has an equal chance at being passed on to the offspring?","Does garden pea, Pisum sativum has a discontinue character on height, colour...? mostly those characters are continuous, they are controlled by many genes."
N/A,How can we identify that after breeding multiple times we have got a homozygotic offspring and does multiple breeding results in a homozygote  offspring ?,"When 2 parents breed, they each have a genotype, let's say one is AA, the other is aa. Both are purebred and homozygous. In its offspring, they create a new genotype, one letter from each of the parent's genotype. This creates many outcomes, including the heterozygous, Aa."
N/A,"why did he use pea plants, why not any other flower?",because pea was an annual plant and its was a self fertilizing plant and its easy to manually fertilize it
N/A,what is difference between geneotype and phenotype,Genotype is the specific gene alleles where as the phenotype is the physical expression of the alleles.
N/A,How it can be explained if Gregor Mendal studied eight character?,"Who knows, really depends on what 8 character was. What really important is that those traits are not linked (on the same chromosome) and that those traits are comparable (for example tall and short) and easily distinguishable.


All 3 Mendelian Laws would probably stay the same."
N/A,"If a tall plant and a short plant bred together, how would all of the plants end up being tall? Wouldn't 75% become tall and 25% become short based on the 3:1 ratio?","All plants would end up being tall if the parents are homozygous for the traits controlling each character. 75% would be tall if and only if the p generation is heterozygous for the character while 25% would be short, which conforms to the 3:1 ratio."
N/A,What does F1 generation mean? It doesn`t make sense.,"The F stands for filial, which comes from the Latin word _filius_, meaning son.  F1 means the first generation of children (or baby pea plants)."
Pedigrees review,How can you tell if someone is a carrier?,"For Autosomal dominant and X-linked dominant, there is no question of a carrier since the affected allele will be dominant.
For *X-linked recessive*, the carrier will always be the mother/female. Since she has 2 X-chromosomes, one can compensate for the function of the other non-functional chromosome. The father/male can never be the carrier because he has only one X-chromosome, which, if affected, will be indicated on the pedigree chart.
For *Autosomal recessive* cases, it is a little tough to figure out the carrier without sufficient information. We can only know that the affected individual will be homozygous recessive, but we have no way to know if the unaffected individual is a dominant homozygote or a heterozygote (carrier). The only exception to this will be when one parent is homozygous recessive (affected). Then we can say that the offspring will definitely be carriers of the condition.
Hope that is helpful!"
Pedigrees review,"If a recessive trait shows up in all the generations, how can we figure out that the trait is recessive?","For autosomal recessive where there is no skipped generation, the other parent must be heterozygous for the trait, which would mean the children have a chance of having the recessive trait through inheriting the recessive chromosome from the carrier parent.
For X-linked recessive, the same is true, with one parent being a carrier. Ways to prove X-linked recessive are that if the trait is recessive, there will be mother-son and/or daughter-father links. This means that if the mother is affected, the son must be as he must inherit one of her affected X chromosomes. The same is true with daughter-father links. If the daughter is affected then the father must also be as she will inherit one of her X chromosomes from him.

Hope this helps someone."
Pedigrees review,how dow we know if it is autosomal?,Equal number of males and females affected i think
Pedigrees review,"So if a parent is a carrier but doesn't show, it has to be female as a male would have to express it. 
Am I correct?  
thank you for correcting me if it is required.","for sex-linked genetic disorders/diseases, you are correct. This is because the alleles expressing the disorder/disease are usually only present in the x chromosome, although some (few) genes are expressed in both x and y chromosome. This is due to the fact that the y chromosome is smaller.
If you are female, you have xx chromosomes, while you have xy chromosomes if you are a male. 
As mentioned earlier, genetic disorders/diseases are usually found only in the x chromosome. Hence, if the allele for the disorder/disease is recessive, to be a carrier, the person must be heterozygous. 
Because females have two x chromosomes, they can either get the disease (homozygous recessive), be a carrier (heterozygous), or just not have it at all (homozygous dominant). 
But for men, as they only have one x chromosome, only one chromosome can express it, so they can either have it (one recessive allele), or not have it at all (one dominant allele)."
Pedigrees review,whats the difference between x-linked and sex linked?,"Genes that are carried by either sex chromosomes are said to be sex linked.
Men usually have a combination of X and Y sex chromosome, while women have two X’s. since men inherit Y chromosomes, they are the only ones to inherit Y-linked traits.
Hope that helped 👍"
Pedigrees review,Can you have a male who is a carrier of an x linked recessive trait but doesn't express it?,"No that is not possible. Since males only get one x, it is impossible for them to be only carriers of a trait and not express them. Females, on the other hand, have two x chromosomes, which means they can be a carrier for an x-linked trait.




Hope this helps!"
Pedigrees review,how to understand whether a trait going within a pedigree chart is recessive or dominant,"If both parents do not have the trait and the child does, it is recessive. If one parent has the trait and the child does or does not, it is dominant."
Pedigrees review,"On a pedigree chart, how do you show that a person is a heterozygous carrier for a particular recessive allele that is not expressed in the phenotype? For example, how do you visually show that someone is an UNAFFECTED carrier for a genetic disorder?","I've seen carriers denoted by squares or circles that are half shaded, sort of like a full moon. 

Edit: What? Not a full moon, a half moon"
Genetic linkage & mapping,Is 50% always the highest recombination frequency or could it theoretically be exceeded if a small enough population of flies were used?,"If you draw out a punnett square, you will see that it is impossible to exceed 50%. You see, when you perform a punnett square you are assuming independent assortment. You are already assuming that the alleles will distribute themselves completely randomly. Even when you make that assumption, you get only a 50% maximum rate of recombination. If I could go through a punnet square with you it would be easier to see. Go through yourself and try to design a scenario where you get greater than 50% recombination."
Genetic linkage & mapping,what percentage or map units is considered close? is anything lesser than 50 map units considered close??,"Anything below 25 map units is considered close. The lesser the distance, the lesser the crossing over, and the more the chances of the gamete being parental."
Genetic linkage & mapping,How do we know if alleles are on the same chromosome?,"Alleles are different versions of the same gene, so they will always be at the same locus. If you mean how do we know that genes are on the same chromosome, it has to do with recombination frequency. If the frequency is 50% they are not on the same chromosome and therefore assort independently of one another. If the frequency is less than 50%, they are being assorted into the same gametes at a higher frequency because they are physically attached to the same chromosome."
Genetic linkage & mapping,"If RF is 0.5, how can I find out if genes are on the same chromosome far apart or on different chromosomes?","Based on _RF value alone_, you cannot obtain that kind of information.
Because it could be either 0.5 value for genes on the same chromosome, or 0.5 value for two genes on different chromosomes. (as it is stated in the article below how is that possible).


You need to have more RF values (e.g. for A-B, A-C, B-C) to calculate and guess their position."
Genetic linkage & mapping,"How can you create a tester to test if the trait is sex-linked? Eg. White eyed fruit fly could only be produced as a male, wouldn't it be impossible to breed a tester?","A cross between a female fly that is heterozygous for white eyes and a male that is white-eyed could produce female progeny with white eyes, because the mother makes two kinds of gametes: one X chromosome that encodes red eyes, and one X chromosome that encodes white eyes. If the gamete encoding for white eyes is fertilized by the X chromosome from the father, then female white-eyed flies result."
Genetic linkage & mapping,"In the finding recombination frequency section it showed the formula as Recombination frequency (RF)= 
Total offspring/Recombinants ×100% I tried doing the equation myself but I could not get the final answer I kept getting 0.1074321 instead of the answer which is 10.7 where did I go wrong?",0.1074321 x 100% is 10.74321%. Rounded down to one decimal place = 10.7%
Genetic linkage & mapping,What if I were to do an F1xF1 cross (Both parents are heterozygous for both genes)? I know the expected phenotypes should be 9:3:3:1 but how would I calculate the recombination frequency then if the parental phenotype prevails disproportionately? Would it just be all the recombinants / total offspring * 100 again? Or is that ONLY for a test cross with a homozygous recessive parent?,"Interesting question — I've never done or seen anyone else work out recombination frequencies for an F1xF1 cross and I suspect it would be a nightmare — its giving me a headache just trying to work out whether this could even work theoretically.

One significant problem is that both parents are undergoing recombination, so when those gametes combine the recombinations will sometimes cancel out (e.g. if the F0 parents were AB/AB and ab/ab, the F1 generation would produce parental (AB, ab) gametes, but also recombinant (Ab, aB) gametes.  AB x ab and Ab x aB could only be distinguished by a test cross!
 
I think you are safe in assuming that this is only done for test crosses!

However, I think it would be a great exercise to try working this out by starting with a range of known recombination frequencies and seeing how they would affect the 9:3:3:1 ratio.  If you do try this exercise, please share your results in a comment!"
The law of independent assortment,"I understand this, but I still get confused on the Mendelian laws.
Here is what I think I know:
The law of segregation states that the two alleles of a single trait will separate randomly, meaning that there is a 50% either allele will end up in either gamete. This has to do with 1 gene.
The law of independent assortment states that the allele of one gene separates independently of an allele of another gene. This has has to do with 2 genes.
Is my understanding of these laws correct?","That is correct. But as an addition, there is also the concept of *linkage*, where the allele of one gene is very close to an allele of another gene in the same DNA strand, that it is very unlikely for the two allele to separate independently (in other words, they are inherited as one unit). This has to do with 2 genes. This concept is essentially independent assortment, but deals with *unit of multiple alleles*, rather than *just an allele*."
The law of independent assortment,Why is science soooo complicated??😩,Because Adults
The law of independent assortment,What is the difference between segregation and independent assortment? :),"Segregation means that the chromosomes or any gene present on chromosome did not lose its identity or get mixed up with other genes. During gametogenesis it keeps its identity. 
While independent assortment means that the chromosomes whether dominant or recessive after gametogenesis goes into any of the gametes i.e in simple language the movement of chromosomes is not affected by movement of other chromosomes"
The law of independent assortment,For the experiment of F1 generation how did Mendel know for sure that the tall parent's genotype is (TT) ?,"The pea plants he used self-fertilized, meaning that each parent ends up having the same set of genes as the offspring. (This is _before_ he crossed them.) This means that there were pure lines of descent from the original pea plants without variation. The genotypic variation of the offspring (heterozygotes) was introduced by Mendel, who crossed 2 plants of different traits."
The law of independent assortment,"The phenotypes are a 9:3:3:1 ratio, but what are the possible genotypes?","there are 9 different genotypes in a F1 dihybrid cross and the ratio is
1:2:1 :2:4:2: 1:2:1

in a monohybrid cross the phenotype ratio is 3:1 which gets compounded when doing a dihybrid cross into 9:3:3:1

the genotype ratio in a monohybrid is 1:2:1
and gets compounded to my answer in a dihybrid cross. I show the work below.

F1 generation is heterozygote for both traits: AaBb or Aa and Bb 
  A  a
A AA Aa
a Aa aa
and 
  B  b
B BB Bb
b Bb bb

here are the possible genotypes and ratios made from the squares above:
AABB(1) AABb(2) AAbb(1) AaBB(2) AaBb(4)Aabb(2)aaBB(1) aaBb(2) aabb(1)

this is nothing more than a 1:2:1 compounded to two characters."
The law of independent assortment,"Does this mean that any living organism (Pea plant, dogs etc.)
will show phenotypic ratio of 9:3:3:1 ? Where 9 plants have all dominant alleles and 1 plant has all recessive alleles ?",Just know that a 9:3:3:1 ratio happens when you cross TWO Heteroygous pairs. Also....Look over what a Dihybrid cross is. Dihybrid cross is when your crossingg 2 different types of Genes. So you should get an out come out of 16...
The law of independent assortment,"Can you explain to me what is the difference between linked and not linked. Also, how to identify if an allele is not linked.","Linkage or whether 2 genes are linked or not depends upon the distance between them. If the distance between 2 genes are small or if they are next to each other in a chromosome, most probably when meiosis occur these genes remain together. So genes that remain together and almost never segregate are called linked genes.  
Hope this helps."
The law of independent assortment,Does the law of independent assortment apply to two genes on different chromosomes or two alleles on different chromosomes?,"Law of independent assortment applies to two genes of different chromosomes _and_ two alleles of same genes.


What does it mean_ It means that alleles are inherited independently and do not affect alleles from _other_ genes."
The law of independent assortment,"If the genes are the same, then why is it that many people look different form their parents?
That's just if they were the same though.","In each of your parents, there are genes coding for their appearence, i.e bone structure, hair color, eye collar, that are shown. However, there are also genes that aren't expressed by your parent that they have, such as something different. Considering there are billions of genes that code for even one thing, there is an extremely high liklihood of you expressing a gene that wasn't expressed in your parents, (but was still there)"
N/A,"In the second paragraph of the section titled "Sex Chromosomes in Humans", do Chromosomally female (XX) embreyos that develope into males make them have a more girlish appearance? Do Chromosomally male (XY) embreyos that develope into females make them have a more boyish appearance? Some boys might look a lot like girls or vice versa.","Hi Tanya, my understanding is that XX individuals with an SRY translocation (who develop as male-bodied) may need hormone supplementation at puberty to develop some male secondary sex characteristics (e.g., facial hair). However, they generally have what their cultures recognize as a male appearance. You can learn more in the Genetics Home Reference entry about SRY translocation: https://ghr.nlm.nih.gov/condition/46xx-testicular-disorder-of-sex-development."
N/A,""SRY is found on the Y chromosome and encodes a protein that *turns on other genes* required for male development.
 
If an SRY-bearing X chromosome fertilizes a normal egg, it will produce a chromosomally female (XX) embryo that develops as a male."
So, the SRY induces other genes to produce male character.
 Does that mean that the X chromosome also contains *other genes* that are required for male development?(genes that would be dormant in the absence of SRY)","I'm not an expert on this, but my understanding is that SRY† is (usually) sufficient for embryonic testis formation and that the hormonal effects of having testis are (usually) sufficient for male primary and some secondary sexual traits§.  One way of looking at this is that male and female sexual anatomy aren't as different as they appear, they just have different structures emphasized and elaborated with a few small changes in "plumbing".

UPDATE:
†Note: SRY encodes TDF (testis determining factor) a transcription factor that enhances expression of genes needed for testis development and possibly suppresses expression of genes that promote ovary development.  This is an active area of research and there is evidence that SRY is not always necessary for male development and also may not always be sufficient for male development. 
If you want to learn more about this, here is a good (and freely available) review article:
https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1001899

§Note: Some other genes on the Y chromosome are necessary for sperm production, but they don't appear to be needed for "maleness"."
N/A,What is Gene-linkage? How is it different from the Sex-Linkage?,"Sex linkage referes to a gene being linked to (or "on") a sex chromosome. Gene linkage refers to two genes that are on the same chromosome, and are thus "linked" (inherited/transferred together). :)"
N/A,"It says in the 2nd paragraph of 'sex chromosomes in humans' that the X chromosome has 800-900 protein-coding genes while the Y chromosome has only 60-70, half of which are responsible for roughly the same task or processes in the same area. How does the male genome make up for that lack of proteins? Are they just not needed or are they found somewhere else? Surely the second X chromosome in females carries something which would be important in males too.","Any time you have dominant and recessive alleles of a gene it is only the dominant allele that gets expressed. There doesn't have to be a second allele for the trait to be present.  

A male having a single X chromosome any genes that are on the X that are not present on the Y chromosome become by default dominant."
N/A,all the x linked alleles a man has come from his mother,"Yes all the x-linked alleles a male has comes from his mother. As you may know, a male is XY while a female is XX. For a male to be a male, he has to get the Y allele from his dad. This makes it 100% certain that the male gets his X allele from his mother."
N/A,"If the father is colorblind, but the mother is not, then their children can't be colorblind. The males would get their dad's Y and the non-colorblind X. Thus, they would not be colorblind. The females would have a colorblind X, but it would not be expressed, because it is recessive. Is this correct? Am I understanding this correctly?","Yes, that is correct."
N/A,Is it impossible to have parents with twelve kids that pass on an infected trait to 6 of the males and 1 female. I was given this problem on another site and got it wrong when I said no. Help!,"The question didn't mention that it is X-linked or Y-linked, so you cannot assume it is sex linked. (Or perhaps it did, but as you didn't mention, then I'd assume the question didn't)

The only way for a pair of unaffected parents to have affected offspring is for the allele for the disease to be recessive, both parents must have a dominant allele and parents must be heterozygous so they have a dominant allele. To have a heterozygous male, the allele cannot be on the non-homologous portion of the X chromosome. (Note that this doesn't mean it cannot be on the X chromosome.)
*Also I want to mention that as the question asks whether it is possible to have 6 affected males and 1 affected female, but does not state that there are that number of affected males and females. Therefore @Anson Chan you cannot prove the allele is recessive by that. And it did not mention how many female and male offspring they have in total, and this is not important. It is sometimes fatal to assume something the question has not said, even though in this case, there isn't much difference.
**Idk if I sound harsh, bu no offence. I am just trying to share my experience

Back to the question, in the case I just mentioned (heterozygous parents for the disease caused by recessive alleles) it is possible for 6 males and 1 female to have the disease if they inherit both recessive alleles from both parents.

As the aforementioned case suits the situation of the question completely, the answer is yes.
------------
Now I have finished explaining this question, let's go for something extra.

So this situation can happen when the locus of this allele is on a pair of autosomes.

Now let's assume there are six boys and six girls among the offspring. (You cannot assume this when solving the question because it's not mentioned, but as a case study, we'll assume this. And don't worry, it is a possible case)

Now the rate of the male offspring getting the disease is 100% while that of female offspring is just 16.7%. Why the great difference? One possibility is that the allele is on the homologous portion of the sex chromosomes. The allele from the father is on his Y chromosome. Therefore the rate of male offspring getting the disease is much larger. Then why does one girl get the disease? That's because crossing over may occur and the allele causing the disease shifted to the X chromosome of the sperm that.

Anyway, this whole case isn't very likely because for the male offspring, even if they all receive the defective chromosome from the father, there is still half the chance they receive a dominant good allele from their mother.

Happy learning to all of you!"
The chromosomal basis of inheritance,What is another definition for "hemizygous?","A chromosome in a diploid organism is hemizygous when only one copy is present. The cell or organism is called a hemizygote. Hemizygosity is also observed when one copy of a gene is deleted, or in the heterogametic sex when a gene is located on a sex chromosome."
The chromosomal basis of inheritance,"What if a white eyed male fruit fly (genotype XwY) is crossed with a heterozygous (i.e. with genotype Xw+Xw) female fruit fly?
Don't we get a white eyed female fruit fly?","You may get a white female with a XwXw genotype or a red-eyed female with a XwXw+ genotype. Morgan used this to verify his hypothesis further.
Open the hidden experiment tab under the "Confirming the model" subheading above.
Hope this helped. :)"
The chromosomal basis of inheritance,"Hello! I dont understand why the mutant is on the X chromosome if we said that it is defining by the sex chromosome?? if it's only for male (XY) and female has both XX, I would predict that the mutant would be on the Y chromosome, which only the male has.
thnks!","If the white eye trait was linked to having the Y chromosome, then you would expect that:
a) all male offspring of white-eyed males had white eyes, because they should all inherit their father's Y chromosome. In actual case they had red eyes though.
b) It would not be possible to have white eyed females, because they don't have a Y chromosome. However, in the actual case, Morgan performed experiments by crossing females which were offspring of a white-eyed male with another white eyed male, and found you can get white eyed females, so the trait is not linked to the Y chromosome. This suggests the white eyed trait is X-linked but recessive, so females only show this phenotype when they have two copies of it, and no red-eye version. 
Hope that helped!"
The chromosomal basis of inheritance,"It is stated in the second to the last paragraph that Bridges showed more detail about Morgan's findings wherein he showed that rare male or female flies with the unexpected eye colors were produced through nondisjunction of sex chromosomes during meiosis, and since it is meiosis they should bed divided. What then is left in the cell? Does it have both X and Y? If so what about the other cell that was supposed to inherit the other sex chromosome.","Bridges found rare flies with surprising inheritance patterns: daughters that inherited X-linked traits (like eye colour) only from their mother, and sons that inherited their X-linked traits from their father. Due to these inheritance patterns he suggested that these daughters were XXY, and the sons were XO (unlike in humans, in drosophila, sex is determined by how many X chromosomes are present, rather than depending on the Y chromosome). His explanation was that nondisjunction had occurred during meiosis in the mother, producing egg cells with XX or no sex chromosomes. When these rare eggs were fertilized by sperm carrying either X or Y, the offspring were the XXY daughters with 2X chromosomes from the mother, and X0 sons inheriting an X from the father (those with XXX and Y0 combinations died). He also looked under a microscope and saw that these were indeed the chromosome combinations that the flies had. This work provided further evidence that inherited traits, which could be studied using the breeding experiments of genetics, are linked to physical chromosomes, that were being studied for example with dyes and microscopy. 

There is more information where I read most of this, here: https://embryo.asu.edu/pages/calvin-bridges-experiments-nondisjunction-evidence-chromosome-theory-heredity-1913-1916
And here is another interesting article on the chromosome theory, Bridges' contribution, and its impact http://www.genetics.org/content/202/1/15"
The chromosomal basis of inheritance,"Is this a mistake in the text? Emphasis mine.

_Morgan did lots of other experiments to confirm an X chromosome location for the eye color gene. He was careful to rule out alternative possibilities (for instance, that *it was simply impossible to get a white-eyed female fruit fly*).

By mating the F2 files [sic] from the cross above, *Morgan was able to obtain white-eyed females*, which he then crossed to red-eyed males. All the female offspring of this cross were red-eyed, while all the males were white-eyed._

Other comments suggest readers are getting thrown off by the contradiction. Personally I can see how a white-eyed female can be born to two parents carrying the recessive allele.","There is no mistake or contradiction. Note the statement preceding it: "He was careful to rule out alternative possibilities"

He ruled out that it was impossible to get white-eyed females by obtaining white eyed females."
The chromosomal basis of inheritance,Why was the idea initially controversial? What did it initially lack?,Gregor Mendel's work didn't explain co-dominance and so many other factors but was later found out to be the basic building block of genetics.
The chromosomal basis of inheritance,"where did the first white eyed fly come from?
if there were no white eyed flys to begin with where did he get the white genotype? Please help.","The first mutant white allele isolated (called w1) arose spontaneously because of transposon insertion.
There are now many strains of flies with different mutations in the white gene (you can find a long list here: http://flybase.org/reports/FBgn0003996.html).
Some of these have far smaller mutations, such as just one amino acid change like described here: https://www.sciencedirect.com/science/article/pii/S0005273699000644"
The chromosomal basis of inheritance,so whats the role of the cromosome y in the eye color here?,"The role of the Y chromosome is to determine the sex. As for eye color, nothing."
The chromosomal basis of inheritance,I thought it wasn't possible t obtain a white-eyed female because of the differing chromosomes in the two sexes?...,"If you breed a homozygous red eyed female with a white eyed male, the female offspring will be heterozygous and have one copy of the mutant allele, even though the eyes are still red. Then if you breed such a female with a white eyed male, some of the female offspring will receive an X chromosome from the mother containing the white mutation, as well as the white mutant allele on the X chromosome from the father. Such females have two mutant copies and no 'normal' alleles to compensate, so would have white eyes."
The chromosomal basis of inheritance,Couldn't we have a White EYE female fruit fly in the F3 Generation ?? PLEASE HELPP,"The previous comment is incorrect, the logic is flawed. If a white eyed female required a white eyed female, you would have an infinite regression. You can have a white eyed female in generation 3, by mixing a red eyed female with the white eyed gene with a white eyed male."
The law of segregation,Who came up with  the punnet squares,"As the name suggests, a Mr./Ms. Punnett, Mr. Reginald Punnett to be exact."
The law of segregation,explain why is it possible for browned eye parents to have a blue eyed child ?which law does it indicate??,"This demonstrates recession and dominance.  Brown eyes are dominant; blue eyes are recessive.  The phenotype is what the appearance is - mother and father have brown eyes.  The genotype, is what the genes they have code for - in order for mother and father to have a blue eyed child, they must have a genotype that includes both brown and blue.  If father and mother each give their individual blue eye gene to their child, the child will have two blue eye genes and no brown eye genes, so eyes will be blue."
The law of segregation,what is epistasis,"It is when one gene affects the expression of another gene. For example, mice have a color gene and can have an allele for black (B) fur color and an allele for brown (b) fur color (black being dominant), BUT they also have a gene that determines pigmentation; one allele C produces pigment (fur color shows) and the other allele c does not (fur color is white/mouse is albino).
So, the possible genotypes would be:
- CCBB, CCBb, CcBB, CcBb (phenotype: black)
- CCbb, Ccbb (penotype: brown)
- ccBB, ccBb, ccbb (phenotype: white, pigment is not produced and therefore fur color cannot be expressed)
I hope this example clarifies things a bit! (:"
The law of segregation,Why does both Geno and phenotype influence from the environment??Are they  talking about the environment that the Gene's are placed or just mean the environment in general? Question No.2,"Genes mainly influence phenotype. However, the environment also influences gene expression.

Phenotype relies on the grade of gene expression."
The law of segregation,Doesn't the crossover between the homologous chromosomes mix up the alleles?,I'm not sure what you mean by "mix up" the alleles — a major benefit of crossovers is that it can create new combinations of alleles (and sometime even new alleles if the crossover happens within a gene).
The law of segregation,How did Mendel derive his law of segregation from this monohybrid experiment? (It is not clear to me in the article).,"If gamete can pass down both alleles, the possibility will be 1/16. The fact that the possibility of 1/4 exists, suggests that only 1 of the 2 alleles is passed down by the gamete."
The law of segregation,"when it says self fertilization, I think I understand the concept of how one of a plant's sperm fertilizes the same plant's seed/ but I also know that usually in human life when like 500 years ago, the kings used to marry his sister to keep the royalty in the same family and when they would have kids, those kids would have serious problems like internal bleeding and many disabilities. so my question is, do the pea plants that come out of self-fertilization have any sort of problem or are they perfectly healthy?","I think they're healthy. Many kinds of plants are able to self-fertilize without any issues, and since these pea plants did it, I assume their offspring is healthy."
The law of segregation,if your parents are one brown and blue eyed and the child is brown eyed. in the future can the child's child be able to have blue eyed if he/she marries brown eyed person?,"The child's child would only be able to get blue eyes (25% of the time, like Okapi said) if both parents were Bb.  Zero chance if either, or both were BB."
The law of segregation,what are homologous genes,"i don't think the other posted answer is right. The question was "what are homoLOgous genes", but the answer seemed more lined up for "homoZYgous" genes. I am still learning this stuff, but my understanding is
- Homologous means genes controlling the same inherited character - may have different versions of same gene. For example - flower colour, may be purple, or white, but still homologous because it's flower colour.
- Homozygous means the genes carry two identical alleles, PP or pp.
- Heterozygous means the genes carry two different alleles, Pp."
Probabilities in genetics,What is the probability of having 5 boys in a roll,"Probability for sex ratio is always 1/2, but since we are speaking of having 5 boys in a row, probability changes.

1/2 x 1/2 x 1/2 x 1/2 x 1/2 = 1/32"
Probabilities in genetics,"If monohybrid crossing is something like this Aa x Aa and dihybrid  crossing is something like this AaBb x AaBb, then is this AaBbCc x  AaBbCc called trihybrid crossing and this AaBbCcDd x AaBbCcDd called tetrahybrid crossing? 
Or is there a specific word for crossings that involve more than one pair of alleles?
Perhaps polihybrid crossing?","Not really, but I agree. We need a word to group all these together."
Probabilities in genetics,Why do possible outcomes change? Why can you not guarantee the total outcome in a punnett square?,"There's still chance involved. It's like if you tossed two coins. Each has a 50% chance of landing heads side up, but you can't say that there will definitely be one that lands heads up and one that lands tails up. 

The same goes for genetic probabilities. In the article's example with the dogs' fur color, there might be a litter of eight puppies in which five puppies have the lighter color. Even though each puppy only has a 1/4 probability that it would have light fur, it's not like the genes are sorting themselves out and saying "Well we already have two puppies with light fur, so we have to stop allowing those genotypes to happen now." Each is an independent event.

Hope this helps!"
Probabilities in genetics,I'm still a little confused about the whole probability thing could somebody explain it in a more understandable way please?,"basically, you use the punnets squares to determine all the different possible combinations u have. u line them up and cross them to tell the combos. and then u look and see: how many times does, lets say, AA occur? u look and it occurs 2/4 times in the box, so u know there is a 50% chance of the cross producing an AA set. do u understand the whole punnett square thing, or...?"
Probabilities in genetics,What's an example of an "or" situation (either Event X or event Y) that is NOT mutually exclusive?,"If two events are not mutually exclusive, it would be the same as "and" situation."
Probabilities in genetics,"If I am given 50% of AD and 30% of BC and 30% of AC and 10% of AB, (not precise percentages). How can I figure out the alleles of the "parents" that have ABCD combinations? Or work the math backwards?","If both parents had ABCD alleles, then it would be equal percent for all combinations, which is not given by this task.


Also, I see no CD combination.

Since there is no CD, my projection is it is 0% that both parents have ABCD alleles."
Probabilities in genetics,"If the baby came from the mom , would we have more of the moms genes?","No, as the genes are formed from a 50% contribution from the genes of both male and female gamete."
Probabilities in genetics,what is the reason for the 9/16 probability,"Because, 3/4*3/4=9/16. You get multiply these due to the probability rule of multiplication."
Probabilities in genetics,how do solve all recessive traits?,"It 0% since in every possibility of getting CC and Cc, there will be a dominant trait.  If you multiply that by anything, the answer will still be 0%.

If you want to know for any case that does not come out to be 0%, then you would make a punnet square for each trait separately and multiply the probabilities. For example, if you have AaBb and aabb, you would make a punnet square for Aa and aa and another punnet square for Bb and bb. Then you calculate the probability of a recessive trait coming up and multiply them. In this case, there is a 2/4 chance for a recessive trait for the first one and a 2/4 chance for a recessive trait for the second one. 

2/4 * 2/4 = 4/16 = 1/4 

In this case, there is a 1/4 chance for all recessive traits."
Variations on Mendel's laws (overview),Is people with multicolored eyes (like one eye brown and the other blue) an example of incomplete dominance?,"No; genetic heterochromia is the result of a mutation on at least one gene that determines eye color (scientists discovered that eye color is controlled by at least eight genes in what is called polygenic inheritance). An individual may have also acquired it because of an injury, meaning that it had nothing to do with genetics at all.

Did this help?"
Variations on Mendel's laws (overview),what is lethal alleles?,"think about the word lethal it means something deadly and alleles means it is a specific form of gene, so lethal genes means alleles that preventing us to live"
Variations on Mendel's laws (overview),"How does epistasis relate to getting a 9:7 ratio? how does this concept work? is there an example we can relate this to?

also does complementary gene mean the same as principle of complementation? cos from what I understand of complementation, is when two mutant pure breeding parents cross and give rise to a progeny all with wild type phenotype. I don't get the explanation of recessive alleles of two different genes giving rise to the same phenotype.","You will get 9:7 fenotipe ratio in Duplicate Recessive Epistasis (DRE) for P: AaBb x AaBb, then the F1's genotipes will be 9:3:3:1 (9[A_B_], 3[A_bb], 3[aaB_], 1[aabb]). In DRE, any recessive homozigote is epistatic and they all give the same fenotipe. So we look for how many of the F1's genotipes that doesn't has any recessive homozigote then compare to how many of those that has recessive homozigote (epistatic gene, it means all of them have same fenotipe), then we got 9:7.

Example: Snail Shell Color
https://www.youtube.com/watch?v=0HfkCppZLfo&t=6m

Also, Complimentary genes are those genes in DRE. They are complimentary because for a hypostatic fenotipe to occure needs all of them to be homozigotely or heterozigotely dominant (which are also hipostatic to the homozigotely recessive genes)."
Variations on Mendel's laws (overview),"Is the Incomplete dominant same as the bleeding rule, which was proposed before the Mendel genetics?","No
In incomplete dominance, no blending takes place. It happens due to incomplete enzyme or no functional enzyme.
Basically, it is the enzymes that produce the phenotypic character. In the nucleus, mRNA is produced from the DNA. This mRNA goes into the ribosome, the protein synthesis house, wherein these enzymes are synthesized. Sometimes, the enzyme malfunctions or is produced in insufficient amount. Hence, the phenotypic character is affected.
This phenomenon is observed in the plant snapdragon or _Antirrhinum majus_"
Variations on Mendel's laws (overview),can a kid from two different parents look the same as your parents resulting to be more alike to your parents as if he/she was their child?,"The genetics of a organism like a human is far more complex than the genetic of peas that Mendel studied. 

The simple way it is usually explained you get the idea that a specific gene allele is directly mapped to a specific trait.  This is rarely the case in complex organisms.  

Often it is a set of genes (gene complex) is responsible for a trait and a specific trait may be caused by multiple combinations of the genes alleles.  

So just because someone may look more like someone elses parent  doesn't mean that they are more genetically similar."
Variations on Mendel's laws (overview),can humans also exhibit incomplete dominanace in their phenotypes.,"Yes. One of the most well-known examples of this has to do with the genes for straight and curly hair. If an offspring has inherited both a curly hair gene and a straight hair gene (they are heterozygous), they get wavy hair. Their hair does not curl, but it is not straight either."
Variations on Mendel's laws (overview),complementary genes mean that it is all the same right,No. It just means that different combinations give the same phenotype.
Variations on Mendel's laws (overview),what is the relationship between mendels law to genetics,"Gregor Mendel was basically the one who invented genetics, He documented his experiments with pea plants, and his findings are known as Mendel's law. So, without Mendel's law, we wouldn't have genetics."
N/A,What is another definition for "hemizygous?","A chromosome in a diploid organism is hemizygous when only one copy is present. The cell or organism is called a hemizygote. Hemizygosity is also observed when one copy of a gene is deleted, or in the heterogametic sex when a gene is located on a sex chromosome."
N/A,"What if a white eyed male fruit fly (genotype XwY) is crossed with a heterozygous (i.e. with genotype Xw+Xw) female fruit fly?
Don't we get a white eyed female fruit fly?","You may get a white female with a XwXw genotype or a red-eyed female with a XwXw+ genotype. Morgan used this to verify his hypothesis further.
Open the hidden experiment tab under the "Confirming the model" subheading above.
Hope this helped. :)"
N/A,"Hello! I dont understand why the mutant is on the X chromosome if we said that it is defining by the sex chromosome?? if it's only for male (XY) and female has both XX, I would predict that the mutant would be on the Y chromosome, which only the male has.
thnks!","If the white eye trait was linked to having the Y chromosome, then you would expect that:
a) all male offspring of white-eyed males had white eyes, because they should all inherit their father's Y chromosome. In actual case they had red eyes though.
b) It would not be possible to have white eyed females, because they don't have a Y chromosome. However, in the actual case, Morgan performed experiments by crossing females which were offspring of a white-eyed male with another white eyed male, and found you can get white eyed females, so the trait is not linked to the Y chromosome. This suggests the white eyed trait is X-linked but recessive, so females only show this phenotype when they have two copies of it, and no red-eye version. 
Hope that helped!"
N/A,"It is stated in the second to the last paragraph that Bridges showed more detail about Morgan's findings wherein he showed that rare male or female flies with the unexpected eye colors were produced through nondisjunction of sex chromosomes during meiosis, and since it is meiosis they should bed divided. What then is left in the cell? Does it have both X and Y? If so what about the other cell that was supposed to inherit the other sex chromosome.","Bridges found rare flies with surprising inheritance patterns: daughters that inherited X-linked traits (like eye colour) only from their mother, and sons that inherited their X-linked traits from their father. Due to these inheritance patterns he suggested that these daughters were XXY, and the sons were XO (unlike in humans, in drosophila, sex is determined by how many X chromosomes are present, rather than depending on the Y chromosome). His explanation was that nondisjunction had occurred during meiosis in the mother, producing egg cells with XX or no sex chromosomes. When these rare eggs were fertilized by sperm carrying either X or Y, the offspring were the XXY daughters with 2X chromosomes from the mother, and X0 sons inheriting an X from the father (those with XXX and Y0 combinations died). He also looked under a microscope and saw that these were indeed the chromosome combinations that the flies had. This work provided further evidence that inherited traits, which could be studied using the breeding experiments of genetics, are linked to physical chromosomes, that were being studied for example with dyes and microscopy. 

There is more information where I read most of this, here: https://embryo.asu.edu/pages/calvin-bridges-experiments-nondisjunction-evidence-chromosome-theory-heredity-1913-1916
And here is another interesting article on the chromosome theory, Bridges' contribution, and its impact http://www.genetics.org/content/202/1/15"
N/A,"Is this a mistake in the text? Emphasis mine.

_Morgan did lots of other experiments to confirm an X chromosome location for the eye color gene. He was careful to rule out alternative possibilities (for instance, that *it was simply impossible to get a white-eyed female fruit fly*).

By mating the F2 files [sic] from the cross above, *Morgan was able to obtain white-eyed females*, which he then crossed to red-eyed males. All the female offspring of this cross were red-eyed, while all the males were white-eyed._

Other comments suggest readers are getting thrown off by the contradiction. Personally I can see how a white-eyed female can be born to two parents carrying the recessive allele.","There is no mistake or contradiction. Note the statement preceding it: "He was careful to rule out alternative possibilities"

He ruled out that it was impossible to get white-eyed females by obtaining white eyed females."
N/A,Why was the idea initially controversial? What did it initially lack?,Gregor Mendel's work didn't explain co-dominance and so many other factors but was later found out to be the basic building block of genetics.
N/A,"where did the first white eyed fly come from?
if there were no white eyed flys to begin with where did he get the white genotype? Please help.","The first mutant white allele isolated (called w1) arose spontaneously because of transposon insertion.
There are now many strains of flies with different mutations in the white gene (you can find a long list here: http://flybase.org/reports/FBgn0003996.html).
Some of these have far smaller mutations, such as just one amino acid change like described here: https://www.sciencedirect.com/science/article/pii/S0005273699000644"
N/A,so whats the role of the cromosome y in the eye color here?,"The role of the Y chromosome is to determine the sex. As for eye color, nothing."
N/A,I thought it wasn't possible t obtain a white-eyed female because of the differing chromosomes in the two sexes?...,"If you breed a homozygous red eyed female with a white eyed male, the female offspring will be heterozygous and have one copy of the mutant allele, even though the eyes are still red. Then if you breed such a female with a white eyed male, some of the female offspring will receive an X chromosome from the mother containing the white mutation, as well as the white mutant allele on the X chromosome from the father. Such females have two mutant copies and no 'normal' alleles to compensate, so would have white eyes."
N/A,Couldn't we have a White EYE female fruit fly in the F3 Generation ?? PLEASE HELPP,"The previous comment is incorrect, the logic is flawed. If a white eyed female required a white eyed female, you would have an infinite regression. You can have a white eyed female in generation 3, by mixing a red eyed female with the white eyed gene with a white eyed male."
Polygenic inheritance and environmental effects,how environment causes pku?,"The environment doesn't actually cause the PKU -- that is genetic. But the environment can cause it to express in the phenotype -- create symptoms -- based on the environment. The PKU gene simply causes a person to be unable to properly process phenylalanine (they lack an adequate amount of the necessary enzymes). If that person eats foods that are high in it, they can begin to express symptoms of that genetic mutation. If they limit or eliminate those foods, they often will have no symptoms."
Polygenic inheritance and environmental effects,"What's the difference between polygenic and epistasis?
It sounds like in both of them, multiple genes affect one trait.","While a polygenic phenotype can occur without epistasis, if you have epistasis you must be dealing with a polygenic phenotype.

Polygenic just means that there are multiple genes involved in a phenotype.  
Epistasis refers to situations where one allele masks the phenotypic effect of one or more alleles of another gene."
Polygenic inheritance and environmental effects,how are we able to walk on the earth,"Gravity. I personally wouldn't ask this question in the genetics unit, though."
Polygenic inheritance and environmental effects,Does anyone know anything about syndactyly and its genetic inheritance?,"Syndactyly is a mendellian dominant trait, so it is inherited much like any other gene."
Polygenic inheritance and environmental effects,"Can a disaster, natural or man-made, affect human traits?","Quite interesting question!

I can think of radiation which causes *mutations*.

Definitely causes of mutations can affect human traits and phenotype, but not in the form that it will _favor_ survival. Nonetheless, future generations may be less adaptable and degenerated (recall Chernobyl nuclear plant disaster or Minamata disease in Japan (caused by excessive mercury due to chemical industry).


My answer is *definitely yes*. *Negative impact*."
Polygenic inheritance and environmental effects,"So I am very short for my age , yet my mom and dad are both tall but my mom is a little shorter than my dad . Why is that? Do i have a disease or something that affects my growth ?","A short stature can be caused by a variety of causes. It could be genetic, a hormone known as growth hormone could be low in the body, or, in more serious cases, an underlying disease or condition may have contributed to your stature (I.E: tumors, malnutrition, mitochondrial disease). If you are otherwise healthy, it is most likely either genetic or hormonal.

Does this help?"
Aneuploidy & chromosomal rearrangements,"And what about a cell/organism containing 2n - 2 chromosomes, supposing these two missing ones are paired up? Is this cell/organism considered aneuploid or euploid?","It is anueploid. The number of chromosomes for a species is fixed. For example, if a human cell had 44 chromosomes instead of 46, it is anueploidic in nature; nullisomic in fact (2n-2). Just because 44 is an even number doesn't mean it is euploidic! Hope this helped :-)"
Aneuploidy & chromosomal rearrangements,How is chromosomal "rearrangement" different from "crossover"?,"Crossovers (recombination events) occur between homologous chromosomes (actually sister chromatids).  Meaning, recombination occurs between chr13 sister chromatid from Mom crossing over with sister chromatid of chr13 from Dad. 
Duplications and inversions can happen on a single chromosome. So, you can have a region of, let’s say, chr22 duplicated. Or that region might get inverted. Translocations can involve a region of (for example) chr13 swapping places with a region of chr22. 
I think the key is that crossovers are typically between homologous chromosomes whereas rearrangements are a broader category where they CAN be between homologs but there are also non-homologous chromosomal rearrangements."
Aneuploidy & chromosomal rearrangements,"If there was an instance of a gamete with -1 chromosome and a gamete with +1 chromosome that joined together, would that individual be considered "normal"?",That’s a really good question. I think you’re right! Though the odds of that happening are extremely rare. Cool thought experiment though!
Aneuploidy & chromosomal rearrangements,"If there's a diploid (2n) cell that went through the cell cycle but somehow all of the chromosomes stuck together and went to one daughter cell while the other daughter cell had no chromosomes, is the daughter cell with the chromosomes considered tetraploid (4n) at that point because there are now 4 chromosomes per homologous pair, or would it actually be considered 2n+2n? For instance, if n=12, then it would be 2n+24?","The likelihood of that actually happening is very rare. But that does not mean it's impossible, there's never a 0% (or 100%) of anything in science (in most cases). 
If that was to happen it would be called tetraploid a form of polyploidy. It's not likely to happen but it has happened a species of frogs (from the genus Neobatrachus) has been found where they actually contain 4n instead of the usual 2n. The probability of one of these mutations to occur is low, and then to have this happen [at least] twice and to find each other to mate was probably close to 0%."
Aneuploidy & chromosomal rearrangements,does nondisjunction automatically lead to one monosomy and one trisomy?,"Mitotic nondisjunction can occur with the inactivation of either topoisomerase II, condensin, or separate. This will result in 2 diploid daughter cells, one with 2n+1 and the other with 2n-1.

If nondisjunction occurs during meiosis I, it is the result of the failure of the tetrads to separate during anaphase I. At the end of meiosis I, there will be 2 haploid daughter cells, one with n+1 and the other with n-1. Both of these daughter cells will then go on to divide once more in meiosis 2, producing 4 daughter cells, 2 with n+1 and 2 with n-1.

Nondisjunction in meiosis II results from the failure of the sister chromatids to separate during anaphase II. Since meiosis I proceeded without error, 2 of the 4 daughter cells will have the normal haploid number. The other 2 daughter cells will be aneuploid, one with n+1 and the other with n-1. 

_If meiotic nondisjunction, then yes. The result is monosomy and trisomy._


https://www.ncbi.nlm.nih.gov/books/NBK482240/"
Aneuploidy & chromosomal rearrangements,Is translocation essentially formed from the process of crossing over?,"Good question!

Translocations can be the result of crossing over between sequences that are similar but located on different chromosomes.  

One source of these events are the repetitive elements§ that make up most of the genome in many species including humans.


Another way that translocations can happen is if the DNA is broken in multiple places — e.g. by exposure to radiation. 
 In some cases the DNA will heal, but with the "wrong" parts of chromosomes stuck together.


§Note: A major component of the repetitive DNA comes from the many different families of transposons — pieces of DNA that can copy themselves to new places within the genome."
Aneuploidy & chromosomal rearrangements,"What happens if nondisjunction occurs during mitosis? I assume the cell would likely undergo apoptosis, but I'm not sure...","In many cases, polyploidy takes place and one cell ends up with zero chromosomes, while the other one has doubled garniture.

It leads to apoptosis of thew one cell without chromosomes."
Aneuploidy & chromosomal rearrangements,I think the diagram for nondisjunction in meiosis I is incorrect. It looks like sister chromatids failing to separate during mitosis.,"Yes, it is correct. Maybe it looks like that but it is correct. Look at it again. :)"
Inheritance of mitochondrial and chloroplast DNA,how mitochondria can survive in the cell even if it have a foreign DNA relative to cell.? why it is not detected for phagocytosis by the cell for  having foreign DNA ..?,"If the zygote has mutant mitochondria in it, that cell will replicate not knowing that the mitochondria is unusual because all immune cells differentiate from the zygote. Since the immune cells do not see the mutant mitochondria as "mutant", they do not attack it. It's kinda similar to how you get used to your mother's cooking, and when you go out and order the same thing, it might taste weird or gross to you, just because you grew up tasting certain foods."
Inheritance of mitochondrial and chloroplast DNA,"what does DNA in chloroplasts do? what is the need for the DNA , RNA and Ribosomal units to be present in chloroplasts? Do they have a major role in photosynthesis and making of glucose?  or do they only help in respiration of the plant by making enzymes? Can you please make this clear to me?","DNA in chloroplasts codes for the production and function of chloroplasts.

Since chloroplasts are quite complex organelles and very important (converting energy) they require its own DNA and control.

So DNA is converted to RNA and to proteins (dogma of molecular biology)."
Inheritance of mitochondrial and chloroplast DNA,"My family has a history of Breast cancer. My grandmother, her mother, and her mother has had it, all on my dad's side, but he hasn't had it. Is it possible that I, another female in the line, may have it? It seems to only passed on by the women in our family, so I am unsure.","There is a possibility. Judging by how your father's bloodline suffered from it, there is a chance that the breast cancer that they all had could be hereditary. This does not mean that you are automatically going to suffer from breast cancer, however; other genetic factors may have a larger role in determining whether you have cancer, such as mutations on other chromosomes. 

According to the CDC, you are more likely to have a hereditary breast cancer if:
-Many members in your bloodline had breast cancer. 
-Any one of your relatives had ovarian cancer or breast cancer together with overian cancer.
-Any one of your relatives had breast cancer before age 50, or had it on both of their breasts.
-A male relative had breast cancer.
-You are of Ashkenazi Jewish descent (those who are of such a descent have a higher breast cancer gene mutation incidence).

Note that this is not intended to incite fears over inheriting breast cancer; you are more likely to get it from a non-genetic cause. 

Did this help?"
Inheritance of mitochondrial and chloroplast DNA,What are some examples of diseases gained from mitochondria DNA?,"Mitochondrial encephalopathy, lactic acidosis and stroke-like episodes syndrome (MELAS)  as well as Myoclonic epilepsy, several visual imperments and some forms of Liegh syndrome. Apparently there is mitochondrial DNA factor in mental illnesses like dementia and Alzheimer's.
Grim.
Hope that helped!"
Inheritance of mitochondrial and chloroplast DNA,when mitochondria inheritance happen?,"The maternal mitochondria is inherited when the female ovum and male sperm fuse to form the zygote which contains the maternal mitochondrion.
P.S.: You can see it in the picture of mitochondrial inheritance above"
Inheritance of mitochondrial and chloroplast DNA,"So what about plants that are red or other colors? Do they simply create a differently colored pigment, or does their lack of pigment cause them to be colored differently?","Plants that photosynthesize probably all have chlorophyll, but there might be other pigments that dominate, so that the green can’t be seen. For dying leaves, chlorophyll is broken down so that it doesn’t damage the leaf, and other pigments’ colors show."
Inheritance of mitochondrial and chloroplast DNA,How often do these cases of (extra) chromosomal inheritance occur in a population?,"Maybe I'm misunderstanding your question, but every eukaryote that has mitochondria (essentially all of them) gets those mitochondria (and the mitochondrial genome) from the previous generation. 

The same is true for plastids.

Since most eukaryotic cells can't survive without mitochondria (or are at a severe competitive disadvantage without them), this happens for (essentially) all populations of eukaryotes more-or-less 100% of the time ...

Does that help?"
Inheritance of mitochondrial and chloroplast DNA,What are the alleles for mitochondrial inheritance? Why can a man inherit it from his mother but none of his own offspring can inherit it from him?,"The thing is that people inherit the mitochondria from their mothers. He could get is from his mother, but being a father and not a mother himself, his children can't inherit that from him."
Meiosis,is there random orientation in metaphase 2?,"Good question!

I think that is assumed to be generally true, but it would be very hard to test in most organisms.

The only evidence for this being true that I know of comes from the fungus _Neuropsora crassa_ that makes a linear§ ascus (sac containing the meiotic products).  

This allows us to see that in this species independent assortment also occurs in metaphase II.

§Note: The order of the spores within the ascus reflects the meiotic divisions.

References:
•http://mcb.berkeley.edu/courses/mcb140/Syllabus/AmacherLecture/Lecture6.pdf
•https://link.springer.com/referenceworkentry/10.1007%2F978-1-4020-6754-9_16853"
Meiosis,In meosis 2 when did the chromosomes duplicate?,there was no chromosomal duplication in meiosis II only the centrosome duplicated. If there would have been chromosomal duplication cells would never have been able to produce haploid gametes the cell used in meiosis II are the product of meiosis I
Meiosis,"When the new nuclear membrane forms around the chromosomes, how does the cell make sure the centrosomes are outside the nucleus and ALL chromosomes are inside?","Well, it works based on patterns of nuclear defragmentation. On the places where old fragments of a nucleus are, new form. Also, thanks to cytokinesis, the cell splits exactly half its length."
Meiosis,Please specify if the number of chromosomes becomes haploid in meiosis I or meiosis II? And if does in meiosis I then how? In meiosis I chromatids are not separated then how come chromosome number reduces to half??,"The number of chromosomes becomes haploid in meiosis I, because the actual sister chromatids are not pulled apart by spindle fibers. For example, if a cell was undergoing meiosis, and had a total of 4 chromosomes in it, then 2 of them would go to one daughter cell, and 2 of them would go to the other daughter cell. That makes 2 haploid cells. 

Then, in meiosis II, each of the 2 sister chromatids in the daughter cells would be split apart by spindle fibers, giving each cell 2 chromosomes. As you said, the fact that in meiosis I chromatids are not separated means that the entire chromosome is moved to one cell; if there were 4, then they would be moved to each daughter cell equally. I hope that helps; if you still have trouble please say so!"
Meiosis,"If the starting cell has 46 chromosomes, then how can it produce four cells with 23 chromosomes?","Remember that when replicating in interphase, the chromosome number DOES NOT CHANGE 

in interphase before S (replication phase) we have 46 single stranded chromosomes: 23 are from mom and 23 are from dad (they code for the same things meaning chromosome 1 of mom codes for the same thing as chromosome 1 of dad. Likewise chromosome 5 of dad is similar to chromosome 5 of mom)

after replication how many chromosomes do we have? 
answer: still 46, but what's different?
the single strand chromosome (1 chromosome) became two stranded yet attached identical sister chromatids (still 1 chromosome)

it is only when the sister chromatids separate are they each considered separate chromosomes.

This means that in meoisis II when we split the sister chromatids:
the parent cell starts with 23 chromosomes (EACH double stranded=two sister chromatids, so there are 46 chromatids. Anaphase II splits the sister chromatids which now separate (23 chromatids go to one pole and 23 chromatids go to other pole). When the chromatids are separated they are now called chromosomes 

so a haploid parent cell of 23 chromosomes (double strand) just created two haploid daughter cells of 23 chromosomes (now single strand).

The above is also how a 46 chromosome (double strand) cell in mitosis can result in 2 daughter cells each with 46 chromosomes (single strand). 

Even Sal admits how confusing this is, but he explains all this visually in a separate video differentiating the terms chromatid, chromosome, and chromatin."
Meiosis,why is interphase not included as a stage of cell-division in both mitosis & meiosis?,"Interphase _is_ stage of the cell cycle, but _not_ a stage of _cell division_ (meisosis).


Interphase is that gap phase (exactly G0) where cell cycle stops, DNA and organelles grow and synthesize."
Meiosis,"So meiosis is just to make a zygote? What happens after that? Also, why are there different processes of meiosis for sperms and eggs if they only have to join. Someone help, I'm really confused","Yes, meiosis's goal is to make a zygote. This zygote will (hopefully) turn into an embryo, then a fetus, which eventually becomes a human if everything works out. Meiosis in sperm and eggs is different because, well, sperm and eggs are different. A spermatocyte needs to split into four cells, while an oocyte needs to split into only one because many sperm are needed to fertilize a single egg. Once a sperm reaches the egg, it is only then that they join."
Meiosis,The male transfers sperm to ovaries then sperm is spreading in the ovaries then ultimately it becomes offspring. Am I right?,You're almost correct. Males transfer sperm to the female and only one of the many sperm ends up fertilizing the egg. Then the fertilized egg becomes a zygote that ultimately grows into a baby. I hope this helps!
Meiosis,Different between karyogenisis and dikaryogenesis,"Karyogenesis is the formation of a nucleus. Dikaryogenesis is almost non existent on the Internet, but supposedly it has to do with the formation of 2 nucleuses, and there may be a preference in the expression of one of them."
Meiosis,"will you please explain me all the stages of prophase-1 in meiosis

how can we find the order of stability of covalent compounds by inductive effect","1. Chromosomes condense and homologs loosely pair along their lengths, aligned by gene.
2. The paired homologs become physically connected along their lengths through a process called synapsis.  This forms a synaptonemal complex.
3.The random rearrangement of corresponding genes occurs between the non sister chromatids (because at this stage each chromosome consists of two sister chromatids).  
4. Synapsis ends, and the homologs move slightly apart, no longer bonded along their lengths like in the synaptonemal complex.  
5.  Some of these homologs have one or more chiasmata, an X shaped region where a genetic rearrangement has occurred.  This formation occurs because of sister chromatid cohesion, where a gene that has been given to the homologous pair in synapsis is still bonded to the corresponding part on the sister chromatid of its former chromatid.  
6. Centrosomes move to opposite ends of the cell, and the nuclear envelope dissolves.  
7. Microtubules from one centrosome attach to the kinetochore (protein structures at the centromeres) of one chromosome from each of the homologous pairs, while the other centrosome connects to the kinetochore of the other chromosome in each homologous pair, and each homologous pair moves towards the metaphase plate (where they line up before anaphase)."
Evolution of viruses,"I know this will most likely be impossible but is it possible for a virus to evolve rapidly enough to spread and wipe out life on earth, I mean the H1N1 pandemic looked bad enough right?","Viruses could never wipe out life on Earth. There are two reasons for that.

1) The more successful the host is, the more successful is the virus going to be. Humans are very widespread specie, which means that viruses that attack us have very good chances of spreading from one victim to another. But, as the population of their hosts declines, viruses will have more trouble in spreading. In the end, when there would be only a few isolated groups of people left, our imaginary deadly virus wouldn't be able to spread anymore.

2) Someone will be immune to virus. Those people will survive and continue the humanity. Their children will have their genes and they will all be immune to that specific virus. Spanish flu couldn't affect everyone, HIV can't affect everyone, none virus can affect everyone. It's just how things work."
Evolution of viruses,"If the HIV virus only has a lifespan of 52 hours, then wouldn't the HAART "cocktail" therapy be able to block the HIV virus for at least 52 hours, thus causing the death of the virus? Unless the HIV virus evolves and mutates within those 52 hours, which I highly doubt is always and/or mostly the case.","Good point. In that case, cocktail therapy would perfectly work and ensure no viruses escape."
Evolution of viruses,how does the virus affect human population?,"One virus can affect human population only if his infection becomes epidemic or pandemic.

Epidemic - a sudden increase in the number of cases of a disease to a level that is greater than the expected level in a given population in an area.

Pandemic -  an epidemic of world-wide proportions

https://www.infoplease.com/askeds/pandemic-vs-epidemic"
Evolution of viruses,What would happen if 3 viruses combined?,"Probably recombination of genetic material would happen.

Now, you may take 3 of the deadliest viruses in the world, but the resulting virus may be something harmless or low degree dangerous.

Or maybe each one may infect and cause disease on its own.

Genetical rearrangements can end up in any kind of results."
Evolution of viruses,How does the influenza virus affect the human body?,"Influenza virus has two different glycoproteins on it's lipid envelope called neuraminidase (helps the virus to leave the host cell)and haemaglutinin(aids the virus to enter the host cell).

In humans,haemaglutinin binds to (saliac acid) receptors on the epithelial cells in the upper respiratory tract and then the virus enters the cell through a process called 'endocytosis'.
Once in the cell , the negative sense Rna is replicated into positive sense ss rna which then helps in the process of progeny production.
Now viruses mutate very rapidly...Therefore the daughter viruses have slightly different glycoproteins than their parent and other progeny viruses.
This is why you can get flu every year or even twice or more in a year.

Now, neuraminidase is a receptor destroying protein which is why it aids the virus to elude from the cell by destroying saliac acid receptors."
Evolution of viruses,Why is it that the article says that the average human cycle is only 20 years?,When looking at generations of an organism you measure the average time between birth and having offspring.  For humans the figure of 20 years has been used but may very depending on the area and time period used.
Evolution of viruses,What does rna mean?,"RNA stands for RiboNucleic Acid.  It is described in the section on nucleic acids, over here:

https://www.khanacademy.org/science/biology/macromolecules/nucleic-acids/v/dna-deoxyribonucleic-acid"
Evolution of viruses,Can a virus wipe out the dinosaurs or cause a mass extinction event?,"I know there will be people who disagree with me, but i firmly believe the answer to both questions is no.

(Just as a side note, dinosaurs aren't extinct. Present-day birds are indeed dinosaurs.)

To cause a mass extinction, a virus would have to be able to infect a broad variety of species and cause disease with a mortality rate of 100 %. To my knowledge, no known type of viral disease has such a high mortality rate (even though some are close to that number!). The more lethal a virus is, the sooner it will run out of possible hosts. Earlier types of ebola virus were very lethal (the highest recorded mortality rate was 90 % during the 2003 epidemic in DR Congo), but those viruses didn't cause massive epidemics. Each outbreak had several hundreds of casualties.

Some scientists speculate that viruses could have caused several smaller extinctions in the history of life on Earth. Fossil records confirm that in between so-called mass extinctions, there were also smaller extinction events which happened during periods of relatively stable environmental conditions. So what was the cause? Even though some believe it was because of the viruses, as of now we have no evidence to support that claim.

That's just my opinion. The topic is still very controversial, and i would be interested to hear others' opinions."
Evolution of viruses,"Vaccines provoke the host's immune system to produce appropriate antibodies against the antigen in the vaccine. In relation to the section, Case study: HIV, why do vaccines for viral infections/viruses become ineffective over time? Is it because as viruses mutate, antigens develop on their surfaces which are different to the original antigens on the virus before mutation, and hence require the production of different antibodies to be granted immunity against the new, mutated virus?","A person's immune system is introduced to the protein on the surface of a dead or weakened virus so that it can be recognized as a foreign without the chance for the virus to overwhelm the immune system.  That person's immune system is primed to recognize and eliminate anything with that protein on it.  

If the virus mutates or is somehow changed so that the protein coat no longer has the same protein on its surface that person's immune system will not immediately recognize it as foreign and the virus has a chance to insert itself into a cell for replication before it is detected.  

A lot of research is needed to identify what parts of the virus protein coat are not likely to change over time so that a vaccine will continue to work even of the virus changes."
Nucleic acids,How do mRNA and tRNA communicate with eachother during the formation of the proteins?,"mRNA is like a recipe from a cookbook; a list of ingredients to make a protein. mRNA is a chain of nucleotides (A, U, C, and G, not T since this is RNA). A group of three nucleotides is called a codon. A codon matches with three nucleotides, called an anticodon, on a single tRNA molecule while in a ribosome. The tRNA carries an amino acid, our ingredient to make the protein.
So mRNA is the recipe, tRNA matches to the recipe bringing an ingredient, and the line of ingredients become a protein."
Nucleic acids,"If A-T bonds have 2 hydrogen bonds and G-C bonds have 3... Would it be true that longer periods of A-T bonds in DNA (so like: AATAATTATTTTAATTAAAA) are less stable parts of the DNA helix than parts that have more (or only) G-C bonds in them? And if this is true, are these parts (AT only parts) more prone to mutations?","The first part is true, T-A bonds are less stable and more likely to come apart. The A-T bond strands also signal where DNA needs to separate for commonly transcribed genes, such as the TATA Box commonly found just before the beginning of gene sequences.

I'm not sure if they are more prone to mutations though."
Nucleic acids,"DNA is common to all organisms, all organisms use the same 4 nitrogenous bases, A T, C G

is that right?","Entirely true. Also, AT/GC are found in DNA while RNA is made from AU/GC. Just keep in mind that, even though all life forms have DNA, not everything that has DNA is alive: viruses can have DNA but are not living."
Nucleic acids,"Why do some nitrogenous bases have two fused carbon rings while other have one? Would it be possible for there to be nitrogenous bases with more than two fused carbon rings? Could there ever be an instance where there are more than just five kinds of nitrogenous bases (Adenine, Thymine, Guanine, Cytocine and Uracil)? If it could be possible how would DNA and RNA have to rearrange themselves? Would it be possible for DNA and RNA to use other sugars aside from Deoxyribose and Ribose? If so, like what? If not, why?","https://www.khanacademy.org/science/organic-chemistry/aromatic-compounds/aromatic-stability/v/aromatic-heterocycles-i

https://en.wikipedia.org/wiki/Heterocyclic_compound

https://en.wikipedia.org/wiki/Abiogenesis

https://en.wikipedia.org/wiki/Nucleic_acid_analogues

Hope this helps!"
Nucleic acids,Are the functions of nucleic acids guided only by molecular forces and just appear to have intention or are there other forces at work that I'm not aware of? How do these macromolecules "know" what to do?,"A creationist would say that this is part of the intelligent design. An evolutionist would say it's all down to chance. Two spanners to consider - 1) one molecule of hormone, once recognised by the cell, leads to prduction of thousands of times more molecules, and types of molecules, than a mere chemical would suggest, and such secretions can be brought about by tiny changes in brain activity. 2) DNA is just for storage. It is a molecularly inert form for the passing on of genes without having a massive effect upon the rest of the body - and so the active form is the sticky stuff of RNA and these determine how the proteins are folded together."
Nucleic acids,"When transcription takes place and the DNA is broken into two, and then mRNA is formed with one of the DNA strands or for BOTH the DNA strands?","Within a gene *usually* only one strand is transcribed, but there are many examples where transcription happens from the both strands. This is especially common in viruses.

Also, the strand that is transcribed for one gene may not be the same as the strand being transcribed for a neighboring gene.

Finally, the whole DNA double helix is not separated - just a small bubble is opened around each RNA polymerase as it works its way along the DNA."
Nucleic acids,"In the first paragraph of the section "Regulatory RNA (miRNAs and siRNAs)" it says "They bind to specific mRNA molecules (with partly or fully complementary sequences) and reduce their stability or interfere with their translation, providing a way for the cell to decrease or fine-tune levels of these mRNAs."

Does this mean that the purpose of microRNAs (miRNAs) and small interfering RNAs (siRNAs) it to make sure that there are not too many mRNA molecules producing proteins? They are regulating the amount of protein produced by the cell? Am I understanding this correctly?

Please help! Thanks. :)","Yes, miRNA regulates protein synthesis in a way it binds to mRNA transcript and 'silence' it."
Nucleic acids,how are DNA and RNA different and alike to each other?,"As stated in the summary at the end of the article, DNA and RNA have different functions. While DNA stores genetic information, RNA is involved in protein synthesis and gene regulation, as well as storing genetic information in some viruses. DNA and RNA also have different structures; DNA's phosphate-sugar backbone contains deoxyribose, while RNA's contains ribose. While DNA is double-stranded and has the nitrogenous bases adenine, thymine, cytosine, and guanine, RNA is usually single-stranded and contains uracil instead of thymine.

As for the similarities between DNA and RNA, they are both important biological polymers and contain four bases and a phosphate-sugar backbone."
Overview: Gene regulation in bacteria,"what is the evolutionary advantage of regulation of prokaryotic gene expression?
what are the drawbacks?","Great question. The upsides of gene regulation is a conservation of energy within the body, as it is not being used for unnecessary functions. The drawbacks could maybe be the possible mutations? If there was a mutation that were to transcribe a protein non-stop, it could satiate the cells or use up available resources for no reason."
Overview: Gene regulation in bacteria,What does it mean for there to be a negative and positive gene regulation? What's the difference?,Positive gene regulation controls the production of genes by turning them on while negative gene regulation controls the production of genes by turning them off.  Positive gene regulation allows for the production of a gene that is needed for use at a particular time/situation in a cell while negative gene regulation prevents the overproduction of a gene at a particular time/situation in a cell.
Overview: Gene regulation in bacteria,Can you give a couple examples of rare eukaryotic operons?,"The examples that I found for mammals are all bicistronic (operons with two genes):
LASS1-GDF1, SNRPN-SNURF, MTPN-LUZP6 and MFRP-C1QTNF5

You can search for those gene pairs, but there doesn't seem to be a huge amount of information available and in many cases one of the genes is almost completely uncharacterized.

Eukaryotic operons (aka polycistronic mRNAs) are apparently very common in nematodes (round worms) and also frequently seen in _Drosophila_ (a fly).

Unfortunately I have only found academic papers that cover this interesting phenomenon:
•https://academic.oup.com/bfg/article/8/1/68/219251

•https://pdfs.semanticscholar.org/24c6/239e22766cbf11e8a717d3beff6f69be594e.pdf

Does that help?


ADDENDUM:
Also, the mitochondrial genome uses operons (polycistronic genes), but since the mitochondria is descended from a bacteria it seems like cheating to count that ..."
Overview: Gene regulation in bacteria,Why is it beneficial for bacteria to be able to regulate the production of proteins?,So that they do not use energy to make something that they do not need.
Overview: Gene regulation in bacteria,How can the cell know that the genes in an operon are separate? Wouldn't the cell create all the genes in a operon as one gene and make them all as a whole protein?,"Good question!

Even though all the genes in an operon are transcribed together, they are *not* translated together.  There are untranslated sequences between each gene that contain a RBS (ribosome binding site).  When the mRNA is being translated, the RBSs for each gene will independently bind to different ribosomes and so they all make separate proteins.

This figure may help make things clearer:
https://en.wikipedia.org/wiki/Operon#Overview"
Overview: Gene regulation in bacteria,Are the operator and enhancer exist at the same time?,"Yes. there could be enhancer or silencer.

The operator is a place of operon where repressor binds while enhancer is a place where activator binds. They could easily be neighboring coding sequences on the same operon."
Overview: Gene regulation in bacteria,What's the difference between operons and other normal genes?,"Operons are groups of genes that are transcribed together as a unit, and share one promoter."
Overview: Gene regulation in bacteria,Is operator a kind of silencer?,"Not operator itself, it is just place where repressor binds. But when repressor binds it is *silencer*."
Prokaryote structure,does bacteria have a Hayflick limit (limit of division) like normal human cells do?,"Okay, so this is very complicated question to answer and it requires a lot of molecular biology. If any part of my answer is incomprehensible, please let me know.

The main difference between our genome and bacterial genome is that our DNA molecules are packed into structures we called chromosomes and they are linear, meaning they have a starting point and an end point. Bacteria don't have chromosomes and their DNA is circular.

Due to the mechanism of DNA replication, our DNA isn't completely replicated. That is, "the mother" DNA and "the daughter" DNA (those are not official terms) aren't identical. "The daughter" DNA will always be a bit shorter.

What does that mean for us? How much of DNA do we use per one cell division? Well, on the both ends of our linear DNA there are what we call telomeric regions, or telomeres. Those are long repeated sequences that don't code for any protein. Their only purpose (as far as we know) is to save the important part of DNA from being lost during the replication process. Instead of losing important genes, we lose a small part of telomeres in every cell division. After 40 - 60 divisions telomeres reach critical length and they can't be sacrificed anymore. This is where DNA replication and hence cell division stop happening.

Because bacteria have circular DNA, they don't have those problems. Their polymerase can replicate an entire genome without losing one single part of it. They don't need telomerases and therefore they don't have any limits in cell division. If a bacterial specie had Hayflick limit they would stop reproducing after some number of divisions and that would be the end of the specie.

What you should ask now is: what about cancer cells? They seem to be immortal and divide without any limits. What about single celled eukaryotes, like amoeba? They have chromosomes too (linear DNA) but they don't have Hayflick limit. The answer to those questions is very interesting and rises a lot of possibilities for us. There is an enzyme called telomerase. This enzyme extends telomerases and prevents them from being lost after a number of replication cycles. It works forever in cancer cells, but for some reason it stops working in "normal" cells. Why? We don't know yet, but we're on our way to find that out. This means we could treat cancers with telomerase inhibitors - if we prevent telomerase from extending their telomeres, cancer cells will stop multiplying after reaching Hayflick limit. Could we treat our normal body cells with telomerase and prevent them from reaching the limit? The answer might be yes. Would that mean we could become immortal in such a way? We don't know yet, but we're certainly going to dig deeper into the problem.

Thanks for asking such an interesting question!

Alex"
Prokaryote structure,Can bacteria get cancer if so what happens?,"No, bacteria cannot get cancer. Cancer is the uncontrolled growth of cells in a multicellular organism, and bacteria are single cellular."
Prokaryote structure,what is the advantages of prokaryote with absence nucleus,"Essentially, prokaryotes are simpler than eukaryotes. This may not sound like an advantage, but it means that it's really easy to make new prokaryotes, which means that prokaryotic cells reproduce much faster than do eukaryotes. Also, this faster reproduction means that these cells can adapt faster as there are faster generations, which can be an advantage."
Prokaryote structure,"how were the fossil of the prokaryotes found?
Here it says that fossils of prokaryotic were found, how was it understood that it was a prokaryotic?
i dont think that something so small like a bacteria could actually leave a imprint like a fossil.
thank you","Bacteria generally don't leave fossils, and at most we can infer their existence based on evidence of their effects on other fossilized creatures, such as infections. However, some bacteria have been known to create iron or clay sort of shells that survive after the bacteria has died, creating a sort of model of the bacteria. Bacteria have also been found in fossilized amber, and some cyanobacteria can create stromatolites, which are rocks created by cyanobacteria, calcium carbonate, and the surrounding sediments. Stromatolites can be fossilized, and when cut open, there are sometimes layers or fossilized cyanobacteria inside, protected by the stromatolite."
Prokaryote structure,can eukaryotes have flagella and pilli? or is that only for prokaryotes?,"Yes, and the flagella of motile bacteria differ in structure from eukaryotic flagella. 


However, Eukaryotes do not have pili or fimbriae."
Prokaryote structure,"Do Prokaryotes, specifically Archea, have ribosomes?","Yes they do.  Ribosomes in prokaryotes are similar to, but smaller than, those in eukaryotes."
The trp operon,"I don't understand the point attenuation.
Attenuation of the operon allows the cell to stop (or not) the transcription of the operon before the genes coding for the enzyme, right?
But, if the levels of tryptophan are high in the cell, wouldn't the translation of the Trp genes be already regulated via the repressor fixed on the operator ?

What is the point in attenuation of the polymerase cannot fixe itself first? When is it used by the cell as a mean of regulation?","Great question!

In general biological systems are quite error prone — in the case of the _trp_ operon the repressor is reported to decrease expression by about 70 fold.  Attenuation can add another 10 fold decrease in expression.  

Both mechanisms thus work together to give a better level of control."
The trp operon,what is the product of trp operon?,"There are 5 structural components of trp operon as described above they produce different enzymes namely, trpE-anthranilate synthase component I, trpD - anthranilate synthase component II, trpC- N-(5'-phosphoribosyl)-anthranilate isomerase, trpB- tryptophan synthase β, and trpA- tryptophan synthase α. All of these enzymes have a combined role in production of tryptophan."
The trp operon,What is the co-repressor in the trp operon?,"Tryptophan.

I guess the section titled `Turning the operon "on" and "off"` could have made this a bit clearer ..."
The trp operon,"What does the tryptophan actually do when produced by the trp operon? If it is just produced to block the trp operon from producing more of the same substance, I don't see the point of tryptophan.","Tryptophan is an amino acid, and it is used to build some proteins."
The trp operon,"Why when the 1+2 và 3+4 hairpin is formed, the RNA Polymerase detaches? It's hard to understand this point...","Look. Compare photos above and photo below. In the photo above region 4 is free to bind to RNA polymerase. Why is it important? because it encodes attenuator and promotes translation.

However, when there is High TRp, mRNA folds and 3 and 4 region form loop. Loop makes it region 4 hidden and detaches from RNA polymerase. 

Just follow the photos and obserev them as long as you need. Tryto reproduce on paper (schematically).


Ask more specific which part does not make sense."
The trp operon,"What would be the easiest way to make large amounts of tryptophan, using a strain of E-Coli (through genetic engineering)? Could you please direct me in the right direction?","Hmm...I would say that you might want to use some of the components described in this article, but with modifications that would "break" the negative feedback loops that limit the amount of Trp produced.

For instance, you would probably want to express the _trp_ operon under a constitutive ("always-on") promoter, and you might also want to alter the sequence of gene encoding the gatekeeper enzyme (the one that is negatively regulated by feedback inhibition) to make it insensitive to tryptophan binding, i.e., by disrupting the tryptophan binding site. Finally, you would probably want to not include the leader of the _trp_ operon when making the version under the constitutive promoter, or else the attenuation mechanism would prevent the accumulation of large amounts of Trp in the cell.

I'm sure there are other ways to do it, but that would be my first thought (that you would basically need to reconstruct a version of the system that is no longer self-regulating). Hope that helps!"
The trp operon,why there are two codons trp? what happen if there is only one codon trp?,"Thank you for your help, now I think I may help you.

So, there are 2 pairs of regulating genes (GDCF) but that is less relevant here. We are interested in regulating starting sequence operon.
The operon is composed of *3* promoters (3 places for binding) *but* it has two Trp residues to bind two sensing signals.

It binds L- Trp, and the other codon binds tRNA trp (charged or uncharged).

The question arises about what would happen if only one is present (let's imagine mutation happened).

They can function without each other. That is a form of double control.

We can say that the principal promoter is the one binding L-Trp while Terminator is the one binding charged or uncharged tRNA Trp.

If Trp binds to L-Trp, then it activates corepressor and diminishes the production of TRp. (it is logic high Tryptophan = no need for a synthesis of Tryptophan). However, the synthesis does not simply stop. There is wehere another promoter (terminator) that comes into place. Uncharged tRNA Trp binds and termination stops at the leading place. Meaning now translation.

Now, what if the tRNA TRp terminator is missing? It means that translation will proceed but at a slower pace.

What if the first codon is missing? It could potentially impair the Trp operon regulation severely. Because cells would not be able to sense whether Tryptophan is present in the cell or not.



Hope this helps :D


For reference, click on the https://rnajournal.cshlp.org/content/13/8/1141.full.pdf+html 
page 2 figure 2."
The trp operon,What does the Trp stand for ?,"`Trp` is the accepted three letter abbreviation for the amino acid tryptophan.  

You might wonder why they didn't use `Try` – in addition to `Try` being a word, there is another amino acid called tyrosine, whose code is `Tyr`, so they decided to try something a little more different :-)"
N/A,The hairpin somewhat appears to look like a tRNA molecule. Am I wrong in saying that tRNA is formed from these hairpin structures?,"No, you're not wrong. A tRNA contains hairpins as well, though the hairpins play different roles in the two cases. In transcription termination, the hairpin causes the RNA polymerase to stall and the transcript to separate from the DNA. In a tRNA, multiple hairpins form and give the tRNA molecule the 3D shape it needs to perform its job of delivering amino acids."
N/A,"if introns are not important, why are introns are formed?","Good question!

Introns have multiple roles in biology including the regulation of gene expression.

Other introns have functions after they are spliced out from the transcript and can act as signaling or regulatory molecules.

Some relatively rare types of introns appear to be parasitic DNA molecules — they insert copies of themselves into genes and then splice themselves out from the RNA presumably to keep the host cell alive.  It is possible that the more typical introns originated from such parasitic DNA elements.

This is still an area of active research and it is quite likely that more functions for introns will be uncovered in the future.

If you wish to know more, you could start with this section of the wikipedia article on introns:
https://en.wikipedia.org/wiki/Intron#Biological_functions_and_evolution"
N/A,do the presence of introns indicate something related to evolution?,"Not really. Introns enable one gene to produce multiple polypeptide sequences, thereby creating a more efficient genome. This will make more sense if you look at the examples in the pre-mRNA processing article. I think you're thinking of pseudogenes, which are non-coding regions remaining in an organism's DNA from ancestral roots. You're correct in your conclusion that introns are non-coding, but just because a sequence is an intron in one pre-mRNA sequence doesn't mean that it can't be included in the exon sequence in another."
N/A,"Hi, this isn't mentioned in this article, but I would like to ask,
What is the difference between a gene and a cistron? Why do we need the term , cistron, in the first place?
And what do the terms monocistronic and polycistronic mean?","Really there isn't much difference — as far as I know the existence of the two terms is an accident of history — my advice would be to use gene.

Many prokaryotic (and a few eukaryotic) genes are transcribed together into a single mRNA and then translated separately from the single mRNA.  These situations are described as "polycistronic".  The more common condition of one transcript encoding a single protein is thus "monocistronic".

Confusingly, the entire multigene (polycistronic) unit will often be referred to as an operon.  Operons are typically made up of genes encoding proteins that work together in an organism and this structure ensures that they are all made at the same time and in similar quantities.

You can read more about this here:
https://www.khanacademy.org/science/biology/gene-regulation/gene-regulation-in-bacteria/v/operons-and-gene-regulation-in-bacteria

And for a bit more detail:
https://en.wikipedia.org/wiki/Operon"
N/A,I thought helicase was the enzyme that separates the DNA helix for the SSB to keep the DNA strands separated?,"Yes, helicase was the enzyme   that makes the DNA to unwinds its strands  by breaking the Hydrogen bonds between the nucleotides."
N/A,What I don't understand is: If the Promoter is located at the 5' end of a gene how does RNA polymerase start there if it reads from 3' to 5' and syntetase RNA from 5' to 3?,The RNA is actually synthesized using the antisense (complementary) strand as the template.
N/A,Are there other ways that the mRNA strand could detach from the DNA strand instead of the hairpin turn? And what would happen if the mRNA nucleotide accidentally gets changed instead of the normal one ie. a mutation?,"This is briefly covered in the next article — short answer: yes, but transcription termination is still being actively studied and is not completely understood.

Additional reading:
https://en.wikipedia.org/wiki/Eukaryotic_transcription#Termination
https://www.nature.com/scitable/topicpage/dna-transcription-426


I'm not completely sure I understand your second question — are you asking what would happen if the "wrong" base was incorporated into an mRNA?

If so, probably not much since each gene typically will make multiple transcripts and most mRNAs have a very short lifetime.  (Note that this is almost certainly something that happens all the time since all biological processes make errors.)  

While I've never see any evidence that any of this ever actually happens, it seems possible that in rare cases the change might make an mRNA encode a toxic protein that could kill a cell or worse yet trigger cancer formation.  I suppose if you were spectacularly unlucky it might even promote prion formation (a contagious toxic protein structure)."
N/A,"Won't the RNA have the wrong sequence if the introns are spliced, or is it predetermined to omit the codons in the introns in order to have the "perfect" code in the mature RNA?","Introns are actually noncoding DNA segments (in other words, they do not code for proteins), so splicing them out actually helps produce a functional protein rather than potentially disrupt protein function. However, this doesn't mean introns are useless either; in fact, they are actually very important for regulating gene expression. 

We've learned a lot about introns since their discovery but many questions about them and their functions still remain unresolved. You can learn more about them in the link below. Hope that helps!

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3325483/"
N/A,"Does the transcribed region always start with bases TAC, so that the RNA will start with bases AUG, which codes for methionine?","No, transcription starts upstream of the AUG, so the mRNA contains a 5' untranslated region. Then ribosomes translate starting from the AUG in the mRNA. The details of how they find the AUG is different in eukaryotes and prokaryotes."
N/A,does the hairpin structure come in to play in transcription?,"A hairpin loop is an unpaired loop of messenger RNA (mRNA) that is created when an mRNA strand folds and forms base pairs with another section of the same strand. The resulting structure looks like a loop or a U-shape.

Hairpins are a common type of secondary structure in RNA molecules. In RNA, the secondary structure is the basic shape that the sequence of A, C, U, and G nucleotides form after they are linked in series, such a folding or curling of the nucleic acid strand. mRNA hairpins can be formed when two complementary sequences in a single mRNA molecule meet and bind together, after a folding or wrinkling of the molecule. Hairpin loops can also form in DNA molecules, but are most commonly observed in mRNA.

There are many instances of the hairpin loop phenomenon among nucleic acid strands. One example of a hairpin loop is the termination sequence for transcription in some prokaryotes. Once a polymerase meets this loop, it falls of and transcription ends. Another more general example is tRNA, a central player in protein synthesis, which is partially formed by hairpin loops. The tRNA molecule actually contains three hairpin loops that form the shape of a three-leafed clover. One of these hairpin loops contains a sequence called the anticodon, which recognizes and decodes the mRNA molecule three nucleotides (one codon) at a time during translation. This clover-leaf structure supports the eventual connection between every codon, anti-codon and amino acid.

http://www.nature.com/scitable/definition/hairpin-loop-mrna-314"
Gel electrophoresis,""All DNA molecules have the same amount of charge per mass. Because of this, gel electrophoresis of DNA fragments separates them based on size only."

I don't get it.
F=qE
ma=qE
a=qE/m
and (q/m) is a constant.
If all fragments have the same acceleration, then shouldn't they all move with the same speed?","Great question.
Your equations are correct but your model has assumptions. When you define that a=qE/m ,you assume that the only force acting on the DNA is the electric force from the electric field so that's why your calculation takes this as the resultant force since it is the resultant force which will accelerate a body according to Newton's second law. 

However, there's one more factor that comes in play. The DNA fragments move through the agarose gel so they are experiencing viscous drag as they move through the gel. This viscous drag is proportional to the mass of the DNA fragment . Let me explain why. 

The mass of the DNA fragment  depends on the length of the DNA fragment. The longer the DNA fragment ,the more atoms it contains so the more electrons it contains . The more electrons in the DNA fragment ,the stronger the intermolecular london forces of attraction between the DNA fragment and the gel molecules so the greater the viscous drag experienced by the DNA fragment. Yes all your equations are correct and they travel at the same acceleration but it's the viscous drag through the gel that causes heavier DNA fragments to move slower than the lighter DNA fragments .I myself once had the same question in my mind but realized that the viscous drag is the game changer of the scenario. Hope I answered your amazing question."
Gel electrophoresis,Is it possible to make gel electrophoresis determination machine in home ?,"I personally don't know, but if you Google search on "how to make your own gel box," some hits come up - maybe one of those would help you? Good luck! :)"
Gel electrophoresis,Which poles are known as the cathode and anode? Sorry I get a bit confused with these two :\,"In a *galvanic (voltaic) cell*, the anode is negative and the cathode is positive. However, in an *electrolytic cell* such as we have here, it's the reverse: the anode is *positive* and the cathode *negative*.
This is because the flow of electrons goes in the opposite direction in the second system."
Gel electrophoresis,Are there more recently devloped methods to measure DNA length?,I would also add that researchers almost always use gel electrophoresis to at least check that the PCR was successful as sending a failed PCR product to another lab for sequencing etc. would be a complete waste of money and it's not cheap yet!
Gel electrophoresis,why do the bands appear to be of the same size while the DNA fragments vary in their sizes?,"The bands that you see are as a result of loading dye, which helps scientists see the DNA they're loading into the gel. The DNA fragments are typically illuminated under UV light, and aren't visible in visible light."
Gel electrophoresis,"what does it mean to have multiple bands for same sample (for ex: sample#3 above). Also when two or more bands appear for the same sample, which band do we use to determine the size?","Multiple bands mean DNA fragments with different size and lengths. Realistically when doing   gel electrophoresis you'll see many more bands for the same sample. To determine the bp size, you estimate using the reference DNA."
Gel electrophoresis,I'm doing a lab in class on gel electrophoresis where a married lady was raped and she wants to find to whether her baby is from her husband or the rapist. The gel electrophoresis shows more shared bands between the child and the husband than the child and the rapist. I was wondering how accurate this procedure is and what more someone could do to be more certain that it is the husband. Can more DNA from these people be tested?,"I think this method is pretty accurate, but again, including more reference DNA would be more helpful. Let's assume that rapist and husband are not genetically rated - in that case, it is easy to distinguish them."
Gel electrophoresis,"I don't understand how the length of a DNA fragment can be used to identify a person. 

Here's how I'm guessing it happens and the questions I have about it. There's much that might be wrong, so please let me know:

Let's say you do PCR for a specific sequence on a hair cell from a crime scene. Firstly, how would you select the sequence to do PCR with?

Then, let's say you did gel electrophoresis and found out the DNA for the chosen sequence is 5000 bp long. (Side question: why wouldn't you know the length of your target sequence before doing PCR?)

Then, you take the hair cells of a few suspects (for simplicity, you know for sure that the culprit HAS to be one of them) and do PCR for the same sequence and gel electrophoresis. At this point, why would the different suspects have different lengths for that sequence? Doesn't a certain sequence have a fixed length?

Let's say, somehow, only one suspect has 5000 bp for that sequence. Why does this mean that they are a match for the crime scene hair? How does having the same length for a sequence indicate identical genomes?

Sorry about how long this was but I'm pretty confused so it'd be great if someone could explain.","For your first question:
You will do PCR of the entire sample. Then a restriction enzyme is used to cut the part you want. One restriction enzyme will make the cut on the same place in all samples. So you will have the fragment containing the same sequence."
Gel electrophoresis,"So when fragments of DNA are put in the gel electrophoresis box, do they keep moving toward the positive end until they reach a certain point where they stop, based on how many base - pairs long they are, indicated by the ladder? In other words, do they stop at a certain point that tells scientists how long they are? Because if they just kept moving toward the positive end (at different speeds), then the fragments would just pass each length interval on the ladder, and then scientists wouldn't know how many base - pairs long they actually are. Hope this makes sense.","Everything (including the ladder) gets loaded at the same time in separate wells (slots/holes in the gel).  

This is done with the power supply turned off so there is no electric field.  

After loading the samples into the well you turn on the power§.  

This allows the DNA from the standard(s) (usually referred to as a ladder) and sample(s) to migrate in parallel.

This means you can compare the sample(s) to the ladder(s) at any time.  

In general, the longer the gel is run the more separation you get, but the bands will also get fatter (more spread out).


We generally decide when to stop the gel (turn off the voltage) based on the migration of one or more dye molecules included in the samples.  

These molecules migrates at known rates similar to those of a small DNA molecule.


Does that help?


§If you're smart you also double check that the samples are moving in the correct direction! (ADDENDUM: not that _I've_ ever committed "retrophoresis", nope not me, I also didn't (re)invent a name for it ..."
Eukaryotic gene transcription: Going from DNA to mRNA,"I'm sure RNA interference has been tried in the treatment of Covid-19. Is there a particular reason why the process worked for one virus, Ebola, but does not work for another virus, Covid-19? Granted, they are different types of viruses, but the idea is to interfere with the purpose of mRNA in general not a specific type of mRNA.",if it interfered with the purpose of mRNA in general we would all be dead.
Eukaryotic gene transcription: Going from DNA to mRNA,"The 5'Cap G is different than a regular G found in the DNA or mRNA, right? It's methylated? Does that affect the function or reading at all? Does that stay on the mRNA for translation?",It is methylated so it would be a little different than DNA/mRNA. It does not affect the function/reading because the ribosome docks onto the Shine Dalgarno Sequence (in prokaryotes) and the Kozak Sequence (in eukaryotes). Once it docks here it will start transcribing at the start site (AUG). It does stay on the mRNA while translation happens and actually serves as a site for the docking of proteins but that is beyond the scope of the material on the test.
Eukaryotic gene transcription: Going from DNA to mRNA,"Is there a reason that a deoxyribose and Thymine are changed, in order for mRNA to leave the nucleus? I can't see how that one hydroxyl or, moreso, that methyl group makes a difference; is this known?","This is kind of a basic explanation, and it would be hard to get into the nitty gritty details, but I hope it helps you understand.
Thymine is changed to Uracil because Uracil is easier to produce. DNA contains Thymine because it is more stable, but RNA does not need to be around as long.
The hydroxyl group on RNA is there for a similar reason. This group makes the molecule more susceptible to hydrolysis (to recap, the splitting of a molecule using water), so RNA can be more easily decomposed. DNA uses deoxyribose because, like Thymine, it is more stable.
Even though this question is 3 years old, I hope it helps people who might be wondering the same thing."
Eukaryotic gene transcription: Going from DNA to mRNA,"If the introns are going to be removed anyways, what's the purpose of having them in the DNA?","Here is the awnser that I found in my textbook
Introns are crucial because the protein repertoire or variety is greatly enhanced by alternative splicing in which introns take partly important roles. Alternative splicing is a controlled molecular mechanism producing multiple variant proteins from a single gene in a eukaryotic cell."
Eukaryotic gene transcription: Going from DNA to mRNA,is there videos and power points?,No unfortunately. But there is a transcript under the video
Eukaryotic gene transcription: Going from DNA to mRNA,"In the mRNA processing, does the slicing of pre-mRNA goes before the Protection phase, or the other way around?  Thanks!","I've always understood that they are near simultaneous. The important fact is that the primary RNA transcript (pre-mRNA) must have the Introns spliced out (splicing phase), and have the 5' cap and 3' Poly-A tail added (Protection phase) to become true mRNA. Only once these changes have occurred can the mRNA exit the Nucleus to be translated into a protein."
Eukaryotic gene transcription: Going from DNA to mRNA,"on the answer to the second question macias said that the ribosome attaches to the shine dalgarno sequence and then starts transcription  .
i was wondering if that is in both transcription and translation i though it was only translation can some one clarify please.
also the video on translation does mention it  but not on transcription.","Let's see if this helps:
(1) The *Shine Dalgarno sequence* is in a prokaryotic mRNA.
(2) *mRNA* and *ribosome* are only involved in the _*translation process*_
(3) Because of (1) and (2), *Shine Dalgarno sequence* does not apply to the _*transcription process*_"
The genetic code,"Are Glutamate (Glu) and Glutamine (Gln) interchangeable? or there is something wrong with the example on reading the codon table, because CAG codes for Gln, not Glu.","They are 2 different amino acids, so no they cannot be use interchangeably."
The genetic code,When does the tRNA know when to use AUG as a start codon and when to code Methionine? Are there other influencers,"Excellent question!

Translation is quite bit more complicated that this introductory material can cover.

The sequence of the mRNA around a potential start codon influences whether or not it will be used§.  These sequences are bound by proteins that help guide the ribosome to assemble at the correct place to start translation.
(In fact, codons other than AUG are sometimes used as start codons!) 

This is covered in a bit more detail in another article:
https://www.khanacademy.org/science/biology/gene-expression-central-dogma/translation-polypeptides/a/the-stages-of-translation

I also encourage you to look at some of the references for that section, which will help give you more detail on this high complex process that is still being actively studied.


§Note: The mechanisms are very different in prokaryotic and eukaryotic organisms — they can also vary between different species and even for different genes!"
The genetic code,would it be possible to use the "coding language" of RNA to synthesize chemicals?,"Yes, proteins are made of amino acids which are coded within the DNA sequence, so yes, recombinant DNA may be used.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2845543/


Also, there are already efforts to use DNA as a digital store of information:
https://www.youtube.com/watch?v=NsfuBSsF1Fk
https://www.ebi.ac.uk/research/goldman/dna-storage
https://www.nature.com/news/how-dna-could-store-all-the-world-s-data-1.20496"
The genetic code,"Why is `AUG` a start codon and `UAA` , `UGA` and `UAG` stop codons?",No one knows exactly why evolution chose which specific codons represent each amino acid.  This likely happened in an arbitrary manner very early in evolution and has been maintained every since.
The genetic code,I have heard that the 3' end of mrna is rich in stop codons so that in case of a mutation the peptide gets released but I am unable to find an article about that. Can someone confirm if this is true or not?,"You are correct.

Usually nucleotides present in mRNA channel downstream the A site help determining the future.
 The expected hierarchy in the intrinsic fidelity of the
stop codons (UAA>UAG>>UGA) was observed, with
highly influential effects on termination readthrough
mediated by nucleotides at position +4 and position
+8. 


https://watermark.silverchair.com/gkx1315.pdf?token=AQECAHi208BE49Ooan9kkhW_Ercy7Dm3ZL_9Cf3qfKAc485ysgAAAlcwggJTBgkqhkiG9w0BBwagggJEMIICQAIBADCCAjkGCSqGSIb3DQEHATAeBglghkgBZQMEAS4wEQQMiuKY1yQvGdfscjqKAgEQgIICCmJx0U3b-ecY2oxn1QYcqc6a6QXYNlX9FCUngn9zbbPC6TWDitK20Cl65tVkDb6ARGxakyB0TEEbjl2c5gg6rg2qBTOI7x9Vy8585GIls0cxO0YkUJjM5nl4tIHHoOTo9GSTyGAW827IJoH0xMHIBZC6tWuwCiR6jqOaN1HrKwsQVlraRvdQyJb9eCxJcVkE-No67IraffHateNr-8Xin1lgr4vGQAfQXU9PjGDIReo41KpdTVC4ROs0BWMsX5SiIrOq0CT2I_d8aPe3BoxnnN5Vwdb-tIzNAmBaBiIlyQa2NBwBvWioTTqoTIlkqhVX4USGtnaevTT72XcMrlPPZm-hY4KtVOzqRFEiJZvumj8GsYH5VL8XA-vT_ZHLfZxscDuS2AaEIts5h3YNsYXoB_VtpESmnQzfU8QXfocNOamKdN2HvESBttG-e1DGLH7er75hfzVjy99742-LR77NeJApSW8uphwYIJGkdiRMkKm33yLfYQi2FH7UjzzmPuBukRAYG9gDCtTozVMKGh25SeJhmtQ2ASplMszMGS0eHfdOEFXsP3xM7Y_qNU8Bp3Er0_1f-3QzZrvK4R0HBzKUFaBhBxzm36nDFx7kMyvupiurNRcLbGuj65jWL5ezK4Rel-eplBH3Zv087GDxgvSEss9ZFntFfyS1O0Ra3yW8F6OFRZNJY86-N0puzw

There are also cases where there are mutations non-stop codon so transcription cannot stop.

https://www.cell.com/cell/pdf/S0092-8674(16)30788-7.pdf"
The genetic code,"In the section, Reading Frame, frameshift  mutations are mentioned.

Point mutations will shift the frame of reference.
The insertion or deletion of three(or it's multiple )bases would insert or delete one or more codons or amino acids, without shifting the reading frame. But addition or subtraction of amino acids from a polypeptide would transform it..... How is this dealt with?","How small "in frame" indels (insertions and deletions) are dealt with depends on many factors including where in the gene the indel happens — so the short answer is "it depends".

For example, if you disrupt the catalytic site of an enzyme the effect will probably be the same as if the protein was never produced at all — this is likely to lead to a complete loss (assuming the mutation is homozygous) of that enzyme activity — the effect on the cell could be anything from fatal to unnoticeable (depending on how critical that enzyme activity is in that cell).

On the other hand, some proteins have loops of amino acid sequences on their surfaces that do not appear to be critically important and making those loops a little longer or shorter might have little or no effect on the protein function.

(Note that we only use "point mutation" to refer to mutations that change a base — not for deletions of a single base pair.)"
The genetic code,"So the genetic code is the mRNA sequence of bases and it starts from the 5' to the 3' and it is the coding strand. Now if we want to find the tRNA sequence, which is the template or the non-coding, for ACU, for example, we start at 3' to 5' and we write it as TGA? Is that the correct way or am I missing something?","Just one correction. You do not write it TGA but UGA.

There is no Thymine in RNA, but Uracil. Everything else is right. :D

화이팅!
같이 공부합시다."
The genetic code,Are proteins made at the same time as new DNA? Does DNA unwind when it makes proteins?,"The DNA that isn't being utilized is very tightly packaged, and contrarily, the DNA that is being utilized is unwound, so yes, in a sense, but your choice of words is slightly off... DNA unwinds to be transcribed into RNA, which eventually makes its way to a ribosome, which then gets translated into protein. So you are somewhat correct, just your word choice is off. Don't forget the central dogma: DNA->RNA->protein, that middle molecule is essential."
Aneuploidy & chromosomal rearrangements,"And what about a cell/organism containing 2n - 2 chromosomes, supposing these two missing ones are paired up? Is this cell/organism considered aneuploid or euploid?","It is anueploid. The number of chromosomes for a species is fixed. For example, if a human cell had 44 chromosomes instead of 46, it is anueploidic in nature; nullisomic in fact (2n-2). Just because 44 is an even number doesn't mean it is euploidic! Hope this helped :-)"
Aneuploidy & chromosomal rearrangements,How is chromosomal "rearrangement" different from "crossover"?,"Crossovers (recombination events) occur between homologous chromosomes (actually sister chromatids).  Meaning, recombination occurs between chr13 sister chromatid from Mom crossing over with sister chromatid of chr13 from Dad. 
Duplications and inversions can happen on a single chromosome. So, you can have a region of, let’s say, chr22 duplicated. Or that region might get inverted. Translocations can involve a region of (for example) chr13 swapping places with a region of chr22. 
I think the key is that crossovers are typically between homologous chromosomes whereas rearrangements are a broader category where they CAN be between homologs but there are also non-homologous chromosomal rearrangements."
Aneuploidy & chromosomal rearrangements,"If there was an instance of a gamete with -1 chromosome and a gamete with +1 chromosome that joined together, would that individual be considered "normal"?",That’s a really good question. I think you’re right! Though the odds of that happening are extremely rare. Cool thought experiment though!
Aneuploidy & chromosomal rearrangements,"If there's a diploid (2n) cell that went through the cell cycle but somehow all of the chromosomes stuck together and went to one daughter cell while the other daughter cell had no chromosomes, is the daughter cell with the chromosomes considered tetraploid (4n) at that point because there are now 4 chromosomes per homologous pair, or would it actually be considered 2n+2n? For instance, if n=12, then it would be 2n+24?","The likelihood of that actually happening is very rare. But that does not mean it's impossible, there's never a 0% (or 100%) of anything in science (in most cases). 
If that was to happen it would be called tetraploid a form of polyploidy. It's not likely to happen but it has happened a species of frogs (from the genus Neobatrachus) has been found where they actually contain 4n instead of the usual 2n. The probability of one of these mutations to occur is low, and then to have this happen [at least] twice and to find each other to mate was probably close to 0%."
Aneuploidy & chromosomal rearrangements,does nondisjunction automatically lead to one monosomy and one trisomy?,"Mitotic nondisjunction can occur with the inactivation of either topoisomerase II, condensin, or separate. This will result in 2 diploid daughter cells, one with 2n+1 and the other with 2n-1.

If nondisjunction occurs during meiosis I, it is the result of the failure of the tetrads to separate during anaphase I. At the end of meiosis I, there will be 2 haploid daughter cells, one with n+1 and the other with n-1. Both of these daughter cells will then go on to divide once more in meiosis 2, producing 4 daughter cells, 2 with n+1 and 2 with n-1.

Nondisjunction in meiosis II results from the failure of the sister chromatids to separate during anaphase II. Since meiosis I proceeded without error, 2 of the 4 daughter cells will have the normal haploid number. The other 2 daughter cells will be aneuploid, one with n+1 and the other with n-1. 

_If meiotic nondisjunction, then yes. The result is monosomy and trisomy._


https://www.ncbi.nlm.nih.gov/books/NBK482240/"
Aneuploidy & chromosomal rearrangements,Is translocation essentially formed from the process of crossing over?,"Good question!

Translocations can be the result of crossing over between sequences that are similar but located on different chromosomes.  

One source of these events are the repetitive elements§ that make up most of the genome in many species including humans.


Another way that translocations can happen is if the DNA is broken in multiple places — e.g. by exposure to radiation. 
 In some cases the DNA will heal, but with the "wrong" parts of chromosomes stuck together.


§Note: A major component of the repetitive DNA comes from the many different families of transposons — pieces of DNA that can copy themselves to new places within the genome."
Aneuploidy & chromosomal rearrangements,"What happens if nondisjunction occurs during mitosis? I assume the cell would likely undergo apoptosis, but I'm not sure...","In many cases, polyploidy takes place and one cell ends up with zero chromosomes, while the other one has doubled garniture.

It leads to apoptosis of thew one cell without chromosomes."
Aneuploidy & chromosomal rearrangements,I think the diagram for nondisjunction in meiosis I is incorrect. It looks like sister chromatids failing to separate during mitosis.,"Yes, it is correct. Maybe it looks like that but it is correct. Look at it again. :)"
N/A,Lactose enter into cell with Help of permease....but permease enzyme is produced by lactose? Which one is first. Lac or permease?,"Although when the repressor is bound (Or when CAP is unbound) transcription becomes incredibly difficult, it still occurs but just very, very inefficiently. So there will be tiny amounts of permease produced normally through these rare chance events, which can "kick start" the process if there happens to be lactose outside the cell :)"
N/A,"If the expression of the lac operon is induced by the isomer of lactose, allolactose, and beta-galactosidase, the protein product of this operon, is the enzyme responsible for lactose isomerisation, where does the initial allolactose come from?

Is it a natural mechanism, as in, in happens spontaneously, or is some of the beta-galactosidase present in the cell anyway?","Very good question!

To understand this it helps to keep in mind that very few things in biology are 100% — this sloppiness or leakiness turns out be absolutely critical for many biological processes.

In the case of the _lac_ operon, there is a low level of expression even when it is shut-off by the _lac_ repressor.  This means a small amount of the ß-galactosidase (encoded by _lacZ_ ) is always present.  
(The low level expression of the symporter encoded by _lacY_ (ß-galactoside permease) is also required to allow lactose into the cell.)

There is a very extensive Wikipedia article on this:
https://en.wikipedia.org/wiki/Lac_operon"
N/A,Why is lac operon so important in modern molecular biology?,"Great question. The reason I have found that the lac operon is so important, is that it is the most study operon and has become the most classic example of how an operon works. My biology teacher for AP said that is the most common example. Hope that helps!"
N/A,"Is lac operon only related to lactose metabolism in E.coli?
Does humans need any such operon to metabolise lactose??","Operons only occur in Prokaryotic genomes. E.coli is a prokaryote and is one of the most known and studied one, so it is easy to use it as an example."
N/A,are there still sigma factors involved in recruting the RNA polymerase to the promotor?,Yes. sigma factors are the predominant factors involved in transcription regulation in bacteria. These factors can recruit the core RNA polymerase to promoters with specific DNA sequences and initiate gene transcription.
N/A,what happens to the metabolism of laactose if there was a mutation in the promoter and operator region?,if there was a mutation in the operator the repressor protein will not bind to the operator if there is no lactose in the environment. Due to this the transcription will not be stopped. and there will be continuous transcription.
N/A,Alright but I still don't understand what is the difference between a general transcription factor and a specific one.,"General, or basal, transcription factors simply assist in the binding of RNA polymerase to the promoter. Other types of transcription factors include activators and repressors. These transcription factors affect transcription in different ways; activators assist in the binding of RNA polymerase and repressors stop transcription."
N/A,can a single mRNA strand be translated multiple times?,"Yes, it can even be read by several ribosomes at once."
N/A,Are enhancers required for transcription to occur?,"Generally, enhancers can be bound by activators to increase the likelihood that a particular gene will be transcribed. Therefore, they are not strictly required."
N/A,"does prokaryotes have any transcription factors?
if yes, kindly mention their names??","Yes, prokaryotes have transcription factors. Think about E. coli and the lac operon. The activator and repressor proteins involved in lac operon expression are the transcription factors. However, the mechanisms by which transcription factors work are simpler than those in eukaryotes."
N/A,are all transcriptional factors  proteins? if not what are different transcription factors?,"Yes, all transcription factors are proteins. They are coded for by regulatory genes, which are genes that encode a protein involved in regulation of gene expression (such as a transcription factor). However, recently people are discovering that transcription factors can have bits of sugar and other non-protein stuff added to them to regulate their activity. But yes, all transcription factors are proteins."
N/A,"Does general transcription factors always bind to proximal control elements, and specific transcription factors to distal?

Also, are the bindings to specific transcription factors essential for that individual gene to start transcription? 

I would very much appreciate the help.","Good question!

While I believe the pattern you describe (with the general transcription factors binding to proximal elements) is common, many promoters (possibly most) don't follow that pattern.

For example, according to a 2014 review† only ~20% of RNA polymerase II promoters contain a TATA box (which means that ~80% aren't bound by TATA binding protein) and ~30% have no recognizable promoter elements!

Another example is that many (but not all) genes transcribed by RNA polymerase III have promoters within the gene§.


†Note: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4214234/


§Note: See the first figure in this review for details:
http://genesdev.cshlp.org/content/16/20/2593.full


As for your second question, it appears that some "housekeeping"¶ genes  (including many of the TATA-less pol II promoters) lack specific factor binding sites.


¶Note: "housekeeping" genes (e.g. translation factors and ribosomal proteins) are expressed everywhere and at a so their expression doesn't require a lot of fine tuning."
N/A,Which ways would you test if a mutant gene was affecting a transcription factor?,"Knock-out a gene.Targeted gene deletion in order to study the efefct of gene mutation.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4597246/"
Polymerase chain reaction (PCR),Would you define "marker" a little better. I'm a little confused about it's meaning.,It's a standardized test solution of specific marked DNA which allows scientists to have a comparison to the sample DNA placed in the wells.
Polymerase chain reaction (PCR),"Taq polymerase is acquired from bacteria ,it is DNA pol III (responsible for elongation in prokaryotes) of a prokaryote. So, how can it elongate a eukaryotic DNA in PCR when it is meant to elongate a prokaryotic DNA?","While there can be differences in the DNA from different species, those differences generally do not affect the ability to be copied by different DNA polymerases.  

It is perhaps surprising, but we frequently take DNA from one organism and put it into another and have it replicated and even transcribed and translated!
(To do this we put the DNA into something called a vector, which provides the right signals to the host cell so that these processes can happen.)"
Polymerase chain reaction (PCR),"During the annealing process, isn't there a possibility of the DNA templates joining back to each other instead of the primer or what measures are taken to ensure that doesn't happen. Also, when does the polymerization of a cycle stops","Yes, the binding of primers to each other is possible. These are often called "primer dimers.""
Polymerase chain reaction (PCR),"if we don't know the exact sequence of the gene, what ways can we can still use PCR to amplify that gene?","PCR is usually used for amplification of known genes. Why? Because you need to have primers. how are you going to design or to use pre-existing primers if you do not know what sequence to they are aligned to?

So to start the PCR, one has to design degenerate primers. 
First, to obtain reference sequence, use Bioinformatic software and databases NCBI, and Ensembl for finding _most similar gene sequences_ from closely related species.

Once one finds it, use Ensembl to recreate exon sequences and therefore primers. 

https://www.researchgate.net/post/How_can_I_design_primer_for_unknown_DNA_sequence_of_different_species
https://bitesizebio.com/18992/a-primer-for-designing-degenerate-primers/"
Polymerase chain reaction (PCR),What is a genetic marker?,*Genetic marker* is known gene or DNA sequence (with a known location on the chromosome) used to identify individual or species.
Polymerase chain reaction (PCR),Are restriction enzymes used during PCR or are they the same as the primers?,"Hello dixit.anusha02, 
At first - restriction enzymes are enzymes, i.e. biological macromolecules. Some of them occur naturally in cells to destroy damaged DNA.
Primers on the contrary are short artificial pieces of single-strand DNA, where the amplification starts. As you see, restriction enzymes and primers have quite little in common.
In the PCR you need the DNA sample, nucleotides, buffer solution and primers. The PCR is used to produce many identical DNA samples.
The restriction enzymes are used for a restriction digest, where the DNA is cut into pieces. This is useful for an analysis of the DNA (I can't explain it in a sentence). You often have to make a PCR before a restriction digest in order to have enough DNA for it, but as you see these are two different things. I hope this helps!"
Polymerase chain reaction (PCR),What will happen if you add another primer between the two original primers? How many DNA strands will then be cloned?,In PCR ushually the primers are specific because want to amplify a specific part of DNA sequence.
Overview: DNA cloning,Why does the DNA need to be in the form of a plasmid when pasted in a bacteria and not just the string of DNA cut by the restriction enzyme?,"There are several reasons:

1) Linear DNA is unstable because there are enzymes present within all organisms (including bacteria) that degrade linear DNA molecules.

2) Vectors contain a sequence (known as the origin of replication) that causes the DNA to be replicated within the bacteria — this is necessary to maintain at least one copy of the new DNA per bacterium as the cells divide.

3) Vectors usually contain at least one sequence that allows selection for the vector (e.g. antibiotic resistance) — this is discussed in this article.

4) Vectors can also be used to do different things with the DNA.  A common example of this would be an expression vector — this causes the DNA to be transcribed and translated and would allow you to examine the protein encoded in the cloned DNA.

Does that help?"
Overview: DNA cloning,When the bacteria taking up the plasmid. How can we be sure that the bacteria used aren’t having any plasmid in it? To make sure that when we grow it on agar the bacteria got the recombinant DNA. What if. The original bacteria we use to take up the recombinant  plasmids are already having its own plasmid. So how can we differentiate them then?,"Good question :-)

It could be difficult to know if you were just using a random bacteria isolated from nature — especially since there are likely to be many thousands of different plasmids (1730 were present in a sequence database as of 2009).  We could sequence all the DNA inside the bacteria, but that is still a lot of work ...

However that doesn't matter as much as you might think.

For example, assume we are using a plasmid that contains a marker (selectable gene) encoding resistance to ampicillin.  All we need to know is that the bacteria were are transforming are not already resistant to ampicillin.  This is easy to test — we just try growing the bacteria in the presence of ampicillin, if they don't then we can use our plasmid.

In practice microbiologists have domesticated strains of bacteria (a favorite is _Escherichia coli_  — often abbreviated to _E. coli_) that have been studied for decades.  In almost all cases you would be using one of these well characterized strains and so would not need to worry about whether there were unknown plasmids."
Overview: DNA cloning,"Do the bacteria ever make mistakes in the replication process? If not, why? If they do, how can we still call Dolly the sheep a clone if the original sheep is actually slightly different?","This is DNA cloning, not the actual cloning of organisms. For more information on cloning, visit this webpage: https://en.m.wikipedia.org/wiki/Cloning. Hope you find it useful! :)"
Overview: DNA cloning,Are identical twins also clones ?,"The short answer is no. While they share a lot of DNA, there are also mutations that naturally occur within your cells, so no two people can share exactly the same DNA."
Overview: DNA cloning,How is the cutting and joining of DNA monitored?,"To assess whether a "digest" (restriction enzyme cutting reaction) is complete, we usually run a small sample of the digest on an agarose gel§ with a "ladder" sample containing fragments of known sizes and a small sample of uncut DNA.

This comparison allows us to see whether we got fragments of the expected sizes and how much uncut plasmid still remains.


We generally don't directly check whether a ligation has worked — ligation is very reliable and it is usually easier to just transform the DNA into a new host bacteria.  
We then purify plasmid DNA and use restriction digests, PCR †, or sequencing to test whether we got the desired outcome.


§For details see:
https://www.khanacademy.org/science/biology/biotech-dna-technology/dna-sequencing-pcr-electrophoresis/v/gel-electrophoresis-dna

†For details see:
https://www.khanacademy.org/science/biology/biotech-dna-technology/dna-sequencing-pcr-electrophoresis/v/the-polymerase-chain-reaction-pcr"
Overview: DNA cloning,How can we clone a gene that is unknown sequence ?,"You can use partial digestion method and expression in bacterial vectors and finally antibiotics to select your cloned vectors.

Look at this:
https://www.researchgate.net/post/How_do_i_clone_genes_with_unknown_sequence

particularly this paper has protocol:
https://www.researchgate.net/publication/10637344_Partial_characterization_of_a_transposon_containing_the_tetA_determinant_in_a_clinical_isolate_of_Acinetobacter_baumannii using tetA resistance gene as a marker on a plasmid (resistance to Tetracycline)."
Overview: DNA cloning,Why bacterias without plasmids will die?What are the functions of plasmid?,"*Plasmids* are usually present in bacteria, and plasmids can replicate its own DNA independently of the bacteria, which is why it is often used in DNA cloning. Plasmids usually have an *antibiotic resistant gene*, so the bacteria won't die in the antibiotic. For more information, visit this webpage: https://en.m.wikipedia.org/wiki/Plasmid. I hope this answers your question! :)"
Overview: DNA cloning,"Could you have a vector other than the bacterial plasmid
for instance a bacteriophage","Yes, though every case I know of involves a phage based plasmid (known as a "phagemid") that is manipulated as a bacterial vector before being converted into a bacteriophage.

I haven't personally used phagemids and suspect they are no longer commonly used, but you can learn more about this technology here:
https://en.wikipedia.org/wiki/Phagemid

Does that help?"
Overview: DNA cloning,"In "Steps of DNA cloning" step 2, how can a plasmid be transformed into bacteria? Shouldn't it be "Insert the plasmid into bacteria"?","Transformed with CaCl and heat - called heat shock.

Ca makes bacterial membrane porous and susceptible to the plasmid."
Overview: DNA cloning,"After you finish cloning the gene into the plasmid, how could you check to see if your gene is actually inside the plasmid? Could restriction enzymes be used to determine this?","Many scientist send their plasmid samples to a laboratory for sequencing, so  they do not have to do it by themselves."
N/A,"is it possible to become inhuman (superhuman, meta human) if biotechnology found traces of DNA that had a ability to have powers?","That is doubtful. If you are thinking about powers such as telekinesis this is not possible. on the contrary if you are thinking about powers which animals have (e.g., wings from birds or camouflage from octopi) this is a possibility."
N/A,"This is a really weird question, but if a zygote is cloned from birth, and both are grown at the same time at the same place such that when they are born, they look exactly the same, is there a way to tell which one is the original baby and which one is the clone? :)","I am hesitant to believe that cloning is so accurate, if you monitored them you would see differences I am sure."
N/A,is it possible to use gene therapy to make your body circulate a cell that can produce rapid regeneration of lost limbs or organs or wounds?,"It's not yet discovered, but who knows? :)"
N/A,Who's this Dolly the Sheep??,"Dolly the sheep is the first mammal that was successfully cloned from an adult cell in 1996 and lived for six years. Well, the process was done by using a somatic cell which contain 46 chromosomes or embryo  and placed in the surrogate mother egg cell with no information (DNA) in the womb. I hope this help!"
N/A,What is the difference between penicillin and penicillium?,"Penicillum is the antibiotic medicine, and penicillum is a genus of fungi, the mold that the article says penicillin is produced by. Members of Penicillum are also used to make cheeses like Blue and Brie."
N/A,If you decide to clone a live mammal with diseased the cloned one will have that disease too or there won't be any effect of that disease. Or you should present a healthy one not a diseased one?,"Well, it depends on the disease. 

If it was a genetic disorder causing the disease, then the cloned mammal should present with the same genetic disorder since the genome should be identical (excluding epigenetic variations). 

Things become more complicated regarding a viral and bacterial infection. For instance, certain viral infections like HIV can embed its genome into the host's cells, therefore in this case, the viral infection would hypothetically transfer into the clone because you are copying the genome (including the viral genome) from mammal. 

Still, mammalian cloning is in its embryonic stages (no pun intended), so much biological machinery and attendant effects are unknown."
N/A,who is dolly the sheep,Dolly was the first cloned animal.
N/A,summerize how gene threapy works,"On it! 

Suppose that a girl is affected by a genetic disease caused by a recessive allele (aa) that lowers the rates of production of a specific protein. What we are gonna do is take some somatic cells from her and alter their DNA so that she has the dominant (and healthy) allele (Aaa). Then we are gonna re-inject the cells in the girl. As a result, the girl will produce normal amounts of that protein because the expression of the dominant allele censors the one of the recessive!

Hope this helps!"
DNA sequencing,"This might be a bit off topic, but I am a chemistry student and I want to get a tattoo of my father DNA. Now I know the human DNA contains too many basepairs to fit as a tattoo. But if a small segment of the sequence is used, how likely is it that that sequence also belongs to a different person?","Technically speaking, you could use the sequence from DNA fingerprinting (the method used to identify a person), but it would be still a lot of material for a tattoo, it's typically thirteen sequences of varying length... I think it would be pretty big tattoo.
Another option would be getting a tattoo of "DNA ladder" (the DNA fingerprinting pattern seen on electrophoresis), this is also unique for a person and DNA related. And add only two or three nice, detailed basepairs next to it."
DNA sequencing,"Why can't the die molecule be attached to a regular nucleotide, and then the entire DNA chain could be read as a single item?","you cannot read the entire dna chain as a single item, even if each base pair were to be dyed since you would be getting the four colours at once due to the small size of the molecule. you use ddntp to stop the synthesis for a strand and get fragments of all possible lengths that move in ascending order of length. this lets you to exactly know which base comes at what point."
DNA sequencing,How do we know the specific primer if we already don’t know the DNA fragment sequence ?,"If we want to amplify a fragment of DNA, but don't know the sequence a technique known as "Ligation-mediated PCR" can be used.  This technique starts by adding (ligating) the primer sequences to the ends of the DNA fragment."
DNA sequencing,"Are there two systems to sequencing?
one with light (laser) and the second with electric field?","In traditional (Sanger) sequencing, both electric fields and lasers are required for slightly different, but interdependent, purposes. The electric field is applied to the DNA in the capillary tube, and it pulls the DNA pieces through in order from shortest to longest. As the pieces pass the laser (moving through because of the electric field), they are excited and detected by the detector.

Some next-generation sequencing does not use lasers at all. Instead, it uses H+ ion fluxes to determine whether bases have been added. I'm not super familiar with this technique, but you can read more in this Wikipedia article: https://en.wikipedia.org/wiki/Ion_semiconductor_sequencing.

Hope one of those answers addresses your question!"
DNA sequencing,in a chromatogram why are the peaks of different heights?,The height of each peak is in proportion to the amount of the particular component present in the sample mixture injected into the chromatograph.
DNA sequencing,Does a 2000bp or a 500bp migrate faster throgh this agarose gell,"In other words, the 500bp would migrate faster."
DNA sequencing,Why do the nucleotides used here have 3 phosphate groups instead of 1?,"It's to provide it with energy. The regular DNA replication also uses 3phosphate groups because by removal of each one of them, it gets enough energy to bind to the previous nucleotide."
Nucleic acids,How do mRNA and tRNA communicate with eachother during the formation of the proteins?,"mRNA is like a recipe from a cookbook; a list of ingredients to make a protein. mRNA is a chain of nucleotides (A, U, C, and G, not T since this is RNA). A group of three nucleotides is called a codon. A codon matches with three nucleotides, called an anticodon, on a single tRNA molecule while in a ribosome. The tRNA carries an amino acid, our ingredient to make the protein.
So mRNA is the recipe, tRNA matches to the recipe bringing an ingredient, and the line of ingredients become a protein."
Nucleic acids,"If A-T bonds have 2 hydrogen bonds and G-C bonds have 3... Would it be true that longer periods of A-T bonds in DNA (so like: AATAATTATTTTAATTAAAA) are less stable parts of the DNA helix than parts that have more (or only) G-C bonds in them? And if this is true, are these parts (AT only parts) more prone to mutations?","The first part is true, T-A bonds are less stable and more likely to come apart. The A-T bond strands also signal where DNA needs to separate for commonly transcribed genes, such as the TATA Box commonly found just before the beginning of gene sequences.

I'm not sure if they are more prone to mutations though."
Nucleic acids,"DNA is common to all organisms, all organisms use the same 4 nitrogenous bases, A T, C G

is that right?","Entirely true. Also, AT/GC are found in DNA while RNA is made from AU/GC. Just keep in mind that, even though all life forms have DNA, not everything that has DNA is alive: viruses can have DNA but are not living."
Nucleic acids,"Why do some nitrogenous bases have two fused carbon rings while other have one? Would it be possible for there to be nitrogenous bases with more than two fused carbon rings? Could there ever be an instance where there are more than just five kinds of nitrogenous bases (Adenine, Thymine, Guanine, Cytocine and Uracil)? If it could be possible how would DNA and RNA have to rearrange themselves? Would it be possible for DNA and RNA to use other sugars aside from Deoxyribose and Ribose? If so, like what? If not, why?","https://www.khanacademy.org/science/organic-chemistry/aromatic-compounds/aromatic-stability/v/aromatic-heterocycles-i

https://en.wikipedia.org/wiki/Heterocyclic_compound

https://en.wikipedia.org/wiki/Abiogenesis

https://en.wikipedia.org/wiki/Nucleic_acid_analogues

Hope this helps!"
Nucleic acids,Are the functions of nucleic acids guided only by molecular forces and just appear to have intention or are there other forces at work that I'm not aware of? How do these macromolecules "know" what to do?,"A creationist would say that this is part of the intelligent design. An evolutionist would say it's all down to chance. Two spanners to consider - 1) one molecule of hormone, once recognised by the cell, leads to prduction of thousands of times more molecules, and types of molecules, than a mere chemical would suggest, and such secretions can be brought about by tiny changes in brain activity. 2) DNA is just for storage. It is a molecularly inert form for the passing on of genes without having a massive effect upon the rest of the body - and so the active form is the sticky stuff of RNA and these determine how the proteins are folded together."
Nucleic acids,"When transcription takes place and the DNA is broken into two, and then mRNA is formed with one of the DNA strands or for BOTH the DNA strands?","Within a gene *usually* only one strand is transcribed, but there are many examples where transcription happens from the both strands. This is especially common in viruses.

Also, the strand that is transcribed for one gene may not be the same as the strand being transcribed for a neighboring gene.

Finally, the whole DNA double helix is not separated - just a small bubble is opened around each RNA polymerase as it works its way along the DNA."
Nucleic acids,"In the first paragraph of the section "Regulatory RNA (miRNAs and siRNAs)" it says "They bind to specific mRNA molecules (with partly or fully complementary sequences) and reduce their stability or interfere with their translation, providing a way for the cell to decrease or fine-tune levels of these mRNAs."

Does this mean that the purpose of microRNAs (miRNAs) and small interfering RNAs (siRNAs) it to make sure that there are not too many mRNA molecules producing proteins? They are regulating the amount of protein produced by the cell? Am I understanding this correctly?

Please help! Thanks. :)","Yes, miRNA regulates protein synthesis in a way it binds to mRNA transcript and 'silence' it."
Nucleic acids,how are DNA and RNA different and alike to each other?,"As stated in the summary at the end of the article, DNA and RNA have different functions. While DNA stores genetic information, RNA is involved in protein synthesis and gene regulation, as well as storing genetic information in some viruses. DNA and RNA also have different structures; DNA's phosphate-sugar backbone contains deoxyribose, while RNA's contains ribose. While DNA is double-stranded and has the nitrogenous bases adenine, thymine, cytosine, and guanine, RNA is usually single-stranded and contains uracil instead of thymine.

As for the similarities between DNA and RNA, they are both important biological polymers and contain four bases and a phosphate-sugar backbone."
Molecular mechanism of DNA replication,Is topoisomerase same as DNA gyrase ?,DNA Gyrase is a topoisomerase. There are several kinds
Molecular mechanism of DNA replication,How are the histone proteins taken care of during eukaryotic DNA replication?,The DNA is first unwound at origins of replication and the displaced histone proteins move onto to other parts of the DNA that haven't been unwound so that those parts can maintain their chromatin structure.
Molecular mechanism of DNA replication,"In the last section "DNA replication in Eukaryotes" it says that in eukaryote cells a little DNA at the ends of the chromosomes gets lost. If this is the case, will we eventually loose enough DNA to stop functioning properly?

You might say that this is indeed why we die eventually. Each time our cells divide and our DNA gets copied some of it gets lost placing a limit on how many times our cells could divide and still function properly. However, consider that DNA is also copied before meiosis. This means that the DNA that was lost when the ancestors of my cells (in my parents) divided was never passed on to me. And the DNA that got lost when my cells divided to form my germ cells will never get passed on to my sperm cells. Will humanity eventually loose its entire gene pool?",At the ends of DNA strands there is a section non-coding nucleotides that we call a telomere.  The telomere is what gets shorter every time a cell divides and when the telomere is gone is when the cell spontaneously dies.  There is no loss of coding DNA in this process so there is no loss of genetic information between generations.
Molecular mechanism of DNA replication,"The part of the article that deals with the Okazaki-fragments states that:

"DNA polymerase I and DNA ligase are also needed (more infrequently) for the leading strand. DNA polymerase I removes the primer at the very beginning of the strand, and DNA polymerase seals the remaining gap."

Shouldn't the gap between the Primerreplacement and the new Nucleotide chain be sealed by DNA-Ligase instead?","Yep, that was a typo! I've fixed it now and it should be corrected on the site shortly. Thanks for noticing!"
Molecular mechanism of DNA replication,""Many DNA have proofreading activity" mentions : "In most cases, the correct nucleotide is indeed added, because the DNA polymerization reaction won't usually occur unless the incoming nucleotide base-pairs correctly with the template." If the reaction cannot occur unless there is correct base matching, how then can the DNA polymerase still make an error?","The key word is the "usually." The reaction won't occur with a mis-paired base in most cases. However, about 1 in 10^5 base pairs will involve an incorrect pairing. This may not same like a high rate of errors, but it is high enough to cause a lot of mutations in a cell. The role of the proofreading is to fix these occasional but still problematic errors."
Molecular mechanism of DNA replication,Why are the DNA polymerases numbered here? (I/II/III) I though that Eu-k were named by alpha beta delta etc,"Prokaryotes have DNA polymerases I, II, III, eukaryotes have alpha, delta, epsilon and such."
Molecular mechanism of DNA replication,"In the paragraph 'DNA polymerases' it says that polymerase II has a DNA repair function, but in 'Many DNA polymerases have proofreading activity', it is stated that DNA pol. I and II have proofreading activity. Does DNA pol. II aid in a different repair mechanism than proofreading?","Great question! Yes, DNA polymerase II is involved in repair of damage that occurs outside the context of DNA replication, such as cross-links between strands caused by certain chemical agents. There is a little more detail in the Wikipedia article if you are curious: https://en.wikipedia.org/wiki/DNA_polymerase_II."
Molecular mechanism of DNA replication,"'A DNA molecule “unzips” as the hydrogen bonds between bases are broken, separating the two strands.' What makes this happen?","Helicase enzyme. It binds at replication initiation site and moves along DNA, in front of polymerase III, opening replication fork."
Molecular mechanism of DNA replication,"Genome refers to the haploid content of DNA in a cell, so how can it consist of  3 billion base PAIRS? Or is it the diploid content in any cell?","Most DNA exists as a double-stranded DNA in a double helix — the strands are held together by base pairs and we usually think of this as a single molecule (even though there are no covalent bonds between the two strands).

So, each haploid chromosome has at its core a (mostly) double-stranded DNA "molecule" and a human haploid genome contains ~3.2 billion base pairs.

A diploid cell has two of each haploid chromosome (each of which contains a double-stranded DNA "molecule"), so a diploid human genome contains ~6.4 billion base pairs.

Does that help?"
Molecular mechanism of DNA replication,"Topoisomerase works at the region ahead of the replication fork to prevent supercoiling.

What does it mean? I can not understand supercoiling.","Take a piece of rope and start twisting it — at some point it will begin to shorten and form a twist perpendicular to the rope between your hands.  

This is supercoiling!

See for example, this video:
https://www.youtube.com/watch?reload=9&v=BjcJu-o3YwY

There is also a relevant wikipedia article:
https://en.wikipedia.org/wiki/DNA_supercoil"
N/A,"Why in the last example, using an actual RNA molecule, is methionine coded by the codon AUC? Methionine is referenced as being coded by the codon AUG in the table provided.",That was a mistake! Thank you for noticing and pointing it out. It should be fixed now :)
N/A,Why are the introns referred to as "junk" (RNA splicing section)? Don't they play a role in gene expression regulation? Thank you.,"I think they are only considered "junk" in terms of what they contribute to the resultant protein. They do likely play a role in regulation, but because they are spliced out before translation, they will not effect the protein that results from translating the mature mRNA sequence."
N/A,Is it possible that DNA introns/splicing exist so that bacteria can't copy eukaryotes' DNA and express the same proteins? As they are known to steal DNA that floats around in general..,"I am not aware of that but sounds interesting! 
That is interesting point of view because Prokaryotes do not have introns (and can't because of couples translation to transcription)."
N/A,why does the introns exist at the first place just waiting to be splice ?,"Lim Pin Seng, 

Introns allow for alternative splicing; generating multiple proteins from a single gene. It adds a layer of complexity to an organism, without having to drastically extend the genome length. In return, it may also save energy as the cell does not have to replicate as long of a genome - a reasonable explanation as to why introns may be favored. 

Further, introns may possess regulatory processes or code for functional RNA products. In addition, introns may also be mobile elements, contributing to the overall variation of the genetic pool.

Hope this helps!"
N/A,"In the little drop-section explaining more about spliceosomes, it states "Once the intron has been cut out, the spliceosome will "glue" (ligate) the flanking exons together." How would this work with alternative splicing? Additionally for alternative splicing, can only one exon be removed? More alternatives could be created through removing two exons or switching the exons around. Ex: 145 and 14235","Good question!

Control of alternative splicing is very complex — it often involves binding of proteins or small RNAs to the pre-mRNA in ways that favor or inhibit use of specific splice sites.

The wikipedia article on this seems like a good place to start learning more:
https://en.wikipedia.org/wiki/Alternative_splicing


While skipping an exon is very common, there are probably examples of almost any pattern you can think of!


An extreme example of how complex alternative splicing can get is the _Dscam_ gene of _Drosophila_ (a fly), which apparently has ~38,000 different splicing variants and roles in both the immune system and nervous system development†.


Does that help?


†Reference: https://www.cell.com/cell/fulltext/S0092-8674(00)80878-8"
N/A,Why prokaryotes do not require these post trancriptional mechanisms as needed in case of Eukaryotes? Does it mean that Eukaryotes' trancripts are free of introns?,"Prokaryotes do have some post-transcriptional modifications, but introns are much less common and as far as I know are always self-splicing — i.e. don't require a spliceosome.

Mature mRNAs in eukaryotes generally lack introns, but note that alternative splicing means some sequences can act as either introns or exons,"
N/A,"With so many mRNA molecules being manufactured all the time, shouldn't all that splicing create a build up of spliced out introns  in the nucleus?
Evolution wouldn't waste resources..What happens to them?","Good question!
As is often the case in biology the answer is "it depends".

Many introns are broken down to individual ribonucleotides by enzymes (ribonucleases) that are then reused.

However, some introns have second lives and can act as signaling or regulatory molecules.

This is still an area of active research and it is quite likely that more functions for introns will be uncovered in the future.

If you wish to know more, you could start with this section of the wikipedia article on introns:
https://en.wikipedia.org/wiki/Intron#Biological_functions_and_evolution

Does that help?"
Overview of translation,You state that AUG is the start codon and also the codon for Methionine. Do all proteins made in cells start with MET?,"N-terminal initiating methionine, although being the first amino acid, is not present at N-terminus of all proteins. This is because of a process that is known as post-translational modification. There are more than a hundred post-translational modifications known, one of which is the removal of methionine from the N-terminus of a polypeptide. N-terminal methionine is removed from a polypeptide by the enzyme methionine aminopeptidase."
Overview of translation,where are the amino acids attached to the transfer RNA coming from? in the pictures it makes it seem like they just magically appear and float into the ribosome.,The amino acids are actually brought by the tRNA from the cytoplasm to the ribosome. These types of RNA "transfer" the amino acids to all these sites.
Overview of translation,"Hi there

I am curious - what stops a ribosome from attaching to another location that may be misread as an AUG when it might be uAU|Guu (Tyr + Val) for instance?","Excellent question!

Translation is quite bit more complicated that this introductory material can cover.

The sequence of the mRNA around a potential start codon influences whether or not it will be used§.  These sequences are bound by proteins that help guide the ribosome to assemble at the correct place to start translation.
(In fact, codons other than AUG are sometimes used as start codons!) 

This is covered in a bit more detail in a later article in this tutorial:
https://www.khanacademy.org/science/biology/gene-expression-central-dogma/translation-polypeptides/a/the-stages-of-translation

I also encourage you to look at some of the references for that section, which will help give you more detail on this high complex process that is still being actively studied.


§Note: The mechanisms are very different in prokaryotic and eukaryotic organisms — they can also vary between different species and even for different genes!"
Overview of translation,Why is an actual gene that codes for a protein likely to be longer?,"This is because when a gene is transcribed by RNA polymerase into pre-mRNA, it contains both coding (exon) segments and non-coding (intron) segments. After the complementary pre-mRNA strand has been synthesised, the intron segments which do not code for any part of the protein are removed from the sequence, and the remaining exon segments are spliced together via action of RNA ligase. The removal of the introns causes the mRNA strand to be shorter than it was originally, possessing less codons. However, the loss of introns ensures that the protein translation will not be interrupted by non-coding genes."
Overview of translation,"Is the tRNA made from DNA, or its a preexisting molecule?","The tRNA is a modified version of the mRNA , which is in turn made with the help of DNA"
Overview of translation,what is the open reading frame? how does that fit into all of this?,"An open reading frame (ORF) is a series of codons that begins with a start codon (usually AUG) and ends with a stop codon.  There can be no additional stop codons within that sequence. 

In genes that lack introns (e.g. most prokaryotic genes), an ORF in the DNA sequence will define the entire translated region.  If splicing occurs (i.e. in genes with introns), a final processed mRNA (transcript from a protein coding gene) will have a long ORF that directs ribosomes to produce a polypeptide.

Does that help?"
Overview of translation,What happens to the mRNA after being translated? Can it be translated again?,"Yes it can, although it has a very short lifespan (a few hours)."
Overview of translation,"After it goes through A P E sites, does the site migrate or does the mRNA move for new codons to be translated ?","In one of the previous sections, it was stated that the ribosome moves; since the A P & E sites are part of the ribosome, the sites move."
Overview of translation,"Are there any important enzymes involved in translation? In the article it says "the ribosome also acts as an enzyme, catalyzing the chemical reaction," but is the ribosome an enzyme or does it just ACT as an enzyme? Thanks.","Well, there is one enzyme which is crucial for translation and that is "aminoacyl tRNA synthetase".  This enzyme attaches an amino acid to the tRNA. There is a different version of this for every different amino acid (so 20 of these in human bodies).  

The enzyme is a "synthetase" because it creates a new structure called "aminoacyl-tRNA", which is the tRNA which has an amino acid linked to it. The word "aminoacyl" means that an amino acid is linked to something, in this case tRNA. 

This process happens BEFORE the tRNA enters the ribosome and it takes place in the cytosol. ATP is required for that reaction. 

I hope that helps ^^"
Overview: Eukaryotic gene regulation,what is the difference between Eukaryotic gene regulation and Prokaroytic gene regulation,The two major differences have to do with the fact that there is no nucleus in prokaryotes and it is linear DNA.
Overview: Eukaryotic gene regulation,two exambles of epigenetic effects that control gene expression in eukaryotic cells,"Epigenetic inactivation of the X chromosome in females - from pharmaceuticals.

Honeybees are genetically identical but queen bees can produce as many as 2,000 eggs in a single day, whereas worker bees are sterile."
Overview: Eukaryotic gene regulation,"When it says that "almost all cells have the exact same DNA", does that mean that some cells have different DNA than the rest of the body? (are they talking about sex cells?)","Yes that is one example. Another would be red blood cells, when they are mature they no longer have a nucleus. Also in some immune cells, DNA is modified to make more variety so you can have lots of different antibodies. But in that case, only very small region of DNA is changed - most genes are left the same. Maybe there are a few more exceptions, but most cells have the same DNA."
Overview: Eukaryotic gene regulation,Is this the same or related to epigenetics?,"Epigenetics refers to changes that can be inherited by daughter cells (and sometimes even offspring), but don't involve changing the sequence of the DNA.

These changes typically involve alterations in chromatin accessibility, but some alterations in chromatin accessibility are not heritable (and thus aren't epigenetic).

So, I would classify epigenetics as one type of gene regulation.


Khan Academy has more material on this, which can be found by entering "epigenetics" into the search field found near the top of every page — this will lead you to these results:
https://www.khanacademy.org/search?page_search_query=epigenetics

Some additional resources for learning more:
• https://ghr.nlm.nih.gov/primer/howgeneswork/epigenome

• https://en.wikipedia.org/wiki/Epigenetics"
Genetic variation in prokaryotes,How does a transposable element do the cutting and pasting? Does it use an enzyme from the cell or does it have its own enzyme?,"Many§ transposable elements will encode a transposase — an enzyme to catalyze its movement to another location.  The exact mechanisms vary among different types of transposons, but cutting and pasting is done by some of them.

You can read more about this in these wikipedia articles:
https://en.wikipedia.org/wiki/Transposase
https://en.wikipedia.org/wiki/Transposable_element

§Note that transposons can also have parasites — these are known as non-autonomous transposons.  They tend to be smaller versions of the autonomous transposons and "steal" the enzyme produced by autonomous transposons to move themselves."
Genetic variation in prokaryotes,Can you tell the enzyme how is catalyzes transformation,"Good question, but there is not one specific enzyme responsible for transformation. Transformation requires the expression of about 40 genes, each of which could express a unique protein. It's a complex process and people are still working out the details of how it actually works. Some of the proteins involved are probably enzymes but we don't know exactly what they all do."
Genetic variation in prokaryotes,"Why are the process of transformation, conjugation, and transduction “easy” to do with prokaryotic cells like bacteria, but much less commonly encountered in eukaryotic cells?",Because prokaryotes' DNA exits as a single loop and is relatively shorter than for eukaryotes due to the fact that multicellular organism have a greater need for a variety of proteins.
Genetic variation in prokaryotes,What is the relationship between a sex pilus and a mating bridge?,"A mating bridge is a connection between two bacterial cells that provides a passageway for DNA in bacterial conjugation.
A mating bridge is different from a sex pilus, which is a structure made by an F+ strain bacterium in bacterial conjugation

Sex pilus acts as an attachment site that promotes the binding of bacteria to each other. In this way, an F+ strain makes physical contact with an F− strain. Once contact is made, the pili shorten and thereby draw the donor and recipient cells closer together. A conjugation bridge is then formed between the two cells, which provides a passageway for DNA transfer."
DNA structure and replication review,"What is the difference between:
Replication fork
Replication complex
Replication unit
Origin of replication 
Replication bubble","The replication fork is the branched (forked) DNA at either end of the replication bubble.

The replication complex is the group of proteins that help synthesize the new DNA strands.

A replication unit is any chunk of DNA that is capable of being replicated — e.g. a plasmid with an origin of replication (ORI) is a replication unit.  Alternatively, this can also mean a region of DNA that is replicated together.

An ORI is a DNA sequence at which replication is initiated.  ORIs are recognized by the replication machinery — specifically the pre-replication complex.

A replication bubble is the region of DNA where new strands of DNA have been or are being synthesized.  A replication fork is found at each end of a replication bubble.

You can find more details and (many) of these terms in this free online book chapter:
https://www.ncbi.nlm.nih.gov/books/NBK26826/


This seems like a reasonable source for quick definitions of terms:
http://dictionary.sensagent.com/"
DNA structure and replication review,What does it mean to have a 3' end as opposed to a 5' end?,"5' ends with the phosphate, and 3' ends with the deoxyribose sugar."
DNA structure and replication review,"1-Unwinding the (origin of replication) is done when certain proteins are attached to the site (which is AT rich) , I mean not by Helicase , right?


2-who removers the primers in the lagging strand?
Is it the same DNA pol ?

3-Why does polymerization rate in prokaryotes is faster than in eukaryotes?","1) My understanding is that many proteins are involved in unwinding the origin of replication including at least one helicase.  
Note that helicase is a type of activity, not a single protein — for examples and more details see:
https://en.wikipedia.org/wiki/Helicase

2) The primer is removed by an endonuclease that recognizes RNA:DNA hybrids (RNase H) and then exonucleases that remove the RNA nucleotides.  In _E. coli_ this exonuclease activity is performed by DNA polymerase I.

3) Eukaryotic DNA is generally much longer, more complex (typically multiple linear chromosomes with ends vs. usually circular DNA), and is highly packaged into nucleosomes (and higher order structures).  All of these factors mean that it takes longer to replicate eukaryotic DNA.


References and further reading:
https://www.ncbi.nlm.nih.gov/books/NBK9940/

https://sydney.edu.au/science/molecular_bioscience/PHAR2811/PHARlectures/PHARlecture5/PHARlecture5notes.pdf"
DNA structure and replication review,which enzyme breaks the h bonds?,"As enzymes breaks the hydrogen bonds that hold the double helix together,so the two strands unwind and separate and that enzymes is helicase"
DNA structure and replication review,is there any case in which primer exist in DNA after replication,"Usually, there is not because DNA Polymerase always replaces the RNA nucleotides with the DNA nucleotides. Unless for some reason, the DNA Polymerase fails to function, it may happen but proofreading should catch it. Otherwise, there should not be any errors."
DNA structure and replication review,lagging strand how to memorize it,"leading strand synthesized continually whereas lagging strand is synthesized in fragments(Okazaki fragments)
Memorize it this way: Lagging strand lags behind and does his homework(replicating dna) in bursts when he feels like it. Leading strand leads the way and is a good model. lol"
DNA structure and replication review,"I may be understanding this wrong, but when DNA separates, a new strand forms that is identical to the one it separated from. So, wouldn't those double helices of DNA be identical to each other?","When DNA separates to replicate, DNA polymerase (and the other enzymes) attach new bases to each strand, and those new bases are each complementary to the template strand, matching the other original strand that the template strand just broke off from. The end result of this is two completely identical DNA molecules, each having one strand from the original DNA and one strand of new DNA made from surrounding materials, put together by DNA polymerase and other enzymes."
DNA structure and replication review,isnt the leading and lagging strand different because when unzipping the DNA the halfs are pointing in oppisite directions of one another?,yes the leading strand goes towards the replication fork and the lagging strand goes away from the replication fork in okazaki fragments
Intro to gene expression (central dogma),Why there are 61 codons? Why not 64??,3 of them are stop-codons which terminates translation (61+3=64).
Intro to gene expression (central dogma),what  happens to the mRNA after translation process i.e after proteins are produced?,"Hi Srinidhi,

After mRNA is translated, is either stored for later translation or is degraded. The eventual fate for every mRNA molecule is to be degraded. The process of degrading mRNA molecules happens at a relatively fixed rate.

Hope this helps!

Jonathan Myung"
Intro to gene expression (central dogma),"I'm still confused on two things. One, what is a TATA box? ANd two, what are the poly-a tails and 5' caps?",The TATA box tells where a gene begins so that it can be transcribed.  The Poly-A tail is a string of (mostly) adenines on the 3' end of the mRNA that gets eaten away by hydrolytic enzymes.  It is there so that the coding section of the mRNA doesn't get eaten.   (The hydrolytic enzymes themselves are there to protect from viruses.)   It is also recognized by the nuclear pore and allows the mRNA to leave the nucleus.  The 5' cap tells the ribosome where to begin translating.
Intro to gene expression (central dogma),What happens if a mRNA breaks? Will part of the protein be produced from the broken piece?,"Yes, most likely. If the context of the mRNA fits with the translational machinery (applicable  for the part of mRNA with the initiation codon only. The part without the initiation codon would not be translated), it might produce a truncated protein where the N-terminal part would be present but the C-terminal part (wrt to the original full length protein) would not be there.  However, most of these truncated proteins are recognized by the cellular repair machinery as abnormal and they are recycled. Sometimes though, such proteins can linger and may even participate in cellular functions (in a positive or detrimental way). Most likely source of truncated proteins is DNA rearrangement though, and mRNA breakage would not likely have a major effect (it might, depending upon the need of the original protein) as there would be other full-length mRNAs that would be translated into the protein of interest. Hope this helps."
Intro to gene expression (central dogma),Can a DNA end in 3' and the last molecule in this end is a phosphate? Why not??,"Phosphate is always attached to 5' end, and OH group to 3' end, because of the chemical structure of DNA."
Intro to gene expression (central dogma),It is essential that we need RNApolymerase for transcription. But to synthesize this enzyme we need transcription to happen .  So either RNApolymerase has to be present from the start or there should be another mechanism by which polymerisation of RNA happen. So how is it done for the First Time ??   How is it possible ?,"Some proteins and other molecules come from the previous cell, so the new cell can start its own production. Another thing is that some RNA can act as an enzyme and catalyzes reactions, though it occurs much less often."
Intro to gene expression (central dogma),Why do the number of A's on the poly-A tail vary?,"Each time a mRNA is read, an ''A'' of the poly-A tail is cut off, when there's no more ''A'' in the tail, the mRNA can be degraded. A mRNA (let's call it mRNA 1) can have more ''A'' in its tail than another mRNA (mRNA 2) depending on how much the cell needs that product  (1 instead of product 2)."
Intro to gene expression (central dogma),"It is mentioned in The Genetic Code, that,
One codon is a "start" codon that indicates where to start translation. The start codon specifies the amino acid methionine, so *most* polypeptides begin with this amino acid.

AUG codes for methionine, which contains sulfur. In the Hershey-Chase experiment, they made use of the fact that all proteins contain sulfur (because of the presence of methionine, I guess)
Are there proteins which do not begin with methionine?","There are, but this is (usually) due to removal or modification of the amino-terminal (start) methionine.  For example enzymes called "methionine amino-peptidases" cut off this amino acid from the beginning of some proteins — this is an example of what is known as a "post-translational modification".

It is also quite common for the first part of a protein (including the starting methionine) to be removed during processing — an example is secreted proteins that have their signal sequences removed during secretion or membrane insertion. 

Methionines can also be oxidized to form chemically related residues."
Intro to gene expression (central dogma),Why is amino acid sequence not directly read from a template DNA strand? Why do we need an intermediary mRNA ?,"This is an interesting question to think about, but "why" questions in biology are often very difficult to answer in a meaningful way.  

Below I've listed one possible evolutionary reason for the use of mRNA as an intermediary and then some advantages to this system.


One strongly supported hypothesis is that RNA actually came first — this known as the "RNA world hypothesis"§.  

This means that we use RNA because "life" has always used RNA and getting rid of it by evolutionary processes would be essentially impossible.  (You'd have to redesign life from scratch!)


Making mRNA also allows efficient production of proteins from a single gene.  

This is because many mRNAs can be transcribed from a gene and then each mRNA can be translated independently (and multiple times).


There are also multiple levels of regulation that can control how much mRNA is present, what parts of the mRNA get kept‡, and how frequently the mRNAs get translated.  

This allows cells to be much more responsive to changing conditions.


In addition, in eukaryotes DNA is kept in the nucleus, while translation happens on ribosomes (found in the cytoplasm).  

Having an RNA intermediate allows the information in DNA to travel from the nucleus to the cytoplasm.


There are probably more advantages that I haven't thought of — I encourage you to keep thinking about your question as you learn more about how cells work!


Does that help?



§Note: For more information see:
https://en.wikipedia.org/wiki/RNA_world


‡Note: For example alternative splicing in eukaryotes — to learn more see:
https://www.khanacademy.org/science/biology/gene-expression-central-dogma/transcription-of-dna-into-rna/a/eukaryotic-pre-mrna-processing"
Intro to gene expression (central dogma),What happens in a mutation where the Stop Codon is removed/altered? What does the cell do then? does it perform apoptosis?,"There are repair mechanisms. That one is called *Non stop Decay* that mechanism is able to detect mRNA which cannot be degraded because there is no STOP codon. It has to detach mRNA from the ribosome so it can translate the next mRNA sequence.

Nonstop decay is the mechanism of identifying and disposing aberrant transcripts that lack in-frame stop codons. It is hypothesized that these transcripts are identified during translation when the ribosome arrives at the 3′ end of the mRNA and stalls. Presumably the ribosome stalling recruits additional cofactors, Ski7 and the exosome complex. The exosome degrades the transcript using either one of is ribonucleolytic activities and the ribosome and the peptide are both released. Additional precautionary measures by the nonstop decay pathway may include translational repression of the nonstop transcript after translation, and proteolysis of the released peptide by the proteasome.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3638749/"
Phylogenetic trees,"Can a phylogenetic tree show which organism is more evolved, if they evolved at the same nod?","Look at (or make) a tree showing your family going back at least to your grandparents.

First question: What does this tell you about people in your family?

Phylogenetic trees are really very similar, but for species rather than individuals within a family.

Second question: What do you mean by "more evolved"?

Does this help?"
Phylogenetic trees,how to represent an extinct specie in a tree diagram,Ending a line before present day shows that a species is extinct
Phylogenetic trees,What phylogenetic trees can and can’t tell us,"One example that comes to mind is that a phylogenetic tree determines where two organisms diverged from their common ancestors but not specifically when. These diagrams are not chronological in a direct way, more so a before and after situation. (Hope I helped, correct me if I am wrong)"
Phylogenetic trees,how did a common whale evolve from a common ancestor?,"I'm not sure what you mean by a "common whale".

The following has information on whale evolution:
https://evolution.berkeley.edu/evolibrary/article/evograms_03

If that doesn't help, can you please clarify your question?"
Phylogenetic trees,how does phylogenetic classification related to phenetic  classification?,"Phenetic speciation means classification of species by appearance alone. For example if two frogs look similar they are called a species even if they cannot mate.
Phylogenetic classification does consider appearance and phenotype, but it also goes much further in terms of looking at functionality, and comparison of genomes. Phylogentics explains an organisms evolutionary history. This is a more rigorous system than phenetics."
Phylogenetic trees,What are the characters used to determine the most accurate evolutionary trees?,The most accurate phylogenetic tree will have the fewest nodes. It's something called parsimony which means that the best tree is the simplest.
Phylogenetic trees,Can someone explain to me the process when a new species will emerge on the tree? Thank you,"Speciation is a huge topic and still being researched — I recommend starting with the following material on KhanAcademy:
https://www.khanacademy.org/science/biology/her/tree-of-life/v/allopatric-and-sympatric-speciation
https://www.khanacademy.org/science/biology/her/tree-of-life/a/species-speciation

You can also browse through the KhanAcademy material on evolution to learn more:
https://www.khanacademy.org/tag/evolution"
Phylogenetic trees,"The fact that branches can be rotated and still remain true indicates that branching order (the order in which species are listed) doesn't matter. If that's the case, I don't understand the purpose of polytomy. This article says it's because we don't know the branching order, but why does that matter?","I think you may have misunderstood what branching order means — confusingly it doesn't mean the order of the branches!  

Rotation doesn't change the branching order — it rearranges the order of the branch tips, which we all agree isn't significant.

Branching order is being used to describe the sequence in which species split from each other.

Thus, a polytomy is a way of acknowledging that there is not yet enough information to say which of the species split off from the common ancestor first.

Take the example PQR polytomy — we know that the ancestral population ("PQR") probably first split into one of the following: 
P + "QR"
Q + "PR"
R + "PQ"

And then the second population split again.

This is what the article means by branching order.

Does that help?"
Phylogenetic trees,"In the phylogenetic tree containing A,B,C,D,E, what is the closest relative to E?","E's closest relative is whatever species is at the first node (the first 2 branches that extend from the root, or trunk)"
Phylogenetic trees,How would you draw a phylogenetic tree given simple DNA sequences between species?,"It is a difficult task. What you are asking is phylogenetic reconstruction from genomic sequence analysis. There are some ways to do this. One obvious way is to consider two species closest if they match at more base pairs. But what is difficult is to decide if one arose from the other or if they are at the same level, arising from a different common ancestor. 

All of this is very difficult and many algorithms are available, especially since genomic data itself is large, complex (different kinds of genomic data is available - RNA, DNA, Methylated DNA etc) and also based on what we know of the function of the genes (difference in functional gene is a more significant difference than the difference in non-functional genes).

If you are interested, look up maximum-parsimony methods of phylogenetic tree reconstructions."
Evidence for evolution,"I understand that a fossil not being found doesn't mean the organism didn't exist, simply that it hasn't been found yet (or never fossilized). But several fossils that do exist don't seem to fit in with the theory of evolution.  What about pollen from Cambrian or older sediments the Romairma formation in South America or in the Hakatai Shale in the Grand Canyon in North America? Flowering plants are highly advanced and wouldn't have existed in the Cambrian or Precambrian epochs.",There are multiple possible explanations for those examples you cite. The fossils or their age could have been misidentified. It is also possible that our current understanding of the sequence of events is incorrect. Hopefully future scientific inquiry will decrease apparent contradictions.
Evidence for evolution,"This article admits, under Evidence For Evolution: Fossil Record, that the record is incomplete. So how is it that we can actually teach this as fact when there is no evidence for macro evolution. The tree shown that all species share a common ancestor is a hypothesis that remains unproven, why not also teach the idea of creation? Creation explains more of what we see than these hypothesis displayed as fact.","Scientific theories are never proven, proofs are for mathematics.  The theory of gravity and quantum mechanics are not proven but but you do not question them being taught.  

Evolution is a scientific theory and has a bunch of supporting verifiable evidence.  It is a theory that accurately describes observations and has made predictions that we have been verified.  

Gaps in the fossil record do not disprove evolution.  Fossils are rare events so there are are going to be gaps.  

There is evidence for macro evolution.  What you call macro evolution is just micro evolution over a longer period of time.  

There is no verifiable scientific evidence for creationism.  There is no more evidence for the world having been created 5,000 to 7,000 years ago than there is for it having been created last week."
Evidence for evolution,the possible explanations for the examples you may cite not the fossils or the age you could also have been misidentified. and it can be possible that the current understanding of the process of events is incorrect.,"The identified age is counted as evidence for evolution. In the pictures showing the evolution of horses, there are dates shown. Why do you think those are more accurate then evidence against evolution."
Genetic drift,"I still don't understand. How come that genetic drift is beneficial for endangered species, isn't genetic drift reducing the allele frequencies and thus creating less variation where natural selection could wipe out the entire population?",Genetic drift is random and doesn't decrease the genetic diversity of a species.  If anything it would increase the diversity since the genetic changes are not the same throughout the population.
Genetic drift,"How could genetic drift ever create some type of allele that hampers a species or organism from living or reproducing? Wouldn't natural selection kick in over a few generations and take out the gene hampering these actions, no matter the severity of the genetic drift, or bottleneck event? If so, such "bad genes" would not last long, even in extreme bottleneck scenarios. Am i right?","Genetic drift is more common in smaller populations.  Imagine an island where 5 white rabbits and 10 grey rabbits live.  Perhaps grey rabbits have better camouflage against the island's rocks.  If a storm randomly kills 10 grey rabbits and 2 white rabbits, only the white rabbits survived to pass on their genes.  Even though grey is preferred, it obviously would not give them an advantage against a storm.  

Natural selection is dependent upon variation.  If all the rabbits possessing the grey allele are killed, that gene (and that phenotype) could literally be lost forever in the small island population."
Genetic drift,"It may sound pedantic, but is there any sort of practical occasion where genetic drift acts as a truly random evolutionary mechanism? This article states that "allele benefit or harm doesn't matter" for genetic drift, but is this even possible? I mean even during virtually random events, like an asteroid hitting the Earth and causing a major extinction, natural selection can still act upon allele fitness for this post-apolytiptic scenario - as for non-avian dinosaurs during the K–Pg extinction event.

I can't really think of an event that creates that supposed "random" allele selection - and as such I can't see much of a pratical, tangible difference between genetic drift and natural selection. How can allele frequency, which heavily depends on genotype survival/fitness, not be dictated by natural selection?","In the scenario of the asteroid causing a mass extinction, the asteroid wipes out many of the alleles present in the gene pool, regardless of whether they are beneficial or not. The 'fitter' alleles of this reduced gene pool are passed down to the subsequent generation. Natural selection without the asteroid (i.e. genetic drift) would have produced significantly less alteration in the gene pool, (and subsequently allele frequency), at least for the same time period . This is not to say that genetic drift (here, the bottleneck effect) occurs independently of natural selection, just that in scenarios such as natural disasters, it has a much greater impact. Also, in some cases (e.g. color of fur and eyes) there really is no such thing as a 'beneficial' allele. Evolution in this case is solely dependent upon genetic drift."
Genetic drift,"lets say that there is a population of equal no.s of alleles of blue ,yellow and red. now 2of each alleles migrate to a different place . and the new population consists of 2 blue alleles ,2 yellow alleles and 2 red alleles.will it still be called a founder effect?","No, it would be called founder effect if you isolated *only one* allele. From what we can see, again, all types of alleles are present (regardless of the quantity of each)."
Genetic drift,why Genetic drift effect is strongest in small populations ?,"In small populations it is more likely that chance events will significantly change the frequencies of alleles in the population.

For example: 
Imagine a population of 4 organisms which have one gene for color with two alleles - lets say a dominant allele called `A` and a recessive allele called `a`.   
The individuals have the following genotypes:
#1=`AA` 
#2&#3=`Aa`
#4=`aa`
A storm happens and by chance a tree falls on individual 1 and kills it – so sad!

What has happened to the frequency of the alleles?

What would happen if the tree had fallen on #4?  How about #2 or #3?

Now imagine there were 40 organisms with the same mix of genotypes – even if something killed off 1/4 of the population what are the chances it would get all 10 `AA`s?

Does this help?"
Genetic drift,"In the above example for founder effect, 
_'It is believed that a single couple out of the original 200 founders carried a *recessive allele* for Ellis-Van Creveld syndrome. Genetic drift, in combination with reproductive isolation, caused *this allele* to increase in frequency in the population.'_
can someone please explain this.
how does recessive allele increase in frequency? is the dominant one having the syndrome or the recessive one?","if the couple has several has several children, then all of them would carry the recessive allele. if the other couples have an average offspring count less than that of the aforementioned couple, the allele would increase in freq. then if the children grow up and have offsprings, their children would also carry the recessive gene. the example is talking about the allele freq., not the actual number of people who have the syndrome (just to make that clear)
I think the recessive one would cause the syndrome."
Genetic drift,Some of this is right. See if a population continued to stay separated from each other (like in a colony as mentioned above) the chance for genetic drift could end up taking away bad genes or creating new ones. But if the population was already mostly wiped out it stands little chance of survival.,"but they would still be alive, and a smaller population means more resources for individuals. some creatures do not need to be in large groups to survive. also, as long as the remaining population has offsprings, then the populations won't die out."
Genetic drift,"What if the founding population say migrates to another environment and is not fit for that environment? Will they just die off? Is the case where beneficial alleles can be lost and harmful ones can be fixed only if the founding population is fit for its new environment, and therefore can survive and reproduce?","In that case, what has been labeled as 'beneficial' is no more beneficial and same applies for harmful alleles.

New environment dictates new mutations and new rate of survival.

No, not the whole population will die off."
Genetic drift,How can some phenotypic variations significantly increase the fitness of the population using sickle-cell anemia,Comparing sickle cell phenotype to normal phenotype says that their survival is lower. I do not see how that phenotypic 'change' can increase fitness since sickle cell phenotype is a priori destined for destruction.
Genetic drift,Does this mean that evolution can actually take a step back in cases were adaptive genes are lost and genes with harmful effects stay?,"Evolution doesn't go in a direction, it is a continuing process."
Building a phylogenetic tree,"One thing that I am unsure of is regarding the idea of a common ancestor. Is a common ancestor an individual or a population? Is the last universal common ancestor an individual or a population? Or is it impossible to know?
If the common ancestor of humans is two individuals, this would mean there is a theoretical 'Adam & Eve' type situation. But that would surely be too small a population from which to develop a species, there wouldn't be enough variation. So the common ancestor must refer to a population that split off to cause speciation - is that correct?","Good Question! A common ancestor is a species. This may consist of multiple populations. For example, our most recent ancestor with chimps was Australopithecus afarensis. There were multiple populations of this species, so there was enough genetic diversity to evolve into both humans and chimps. Some populations gradually became human while others gradually became chimps."
Building a phylogenetic tree,"In the phylogenetic tree, the finished diagram with maximum parsimony, in the last step, does it matter where you branch off the alligator and where you branch off the bald eagle?","It's personal preference. If you wanted, you could switch the two."
Building a phylogenetic tree,"Seven species ABCGEFG AND THREE ANCESTRAL TRAITS MEDIUM MOLAR ENAMEL, ROUND SHAPE OF THE ORBITS, CURLY TAIL  A= med,round,curly. B= med,square,curly C= med,round,none D= med,round,none E= thick,square,curly F= med,round,none G= thin,square,none. How would I construct a phylogenetic tree?","C/D/F-A-B/E-G coming off of B. My logic is C/D/F are the ancestral species. I than build the tree starting with the species with one derived trait, than two, and than three where they no longer share any of the specific ancestral traits."
Building a phylogenetic tree,"If a phylogenetic tree is meant to be a reconstruction of an evolutionary sequence, can there be more than one correct set of relationships among a group of species?",Usually the tree u can find in publication is said to have the best fit of the mathematical model in the background and its data. It is the most probable solution of a set of different solutions.
Building a phylogenetic tree,"Can a phylogenetic tree be illustrated as lines branching off of other lines, like in this example or can they be made from brackets connecting two groups and within those groups, more brackets connecting other groups together?",You can do it any way that illustrates the branching of the species from common ancestry points.
Building a phylogenetic tree,What is the difference between a cladogram and phylogenetic tree?,"A cladogram is a diagram that shows the relationship between different organisms based on their similarities. A phylogenetic tree is a diagram that shows the genetic history in which organisms evolve and adapt. So, basically the difference is that phylogenic trees have a time scale"
Building a phylogenetic tree,"If there is a change on the E lineage and the descendants of E, F and G, have no tails, since taillessness is also present in its most recent common ancestor with A, B, C, and D, should taillessness still be a derived trait? Which ancestor should I compare a species to when looking for a derived trait? Thanks in advance.","In that case, taillessness would still be a derived trait.  When looking for derived traits, the species should be compared with the species closest to it on the phylogenetic tree - in this case, it's D, so if D possesses a tail, tailless E has a derived trait."
Building a phylogenetic tree,Which gene we basically choose to create a phylogenetic tree?,If you want to compare species then you will chose a gene which you can find in all of them. Some genes can be found multiple times in each species' genome so to avoid taking the "wrong" one you should pick a gene which is only present once. This is an active area of research.
Mechanisms of evolution,What is the point of using the Hardy Weinberg equation if there is no population that fits the conditions anyways?,It provides a baseline and lets us compare populations and also monitor and differentiate factors that change those populations.
Mechanisms of evolution,"Shouldn't the allele frequencies technically be labeled as allele proportions? They are a proportion of the total amount of alleles. A frequency would not tell us anything about the total, simply how many alleles there are.","I think knowing how many alleles there are is quite a key to knowing how many total individuals there are. The alleles help identify the amount of homozygous recessive or dominants,and the heterozygous dominants, which is basically enough to know the total alleles of a population"
Mechanisms of evolution,"In the article there is the statement: "Non-random mating won't make allele frequencies in the population change by itself, though it can alter genotype frequencies." I was perplexed by this but then realized that I think the author must be using a narrow definition of "non random." If some individuals are so unattractive that that mate less often that would be a type of non randomness and would, obviously, lead to changes in allele frequency. Am I correct?","Yes you're right. In Sal's example, all of the organisms in the population get an equal opportunity to mate. For example if all the black beetles mate with other blacks, and whites with whites, then you wont get any 'mixed genotype', but all of the alleles are still passed on. However, if all beetles preferred to mate with black beetles, then the alleles for darker pigment would have a higher chance of being passed on. But in that situation there is an unequal opportunity to mate. In summary I agree with you - Sal is just pointing out a curious but unlikely situation where the allele frequence sticks to the HW equilibrium but the genotype frequency does not."
Mechanisms of evolution,How does evolution unify the biological sciences?,"It explains biological observations, considering evolutionary factors as reasons."
Mechanisms of evolution,"In the conditions for the Hardy-Weinberg Equilibrium , how does random mating stabilize the allele frequency?","It seems to me that rather than random mating stabilizing the frequency, it's non-random mating that destabilizes the allele frequency (or the genotype frequency). For example, if we are talking about a population of beetles, and the females prefer to mate only with larger males if they can, then the alleles present in the smaller beetles will be less likely to pass on than the alleles in the larger beetles. Therefore, the allele frequency will not be stable and the HW equilibrium will no longer be applicable.
In other words, the allele frequency can ONLY be stable if certain conditions are met including random mating (and all the other assumptions must be met too!)."
A brief history of mass extinctions,Is there any evidence that there were ever any epidemics plaguing dinosaurs? Like the bird flu?,"Yes, the dinosaurs were subject to the plague, but that's not the huge way they go extinct."
A brief history of mass extinctions,If the sunlight was blocked how the plants  survived ?,"Well first, sunlight wasn’t completely blocked out and prevented from reaching the Earth’s surface. The amount reaching the surface was greatly diminished, but still some sunlight made it through. 

Second, not all plants have the same demands. Some plant species adapted to life with limited sunlight. Some plant species surely died off, but the ones which evolved to be more hardy survived."
A brief history of mass extinctions,How did the mass extinction start?,by an asteroid
A brief history of mass extinctions,"So, did T-Rex go extinct?","T-rex itself is extinct.  There are no more T-rexs living anywhere at all.  However, modern birds are closely related to dinosaurs, based on biology, fossil records, and evolutionary studies.  That does not mean today's chickens and turkeys are dinosaurs like you would see in Jurassic Park or other dinosaur movies.  But it does mean our birds today have dinosaurs in their very ancient family tree, and so sometimes birds are considered "living dinosaurs"."
Species & speciation,"There are now evidence showing that Homo sapiens interbred with Neanderthals and produced offspring. These offsprings seems to be fertile since the study found traces of Neanderthals DNA in modern humans. (see http://www.wired.co.uk/article/dna-analysis-humans-neanderthals-breeding)

So, if organisms which can interbreed to produce viable, fertile offspring means that they belong to the same species, does this mean we (modern day human, Homo sapiens) is the same specie as the extinct Neanderthals?","Hybridization is known to happen between what are generally accepted to be different species — sometimes this leads to new species, other times some traits from one species become incorporated into another species.  This second possibility is what seems to have happened with _Homo sapiens_ and _Homo neanderthalensis_.  However, some people now argue that Neanderthals were in fact just a subspecies.

Note that the definition of "species" is hotly debated among evolutionary biologists and none of the (numerous) proposed definitions seems to adequately cover all cases. (This is a lot like our attempts to define "life" — we can list characteristics, but they don't all apply in all situations.)

This website has an accessible discussion of some of the complications associated with trying to define species:
https://evolution.berkeley.edu/evolibrary/article/evo_40"
Species & speciation,Why haven't dogs undergone speciation yet? What major changes must one breed undergo in order that they become incompatible to mate to another bread?,"Dogs are currently undergoing speciation. However, because they have only recently have split into many breeds, it will take much more time for them to become different species. One breed must keep mating with it's own kind for a long period of time and must not mate with the other breed. Eventually the genetic information of the first breed will become so different from the genetic information in the other breed that the two breeds will become separate species and will be unable to have fertile offspring or offspring at all."
Species & speciation,"Suppose that two groups of animals are reproductively separated due to a mechanical barrier, but if we artificially fuse their gametes and implant the resultant zygote in a female womb, the zygote can develop into a healthy fertile organism. Now should we consider the two groups separate species or not?","No, because the offspring is able to reproduce which means that the two parents are of the same species.  Plus, just because organisms live in different places doesn't necessarily mean that they are of different species.  Hope that helped."
Species & speciation,What can speed up speciation process?,The biggest factor is with the rate of creating offspring.  The shorter the time between generations the faster that speciation can occur.
N/A,Where can you find a wild cow?,"Well, to answer your question it's pretty simple In the wild .w."
N/A,"Unless it provides a selective advantage, a heritable mutation would not, in most likelihood, persist. What kind of advantage does _lactose intolerance_ provide?","You have that backward.  

The ability to digest milk past infancy is not common in nature.  There is no benefit for a mammal to continue to produce the enzyme lactase past infancy unless milk is consumed later in life.  

For human populations that keep herds of animals the milk they produced things like cheese and yogurt that changes the lactose in the milk so it is slightly more tolerated and provided good storage of food.  This was a benefit so individuals that developed the ability to digest lactose after infancy had an advantage so that trait started to spread."
N/A,can artificial selection bring back extinct animals?,"It is definitely feasible; however, there are several things to consider:

-Is the climate suitable for this organism anymore?
-Why not spend the money protecting organisms that are going extinct right now?
-Will there be a suitable food source for the organism?
-Will the organism be healthy? Organisms that have been genetically altered in such a fashion are typically not in the best health. Clones like Dolly the sheep do not live for long, and hybrids like the mule are sterile.

Did this help?"
N/A,How does artificial selection help to prove evolution taking place in bacteria,"One thing to keep in mind is that in science no theory is ever proven.  

The genetic code for a organism can be different from the genetic code that is passed to offspring because of genetic damage or errors in the process of replication of DNA.  These changes are fairly random.  This is an observed fact.  

This difference in genetic code between organism and offspring leads to random changes in the genetic code of the gene pool of the organism and its offspring.  

Genetic changes in a gene pool of an organism can cause changes in the organisms that affect how an individual organism functions.  This is an observed fact.  

The natural or artificial selection based on these functional changes has been observed to cause specific genetic information to become more prevalent in a gene pool.  This is also an observed fact.

Based on these observation any many others is the basis of the modern theory of evolution.  

Artificial selection on bacteria is like a proof of concept of the theory of evolution.  It is a study of these changes in a controlled and simplified environment to understand the process before looking for these types of processes and influences in nature."
N/A,What different between human breed selection and artificial selection?,Artificial selection and selective breeding are the same. Humans chose desirable traits in a species and breed them together to pass on those traits.
N/A,Does artificial selection affect the species negatively?,"It depends on the situation. For example, pugs have been bred and inbred so much for many years to the point that they are born very unhealthy. Artificial selection can also be beneficial, for example with corn. Corn used to be very slim and did not look at all like how it does today. Thanks to selective breeding, corn is now plentiful and larger."
N/A,Do dogs get smaller I don't think so?,"Dogs started out as wolves before humans selectively bred them. Not all breeds are smaller now, but something like a Chihuahua definitely got smaller compared to its wolf ancestors. 

Does that help?"
N/A,My brother asked me to ask: Why do dogs have different size ball,"Female dogs mate with multiple males (often in a brief period). 
So there's a competition - among the males and among the plethora of sperms to fertilize the egg. 

More the number of sperms of a male, the higher are the chances that the offspring would be related to that male. Well, for producing more sperms, you need bigger sperm factories aka testes. And these sperms had a chance to carry the traits for large testes.

So, this trait of bigger testes, remained more and thus got selected.
If the dog belonged to a breed where female multiple-matings were less likely, it is possible there wasn't any advantage of larger gonads. So, there wasn't any selection in this aspect. 


P.S. Note that small testes trait wasn't wiped out at all.

https://www.sapiens.org/biology/sperm-competition-testicle-size/

Does that help?"
Evolution of viruses,"I know this will most likely be impossible but is it possible for a virus to evolve rapidly enough to spread and wipe out life on earth, I mean the H1N1 pandemic looked bad enough right?","Viruses could never wipe out life on Earth. There are two reasons for that.

1) The more successful the host is, the more successful is the virus going to be. Humans are very widespread specie, which means that viruses that attack us have very good chances of spreading from one victim to another. But, as the population of their hosts declines, viruses will have more trouble in spreading. In the end, when there would be only a few isolated groups of people left, our imaginary deadly virus wouldn't be able to spread anymore.

2) Someone will be immune to virus. Those people will survive and continue the humanity. Their children will have their genes and they will all be immune to that specific virus. Spanish flu couldn't affect everyone, HIV can't affect everyone, none virus can affect everyone. It's just how things work."
Evolution of viruses,"If the HIV virus only has a lifespan of 52 hours, then wouldn't the HAART "cocktail" therapy be able to block the HIV virus for at least 52 hours, thus causing the death of the virus? Unless the HIV virus evolves and mutates within those 52 hours, which I highly doubt is always and/or mostly the case.","Good point. In that case, cocktail therapy would perfectly work and ensure no viruses escape."
Evolution of viruses,how does the virus affect human population?,"One virus can affect human population only if his infection becomes epidemic or pandemic.

Epidemic - a sudden increase in the number of cases of a disease to a level that is greater than the expected level in a given population in an area.

Pandemic -  an epidemic of world-wide proportions

https://www.infoplease.com/askeds/pandemic-vs-epidemic"
Evolution of viruses,What would happen if 3 viruses combined?,"Probably recombination of genetic material would happen.

Now, you may take 3 of the deadliest viruses in the world, but the resulting virus may be something harmless or low degree dangerous.

Or maybe each one may infect and cause disease on its own.

Genetical rearrangements can end up in any kind of results."
Evolution of viruses,How does the influenza virus affect the human body?,"Influenza virus has two different glycoproteins on it's lipid envelope called neuraminidase (helps the virus to leave the host cell)and haemaglutinin(aids the virus to enter the host cell).

In humans,haemaglutinin binds to (saliac acid) receptors on the epithelial cells in the upper respiratory tract and then the virus enters the cell through a process called 'endocytosis'.
Once in the cell , the negative sense Rna is replicated into positive sense ss rna which then helps in the process of progeny production.
Now viruses mutate very rapidly...Therefore the daughter viruses have slightly different glycoproteins than their parent and other progeny viruses.
This is why you can get flu every year or even twice or more in a year.

Now, neuraminidase is a receptor destroying protein which is why it aids the virus to elude from the cell by destroying saliac acid receptors."
Evolution of viruses,Why is it that the article says that the average human cycle is only 20 years?,When looking at generations of an organism you measure the average time between birth and having offspring.  For humans the figure of 20 years has been used but may very depending on the area and time period used.
Evolution of viruses,What does rna mean?,"RNA stands for RiboNucleic Acid.  It is described in the section on nucleic acids, over here:

https://www.khanacademy.org/science/biology/macromolecules/nucleic-acids/v/dna-deoxyribonucleic-acid"
Evolution of viruses,Can a virus wipe out the dinosaurs or cause a mass extinction event?,"I know there will be people who disagree with me, but i firmly believe the answer to both questions is no.

(Just as a side note, dinosaurs aren't extinct. Present-day birds are indeed dinosaurs.)

To cause a mass extinction, a virus would have to be able to infect a broad variety of species and cause disease with a mortality rate of 100 %. To my knowledge, no known type of viral disease has such a high mortality rate (even though some are close to that number!). The more lethal a virus is, the sooner it will run out of possible hosts. Earlier types of ebola virus were very lethal (the highest recorded mortality rate was 90 % during the 2003 epidemic in DR Congo), but those viruses didn't cause massive epidemics. Each outbreak had several hundreds of casualties.

Some scientists speculate that viruses could have caused several smaller extinctions in the history of life on Earth. Fossil records confirm that in between so-called mass extinctions, there were also smaller extinction events which happened during periods of relatively stable environmental conditions. So what was the cause? Even though some believe it was because of the viruses, as of now we have no evidence to support that claim.

That's just my opinion. The topic is still very controversial, and i would be interested to hear others' opinions."
Evolution of viruses,"Vaccines provoke the host's immune system to produce appropriate antibodies against the antigen in the vaccine. In relation to the section, Case study: HIV, why do vaccines for viral infections/viruses become ineffective over time? Is it because as viruses mutate, antigens develop on their surfaces which are different to the original antigens on the virus before mutation, and hence require the production of different antibodies to be granted immunity against the new, mutated virus?","A person's immune system is introduced to the protein on the surface of a dead or weakened virus so that it can be recognized as a foreign without the chance for the virus to overwhelm the immune system.  That person's immune system is primed to recognize and eliminate anything with that protein on it.  

If the virus mutates or is somehow changed so that the protein coat no longer has the same protein on its surface that person's immune system will not immediately recognize it as foreign and the virus has a chance to insert itself into a cell for replication before it is detected.  

A lot of research is needed to identify what parts of the virus protein coat are not likely to change over time so that a vaccine will continue to work even of the virus changes."
"Darwin, evolution, & natural selection","In the example of the mice and hawks, what if due to natural selection the hawk's ability to spot out black mice increases? Will that cause the mice to 'counter evolve' and will this cycle of evolutions on the prey and predators' part continue?","Very good!  You've correctly deduced an important evolutionary process known as co-evolution.

This phenomenon is a key to understanding not just predator-prey interactions, but also many other ecological phenomena such as: host-parasite interactions (including disease evolution), and the interaction between many flowering plants and their pollinators (an extreme example being orchid flowers that mimic female insects to get their pollen transferred by male insects).  

More info:
https://www.khanacademy.org/science/biology/crash-course-bio-ecology/crash-course-ecology-2/v/crash-course-ecology-01

https://en.wikipedia.org/wiki/Coevolution"
"Darwin, evolution, & natural selection","How would have homo sapiens evolved from the apes , why did the characteristics of standing erect dominate over bending forward. would it be a transmission of the lifestyle of apes eating food from the ground to hunting ?","From the Homo Sapiens book, Yuval shared a very simple but reasonable concept that standing on 2 legs on the ground will give more broad and wide of view instead of 4 legs. 

Climbing on to the tree will give more advantage but more effort just to check the surroundings. So standing on 2 legs dominated over time for our species to become."
"Darwin, evolution, & natural selection",If natural selection is favouring traits which are beneficial for the environment then couldn't it be stated that as a human choosing to have less children is a trait which is favourable to pass onto your children?,"Natural selection favors traits that are better for the ORGANISM'S survival and reproduction not for the environment. So actually the inverse would be true. A human who has a gene (not conscious choice, as genes - not thought - are passed onto offspring) that makes him susceptible to having more children will pass on that gene (as it is likely that more of his children will survive than someone who has, say 1 child) to more offspring and will thus be selected for."
"Darwin, evolution, & natural selection","I have a doubt, is it possible for natural selection to reduce the size of an organism? If possible, are there documented cases of this?","Of course, natural selection just selects for the organisms that will be the most fit (have the most offspring) in a particular environment.  


One situation where selection can often favor being smaller is on islands and other isolated ecosystems where limitations in food supply and the inability to migrate can mean that smaller organisms are better able to survive famine.

This phenomenon is known as "insular dwarfism" — there is an entire wikipedia article on this subject including numerous examples here:
https://en.wikipedia.org/wiki/Insular_dwarfism

Perhaps the most dramatic example of this are the numerous (extinct) species of dwarf elephants:
https://en.wikipedia.org/wiki/Dwarf_elephant


Does that help?"
"Darwin, evolution, & natural selection",How does natural selection occur in both plants and animals?,"Natural selection is a mechanism that makes any species - be it a plant, animal, fungus, bacteria, you name it - better adapted to their environment. For herbivores (i.e. plant eaters), the plants are indeed part of their environment. In such a situation, the evolution of the plant may affect the evolution of the plant eater (which may in turn affect the evolution of the plant). This process (or feedback) is called coevolution.

Coevolution may also occur with predator and prey, parasite and host, and many other cases where two species are dependent on each other."
"Darwin, evolution, & natural selection",All theories must be testable with many pieces of evidence to back it up.  Is there any examples of famous experiments used to test this theory?  Or any sources the support this theory?,"That's not how science works. You can come up with any ridiculous theory and find as many evidences for it you please. What you should do is to create an experiment that can _overthrow_ the theory. If your theory falls, it's dead. If it survives, it lives as long as some experiment doesn't overthrow it.

As for the theory of evolution, Darwin and Wallace (and some people before them who are usually not given any credit whatsoever) came up with it after observations in the nature. Since then, theory of evolution has survived every attempt of overthrowing. Evolution is a long process, so it's not easy to come up with an experiment to test it. That's why there are still many people who are really skeptical about it.

Probably one of the most famous experiments (or projects...) that has anything to do with evolution is the domestication of red fox in Siberia. Check it out:
https://en.wikipedia.org/wiki/Russian_Domesticated_Red_Fox"
"Darwin, evolution, & natural selection","on the second to the last paragraph,i would like to ask if such heritable differences occur to the point that the groups can have different numbers of chromosomes? If so, how?","Not sure about animal species.

In-plant kingdom it occurs and helps the creation of new species or more 'potent' for agriculture, such as watermelons ets- Polyploidy (multiplying sets of chromosomes) do exist in plant kingdom.


As for animals, polyploidy is incompatible with life. Aneuploidy, on the other hand, is compatible but _always_ leads to errors and diseases in animals.


You propose some error/event occurring where two chromosomes fuse and it results in one less or 2n-2 chromosome garniture resulting in evolving species?

Not sure about genetic mechanisms, maybe that is possible in unicellular organisms."
"Darwin, evolution, & natural selection","How old was Darwin in 1831 when he set sail on the 
HMS Beagle?",22 years old
"Darwin, evolution, & natural selection",What are the three observations that Darwin's concept of natural selection was based on?,"Darwin's concept of natural selection was based on several key observations:

-Traits are often heritable. In living organisms, many characteristics are inherited, or passed from parent to offspring. (Darwin knew this was the case, even though he did not know that traits were inherited via genes.)

-More offspring are produced than can survive. Organisms are capable of producing more offspring than their environments can support. Thus, there is competition for limited resources in each generation.

-Offspring vary in their heritable traits. The offspring in any generation will be slightly different from one another in their traits (colour, size, shape, etc.), and many of these features will be heritable."
"Darwin, evolution, & natural selection",Is there other theory that doesn't agree with Darwin's theory of evolution,There have been other theories but they disagree with observations that the theory of evolution through natural selection explains.
Allele frequency & the gene pool,"In this lesson, there was an explanation of what 'alleles were.  I am interested in historical population genetics, and am wondering if the HVR numbers that come with mTDNA are equivalent to the alleles that go with the Y Chromosome.  Thank you.","I assume mTDNA is shorthand for mitochondrial DNA - DNA inside mitochondria and HVR is short for hypervariable region or a place where base pairs are repeated, generally within the mTDNA, but also sometimes in the nucleus. mTDNA is always inherited from the mother and goes into mitochondria in each cell in the child. It does not seem to serve any function as far as I know. The alleles on the Y chromosome are different. They function to change certain processes in the human body to make the offspring male. 

In short, they are not equivalent."
Allele frequency & the gene pool,"If there are only 2 alleles at a locus and one is at frequency 0.3, what is the frequency of heterozygotes and how do you figure it out?","you can figure it out by making use of hardy-weinburg equation which is p+q=1.
let say p is the frequency of 0.3 and we are looking for the frequency of q.
p+q=1
0.3+q=1
q= 0.7 or 70%
i don't know maybe this is right but someone else can also answer it and you compare"
Allele frequency & the gene pool,Could you please further explain how to find allele frequencies of a new generation?,"To furtherly explain that, all you need to do is to repeat that same process you've used to solve for the old generation."
Allele frequency & the gene pool,"How does looking at all the copies of all the genes in a population, How can  we can see globally how much genetic variation there is in the population.","THat's why the Human Genome Project was so important.

PCR and other gene sequencing methods are now used. Everything is stored in databases so nowadays it is relatively easy to obtain wanted information and compare whole genomes."
Allele frequency & the gene pool,What is the difference between genome and genotype?,"The genome is the collective term for all the genetic material in a cell.

The genotype is what alleles are present for one or more genes.

Does that help?"
Intro to eukaryotic cells,Why are plant cells typically square (if they are) and why do they have a much larger vauole than animal cells?,"They are squarish because they have a stiff cell wall that forces them into that shape. If you meant vacuole, I think they have a larger vacuole because they have more need to store food than animals. In case of drought or famine, animals can move on to somewhere else if they need to get food or water, plants can't."
Intro to eukaryotic cells,In the above diagram the author gives us an example of what a plant cell looks like and I noticed that the cell has an abnormally thick cell wall. What is the reason for thick cell walls in plants?,"Cell walls not only provide structure, and protect from mechanical damage, they also prevent the cell from bursting as plant cells need to continually absorb water to survive."
Intro to eukaryotic cells,how come animal cells don't have a cell wall,"An animal cell needs to allow mobility for that animal so only has a cell membrane, a plant cell however has a cell wall to give the cell ridged structure and a plant doesn't move by itself so doesn't need mobility but rather it have protection."
Intro to eukaryotic cells,Why don't plant cells have lysosomes?,"Plant cells don't have lysosomes, because their cell walls are tough enough to keep out foreign substances that lysosomes would have to digest out of the cell."
Intro to eukaryotic cells,"The Endoplasmic Reticulum in a eukaryotic cell is the transport network of the cell and it extends from and connects the nuclear membrane to the plasma membrane of a cell. But then whenever we draw a diagram of a typical plant or animal cell, we never extend it to the plasma membrane- we always leave it somewhere in the cytoplasm. So, it should be extended, shoudn't it? And in that sense all our diagrams are theoretically wrong?","Well, from endoplasmic reticulum vesicles are formed and transport things to Golgi apparatus, where it may be modified somehow, sent back to ER or further to cell surface. So the whole network is: ER -> vesicle -> Golgi -> vesicle -> cell plasma membrane"
Intro to eukaryotic cells,Procaryotic cells lack vacuoles too then?,Yes. Only eukaryotes have vacuoles.
Intro to eukaryotic cells,Does the nucleus have a phospholipid bilayer?,Actually it is surrounded by a double membrane which has 2 phospholipid bilayers each.
Intro to eukaryotic cells,Why is there a nucleolus? Shouldn't the production of DNA just be spread evenly around the nucleus?,The nucleolus is a region from the nucleus where the different RNAs are found. It is also the site where ribosomes are joined. It´s important to mention that ribosomes are made 1/3 from proteins and 2/3 from RNA. Proteins for the ribosome are exported from the cytoplasm  to the nulcleus trough the nuclear pores.
Intro to eukaryotic cells,what is the function of a peroxisome?,"it is main function is to break down long chains of fatty acids and to detoxify substances, 

it produces H2O2 as a result, which can be harmful to the cell as a whole if not regulated, which is why it contains enzymes that is able to break down H2O2 into water and oxygen."
Intro to eukaryotic cells,"are there any unicellular eukaryotes? if there are, names ?","Yes, there are many unicellular eukaryotes. In fact, they have their own kingdom in the standard five kingdom classification scheme in biology called Kingdom Protista. Kingdom Protista is divided into subkingdoms of Protozoa and Algae. In Subkingdom protozoa, you have organisms like amoeba, euglena, volvox, paramecia, even plasmodia (the microorganisms that causes malaria), just to name a few. Most types of algae are also unicellular eukaryotes."
RNA world,What makes the fruit fly so suitable for research?,"it has short life span and few chromosomes, so it is much simpler to study them."
RNA world,So they say that the first organisms were RNA? Or not?,"Yes, scientists claim that RNA formed first (possibly at the bottom of the sea) and then fused into double-stranded DNA organisms. That's what the RNA Life Theory is. Hope that helped"
N/A,"If disruptive selection occurs on a population, is it possible that it could result in two separate species where each specializes in a certain area based on it's phenotype?",It is possible but one of the things that need to happen for speciation to occur is for the two different populations to decrease or stop intermingling their DNA.  If the two populations are still breading with the other the gene pool will continue to have both phenotypes until one disappears form the gene pool.
N/A,Can directional selection lead to allopatric speciation?,"That is an interesting question. Directional selection helps the survival of the most extreme phenotype. And now you are looking at it from a broader perspective.

I think it can. So you mean that the phenotype which survived creates new species? Possible."
N/A,Why is it important to examine the fitness of each individual relative to others in the population?,To see what is possible fate of each individual and population itself. To follow the evolution and the process of speciation.
N/A,"If disruptive selection of this type persisted for a prolonged period, what would be the likely outcome?","I Suppose that if disruptive selection persisted for a prolonged extent of time, this will lead to the extinction of moderate phenotypes."
N/A,Why would the Disruptive selection not work fro the medium colored beetles?,"Because they have nowhere to hide. There is no "medium" colored shrub for them to hide in, whereas for the light and dark colored beetles they can hide in the moss and the shrubs, respectively. So the medium colored beetles would be quickly picked off by predators."
N/A,"When applying the mechanism of natural selection, how does a population become suited to their environment?","Consider that natural selection will lean toward fitness-increasing alleles becoming more common in a population. _Fitness_ is a measure of reproductive success, so consider the following example: 

You have two organisms, organism A and organism B. Both organism A and organism B live in the same environment. The environment is subject to extreme heat throughout the year. Organism A handles extreme heat very well, while organism B does not have traits that contribute to handling extreme heat. 

In this case, organism A is more likely to survive than organism B, meaning that organism A will be the one to successfully reproduce. Therefore, organism A's genes that contribute to survival in a hot environment will be passed down and future generations will be better adapted to handle the hot environment.

The example above exemplifies one case where a population becomes better suited to their environment through natural selection. You can think of many such cases, so feel free to brainstorm!"
N/A,"Using relative frequency and graphical analysis,  how do you determine whether or not a population is evolving","If you measure the allele frequencies in a population this year, then again next year; if they differ significantly, then allele frequencies have changed, the population has evolved"
N/A,can natural selection have negative effects on an environment?,I do not think so. haven't seen any case so far.
Hypotheses about the origins of life,"Could another experiment much like the Miller-Urey experiment be conducted again with slightly different components today? If so, could we learn anything new from it?",Clicking on the expandable 'What about Nucleotides?' link revealed an answer to your question. It's noted that "one recent study using a different approach (not an approach similar to Miller and Urey) found that RNA nucleotides could be formed from inorganic components under conditions thought to resemble those of early Earth."
Hypotheses about the origins of life,"Does it mean that DNA is the evolution of RNA?
Is it possible that Panspermia and Abiogenesis happened at the same time ?","Hi, Bintia and thank you for your questions.

DNA evolved from RNA, that's our current belief. When i was a student i was constantly searching for some kind of info on that process (in other words, how did DNA became from RNA) but i found almost nothing. Some scientists believe that viruses "invented" DNA because they are the only "living" beings who have both RNA and / DNA for their genetic material.

I would say it is possible that panspermia and abiogenesis happened at the same time, however we can only speculate about that. Abiogenesis might be still happening in some obscure thermal vents somewhere in the depths of oceans, who knows."
Hypotheses about the origins of life,"Why is it that the RNA world hypothesis is more favored  over the Metabolism-first hypothesis? (In other words, how is the RNA hypothesis more reasonable?)","I assume that's because RNA molecules have many abilities and in general have more diverse functions than proteins. RNA can be a genetic molecule (like in some viruses), it can epigenetically control the expression of genes (like micro-RNA molecules), it can have enzymatic abilities (like ribozymes) and so on. Proteins, on the other hand are mostly known as enzymes.

So, from our current perspective, it looks like an RNA molecule had better chances of catalyzing its own replication because, in theory, it can do that. Proteins are good enzymes, but they can't serve as genetic material and therefore they can't make copies of themselves.

I should also note that the discovery of prions in 1980's dramatically changed our view on the topic. It happened in the moments when most people in the scientific community already declared RNA's as winners in the battle against proteins but then, all of a sudden, Stanley Prusiner discovered proteins that can turn other (but similar) proteins into their own clones.

Even though it still looks like RNA molecules are better candidates, the battle is still going on."
Hypotheses about the origins of life,Do you believe that the diversity we see around us comes from a single ‘origin of life’ event or multiple ‘origin of life’ events?,"All life on earth appears to be related — this is based on the presence of ancient genes that are found in (essentially) all living organisms.  

This progenitor of all known life is referred to as the "Last universal common ancestor" (LUCA).

You can start learning more about this here:
https://en.wikipedia.org/wiki/Last_universal_common_ancestor"
Hypotheses about the origins of life,"So how exactly, do the inorganic elements on early Earth turn into the organic maters that are the building blocks of life","The amino acids that are the base building blocks of life are simple to make.  In the 1950's scientists combined ammonia, hydrogen, methane, and water vapor and added energy in the form of electrical sparks and 11 of the common amino acids were formed."
Hypotheses about the origins of life,This is so confusing!!,i know it may look confusing but its how life works.Life keeps going and going and soon we have the animals today and cells help all life stay alive
Hypotheses about the origins of life,"Since there is so much diversity on Earth,is it more or less likely to have an ‘origin of life’ event today than 4 billion years ago? Is there a limit to mutations?","We think that any newly originated organism (or proto- organism) would be very unsophisticated and unlikely to survive competition with existing organisms.  This suggests that successful "origin of life" events (i.e. where the new organisms persist in the environment) are very unlikely.

Beyond that, we aren't sure exactly what needs to happen for an "origin of life" event to occur so it is difficult to know whether current conditions would enhance or inhibit these events.

We do know that the early earth's atmosphere was reducing (didn't contain oxygen) and it is quite possible that oxygen would interfere with the chemistry necessary for an "origin of life", so my _guess_ is that a new "origin of life" is unlikely on this planet ..."
Hypotheses about the origins of life,what is difference between Miller and Operian  hypotheses and who was right?,"The Operian hypothesis suggests that simple, inorganic molecules gave rise to more complex organic ones (such as amino acids), and then those combined to create the most complex molecules of life (such as proteins). Miller and Urey, on the other hand, performed an experiment in which they simulated an early earth environment and proved that small inorganic compounds can combine to create more complex organic ones under such conditions. In short, the Miller experiment provided scientific support for the Operian hypothesis."
Hypotheses about the origins of life,How is it that the RNA World hypothesis is still being considered?   See this article from retraction watch:  https://retractionwatch.com/2017/12/05/definitely-embarrassing-nobel-laureate-retracts-non-reproducible-paper-nature-journal/,"A quick search of pubmed for the phrase "RNA world" finds 914 papers:
https://www.ncbi.nlm.nih.gov/pubmed/?term=%22RNA+world%22

Why do you think retraction of a single paper (about one possible contributor to a protein independent RNA replication) invalidates this hypothesis?

If you are really interested in this subject I encourage you to start learning more by looking at some of the references at the bottom of this article.

Two examples:
•http://www.ncbi.nlm.nih.gov/books/NBK26876/

•http://evolution.berkeley.edu/evolibrary/article/ellington_03"
Evidence for evolution,"I understand that a fossil not being found doesn't mean the organism didn't exist, simply that it hasn't been found yet (or never fossilized). But several fossils that do exist don't seem to fit in with the theory of evolution.  What about pollen from Cambrian or older sediments the Romairma formation in South America or in the Hakatai Shale in the Grand Canyon in North America? Flowering plants are highly advanced and wouldn't have existed in the Cambrian or Precambrian epochs.",There are multiple possible explanations for those examples you cite. The fossils or their age could have been misidentified. It is also possible that our current understanding of the sequence of events is incorrect. Hopefully future scientific inquiry will decrease apparent contradictions.
Evidence for evolution,"This article admits, under Evidence For Evolution: Fossil Record, that the record is incomplete. So how is it that we can actually teach this as fact when there is no evidence for macro evolution. The tree shown that all species share a common ancestor is a hypothesis that remains unproven, why not also teach the idea of creation? Creation explains more of what we see than these hypothesis displayed as fact.","Scientific theories are never proven, proofs are for mathematics.  The theory of gravity and quantum mechanics are not proven but but you do not question them being taught.  

Evolution is a scientific theory and has a bunch of supporting verifiable evidence.  It is a theory that accurately describes observations and has made predictions that we have been verified.  

Gaps in the fossil record do not disprove evolution.  Fossils are rare events so there are are going to be gaps.  

There is evidence for macro evolution.  What you call macro evolution is just micro evolution over a longer period of time.  

There is no verifiable scientific evidence for creationism.  There is no more evidence for the world having been created 5,000 to 7,000 years ago than there is for it having been created last week."
Evidence for evolution,the possible explanations for the examples you may cite not the fossils or the age you could also have been misidentified. and it can be possible that the current understanding of the process of events is incorrect.,"The identified age is counted as evidence for evolution. In the pictures showing the evolution of horses, there are dates shown. Why do you think those are more accurate then evidence against evolution."
N/A,What damage can European starling do,"The article states, "The European starling, Sturnus vulgaris, may compete with native bird species for nest holes." This means they can take nesting holes away from the native birds, profoundly reducing the native bird's population."
N/A,Can releasing a pet into the wild like a turtle or an ant potentially turn it into an invasive species? Has this happened?,"Releasing a single pet into the wild is not likely to cause a problem but that is rarely the case where a single animal is released.  

For example the seemingly innocent goldfish is a species of carp that is not native to the US and is a fish that can grow to be 16 to 19 inches and weigh more than two pounds and has few natural predators and reproduces fairly quickly.  They out compete other species and even eat their eggs.  

Pet Burmese pythons being released have cause a drastic reduction in population of raccoons, foxes and bobcats in the ecosystems they have now become common in."
Innate behaviors,When the two mouse interbreed do their burrows turn into something different? Or do they inherit on or the other?,They always inherit the beach mouse style of burrowing behavior
Innate behaviors,"It's hard to imagine reflexes begin; could these innate behaviors start as haphazard habits? For instance, sometimes I twitch uncontrollably when I'm bored. The way I'm seeing it, does that mean that if that habit helps me survive, it could become a reflex?","Excellent question!

They can! Even though I do not personally know of any example, but yours is great."
Innate behaviors,how would the offspring of the beach and the deer mouse act to survive in the wild?,"We need to crossbreed them and see. However, not sure whether they will give fertile offspring."
Innate behaviors,what's the difference between reflexes and fixed-action patterns?,"A *fixed-action pattern* is more complex in that it consists of a series of actions, whereas a *reflex* consists of a quick action (or reaction)."
Interactions in communities,"In the overview, they made mention of herbivory. is there any such ting as carnivory or omnivory? and if there was, what would have been the effect, considering the predator and prey relationship.","Yes, there are such things as carnivory and omnivory, the *predator-prey relationship* will still be +/-, because the predator benefits from eating the other organism but it harms/kills the prey. I hope you find this useful! :)"
Interactions in communities,"Is there a type of interaction for a plant eating an animal, like a Venus flytrap eating a fly? It doesn't seem like a predatory interaction, but it also doesn't seem like a herbivorous interaction.",That would be predation. One species is eating another.
Interactions in communities,Where do we draw the line between parasitism and predation. Would a mosquito sucking on our blood or lice eating our scalp be parasitic or predatory?,"The examples you have given are both parasitic but the way I understand it, the difference lies between host and prey.
A parasite can cause death but it's kind of counter-intuitive for them to do so. They usually want to live and continue to feed from a host for some time. Also unlike a predator which consumes the majority of it's prey, a parasite can only feed off a small part of it's host.
Hope this helped🍀"
Interactions in communities,"What about *0/0* relationships, where both species live in the same environment, but _do not affect each other?_","The definition of relationship is that two things have some effect or are connected in some way. If they both do not affect each other, then there is no relationship."
Interactions in communities,is (-/0) type of interaction not a thing?,"Technically not, but I think that this -/0 still exists. For example, stepping on an ant: You don't notice it, but the ant is killed."
Interactions in communities,why does the secondary consumer still depend on the producer despite consuming the primary consumer?,"It's a chain of interactions, where all levels can affect all other levels. For example, if all the producers died off due to a disaster, the primary consumer population would drop drastically, which of course would affect the secondary consumers."
Interactions in communities,"Can anyone give me separate examples of the various types of adaptations in preys (mechanical, chemical and behavorial)?","How about this:
Mechanical: something like antelope that can run fast to escape, or a tortoise hiding in its shell. Camouflage is very common, as is its inverse, aposematic (warning) coloration
Chemical: A skunk spraying! Many insects have similar chemical defenses
Behavioral: Parrots flocking, quail "exploding" into flight suddenly and noisily (maybe this is mechanical too?). Herds of ungulates stick together to make it harder for the predator."
Learned behaviors,"Through training, can we improve the gorilla's IQ?",Yes probably we could. But gorillas have a lot of IQ of their own and we can't change that through boxes and bananas. In other words we can't train them out of their  Innate behaviors.  Its sort of like this: When you go to the doctors do they use a small hammer to bump your knee? They probably do. They are supposed to anyway. Do you flinch? If so this is one of the Innate responses and you can't be trained to stop doing it.
Learned behaviors,why are animals are alert when they are getting food?,Because that is a reward to the body - getting energy source: dopamine is produced in the brain. mother nature wired animals (including us humans) that way.
Learned behaviors,"if you raised a baby whooping crane in captivity, by humans, how would you teach it to fly?","Quite interesting question so I had to research a little.

It is possible if humans take the role of a bird and 'teach' baby bird with _reinforcement_. (since humans cannot fly and demonstrate flying to a bird).

'The main source of motivation for baby birds is food. The baby bird knows nothing more than that at regular intervals their mother will come and drop some food off in their mouth. Slowly the mother bird will stand farther and farther away from the nest, forcing the baby bird to come out of the nest in order to get food. The bird realizes it needs this food to survive and this is the motivation for them to venture out onto a branch'.

http://blogs.bu.edu/bioaerial2012/2012/10/09/nature-vs-nurture-how-do-baby-birds-learn-how-to-fly/


Meaning that humans may imitate parent birds. :D"
Learned behaviors,"why is habituation considered as a learned behavior ? I mean if the ducks recognize their "mother" the moment they hatch ( 0 experience), shouldn't it be an innate behavior?","First of all habituation is not the same as imprinting (just be careful not to confuse the terms).
Secondly: the interesting thing about imprinting is, that it actually combines innate parts with learned ones. It is innate for ducks to follow objects that move and make noises. But the ducks can't know how their mother locks exactly and have to learn a picture of her first (13-16 hours after they hatch).
So sure, it is inborn for ducks to learn the picture of their mother - but they have to learn it first (it is actually obligatory for them to learn as they have to be able to distinguish between their mother and other adult ducks)."
Learned behaviors,"So how does the mat maze work?
Do they let them see the maze from above or what?",No.They create a maze in their brain to the food or whatever. so they find a way to the thing they need so the have something like a maze creator i their brain
Learned behaviors,Can you give an example of a human expressing habituation because I can't think of anything.,"Where do you live? If you live in a city, do traffic noises bother you at night when you're sleeping? Or if you live near train tracks, do trains in the middle of the night disturb your sleep? Someone living in a rural area, or away from trains, may find those sounds disturbing."
Learned behaviors,"I was wondering, what is the term for when a new behavior is being taught, an old one breaks down? For example, if my dog knows how to sit and I am training him to lay down, he now is not sitting or presenting the sit behavior in a more broken and uncertain way.","Simple: the dog forgets trick 1 because the trick is not taught alongside trick 2. 
I make sure that my dog remembers all of her previously taught commands by praising her for old tricks and new ones, acknowledging both."
Learned behaviors,why do animals imprint at a early age?,It could be because of natural selection. I baby animal that knows who and where their mother is will more likely survive than a baby animal that wanders away from the mother.
Population regulation,is  Population stays under carrying capacity logistic or exponential.,"logistical population growth has a carrying capacity, exponential doesn't."
Animal communication,How do animals know if other of their same kind is trying to threaten them??,"Some animals see thermal activity which allows them to see animals around them, if they see movement they are on alert and will either use a defense mechanism or try to run for it. If they relize it is not a threat then they will calm down."
Animal communication,How did communication between organisms evolve?,"From signaling one type of molecule and sensing it among unicellular Prokaryotes to nowadays using colors, shapes, touches, songs, etc among animals and of course using speech in humans."
Animal communication,Can one type of animal communicate with another type?,"Sure, my dogs communicate with me all the time. They tell me when they're hungry, thirsty, want to go outside for a walk, when strangers are at the front, etc..."
Animal communication,Can animals on land communicate to animals underwater?,"It depends on how loosely you define communication. A fish will understand if an osprey communicates its desire to eat the fish by, well, trying to grab the fish. Perhaps there's some poisonous fish that live near the surface and are brightly colored like poison dart frogs. But I'm not sure of any deeper communication than a predator-prey interaction that goes on between land and sea animals."
Animal communication,Whales come to surface for bathing oxygen but when they mistakely come on shore and can't get back why do they die they have all the oxygen they want,They don't suffocate when they're beached. They usually die of dehydration or other injuries due to being beached.
Animal communication,Why is communication important for animals?,"One of the key points at the beginning of the article: Communication behaviors can help animals find mates, establish dominance, defend territory, coordinate group behavior, and care for young.
Those are some reasons!"
Population ecology review,"How isn't population growing when people are having babies and, what is a negative growth rate","Human populations are growing as long as the death rate doesn't surpass the birth rate. In case it does, we're speaking of a *negative growth rate*.

Hope this helps!"
Population ecology review,If people have babies shouldn't the population increase .?,it is increasing and the only way it would stop is if the death rate surpassed the birth rate
Population ecology review,How might a population capacity change in an environment; what's an example?,"If a population is at capacity due to predators, and then some of those predators die due to a virus. The population then doesn’t have as many predators holding it back and the population is able to increase."
Population ecology review,Did  ever find a solution to what happened in Australia?,I heard about a time when Napoleon was hunting and was swarmed by so many bunnies he had to retreat. Haha!
Community structure,"Is it possible for there to be more than one keystone species in an area, as well as foundation species?","Yes, there can be more than one keystones species and foundation species in an area. The densities will be similar for the species but one species can have reduced biomass than the other."
Community structure,Explain why we would expect low species diversity when disturbance/predation occur with a high frequency.,If a lot of the spices are being eaten by predators and disturbances are stopping the species from surviving and reproducing then the species will die off and it will lead to low diversity
Community structure,"Can you explain how, for example, an area with only 7 types of species and a total 27 individuals has greater biodiversity than an area with 10 different species and a total 48 individuals?","Because in the first case there is a smaller number of individuals.

7/27 = 0.25
10/48 = 0.20

Biodiversity is greater in the first case."
Community structure,How does climate shape a biological community?,"Climate is one of the abiotic factors that can introduce variation. According to the videos on niches and competition, no two species can coexist indefinitely if they use the same survival strategy. For example, both wolves and foxes may hunt rabbits, but wolves can run faster so they will eventually outcompete the foxes, driving them to extinction and reducing overall biodiversity. With temperature variation, the foxes' strategy might actually prove better in some years. For example, foxes might have better vision and find it easier to spot rabbits against snow, so they would do better in years with more snow, while wolves will do better in years with less snow. The constant change of climate allows both species to find a niche in otherwise identical conditions and therefore coexist. 

Another example would be tree populations - taller trees grow better because they get more sunlight, so if a single tree was to grow much taller than all the others and grow in an umbrella shape, blocking out sunlight and killing all the trees around it, giving other tress 0 chance of survival. If a tree would be much taller that all other trees, it would be more susceptible to breaking due to wind as it would have to take all the wind resistance by itself. A forest full of trees roughly the same height help each other break wind thus climate (wind intensity or lightning bolts) prevent one tree from pushing out all the others."
Community structure,what are the factors that affect species diversity in an ecosystem,"Several notable factors are listed in the article. I have copied/paraphrased them here.
- Climate of the community's location.
- Geography of the community's location. 
- Heterogeneity (patchiness) of the environment
- Frequency of disturbances, or disruptive events.
- Interactions between organisms
Hope this helps!"
Community structure,what are Dominant species?,"Generally, the predatory species, or species that have a greater amount of members end up being dominant. Hope that helps!"
Endotherms & ectotherms,What is the point of life?,To disappoint your parents.
Endotherms & ectotherms,"I have a question 
Are tuna endotherm or ectotherm? I have ever studied that tuna is Homeotherm in ectotherm. Now I feel confused.","I found this online.

"An *endotherm* is able to regulate its body
temperature via metabolic processes, these are commonly known warm blooded animals.
An *ectotherm's* body temperature is dictated by the environment surrounding it, the animals are commonly and incorrectly known as cold blooded. 
--
*Poikilotherms* are animals that do not require a fixed body temperature, their temperatures can fluctuate with little to no adverse effects to their overall health. Most terrestrial
ectotherm's are poikilotherms, such as snakes and many lizards, also the naked mole rat is considered to be the only mammal poikilotherm. *Homeotherms* are animals that maintain a constant body temperature. All endotherms are homeothermic, but some ectotherms, like desert lizards, are so good at maintaining their body temperature with behavioral means that they are
considered homeothermic."

source: https://faculty.mtsac.edu/trevell/bio2/bio2resources/thermo"
Endotherms & ectotherms,"I have two questions. 
First, is the thermoneutral zone for humans around 24 Celsius or 37? 
And second, why do we feel hot when the environment temperature is 37 Celsius, when 37 is the temperature we want our body to have?","Thermoneutral zone for humans is around 24, not 37.
The thermoneutral zone is defined as the range of ambient temperatures where the body can maintain its core temperature solely through regulating dry heat loss, i.e., skin blood flow. 

*This paper explains*
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4977175/

Why not 37? Because imagine even if we were nude at that temperature (anything above 30 is too much).
Also while it is plausible for our basal metabolic rate, not suitable for _any_ kind of work.

Have you noticed that slightest amount of work even at 27 makes you sweat?

We feel hot because we are _not static objects_ which just conduct temperature. We also _produce_ temperature in our core, plus have a skin which is _an insulator_.

So the reason why you feel hot at 37 is mainly that you have skin _whose surface temperature is lower than 37_ so your body surface is colder and starts absorbing environmental temperature."
Endotherms & ectotherms,Why would one expect the Q10 value of an ectotherm to be around 2?,"If Q10 is 2 it means an increase in the surrounding temperature with an increase in 10 ◦C, and usually resulted in a doubling of the reaction rate.

The Q10 values can be determined from the Arrhenius plots. (In chemical kinetics, an Arrhenius plot displays the logarithm of a reaction rate constant, (, ordinate axis) plotted against reciprocal of the temperature (, abscissa).)
https://www.google.com/imgres?imgurl=https%3A%2F%2Fupload.wikimedia.org%2Fwikipedia%2Fcommons%2Fthumb%2Ff%2Ff6%2FNO2_Arrhenius_k_against_T.svg%2F1200px-NO2_Arrhenius_k_against_T.svg.png&imgrefurl=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FArrhenius_plot&docid=knFyGYn7H893XM&tbnid=k3xTzrdU8e6HCM%3A&vet=10ahUKEwiC3IGzg8blAhUPKlAKHd82DDcQMwhNKAEwAQ..i&w=1200&h=912&bih=625&biw=1366&q=arrhenius%20plots%20for%20temperature&ved=0ahUKEwiC3IGzg8blAhUPKlAKHd82DDcQMwhNKAEwAQ&iact=mrc&uact=8

So I found the paper where Researchers have experimented on _Pseudomonas sp._ (ectotherm, relying upon external temperature) and phenol degradation was referent variable to detect metabolism of _Pseudomonas_.

https://www.researchgate.net/publication/322925209_Estimation_of_the_Q10_value_the_Temperature_Coefficient_for_the_Growth_of_Pseudomonas_sp_AQ5-04_on_Phenol


Again, your questions as *why is that so*?
And I cannot tell you for sure _why_ the rate usually is 2, it was experimentally obtained and concluded.

Probably it has to do something with Laws of Thermodynamics and logic.

Think about it, if it was 3, 4, or 7, what would it mean in BIological terms?! That metabolism would be super fast, and at 30*C, the organism may just burn out in half an hour. And it does not make sense."
Endotherms & ectotherms,"Which between a unicellular organism, ectotherm and endotherm has the highest BMR and which one is the lowest?","This is one of those questions that seem reasonable, but are so dependent on the specific organisms that they are probably impossible to get a useful answer for.

For example, unicellular organisms are incredibly diverse (contain organisms from all three domains of life and from multiple eukaryotic kingdoms) — they will not have similar metabolic rates.
Furthermore, unicellular organisms can't even all be grown at the same temperature — how would you meaningfully compare the metabolic rate of a marine bacterium that lives in arctic waters (prefers 4°C) vs. the rate for an archaebacterium that grows only on a "black smoker " (undersea thermal vent) and prefers 98°C (can grow at up to 122°C):
https://ocean.si.edu/ecosystems/deep-sea/microbes-keep-hydrothermal-vents-pumping

Another example, is what kind of endotherm — a blue whale? an elephant? a shrew? a hummingbird? an ostrich?

...

Well, hopefully you found some of that rant interesting or at least mildly entertaining ..."
Endotherms & ectotherms,Why does temperature affect the breathing and heart rates of ectothermic organisms?,"Because temperature per se affects any kind of work. At higher temperatures, the working machine (or int his case heart) has to work harder and easier gets overheated.

The same way temperature affects Ebdithersm, it also affects Ectitherms, especially because they _rely_ on the temperature. Because temperature directly correlates with metabolism rate.

The greater the temperature faster the metabolism and vice versa.

Here is one interesting paper depicting how also Ectotherms may have energy costs in their metabolisms because sudden increases and decreases impose some kind of stress on bodies. They are physiologically dependant on external temperature and their viability is reduced at extremes.

https://www.sciencedirect.com/science/article/pii/030645659400023C"
Community structure,"Is it possible for there to be more than one keystone species in an area, as well as foundation species?","Yes, there can be more than one keystones species and foundation species in an area. The densities will be similar for the species but one species can have reduced biomass than the other."
Community structure,Explain why we would expect low species diversity when disturbance/predation occur with a high frequency.,If a lot of the spices are being eaten by predators and disturbances are stopping the species from surviving and reproducing then the species will die off and it will lead to low diversity
Community structure,"Can you explain how, for example, an area with only 7 types of species and a total 27 individuals has greater biodiversity than an area with 10 different species and a total 48 individuals?","Because in the first case there is a smaller number of individuals.

7/27 = 0.25
10/48 = 0.20

Biodiversity is greater in the first case."
Community structure,How does climate shape a biological community?,"Climate is one of the abiotic factors that can introduce variation. According to the videos on niches and competition, no two species can coexist indefinitely if they use the same survival strategy. For example, both wolves and foxes may hunt rabbits, but wolves can run faster so they will eventually outcompete the foxes, driving them to extinction and reducing overall biodiversity. With temperature variation, the foxes' strategy might actually prove better in some years. For example, foxes might have better vision and find it easier to spot rabbits against snow, so they would do better in years with more snow, while wolves will do better in years with less snow. The constant change of climate allows both species to find a niche in otherwise identical conditions and therefore coexist. 

Another example would be tree populations - taller trees grow better because they get more sunlight, so if a single tree was to grow much taller than all the others and grow in an umbrella shape, blocking out sunlight and killing all the trees around it, giving other tress 0 chance of survival. If a tree would be much taller that all other trees, it would be more susceptible to breaking due to wind as it would have to take all the wind resistance by itself. A forest full of trees roughly the same height help each other break wind thus climate (wind intensity or lightning bolts) prevent one tree from pushing out all the others."
Community structure,what are the factors that affect species diversity in an ecosystem,"Several notable factors are listed in the article. I have copied/paraphrased them here.
- Climate of the community's location.
- Geography of the community's location. 
- Heterogeneity (patchiness) of the environment
- Frequency of disturbances, or disruptive events.
- Interactions between organisms
Hope this helps!"
Community structure,what are Dominant species?,"Generally, the predatory species, or species that have a greater amount of members end up being dominant. Hope that helps!"
N/A,"reptiles are mostly have 3 1/2 chambered heart which makes them cold blooded
but as an exception crocodiles have 4 chambered heart  but then also they too are cold blooded
why?","Homeostasis is only possible when cardiovascular system is working properly. This means that the system needs to deliver oxygen and nutrients to the tissue fluid that surrounds the cells and also take away the metabolic waste. The heart is composed of arteries that take blood from the heart, and vessels that return blood to the heart. Blood is pumped by the heart into two circuits: the pulmonary and systemic circuits. The pulmonary circuit carries blood through the lungs where gas exchange occurs and the systemic system transports blood to all parts of the body where exchange with tissue fluid takes place. The cardiovascular system works together with all other systems to maintain homeostasis. Homeostasis is the property  which makes an organism either cold blooded or warm blooded.
Though you are guessing right but crocodiles can be said as organisms  which lead to homeostasis by developing  4 chambered hearts coz birds and mammals both evolved from reptiles. Like humans, crocodiles perform homeostasis when the body regulates body temperature in an effort to maintain an internal temperature. They remain in their burrows during the day, coming out at night to hunt in the water, along the banks of the river or pool and into the forest. During the dry season (for those living in savanna areas) they may spend longer period within the burrow."
N/A,"What are mesotherms? I found something on them on another website, but I cannot seem to find what they are, or how something can be sort of warm blooded and sort of cold blooded.","Mesotherms are animals that are neither endotherms nor ectotherms.

animals including tuna, lamnid sharks and leatherback turtles are mesortherms, plus there is the hypothesis that dinosaurs were mesotherms:
https://www.nature.com/news/dinosaurs-neither-warm-blooded-nor-cold-blooded-1.15399

Mesotherms burn energy from within to regulate their body heat, but not to a constant temperature as a mammal or bird would do. Tuna, for instance, stay up to 20 °C warmer than the surrounding water, except when they dive deep into colder waters when their metabolic rate can also plunge.

On the example fo dinosaurs see the advantages:  They would have been able to move around the landscape more quickly than a crocodile but would require less food than a similar-sized mammal. 


Mesotherms have two basic characteristics:

Elevation of body temperature via metabolic production of heat.
Weak or absent metabolic control of particular body temperature.

https://en.wikipedia.org/wiki/Mesotherm"
N/A,how do lizards maintain core heat,"The circulatory system of an ectotherm also plays a major role in temperature regulation. The blood travels everywhere in the body, so if the blood is warm, it keeps the cells warm. Ectotherms have their blood vessels close to the skin for quick heat exchange. Most heat exchange occurs in an ectotherm’s extremities, such as its feet or tail. When it’s cold, they can restrict blood flow to those regions and focus on keeping the vital organs warm.

https://www.osbornepetsupply.com/news/reptile-temperature-regulation/

Which means lizards are capable of maintaining core heat the same way Endotherms are, by using vasoconstriction."
N/A,Is torpor a form of Behavioral strategy or Controlling the loss and gain of heat?,"I think it is both. First of all, it is a behavioral strategy since animals change their behavior, but then again, it directly helps controlling loss and gain of heat and without eating thermoregulation would be much harder.


take a look at some articles:
http://ocwtest.freeculture.ca/bitstream/handle/10680/1503/Breit%20-%20Thesis%20Final%20Copy.pdf?sequence=1&isAllowed=y
https://link.springer.com/article/10.1007/s00442-015-3328-0
https://link.springer.com/article/10.1007/s00360-016-1045-6"
N/A,Do ectotherms use evaporative mechanisms?,"It is noticed in Amphibians:
increased secretions of mucus on some amphibians' 
skins to cool the body with evaporation.

https://socratic.org/questions/how-do-ectothermic-organisms-regulate-their-body-temperature"
N/A,Why do we blush?,"Blushing is caused by an increase of blood flow into the capillaries of the skin on the face. It's typically caused by strong moods, like anger, embarrassment, infatuation, etc.

Did this help?"
Exponential & logistic growth,Why can we just say that the carrying capacity of the seals is 7500? Just because the data seems to imply that?,"Yes! It's an interpretation of field observations. When someone analyzes real world data, the trends that appear can usually be fit to a known mathematical function. In this case, the logistic curve of the data had a carrying capacity of 7500 so that is the inferred capacity for that population. It's a great question though, and considering the spread of that data it might have a significant standard deviation (so 7500 might not be the "exact" carrying capacity)."
Exponential & logistic growth,My textbooks says that "The intrinsic rate of natural increase is biotic potential." what does it mean?,I believe "biotic potential" refers to the availability of resources.
Exponential & logistic growth,Is there any way to include the bounces into an equation? I am talking about the bounces in the last graph.,"You could add error bands to the graph to account for the deviations of the observed values from the values the model predicts. These would not tell the viewer whether a given observation was above or below the predicted value, but they would remind the viewer that the equation only gives an approximation of the actual values."
Exponential & logistic growth,"In Exponential growth there is a line:
"the number of organisms added in each generation—increases as the population gets larger" and
"In exponential growth, a population's per capita (per individual) growth rate stays the same regardless of population size, making the population grow faster and faster as it gets larger." 
Aren't these contradictory?","No, if you have a growth rate of 1 per every 10 people.  If you have a population of 100 people then the number of people added to the next generation is 10 giving a population of 110, the next generation no adds 11 people for a population of 121.  If you continue this table you get this:
```
# added  Total
         100.00
10.00    110.00
11.00    121.00
12.10    133.10
13.31    146.41
14.64    161.05
16.11    177.16
17.72    194.87
19.49    214.36
21.44    235.79
23.58    259.37
25.94    285.31
28.53    313.84
31.38    345.23
34.52    379.75
37.97    417.72
41.77    459.50
45.95    505.45
50.54    555.99
55.60    611.59
```
Each of these generations adds  1 person for every 10 people of the previous generation but since the generations get larger the number of people added get larger as well."
Exponential & logistic growth,My textbook mentions "Geometric Growth" in addition to Exponential and Logistic growth. Could you explain this? Thank you!,"Geometric growth is a situation where successive changes in a population differ by a constant ratio. So while exponential growth is a drastic amount of growth in a short amount of time and logistic is growth that practically stops at some point, geometric growth would be a growth rate that almost never changes. For example, a growth of 2x per hour is geometric growth; every hour, a population doubles, with that rate never changing. So if that population starts with 2, the next hour is 4, then 8, then 16. Exponential growth would be more like 2x^y of growth. Does that make sense? That's the clearest I can think to explain it. Sorry if it's a little confusing."
Exponential & logistic growth,how is a carrying capacity of an ecosystem affected?,"humans have used technology.  When the idea of food as a limitation was providing part of the capacity of a smaller ecosystem, technology that harvested and grew food more efficiently increased how many people the ecosystem could support"
Human impact on ecosystems review,Why doesn't the government do anything like reducing oil mines or cutting down trees.,"It's not really that simple. We need trees for coal and oil mines for well, oil. Without coal and oil, we can't create materials like, well, the device you wrote this comment on. We need to find a better alternative because we can't just stop. As long as people will be buying things, trees will be cut down."
Human impact on ecosystems review,What are the positive human impacts on ecosystems?,There are many positive things happening in ecosystems around the US.  There are many conservation agencies and organizations focused on improving water quality and biodiversity that have shown positive impacts on protecting watersheds and other key conservation targets.  Look at groups like your local Soil and Water Conservation District or The Nature Conservancy in your state to find a few positive examples.
Human impact on ecosystems review,How many new born animals die each day ?,30 million newborns will die within the first 28 days of life between 2017 and 2030. That's sad Dx
Human impact on ecosystems review,Is anything even being done about climate change and why is nothing be said.,"So much is being done!
The problem is that the focus is rarely on what is being done to fix climate change problems and is more on the negative. Many people, like you! have tried to put these issues in the spotlight through little things. So, it is incorrect to think that nothing is being said against these problems or is being done. Look into some of the many ways that are today!"
Niches & competition,What makes a niche an ecological functional role rather than just ecological space,"The majority of species exist in a standard ecological niche, sharing behaviors, adaptations, and functional traits similar to the other closely related species within the same broad taxonomic class, but there are exceptions."
Niches & competition,Why is it not possible for two organisms to occupy the same niche at the same time?,"If two species occupied the same niche, they would be competing for the exact same resources. The competitive exclusion principle states that one of the species would drive the other to extinction. 
NOTE: You probably mean a "species," not "organisms." A species is composed of many organisms, and since those organisms are part of the same species can share the same niche and coexist."
Niches & competition,What are ecological parameters?,"A variable, measurable property whose value is a determinant of the characteristics of an ecosystem."
Niches & competition,What is a Niche? How is it different from habitat? I don't understand.,A habitat is where organisms live (their "house"). A niche is like the organisms "job" they do in the environment.
Life history strategies,Insects come under semelparity or iteroparity?,"I think it depends on the insect. Most insects, such as praying mantises and some moths would fall under semelparity, because they die right after reproduction. (some moths don't even have mouths!) But other insects, like the monarch butterfly, can come back year after year, so that would be iteroparity."
Life history strategies,How can you tell from a life table that the population of the organism is iteroparous or semelparous?,"You might not be able too,  but if you look at multiple tables over week periods, you will notice how a ton of elderly die and the base widens in *semelparity*. When it is *iteroparous*, the pyramid tends not to fluctuate as much."
Life history strategies,"Is there a connection between semelparity/iteroparity and fertilization? Could it be that when the female egg is fertilized frequently throughout an organism's lifetime, iteroparity will occur?",Exactly. The sexual behavior of an animal is intertwined with their parity.
Life history strategies,"Is it true that the more offsprings of one organism survive, the more fit one organism is?","Yes, that is the accepted definition for fitness in evolutionary biology.

To learn more:
https://en.wikipedia.org/wiki/Fitness_(biology)"
Life history strategies,How can you maximize the number of plant species (richness) in the smallest area you can?,To give area with many factors and different niches so plants are not in competitive relations to each other.
Intro to animal behavior,"Do humans exhibit any signs of hibernation, estivation, or migration in response to cues?","Humans don't really hibernate, estivate and migrate in response to cues actually. We don't really have a built-in system of doing these, so i hope this answers your question :D"
Intro to animal behavior,What are barnacles? Do they count as estivation?,"barnacles are a type of arthropod, relating closely to crabs, lobsters, and shrimps. they are often hermaphrodites, meaning they have both female and male sex organs within their bodies, allowing them to be both carriers and distributors in the reproduction process. barnacles don't survive by estivation, as they don't necessarily face the need to hibernate during the day, they just secrete a sticky "glue" and stick themselves to something or the other, and hitch rides until they die."
Intro to animal behavior,"Scientists have this theory that we evolved from apes. If it is true, have humans developed some innate behaviors that apes get? If we don't have them all, doesn't that mean we grew out of habits that were hardwired in our brains. In your opinion, do you think animals will grow out of those behaviors as we go into the future?","Keep in mind that the species that humans evolved from no longer exist, both modern apes and humans (humans are technically still under the classification of ape) evolved from a common ancestor.   

So there may well be innate traits shared between humans and other ape species but they would have been inherited from that common ancestor not each other."
Intro to animal behavior,If a Zebra Finch was raised in captivity but the person who raised it played music would the bird learn to sing a song that is related to the music that was played as it grew up?,"Hi There

That is an interesting question. I'm not sure if there really is a wrong or right answer for this question as the hypothesis would have to be thoroughly tested before one could undoubtedly give an answer. Since Zebra Finches' songs are partly innate and partly learned, I think it would have to depend on the music as well as many environmental factors. For example, if pop or rock music were to be played to it, I doubt any of music would be implemented into its song and it could have affect the birds mental health (and certainly not in a good way). On the other hand, many birds enjoy listening to classical music (which has positive effects on the brain), and parrots specifically, either imitate or show they enjoy it. Although the Zebra Finch would not imitate it exactly, there is the possibility that it would use patterns from the song. I'm honestly not 100% sure though as to whether or not it would use patterns found in the music. 
That said, picture a Zebra Finch which has been raised by humans who acquired it whilst it was still inside the egg. This little Zebra Finch never heard music and it was not was exposed to any other avians. The bird would not have learnt any specific songs, but without doubt, the bird would still sing, creating its own song/s and using different patterns. Likewise, there is a strong possibility that it would not relate its song to the music.

Hope this helps! :)"
Intro to animal behavior,"So, the mother cukcoo bird puts the her egg in some other birds nest, and the bird grows up with a totally different parent. Is it an innate behavior for all cukcoo birds to do that or, when they grow up do they see other birds that look like them doing it. This always confused me. :/ (I read an article on it and I thought it was best to ask the question here.)","I think it's innate. I do also know that the mother cukcoo comes back. If the egg is pushed out, the mother will destroy the other bird's nest and all her eggs/chicks."
Intro to animal behavior,When people started Natural Selection how did those traits and DNA come to mix and Them learn traits from eachother and pass it on from diffrent learned traits and how did they cope?,"DNA is where the information about how specific biological features or processes are encoded.  For example the trait of fur color is controlled by the pigment proteins that specific genes in the DNA code for.  The fur color can help the animal hide or attract a mate.  The better or worse the fur color is at allowing hiding or getting a mate will affect how well the animal is able to have offspring to carry its DNA into later generations.  

For things like learned learned actions it is not the learned actions that are encoded into DNA and passed on but the organisms ability to learn an adapt, this is indirectly the trait that natural selection acts on."
"The periodic table, electron shells, and orbitals","If the Bohr model is an inaccurate representation of electron's movement, why is it so universally accepted?","Because in Bohr’s model for hydrogen atom we consider only Coulombic interactions between one proton and one electron.

It cannot be extended for other atomic species containing more than one electron. Because in this case in addition to the interaction between nucleus and electron there arises the interactions between electron and electron of the same species. Bohr couldn't solve this problem and this problems are successfully explained on the basis of later developed quantum mechanics.o

But Bohr's model can be applied successfully for hydro genic species like He+, Li2+ etc……."
"The periodic table, electron shells, and orbitals","I'm kinda also confused on what an electron shell is and what an electron subshell is. Is the elctron subshell the s, p, d and f orbitals? And is it a probability function describing where an electron is likely to be? What's the difference between an electron shell and subshell?
Thanks c:","All atoms are made up of energy levels (called shells) that hold 1 or more subshells.
Each subshell holds a certain type of orbit.

Each individual subshell has slightly varying energies from its "shell" energy level, depending on the distance from the nucleus.

Every subshell has a # of orbits s/p/d/f that can each hold 2 electrons each (one has the opposite spin of the other).

The first shell (of all atoms) has 1 subshell of s-orbitals containing 1 s orbital. This means that the first shell can hold 2 electrons.
The second shell has 2 subshells: 1 s-orbital and 3 p-orbitals. This means that the second shell can hold 8 total electrons.

Every orbital is a shape (that can be determined by a trigonometric function I believe). This shape tells us where it is likely to spend most of its time, so in a sense it is a probability function.

Hope this helps someone. :-)"
"The periodic table, electron shells, and orbitals",How can you determine the number of outer shell electrons based on the full electron configuration?,"I'll try to explain with the help of an example. Consider Sodium (Na)
Its electronic configuration is 1s2, 2s2, 2p6, 3s1
The largest value of the Principle Quantum Number (n) is 3, so that is the outermost orbital.
Counting the number of electrons, we find that only the s orbital is present and it has only one electron. So Na has one electron in its outermost orbital.

Another example that I'll use is Fluorine (F).
Its electronic configuration is 1s2, 2s2, 2p5.
Since the largest value of n is 2, we count all the electrons in the s and p orbitals that have n = 2. So we get 2 + 5 = 7. So fluorine has 7 electrons in the outermost shell.

Basically, count the number of electrons in the orbitals with the highest principle quantum number, and that'll give the number of electrons in the outermost shell."
"The periodic table, electron shells, and orbitals","I'm confused about all the 1s2 2s2 and 2p6.  It's hard for me to understand, I was wondering if you could help out with that?","The 1s is the first orbital electron shell and it is closest to the nucleus. The 2n is the second shell. It consists of the 2s and 2p shells. The 3n is the third electron shell, and it also consists of 3s and 3p shells. The number after it stands for the amount of electrons in each orbital."
"The periodic table, electron shells, and orbitals","In the second last paragraph, I don't really get why because of the d subshell having more energy, argon is stable with 8 valence electrons? Thanks",I am not sure where the confusion is. Argon has a full outer shell of electrons already. It will not have a d-subshell
"The periodic table, electron shells, and orbitals",How do scientists figure this out? Do we have microscopes powerful enough to view atoms and observe this behavior or is there some other method?,"No, it can't be figured out using microscopes. Most of it is based on theory worked out using a lot of maths. Experimental observations, such as the energy released or absorbed when electrons move from one state to another, corroborate the theory.

Experimental observations, using techniques such as X-ray crystallography, provide information on the shape of molecules which, in turn, corroborates the theoretical shapes of the orbitals."
"The periodic table, electron shells, and orbitals",How much space does electrons take up,"Overall, the electrons are much smaller than the protons and neutrons. But, they take up more space when you think about how they move. They are constantly moving, and at different wavelengths and frequencies. And, they also move fast and they act like gas particles, in a way."
"The periodic table, electron shells, and orbitals",Can Hydrogen lose its only valence electron? Can an element exist without electrons?,"Hydrogen can lose its one electron and became an ion, or the hydrogen cation H^(+). However, it is so reactive that it does not exist for long before reacting with other atoms.  

Hope that helps."
Photoelectron spectroscopy,Is there a substantive reason for the distinction in terminology between the work function and the binding energy? Does the difference simply exist to dinstinguish between contexts?,"The distinction between work function and binding energy exists primarily to distinguish between different contexts and conceptual frameworks.

The work function refers specifically to the minimum energy required to emit an electron from the surface of a material into vacuum. It is considered in the context of electrons interacting with a material surface.

Binding energy, on the other hand, refers more generally to the energy required to separate constituents that are bound together. It is used in a variety of contexts beyond just electrons and material surfaces.

So the work function deals specifically with the energy required to remove an electron from the surface of a material, while binding energy is a more general term that can refer to the energy required to separate any kind of bound particles or entities.

Though numerically these values may be similar for a given system, the work function and binding energy terminology serve to clarify the conceptual framework being considered:

• Work function - focusing on electrons interacting with a material surface

• Binding energy - considering a more general interaction between any type of bound particles

So in summary, while the numerical values may coincide in some cases, the work function and binding energy concepts originate from different frameworks and serve different purposes. The distinction in terminology helps clarify whether we are focusing specifically on electron emission from a material surface or considering a more general separation of bound particles. The difference is primarily one of context and emphasis rather than substantive numerical difference."
Photoelectron spectroscopy,"In the third paragraph, how the energy analyzer "count" number of electrons correspond with one determined ionization energy ? Are there any proportion of energy to that number !","I don't think there can be a simple proportion of ionization energies from element to element. Remember, the Bohr model [E=(1/n^2)*13.6eV] fails beyond H and He+ so the ionization tables that this article refers to are empirical."
Photoelectron spectroscopy,"When analyzing the binding energy of an element, does it matter what type of ionizing energy is first used to eject the electron(s) from a sample? 

For example if you first bombarded a sample with XPS (according to the description under the subtitle "The basics of photoelectron spectroscopy" this would in theory eject the core electrons) would this alter the binding energy data? If the core electrons were ejected prior to the valence electrons, wouldn't shielding effects be attenuated and consequently, the binding energy of the outer-shell electrons would be increased?","Yes, your thinking is correct. However, we can quite safely assume that you would not hit the same atom twice during the experiment. Hence, you should not see this effect in the spectra."
Photoelectron spectroscopy,"The PES spectra show all electrons in a given shell to have the same binding energy. But that leads me to two questions on the same topic. If it were because other electrons were blocking it, than wouldn't further ionizing an already ionized sample make it easier? Or, if it had to do with the fact that protons are positive and electrons are negative, and therefore it takes more energy to remove more electrons to counteract the unequal charge, wouldn't the positive charge increase even more the moment one electron in a shell is removed, therefore increasing the binding energy for every electron rather than for every shell?","You are correct that after the first ionization event, the energy of the orbitals changes. However, in PES we can safely assume that you will not ionize the same atom twice. Hence, all peaks correspond to the ionization of the neutral atom."
Photoelectron spectroscopy,"I thought an electron has a huge amount of kinetic energy in the atom, I heard that it is moving at a third of the speed of light. Why is this not taken into account?","Electrons do have a significant amount of kinetic energy in atoms due to their high velocity. However, this kinetic energy is generally not taken into account when calculating work functions and binding energies for a few reasons:

The kinetic energy of electrons in atoms is not well-defined. Due to the Heisenberg uncertainty principle, we cannot precisely know both the position and momentum of an electron at the same time. So while we know electrons move fast, we can't pinpoint their exact location and velocity.

The important energy for work function and binding energy calculations is the potential energy, not the kinetic energy. The potential energy determines how strongly the electron is bound to the atom and how much energy is required to remove it. The kinetic energy, while large, does not reflect the strength of this binding.

When an electron is removed from an atom, its initial kinetic energy is lost and it gains new kinetic energy based on the work function or binding energy. So its final kinetic energy depends on the difference in potential energies, not its initial kinetic energy within the atom.

Work functions and binding energies are measured experimentally by seeing how much energy is required to remove an electron. This measures the change in potential energy, not any initial kinetic energy the electron may have had.

So in summary, while electrons do have significant kinetic energy due to their fast motion within atoms, this kinetic energy is generally ignored when calculating work functions and binding energies. The important factor is the change in potential energy, which determines how strongly the electron is bound and how much energy is required to remove it from the atom. The initial kinetic energy is lost during this process."
Photoelectron spectroscopy,"can you have the PES graph of an ion like Li+? If so, how would you be bale to tell the difference from the graph of an element that looks the same like He in this case?","I don't know the answer but from what I have read so for in this article once you eject an electron from one of its shell the binding energy changes. Lets say you would eject an the valence electron in this case the 2s electron from Li. Since the nucleus of Li has three protons and Helium has two 1s^2 electrons the binding energy for the remaining 1s^2 for Li+ would be different compared to the binding energy of the 1s^2 from He. I would belive this to be the case since the effective charge of the nucleus is not the same as for He. So I would believe if one could have a PES graph for ion like Li+ it would be different from the graph of He. 
Could it be so that the the binding energy would by shifted by som factor for the two peaks compared with the peaks of He? Lets say He has it 1s^2 peak at 100 MJ/mol would it be the case then that Li+ (assuming that the 2s electron was ejected) would have it lets say a PES graph of peak of 130 MJ/mol. The 130 is just arbitrary I'm thinkin of som factor a>1 => 100*a is the new peak."
Photoelectron spectroscopy,"I'm curious - is there a way that a travelling electron can further increase its kinetic energy? For instance, if it was hit by another photon or traveled next to a negative charge. Or will it maintain the energy once got knocked off, until affected by other charges..","You can increase the kinetic energy of charged subatomic particles by accelerating them through an electric field. This is the basis of particle accelerators.

I don't think a travelling electron can absorb energy from a photon - at least, I've never heard of that happening but it might be a question better answered by a physicist."
Photoelectron spectroscopy,"It states that, "However, the binding energy of the 
1s peak is not equal to the second ionization energy of lithium. Once the first electron is removed from lithium, the 1s,  electrons will be held even more tightly by the nucleus, increasing the binding energy of these electrons." 

So it's saying that the second ionization energy is not equal to the second binding energy, in the sense that when you ionize it initially it changes the electron configuration making the electrons closer to the nucleus less shielded by the outer electrons. However, I don't see the difference between sequentially removing an electron from an atom and measuring the electron ionization energy to photoelectron spectroscopy's binding energy. 

Both of those methods remove electrons sequentially and measure their energies, so why can't you determine the second ionization energy from a photoelectron spectroscopy chart?","at first glance, it may seem like photoelectron spectroscopy binding energies should correspond directly to ionization energies. However, there are a few key differences:

Ionization energies measure the energy required to remove an electron from a neutral atom, leaving an ion. Binding energies, on the other hand, measure the energy of electrons within an already ionized atom.

As you noted, removing the first electron changes the electron configuration, pulling the remaining electrons closer to the nucleus and increasing their binding energy. This effect is not accounted for in ionization energy measurements, which consider the removal of each electron independently from the neutral atom.

Ionization energies refer specifically to the process of electron removal - ejecting an electron into vacuum. Binding energies, however, reflect the energy of the remaining electrons within the ionized atom, not just the energy required to remove them.

Experimental measurements of ionization energies and binding energies involve different processes. Ionization energies are measured by exposing atoms to radiation or electric fields and detecting the ejected electrons. Binding energies are determined from the kinetic energies of photoelectrons ejected from ionized atoms."
Photoelectron spectroscopy,what is first ionization energy and second ionization energy ?,"Ionization energy is energy required to remove the outer most electron from an atom. The first ionization energy would be the energy required to remove the first electron, the second ionization energy would be the energy to remove the second electron, and so on. The reason it's called ionization is that when you remove an electron from a neutral atom, it becomes a positively charged ion, or cation, having lost a negatively charged electron. Hope that helps."
Isotopes and mass spectrometry,"What is a neutrino? Also, what are quarks, gluons, mesons and bosons? A detailed explanation, please.","Neutrinos are fundamental particles similar to electrons but without a charge. Electrons and neutrinos are in a class of particles called leptons. 

Quarks are fundamental particles that are the constituent particles of matter. They combined to form a class of composite particles called hadrons. Hadrons include protons and neutrons, as well as mesons, which are quark-antiquark pairs.

Bosons are force carrying particles. They include: photons which mediate the electromagnetic force, gluons which mediate the strong force, W and Z bosons which mediate the weak force, the hypothetical graviton which mediates gravity, and the Higgs boson which mediates the Higgs field. Gluons are the bosons that quarks use to 'stick' together, but they also have the unusual property that they can stick to themselves too."
Isotopes and mass spectrometry,"At the end of this reading material, when determining the atomic weight of zirconium, why is the answer to the product of (0.0280 x 95.908u) equal 2.68u and not 2.69u?  I actually got 2.685424 and rounded up, but in the equation they figured, they did not round up as done normally in math.  I'm lost.  I actually got 91.24 to this equation.  So...can someone please explain the reasons behind not rounding up when appropriate??",I just want to mention here about significant figures. In science all numbers are rounded using significant figures. A nice video on khan academy teaches how to round in this way https://www.khanacademy.org/math/arithmetic/decimals/significant_figures_tutorial/v/significant-figures
Isotopes and mass spectrometry,"In the 5th paragraph it is said that "1 u is equal to exactly 1/12 of the mass of a single neutral atom of carbon-12". However if you add:
6 protons times |.007 u + 6 neutrons times 1.009 u= 12.096  (mass of carbon-12)
and then we divide by 12 we get something greater than 1 u.
Should n´t the mass of 1 u be  between the mass of the proton and the neutrón   1 p < 1 u <1 n?  So that the atomic mass for carbón-12 be exactly 12 u?","The total mass of 6 protons + 6 neutrons is indeed 12.096 u.
But these are *isolated* protons and neutrons.
Energy is released when you bring them together to form a carbon-12 nucleus.
Energy is equivalent to mass (E =mc²), and the energy released is equal to 0.096 u.
This difference is called the *mass defect*.
So the mass of a carbon-12 atom is 12.096 u – 0.096 u = 12.000 u"
Isotopes and mass spectrometry,"Historically, the units u and amu were defined slightly differently. Can someone please clarify?",Atomic mass units used to be defined on oxygen and it wasn't consistent in definition between chemistry and physics. It was redefined to Carbon-12 to unify all measurements in physical and chemical sciences and to be consistent. This was officially termed 'unified atomic mass unit' and the symbol set as _u._
Isotopes and mass spectrometry,Hey everyone...i just started learning chemistry (yep i'm a newbie) and i still can't understand the meaning of a charge...could i request a little help please? thankiew:),"Charge is just a fundamental property of an object or particle, just as mass is.  An object's mass tells you how hard a gravitational force will pull on the object.  An object's charge tells you how hard an electrical force will pull on the object. 

There's a lot more about it here
https://www.facebook.com/notes/ask-andrew-high-school-physics/electric-charge-and-field-ib-topic-51/675755755903814"
Isotopes and mass spectrometry,"why is it that 0.0280×95.908u = 2.68u
I used my calculator got this: 2.685424
if you round it to the hundredths place
you would get 2.69  [5 is a midway number, 
   so we should round it off to the higher hundredth]
Please explain what is going on.
thanks","Yeah, you’re right, they rounded that last number incorrectly, it should be 2.69 u if they wanted only three sig figs (or two decimal places). In this case whether it is 2.68 or 2.69, the final answer, with sig figs, remains the same. 

Really though, we shouldn’t be rounding for intermediate answers like the multiplication parts and only round at the very end to limit rounding errors affecting the final answer.  

Hope that helps."
Isotopes and mass spectrometry,Are there any disadvantages of mass spectrometry,"No "disadvantages" but limitations instead: mass spectrometry will not tell you anything about a structure directly. Also, some types of spectrometry will not allow every molecule to be fragmented in every possible way."
Isotopes and mass spectrometry,"In the section "Calculating the atomic weight of chlorine" you state:
atomic weight of chlorine=(0.7576×34.969 u)+(0.2424×36.966 u)
Where did the numbers 34.969 u and 36.966 u come from?  
Shouldn't they be:
for Cl 35 = 17 protons + 18 Neutrons = 17 x 1.007u + 18 x 1.009u = 35.281 u
and
for Cl 37 = 17 protons + 20 neutrons = 17 x 1.007u + 20 x 1.009u = 37.299u

FOLLOW UP TO QUESTION ABOVE:
okay, I found a table of atomic masses for all elements and their isotopes and the numbers you give are the same as what they give on the table. However, this confuses me even more.  You did say in the lesson above that "a proton has a mass of... 1.007 u.... A neutron is slightly heavier, with a mass of }1.009 u". Those are the numbers I used in my calculations above.  But to make the calculation work, the atomic masses have to be less than those I used (as per the table).  How can the weight of a proton and neutron change from element to element?","Adding up the individual masses of protons and neutrons doesn't work. You also need to account for the mass of electrons (yes, these make a small difference in getting to the exact mass) and binding energy when calculating the total atomic mass of an atom. Binding energy needs to be looked up for each individual isotope you are working with as it varies."
Isotopes and mass spectrometry,What is a subatomic particle?,""sub-atomic" literally means "below the atom." When we discuss subatomic particles, we talk about any particles smaller than the atom. These could be quarks (up/down quarks, which make up protons and neutrons), leptons (neutrinos but also electrons), as well as bosons. These are typically discussed in particle physics and less often in chemistry."
Isotopes and mass spectrometry,"Oh come on, I got 91.31u because I didn't round at each step, only at the end?","We really shouldn’t be rounding at intermediate steps, only at the final step. The issue is that when we round too soon it introduces rounding errors which trickle down to the final answer. It is important to keep in mind the amount of significant figures allowed after each operation to know how much you need to round off your final answer. 

If you do the full calculation without any premature rounding you should get 91.22377 if you do everything correct. Which would round off to 91.22 using proper significant figures. 

Hope that helps."
Oxidation–reduction (redox) reactions,Shouldn’t equation H2 + O2 -> 2 H2O be balanced to 2 H2 + O2 -> 2 H2O?,"I'm not seeing that original equation you wrote. Did they change the document above?

EDIT: I guess, they did."
Oxidation–reduction (redox) reactions,"In the last paragraph, it states  that there is a transfer of electrons. Is there not always a transfer of electrons?","There is not always a transfer of electrons (not all reactions are redox reactions). An example of a reaction that is not a redox reaction might be a neutralization reaction:
H3O+ + OH- ---> 2 H2O
The oxidation number of H is +1 and the oxidation number of O is -2 for for both the reactants and products, so it is not a redox reaction."
Oxidation–reduction (redox) reactions,"Is it possible to have reaction where only oxidation or reduction happens, or does the occurrence of one result in the other? Thank you.","They must both occur. The sum of all the oxidation states cannot change unless there is a change in the overall charge of the ion/molecule. Even with a change in the charge, there must be somewhere else that the change in charge (and thus oxidation states) is exactly offset. That is because of conservation of electrical charge."
Oxidation–reduction (redox) reactions,What is the difference between a monatomic ion and an atom in its elemental state?,"An ion is an atom that has gained or lost electrons. Atoms in their elemental state are not ionised. 

Also, atoms in their elemental state can be joined to other atoms. For example, H2 is the elemental state for hydrogen."
Oxidation–reduction (redox) reactions,"Above it says, "oxygen is usually assigned a −2 oxidation number (except in peroxide compounds where it is −1, and in binary compounds with fluorine where it is positive);"

The part where it says "...with fluorine where it is positive", did they mean +1 or +2? Or did they mean, it varies depending on the binary compound with fluorine but it'll always be positive?",With Florine it forms OF2 where it shows +2 oxidation state otherwise it shows a -1 or -2 oxidation state
Oxidation–reduction (redox) reactions,do we have to memorize these rules?,"I mean, if you want to solve redox problems, yeah."
Oxidation–reduction (redox) reactions,What is the use of knowing about oxidation numbers ?,"Knowing oxidation numbers allows you to predict what compounds or reactions will form when different elements mix together. This is really important, as you will need to be able to write compounds and reactions to do everything else you will learn in chemistry.
I hope this helps!"
Oxidation–reduction (redox) reactions,Does anyone know what the OH radical is? It is in one of my compounds for my experiment,The OH radical (hydroxyl radical) is the neutral form of the hydroxide ion. Hope this helps.
Stoichiometry,"1 mole of Fe2O3" Can i say  1 molecule ? Because im new at this amu/mole thing,"No, because a mole isn't a direct measurement. Mole is a term like dozen - a dozen eggs, a dozen cows, no matter what you use dozen with, it always means twelve of whatever the dozen is of. So a mole is like that, except with particles. There are always 6.022*10^23 atoms in a mole, no matter if that mole is of iron, or hydrogen, or helium."
Stoichiometry,"How did you manage to get [2]molNaOH/1molH2SO4. 
How will you know if you're suppose to place 3 there? Or 4?","Go back to the balanced equation.
2 NaOH + H2SO4 -> 2 H2O + Na2SO4
Look at the left side (the reactants). You have 2 NaOH's, and 1 H2SO4's. The ratio of NaOH to H2SO4 is 2:1. So you get 2 moles of NaOH for every 1 mole of H2SO4. I hope that answered your question!"
Stoichiometry,Where did you get the value of  the molecular weight of 98.09 g/mol for H2SO4?? Are we suppose to know that?,"To get the molecular weight of H2SO4 you have to add the atomic mass of the constituent elements with the appropriate coefficients.
Here the molecular weight of H2SO4 = (2 * atomic mass of H) + (atomic mass of S) + (4 * atomic mass of O)
Hope that helped!"
Stoichiometry,Is mol a version of mole? I just see this a lot on the board when my chem teacher is talking about moles.,"Mole is the SI unit for "amount of substance", just like kilogram is, for "mass". And like kilograms are represented by the symbol 'kg', moles are represented by the symbol 'mol'. That's it! :)"
Stoichiometry,I not able to get it,What do you need help with?
Stoichiometry,"hi!
i am new to this stoichiometry,i am a bit confused about the the problem solving tip you gave in the article.","What it means is make sure that the number of atoms of each element on the left side of the equation is exactly equal to the numbers on the right side. The equation is then balanced. 

If the numbers aren't the same, left and right, then the stoichiometric coefficients need to be adjusted until the equation is balanced - earlier videos showed how this was done.

When counting up numbers of atoms, you need to take account of both the atom subscripts and the stoichiometric coefficients. For example, Fe2O3 contains two iron atoms and three oxygen atoms. However, if it was 2Fe2O3, then this would be four iron atoms and six oxygen atoms, because the stoichiometric coefficient of 2 multiplies everything."
Stoichiometry,Can someone tell me what did we do in step 1? why did we multiply the given mass of HeSO4 by 1mol H2SO4/ 98.09 g HeSO4?,"That is converting the grams of H2SO4 given to moles of H2SO4. When we do these calculations we always need to work in moles.
Why moles? Because 1 gram of hydrogen has more atoms than 1 gram of sulfur, for example. But 1 mole of hydrogen has exactly the same number of atoms as 1 mole of sulfur."
Stoichiometry,What is the purpose of crossing out some of the units in these stoichiometry calculations?,It's to figure out what the units are for your answer. for example. Let's say you have 3 moles of carbon. And you want to find the mass of your sample. The molar mass of carbon is about 12 g/mol. so 3 mol*12 g/mol. You cross out the moles on both sides of the fraction to give you grams for your units. So 36 Grams of carbon.
Stoichiometry,What is the relative molecular mass for Na?,58.5g is the molecular mass of na
Stoichiometry,Is there a simpler way to to this?,This is the simple way.
Balancing redox equations,"Why is the reduction half reaction is written like this:
2H​+​​(aq)+2e​−​​→H​2​​(g)
Isn't it:
H​+​​(aq)+2e​−​​→H​2​​(g)

Since the base equation contains:
H​+​​(aq) -> H​2​​(g)

I do not understand this...","H​+​​(aq)+2e​−​​→H​2​​(g) balances neither the charge nor the mass.
Left side: Charge of -1; one H
Right side: 0 charge; 2 H atoms (bonded as H2)
For balancing Redox reactions, it is necessary to first balance the main atoms (through adjusting stoichiometric coefficients), then the charges (through electron transfer and as per conditions - acidic/neutral/basic)."
Balancing redox equations,"In the example of combustion reaction, the oxidation number of C in C8H18 comes out to be -9/4. How is this possible? Electrons cannot be transferred in fractions right?","It may be better to consider that there are two different carbon oxidation numbers rather than the fractional one. 

The two on each end are bonded to 3 hydrogens so are -3, the six in the middle are bonded to 2 hydrogens so are -2"
Balancing redox equations,"It says above for Disproportionate Reaction: "If we analyze the oxidation numbers for chlorine, we see that the reactant ClO− ​is being oxidized to ClO​3​− (where the oxidation number increases from +1 to +5)."

I can't see what goes from +1 to + 5. Is it Cl? If so, how so?","Cl is +1 in ClO^- and goes to +5 in ClO3^-

As oxygen is more electronegative than chlorine (in the Pauling scale), we assign it its preferred oxidation number which is -2. 

In a molecule the oxidation numbers of all atoms sum to the charge. 

So in ClO^- the oxidation numbers need to sum to -1. If oxygen is -2 then chlorine needs to be +1

-1 = Cl + O
-1 = x + -2
x = +1

For ClO3^- it's the same idea, but now we have 3 oxygens. 

-1 = Cl + 3O
-1 = x + -6
x = +5"
Balancing redox equations,"In the Practice question above, it does not specify what type of redox reaction it is. How do I know what type it is and what to put in as my answer? P.S. I got it wrong.","Compare the reaction to the types explained in the article -- 
1) Is there molecular oxygen (O2) involved? *NOPE* not oxidation
2) Has a single reactant undergone both oxidation and reduction? *NOPE* not disproportionation
3) Are two elements trading places within a compound? 
Doesn't look like it, but what if we look at the complete equation (rather than the net ionic equation we are given).
• there must be a counter ion that came with the "H+" ... let's pretend that we added HCl ...
This gives us the reaction:
`Al(s) + HCl(aq) → AlCl3(aq) + H2(g)` 
Now we can see that it fits the definition for a single replacement reaction!


To answer the question you don't need to know what type of reaction it is, you just need to make sure that you've balanced electrons (charges) as well as atoms.

The method shown above is to separate the oxidation and reduction reactions into half reactions ... did you try that?"
Balancing redox equations,What do you mean by saying "we can check to see if any reactants and products appear on both side"? Do you have an example?,"In this context, I think what he means is that if any ion is in an identical form on the left and right side of the equation then they cancel out and can be crossed out. In other words, identify any spectator ions."
Balancing redox equations,Why is MnO4 reduced and not oxidised ? It was an anion (permanganate) and became neutral MnO2 so it must have LOST electrons?,"We compare the oxidation states of atoms to determine if they’ve been oxidized or reduced. For the half-reaction of permanganate going to manganese dioxide, we’re comparing the oxidation states of the manganese and oxygen atoms individually, not the entire ions. Oxygen almost always has a -2 oxidation state so it stays constant here and is neither reduced or oxidized. Manganese begins with a +7 oxidation state in permanganate and is reduced to +4 in manganese dioxide. Since the oxidation state decreased, it was reduced. 

Hope that helps."
Balancing redox equations,Where does the water from the combustion example go? (car engine example) Steam?,"Yes, you are correct in the form of vapour it comes out of the engine and enters the air."
Balancing redox equations,"For Fe2O3, I know that the oxidation mu,her for oxygen is always -2 but then it says that the oxidation state of iron is +3. How does that make the compound neutral? Wouldn't the charge be +1 and not neutral?","You aren't taking in to account that there are 2 iron atoms and 3 oxygen atoms in one Fe2O3 molecule. 

3 oxygens with oxidation numbers of -2 each, -2 * 3 = -6
Fe2O3 is a neutral molecule so we know the oxidation numbers all must sum to 0
So the two irons must have oxidation numbers that equal +6, +6 / 2 = +3"
Balancing redox equations,"1.)Im not sure how to recognize if the oxidation number is -2 or +2.....
2.)For example, in CO2, is 2 the oxidation number or the number of atoms or the valency??
Pls answer in detail...Im really confused.","The oxidation number is the number of valence electrons an atom is assumed to have when the electrons are counted according to certain arbitrary rules.
Two important rules are;
1. The oxidation number of O in its compounds is almost always -2.
2. The charge on a molecule or ion is equal to the sum of the oxidation numbers of its atoms.
Thus the oxidation number of an O atom in CO₂ is -2.
The two O atoms have a total oxidation number of -4.
Since CO₂ is neutral, the oxidation number of C is +4."
"Molecular, complete ionic, and net ionic equations","Just to be clear, in the problem H and OH are not spectator ions because they form a compound with a covalent bond as a product, rather than one with an ionic bond?","Yup! To be more specific, they form a covalent molecule as opposed to a soluble ionic compound (if they made an insoluble ionic compound, they would not get cancelled out as spectator ions either)."
"Molecular, complete ionic, and net ionic equations",how do you know whether or not the ion is soulable or not?,You need to know the dissociation constant but it is not uncommon for ionic salts to dissolve in water
"Molecular, complete ionic, and net ionic equations","In getting the net iconic equation from the above equation, why did we have to get rid of the stoichiometric coefficient in front of each  chemical species in the net ionic reaction in order for the answer to be correct?","I'm assuming that you're talking about the last reaction—H2SO4 (aq) + 2 NaOH (aq) → Na2SO4 (aq) + 2 H2O (ℓ).

When we break this up into its ions, we get H2 (aq) + SO4(2−) (aq) + 2 Na+ (aq) + 2 OH− (aq) → 2 Na+ = SO4(2−) (aq) + 2 H2O(ℓ). So we can "cancel" the 2 Na+ (aq) and the SO4(2−) (aq) on each side. Okay.

Then the resulting reaction is H2 (aq) + 2 OH− (aq) → 2 H2O (ℓ). But when diatomic hydrogen dissolves in water to form H2 (aq), the protons are separated, so we really just have 2 H+ (aq) + 2 OH− (aq) → 2 H2O (ℓ). *Now* the factor of two is redundant, so we factor it out to get the result listed: H+ (aq) + OH− (aq) → H2O (ℓ)."
"Molecular, complete ionic, and net ionic equations","How can we tell if something is a strong base or acid? It seems kind of important to this section, but hasn't really been spoken about until now.","Memorize the six common strong acids: HCl, HBr, HI, HNO₃, H₂SO₄, and HClO₄.
At this stage, if your acid isn't one of these, it is almost certainly a weak acid.
Most metal hydroxides are strong bases.
If your base isn't one of these, it is probably a weak base."
"Molecular, complete ionic, and net ionic equations",I have a question....I am really confused on how to do an ionic equation....Please Help!,"Without specific details of where you are struggling, it's difficult to advise. But often, if you don't understand one tutor's presentation then it's worth seeking out other teachers who might explain the topic differently. 

If you put _ionic equations_ into YouTube there are lots of videos that may help you."
"Molecular, complete ionic, and net ionic equations","Why when you divide 2H+ by two do you get H+, but when you divide 2Na- by two it goes away?","You're not dividing the 2Na- to make it go away. It goes away because it's a spectator ion (it's unchanged during the reaction so it is present on both sides of the equation and you can cross them out).

You should end up with:
 2H+(aq)  +  2OH-(aq)  -->  2H20

You can then divide all of these by 2 (like simplifying a math problem) to get:
H+(aq)  +  OH-(aq)  -->  H20"
"Molecular, complete ionic, and net ionic equations",What are cation and anions,"Cations are atoms that have lost one or more electrons and therefore have a positive charge.
Anions are atoms that have gained one or more electrons and therefore have a negative charge."
"Molecular, complete ionic, and net ionic equations",how come AgCl doesnt dissolve in water is it not a salt like NaCl? what is the difference between the two that makes one not dissolve in water?,"While both are sodium chloride and silver chloride are ionic compounds, sodium chloride is soluble and dissolves easily in water while silver chloride is insoluble and does not dissolve much into water. The key is the energy associated with the dissolving process. An energy input is required to break bonds, and energy is subsequently released when bonds are formed. The same is true here. 

For an ionic solid to dissolve, the solvent (in this case water) has to break the ionic bonds then surround the ions and form new ion-dipole bonds in a solvation shell. For the dissolution process to be successful, we must release more energy than is required to break the bonds. If more energy is required to break the bonds than is released during bond formation, then the solid is insoluble. In sodium chloride, the ion-dipole bonds release more energy than was required to break the ionic bonds so it is soluble, but for silver chloride the ion-dipole bonds release less energy than is required to break the ionic bonds so it is insoluble. 

Hope that helps."
"Molecular, complete ionic, and net ionic equations","I know this may sound silly, but can we subtract or add a reactant to both sides just like in mathematics?","Mathematically it's completely acceptable to do so, however we have to consider the actual chemical makeup of our reaction if we do so. For ionic equations like these it's possible for us to eliminate, essentially subtract out, spectator ions from an equation. So these are ions which are present in the reaction solution, but don't really participate in the actual reaction (they don't change as a product compared to when they were a reactant). So since they're not participating in the reaction, subtract them is allowed because it doesn't affect the reaction if they're absent from the equation.

In redox reaction it's common to add water, H+, and OH- ion to the equations when balancing them. Now in this case where we're adding chemicals to the equation it may just seem like we're adding chemicals out of convenience to make the math work out. However if it's an aqueous solution, these added chemicals are technically always present in the reaction solution and what we're actually doing is recognizing that some of them are actually part of the redox reaction. So it's not much that we're adding chemicals rather we're discovering the actual reaction occurring.

So we can add/subtract in chemical equations, but its can't just simply make mathematical sense, it also has to make sense in a chemistry context.

Hope that helps."
"Molecular, complete ionic, and net ionic equations",why can the reaction in "Try it" happen at all? There is no solid in the products.,"A solid precipitate isn't the only thing you look for in net ionic equations, you also look for neutral covalent compounds like water forming. In acid/base reaction it's common for the H+, OH-, and H2O to be the only species left in a net ionic equation after all the other spectator ions have been eliminated. Hope this helps."
Limiting reactant and reaction yields,"It said that if you get a percent yield over 100 it'sometimes because you made a mistake in the lab, which makes sense to me, but I've heard that there can be other, more scientific reasons.... how does that work?","Nice question! The theoretical yield is maximum 100% by definition. You can run an experiment correctly and still get >100% although It's not quite a "mistake" as you say: your final product will often include impurities (things other than your pure desired compound) so it will seem like you made more than you could have gotten because you also weigh the impurities. The other, simillar, reason is that your final product is not completely dry, in which the "impurity" would be water."
Limiting reactant and reaction yields,"In Step 3, Calculation of Percent Yield  the equation shows 1.82/2.15 as equaling 83.9%. I believe it should say 84.7%, If I'm incorrect in this I blame Texas Instruments the producer of my calculator. ","You are correct. The answer is not 83.9, but 84.6.
It's 84.6 instead of 84.7 because of minor rounding issues.

Kudos to Texas Instruments."
Limiting reactant and reaction yields,Where do you get the actual yield from? Thanks:),"If speaking in terms of doing a lab or experiment, the actual yield comes from the actual result of the lab (hence the name)."
Limiting reactant and reaction yields,"For the percent yield equation, must the equation be in grams or can it be done in moles as well?","You can use whatever units you wish, provided the actual yield and the theoretical yield are expressed in the same units."
Limiting reactant and reaction yields,"On a standardized test, how would you distinguish differences between a solely stoichiometric problem and a limiting reagent problem?",The amount of the reactants would be given to you.
Limiting reactant and reaction yields,So there isn't a way to find the actual yield without doing an experiment?,"Theoretical yield is what you think should happen:,
and is a calculated amount derived through stoichiometry. 
        Actual yield is what you observed to happen or you have been told happened:
and is derived by measurement in an experiment or manufacturing  process.
Expected yield is the amount that has been consistently reported, when control measures are used.
       So there is another way to figure yield as expected yield,  which would include the parameters and control methods used to increase yield in a real life manufacture of a chemical process.
We can use theoretical yield or expected yield to calculate percent yield."
Limiting reactant and reaction yields,why are there no videos for the hard stochiometry for unit 6?,```They want to challenge us.```
Limiting reactant and reaction yields,How would you express the actual yield if a side reaction occurs?,"In general, the theoretical yield is calculated assuming no side reactions will occur (this is almost never actually the case! But still that is the assumption that is usually made). In the case that there is a side reaction, you would calculate the actual yield based on how much pure product you were able to make. This means you need to be able to either separate your product from the side products (or leftover reactants), or you have some analytical method to analyze the purity of your product."
Limiting reactant and reaction yields,Could anyone give more detail about why the actual yield is almost always lower than theoretical? What exactly is meant by side reactions and purification steps?,"The theoretical yield assumes that all of your reactants (100% of them) react together in the desired reaction to produce your products. But real life is more messy than idealized math solutions and mistakes happen. Your actual yield is almost always going to be less than your theoretical yield because you do not obtain the entirety of your product.

One reason is that you can simply have unreacted reactants which do not produce products. This can be remedied by increasing the contact reactants have with each other such as by better (or constant) stirring. 

Another reason if that often you are transferring solutions to and from glassware for entire reactions and products can simply be spilled by accident. Or they can be left in the glassware attached to tiny scratches on the inside of the glassware where you are unable to collect it. This is mendable by having good quality glassware and being careful as a chemist when transferring solutions.    

Another common frustration is the occurrence of side reactions, or undesired reactions which creates a product that you did not wish to have. This can actually create a scenario where your percent yield is actually higher than your theoretical yield because it is contaminated with impurities. These can possibly be fixed by being extra cautious to not expose your reaction to air since chemicals like water vapor in the air can react with your reaction to create impurities. 

That being said if you performed your reaction well and produced a pure sample your percent yield will be less than 100%. An excellent percent yield would be somewhere in the 90% range. 80% is considered good. Around 50% is considered adequate. 

Hope that helps."
Reaction mechanism and rate law,How do we determine the slow or fast step?,"There are multiple ways to find which step is the slow/fast step without it being given to you.

1) Look at k. The smaller k is probably the slower step.

2) Look at the activation energy for each step. The step with larger activation energy is the slower step (as the fraction of collisions w/ enough energy to react will be smaller - activation energy requirement is higher) This derives from the Arrhenius equation:

k = A * e^(-Ea/RT)

where A and R are constants, T = temp, and Ea = activation energy.  As you can see, as Ea increases, k decreases. Thus, the higher the Ea, the slower the reaction rate."
Reaction mechanism and rate law,"The article says, "Intermediates are produced in one step and consumed in later step, so they do not appear in the overall reaction equation or overall rate law." What if the rate determining step involves a reaction intermediate? Then shouldn't the overall rate law contain the intermediate as well? Please tell what am I missing.","They don't go over this, but from what I've learned from my textbook, it is possible to have a rate-limiting step containing an intermediate. However, algebraic maneuvering is required to substitute an expression for the concentration of the intermediate so that it's removed from the overall rate law. These reactions will often have a fast equilibrium reaction as their first step."
Reaction mechanism and rate law,"How can you determine which step is fast or slow if you are told reaction order. For example, if you are told the reaction is a first order, how do you know which step is fast or which is slow?","If you are provided the complete mechanisms and the rate law of the overall reaction, it may be possible to infer the bottleneck reaction. If a curve that illustrates the change in energy throughout the reaction is provided, then the RDS is the step with the highest summit."
Reaction mechanism and rate law,Are we always going to be given whether or not the elementary steps are slow or fast,"In most formal tests, I think you would be given that, or they'd tell you how fast they are and you would be able to figure out which one is the slowest yourself."
Reaction mechanism and rate law,How do we decide whether a reaction is slow or fast?,By doing the experiment I believe. Or it was given in the question.
Reaction mechanism and rate law,If A + 2B  > C is a third order reaction does it have to be Rate = k {A} [B] squared? If B is mor influential on rate than A?,"No. You have to determine the rate law experimentally. The rate law may be rate = k[A]²[B].
The exponents in the rate law do not have to correspond to the coefficients in the balanced equation."
Reaction mechanism and rate law,"Hi,
I have some questions:
1- How we can determine the intermediate (elementary reactions) for our overall reaction? Assume that we are doing a leaching experiments and we have derived a reaction about our process. Now, how we can derive intermediate reactions? Should we assume them and use the trial and error method?
2- Is there any way, for example fixing some parameters and varying the other one to derive the leaching mechanism? 
Thanks for veryyyyyyy helpful courses :)","In all problems of equilibrium systems and reaction rates, we mainly deal with the gaseous substances. Liquids or solids( in small amount) don't affect the reaction. The leaching experiment doesn't conclude any gaseous substance. So, we can't derive intermediate reaction for a leaching experiment.
For your second question, the same logic can be applied. Leaching experiments are not associated with any gaseous substance. So, if you will change the phases, by varying parameters, it'll not be a leaching experiment any more."
Reaction mechanism and rate law,"Hello friends,
Just to be sure, mechanisms are given, correct? Or you have to perform the experiment. You don't have to just make one up?","Mechanisms don't necessarily have to be given. For example, in a test you may be asked to suggest a possible reaction mechanism considering a certain rate expression. This could mean that there could be multiple possible "correct" answers for the reaction mechanism. So yeah, you may "have to just make one up." I hope this answers your question."
Reaction mechanism and rate law,isn't rate order only determinable through experimentation? How come it says that it's always the coefficient next to the molecule here?,"We can create rate laws based on the coefficients of elementary reactions. And these elementary reactions can be combined to form a single, overall chemical equation. The rate law from the slowest elementary reaction will be the same as the rate law for the overall reaction. 

The issue is that we can potentially create several combinations of different valid elementary reactions which will combine to create the same overall chemical equation. This is what is referred to as a reaction’s mechanism, or how exactly it progresses from the original reactants to the final products. The question becomes, how do we determine which of these mechanisms is the actual one the reaction is progressing with? And now this is why we need to experimentally determine the rate law and the orders of the reactants. 

The rate law we determine experimentally will tell us which mechanism is correct because the rate laws (for the slowest elementary reaction) will be identical. So we can create any number of possible rate laws, but to know the true one we use experimental kinetic data.

Hope that helps."
The carbon cycle,What is carbon fixation,"Carbon Fixation is the process where inorganic forms of Carbon, like CO2, are converted or "fixed" by photosynthetic organisms into organic and biologically accessible molecules"
The carbon cycle,"hey 
Anyone, please answer my question.

THANKYOU",You can take whichever. The NGSS is just the updated version or something like that. I’m taking the NGSS first and then the normal one.
The carbon cycle,"hello everyone
I have recently joined the Khan Academy. I'm confused between HS BIOLOGY AND HS BIOLOGY NGSS. Which one should I take?. Can anyone please help me with that?
THANKYOU","The lessons in NGSS are going to be aligned to certain learning standards that may or may not be used at your school, whereas the other one is going to be more general. Both are certainly useful! I would recommend looking through some of the lessons on each to decide which one aligns more closely with what you are looking for."
The carbon cycle,what's the carbon cycle,see above article and previous video
The carbon cycle,How does carbon form shells?,"when carbon enters the oceans, it becomes carbonate. Calcium carbonate is what shells are made of."
The carbon cycle,whats CO2,"carbon dioxide. 1 carbon atom, and 2 oxygen atoms."
The nitrogen cycle,"Can a plant ever fully grow? I mean a plant is always growing, grass for example, every time you cut it it regrows and continues to grow until it breaks itself then it just starts the prosses over again. trees also never stop growing. So can a plant ever truly fully grow?","Due to the seasons and type of plants (ex. perennials, annuals, biennials, etc.), each plant has a "life-span", if you will. That being said, each species has a specific growing period and an average range of height that it will reach. Perhaps grown indoors and under very specific care plants could continue growing, but the seasons, temperatures, resources available (light, water, soil, air quality) along with the nature of each plant ultimately determine the growing span and height."
The nitrogen cycle,Why can't nitrogen be directly used by plants? Why does it have to be converted into ammonia first?,It can't because plants are not strong enough to break the strong triple-bond of nitrogen. The bacteria and lightning are strong enough.
The nitrogen cycle,"What does the plant on the right represent, I do not understand how the plant is using nitrates?","The plant absorbs the nitrates from the soil. Bacteria then use denitrification (process of reducing nitrates back to molecular nitrogen/N2) in order to convert the nitrates to N2. The N2 is released back to the atmosphere, and the process will start again -- bacteria will convert the N2 to ammonia, other bacteria will convert the ammonia into nitrites and nitrates, and then denitrifying bacteria will convert it back to N2 again! (The plants are taking in the ammonia, nitrites, and nitrates all the while. The bacteria needed are present in the soil.)"
The nitrogen cycle,Fixed nitrogen can be taken up by plants and incorporated into biological molecules in the plants’ tissues but where would it go into there is no opening in the tissue so therefore how would it enter and then do it thing.,"Tissues are made of cells. Cells are made of macromolecules (carbohydrates, DNA, RNA, proteins, and fats). Macromolecules are made of molecules like NH4-, NO3-, and NO3-. Molecules are very small compared to tissue, so there doesn't need to be a hole for molecules to be incorporated into tissue.

Plants have stomata, which are pores in the leaves and stems.  It is through the stomata that plants "breathe" in gases like N2.  A stomate is made of specialized cells and is found on the plants external tissue.  Gasses like N2, CO2, and O2 can pass through cell membranes freely, and do not require transporters."
The nitrogen cycle,How long does it take a plant to fully grow.,You have google
Terrestrial biomes,How would the animals adapt due to the change of temperature? How would it also affect with the biomes?,"Animals are 'shapeshifting' as the planet warms, as limbs, ears and beaks change size to adapt to rising temperatures. While these adaptations may alleviate overheating in the short term, these species can't adapt forever. It can also affect the biomes by overwhelming the capacity of ecosystems to mitigate extreme events and disturbance, such as wildfires, floods, and drought."
Terrestrial biomes,Why do we have biomes?,We have created and classified our world into "biomes" because it helps us better understand the individual enviornments in our world. Looking at the Earth as a whole would be too much for ecologists to study at once.
Terrestrial biomes,How do animals adapt to new environments and how long does it usually take them?,It can take many years for them to adapt to a new environment
Terrestrial biomes,How are the animals able to adapt to the different enviroments?,through natural selection
Terrestrial biomes,How are the animals able to adapt to the different temperatures?,"Every individual animal is genetically slightly different and these genetic differences will mean that some individuals are marginally better suited to their environment than others. These individuals are more likely to survive for longer and to be successful at finding a mate and breeding, meaning their well-suited genes are more likely to be passed on while individuals that are not so well-suited are more likely to die out without reproducing as much. This means that the population generally becomes better suited to its environment over time. 

This is the case regardless of whether the environmental conditions are constant or gradually shifting - in other words, whether a habitat is constantly hot or gradually becoming hotter, the animals in it who are best able to thrive in hot conditions are the ones who will be most successful.

To give a specific example, fennec foxes are well-suited to hot environments because their large ears help them regulate their body temperatures. Therefore, foxes with small ears will struggle to regulate their temperature and will be unlikely to survive or thrive in high temperatures, so they will not be able to pass on the "small ear" gene. In contrast, foxes with large ears will be very successful, live long lives (or at least, won't die as a result of overheating) and have lots of opportunities to reproduce and pass on the "big ear" gene. Over time, there will be fewer and fewer poorly-adapted small-eared foxes and more and more well-adapted big-eared foxes. If the temperature of their habitat was to drop considerably over a long period of time (decades), this would reverse and you would see more and more small-eared foxes, who are better able to retain heat, and fewer big-eared foxes, who lose their heat through their large ears and become vulnerable to the cold."
Terrestrial biomes,how the animals adapt to different environments?,"Animals adapt to different environments in different ways. For example, let's talk about tiger. How do tigers adapt to their environment? Well, their fur is striped and is the color of the weeds. That helps them to hide. Polar bears have such thick fur two keep them warm. I hope that makes a little sense!?"
Terrestrial biomes,is this stuff still going on or in the world i would say,Yes of course. Biomes aren't something that last for a short period of time.
Terrestrial biomes,how long does a animal evolution take,"We can measure evolution by the change in the genetic makeup of a population form one generation to the next. So evolution can happen between two generations. As for how long, well it depends on how fast a species can reproduce and for the young to reach sexual maturity since we need to compare two generations.

Hope that helps."
Symbiotic relationships within ecosystems,are parasites needed?,"That question has many answers, depending on perspective. 
(a) parasites are a part of keeping a balanced ecosystem.
(b) parasites as a whole are bad.
(c) the only bad parasites are the ones that don't have a predator to keep them in check.
(d) parasites that are introduced into a different ecosystem (an invasive species) are bad.

From _my_ perspective, humans who do not respect the Earth are parasites. 
I'd rather live among the beasts of the Earth than among humans..."
Symbiotic relationships within ecosystems,is there a relationship where both species hurt each other?,"Yes, these relationships are called competition where two or more species utilize a shared resource and limit each other's ability to use it. As a result, both species may experience reduced fitness and/or growth rates."
Symbiotic relationships within ecosystems,can some parasites benefit the host ?,"No. By definition, parasites are harmful to their hosts. When the host benefits, it would be considered *mutualism* or *commensalism*, depending on whether both sides benefit or one does and the other isn't affected."
Symbiotic relationships within ecosystems,does a anemone actually sting,An anemone does actually sting. It does this with a bunch of pointed cells covering the surface of its body. They put microscopic incisions in the skin of fish crustations and people if they're not careful.
Symbiotic relationships within ecosystems,How do fish stay alive in the sea.,The fish's gills allow it to breathe underwater.These gills capture oxygen in the water allowing the remainder to pass through
Symbiotic relationships within ecosystems,Is there a relationship that both species can end up hurting each other instead of benefiting ?,"Yes. That is called competition.(-/-) If you want something and the same species gets more of what you want, that is bad for you; and vice versa. Example:Let's say that you are a plant that is getting sunlight. If another plant takes more sunlight than you, it's bad for you; and vice versa. Hope this helped!"
Symbiotic relationships within ecosystems,can mutualism turn into parasitism,"No, it shouldn't be able to suddenly change so much."
Freshwater biomes,Why do transition zones have less oxygen?,"water that moves faster has more oxygen because the movement helps add air to the water.  Since the transition zones move more slowly than the source zone, it has less oxygen."
Freshwater biomes,Is there an easier way to memorize all of this?,lol me too
Freshwater biomes,how can salt water and freshwater meet together in a river?,When the river meets the sea there are zones called estuaries where the freshwater and salt water mix
Species diversity and ecosystem resilience,How can we increase Species richness on urban areas?,"Provide Wildlife Corridors and Connections Between Green Spaces. 
Use Organic Maintenance Methods and Cut Back On Lawns. 
Use a Native Plant Palette and Plant Appropriately. 
Utilize Existing Green Space Connections.
Be Mindful of Non-Native Predators."
The water cycle,"I am wondering, how can we empty aquifers faster than they replenish? Shouldn't they be filled up continuously since it's all a cycle? Or is the water that we use from these aquifers raining down, or flowing down, into other areas or the ocean?","it's all a cycle, but there are factors influencing precipitation such as global warming or deforestation etc, pollutants can also be another way of disrupting the fresh ground water."
The water cycle,Can water pollutants and air pollutants interfere with the water cycle and the ecosystem around it?,"Yes. Air pollutants such as sulfuric acid can acidify precipitating rain water, causing acid rain. Water pollutants can render clean drinking water undrinkable, affecting many animals and especially humans who need the most water for uses such as cooking and bathing."
The water cycle,why is clouds white colour?,because vapor is kind of white and combined with dust i guess it pretty much makes a white thing
The water cycle,how do aquifers help the water cycle ?,"Aquifers show up as springs in some places. Sometimes, they even form underground rivers which eventually may join a surface river. In this way, they contribute to the water cycle. Sometimes, they may choose to stay confined in the underground regions."
The water cycle,what's the difference between permeability and porosity?,"*Porosity* is a measure of how much surface is open space.

*Permeability* is a measure of the ease with which a fluid (water in this case) can move through a porous surface."
The water cycle,How is aquifer faster then they replenish.,Groundwater can become depleted if we use it at a faster rate than it can replenish itself. The replenishment of aquifers by precipitation is called recharging. Depletion of aquifers has increased primarily due to expanding agricultural irrigation
The water cycle,What process contributes to the formation of groundwater?,"In the soil there are small holes that get filled with air and are also useful for plant roots. So when it rains, some water seeps into the soil and flows into those small holes."
The phosphorus cycle,"Since plants use phosphorus quick, and the replenishment is slow, is there a possibility of running out of usable phosphorus, especially since it gets compacted back into the earth when plants die?",Phosphorus is a chemical element found on Earth in numerous compound ... Animals absorb phosphates by eating plants or plant-eating animals.
The phosphorus cycle,What happens to the valcano when it touches the water.,"First, the water boils away into nothingness, and the salt that's left behind is super-heated. Then yes, the lava cools, but it turns into something called volcanic glass. That doesn't sink in fact it shatters into tiny pieces that combine with the evaporating sea water to create a plume of laze.
laze is the forming a plume of hydrochloric acid and steam with fine glass particles."
The phosphorus cycle,What atomic number is phosphorus?,Phosphorus is a chemical element with symbol P and atomic number 15.
Survivorship curves and K-/r-selection,I think Alabama should be its own state,that is the right opinion on the matter.
Survivorship curves and K-/r-selection,"What are examples of Types 1, 2 and 3?","Here are some examples:
Type 1) Humans, whales, elephants, etc.
Type 2) Squirles, turtles, birds, etc.
Type 3) Fish, invertebrates, insects, etc.
*PS pls upvote me"
Survivorship curves and K-/r-selection,"Are types 1, 2, and 3 related to the k and r related species?","Yes. Type 1 describes K-selected species, while Type 3 describes r-selected species. Type 2 is something between those."
Survivorship curves and K-/r-selection,i don´t understand this chart,"The y-axis scaling by x10 instead of +10 and represents the number of organisms alive. The x-axis basically represents age (but as a percent of how long they could possibly live, for example, if the maximum lifespan of a fish is 10 years, then the graph at 50% it shows the fish at age 5). This means that the graph shows the number of organisms alive at each age."
502 Bad Gateway,Does older Population have lower rates,Both the American population and the population of the world are adding oldest-old members at a much faster rate than any other age group.
Earth's atmosphere,why does the earth have diffrent layers.,because it does
Soil horizons and erosion,what is parenting material,because of weathering soil is produced by rocks
Soil horizons and erosion,what factors contribute to the change of earth,"These have been caused by many natural factors, including changes in the sun, emissions from volcanoes, variations in Earth's orbit and levels of carbon dioxide (CO2). Global climate change has typically occurred very slowly, over thousands or millions of years."
Solar radiation and Earth's seasons,"how would part of the planet be winter and the other be summer or spring and autumn, because that would mean that if I lived in the northern hemisphere it might be winter and then if I hopped on a plane and moved to the southern hemisphere it would be summer. how would I have either gone forward two seasons or gone back two seasons?","you haven't gone forward or backward, it's just that January is warm in the southern hemisphere, so you haven't gone forward or back you have just gone to an area with different temperatures. The same way that places like California is warmer than somewhere like Canada."
Sustainable agriculture,how does limestone benefit soil quality,"Limestone, AKA calcium carbonate, is a 'base substance'(high Ph). When the solid rock breaks down into molecules, those molecules cancel out 'acid substances'(low Ph), and non-acidic soil is more fertile."
Aquaculture,what is a major disadvantage of aquaculture,"They can have an unfavorable effect on the local environment. For example, antibiotics and chemicals that are used to treat fish. Fish farms can also produce large amounts of effluent, which can affect the immediate location."
Aquaculture,Why is aquaculture an efficent practice?,"It decreases overfishing in wild areas, keeping species of fish from going extinct."
N/A,Does Nebraska exist as a country?,No...? Nebraska is a state.
N/A,open da noor,so real
N/A,"what happens when water is withdrawn from an aquifer
faster than it can be recharged","Pumping groundwater faster than it can recharge can lead to dry wells, especially during droughts."
N/A,What is a farming technique that reduces runoff,"'Rationing' fertilizers and making sure that there are plants surrounding bodies of water to hold the soil in place.
The key is maintaining root systems."
N/A,What is an effective alternative to using aquifers,Alternative water is water supplied by sustainable sources that can be used to help offset the use of fresh surface water and groundwater (such as lakes).
Renewable and nonrenewable energy sources,which is better?,"renewables are always going to be the better option. the sun will shine for at least another couple billion years, and the wind will continue to blow. as compared to non-renewables which are currently destroying our lives with "natural" disasters directly caused by the use of fossil fuels."
Renewable and nonrenewable energy sources,Is every natural resource all renewable resources.,"Natural resources are usually either renewable or non-renewable. The former refer to those resources that can renew themselves in time. These include living resources like forests or non-living ones like wind, water, solar energy."
Global energy use,Why do some places use up more energy than others?,Regions with colder climate have to consume more energy to keep themselves warm. (that's one perspective)
What is volume flow rate?,"In the paragraph titled, "What is the equation of continuity?" it says that the volume in must equal the volume out. I am a physics novice/dunce so I really need this spelled out for me. It has a "for instance" that I am struggling with. I am hoping it is a mistake, but honestly with my physics knowledge I can't be sure. 

 "For instance, if in one hour you pump 2 meters cubed of water into a pipe that is already full of water, 3 meters cubed has to flow out of that pipe during that same hour. "

Is this correct? I am trying to understand why the two numbers wouldn't be the same...Please let me know if I am missing something! Thanks!","Hi J

You are correct in thinking this is a typo. The volume flowing in and out of the pipe are the same so the statement should read, "if in one hour you pump 2 meters cubed of water into a pipe that is already full of water, *2* meters cubed has to flow out of that pipe during that same hour.""
What is volume flow rate?,""People often mix up the ideas of volume V and speed v since they look so similar." Wait a second, I thought v stood for velocity, not speed! Am I mistaken, or is the text wrong?","You're correct, but in this case, velocity and speed are the same thing. Speed is a magnitude (in other words, a number representing distance over time) while velocity is a vector - a speed that has a direction. Since liquid through a pipe is flowing in one direction, the direction part doesn't matter. Sal probably used the word speed to make it easier to understand."
What is volume flow rate?,"In the Mountain Dew problem,  the soda is carried from downstairs to upstairs. Should we consider the pressure that is needed to pump the soda up?","If you only want to relate the speeds and areas of the pipe, you don't need to consider the pressure. The continuity equation Av=Av has to be true for any incompressible fluid (since the volume flow must be constant) )even if the pressure and height changes. If you wanted to determine the pressure necessary to pump the Mountain Dew, you would need to use Bernoulli's equation as well as the equation of continuity."
What is volume flow rate?,"as per the continuity equation A1vi = A2v2  it says that the value of Avhas a constant value throughout the pipe. So, if the area, A of a section of pipe decreases, the speed, v of the liquid there must increase so that the product, Av remains the same.
 So, if the area, AAA, of a section of pipe decreases, the speed, vvv, of the liquid there must increase so that the product, AvAvA, v, remains the same. This means that fluids speed up when they reach a narrow section of a pipe and slow down when they reach a wider section of a pipe. This matches everyday experience—think about what happens if you block a portion of the water hose with your thumb, effectively reducing its area, AAA. The water must come out with higher speed, v, to ensure the volume flow rate, Av remains the same. This is why narrow nozzles, which reduce the area (A), attached to water hoses cause a significant increase in the speed, v of the fluid at that point.
but  i noticed that in my home tap , when i fully open the tap it  fills the bucket quickly as compared to when i open it half,(reducing the opening area of tap).  but as per law of continuity ,bucket  should be filled within same time in both cases.","I hope someone answer this question. 

Nicholas:
Can you elaborate more, I don't get how the tap can regulate the (volume flow rate) by reducing the area. This is clearly doesn't explain the equation of the continuity.

Sharma
"Doesn't the Equation of Continuity have nothing to do with time. Because as per A1v1=A2v2, there is no time"
Equation of continuity has everything to do with time, v is speed, speed is meter per second. 

Furthermore, A1v1=A2V2 ---> volume flow rate at 1 = volume flow rate at 2
This means, the amount of water passing in 1 sec is the same at both ends."
N/A,"It's a lot more difficult than the videos, and if I hadn't watched the videos before, I probably couldn't understand this. 
But I have a question about "steady flow", Do you mean that all molecules have the same velocity at any chosen point? Then, if all the water moves along the pipe, every molecule has its velocity directed along the pipe. Then there's NO molecule moving towards the walls and applying pressure on them, how is that not contradicting with the rest?","Hmm, sorry it was confusing. If other people feel the same way I'll rewrite it. 
As for the steady flow question, the water molecules have randomly directed velocities that can be quite high and cause pressure on the walls of the container, but since these are randomly directed they add nothing to the bulk motion of the fluid along the pipe. The velocity I'm referring to is the overall bulk motion of the fluid causing it to move along the pipe. This is similar to the difference between air pressure caused by the random motion of air molecules, and the bulk motion of air across large distances which we would call wind."
N/A,"Under the explanation of the question "Wait, does that really follow?", I have a question on why when the fluid flows from right to left (From the narrow to wide region), the pressure P1 still acts to the right and P2 still acts to the left? Or why does P2 do negative work?

Im confused here, would anyone clarify?","Fluids exert pressure in all directions. So the parts of the fluid on the left (P1) of the highlighted region are exerting a pressure on the highlighted region _from  the left_. They still exert a pressure in all directions, but the only part of this pressure that is relevant is the part that is pushing the highlighted region. So when the fluid flows from right to left, the parts of the fluid on the left (P1) still exert a pressure on the highlighted region from the left. Similarly, P2 always exerts a pressure from the right because it is on the right side of the highlighted region (the section we are interested in).

Whether work done is negative or positive depends on which direction the fluid is flowing and whether the work done is helping the movement or hindering it.
When the fluid is moving from left to right, work done to the right is positive (as it is in the same direction as the flow) and work done to the left is negative (as it hinders the flow).
When the fluid is moving from right to left, work done to the left is positive and work done to the right is negative.

At least, that's how I understood it. Hope that helps."
N/A,"Hang on, Isn't the pressure always supposed to be constant? I mean, I know from the previous videos that P1 = P2. (Pascal's law). Are we talking about different pressures here?","Pascal's Principle applies to fluids that are initially static. In this case, we have a dynamic fluid whose motion is being analyzed...hope that makes sense!"
N/A,how is pressure on static fluid different from that of a moving fluid?,"Since Bernoullis theorem proved that for a horizontally flowing fluid without the height, the P+1/2*ρv^2 is constant, if the velocity is possessed by the fluid(Which means its in motion) it should have less pressure, to satisfy the constant.
​"
N/A,"Why would we use +9.8 as our gravity, when it acts in the negative direction?","Gravity is not negative or positive, it's just downward.  If you define down as the positive direction, g is 9.8 m/s^2.  If you define up as positive, g is -9.8 m/s^2.  Nature doesn't know or care which way you want to draw your axes."
N/A,"The numbers of the last question don't add. I get a pressure of about 613,890 Pa. Anyone else got that problem?",The numbers in the last question do add up: P1=601229.01 Pa
N/A,"I still don't understand "Incompressible fluids have to speed up when they reach a narrow constricted section in order to maintain a constant volume flow rate. This is why a narrow nozzle on a hose causes water to speed up. But something might be bothering you about this phenomenon. If the water is speeding up at a constriction, it's also gaining kinetic energy. Where is this extra kinetic energy coming from? The nozzle? The pipe?" ?","this is due to the pressure energy...at the constriction, pressure energy decreases so kinetic energy increases"
What is pressure?,Why is not possible to have negative absolute pressure?,If you have no pressure then there are no atoms that can be there.
What is pressure?,why boiling point of water decreases as the pressure goes down? Is here a video that explain this phenomena?,"What applies pressure to the surface of a boiling liquid? You may answer, the air molecules. That is absolutely correct. But what about the molecules of the liquid which are above the surface of the liquid, that have been converted into gaseous phase? It is this pressure that prevents additional molecules of the liquid from escaping from the surface of the liquid. So, greater amount of energy(heat) has to be provided to the liquid to make it boil. So, if the pressure is reduced, you are essentially reducing the amount of molecules above the surface of the liquid(like vacuuming them out of the container). Ah yes, this happens only in a closed container. Now, there is no opposition to the liquid molecules to prevent them from escaping from the liquid phase. Therefore the liquid vaporizes quickly, lowering the boiling point of water.
By the way, the pressure exerted by the gaseous molecules on the surface of the liquid in a closed container is called vapour pressure. So, boiling point is not the temperature at which the liquid boils as the temperature is dependent on the pressure. Therefore, a more precise definition of boiling point would be, 'The temperature at which the vapour pressure of the liquid is equal to the atmospheric pressure.'

Hope this helps"
What is pressure?,"It is said in the article that the weight of air is actually not negligible. My question is: if you're on an open field you would have more air above you than if you were in, say, your house. How come we don't feel that difference at all?","Pressure acts in all directions. When you are in your house, the air is pushed through windows, through doors, through every little crack until the pressure inside is equal to the pressure outside. This is because air is a fluid which conforms to its environment. Solids, on the other hand, behave as you are suggesting."
What is pressure?,""unlike the water example, the density of the air in the atmosphere is not the same at all altitudes."
It seems to me that the density of water should increase, if only slightly, with the massive increases in pressure as one declines to the base of the ocean. (The text implies that there is one atmosphere of pressure increase with every 30 meters below water surface.)
Is it really the case that water's density does not change even under these massive pressures, and if so can you please explain that?","You are right.

Water is often considered "incompressible" to simplify physics calculations, because it is so hard to compress. This is the same kind of simplification as saying that the surface of the Earth is "flat" or that a ball rolling down a hill experiences no friction.

In fact the density of water does increase with pressure. For water initially at normal pressures, you need about 217 atmospheres of pressure per one percent increase in density."
What is pressure?,How can we differentiate Pressure from stress?,"When we are dealing with fluids (liquid and gases) ,, we use the term pressure 
And when we are dealing with metals or any solid object we use the term stress 
That's why most mechanical books use the term stess because they're dealing with solids 

However stress and pressure are basically the same"
What is pressure?,"I have a question, if im in space am i exerting pressure on something?","if there is zero gravity then no .as weight = mg, if g is zero then weight is zero.as there is no force(weight)there is no pressure"
What is pressure?,so can we also say that the pressure of the air above us is counteracted by our blood pressure that is why we feel a bursting sensation from inside of our body when our blood pressure is high ? and feel a squeezing sensation from the atmosphere when our blood pressure is low ?,Generally the pressure inside our blood vessels is 80-120 mm-Hg (gauge pressure). So why we do not burst out: Because of the mechanical strength of our blood vessels. Like a plane flying high in the sky. Note that hypertension occurs if blood pressure rises above 140 mm.
What is pressure?,i understood that the fluid is pushing downwards on the top of the immersed object due to gravity but why does the fluid want to push onto the sides and the botttom of  immersed object and create pressure?,"when you go underwater, where do you feel the pressure? top of your head? or ears?

any deeper, you would feel it on your chest too.


its because you have 'displaced' some water and you could think of it like the water is trying to get back into the space that you are taking...

in fact, the upthrust is equal to the weight of that water that you are displacing


okay??"
What is buoyant force?,"if upward force is more than downward force then in zero gravity, will a object in water will go upward?","You're correct if there was gravity acting on the water but not the object. However, in zero gravity there would be no water pressure at all and therefore the water wouldn't push you upwards. Buoyancy is a result of gravity acting on a liquid."
What is buoyant force?,if we put a cone inside a fluid such that it is in the lowest most point and there is no water beneath it but there is water around it. then the buoyant force should  act downward . but if the density of the fluid is greater than the cone then who will provide the force to float??,"If there is no chance for the fluid to get beneath  the cone, the cone might stay in place. But I've seen a video on which a screwdriver floats in mid air just because the air pressure is decreased at the right spot above the screwdriver. Of course things are a bit different with gasses and fluids. 

Keep looking and asking around and I'm sure you'll find out soon enough how things really are!"
What is buoyant force?,Does the laws stated above also apply to an object moving to the surface of the water??,"Yes they do. It doesn't matter whether it is stationary or moving, the follow the same laws."
What is buoyant force?,"Can we calculate the pressure acting on a submerged object in a liquid, on it's side?","Yes you can! It's more complicated though, because you need to break it down with some of your calculus and geometry tools, see why? The classic types of problem are "calculate the pressure on the sides of a pool, dam, tank.... etc." You should find problems like these in the section of integral calculus applications of many calculus books :) 
If you'd want me to recommend a book and a page with the answers to the problems, i'll be gald to do so. 

Cheers,"
What is buoyant force?,"If I place an object in water. It will exert a force equal to its weight on the water below. Now, the water below will exert a reaction force upwards on the object. Isn't that buoyant force?","sorry but it's not. buoyant force is different from reaction force

1. condition of reaction force
reaction force (normal force in the case of gravity) only works when two objects meet on a surface

2. analogy of reaction force
in the case of a ball in water, we don't treat water or whatever fluid around it as another object. it is environment. as much as we don't consider a freefalling ball in air as having any reaction force from any surfaces, even though it keeps contacting with air pressure (this is a buoyant force too)

3. definition & example of buoyant force
1) definition
then what pushes the object upward (and any-wards)? the whole water itself and its weight by gravity. 
2) example
let's say a ball is inside a sea. then the sea itself has a mass thus weight by gravity. so all the water molecules in the sea are pushed down. and there's something less dense than them. what will happen? they want to occupy that very volume of that less densy invader! in all possible directions. that's what happens inside the mercury barometer we checked previous chapters here. no matter how small the density differene is (vacuum to a tiny tiny mismatch), water molecules don't miss that chance to exploit it and then steal that volume. and the left is what we've learned. h of a lower part of the ball is a bit larger than that of upper part, thus the net force pushes upward it. that's buoyant force. and that very force is not from the ball itself. or its reaction force from water "surface". but from water molecules around it (insdie the entire sea, to be exact)



plus, it's after the ball lands on the bottom of the sea when the reaction force works. the bottom ground functions as a surface. it keeps the ball from drilling down underground by forcing the same magnitude but opposite direction of reaction force to the ball's weight. thus the ball stays still (happily ever after, i hope)"
What is buoyant force?,"why do some objects float when partially submerged, but sink when fully submerged?","Nice answer Charles. (I was thinking bucket :) 

There is also the situation in which 'surface tension' can play a part.

So, for a small object such a a needle, it might float on the surface but this is not due to displacement. When you push it under water, then surface tension can no longer keep it up so it sinks.

ok??"
What is buoyant force?,"As stated above the buoyant force can be calculated by subtracting the downward force  from the upward force exerted by the water on the object.But the upward force itself is buoyant force by water ,then how do we arrive at the above equation?please make it a little clear I'm too confused.",F (upwards) stands for the force applied by water in an upward direction while F(downwards) stands for the force applied by the water on the can in the downward direction. Buoyant force is the net upward force on the can by the water.
What is buoyant force?,"Suppose that we are discussing an ice cube in a beaker containing water. When the cube melts, it takes the volume of the water that was initially displaced by its weight.

My doubt is that at some point of time, there will be saturation of some kind. The water will eventually start coming out of the beaker if we keep on putting ice cubes one after the other and allowing them to melt. When will such a thing happen?",Liquid water is denser than frozen water so as the ice melts.  The volume of water displaced is equal to the volume of water equivalent to the weight of the ice so the level of the waster will not rise or fall while the ice melts.  If you put ice into the beaker and it can overflow when it is put in but if it is not overflowing when you put it in it will not overflow as it melts.
What is the ideal gas law?,"Where do _R, Na(Avogadro's Number) and k(Boltzmann's constant)_ come from and why? Is there an explanation for how they have been calculated? Thanks in advance. I wouldn't mind if the answer involved calculus.","No calculus needed :-) Like most any constants, they are simply needed if there is always that same factor missing in an equation. 
For example, in statistical mechanics you have a formula that is: S=k*ln(W). If you know S and W for at least two cases, then you might realize that, _for both cases,_ S = ln(W) only if you multiply the right side by k constant"
What is the ideal gas law?,"In the section "What is the molar form of the ideal gas law?" and the first example, shouldn't the atm version of the ideal gas constant be 0.082 L*atm/mol*K instead of 0.082 L*atm/K? Or is there some reason the number of moles isn't included?","You are right, the R actually does have the "mol" units, and it should read, as you correctly mentioned, L*atm/mol*K.
Nevertheless, the reason why this was probably excluded here is because the units of n are mol, and then if you combine n and R, the mol units will cancel."
What is the ideal gas law?,How do I know when a gas behaves like an ideal gas?,most real gases do as long as the temperature is not too low and the pressure is not too high
What is the ideal gas law?,"When converting, why should we use Kelvin?","One of the most important formulas in thermodynamics is P1 * V1 / T1= P2 * V2 / T2. However, if we used Celsius or Fahrenheit, what if, for example, the temperature was 0 degrees Celsius? Since you can't divide by 0, the formula would not work. 
The Kelvin scale is made with 0 being equal to absolute zero, the coldest possible temperature, where the molecules stop moving completely. Therefore, you will never get a zero or negative temperature in your formula if you use Kelvin. 
 Kelvin is also the widely accepted temperature scale. If, for example, some people used Celsius and some people used Kelvin, we would all get different answers, so everyone uses Kelvin."
What is the ideal gas law?,"In the "Units to use for PV=nRT" section, It says 1 liter=0.001 m​^3​​=1000 cm​^3.
This doesn't make sense to me. Isn't 1000 cm^3 = ​​10m^3 since c is a SI prefix for 10^-2?
10m^3 isn't equal to 0.001m^3. What am I missing? I'm sorry if this is a silly question.","Your math is a little bit wrong. Check it:
1 cm = (10^-2) m
(1 cm)^3 = (10^-2 m )^3
1 cm^3 = (10^-6) m^3
(1 cm^3)*1000 = (10^-6) m^3 *1000
1000 cm^3 = (10^-6)*(10^3) m^3
1000 cm^3 = 10^-3 m^3 = 0.001 m^3"
What is the ideal gas law?,What factor is found in the ideal gas law which is not in the previous laws?,"Nothing extra. The ideal gas law is the integration of Boyle's, Charles' and Avogadro's laws into a single equation."
What is the ideal gas law?,"Where do we get the gas constant ,R, from?
Thanks","Choose any gas, assuming its ideal. For example, 1 mole of Ar = 39.948 = 22.4 L at standard pressure ( 1 atm) 

Just solve for R using the same formula, PV=nRT or in this case, R = PV/nT

Subsitue values into the equations :- R = (1atm)  (22.4) / (1mole) (273K)

        Solve:  R  =  0.0821 atm L / mol K

There are also alternate values for different units.
If R is needed in units of pressure (kPa)  =  8.314 kPa L / mol K

If R is needed in units of pressure (mm Hg)  =  62.396 mm Hg L / mol K

 I would suggest always using the value of 0.0821 atm L / mol K for R unless stated otherwise.

Hope this helped!"
What is the Maxwell-Boltzmann distribution?,Why isn't V(rms) equal to V(avg) ? Here V(avg) is avg speed of the molecules.,"Hey Nitin, I think I can answer your question. Let's say there are 6 molecules in a sample of gas. These 6 molecules have the following velocities, respectively: -1 m/s, -2 m/s, -3 m/s, +1 m/s, +2 m/s, and +3 m/s. If we want to find the average speed of a molecule in this sample of gas, we need to convert these 6 vector quantities (i.e. velocities) into 6 scalar quantities (i.e. speeds) by removing the signs. After performing this conversion, we have the following speeds: 1 m/s, 2 m/s, 3 m/s, 1 m/s, 2 m/s, and 3 m/s. To find the average speed, v(avg), we need to add these 6 speeds together and then divide the sum by the total number of speeds:

1 + 2 + 3 + 1 + 2 + 3 = 12
12 / 6 = 2

So the average speed is 2 m/s. On the other hand, if we want to find the root-mean-square speed of a molecule in this sample of gas, we don't need to convert those 6 velocities into 6 speeds. Instead, we need to find the square root of the average of the squares of the velocities:

(-1)^2 + (-2)^2 + (-3)^2 + 1^2 + 2^2 + 3^2 = 28
28 / 6 = 4.67
The square root of 4.67 is 2.16.

So the root-mean-square speed is 2.16 m/s, which is greater than the average speed (2 m/s). This is why the root-mean-square speed does not equal the average speed. I hope this helps. If my reasoning is incorrect, please let me know."
What is the Maxwell-Boltzmann distribution?,"Just above the section "What does the area under a Maxwell-Boltzmann distribution represent?", should the 605 m/s quantity be v(rms) instead of v(p)?",Area under Maxwell distribution curve represents the number of molecules in the system
What is the Maxwell-Boltzmann distribution?,"Hello!
 Why is it that the average kinetic energy is proportional to the rms speed instead of the average speed .I understood about squares and roots, but still if i have the average speed of particles it would be normal for me to take the average speed for the average kin,energy?
Thank you.","This is a very good question that gets to the root (pun not intended) of something that is apparently so subtle that it was never explicitly stated to me all the way through second year college physics.  Massive bodies in motion have two parameters that diverge the greater their velocity becomes.  Momentum is simply mass times velocity, while kinetic energy is one half of the product of the mass and the square of the velocity.  So when we look at the simple mode and mean of the Maxwell-Boltzmann distribution (which assumes a uniform mass) we are looking at momentum, but when we consider the rms value we are now looking at a description of kinetic energy.
I'm pretty sure you've already understood that, but are still as unsure as I am about why that matters.  First off, in the context of this lesson, all we need is to be aware that there is a difference, and that at some point in the future it will become significant.
Looking beyond the scope of this lesson, I expect the implications of this follow from the two facts that a) both momentum and kinetic energy must be conserved, in any non-relativistic event at least, and b) they begin to scale at radically different rates as the velocity increases.
At the human scale, if my car hits another car at 1 mph the momentum is conserved as we both continue at 1/2 mph until various frictions bring us to a stop, and pretty much all of the excess kinetic energy is distributed without too much trauma.  However, if I hit the same stationary car at 100 mph and momentum is conserved as we both continue down the road at 50 mph, there is now 10,000 times as much energy to dissipate.  My car retains one half times m times 50 squared in its residual velocity, the second car absorbs the same amount as it accelerates, leaving one half m times 10,000 - 2500 - 2500,  that is fully half the original kinetic energy to be dissipated as a bunch of highway ugliness.
Just how that translates into behaviours at the molecular scale, I am not sure.  Hopefully, I'll get a better handle on this as these lessons progress."
What is the Maxwell-Boltzmann distribution?,"If we're plotting speed on the x axis, is there then a maximum (the speed of light) the individual particles can't go beyond? So the graph doesn't tail off to infinity?","Technically yes, but it is a bit more complex. As particles approach the speed of light they are called relativistic particles. At that point, special relativity must be taken into account. Look up the Maxwell–Jüttner distribution. It describes the distribution of speeds for relativistic particles.
If any of this is incorrect please let me know and I will correct it."
What is the Maxwell-Boltzmann distribution?,"Hi, I don't quite understand the idea of "number of molecules per unit speed" on the y-axis. What is this idea of "unit speed"? Which "unit speed" are we dividing the number of molecules by? Could you explain? Thanks!","The wording is a little confusing.  In order to get a distribution, you are dividing up the molecules into bins according to their speed (like a histogram).  In this case, the bins are so thin that instead of a lot of bars, you get a smooth curve that represents the top of each thin bar.  So when they say "number of molecules per unit speed" they aren't mathematically dividing, it's more like "number of molecules in each bin of speed" with the bins on the x-axis.   But remember that the bins are so thin that we actually refer to them just by the x-value (speed).  So there is a number of molecules at 600.000 m/s, and a number at 600.001 m/s, and a number at 600.002 m/s, and thus you get a continuous curve of number of molecules vs speed."
What is the Maxwell-Boltzmann distribution?,Can V(rms) be equal to V(avg)?,"yes when all the velocity data values are same. 
eg. -3,-3,-3,3,3,3 then V aver.: 3 and V rms : 3 ."
What is the Maxwell-Boltzmann distribution?,"So, why are there three kinds of mean speeds/velocities? i mean why not just one kind but three. Any reason?","It's kind of like how you'd have a mode, mean and median in statistics. They're all averages, but represent different things. For example, here, the most probable speed is equivalent to the mode, and the average speed is equivalent to the mean. Root mean square is a type of generalised mean, I believe."
What are PV diagrams?,If work done by a system is equal to change in pressure-volume. Why does an upward and rightward shift in the pressure-volume diagram cause an increase in internal energy? Work done by the system should reduce the systems internal energy shouldn't it?,"The work done in expanding does in fact take energy out of the system, so the only way the state can shift to a higher PV value while the gas does work is to have even more heat Q added to the gas during the process so that overall the gas gains energy."
What are PV diagrams?,"maybe this is not a good doubt .. but if the gas has been compressed why is the work done on the gas positive?  is nt work  done = PdeltaV
so the work done by the gas should be negative if im not wrong
...
correct me if im wrong","I would say is more a matter of semantics
- The work done on the gas is positive
- The work done by the gas is negative
The conservation of energy (first law of thermodynamics) states:
Internal Energy Change  =  Heat added into the System  +  Work done on the System
or
Internal Energy Change  =  Heat added into the System  -  Work done by the System"
What are PV diagrams?,What if there is a closed path for a cyclic process?- This is confusing me.,"This is now explained in a little pop-up box in the middle of the article, but you may have missed it or it may have been added after your question.

While the cycle is moving L to R (increasing volume) the work done BY the gas (area under the curve) is considered positive.  While the cycle is moving R to L (decreasing volume) the work done BY the gas is considered negative.  The total work of the cycle is the sum of these two works (areas under the curves), but since one is negative, it's essentially the difference.   The difference between the two areas is, by definition, the area *within* the cycle and that is the work done BY the gas during the cycle.

As for the sign, if the cycle is clockwise, that means the higher line (higher work area) was L to R (positive work), so the total W is positive.  if the cycle is counterclockwise, that means the higher line (higher W area) was R to L (negative work), so the total W is negative (work was done ON the gas).  But in the either case, the *magnitude* of the work is still the area inside the PV cycle."
What are PV diagrams?,"The slope of the PV diagram has the units N/m^5, does that mean anything?
Thanks","The slope tells you how fast the pressure is changing with respect to volume. Slope m, is equal to Pressure/Volume, or dimensionally: m=(F/A)/V in SI units, it will be kg/(m^5) or kg*(m^-4)*s^(-2). This tells you how fast the pressure is changing with volume for every kg of gas/atoms in the system per volume. If you think about classical mechanics, for example, a ball heading towards the earth, (neglecting air resistance and approximating the distance near the surface of the earth), the force is F=N=kg*(m/s^2). Intuitively, you can think of it as I need to apply this force to move this object with this mass. And to see how long it takes, you divide by the time interval (1/s). The extra s is to account for the extra time needed to move the object that is already traveling with some velocity.

Sorry if I ended up confusing you more... The slope essentially tells you how fast the dependent variable (y-axis) is changing when you let the independent (x-axis) vary.

- (senior) physics/mechanical engineering"
What are PV diagrams?,"When a gas is doing work yet increasing its pressure, can we say that the pressure increase is definitely due to heat being added?","Unless gas is added, it is. If gas is doing work, its volume is increasing. As pressure and volume increases, T=PV/nR is increasing too. Thus, Delta U = Q - W is positive. As W is positive, Q should be positive."
What are PV diagrams?,"why does the volume change determines work sign in the first place? to me, pressure change would be much more intuitive since thats what causing the imbalance - increasing alerady higher pressure in containter, while decreasing already low pressure in surrounding","Work is force*distance.  The volume change occurs because a wall of the container is being displaced.  If you just increase the pressure and there is no volume change (think about how you would do that), no work is being done."
What is thermal conductivity?,i want a very specific and a very to the point definition of thermal energy. help me .,Thermal energy is the energy that comes from the heat . This heat is generated by the movements of tiny particles within an object.
What is thermal conductivity?,"Can you say that liquid water is a bad thermal conductor? I'm thinking that it often just eats the heat for itself (for example use it to to evaporate) instead of passing it down.

Thanks!","interesting question...

the thing is, water is hungry for heat.... ie it has a large heat capacity. but that is different to conductivity. i guess it depends on the context...ie if you talk about heat passing through, or heat being absorbed

make sense??"
What is thermal conductivity?,"Let's say there are 2 pieces of metal (copper and iron) which have different constants, k and they are put together. To calculate the rate of heat flow, is it still possible to use the formula as stated in the article?","I think that the formula can still calculate the "rate flow" at "a moment of time" because when the time pass the difference of temperature in two material will decrease and also the rate flow. BUT in the example2, they assumed that the temperature inside and outside the window remain constant even the heat was transferred. Sorry for bad English!"
What is thermal conductivity?,Does this equation only work if the temperature on both sides remains constant?,"Nope. If temperature on both sides remain constant, there will be no thermal conductivity. [Don't mistake me. The formula does hold good for this case too!] The formula is meant to be used to find thermal conductivity and that generally happens when there are different temperatures. :)"
What is the first law of thermodynamics?,"I understand that Q isn't the same thing as T, Q is heat that enters/exits the gas. ΔT might increase as Q enters, but ΔT also might stay constant or even decrease as Q enters the system, and so the opposite.
 
But it's still confusing me that from this expression Q = m.c.ΔT it shows that Q is the function of ΔT (delta T) which is the change in temperature, and from this ΔT is proportional to Q.

 I would be grateful if anyone can help me with this confusion.","You say "ΔT also might stay constant or even decrease as Q enters the system, and so the opposite" - that is to do with the effect of W (work done on or by the gas in question), where ΔT is proportional to ΔU. In the expression Q = m.c.ΔT, W is not taken into account as it assumes a constant volume. You're just looking at raising the temperature of the substance with regard to the mass and specific heat capacity of the material, but not really considering the expansion of the gas pushing a piston or the piston pushing down on the gas (W). The Q = m.c.ΔT expression is only really appropriate for a constant volume.

See: https://chemistry.stackexchange.com/questions/4722/when-is-it-okay-to-use-q-mc-delta-t-is-this-equation-only-for-calorimetry-que"
What is the first law of thermodynamics?,why do we need second law of thermodynamics?Is energy really lost in second law of thermodynamics?,"Hello Muhammad,

This law concerns energy conversion. Suppose we had a machine that could convert electrical energy to mechanical energy (motor). In an ideal world it could do so without any loss. In reality the efficiency is not 100% and so we loose some energy to waste heat. The 2nd law of thermodynamics states that  you can NEVER make a machine that converts 100% of the energy. 

Likewise with a battery. When you charge the battery (electrical to chemical energy) there will be losses. When you discharge the battery (chemical to electrical) there will be losses.

Don't let anyone tell you otherwise - there is no such thing as perpetual motion machines!

Regards,

APD"
What is the first law of thermodynamics?,How does doing work on the system increase the kinetic energy of the gas molecules,"If the piston is pushed down (form of work done), its base would collide against the gas molecules, causing them to move faster and hence their kinetic energy is increased.
Hope this makes sense :)"
What is the first law of thermodynamics?,"If the piston moves up when the gas expands (due to heat) and if the volume of the gas does not decrease, what allows the piston to move down again?
Thanks","not sure of your exact question

but if the piston moves back down, it is usually because it is being pushed by a mechanical force to squash (compress) the gas (or to push the gas out of the cylinder as waste)

The mechanical force comes from another part of the engine such as fly-wheel or other picston.


OK?"
What is the first law of thermodynamics?,"In the article it says " temperature and internal energy are proportional", but I still don't understand. Internal energy is every kind of energy that exists in a system, including KE, PE and others. I understand that temperature is proportional to Kinetic energy, but KE is just part of what comprise total energy (Internal energy is every kind of energy that exists in a system, including KE, PE and others). So is temperature directly proportional to internal energy? And by saying A is proportional to B, is it necessarily equal to saying that A=kB, where k is a constant?","I think the case that Internal energy is proportional to kinetic energy is mostly based on monoatomic ideal gas, which means in the system there are no other forms of energy except kinetic energy."
What is the first law of thermodynamics?,"In example 2,Sample 1 I cannot understand how does Heat Exits the system even when the work was done by the gas?
Similary in Sample 4 the heat enters the system even when work is done on the gas.
Explanations please anyone.","the most easy way to clarify this doubt is that consider yourself to be a candle. when it lights there is noble work done by the candle [ giving light to others (thermodynamically, work done by the gas ) ] but sadly the candle itself gets shorter and shorter( i.e thermodynamically heat loss) but when we add a little wax to it ( thermodynamically work done on the gas ) , the height increases ( heat enters the system)"
What is the first law of thermodynamics?,If you measure a liquid's heat (coffee for example) with a thermometer. Do you also lose heat to the thermometer?,"A hot liquid will lose heat to a cooler thermometer.  The thermometer has to absorb thermal energy in order to measure it.  Also a cold liquid might gain heat from a hot thermometer, right?
But note that you don't measure "heat" when you use a thermometer.  You measure temperature.  They're not the same thing."
What is the first law of thermodynamics?,while preparing for the SAT subject tests physics from Barron's I read that they have taken the work done on the gas as positive.But we are told that W=P(change in volume). But if we apply force on the gas then its volume must decrease hence the work done must be negative please explain(its given on page 375),"Its a good question... You will see that W changing sign and meaning throughout your reading unfortunately.

My answer to students is this: use your intelligence to define it within the context (or question) you are lookking at

for example, if a gas is expanding, it is doing work ON the atmosphere. Work is being done BY the gas.

If a piston squashes a gas, then it is doing work ON the gas. Work is being done BY the piston. 

When you know what is doing the work and what its being done ON, then you can fix the signage in your equaitons appropriately. 

Sorry to say, I have seen the negative sign in books given in different ways and not always clear; hence I am reluctant to give signage in equations on this topic : rather give clear understanding of the equaitons mean.


Hope that helps"
What is the first law of thermodynamics?,"If I move a bottle of gas from a low place to a high place (it seems I am doing work, so "W" is positive), according to "ΔU=Q+W", is there an increase in internal energy?","The gravitational potential energy of a system like the bottle is not part of the internal energy since it is not internal to the system, the bottle.  Similarly the kinetic energy of the system from the motion of the entire system is not part of the internal energy.  If you have two bottles of the same size, same amount of material in it at the same pressure and temperature but one is sitting on a table and the other is zipping by in a plane at 1000 meters above the table they have different kinetic energies but the internal energies are the same."
Kirchhoff's laws,When I see the words "voltage on each resistor" - what does that mean? that voltage is getting eaten up or used by the resistor? Is it wasting energy?,"The phrases "Voltage on" and "Voltage across" mean the same thing. One end of the resistor is at a higher potential than the other end. The difference in potential is called the "voltage across" the resistor. It is the nature of resistors that when they have a voltage across them, a current flows. When current flows, there is energy being dissipated. If the circuit is doing something useful, then we say "Nice job using the energy! I like this song." If the circuit is not useful, then we might say "What a waste of energy, how sad"."
Kirchhoff's laws,"How is this affected if there are multiple batteries, and therefore multiple currents? What if the resistors are in parallel?","Kirchhoff's Laws work for every circuit, no matter the number of batteries or resistor configuration.  KCL tells you about the sum of currents at each specific node in the circuit. KVL tells you about the sum of voltage rises/drops around every loop of a circuit. KVL and KCL aren't fooled by multiple voltage or current sources, or parallel resistors. They always work."
Kirchhoff's laws,"Where does the current flow when it enters the node.? What if all the current (arrows) are pointing inward, how is the sum of current zero in that case?","good question.

If all the arrows are drawn as going into the node, then one of the currents going 'in' will have a negative value in your calculations.

Of course, there must be just as much going in as out"
Kirchhoff's laws,what is voltage?,"It is the electric potential between two points. You probably know potential energy, like when a bowling ball is sitting on a skyscraper it has the potential energy stored from gravity because it could fall. Voltage is the same thing but with electrons (negatively charged) that have potential because they will try and move to a postive (or "less" negative) area."
Kirchhoff's laws,is kirchhoff's law applicable for ac circuits?,"Hello Drakshaspodia,

Yes, both KVL and KCL apply to AC circuits. 

You will find AC circuit are more interesting than DC circuits as capacitors and inductors change impedance as frequency changes. Think of impedance as the resistance to an AC signal.

Regards,

APD"
Kirchhoff's laws,"In circuit diagrams for example the circuit diagram before KVL(having Vab,VR1,VR2...) how we can give + and - signs to a voltage I mean how we can give polarity signs to a component","When you apply voltage to a circuit and let currents start to flow, each component will have some current and there will also be a voltage appearing between/across the terminals of the component (by virtue of Ohm's Law). When we put voltage labels on components we are just giving names to those voltages so we can talk about them between ourselves and in equations.

You name a voltage by calling it something and putting + and - signs on it. You might be worried that the signs could be "wrong". Don't worry. We just give them names and signs so we have something to talk about. It's like saying that the top of a map is North. Just a reference direction. If (after we do the analysis) the voltage ends up being the other way around, it just gets a negative value. Just like if I'm walking South, I could say I'm walking -North."
Kirchhoff's laws,what is the algebraic sum?,"It's a fancy way of saying "total summation".
_Example: the algebraic sum of 8, -1, -2 is 5._"
Kirchhoff's laws,"what do we understand from the arrows in the voltage diagrams
what is voltage polarity","Hello 

Here is how you make the arrows. 

1) Assume a direction of current flow.

2) Walk around the loop in the chosen direction of current flow. For sake of argument lets start at the 200 Ω resistor. 

2)  As you walk along the circuit you will encounter a component. Ask yourself if the voltage as you enter this component is greater than or less than the exit terminal. 

3) If the voltage on the terminal you entered is greater than the exit terminal then the entrance terminal gets a “+”. And the other terminal gets a “-.”

For a resister you don’t need to think very hard. If you are traveling in the direction of the current then the voltage on the terminal you enter will be higher than the exit.

The battery is  more interesting. As we travel we will enter the battery on the negative terminal. When we look across we see the positive terminal. Consequently the entrance terminal gets a ‘-’ and the exit terminal gets a “+” symbol.

One last point - if you were tr travel all the way around this loop the sum of the voltages is equal to zero. This property is essential to you study of electronics. We give it the special name KCL (Kirchhoff's Voltage Law).

Regards,

APD

P.S. You could have assumed the opposite direction for the current and everything would have mathematically worked out..."
Kirchhoff's laws,Isn't the answer to the second question for i5 "-6 mA"? The answer key suggests "+6 mA" but this would give you a summation of +12 mA. I believe the description below the problem states the same.,"Hi cptlaurion,
the answer key says "-6mA" going into the node OR "+6mA" going out of the node, they have the same meaning. the "+ve" sign means that your arbitrary direction you suggested is true and the "-ve" sign means that your arbitrary direction you suggested is false and the true current direction is in the opposite one.
I hope you got what you need from my answer."
"Basic electrical quantities: current, voltage, power","I still don't get Amperes, can someone please help with a simple analogy so I can understand better?","Think of a tank of water with a hole in it. The amount of water in the tank is the voltage, aka the potential/volts. The size of the hole is the resistance, aka the ohms. The amount of water that flows would be the amps in this example. If you wanted to add watts into this system, say you put a water wheel in that stream of water. The power produced would be watts."
"Basic electrical quantities: current, voltage, power",what is quantum mechanics ? please explain in brief,a body of principles that explains the behaviour of matter and it's interactions with energy on the scale of atoms and subatomic particles
"Basic electrical quantities: current, voltage, power",Can someone elaborate the formula dU/dt,I posted in tips if you are not familiar with derivatives.
"Basic electrical quantities: current, voltage, power","If water is a poor conductor of electricity, why do we get electrocuted if we stand in water and electricity is introduced?","Pure water is poor conductor of electricity but the water in your tap contains many minerals that  provide the ions for conduction of electricity. Similarly if you take pure water and dissolve a teaspoon of table salt (NaCl), it would become a good conductor because now it would have sodium and chlorine ions to help conduct electricity.

Do note that at very high voltages, even pure water starts to conduct electricity because water molecules become ionized and separate into H+ and OH- ions which results in increased conductivity."
"Basic electrical quantities: current, voltage, power","In the analogy for voltage, where you compare it to a ball rolling down a hill, does voltage increase as it rolls down the hill, i.e. does it build momentum with gravity?","nice question:

OK, so think about potential. : it means stored energy or energy capable of doing work...

So think about the ball, at which point does it have most potential energy? top of hill or bottom??

OK?"
"Basic electrical quantities: current, voltage, power",Why is I the symbol for current?,"intensité de courant, (current intensity) in French. It was used by André-Marie Ampère. You can guess who that guy was.

That is why we use I as symbol for current"
"Basic electrical quantities: current, voltage, power","what's the difference between charges and electron/proton? since in my mind, current is caused by the moving of electron, but the text says that charges cause it.","Current is the movement of charge.  Since electrons are particles with negative charge, their movement creates current."
"Basic electrical quantities: current, voltage, power","The electric power consumed by a device may be calculated by using either of the two expressions P=I^2 R or P=V^2 /R. The first expression indicates that it is directly proportional to R whereas the second expression indicates inverse proportionality


I Know, if you have a constant voltage, increasing the resistance decreases the current flowing in the system by Ohm's law and hence decreases the power consumption

However, if you have a constant current source, increasing the resistance increases the voltage dropped across the resistor and hence increases the power consumption. 


But more intuitively I wanna know about this, with some example....can anyone please explain me? Thanks is advance","Hello Leo,

CAUTION - this is an answer from an electrical engineer...

In my opinion the voltage source is relatively straightforward. Examples include a battery or wall outlet. As you stated as the resistance is decreased more current flows. With more current and a fixed voltage there will be more power.

The current source is a different animal. I'll give you a few examples to consider:

1) The current source is a mathematical construct that maintains a constant current. It will take on whatever voltage is necessary to do so including both positive and negative voltages. It has an infinite impedance. To my knowledge there are no perfect constant current sources. To make one you would need a device that could produce an infinite voltage (not possible).

2) Please search "Thevenin Norton Equivalent." Here you will find that a voltage source with series resistance can be modeled as a current source with parallel resistor. Note that there is no such thing as a perfect constant voltage source. Such a device would demand infinite current (again, not possible in this universe).

3) Please search "inductor kickback." Here you will find than an inductor acts as a constant current source for a limited amount of time. As the inductor is "turned off" it will act as a constant current source and do whatever is necessary to maintain the same current before and after the transition. 

4) Please search "transistor characteristic curves." Here you will find that a transistor appears to operate as an acceptable constant current source. 

I hope you like these examples. Know that it will take some time for the material to sink in. May I recommend you print this note and check things off as you have master the topics. 

Please leave a comment below if you have any questions.

Regards,

APD"
"Basic electrical quantities: current, voltage, power","This is more of a "dumb curiosity" question and is purely hypothetical, but if salt water is as good as copper and silver could it be used to help power most things we use today?","Good day dream question. Salt water happens to be NOT as conductive as copper and silver. Those two metals are _very_ good conductors compared to sea water.

Sea water has a conductivity of 5 x 10^6 S/m
Copper has a conductivity of 6 x 10^7 S/m, or 10 times higher.

But suppose these numbers were closer. Water is a lot cheaper than copper, so that's an advantage for water. Now all you have to do is figure out how to use the water to build the electronic gizmos we all love. That's where water becomes distinctly useless as an electrical interconnect. Can you imagine if all the phone lines and power lines you see going from pole to pole were garden hoses?"
"Basic electrical quantities: current, voltage, power",Is there a reason why proton's charge is called positive and electron's charge is called negative?,"A long time ago, Ben Franklin (the American statesman) proposed a theory of electricity where he thought electricity was a fluid. This was back when the only thing anyone knew about electricity were those static electricity experiments you can do with a comb through your hair or rubbing a balloon on your sweater. Nobody knew about atoms or electrons or protons. Anyway, Franklin proposed an object could have extra electric fluid or lack fluid, depending on what you rubbed it with, and that's what caused the static attraction, the different levels of electric fluid in two materials.  He called the "lacking" material negative, and the extra material "positive". About 150 years later the electron was discovered, and it turned out that the "lacking" materials actually had an excess of electrons. And that's how the electron got its negative sign."
What is Faraday's law?,There is a direction of the current indicated with an arrow on Figure 1 ("Charge in a moving wire."). Shouldn't the arrow point in the opposite direction? I used the formula *V* = L *v* × *B* and the right-hand rule. Thank you.,"I think the figure is very misleading, or maybe just plain wrong, depending on where we are supposed to understand the magnetic field is located.  They have TWO black arrows on the wires, indicating the current going in a loop.  The current is shown going "southwest" in the wire near us, and "northeast" in the wire far from us.  For any wire moving in the direction indicated, the induced current will be SOUTHWEST only.  So if ONLY the near wire is "in" the B field, then the diagram is actually OK.  But if the entire loop (both parallel wires) is in the B field, then there would be no induced current.  The current would be trying to flow southwest in both wires.

Because they only draw B field arrows along a single line which looks like it is BETWEEN the wires, it is a very ambiguous figure."
What is Faraday's law?,"Question on inducing current  in the coil
I  cannot understand why the emf produced in the coil be opposite after the magnet has moved halfway through the coil. Thank you","Because the direction of the flux change is reversing.  At first it's increasing ,then as the magnet leaves, it's decreasing.  The induced EMF depends on the rate of change of the flux.  If the flux goes from increasing to decreasing, that's a reversal in the rate of change, ergo a reversal in the EJMF."
What is Faraday's law?,"If the rate of change plays a role in the amount of induced voltage then why different frequencies of AC voltage still get transformed by the same amount by a transformer? Wouldn't 120hz AC came out higher than 60hz AC on the other end of the transformer? (like lets say we connect 10V 60hz AC and 10V 120hz AC to a 1:2 transformer, why both of these voltages end up 20V at the secondary?)","The rate of change cancels out because induction happens twice in the transformer.  First the primary coils induce a magnetic field, then the magnetic field induces voltage in the secondary coils."
What is Faraday's law?,"If the rate of change plays a role in the amount of induced voltage then why different frequencies of AC voltage still get transformed by the same amount by a transformer? Wouldn't 120hz AC came out higher than 60hz AC on the other end of the transformer? (like lets say we connect 10V 60hz AC and 10V 120hz AC to a 1:2 transformer, why both of these voltages end up 20V at the secondary?)",Keep in mind that going from 0 V to 10 V at 60 Hz it is happening in 1/240 s (a quarter of a cycle) where as at 120 Hz it is happening in 1/480 s.  So the higher rate of change does create a greater change in induced voltage but it acts over a shorter period of time and these offset each other.
What is Faraday's law?,what is the difference between moving the magnet through the coil from the right side versus the left side?,"When you move the magnet from left side ( towards the coil), the coil induces current in a direction to repel the North/South pole ( whichever way you place the magnet).
When you move through the right side , the current direction just reverses from the previous one.

Hope it helps!
:>"
What is Faraday's law?,I don't understand Faraday's experiment : Induction from a magnet moving through a coil . Can some one explain it better for me please,"I'll try to explain it
   Consider that the magnet's north pole moves towards the coil. Upper end of the coil acquires north polarity, hence work is done against the force of repulsion to move the magnet.
   If the magnet is withdrawn from the coil upper end acquires south polarity, so work is done against the force of attraction.
  
    Now we know that as the magnet moves through the coil magnetic flux linked with the coil changes inducing a current. The  direction of the induced current is found from Lenz' law as follows.

   The work done in moving the magnet towards the coil is converted into electrical energy, which gets dissipated into heat energy.The current flows in a direction to oppose the motion of the magnet. If in case the induced current promotes the motion of the magnet, it stars moving at a faster rate and the electric energy(induced) and kinetic energy(of the magnet) starts increasing, without any work done. This is not possible (law of conservation of energy) .
So induced current always flows in a direction that oppose the motion of the magnet.This is Lenz's law.

pheww....Hope it helped!"
What is Faraday's law?,I am not able to understand the difference between potential difference and electro motive force.,"Hello Aryan,

Here is an answer from an electrical engineer's perspective - it may not line up with a physicists answer.

If you have a voltmeter in had you could measure voltage as the difference between any two point in a circuit. The red probe goes to one part of the circuit and the black probe goes to another. It does not matter what is being measured. It could be a battery, solar cell, or coil of wire as shown in this video. We would say the the meter is measuring the potential difference between the two points. This is often called voltage.

Forgive me as I add an analogy that would appear not to belong. Suppose you are riding a bicycle on a level road. You would have a "no-load" speed. As you started to climb a hill you will experience an increased load and start to slow down.

The same thing happens to sources of electrical energy. It will have a certain "no-load" voltage that usually drops when a load is applied. For example, a battery may have a no-load voltage of 13 VDC that drops to 12 VDC when a load is applied.

EMF is the no-load voltage.

Regards,

APD"
What are magnetic fields?,why is the direction of magnetic field is from north to south why not south to north?,"It is not a fact but is an agreement that was once made and is now the standpoint. They are just labels, the north seeking point of an magnet (northpole) turns to the North (magnetic southpole of the earth). The agreement is that all northseeking magnet sides are called northpoles and vice versa."
What are magnetic fields?,"In exercise 1a what would the compass point to when distracted by the magnetic field generated by the current flowing through the wire? And also why does the direction of the current matter, I understand it determines the direction of the field with respect to the wire but how does that affect, the effect the field has on the compass? it still generates a magnetic field regardless of the direction the current flows in and would essentially 'confuse' the compass anyway. Right?... HELP. SOMEONE. ANYONE??","Hello Alex,

Let's consider the compass without the added complexity of the wire. Here the magnetic field of the compass needle is influenced by the magnetic field of the earth.

When current flows in the wire the compass needle moves. It does so because the magnetic field of the wire is considerably stronger than the magnetic field of the earth.

To better understand please research "right hand rule." Also, you may be interested in the Tangent galvanometer.

Ref: 
https://en.wikipedia.org/wiki/Right-hand_rule

http://physics.kenyon.edu/EarlyApparatus/Electrical_Measurements/Tangent_Galvanometer/Tangent_Galvanometer.html

Please leave a comment if you still have questions.

Regards,

APD"
What are magnetic fields?,"Ok, so we say 1 pole is north other is south. But if like charges repel and unlike charges attract, how in the world we know if one is north or south. How can you even tell the difference. Is there any way? Two north repels. Two south repels. South and North attract and North and south attract. There's no way to tell!! :(",The way they are defined is geographic. The north pole points towards the north and vice versa.
What are magnetic fields?,is there something like magnetic compass and geographic compass? or all compasses are the same? and what's the difference between earth's magnetic and geographic poles?,The geographic pole is where the imaginary line representing the earth's axis of spin exits the earth.  The magnetic pole is where a compass points.
What are magnetic fields?,What would happen to a steel ball kept at the neutral point between two magnets?,If it is perfectly balanced between the magnets then it will stay there but it is in what is called an unstable equilibrium and any little change because of vibration or tap would cause it to fall out of equilibrium and the ball would move towards one of the magnets.
What are magnetic fields?,"If all magnetic fields are caused due to moving charges, how do magnets work?",go to youtube and search for "veritasium how do magnets work" and watch both videos
What is magnetic force?,what is electromagnetic induction,"Hello Yashwin,

Electromagnetic induction is what keeps the lights on! 

Our generators operate on this principle. All you need is a wire and a moving magnetic field. Or you could have a stationary magnetic field and a moving wire. Either way, the magnetic field appears to be changing from the wire's perspective. When this occurs a current will be induced in the wire. Sal has done a few videos on this topic. See:

https://www.khanacademy.org/science/physics/magnetic-forces-and-magnetic-fields/magnetic-flux-faradays-law/v/flux-and-magnetic-flux

Regards,

APD"
What is magnetic force?,what is left hand slap rule,">Find out if the charge is negative or positive
>If positive use right hand, if negative use left hand
>hold left/right hand out in front of you
>point thumb in direction charge is going
>the way your palm is facing tells you which way the field is going
> ?
> profit."
What is magnetic force?,"Is exercise 2b correct? The answer when I calculate it is 1.422 x 10^-4 T. Unless I'm entering the information in the calculator wrong, there maybe an arithmetic error here...

Here is what I punched in (even within google, you can copy and paste):
((9.1 * 10^-31) * (2 * 10^7)) / ((1.6 * 10^-19) * .8)",Good spot. Perhaps they rounded it off to 3 significant figures.
What is magnetic force?,""From the left-hand slap rule, we know that the magnetic force is perpendicular to the velocity. This is also the condition that gives rise to circular motion." 

I don't understand how magnetic force when perpendicular to the velocity gives rise to circular motion?","That's how you move in a circle, by constantly accelerating in a direction that is perpendicular to your velocity at that moment.  Review circular motion."
What is magnetic force?,what does 'in/out of the page' mean?,In the page means the vector is pointing straight perpendicular into the page/screen.  Similar for out.
What is magnetic force?,How was the formula F=qvB derived ?  Can somebody explain?,"It's not derived, it's an empirical observation."
What is magnetic force?,I could not understand the exercise 2b solution. I have problem with the cathode ray tube experiment.,I need more understanding.
What is magnetic flux?,Why we use cos( theta ) instead of sin (theta) in magnetic flux density's equation? I mean what is the reason behind using cos ( theta ),"Hello Faria,

Consider COS(θ) as shown in Figure 1. If θ = 0° as shown in part B then the maximum number of flux lines pass through the blue coil. When the coil has physically rotated 90 degrees we find θ = 90° and there are no flux lines passing through the coil.

We could have used SIN(θ) but we would need to rotate our plane of reference (green) to be vertical instead of horizontal.

Regards,

APD"
What is magnetic flux?,"Solution to How do we measure magnetic flux? Exercise 2
I agree with the calculations up until they say
Magnetic Flux Φ = (0.05 m ⋅ 0.06 m) ⋅ (4.1 mT) = 0.451 mWb
As far as I can tell Magnetic Flux Φ should = 0.0123 mWb? I could be wrong, if so please explain what I'm doing wrong. Thanks so much for taking the time to address this!","Yes, it looks like they added .05 and .06 rather than multiplying.  
I have notified the physics specialist at KA.
Good catch.  Thanks."
What is magnetic flux?,"I'm confused as to how the solution for the last exercise was derived. Firstly, how that graph was plotted seems out of context to me, but since it's one of the ways this question can be solved I would think of a different approach. Secondly, the SI unit for magnetic fields are supposed to be in Tesla, but the solution above says Tm (Tesla meters). Why is that? And what other approach can be used to solve this problem?","The graph was plotted by taking the equation for the magnitude of the magnetic field B = (μ0I)/(2πr) and treating it as a function of distance r from the wire:
B = f(r) = (μ0I)/(2πr) [assume I is constant].

To get the flux we need to multiply B times A, but the value of B is changing over the length of the side of area A which is perpendicular to the wire.

This is why we use the area under the curve of the function (the integral) to get a precise sum of the varying magnitudes of B over the length of the side of A moving away from the wire, rather than just multiplying by the value of B at some arbitrary point."
What is magnetic flux?,"Third Paragraph.
Where do we get the Magnetic Field Vector? Is it the Magnetic Flux Density?
I feel like Magnetic Flux is defined as Magnetic Flux Density times the area, and that Magnetic Flux Density is defined as Magnetic Flux divided by the area.","The magnetic field vector B is defined by the force it would apply to a charge moving in it.  
B = F/qv, so the units are (N *s) / (C *m), which we call a Tesla, or T.  This is also called flux density.  Flux is then given by B*A, so it is in T*m^2, which we also call a Weber."
What is magnetic flux?,"I don't get why closed surfaces have zero magnetic flux. Also, how is it different from magnetic flux in a non closed area?","A closed surface is something like a ball or balloon (even if its a weird shaped one). If a magnetic flux line cuts the surface going in, then it must cut the surface on its way out. So the net 'in' = zero

non-closed is like one side of a window or a sheet of paper.  

flux lines usually all go into your side of the paper or come out of it. (Sometimes, if its a loop of flux it goes in then comes back out. )
ok??"
"Light: Electromagnetic waves, the electromagnetic spectrum and photons","Does light have different speeds depending on the medium (e.g. air, water, etc) it is in? If it does, does it change wavelength, frequency, or both? When the speed decreases, does the light has less energy? Does light traveling through air, then water, then air again, has the same speed as it does in the beginning and in the end?","The speed of light can change.
The highest ever recorded is 299 792 458 m / s.
In 1998, Danish physicist Lene Vestergaard Hau led a combined team from Harvard University and the Rowland Institute for Science which succeeded in slowing a beam of light to about 17 meters per second, and researchers at UC Berkeley slowed the speed of light traveling through a semiconductor to 9.7 kilometers per second in 2004.
 Hau later succeeded in stopping light completely, and developed methods by which it can be stopped and later restarted."
"Light: Electromagnetic waves, the electromagnetic spectrum and photons",So do different kinds of lightbulbs give off different spectrums?,yeah! for example some lightbulbs are more "warm" and orangy and some are more white
"Light: Electromagnetic waves, the electromagnetic spectrum and photons",Where do we find a photon in an atom?,"Any kind of Electro-Magnetic wave travels in small energy packets called photons. In the visible range of light these are called photons and in the invisible range, i.e Infrared, UV and others the energy are called quanta. When a electron gains a certain amount of energy then it jumps to a higher energy orbit unless it has absorbed so much energy that its ejected, it again comes back to its original orbit after losing the energy i.e emitting it in form of Electro-magnetic Radiation. That is called emission spectrum."
"Light: Electromagnetic waves, the electromagnetic spectrum and photons","Why do things travel in waves and not in a straight line ?
simply if I throw  a ball , it doesnt make a wave. So why do electrons make waves ?","actually, you thrown ball does make a wave. its just that the wavelength is so small, you could not observe or measure it

DeBroglie said:
Wavelength = h/p h/mv  = (approx) 6 x 10>-34  /  (0.01 kg  x  20m/s)  = (roughly)  3 x 10>-33 m

a nucleus of an atom is about 10>-15 so, the wavelength of your thrwon ball is verrrrry small 

:)

ok??"
"Light: Electromagnetic waves, the electromagnetic spectrum and photons",from where photon is emmited or absorbed?,"Photons can be absorbed by electrons. These will increase in energy and jump energy levels. Afterward, the same electron can emit the photon to jump down energy levels."
"Light: Electromagnetic waves, the electromagnetic spectrum and photons",I am confused: is wave the energy itself or the disturbance in electromagnetic field caused by energy (like throwing a stone into a pond and wave forms),a wave can be described as the transmission of disturbance from one point to another OR the transmission of energy from on point to another
"Light: Electromagnetic waves, the electromagnetic spectrum and photons","Planck's equation for energy of an electromagnetic waves depends on only one factor - frequency or wavelength. Shouldn't amplitude, in some way, be directly related to energy? (I'm saying this after a comparison to sound .. sound is 'louder' when it has a large amplitude or a comparison the energy lost in a resistor in an AC circuit which equal to ((Vrms^2)*t)/R here Vrms is directly related to Vpeak which is the amplitude of the voltage signal. The energy is a directly related to the voltage's amplitude (square relationship) in an AC circuit , same as energy stored in a capacitor ..). All of this could be so wrong.. please correct me.","it might be too late but ill try to answer.
as per my understanding, a photon's energy is dependent only on its wavelength, that's what quantum mechanics tells us. photons do not have a "real" discernable amplitude. However, classical mechanics associates energy with amplitude. here's the problem though, you cannot use classical mechanics to deal with photons. we can approximate that the "amplitude" of a light wave is proportional to the number of photons hitting a particular surface per unit time. in other words, it is proportional to the intensity of the wave. this does not hold true when we consider one photon, only a system of many photons.

I am not an expert so PLEASE correct anything wrong I said :)"
"Light: Electromagnetic waves, the electromagnetic spectrum and photons","So the only thing I'm having trouble with is the relationship between a photon's frequency and a light wave's frequency. Is this correct?:

If you take the "frequency of a light wave" and multiply it by "6.626*10tothe-34" you get the frequency of a photon of that light wave?","First you cannot treat the energy of a classical light wave the same way as the energy of a photon.
The energy of a photon is E = hf.
The energy of a light wave is proportional to the square of the amplitude of oscillation of the electromagnetic wave.
These are two completely different models of light, classical vs quantum mechanical."
"Light: Electromagnetic waves, the electromagnetic spectrum and photons",How do you sole for wavelength?,"c/v gives [m/s] / [Hz]. And knowing that Hz (Hertz) is equal to 1/s, then we have [m/s] / [1/s] which gives us after removing the seconds unit to get meters as the wavelength's unit. Hope this helps!"
"Light: Electromagnetic waves, the electromagnetic spectrum and photons",What are some of the different effects that various frequencies of electromagnetic radiation have when absorbed by matter?,"The different effects light has on atoms can best be understood when considering the energies of types of light. And since energy and frequency are directly proportional, the trend we describe using energy will be the same for frequency. 

Higher energy light such as gamma rays, X-rays, and high energy UV light cause ionizations. They transfer enough energy to electrons so they can escape from the pull of the atom’s nucleus and turn the atom into an ion. 

Low energy UV and visible light cause electron transitions. The electrons are able to move between the energy levels within the atom, but do not have enough energy to escape. 

Infrared light causes molecular vibrations. The bonding atoms of a molecule vibrate back and forth like an oscillating spring. 

Microwaves cause rotational motion where a molecule rotates.

Radio waves cause nuclear spin transitions which is when a proton changes its spin state.

The lower the energy the light, the less work can be done with it by the atom when it absorbs that light. 

Hope that helps."
Bohr's model of hydrogen,what is quantum,"A quantum is the minimum amount of any physical entity involved in an interaction, so the smallest unit that cannot be a fraction."
Bohr's model of hydrogen,"I don't get why the electron that is at an infinite distance away from the nucleus has the energy 0 eV; because, an electron has the lowest energy when its in the first orbital, and for an electron to move up an orbital it has to absorb energy, which would mean the higher up an electron is the more energy it has. So if an electron is infinitely far away(I am assuming infinity in this context would mean a large distance relative to the size of an atom) it must have a lot of energy. Right?

Thanks very much!","you are right!

but what you need to remember now, is that the energy at infinity is DEFINED as being zero. Your next queston might be 'why?' :)

but, knowing that, does it now make sense that nearer to the nucleus, the energy is minus??"
Bohr's model of hydrogen,What does ΔE stand for?,"*The triangle stands for Delta, which also means a change in, in your case, this means a change in energy.*"
Bohr's model of hydrogen,what is the relationship between energy of light emitted and the periodic table ?,"Its a really good question. Here is my answer, but I would encourage you to explore this and similar questions further..

OK: I would say that the periodic table tells us about the number of protons in an element; and, therefore the number of electrons too. 

Now, the energy of the photon emitted from any element does not depend on the number of electrons in the atom. The value of the energies of  photons does depend on the available energy levels in the atom. Hydrogen, for example, although the simplest atom, has a whole range of photon energies that it emits.  This is because the electron can exist in many energy levels... as it switches from one energy level to another, then it emits / absorbs photons. 

We can, however, say that the more electrons there are in an atom, the greater the variety of photon energies there will be so this may be a link worth exploring

I hope that makes sense ok.

As I say, you are asking a great question.... looking for relationships in a meaningful way. I would encourage you to explore further.... maybe compare the number of different energies emitted by an element with its position in the periodic table, or the maximum / minimum energies emitted by the element vs position

Well done and keep up the good work."
Bohr's model of hydrogen,"Actually, i have heard that neutrons and protons are made up of quarks (6 kinds? up down ......)
Is it true? and how does the scientists found that out?","yes,       protons are made of 2 up and 1 down quarks whereas neutrons are made of 2 down and 1 up quarks . hope this helps."
Bohr's model of hydrogen,"Hi, great article. I was wondering, in the image representing the emission spectrum of sodium and the emission spectrum of the sun, how does this show that there is sodium in the sun's atmosphere? If both pictures are of emission spectra, and there is in fact sodium in the sun's atmosphere, wouldn't it be the case that those two dark lines are filled in on the sun's spectrum. The text below the image states that the bottom image is the sun's emission spectrum. Wouldn't that comparison only make sense if the top image was of sodium's emission spectrum, and the bottom was of the sun's absorbance spectrum? 

Thanks!","Sodium in the atmosphere of the Sun does emit radiation indeed. However, after photon from the Sun has been absorbed by sodium it loses all information related to from where it came and where it goes. So re emittion occurs in the random direction, resulting in much lower brightness compared to the intensity of the all other photos that move straight to us."
Bohr's model of hydrogen,Bohr said that electron does not radiate or absorb energy as long as it is in the same circular orbit. But according to the classical laws of electrodynamics it radiates energy. What is the reason for not radiating or absorbing energy?,Bohr did not answer to it.But Schrodinger's explanation regarding dual nature and then equating hV=mvr explains why the atomic orbitals are quantised
Bohr's model of hydrogen,why does'nt the bohr's atomic model work for those atoms that have more than one electron ?,"As far as i know, the answer is that its just too complicated.

With one electron and one proton you can figure out (with some difficulty) how they interact with one another because you have one centripetal force acting in the same 'direction' and analyse-able using classical circular motion etc. 

But with two electrons, now you have three forces; not just centripetal but also electron to electron. You can imagine in the classical view, how complex the change on force would be between the electrons and also the nucleus. It may be tht some one has figured a way of doing it or approximating to it, but, as far as I know this is the reason bohr model is only used for hydrogen."
Bohr's model of hydrogen,"so do we still not know that why do electrons not fall into the nucleus of the atom,i mean they are continuously emitting energy and of course at a point in time they should fall into the nucleus,what is the explantaion for that?","This is one of the main reasons we know that the Bohr model of the atom is wrong.  

In the quantum model of the atom electrons in their lowest possible orbital are in their ground state and can't be in any lower energy state and they do not radiate energy."
Bohr's model of hydrogen,Is Bohr's Model the most accurate model of atomic structure?,"No, it is not.  The quantum description of the electron orbitals is the best description we have."
N/A,what is the difference between ionization energy and the work function of a metal?,"work function refers to the energy required to remove the electron from the sea of electrons in a metal body whereas ionization energy refers to the energy required to eject the electron when it is present in the valence shell of the atom.
hope it explains the difference."
N/A,Do non-metal elements emit photoelectrons?,"Yes, but they have higher binding energies.
You have to use UV light or X-rays to dislodge the electrons.
This is the basis of the technique called *photoelectron spectroscopy*."
N/A,"We know that the photon is mass-less, so what is it's structure, how does it carry energy, where does it store it?
Or is the mass of the photon negligible not zero??",well I technically we cant treat light the same way we treat matter because daily things travel very slowly but when you are travelling at speeds beyond 10^6 ms^-1 the science is different matter and energy are interconvertible (e=mc^2) so it doesn't really store energy it is energy itself.
N/A,"Is intensity the same as brightness? Does it just refer to how much light there is?  Also, I get that if there is more light shining on a metal, the current will increase. However, why does the current not increase when the kinetic energy increases? If the particles are moving faster, wouldn't that speed up the current?

Finally, I don't really understand amplitude. Amplitude is the height of a wave's peak compared to its resting position. So wouldn't high amplitude mean there is a lower frequency and therefore lower energy?","Yes, intensity is the same as brightness.
The only way to increase the kinetic energy of the electrons is to increase the frequency.  If the frequency remains constant. the kinetic energy is also constant.
The amplitude of a wave does not affect its frequency. Two waves of different amplitude can have the same frequency."
N/A,"During the photoelectric effect, light knocks electrons out of metals. So why don't the metals in our home lose their electrons when we turn on the lights? 
Thanks in advance.",The metals in the home have too high a work function for the light to be able to knock out the electrons.
N/A,"I'm having a bit of trouble understanding the wave/particle duality. Is a photon a wave-like particle? When I think of the equation E=hv, I think about frequency in terms of a wave, but I think of the E in terms of a particle-like atom, so it is a bit hard for me to reconcile the two and understand why high frequency of the wave would mean that the photon has a higher kinetic energy.","A photon is a particle of light.   All very small particles sometimes act more like what we think of as waves.  By experiment, we know that the energy of the photon is given by E = hf."
N/A,What will happen if the energy of the photon is just equal to the work function of the metal? will the electron be pulled back in the orbit of the atom?,The electron will be "free" from the atom but will feel a pull because of the positive charge of the atom and likely will get pulled back into the atom.
N/A,How is amplitude proportional to the number of photons with the same frequency?,"The intensity of the light is a result of the number of photons. 
If the light were a wave, the intensity would be represented by the amplitude of the wave."
N/A,Is the quantum realm a real place or is it just a myth in ant man?,"I mean, the quantum realm is a fictional place in the MCU. It’s little more than magic portals made to sound more serious and scientific by adding quantum. 

In the real world quantum usually refers to quantum mechanics, or simply the workings of matter and energy at the very small, atomic level."
N/A,how can light have momentum if it has no mass,Light also has a wave nature which allows it to have momentum
The heart is a double pump,What is diastolic and systolic blood pressure??And please tell me how and why do we get high blood pressure and low blood pressure??,"Diastolic blood pressure measures the pressure in your blood vessels between heartbeats (when your heart is resting). Systolic pressure is the force of blood in the arteries as the heart beats. It is shown as the top number in a blood pressure reading(it should be the higher number between the two). High blood pressure is 140 and higher for systolic pressure. To answer your other questions, there are many reasons blood pressure fluctuates. High blood pressure, known as hypertension, can be caused by narrowing of the arteries, a greater than normal volume of blood, or the heart beating faster or more forcefully than it should-which all force the heart to pump harder then it should have to/ increased pressure against the artery walls. Low blood pressure, known as hypotension, disrupt the body's ability to control blood pressure. Common causes of this commonly include medications and can be a sign to a much more serious problem if detected with more underlying symptoms of illness. There are many types of hypotension and each come with their own causes and implications."
The heart is a double pump,"How much blood is in the lungs getting oxygenated? Does blood go from the right ventricle PUMP, then into the lungs PUMP, then into the left atrium PUMP, then into the aorta? What I'm trying to ask is how long the blood is in the lungs before it gets pumped back into the heart for distribution?",The cardiac cycle lasts for a total of 0.8 seconds.
The heart is a double pump,How long does it take for the heart to pump all the blood in your body?,"Firstly, it is important to try and think about the blood flow being constantly ongoing rather than it being pumped round at intervals. For example, if you take a 70kg man, he may have a total volume of blood of 5L. Some of this will be in the lungs being oxygenated; some will be in the aorta being pumped around the body; some in the brain or other tissues giving up its oxygen to the cells etc. This means that once one group of blood cells have released their oxygen to the tissues, the ones behind in the flow immediately take their place and so on. This is happening constantly, not at intervals, so thinking about certain tissues being oxygenated “more frequently” is not correct. Some organs, like the brain kidneys and heart need more oxygen than others, like the skin, but this is catered for by having more blood flowing to these organs. In some organs it will be faster and some slower, depending on how much that organ needs.

Now that said, let’s work out how long it would take for a heart to pump that much blood through itself. Let’s take our 70kg man with an estimated 5L of blood. Now the amount the heart pumps depends on how much blood it pumps in one beat and also how often it beats. Both of these vary depending on whether the person is at rest or doing exercise, and also how well his heart works. If we take our man to have a resting heart rate of 70 beats per minute and take a stroke volume (amount the heart pumps on each beat) of 70ml (from Wikipedia), he would pump 4900ml (70 x 70=4900) in 1 minute. So he would pump almost the entire volume of his blood through his heart in 1 minute.

However, if we now send our man to run up and down several flights of stairs, his heart rate may then increase to 120 beats per minute. The stroke volume is also likely to increase after the exercise, let’s say to 90ml. Then he would be pumping 10800ml (120 x 90) in one minute. That means that his heart pumps over 5 litres in 30 seconds.

The values here are just estimates to illustrate that the amount the heart pumps can alter depending on what is going on to the body."
The heart is a double pump,What can I compare a 5 mmHg and 120 mmHg pressure to? Is the pressure comparable to e.g. the pressure of a car on your foot? More/less?,The pressure of the atmosphere on a surface near sea level is about 15 PSI (pounds per square inch). There are about 52 mmHg in a single unit of PSI. So if you think about it this way 120 mmHg is equal to somewhere around 2.32 PSI. In my experience the average inflation pressure for a car tire is 22 PSI so that should give you a reference point. We are not tires.
The heart is a double pump,for the blood test blood is taken out from arteries or vein?,"There are a number of reasons why veins receive such preferential treatment by medical professionals around the globe. Firstly, veins are comparatively easier to draw blood from, physically speaking, as the placement of veins is such that they are close to the surface of skin. This makes the process easier by avoiding a deep needle plunge just to draw a bit of blood. On the contrary, arteries are located a bit deeper in the skin, so it doesn’t make much sense to make the process unnecessarily difficult – and potentially dangerous.

The walls of veins are also thinner than arteries, which enables them to hold more blood (more volume). This quickens the process of blood collection and simultaneously results in more blood released into the sample tube.  It’s also easier to pierce a vein than it is to pierce an artery, so drawing blood from a vein is less painful for the subject.

The pressure in the veins is less than that of the arteries, so there’s a smaller chance of blood coming back through the spot where you were punctured by the needle before the tiny wound is healed."
The heart is a double pump,"I'm going through these as a nursing student and I guess it only got interesting asking why have two ventricles.  (don't reptiles have 3 chambers?)  Not necessarily a problem with your program, more my instructor, but you might assume the student knows the proceeding material at least.","Fishes have simple blood circulation: one atrium, one ventricle that pumps blood to gills where the blood flows to tissues and back to the heart.

Reptiles have imperfect double circulation: two atrium and one chamber. Blood flows from tissues to one atrium and to the only ventricle. ventricle pumps blood to the lungs and also to the systemic flow. From the lungs blood comes back to the heart (another atrium) and to the only ventricle where oxygenated blood mixes with unoxygenated.

Birds and mammals have perfect double blood circulation. It's the most efficient because it generates the highest oxygen levels in the systemic flow. So tissues have more oxygen and therefor cells can keep up higher metabolic rate than for example reptile-cells.
Birds and mammals are warm-blooded and our metabolic rate and capability to action is not so determined by the temperature of environment."
The heart is a double pump,"On the last part where they debunk the suggestion that a system without the blood going back to the heart, instead going straight to the lungs, they say it won't work because the amount of pressure required to make the blood move that much would break the capillaries. What if we just had stronger capillaries? Isn't that a valid solution?","It is a valid solution, but not an easily attainable one. To strengthen the capillaries, the wall needs to be thickened at the cost of easy diffusion of materials across it. Or, the collagenous material impregnated with hard salts, loosing the highly flexible nature of capillaries.
Nature, after millions of years of evolution, came up with the perfect amount of tradeoff for a good capillary, which needs to be accompanied by a system which saves it from rupture."
The heart is a double pump,which direction does blood flow? does it change if you are doing a handstand?,"Blood flow: (Pulmonary Circulation)R-Atrium ->R-Ventricle ->Pulmonary Arteries ->Lungs ->Pulmonary Veins -> (Systematic Circulation)L-Atrium ->L-Ventricle ->Aorta ->Arterioles ->Capillaries throughout the body -> Superior and Inferior Veins -> R-Atrium(the starting station).

The direction of blood flow won't change whatever postures you have. Additionally, the valves, such as semilunar valves, tricuspid valves, and mitral valves function to prevent blood from flowing at an opposite direction."
The heart is a double pump,"When you described a hemoglobin being a protein that uses iron to help bind to O2 molecules, what happens when the body lacks iron? Does something happen with the blood flow or does it interfere with binding the oxygen molecules to the hemoglobin?","A lack of iron is called anaemia and means that the haemoglobin protein can't be formed so less oxygen can bind. General symptoms are weakness, fatigue, pale skin and dizziness. On a blood film, red blood cells are small (microcytic) and pale (hypochromic)."
The heart is a double pump,what is a heart,A heart is the organ in the upper-middle part of your chest that filters and pumps blood to the rest of your body.
The heart is a double pump,What is diastolic and systolic blood pressure??And please tell me how and why do we get high blood pressure and low blood pressure??,"Diastolic blood pressure measures the pressure in your blood vessels between heartbeats (when your heart is resting). Systolic pressure is the force of blood in the arteries as the heart beats. It is shown as the top number in a blood pressure reading(it should be the higher number between the two). High blood pressure is 140 and higher for systolic pressure. To answer your other questions, there are many reasons blood pressure fluctuates. High blood pressure, known as hypertension, can be caused by narrowing of the arteries, a greater than normal volume of blood, or the heart beating faster or more forcefully than it should-which all force the heart to pump harder then it should have to/ increased pressure against the artery walls. Low blood pressure, known as hypotension, disrupt the body's ability to control blood pressure. Common causes of this commonly include medications and can be a sign to a much more serious problem if detected with more underlying symptoms of illness. There are many types of hypotension and each come with their own causes and implications."
The heart is a double pump,"How much blood is in the lungs getting oxygenated? Does blood go from the right ventricle PUMP, then into the lungs PUMP, then into the left atrium PUMP, then into the aorta? What I'm trying to ask is how long the blood is in the lungs before it gets pumped back into the heart for distribution?",The cardiac cycle lasts for a total of 0.8 seconds.
The heart is a double pump,How long does it take for the heart to pump all the blood in your body?,"Firstly, it is important to try and think about the blood flow being constantly ongoing rather than it being pumped round at intervals. For example, if you take a 70kg man, he may have a total volume of blood of 5L. Some of this will be in the lungs being oxygenated; some will be in the aorta being pumped around the body; some in the brain or other tissues giving up its oxygen to the cells etc. This means that once one group of blood cells have released their oxygen to the tissues, the ones behind in the flow immediately take their place and so on. This is happening constantly, not at intervals, so thinking about certain tissues being oxygenated “more frequently” is not correct. Some organs, like the brain kidneys and heart need more oxygen than others, like the skin, but this is catered for by having more blood flowing to these organs. In some organs it will be faster and some slower, depending on how much that organ needs.

Now that said, let’s work out how long it would take for a heart to pump that much blood through itself. Let’s take our 70kg man with an estimated 5L of blood. Now the amount the heart pumps depends on how much blood it pumps in one beat and also how often it beats. Both of these vary depending on whether the person is at rest or doing exercise, and also how well his heart works. If we take our man to have a resting heart rate of 70 beats per minute and take a stroke volume (amount the heart pumps on each beat) of 70ml (from Wikipedia), he would pump 4900ml (70 x 70=4900) in 1 minute. So he would pump almost the entire volume of his blood through his heart in 1 minute.

However, if we now send our man to run up and down several flights of stairs, his heart rate may then increase to 120 beats per minute. The stroke volume is also likely to increase after the exercise, let’s say to 90ml. Then he would be pumping 10800ml (120 x 90) in one minute. That means that his heart pumps over 5 litres in 30 seconds.

The values here are just estimates to illustrate that the amount the heart pumps can alter depending on what is going on to the body."
The heart is a double pump,What can I compare a 5 mmHg and 120 mmHg pressure to? Is the pressure comparable to e.g. the pressure of a car on your foot? More/less?,The pressure of the atmosphere on a surface near sea level is about 15 PSI (pounds per square inch). There are about 52 mmHg in a single unit of PSI. So if you think about it this way 120 mmHg is equal to somewhere around 2.32 PSI. In my experience the average inflation pressure for a car tire is 22 PSI so that should give you a reference point. We are not tires.
The heart is a double pump,for the blood test blood is taken out from arteries or vein?,"There are a number of reasons why veins receive such preferential treatment by medical professionals around the globe. Firstly, veins are comparatively easier to draw blood from, physically speaking, as the placement of veins is such that they are close to the surface of skin. This makes the process easier by avoiding a deep needle plunge just to draw a bit of blood. On the contrary, arteries are located a bit deeper in the skin, so it doesn’t make much sense to make the process unnecessarily difficult – and potentially dangerous.

The walls of veins are also thinner than arteries, which enables them to hold more blood (more volume). This quickens the process of blood collection and simultaneously results in more blood released into the sample tube.  It’s also easier to pierce a vein than it is to pierce an artery, so drawing blood from a vein is less painful for the subject.

The pressure in the veins is less than that of the arteries, so there’s a smaller chance of blood coming back through the spot where you were punctured by the needle before the tiny wound is healed."
The heart is a double pump,"I'm going through these as a nursing student and I guess it only got interesting asking why have two ventricles.  (don't reptiles have 3 chambers?)  Not necessarily a problem with your program, more my instructor, but you might assume the student knows the proceeding material at least.","Fishes have simple blood circulation: one atrium, one ventricle that pumps blood to gills where the blood flows to tissues and back to the heart.

Reptiles have imperfect double circulation: two atrium and one chamber. Blood flows from tissues to one atrium and to the only ventricle. ventricle pumps blood to the lungs and also to the systemic flow. From the lungs blood comes back to the heart (another atrium) and to the only ventricle where oxygenated blood mixes with unoxygenated.

Birds and mammals have perfect double blood circulation. It's the most efficient because it generates the highest oxygen levels in the systemic flow. So tissues have more oxygen and therefor cells can keep up higher metabolic rate than for example reptile-cells.
Birds and mammals are warm-blooded and our metabolic rate and capability to action is not so determined by the temperature of environment."
The heart is a double pump,"On the last part where they debunk the suggestion that a system without the blood going back to the heart, instead going straight to the lungs, they say it won't work because the amount of pressure required to make the blood move that much would break the capillaries. What if we just had stronger capillaries? Isn't that a valid solution?","It is a valid solution, but not an easily attainable one. To strengthen the capillaries, the wall needs to be thickened at the cost of easy diffusion of materials across it. Or, the collagenous material impregnated with hard salts, loosing the highly flexible nature of capillaries.
Nature, after millions of years of evolution, came up with the perfect amount of tradeoff for a good capillary, which needs to be accompanied by a system which saves it from rupture."
The heart is a double pump,which direction does blood flow? does it change if you are doing a handstand?,"Blood flow: (Pulmonary Circulation)R-Atrium ->R-Ventricle ->Pulmonary Arteries ->Lungs ->Pulmonary Veins -> (Systematic Circulation)L-Atrium ->L-Ventricle ->Aorta ->Arterioles ->Capillaries throughout the body -> Superior and Inferior Veins -> R-Atrium(the starting station).

The direction of blood flow won't change whatever postures you have. Additionally, the valves, such as semilunar valves, tricuspid valves, and mitral valves function to prevent blood from flowing at an opposite direction."
The heart is a double pump,"When you described a hemoglobin being a protein that uses iron to help bind to O2 molecules, what happens when the body lacks iron? Does something happen with the blood flow or does it interfere with binding the oxygen molecules to the hemoglobin?","A lack of iron is called anaemia and means that the haemoglobin protein can't be formed so less oxygen can bind. General symptoms are weakness, fatigue, pale skin and dizziness. On a blood film, red blood cells are small (microcytic) and pale (hypochromic)."
The heart is a double pump,what is a heart,A heart is the organ in the upper-middle part of your chest that filters and pumps blood to the rest of your body.
What is a stroke?,I have questions : I eat healthy and I play sports everyday but I have a high cholesterol. I am still wondering why I have high cholesterol in my body when I eat healthy and play sports. Can someone help me? Is it like some kind of genetic or what?,"Strokes also have a genetic component. Family history high blood pressure, high cholesterol and diabetes are all major factors that can cause strokes. Its better if you have a periodic health checkup to make sure your cholesterol level and blood pressure are normal, if you have a family history of stroke.  A good diet and plenty of exercise is essential to remain healthy in general, so you shouldn't worry much:)."
What is a stroke?,Why does a stroke happen and is there anyway to prevent it?,"There are two types of stroke.  Ischemic and hemorrhagic.  Ischemia happens when tissue in the brain loses its oxygen supply, most commonly from a blood clot blocking a cerebral artery.  Hemorrhagic strokes usually occur when there is an aneurysm that breaks within a cerebral artery, leading to bleeding into the skull and compression of the brain tissue.  

Age, sex, genes, and family history all have implications in stroke, and are considered "unmodifiable" risk factors.  This means they cannot be changed, and therefore cannot reduce your risk for stroke.  

Diabetes, heart disease, atherosclerosis (cholesterol levels), atrial fibrillation, alcohol intake, smoking, diet, exercise, and blood pressure when high can all increase your risk for stroke.  These are all "modifiable" stroke risk factors, meaning you can control them and lower them to reduce your risk of stroke.

Clinically, if a patient has already had a stroke and we want to reduce their chances of having another one, we give "blood thinners" which lower the blood's ability to form blood clots.  We also try and target the "modifiable" risk factors above with lifestyle modifications and medications.  (BP medicine, cholesterol medicine, etc.)"
What is a stroke?,If a family member had a mini-stroke are you at risk?,"Hello there NaiNai! 
I'm supposing that your question is: Are TIAs (transient ischemic attacks or mini strokes) familial occurrences? 
Here's something interesting. Full strokes actually have been found to run in families! This would lead me to say that you would have an _increased_ risk of TIA if an immediate family member had one. I said _increased_ risk though. Not that you will definitely have one, or that you have a high risk of having one.

The risk factors for TIAs are:
Diabetes
Smoking
Alcoholism
Age
HTN hypertension
CAD coronary artery disease
PAD peripheral artery disease
High cholesterol
High homocysteine

Several of these are modifiable risk factors -- things you can change that will lower your risk. For example, don't smoke, don't drink, eat a lower choleterol diet.

Some of them you can't change, like your age, or already progressed CAD or PAD. You can control them but not change them.

Also consider:

Family members tend to have similar lifestyle habits. They might eat the same way, or they may not exercise. This leads to certain health problems running in families."
What is a stroke?,when you have a stroke can it cause part of your body to go into shock and you become palatalized?,"Paralyzed, and yes, it can. Your muscles freeze up and die without oxygen, and the result is paralysis."
Overview of heart failure,"Thanks this was really useful revision. However, in the section: "How likely are you to get heart failure?" do you mean incidence increases with age rather than prevalence? Im not trying to be facetious, its just that I've only just got my head around these terms and this seems to contradict my own understanding of them.",I think prevalence is a better word because this prevents recounting people in an age bracket who might have recovered from heart failure and then fell back into it.
Overview of heart failure,why do people have  heart probems,"There are  a variety of reasons people can have heart problems, including poor diet, lack of exercise, exposure to toxins (smoke), excessive weight, etc."
N/A,is there any other way to get vitamin d,"There are many food sources of Vitamin D such as cold water fish, mushrooms, tofu, and fortified foods such as cow and nut milks, cereals, and juices."
N/A,If a family member has hypertension are you at risk?,"you have one risk factor, but it doesn't mean you have it too. simply have your blood pressure checked at your doctor's / local clinic and keep a healthy lifestyle :)"
N/A,"My age is 25 I have high blood pressure that is 150/120, is that risky ?",That is risky.  The upper end of the normal range is 120/80.
N/A,what do high blood pressure look like when it is high for people under the age of 20 how do we suppose to know when our blood s high?,"Generally, young people visit the doctor once or twice a year and a routine checkup should include a measurement of blood pressure. If you're worried, most supermarkets with a pharmacy should have a place tucked away where you can sit down and measure yourself at your leisure."
Respiratory distress,"I would like to hear more possible lung sounds, like wheezing and other abnormal findings. Thanks!","Thank you so much for the reference to this website, it will greatly enhance my knowledge as a future physician!"
Respiratory distress,Does your body  make noise inside when you breathe?,good question if u can hear your heartbeat then im sure that u can hear your breathing
Respiratory distress,It talks about stridor in the article. Is that a separate thing than wheezing? Are they related?,Stridor is typically caused by an obstruction to the airway and is characterized by a high pitched or grating whistle emanating from the throat. Wheezing has many causes and is often described as a whistling or rattling sound within the chest.
Anemia: At a glance,Why do men have more red blood cells and hemoglobin in a given volume of blood than women does.,"On average, men are larger, heavier and have more muscle mass than women and thus require a greater oxygen load for their tissues. Men also have larger, heavier skeletons on average."
Anemia: At a glance,Why is sickle celled anemia mostly found in African heritage?,"Sickle cell anemia is a recessive disease, meaning that it only shows up in a person who has no dominant traits in the genetic alleles that determine whether they will have sickle-shaped cells or not. Sickle cell is found more frequently in the African heritage because of the increased risk of catching malaria there. This is because those who have heterozygous alleles in their DNA-meaning they carry both one recessive allele and one dominant allele- are immune to malaria AND do not show any symptoms for sickle cell anemia. These people are naturally selected to survive from the quickly killing malaria that, as I have stated before, is very common in Africa and therefore live to reproduce. When they do, the recessive traits that code for sickle cell in their alleles can still be passed on to their children and so on through the generations, which is why sickle cell anemia is more prevalent in those of African descent."
Anemia: At a glance,"Are there any other factors exept for iron intake with food, I mean could lack of motion, constant depression, etc cause anemia?","No, lack of motion doesn't cause anemia.
It is caused by low iron or/and B12 intake.
But some factors can decrease the level of iron/B12 in your blood.
Tea for instance, is known to decrease iron absorption: if you have tea with a meal, or a short time after a meal, the iron is not absorbed as it should.

Abuse of alcohol is bad for the B12 vitamin absorption, etc...

An increasing number of people have a B12 deficiency
https://chriskresser.com/b12-deficiency-a-silent-epidemic-with-serious-consequences/
, and vegan people have more trouble than other ones to find a good source of B12.
A very good vegan source of B12 is chlorella (rich in B12 and iron) and kefir.
If one plans to take chrlorella, he should begin by small amounts; some people are more intolerant than other, but it's a very good nutrient.

A list of B12-rich food:
http://www.healthaliciousness.com/articles/foods-high-in-vitamin-B12.php"
Anemia: At a glance,Is it anemia or anaemia? I've seen both.,"Anemia in American English, anaemia in the UK."
Anemia: At a glance,"As a nurse, 
what manifestation do you expect from a patient with B12 deficiency ?","A wide variety of signs and symptoms may occur including a decreased ability to think and changes in personality such as depression, irritability, and psychosis. Abnormal sensations, changes in reflexes, and poor muscle function can also occur as may inflammation of the tongue, decreased taste, low red blood cells, reduced heart function, and decreased fertility (Harrington)."
Anemia: At a glance,Does anemia make people go mental?,"Check this out:
http://www.empowher.com/mental-health/content/how-does-anemia-affect-mental-health"
Anemia: At a glance,"Are there any other factors exept for iron intake with food, I mean could lack of motion, constant depression, etc cause anemia?","I assume by lack of motion you mean 'inactivity.' Depression and inactivity are not going to directly cause anemia. These are major risk factors for developing certain diseases though. And there is such a thing as anemia of chronic disease. This is when your organs fail to produce certain components necessary for red blood cell production or hemoglobin production. Also, there can be internal blood loss from chronic disease, such as chron's disease."
What is diabetes mellitus?,"In reference to blood glucose levels, some foods are labeled low glycemic. What properties of such foods make it so? Is it simply the absence of sugar?",a low glycemic food just means it won't create a big spike in your blood glucose levels. Like if you eat potatoes they are really starchy so when that breaks down into glucose it make a big spike . So you feel hyper then tired. A low glycemic food like brown rice would give you slow but constant levels of energy as it breaks down .
What is diabetes mellitus?,"Is this a disease that is more likely to be inherited, lifestyle or environmental?","Type one is an autoimmune disease where the body attacks your beta cells in the pancreas, which means you cannot make insulin. The cause is unknown, although there are suspected genetic links.
Type two is environmental, mostly, although you can have a genetic predisposition to it. Old age, sugary diet and lack of exercise are the hallmarks for type 11."
What is diabetes mellitus?,"Suppose a person has a predisposition to diabetes type 2, once there are many cases in his/her family. Having this in mind, if this person changes his/her lifestyle, trying to eat healthier and exercising, is it possible that this person will never have diabetes type 2?","It is very possible that the person will not have DM type 2 if they live a healthy lifestyle, exercise regularly, and eat healthy while keeping a healthy weight. Generally, if you avoid the risk factors of a disease, you can avoid the disease. That being said though, there are many people who have been diagnosed with type 2 whose only risk factor was genetic predisposition."
What is diabetes mellitus?,Do you get Type 1 Diabetes at birth of can this develop over time? If it does develop over time does the pancreas just stop producing insulin? Also what other endocrine diseases are there?,"It is possible if the child's immune system is going ultra-paranoid and is getting confused between bacteria and the tiny insulin cells at the starting(autoimmunity,something you don't want). No, the cells start to produce less insulin and finally lose the spark that keeps them running."
What is diabetes mellitus?,"For type one diabetes, could increased urination be caused by increased thirst? I would assume increased thirst will result in drinking more water.","There is a good observation here: how much water comes out should (roughly) match how much water goes in. It makes sense that taking in more water would mean that more urine is produced. The problem with this as an explanation is that we've just moved the problem, and now we need to work out why the patient is thirsty.

Thirst happens for 2 main reasons: there's a decrease in circulating volume, or there's an increase in sodium concentrations. Both of these things reflect water leaving the body - so now our question is why the water is leaving.

In diabetes we have a really good explanation for this: there's lots of sugar left in the renal filtrate, and that causes water to be drawn into the urine. Because there's lots of sugar, the sodium-glucose transporters can take most of the sodium back out of the urine. This means that there's lots of water leaving the body but most of the salt is staying behind - which then activates the reflexes for thirst. That thirst reflex then drives the extra drinking to replace all the water that's being lost in the urine."
What is diabetes mellitus?,Why some pregnant develop gestational diabetes?,"One of the hormones released by the placenta is called Human Placental Lactogen. This protein increases insulin resistance in the mother, i.e. her cells do not respond as strongly to insulin, and so do not take up as much glucose, which makes sure that enough glucose is left behind for the baby.

The decreased insulin uptake by the mother can result in higher levels of glucose in her blood than normal, which is termed gestational diabetes.

It's perhaps interesting that human placental lactogen is not very potent under normal circumstances, but becomes important in conditions of starvation, when there is little glucose to go around, and so the placenta tries to reserve the baby's slice of the cake"
What is diabetes mellitus?,"In this article, it says that in Type 2 Diabetes the body cells develop a certain resilience towards insulin, but I've also read that the pancreas does not produce enough insulin to control the blood sugar levels. These are two conflicting statements, which one is it?","Sometimes it is useful to read an article a couple of times because the information is so dense, it is hard to comprehend.  However, in this case, the problem is also complicated.  In this article It says type 2 DIabetes mellitus is a continuum, that means the reasons causing the condition often change over time for the patient.    It says the problem starts with the cells developing a resistance (not resilience) to insulin for reasons that are not fully understood.  Over time, as the condition continues to affect the body, the pancreas slows down its production of insulin.  So, both statements are true because the disease progresses, there is a continuum of symptoms and reasons for those symptoms.
 A person with Type 2 DM may be able to stop the progression with life style changes early on in the condition.  However, if they do not, they start out with 'cellular resistance' to insulin and they progress to having a pancreas that ceases to make insulin.  A type 2 will end up injecting insulin which is how a Type 1 starts out.  Both statements are true, over time.  Happy learning to you."
N/A,Is physiotherapy helpful for parkinsons patients?How?,Yes exercise therapies help patients in better coordination of their body parts and muscles
N/A,Are the XY chromosomes a factor in men getting parkinson's disease more often then women?,That is certainly a possibility! I don't believe they have a specific conclusion yet. You might like this publication: http://jnnp.bmj.com/content/75/4/637.full
N/A,Is there any nervous system disease that has cure without side effects on the medicines prescribed by the neurologist?? almost all nervous system diseases have no cure be it Alzheimer's or Parkinson's or anything?? it really scares me that anybody suffering from these diseases will have to be swallowed by the coils of death. How many people can we protect?:(,Dr Joel Wallach of (Youngevity 90Forlife)is an expert in these areas. See the book"Epigenetics."
N/A,What happens in the last stages of Parkinson's Disease?  It would be nice to understand the stages of progression to death.,"That answer, sad to say, is completely inaccurate. You _can_ die from Parkinson's (as the tremors get worse and worse, dyskinesia becomes lack of movement at all, etc)."
N/A,parkinson's disease is not the same as Addison's disease?,Addison's disease is a hormone disorder having to do with the adrenals and that is a gland disease when Parkinson's deals with neurons they are two different things completely.
N/A,"In the "What Treatments are Available for Parkinson's?" section of the text, the other medications subheading listed Amantadine as a possible option to treat Parkinson's. There is no statement how or why it works, as well as no further statement via www.Drugs.com outside of the information that it is an NMDA Receptor Antagonist. Is there any updated information regarding that specific prescription and how it treats Parkinson's disease, or if there is any new information for treatment?","Amantadine is an adjunct med that is typically given in combination with Levodopa, carbidopa,   MAO type B inhibitors, and COMT inhibitors. As the article states exercise/physical activity is a very beneficial adjust as well, as long as the gait disturbances don't make it contraindicated. Truly the treatment of PD is an art, each patient is unique and requires an optimization of meds and adjuncts to delay disease progression."
N/A,"well, if you say that there's not really a cure for the disease, it might just sound sort of weird because I have never really known that there is a disease that can't be cured.","There are tons of diseases which cannot be cured, their symptoms can only be managed. HIV, AIDS, Asthma, Heart Failure, Angina, Epilepsy, to name a few."
What is Down syndrome?,"In Down Syndrome,  which gender is most likely affected on, females or males?","According to a research, male prevalence was found. You cane check out the research paper here: https://www.researchgate.net/publication/11422875_Sex_ratio_in_Down_syndrome_Studies_in_patients_with_confirmed_trisomy_21"
What is Down syndrome?,Are their any other ways you can get down syndrome besides what they have told us.,"No, down syndrome is a genetic disease. Persons affected have an extra copy of chromosome 21. This can only happen at conception. The syndrome is apearant at birth, so older children or adults cannot randomly get it, when they dont already have it."
What is Down syndrome?,"How can a failure in the oocyte's meiosis II lead to mosaicism? Wouldn't it just be a complete trisomy 21? Since meiosis II happened after fertilization but before the zygote's first division, wouldn't all cells have trisomy 21?","You are correct.  This page has a more correct representation.  Mosaicism occurs with early mitosis.
https://www.ndss.org/about-down-syndrome/down-syndrome/"
What is Down syndrome?,"With mosaicism it says that the incorrect separation happens shortly after fertilisation of the egg cell. Though in the drawing there's also a separation at the first meiosis. Is this drawn incorrectly or does the explanation miss something? Because right now the numbers don't add up (24 from egg cell + 23 from sperm cell should give 47 like with trisomy 21, but it shows 46...)","You are correct.  Good eye.  This needs to be changed.  I am sorry, I was wrong."
What is Down syndrome?,"In the diagrams for Trisomy 21 and mosaicism, the fertilized eggs undergo meiosis II. Why? Is this a mistake or am I just not understanding it?","Egg cells that are ready to be fertilized are temporarily stuck meiosis I, and won't go into meiosis II until fertilized (which is different from sperm cells!). If you remember meiosis should produce 4 cells (and it does in males), but that seems a bit strange because you also know that in humans normally only one egg cell is is ovulated right?

It turns out in meiosis I the one cell becomes the egg and the second becomes a very small Polar Body on the side of the egg. It then waits until a sperm fuses with it membrane, and at that moment the oocyte undergoes meiosis II, creating another polar body and becomes the fully mature "Ovum" which doesn't last long because the sperm 'pronucleus' is already there and headed to join with the ovum's 'pronucleus' to create a "Zygote" with its nucleus."
What is Down syndrome?,"It is stated that down syndrome is not inherited, then why is it also stated that one of the   risk factors can be already having a child having down syndrome. Isn't is purely by chance?","Typically, Down syndrome is by incorrect chromosomal separation during meiosis.  If the person did it once, then they have a higher likelihood of doing it again, that is what is observed.  It is also observed that older women have  higher incidence.  We are unsure why this happens but we know it is not simple chance. https://www.nichd.nih.gov/health/topics/down/conditioninfo/Pages/risk.aspx#f3"
What is Down syndrome?,"Someone with trisomy 21 could pass on Down's Syndrome to their offspring, right, because some of their sex cells would have 2 copies of chromosome 21? Also, can a person with mosaicism pass on the disorder to their offspring? If not, why not? And in a normal person who has a child with Down's Syndrome, what happens to the sex cell that has no copy of chromosome 21? May it also get fertilized? Thank you.","Yes, 50% or so of the ova would have 2 copies of chromosome 21 so approximately 50 % of offspring will also have Down Syndrome.  A mosaic individual has some cells with Trisomy 21 and some normal cells.  So the question would be what % of the ovary cells are affected (assuming a female Down Syndrome patient)..  If all of them are affected, then it would be approximately 50 % as above.  If it was less, then the percentage affected would also be less.  A fertilized cell with only one Chromosome 21 (from one parent) and none from the other parent is not viable, so it might get fertilized, but it would miscarry as it would be unable to develop.."
"Dementia and Delirium, including Alzheimer’s","my grandmother has dementia and she yells at me for no reason, she has stopped taking her meds and locking he car. Also she has yet to take a shower and clean the house since I moved up here to take care of her. every time I speak to her about what she need to do on her life she would yell at me back and never talk to me for the rest of the day PLZ HELP what should I DO ?","Be patient. If it's possible, get a live-in caretaker. It sounds like you can't handle and weren't ready for the responsibility of caring for a dementia patient. If worse comes to worse, there is the option of moving her into a long-term care facility. They make residencies just for people with dementia. 

good luck to you and your grandmother."
"Dementia and Delirium, including Alzheimer’s",What causes Alzheimer's disease?,I've read that countries which don't add floride to public water have much lower rates of Alzheimer's. Is this true?
"Dementia and Delirium, including Alzheimer’s",I am writing my dissertation on memory loss and want to reference this article. I was wondering if you could tell me who wrote this and when it was originally written?,click on attributes and references and it will give you what you need i think
What is depression?,Does anyone know how fear is created?,"Fear is actually learned! Our body does respond to some situations by pumping us full of adrenaline that makes our heart race but one thing might not be scary to you but be very scary to me. I can learn that every time i hear a special bell, someone is going to try and hit me. But if you never learned that, when you hear that bell you will not be afraid. Lots of people learn to be afraid of the same things, bee's (because every time they see bee's they think they are about to get hurt). Fear is a survival mechanism, making us very careful around 1. things that hurt us 2. things we don't understand, and likely many more things."
What is depression?,Do we have more than just the 5 senses?  Do you ever get that feeling when like you are walking alone in the dark and it feels like someone is watching or following you. Or when I walk up the steps to my room and it feels like someone is right behind me....,"We do! Those 5 senses are the main ones but they are broad and we have so many more. For example, we have a sense of time, a sense of balance, a sense of temperature, of pain, of pressure, proprioception (a sense of where your body parts are relatively to the rest of you) and the list goes on and on!"
What is depression?,What happens when somebody has depression but cannot afford treatment?,The sad thing is many can afford it but it isn't always readily available. Some years ago the State and Federal Government stopped supporting Mental health. Now we are dealing with people who are highly dysfunctional but are living under bridges and the "Voices" are telling them to hurt people. These aren't criminals but as they act out without help they quickly become criminals.
What is depression?,"What should I do if I think I have depression but don't want to talk about it with anyone, even though I want and need help.","I'm in that same situation, so I know how you feel... you should't hide that you are depressed because if somebody notices then they could help you, and don't make my mistake when my mom asked me if I was depressed I said I don't know and I got zero help by saying that."
What is depression?,"I have depression ,what should I do?",Speak to a mental health professional about it. It can lead to terrible things and you should get help before it accumulates.
What is depression?,How can I change one's mind if he decided to suicide?,"This is a difficult problem beyond the scope of this site since we are all students here, but I understand you wish to help someone.  There are likely people that can and want to help you and your friend near you.  You can find them by talking to family members, teachers, counselors and health clinics in your area.  In the U.S., there is a national hotline, 1-800-273-8255.  It is very important for you to get help from others because depressed people need many supporters and it is much too big a burden for one.  Please talk to an adult about your concerns so you can get help."
What is depression?,What can you do if you know a person has depression but they don't like you or don't talk to you? How can you help?,"Just be nice and be there for them when and if they are ready to talk to you. They may never open up. If they are showing signs that they may be on the verge of suicide, this is the time you may need to get them help, even if they do not want it. Alot of times when I've been suicidal I actually hoped someone would get me help, and when I finally try getting help for myself, professionals treat you like you must just want attention because of the mentality that suicidal people don't seek help, which is often but not always true. It may be helpful to talk to someone close to this individual in private about your concerns. If they don't like you though it is going to be very hard for you to be there for them in any way unfortunately. I know that when I'm depressed I often stop trusting people, even those I'm close to, there is no way I'd let someone I don't like get close enough to help."
What is depression?,"I have all of the symptoms described and I'm one of the guys who KNOWS that death would be the only way to escape this *bad adjective* life, the major cause of my depression is the fact that i sucks in everything and i'm useless, but i do not have the courage to kill myself. I already tried going to a pshychologist but she tried to give me antidepressant. I'm a science guy but i hate taking medicine. What do you think i should do?","It is great that you have already sought help.  Being given an antidepressant is a common start to therapy, even though it may take a couple of weeks for it to have an affect.  Being offered that is not a reason to break off treatment.  You can go back to that individual and give them another try or you can try a different cognitive therapist or a group You could start exercising for at least 20 minutes a day, walking, running or biking outside.  Listening to music, drawing and keeping a journal can all be helpful ways to pick up patterns in your life.  But just as they say a lawyer should not try to represent himself in a court of law, likewise, a scientist should value the observations of an objective party and be open to the idea that your hypothesis is incorrect.
http://www.nimh.nih.gov/health/publications/depression-what-you-need-to-know-12-2015/index.shtml
http://www.suicide.org/hotlines/international/italy-suicide-hotlines.html
http://www.suicidepreventionlifeline.org"
What is obsessive compulsive disorder (OCD)?,"Great article, do we know if there is a certain threshold a person can pass that makes their OCD irreversible? If it is highly curable why do we need an early intervention?",It is easier to cure when it's in the earlier stages before it progresses too far.
What is obsessive compulsive disorder (OCD)?,How come OCD is common in children?,"All kids have worries and doubts. But kids with obsessive-compulsive disorder (OCD) often can't stop worrying, no matter how much they want to. And those worries frequently compel them to behave in certain ways over and over again.

About OCD
OCD is a type of anxiety disorder. Kids with OCD become preoccupied with whether something could be harmful, dangerous, wrong, or dirty — or with thoughts that bad stuff could happen.

With OCD, upsetting or scary thoughts or images, called obsessions, pop into a person's mind and are hard to shake. Kids with OCD also might worry about things not being "in order" or "just right." They may worry about losing things, sometimes feeling the need to collect these items, even though they may seem useless to other people.

Someone with OCD feels strong urges to do certain things repeatedly — called rituals or compulsions — in order to banish the scary thoughts, ward off something dreaded, or make extra sure that things are safe, clean, or right in some way.

Children may have a difficult time explaining a reason for their rituals and say they do them "just because." But in general, by doing a ritual, someone with OCD is trying to relieve anxiety. They may want to feel absolutely certain that something bad won't happen or to feel "just right.""
What is obsessive compulsive disorder (OCD)?,The article states that up to twenty percent of patients stopped responding to medicine that once worked for them after they stopped taking it for awhile. Why would this be? Is it an immune response?,"This happens with a lot of drugs. As drugs are taken regularly, the body begins to adapt to their use and it takes a larger dose to achieve the same effect."
What is obsessive compulsive disorder (OCD)?,Can traumatic experiences or high amounts of stress over a long period of time cause OCD? This is a great article!,"Yes, but usually someone has to have some sort of risk factor for this to happen. As said in the article, genetics or having other mental health issues can lead to the development of OCD. When someone has at least one of these risk factors, traumatic experiences and long periods of stress can trigger OCD-like thoughts, and eventually develop into OCD itself. Additionally, if the person already had OCD, stress and traumatic experiences will worsen the effects of it."
What is obsessive compulsive disorder (OCD)?,"how can i treat obsessive compulsive disorder without a person knowing, when counselling at church or workplace?","It would be best if you let somebody know so if they see you doing something that the other person does not do then, they would know how to talk to you or help in the situations that you are compulsive. It'd be better understanding:)"
What is obsessive compulsive disorder (OCD)?,Why do some diseases cause OCD?? And how?,"In spite of a range of theories and considerable research, scientists so far have not been able to identify a definitive cause for a person developing Obsessive-Compulsive Disorder (OCD).

However, whilst this may be the case, it is believed that OCD is likely to be the result of a combination of either neurobiological, genetic, behavioural, cognitive, or environmental factors that trigger the disorder in a specific individual at a particular point in time. Below is a summary of some of the suggested theories around the cause of OCD."
What is obsessive compulsive disorder (OCD)?,What are the most common symptoms  of OCD?,"1. Obsessive thoughts that can border on psychotic, such as thinking you can get AIDS from touching a pole on the public bus, believing you have AIDS, and not being able to turn off the obsession on AIDS. 
2. Compulsive behaviors, such as excessive hand washing, checking things (like turning the stove off), and repetitive actions (must turn light on and off exactly 48 times).
3. Major Depressive Disorder is comorbid with OCD, so symptoms of depression may be present.
4. Hoarding
5. Ritualistic behaviors, like a routine (must turn off lights 48 times before bed every day, then fall asleep at 12 a.m.)
6. Unwanted thoughts (sexual, gory, etc.)
7. Symptoms of another anxiety disorder, since anxiety disorders can be comorbid
8. Motor tics in some people
9. Body dysmorphia
10. Self-harm (NSSI)"
What is post traumatic stress disorder?,"Hi, I saw on your second picture (the one with a brain's picture called "normal information processing and ptsd malfunctions in the brain") you wrote under "hippocampus" two parts, one of them has the title "OCD brain", is it a mistake or do we not distinguish in this case "OCD brain" from "PTSD brain"?","I think it must be a mistake. While there may be some similarities, OCD and PTSD are two different things."
What is post traumatic stress disorder?,"If someone were to be exposed to abuse but not undergo it (such as a child witnessing physical abuse between parents, witnessing substance abuse in the household, etc), could that person also develop PTSD? And would that fall under chronic trauma?","Yes absolutely, in fact most countries' laws still classify situations like that as child abuse. Even if the child itself is not physically harmed, the emotional damage that growing up in unsafe households causes is just as much of a trauma and can still definitely cause things like PTSD"
What is post traumatic stress disorder?,How can post-traumatic stress disorder affect the lives of a person? What can a person do to cope with ptsd? What can their family do to help with the person that has ptsd to get through their life without doing something irrational like committing suicide,"Someone with PTSD can become paralyzed to the point they can no longer function.  They no longer care about personal hygiene.  They don't go outside.  They act out aggressively, or hide in constant fear.  They can't hold a job, have friends, go to a movie, or do things people without PTSD take for granted.  If you were living that kind of life you would not think it irrational to commit suicide.  What family and friends can do is to recognize the symptoms of PTSD before it becomes that severe and get their friend/family member help.  Treatment by a professional will help the person learn to cope with the events and the outcomes.  The National Institute of Mental Health, SAMSA, and the Department of Veterans Affairs all have excellent resources for educating yourself on the signs of PTSD and links to local resources in your area.  There is no prevention but there is treatment.  Being there, getting them into treatment, and not belittling their feelings are the ultimate ways to help someone with PTSD.  They are fighting both their mind and a conditioned physical response that has to be reprogrammed into a healthy and responsive mannner"
Drug abuse and drug addiction,"How about foods? since foods like sugar, fat and so on tend to have the same effect on our brain, is it much different from alcohol? i also know a lot of people (including myself) that have a small addiction for protien drinks when taking then through training.","I believe that I have (at least a psychological) addiction to sugar.  I know it's not good for me and I don't like the weight gain it's causing but......    I sometimes find myself being judgmental about a family member who has already had a bout with cancer but yet she still smokes, but what's the difference?  I've been told I'm borderline diabetic and that hasn't stopped me from eating sugar every chance I get."
Drug abuse and drug addiction,Why do people do drugs?,"Lots of reasons - boredom, experimentation, to escape a difficult life, peer pressure, because it makes them feel good, etc."
Drug abuse and drug addiction,Why do people choose to smoke even though they know it is wrong?,"For those that do not smoke and there likelyhood to  begin smoking can be affected by multiple environmental factors such as parents and peers that smoke, ads and media etc. These all can influence their attitude towards it and increase their likelihood of trying it or re exposure. 

For those that currently smoke most feel that the cigarettes calm their nerves, which is ironic because some of the major chemicals in cigarettes are stimulants. This absence of this mild stimulant effect between cigarettes causes their body to crave it again.
The act of smoking another cigarette feeds that need (both mentally and physically) and calms the body. The mind then associates smoking with being a positive thing. The body then can gain an increase in tolerance to the positive effects they feel from smoking causing the person to smoke more often.  
This is just a general overview and one of the many aspects that cause people to smoke and keep smoking.  Other brief reasons
- habits are hard to break
-some people are more genetically inclined to vices
-nicotine is addictive
-peer pressure and social norms make people feel the need to fit in
-etc"
Drug abuse and drug addiction,"Is it possible to get addicted to medication? For instance, your doctor prescribes Methylphenidate Hydrochloride (I mean, Ritalin, as it is known in american stores) is it possible for a teen to actually get addicted that stuff? Also, is it more likely to get addicted to drugs which target the dopamine system as opposed to drugs which target the system indirectly?","It is very well possible to get addicted to a prescription drug, especially in your teenage years."
Drug abuse and drug addiction,I personally think people have the wrong mindset towards cannabis. Its a plant that can help with many medical problems but I do agree that street weed can be very dangerous now a days considering the rates of cannabis being laced have gone up quite high. :),"It is indeed a double-edged sword. There are addicts,  there are those who need to for medical reasons, and maybe even those who are both. I'd say (like everything else) use with moderation/ only when needed for medical purposes."
Drug abuse and drug addiction,Why do people between the ages of 16 and 17 have a higher risk?,"From someone who is currently taking a course in developmental psychology, the answer is complicated because brains are complicated. Usually a behavioral pattern is attributed to several factors.

In this case, I'd say that teens are more likely to develop a substance use disorder because they are in a developmental stage where taking substances seems like a good way to assert that they are more mature than their peers (or just younger children). They also haven't lived very long, so they're less likely to have experienced anything damaging, giving them the impression that they are "immune" to addiction.

From a physiological standpoint, the prefrontal cortex has not completely developed by this point. That's the part of the brain that houses your "higher thinking." That means it's in charge of your impulse control and ability to think of long-term consequences. Psychologists fight constantly about other compounding risk factors for teens, so there's a host of research to explore if that interests you."
Drug abuse and drug addiction,"If a woman takes drugs and smokes while pregnant, would the baby be more likely to do the same? (When it's older of course)","My guess is likely, not because she was doing them while pregnant, but because she would had continued afterward, creating a drug-positive environment as the child grows up around their mother doing drugs. Another reason why they would likely do the same when they're older because drugs can go into the fetus through the blood-brain barrier, making the baby addicted. This addiction is treated in the hospital after birth, but gives the baby a much higher chance of becoming addicted and doing drugs later on in life."
What is ADHD?,"If ADHD  impacts 5%  of kids and only 2.5% of adults, does that mean some people grow out of ADHD?","A problem in math in here. There is a bigger population for the category of adults than kids. That's only a percentage. Research for the actual figures for each age level. In addition, there is an increasing incidence of ADHD each year for children developing the condition which could as well explain your concern. Also, symptoms of ADHD can be managed through behavioral therapy and medications. Cures are yet to be discovered."
What is ADHD?,"Is it possible for someone to have mild ADHD? For example a kid who doesn't really have problems sitting still but still notices a lot of things around them, but kinds of things kids without ADHD wouldn't really pay attention to.","I will look into that for you. to be honest I'm curios about that too.
(a few minutes later.)
Google has a list of symptoms, and it list stuff like anxiety, short attention span, hyperactivity, 
impulsivity, aggression, etc. you might want to take a look at it your self. 
so I think mild ADHD is possible, just like mild phobias are possible. imagine it like salsa.
there's mild, medium, spicy, and super spicy. how severe it is varies.
There are kids who are simply more active than normal, yet not hyperactive. And some people are great at noticing things. If you don't have ADHD and are still easily distracted, you may just have more sensitive senses."
What is ADHD?,"But how do we know that some people who are diagnosed are just simply, you know, active, and learn better with hands on work, or doing more than just sitting when they learn? And another symptom of the medicine, isn't it depression?","There are diagnostic criteria to meet. Below 17 yo children need to meet at least 7 sxs while people older than 17 need to meet at least 5 sxs that persisted for at least 6 mo. Check DSM 5 for the list of the symptoms. There are some psychological tests and behavioral assessment that are needed to be conducted too. Also, there is a chance that the child has developed another disorder other than ADHD. We cannot set aside that possibility."
What is ADHD?,"Is the difference between diagnosis of boys and girls ("Males are twice as likely as females to be diagnosed with ADHD, but females are more likely to have the inattentive subtype.") due to problems with diagnosing girls or is there a genetic reason making boys more susceptible?","There's not definite answer, but boys with ADHD are more likely to act out based on it, therefore more likely to be diagnosed. There's also a theory that ADHD has something to do with a problem which an X chromisome, which females have two of as a sort of 'backup'."
What is ADHD?,can you grow out of adhd as you get older caue i have adhd and i am having a hard time focusing on typing this question and reading this article,"It isn't exactly "cured", but as you get older, it becomes easier to control."
What is ADHD?,Is there a certificate for ADHD,"No, but it can be diagnosed by a licensed professional. It's not something you get a certificate for."
What is ADHD?,"I found this article very helpful, all of it. My parents do sometimes get frustrated. I tend to ask "non-appropriate questions". It was hard for me to focus on this article, but if anyone knows of good ADHD medicine, please tell me... I am currently taking 20 Milligrams of Methylphenidate.","I have ADHD as do my 3 siblings and my 3 kids so I'm happy to relay what I know about the various medications and how I've seen them work. Questions, were you on your medication when you read the article (how recently had you taken them)? Do you feel your medication is helping you at all? How long have you been on the medication? Im assuming your daily dose is 20mg and you take 10mg twice a day but correct me if Im wrong. This medication lasts 3 - 6hrs so does it last you all day? I was on this as a child 10mg 3xs a day, but the dose depends on the person. For example a petite lady may need 70mg, where as a 6ft solidly built man is perfectly happy taking 30mg. The other main type of ADHD medication is Dexamphetamine. From my experience if you are not seeing or feeling an improvement in your ADHD, basically if life hasn't gotten any easier in all the ways you previously found it really challenging, then your medication needs to be reviewed. There are long acting versions of these medications as well which means you only take one tablet a day, plus there is no forgetting a dose or leaving it too long between doses. Personally I take Vyvanse which is the long acting version of dex and it is amazing.  It takes about an hour to start 'working' which is annoying consider the short acting stuff only took 10mins, but it lasts 12hrs. From me getting back on my ADHD meds after being without them for many years, I got my 3 siblings back on their meds even though they were convinced they didn't need medication. My own children also have ADHD and we started on Ritilian ( methylphenidate) which was ok and then we tried Concerta, the long acting version of it but that was worse than them taking nothing. Everyone in my family has ended up taking Vyvanse. I still say/ask "inappropriate things" off my meds ;) Talk to your parents and your Doctor about your medication. You might find this helpful/interesting to understand more about how your ADHD http://www.drthomasebrown.com/add-adhd-model/"
What is autism spectrum disorder?,"What does the author of this article think of the controversy surrounding ABA therapy, and the viewpoints of some autistic adults who had ABA as children?","The issue is that oftentimes, therapy is trying to change things about an autistic individual that cannot be changed, akin to conversion therapy for homosexuals. Many autistic graduates of these "therapy" programs have come out of it less able to cope with the world, and with anxiety disorders such as PTSD. Sometimes an autistic individual can pretend to be neurotypical, but often this causes more harm to them than good, as it causes them to have to use much of their brain capacity in mechanically erasing their thoughts and feelings and conforming to the world, whereas simply being accepted in the world, much akin to the way that we don't force people who use wheelchairs to walk, would be better for their general well being. The very existence of these therapies masks the ways that we fail to accommodate people with autism in the world and places the burden on the autistic individual to conform, rather than on us to accommodate."
What is autism spectrum disorder?,I have a kid in my class with Autism and I find it hard to deal with him..... what should I do?,"Accept him. Remember, he's still human and born with human rights and dignity. He should be treated that way, like everyone else."
What is autism spectrum disorder?,"In the fourth paragraph, you talk about how it is believed that different environmental factors can influence whether or not a child could develop autism. What are the likely hoods for a chemical research scientist to give birth to an autistic child compared to a mother that isn't a research scientist?","The thing about autism is that the symptoms are different in every child, which make it hard to pinpoint the cause. However, the environment could play a part, and to answer your question, the answer would vary. If the mother who is a chemical research scientist continues to work while pregnant and exposes herself to the chemicals she works with, this could affect her child's likelihood of autism, but it depends on the chemicals she works with."
What is autism spectrum disorder?,"I am very intrigued by mention of an association between ASD and [enlarged hippocampus + difficulty learning new information] (spelling error btw: "f" missing from "information" in actual table).   

The amygdala being enlarged all makes sense.  The enlarged hippocampus also makes sense physically ... but the resulting dysfunction in "learning new" does not.   Does the research perhaps more clearly show "learning new" rate is appropriate or even above-average, but the type of "new information" being learned is rather outside the norm?  For example, the Dustin Hoffman character in Rainman was learning prodigious amt's of stuff, albeit not the stuff most necessary for thriving in the social setting he lived in.","The hippocampus is what allows us to mentally travel away from the present moment. Obviously, this is very helpful when you want to recall a memory or imagine something that could happen. However, too much of this imagining can make it difficult to learn from what is happening in the present moment. This is how I make sense of an enlarged hippocampus leading to learning difficulties."
What is autism spectrum disorder?,How come neurofeedback is not included in your treatment option. It is recommended by american academy of pediatric association.,"Neurofeedback only gets your brain to function. The thing is that you have to be dependent on it, and people who are autistic need to be independent. True, it does help with autism(I have done it myself, because I have mild autism), but it is not a "cure"."
What is autism spectrum disorder?,What do autism vaccinations do?,"There are no vaccinations for Autism. There has been controversy from unscientific articles linking childhood vaccines to Autism which has lead to some parents not getting their children vaccinated. These "anti-vaccine" have lead to a resurgence in many nearly eradicated childhood diseases, despite no evidence ever showing a positive link between Autism and Vaccines."
What are anxiety disorders?,How can I overcome the fear of standing up in front of a crowd to speak,"Based on my personal experience, first try to gain confidence in yourself and what you're doing. If you're not confident about the material, review the content more. You can even ask someone who has a greater understanding of the content to explain it to you more if the Internet sources aren't making any sense. When you gain confidence in your ability to present, you'll do fine. Practice the wording and think about what you want to emphasize. You can slow down slightly, enunciate even more or pause to emphasize certain parts. Once I boosted my self-confidence, it helped me a great deal with public speaking. However, you don't even have to look at people directly if you're in a big crowd. Choose target points and look at those points instead of into their eyes if you have trouble making eye contact. They'll think that you're looking them in the eye when you actually aren't if you can figure out how to look at these target points correctly.
Sometimes, I see people doing presentations and acting like they're the boss, so, I guess sometimes you need to own the presentation a little. 
Before you present, calm down and make sure you're breathing is low and make sure to pronounce your words clearly and in a way that enables the audience to hear you for the entirety of the presentation."
What are anxiety disorders?,why is it that people with social anxiety can still talk to other people in chats on video games?,Because the humanization is lost. There is a big difference between face-to-face conversation and a message board on the internet because it's impersonal.
What are anxiety disorders?,What is the main cause of a panic attack?,"It's not known what causes panic attacks,  but it can be biological, phobia, panic-provoking situations or environments."
What are anxiety disorders?,"While researching common traits among intelligent people, I noticed that one trait that kept coming up in articles and researches was the fact that intelligent people experience higher percentages of anxiety as opposed to those with lower IQs, why might this be? Why would intelligent people be more anxious?","Those with Higher IQ tend to internalize and self-criticize themselves.  They tend to show perfectionist tendencies which leads to stress which can lead to anxiety.  For example, if you have done well in school easily for most of your school career, and suddenly you come across something that is difficult.  It can cause the fight or flight reflex.  Overtime this kind of conditioning can lead to anxiety conditions as students and then adults strive to be the best at everything they do because they believe it is what expected of them not only externally but internally."
What are anxiety disorders?,I am going on a class field trip on June 3rd. The trip is to six flags and I have bad anxiety over rides. How do I help feel calm to go on the rides with my friends?,"Maybe you can make sure to sit beside one of your best friends in the group.  You might want to tell your friend how you feel, so they can reassure you.  If you are a religious person, you may want to pray for help in feeling calm.  But remember, if you don't want to go on a ride, _you don't have to_.  Maybe you can find a less scary ride and go on it instead.  
And it's okay.  Not everyone likes roller coasters.  I DON'T.
I hope you enjoy your trip anyway.
:)"
What are anxiety disorders?,"A dear friend of mine suffers from panic disorder and chronic anxiety disorder,. While the panic attacks are occasional, the anxiety persists, and even in secure environments, she ends up feeling nervous, and afraid. I've talked to er through this, and it seems she does not know why she feels anxious, however she claims that her friends, especially me,  have a calming effect on her somehow. IS there some way i can help her to come out of this, in a more permanent way than my temporary company??","It is nice of you to want to take care of your friend, however, you know this site is not here to diagnose and treat individuals.  People with anxiety should have a physical exam and tests to be sure that hormones, heart problems or other factors are not causing their response. If the health professional doesn't find such a problem, then they will likely encourage the patient to get "talk therapy" with a counselor as that can be very helpful.  Counselors can help Individuals learn more about relaxation exercises, self-hypnosis and alternative ways to think about the situations that cause the anxiety.  Exercising and eliminating caffeine and alcohol can help, also journaling to see if there is any consistent trigger of these events, but the heavy lifting of seeking a diagnosis and working on a treatment plan is something the patient has to pursue.  However, you could check out some other web sites that are involved with treatment such as the Mayo Clinic etc.http://www.mayoclinic.org/diseases-conditions/panic-attacks/basics/definition/con-20020825
http://www.nimh.nih.gov/health/topics/anxiety-disorders/index.shtml
http://www.adaa.org/understanding-anxiety/panic-disorder-agoraphobia"
What are anxiety disorders?,Is it possible to stop a panic attack while it's happening?,"From personal experience you can try to hold it off but for not that long and not completely. All together you try distract  yourself, keep busy or just try to treat each symptom at a time."
What are anxiety disorders?,What is the most common form of anxiety?,"I would personally say performance anxiety from what I've read. (Sorry I don't have any specific ones on hand.) This could include speaking in front of crowds, grades, work performance, even possibly relationships."
What is gastroenteritis?,Can gastroenteritis be called as diarrhea?,"Gastroenteritis is inflammation of the GI tract.  Signs that a person has gastroenteritis maybe vomiting and diarrhea.  Causes of gastroenteritis include viruses, bacteria, parasites and toxins."
What is gastroenteritis?,what is the domain classification for gastroenteritis?,"If you are talking about classification like the animal kingdom, you wouldn't because several different bacteria and viruses cause gastroenteritis. It isn't an organism itself, but something caused by organisms. Hope that helped."
Arthritis and rheumatoid arthritis,Shouldn't the title of this article be "Osteoarthritis and rheumatoid arthritis" instead of just "Arthritis and rheumatoid arthritis"?,"I think it should be called "Types of Arthritis", but that also seems like a suitable title, since it is talking about those only."
Arthritis and rheumatoid arthritis,Has Popping your knuckles been linked yet to Arthritis? Or no?,"No. Scientists haven't found any evidence showing that cracking the joints should be bad. They aren't really sure how the sound is produced, but a new study found that "knuckle crackers" had thickened cartilage (https://www.ncbi.nlm.nih.gov/pubmed/28137441), but the significance of such thickness is unknown. It is safe to pop your knuckles :)"
Arthritis and rheumatoid arthritis,What can you do to help with knee pain?,"Hello dhart!
I would try doing hot and cold compresses. Take a small washcloth or hand towel, put some water on it and stick it in a Ziplock bag, and microwave it for 30 seconds, to a minute, then place it on your knee, making sure it isn't too hot, so as not to burn your skin. Leave it on for 3 minutes, and then take a cloth dipped in ice water, wring it out and place it on your knee for 30 seconds. Continue to the alternations for 15 minutes. This should help with the pain.
If that doesn’t relieve the pain enough, take a raw potato sliced thinly, and lay it on your knee, and cover it with plastic wrap, and sleep with that on. Also you can do the same thing with cabbage leaves, preferably red cabbage. I hope these natural remedies help you with your knee pain, and that I’ve assisted you in some way. Have a great day! :)"
Arthritis and rheumatoid arthritis,What can doctors do to help people with Arthritis and Rheumatoid Arthritis? Is there something to help the joints from rubbing together and causing pain?,"Rheumatoid arthritis (RA) is an autoimmune condition where the immune system attacks the synovium of the joints. Over time, RA leads to severe destruction and deformity of the affected joints, causing significant discomfort and loss of function. The goal of treating RA is to slow or stop the progression of the disease, using medicines to stop the immune system damaging the joints.

For osteoarthritis (OA), the damage to the joint is more mechanical in nature. If it's identified early, then treatments like physiotherapy and appropriate weight-bearing exercise can help to slow the progression of damage to the joint. For large joints like the hip and the knee, they can be surgically replaced with an artificial joint if needed to reduce pain and restore mobility."
Arthritis and rheumatoid arthritis,If you run a track for 1 hour hoe much  wait can you loos .,"If you can pick up the pace to 6 mph, you'll burn about 600 calories per hour if you weigh 125 pounds -- or 4,200 calories per week. At that rate you can expect to lose about 1.2 pounds per week. For a 185-pound person the calorie loss will be about 888 calories per hour or 6,216 per week. That amounts to about 1.8 pounds lost per week."
Ebola: At a glance,Is Ebola contacted by typing in a keyboard an Ebola patient was previously using?,"The virus spreads through bodily fluids, and if a bodily fluid hits a surface, the virus can linger on that surface for days to weeks (viral survival) which is why cleaning of any surfaces (porous and non-porous) is very important. Having said that, the actual chance of an infection is thought to drop within a few hours (viral transmission) after the bodily fluids first come into contact with the surface."
Ebola: At a glance,Is ebola airborne? or just blood borne?,"Ebola is transmitted via bodily fluids, and not thought to transmit through air, water, or food."
Ebola: At a glance,"So, if you are drinking from someone before they contract the disease, would you have Ebola??","If by "before they contract the disease" you mean "after they've been infected but before they show symptoms," then yes I suppose there's a small possibility of getting it from their saliva, but if they aren't showing symptoms yet, there hasn't been enough virus replicated yet to really be all over the place. Best not to share drinks in general. :)"
Ebola: At a glance,"If you unfortunately had contact with something questionable, say you work in a bank and handled cash or coins from someone that was questionable, would using hand sanitizing liquid be a an effective way to kill the virus on your hands?  I know that several people use hand sanitizing liquids  during the flu season. Do the same rules apply here?","Your risk is currently very low, however, alcohol based hand rubs are appropriate and effective hand hygiene when Ebola is of concern. (http://www.cdc.gov/vhf/ebola/hcp/procedures-for-ppe.html)
www.who.int/csr/disease/ebola/faq-ebola/en/"
Ebola: At a glance,what if a person effected with Ebola sneezes is there any chance that it will spread?,"Yes, because if Ebola is in the saliva/mucous propelling from the person's mouth/nostrils(which it probably is), then there is a good chance that Ebola is in your system. (This also depends on the severity of the symptoms of Ebola, how old the person on the receiving end is, how powerful their immune system is, if they already have the virus, 
where the mucous/saliva landed(direct entrance would give you Ebola), and several other factors.) So really, don't be worried. Unless you live in Africa, then you are probably fine."
Ebola: At a glance,How fast can it possibly go around?? 8 of my high school teachers went down to the same town in Texas where it is at. The health "professional" said it will be alright if they keep teaching. is that okay!? there is like 200 kids in the high school!! will the government shut down my town because it is so small and soon all of the kids could quiet possibly get sick? or do we have a okay-ish chance of fighting it?,"Ebola is not airborne, so you, your teachers, and your friends will be just fine. Just make sure not to make any kind of direct contact with someone who feels ill, has a diarrhea, nausea, and all that. You can only get infected by Ebola when the virus actually goes inside your system. The government shouldn't shut down any kind of towns or cities in Texas just because the virus is in there. If you want to fight the virus, you can wash your hands thoroughly, stay off of people with illness, and stay hydrated. (:"
Ebola: At a glance,Strange how the whooping cough is more contagious then Ebola. So is the cause of the whooping more contagious cause its not only able to caught by  becoming in direct contact but can also become airborne?,"Yes that's correct, airborne viruses are a lot more contagious because simply coughing or sneezing can spread a whole cloud of virus particles in the air, and anyone in close proximity can catch these airborne viruses, and they would not even notice."
Ebola: At a glance,What specifically is the meaning of an "airborne disease"?,"Airborne diseases are easily spread between people via the air. Usually it's because the virus infects your lungs, throat, or nose. Often it also makes you sneeze or cough, which helps spray the virus into the air. The virus particles are usually transmitted via tiny droplets that can stay in the air for a long time, so it's likely someone nearby will breathe them in. The viruses often have a shape or design that makes them easier to transmit via air.

Ebola doesn't specifically target your respiratory system and it doesn't specifically make you sneeze or cough. It's mostly present in your blood and your tissues. It's an aggressive virus that tends to get all over your body, though, so your saliva and sweat tend to have virus particles in them.

So, if someone in your class had Ebola and was sick, it would be very unlikely that anyone else would get infected: the only way someone else could catch it would be if they got the infected person's body fluids in their face or in a cut (so if the sick person coughed in your face or if you shook hands with the sick person and then rubbed your eye)."
What is malaria?,Is it possible to spread malaria by touching people who have malaria?,"Malaria is spread by mosquitoes and is caused by parasites in the blood - you can't get it just by touching someone who has malaria.  If a mosquito bites someone who has malaria and then bites you, you can get malaria."
What is malaria?,why is it only able 2 spread via mosquito,"Plasmodium, the parasite that causes malaria, has a complex life cycle where it needs a vector (in which it reproduces sexually) and a host (in which it reproduces asexually and produces gametocytes). The reason for why the mosquito is the only insect it can be transported in is that it is adapted to the particular environment in the mosquito's gut to achieve reproduction. In fact, only female mosquitoes from the Anopheles family can serve as a vector for the parasites that cause malaria in humans. So in short, it has adapted it as a part of its life cycle and can't do the same in other insects."
What is malaria?,"How are malaria and sickle cell anemia related? Does malaria cause the body to weaken and make it susceptible to malaria, or are they connected in some way?","No, people with sickle cell anaemia are immune to malaria. Despite having difficulty breathing and dizziness, people with sickle cell anaemia have sickle shaped blood cells that make them immune to the reproductive lifecycle of the plasmodium protozoa."
What is malaria?,How does the medical treatment help? What does it do to stop malaria?,"Antimalarial medications do not prevent infection with the malaria parasite, rather, they suppress the symptoms of the infection by killing the parasites either in the liver or as they leave the liver and enter the bloodstream."
What is malaria?,"I've read of another species of Plasmodium called P. knowlesi that also causes malaria in monkeys and humans in Malaysia. Is it only confined to that part of the world, and because of that isn't mentioned in the article? How deadly is it compared to other Plasmodium species?","I don't know why it wasn't included, but I suspect it is because it doesn't affect as many people as the other types do and it's not so widespread. It accounted for 70% of Malaria cases in Malasia in 2014, it accounted for "only"  about 2500 cases (1). That is not to say it's not an important subtype, it is severe. The fatality seems to be about 2% (2), while other types can be over 20% (but other factors, like access to health care and overall health, also influence this)

(1) http://outbreaknewstoday.com/malaysia-dengue-cases-top-45000-monkey-malaria-accounts-for-majority-of-human-malaria-cases-26143/
(2) https://academic.oup.com/cid/article-lookup/doi/10.1086/605439"
What is antibiotic resistance?,"As the development of new antibiotics and antibiotic resistance is a growing international concern, why don't scientists and doctors steer their research towards the enhancement of the human immune system? Perhaps a simple upgrade can be achieved through placing greater emphasis on nutritional intake, exercise and outdoor involvement in the natural world. But what I'm talking about is a much superior advancement. For instance, households with domestic animals experience an increase in immunity, or in other words, generally have stronger immune systems relative to families who do not - which is as a result of being subject to a more sufficient level of bacterial exposure. Furthermore, if animals have significantly stronger immune systems, does this not support the understanding that an 'elite' defence system exists, and that the human immune system has not yet reached the pinnacle of its potential? Another huge question is, what potential DO we have? What ARE the possibilities? In advance, thank you for your time! :)","Keep in mind that having a "stronger" immune system isn't a good thing. Our immune system has a very uneasy balance inside our bodies. If it's too slow or weak, we get sick and could die. But if it's too strong or too fast, we get allergies... or worse, an autoimmune disease, where our immune cells get overzealous and start destroying our own cells.

There's even research showing that a stronger immune system might cause more cellular damage over time, accelerating aging. So someone might get sick less often, but end up dying sooner because their body wears out from their immune system causing damage!"
What is antibiotic resistance?,Question from the graph - what caused the decided dip in anti-biotic resistance in the late 90s/early 00s?,"I'm just speculating, but it could have been a change in which antibiotics were being prescribed for that bacteria. Maybe doctors switched to fluroquinolone around that time?"
What is antibiotic resistance?,"i have a doubt. now if many bacterial cells invade my body, i will opt for broad spectrum antibiotic. but will this work against my healthy e.coli bacteria and disrupt it?",Absolutely and it does all the time.  Antibiotics will damage your local flora which can cause anything from gas to diarrhea to yeast infections in women.  Many clinicians now recommend you consume active culture yogurt while on antibiotics to replace the gut bacteria that are being killed off.
What is antibiotic resistance?,"When they talk about the common mutations bacteria undergo, it says "enzymes in the bacteria eat and deactivate antibiotics".  I'm not an English native speaker, so I don't know what is the word to use when talking about the mechanisms of enzymes. Is "eat" is really that specific word or was it used only for it to be more easily undestood?",Eat is indeed a word mostly used here to make it more understandable. You could think of it as an inactivation because the enzyms formed by the bacteria disable the antibiotics.
What is antibiotic resistance?,"When referring to how antibiotic resistance occurs, what does the phrase, "selective pressure" mean? How could selective pressure lead to antibiotic resistance occurring?","'Selective pressure' is any phenomenon in an environment that has an effect on a species' s fittness or ability to survive in that environment.  Because this phenomenon is present, certain organisms or animals are selected because they can survive and reproduce in that environment.  Taking antibiotics changes the human environment, killing susceptible microbes and therefore also selecting microbes that continue to live despite that antibiotic.  Those surviving microbes are resistant to the drug."
What is antibiotic resistance?,What happens when you take antibiotics when not needed?,"This is actually a really big issue and should be prevented as much as possible. If you take antibiotics when not needed (or don't finish a prescription) bacteria in your body can develop resistance to it. This can put you, and others, in danger when you actually need to be treated and all of a sudden these drugs don't work anymore."
What is antibiotic resistance?,"Why does taking antibiotics when one has a viral illness (first bullet point in the last section), or something else not bacteria-related, contribute to antibiotic resistance? How can the bacteria become resistant in the future when it did not exist when taking the medication in the first place?","http://www.cdc.gov/drugresistance/about.html
Some bacteria did exist and were present when the person took the antibiotics while sick with a viral infection.  Sometimes we get antibiotics even though they can't really shorten a virus because the doctor wants to help prevent an additional or secondary infection by a bacteria (the cold might become pneumonia) .  But the antibiotics kill susceptible bacteria and select for bacteria that can multiply in the face of this drug.  Now we have a stronger bacteria that will multiply and make more of these super bugs.  So, when they do cause a disease, they will not be killed by that antibiotic.  Bacteria are on us and in us and are helpful to us, but using antibiotics when they are not necessary selects for a genetically changed population of  bacteria.  For example, they might now have a gene that codes for an enzyme that destroys that antibiotic.  They can also share that gene for the enzyme with different bacteria using a plasmid and then those new bacteria that were not present during the cold would also have this enzyme. Yikes!  The best analogy is war secrets, like a fighter jet .  If the potential enemy gets to see the fighter jet before a real war, they can build a defense against it so the weapon will be useless and they can give this new secret defense to their friends.  Follow the link for more examples from the CDC."
What is antibiotic resistance?,""A curious habit of bacteria is that they love to share information when they meet" How do they know which information to share? They might have a "useless" mutation, so how do they know when it is beneficial to exchange and retain information?","You are correct, the information may not be beneficial. But let us consider if the information is beneficial, then what happens?  Correct, that cell and the receiving cell live longer. What do they do when they live longer? They share that beneficial genetic information with more bacteria. Then what happens? More cells in the bacterial population have this characteristic of being able to survive an antibiotic or whatever the beneficial characteristic provides. Cells that do not have this characteristic die when exposed to the drug, so we say the drug is an artificial selection pressure on the population of bacteria. They do not "know" what is beneficial but they have several methods of transferring genetic information themselves and bacterial viruses can also move genes, so the possibility of one or more bacterial populations evolving quickly is great given the fact that their generation time may be a couple of hours. Even if they did not share the genetic info, if they began dividing where one cell becomes 2 cells, 2 becomes 4 etc, then in a day or so you can have millions of that bacteria and that is yet another thing bacteria do when they live longer and food is plentiful. Again the resulting population is made up of resistant bacteria."
What is HIV/AIDS?,why is AIDS called a syndrome and not a disease?,AIDS is designated as a syndrome since a group of health problems (e.g. AIDS (+) patients are immunocompromised so they can acquire tuberculosis and hepatitis b...etc. at the same time) are characteristic of the disease
What is HIV/AIDS?,If we're so advanced in technology how come  we have not  created a cure for HIV? We have an Ebola Cure and a vaccine. How come we don't have that for HIV?,"The HIV virus easily mutates. That makes it hard to come up with a cure, because by the time we might have one, the virus mutates to the point that it is ineffective."
What is HIV/AIDS?,though macrophages are enlarged monocytes still they belong to lymphoid linegae or lymphoid group why is it so,"Macrophages and monocytes have big roles in the INNATE immune system. They belong to a group of immune cells (specialized in finding and eating bacteria, viruses, etc) called Phagocytes: dendritic cells, MACROPHAGES, and granulocytes. Macrophages start out as white blood cells called monocytes. Monocytes then migrate to the tissue where they turn into macrophages. Once mature, macrophages play a very important role in the immune system. They "eat" up pathogens by a process: phagocytosis. Once inside the cell, the pathogens are broken up, and parts of them are displayed on the surface of the cell. This is to signal to the other immune cells, and alert them to an invading pathogen. Macrophages therefore play a key part in alerting the rest of the immune system of invaders. They are kind of like messengers."
What is HIV/AIDS?,"Although there is no cure for HIV/AIDS yet, how was the discovery made that a 3rd chromosome genetic variation (mutation) called CCR5 Delta-32 discovered that can prevent a person contracting HIV, and how does it actually work and confer immunity?","Well, HIV needs not only CD4 receptors to enter a cell, it also needs coreceptors. There are a lot of coreceptors, but the most common ones are CCR5 and CXCR4. In that case, there is a mutation in the CCR5 gene, which produces the CCR5 Delta-32 protein.  So, the HIV can't bind to the CD4 cell, because it needs the CD4 and the CCR5 or the CXCR4. So, if a cell only express CD4 and CCR5 Delta-32, the HIV can't bind, thus the infection does not occur, but if the CXCR4 is expressed, or also expressed, the infecction can occur. So, these isn't an "immunity" against HIV, only a form of resistance. Even people with the mutation still can contract and have AIDS."
What is HIV/AIDS?,"What about the window, incubation, and full blown stages?
I learnt that when i was in middle school though I was raised in Africa. Does it mean there's different ways AIDS affect people in different parts of the world?","HIV does not affect people differently in different parts of the world, in general. My caution in that answer is that in the US, over 99% of HIV is HIV 1 and there is little HIV 2. HIV 2 is more likely in West Africa and it does have some different characteristics.  But I think this is a detail that does not directly matter in terms of your question.  It is more important to understand that the instructor was trying to give an overview and introduce ideas about the immune system.  He just used different terms then you are used to and it is likely that you already know more about this disease than the average student.  The window, is that time when diagnosis is not reliable because the person may not have circulating viral particles or antibodies and so the diagnosis is missed.  This window varies with the individual and maybe up to 6 months early in the infection, which the instructor did state.  During that time, one has more likelihood of a false negative test. Quick ELISA Tests in the U.S. are testing for HIV 1 and may test for both viral particles and antibodies, depending on the test, which improves their reliability. After unprotected sex, a doctor may advise a patient to have a test after 2 weeks, 3 months and 6 months to be sure that a patient with a negative test remains negative for HIV. However, as soon as a test is positive, it is typically considered reliable.  Check out the CDC pages for reliable information on your questions, https://www.cdc.gov/hiv/default.html
https://www.cdc.gov/hiv/clinicians/screening/diagnostic-tests.html
“HIV window
The window period is the time between when a person gets HIV and when a test can accurately detect it. The window period varies from person to person, and is also different depending upon the type of HIV test. Most HIV tests are antibody tests. It takes time for the body to produce enough antibodies for an HIV test to show that a person has HIV.”"
What is HIV/AIDS?,""A virus is a small infectious organism (...)", so a virus is, alive?","https://www.khanacademy.org/test-prep/mcat/cells/viruses/a/are-viruses-dead-or-alive
Most would say they are not alive."
Antibiotics: An overview,Do antibiotics fight the bacteria or boost the immune system,"it helps the immune system but it is impossible to boost it 
so the antibiotics are fighting the bacteria by destroying the enzymes and the proteins that help the bacteria multiplication"
Antibiotics: An overview,Are some antibiotics toxic to humans?,"There are substances that kill bacteria, but which are harmful for humans (like chlorine, which we use to clean toilets, which kills nearly 100% of all bacteria but is very damaging to humans) but these are never used as antibiotics! Only medicines that kill bacteria without harming humans are selected for antibiotics."
Antibiotics: An overview,I am a college student studying towards my pre pharmacy degree. I am actually writing a paper on antimicrobial resistant bacteria and remembered reading this article on khan academy. But I would like to do a little more research into this topic specifically on how antimicrobials work on bacteria. Is there a resources section for this article that I would be able to dig a little deeper into?,"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2896384/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4378521/
If you are in school go to the research librarian and ask for help citing your articles and finding them.  Center for Disease control and national institute of health will give you reliable information to start your paper.
https://www.cdc.gov/drugresistance/
http://www.cdc.gov/narms/faq.html"
Antibiotics: An overview,"Under the "How were antibiotics discovered" part, in the second paragraph, you said that some bacteria become immune to antibiotics. Does this happen only when it is overused?? And when it DOES eventually become immune, does it only affect the person that's been taking too many pills, or does that entire bacteria become immune to that drug?","A bacteria becomes resistant to a drug (such as penicillin) because it has been exposed to it and it developing an immunity to it. Your body does the same thing when attacked by bacteria or viruses. If the bacteria become resistant and then reproduce, then the new bacteria will be resistant as well. This is the quote, "He had already noted bacteria in his lab becoming resistant to penicillin, just a few years after its discovery!" The part where it says "in his lab" is the key to your question. So, not all bacteria will become resistant to the drug if misused, just the bacteria that are being exposed to the drug. 

Hope that helps!
- Ben Doucette"
Antibiotics: An overview,"Under the  section "What are antibiotic?", it claims that antibiotics only affect bacteria ,but not parasites ,viruses, or fungi. Then what affects the rest (parasite,virus,fungi)?","The only part of your question that I can answer is the virus part.  The antibiotics don't affect viruses simple because of what viruses do.  Viruses are blobs of genetic info, designed to enter your body's cells and turn your cells in to machines that create more viruses.  Their goal is to reproduce.  Some harm you and destroy cells, while others just use the cell for a while then they leave.  In the article it explains how the antibiotics work, so you can see how it wouldn't affect viruses."
Antibiotics: An overview,How Exactly does a bacteria grow resistance to any antibiotic? And how does our body make sure to not breakdown the antibiotic to simpler compounds and how does the antibiotic know where to go?(I mean which part of the body eg: Lungs etc).,"Some bacteria are naturally resistant to the antibiotic.  All the others are killed by the antibiotic, but those few resistant ones aren't.  Then those resistant ones are the only bacteria of that species in the body.  If they divide and grow, then you end up having a large population of bacteria that are all resistant to that antibiotic.

I expect that doctors use compounds which are not easily broken down.

The antibiotics go throughout your body, targeting whatever bacteria they meet.

Hope this helps!"
Antibiotics: An overview,"So,Why Antibiotics doesnot use to destroy cancer ?","Why questions are difficult to answer.  Anti-biotics target micro organisms that abnormally grow and use our body for their nutrition.  The best antibiotic treatments target something unique in the bacteria that mammal cells do not have. Bacteria and cancer are different living cells, they are not the same type of problem.   Cancer is a huge category of human cells that abnormally grow and use our body for their nutrition.  We are eating ourselves, growing tumors.  There is nothing (or little) unique in a cancer cell that is different from a normal cell to attack with a drug except the fact that they are dividing out of control.  These are very different reasons to be ill and they require different treatments.  Antibiotics kill bacteria not human cells.  This 'why' question is like asking why are there so many spices, why don't we just use pepper?  Not all soups benefit from more pepper, some need salt.  That is why."
What is tuberculosis,Is BCG recommended for infants in the USA?,"The BCG vaccine is not used in the USA much.  The thinking is that the incidence of TB is low in general so the vaccine is not needed plus once it is given it will interfere with the skin test by giving a false positive for any vaccinated person.  Check the Center for Disease Control, CDC, website if you need more info."
What is tuberculosis,what dose HIV stand for?,"HIV is an abbreviation for human immunodeficiency virus, the virus that causes AIDS, acquired immunodeficiency syndrome.  This virus multiplies inside T lymphocytes and other specific white blood cells which are cells that are supposed to  protect the body.  These cells are killed by the virus, therefore the body is more likely to become infected with TB and other diseases."
What is tuberculosis,How can people die from Tb and some people live?,"About 1/3rd of the human population are infected with TB. Like many other infectious diseases, the bacteria are dormant as long as they are kept in check by a healthy immune system. Conditions like AIDS (HIV infection) and drugs given after transplant surgery (known as immunosupressants) can weaken the immune system, allowing these bacteria to flourish and result in a deadly active infection."
What is tuberculosis,How does the immune system make the granulomas? How do the granulomas form?,"If I'm not wrong, the very first bacillus reaction in the lungs is to cause an inespecific alveolitis, which activates the macrophages to destroy them. This first immune response still leaves some of them living, and it will multiplicate and activate a new immune response. This 'second' immune response recruits some polymorphonuclear, lymphocytes and plasma cells to the region, in which will grow some fibrinous exudate. Then, a caseous necrosis will begin, surrounded by epithelioid and Langhans cells. Finally, a lymphocytic halo will encircle all that mass, that will be called granuloma or Ghon's nodule. With time it will calcify (like many necrosis processes) and be observable on x-ray."
N/A,"if your partner had sex with someone else before and they didnt wear a condom, but they both tested  negative for std or any diseases. are u still safe with out a condom too?","No. Use a condom.  You are not a 100% safe even with a condom, it can break, slip off etc.  But it is simply better that not using a condom.  Seriously, this is your life. Although we want to believe all tests are perfect, there are errors and disease could be present but not detected.  There can be weeks no detection is possible with some tests. And frankly, we are not perfect either, we don't always tell the absolute truth, what tests, all STDs or just HIV, when were they done, last week , last year how many times was that mistake made.? Love is an amazing wonderful overwhelming emotion, but health is easily lost.  Seriously, If you are sexually active, and you care for each other, protect each other and protect yourself every time, use a condom.  If this person knows they should have worn protection before then why won't they use it now?  https://www.cdc.gov/std/prevention/screeningreccs.htm"
N/A,"What diseases can you get from open-mouth kissing? (PS: partner is a smoker)
Thanks for the article!","There are plenty of diseases that can spread by open-mouth kissing (via saliva), but the most notorious disease is "kissing disease". Seriously. It's also called infectious mononucleosis, mono, glandular fever, or Pfeiffer's disease, caused by the Epstein-Barr virus (EBV) or also known as human herpes virus 4. Hope it helps!"
What is polio?,Which disease is a close relative of polio?,"If polio isn't a disease, then what is it?"
What is polio?,why children are more likely to get polio than adults ?,because children are weaker and their bodies immune system is not as strong as an adults.therefore the polio virus is more likely to infect them .this is my guess .
How can the universe be infinite if it started expanding 13.8 billion years ago?,"If this imaginary space fabric stop stretching at this very moment, ceasing  to no longer stretch nor contract. how long would it take for us here on earth to register this phenomenon??",We probably wouldn't notice anything for a long time.  There is really no expansion occurring within our local cluster of galaxies which is about 10 million light-years across so it would be millions of years before we would see any change in expansion for anything outside our local galactic cluster.
How can the universe be infinite if it started expanding 13.8 billion years ago?,"In the first paragraph, how could the universe be infinitely dense at first? Wouldn't that need infinite matter and dark matter? And wouldn't something have to use infinite energy to make it less dense?","The early universe could have just been infinitely small. If the universe was infinite the early universe must also be infinite (because the universe can never expand at an infinite rate) and, assuming all of the universe has matter, must have contained an infinite amount of matter.  Look at a black hole, it is infinitely dense and does not have infinite energy.  What cause the universe's expansion is not something we currently know, however most theories do not require infinite mass."
How can the universe be infinite if it started expanding 13.8 billion years ago?,"cant understand"In the infinite case, you wouldn’t have enough curvature for spacetime to form the hypersphere."",When you define curvature it is a value that is inversely related to how far away the center of a circle/sphere has to be to match the curve.  If the circle/sphere is infinity big the distance to the center is also infinity far a way and the curvature is 0.
How can the universe be infinite if it started expanding 13.8 billion years ago?,how fast is the universe expanding?,Current measurements of the Hubble constant are about 68 km/sec/Mpc.
How can the universe be infinite if it started expanding 13.8 billion years ago?,Why do the galaxies spread apart from each other?,imagine a balloon as the universe and galaxies as dots on the surface of the balloon. Now if you blow the balloon the whole balloon will stretch and note that also the distance between the dots (galaxies) also increases.
How can the universe be infinite if it started expanding 13.8 billion years ago?,"In the fourth paragraph, what is a hypersphere?","A hypersphere is a sphere, like the universe, that has more than 3 dimensions. This makes the universe infinite, as basically you go back to where you were before."
How can the universe be infinite if it started expanding 13.8 billion years ago?,"If the real universe is smaller than the observable universe, then what is all the other thing outside our universe.Dark matter?",There is no outside the universe.
How can the universe be infinite if it started expanding 13.8 billion years ago?,what is the universe expanding into tho,The universe doesn't need to be expanding into anything.
How can the universe be infinite if it started expanding 13.8 billion years ago?,"I'm still confused about gravity.  Does matter cause a well in time & space causing other matter to fall towards it, or is it a force that attracts other matter?  If It Is not a true Force then It cannot fit into a Unified Theory.",It is both.  The curvature of space-time is caused by mass and energy and the curvature causes what we call the force of gravity.
N/A,"Why will looking at the sun/moon during the total solar eclipse damage your eyes? I get that looking a the sun obviously is not the smartest thing to do, but people emphasize the fact that looking at the eclipse will severely damage your eyes, and it seems like it's a different thing all together.","It is no different than looking directly at the Sun, which is also unsafe."
N/A,Why do we get partial ecpilse.,"Most places on Earth aren't directly in the path of the Moon's shadow, so they only see the Moon partially cover the Sun as it eclipses it."
N/A,"A lot of times in my life, I've heard that I should NEVER looked at a partial eclipse with the naked eye, but I never fully understood why. Does anybody know?",Never look directly at the Sun. Never.  Doing so will cause blindness.
N/A,I don't get it. Why do we have to wear glasses during a solar eclipse? Why will looking at the sun/moon during the total solar eclipse damage your eyes?,The sun is so bright it damages your eyes.
N/A,How expensive were the special glasses?,"You could generally find them for around a dollar or two, depending on when you purchased them and the amount in stock at the time."
N/A,"I don't get what this means. Please Explain.
"It seems like we should get a solar eclipse every month, but we don't. That's because the Moon’s path takes it a little bit above and below the Earth-Sun plane. The spots where it crosses are called nodes."",https://www.exploratorium.edu/eclipse/video/why-dont-we-have-an-eclipse-every-month
N/A,"How come only some people could see it? I'm in NH and I could see absolutely nothing, but I know people from out West who got to see it.","You should have been able to see a partial eclipse in NH, assuming you had clear skies.
Here was the path of the eclipse: eclipse.aas.org/eclipse-america/when-where"
N/A,is there any other way to look at the solor eclipse without the glasses? if so what are they. how bad can it damage your eyes.,One way to look at a solar eclipse without glasses is in the path of totality which is where the moon completely covers the disk of the sun. Another way is to make a pinhole projector https://eclipse2017.nasa.gov/how-make-pinhole-projector-view-solar-eclipse. Other wise I do not believe that there is a way to view the eclipse without glasses.
N/A,Why can't every body on Earth see the solar eclipse,"Why don't people in paris get covered by your shadow?  
It's the same idea. The eclipse is the moon's shadow.  It doesn't fall on everyone."
N/A,If you look at the sun why do you get blind,It burns the retina inside your eye.  Just like when you use a magnifying glass to burn a piece of paper in the sun.  Don't do it.
Defining the standard electrical units,"Is it important to memorize all the units? if so, do you have any tips for memorizing them?","I know OP is probably long gone, but for anyone else wondering no, you need not memorize it at this stage in the course.  V for Volts, A for Amperes, Ω for Ohms gets you going, and will likely be hammered in."
Defining the standard electrical units,Do electrons require energy to flow? Or do they flow just due to the potential difference?,"If there is a potential difference, then energy is imparted to the electrons by the electric field. Compare it to a mass under the influence of gravity. The gravitational field must impart energy to the mass before it moves. Similarly the electric field imparts energy to electrons, making them move."
Defining the standard electrical units,can a middle schooler study electrical engineering,Yes. A middle schooler can get a lot from this EE subject. My curiosity about electricity started when I was about 12 years old and never stopped.
Defining the standard electrical units,"Regarding the first concept check: How many electrons in 1 ampere?

Does it make sense to try to think of some amount of electrons being equivalent to an ampere?   If I understand it right an ampere is a really not a thing, but a rate (things per second)...so isn't this kind of like asking how many inches are in 1 mile per hour?","Electric current is kind of like water current. When we talk about water current we treat the water as a continuous fluid, not as a collection of water molecules. We have units for current like gallons per minute or liters per second. You pretty much never measure current in molecules/second. 

If we treat electric current like it is a fluid the current measurements are analogous. Instead of gallons or liters, we measure charge in coulombs. A coulomb is an amount of charge. Current is a rate, so it measures coulombs/second. A current of 1 coulomb/sec has an honorary name, the ampere. 

Long after people knew about electric current and were happy measuring it in C/sec = A, someone came along and discovered the electron. Current in wires is actually the flow of electrons. There are about 6 x 10^18 electrons in a coulomb. One ampere is 6 x 10^18 electrons per second.

Check out this complete answer... https://spinningnumbers.org/a/charge.html#measuring-charge-by-counting-electrons"
Defining the standard electrical units,Is it importaint to remember all of the units?,"You should remember the most important units that we start using right away, like volts, ampere, ohm, and watt. The rest you shouldn't memorize. Just tuck away that there are lots of units and you might want to come back here some day to review them again."
Defining the standard electrical units,can someone please explain ampere better I didn't really understand that so much. It would be really appreciated.,it means how many electrons flows through wire per second
Defining the standard electrical units,Is the telsa car comany named after the tesla magnetic field strength? The symbol is the same as tesla's logo,"Yes it is. Nikola Tesla is the famous engineer who developed the technology used worldwide to generate AC power. Electric generators work by moving a wire past a powerful magnet. It is very fitting to name the unit of magnetic field strength in his honor.
https://en.wikipedia.org/wiki/Nikola_Tesla"
Defining the standard electrical units,"How do you apply "force" on the wires, as the first figure illustrates?","The force on the wires comes from the current flowing in the wires. The current in each wire generates a magnetic field in the space around the wire. The magnetic fields from the two wires overlap and generate a force, just like if you bring two bar magnets near each other. To do the experiment you measure the force (with a strain gauge, for example). Then you adjust the current in the wires until the measured force is a certain value. At that point, the current in the wires is 1 ampere, by definition."
Defining the standard electrical units,"can someone please explain what
 e​−=−1.602176565×10−19 coulomb
means can someone explain.",that is the electric charge of one electron
Preparing to study electrical engineering on Khan Academy,"What is a "Calculus"  ?
 I have not learn this","_"Calculus is the mathematical study of change, in the same way that geometry is the study of shape and algebra is the study of operations and their application to solving equations."_
-Wikipedia"
Preparing to study electrical engineering on Khan Academy,"I'm in Grade 12, but since I'm ahead a grade, I have two years to finish 12. Unfortunately, my teacher (somehow) severely messed up my math; so I'm just starting Algebra I now :(

Do you think I'll be able to catch up to Pre-Calculus in time to start Electrical Engineering at Uni in 2018?

Also, is there a major difference between Wireless Engineering (A.K.A Telecommunications Engineering) and Electrical Engineering? I'm (far) more interested in the Wireless, but I would have to move interstate to study it. Which should I study?","Wireless engineering is more related to networks and phone services: ensuring that devices can get signal. It is a relatively new and specific type of engineering. 
Electrical is well establish and a broad field.
I, personally, would take electrical over wireless any day because electrical engineering is much more applicable to other engineering fields, whereas with wireless, ... well, ... you are stuck with wireless. You can also go into wireless technology with electrical engineering, and I am certain you will find more exciting fields than wireless too :P"
Preparing to study electrical engineering on Khan Academy,How hard is Calculus?,Calculus is quite easy if you get the intuition. KhanAcademy has a bunch of videos on calculus. (Differential and Integral Calculus)
Preparing to study electrical engineering on Khan Academy,and chemistry? is not that necessary?,"Hello Sara,

Chemistry is an assumption for most EE curriculum. As an example, chemistry would be very important if you were to design / manufacture semiconductor components such as CPUs and transistors.

For the introductory material presented here on Khan Academy chemistry is of minor importance…

Regards,

APD"
Preparing to study electrical engineering on Khan Academy,"I'm only in 7th grade, but I want to prepare for high school. If I do electrical engineering first, would I be at a disadvantage? I'm not ready for trig or calculus, but I plan on doing physics and chemistry this year, so I could just wait for engineering.","Nobody puts themselves at a disadvantage by studying something new. If you are interested in the EE topic then dive right in. It starts with concepts that don't require fancy math, but do stretch your brain (current, voltage). The fundamental laws (Ohm's Law and Kirchhoff's Laws) are great examples of physics in action. Go as far as you can into EE with the math you know. You will eventually get stumped, but that's okay. It's all growth.

To prep for high school I would visit KA and get warmed up on the next math class you plan to take."
Preparing to study electrical engineering on Khan Academy,With electrical engineering is there entrepreneurship opportunities.,"Hello Patrick,

This is an interesting question but it is hard to answer. You see, there are many different types of electrical engineers. In fact, if you want to have some fun put three electrical engineers in the same room and ask them to define what electrical engineering is. You will likely get more than three answers... 

Seriously, after college most EE will work as part of a larger group at a company. This is important time for person in their mid 20's. They will learn the vocabulary, tool, and tricks of the trade. At this point some continue to work for both large and small companies and some do become entrepreneurs.

Know that there are always exception and some people will appear to move faster than others. My recommendation is to seek out older engineers that can guide you along the path. None of us got to whee we are without help.

If you are interested start now. There are so many things you can do. For inspiration take a look at Instructables.com. Challenge yourself to build projects that include an EE flavor.

Regards,

APD"
Preparing to study electrical engineering on Khan Academy,"Hey everybody! I have a question... I love Physics and Math, I really like forces, velocity and acceleration. I can not choose if i should study Electrical or Mechanical Engineering. Can you guys give me a advice?","Hello Daniel,

You need to find yourself a few engineers to talk to. Assuming you live in a good sized city you should be able to locate a few engineers. Here is what you can do:

1) Get access to a “linkedIn” account. Ask to use your parent's account or create your own.

2) Search for electrical engineers and mechanical engineers in your area.

3) Send an email via LinkedIn introducing yourself and request a meeting. If they don’t respond get the company information and call the receptionist. Politely ask him for a direct company email.

I can’t guarantee you will get a response but most engineers would love to talk to you. And all will encourage you to become a X engineer just like they are.

So there you have it , do your research and become an electrical engineer just like me :)

Regards,

APD"
Preparing to study electrical engineering on Khan Academy,my question is how hard is to be a electrical engineer,"Like other engineering fields, it is considered a "hard science," so you need to become quite comfortable with formulas and numbers, and there is no doubt that engineering is more intense than many other non-STEM (science, tech, engineering, math) courses. That said, if you like sciences and mathematics, and have the ambitions to go for engineering, do it because many additional opportunities will come to technically inclined people and those who have put effort to their studies."
"Basic electrical quantities: current, voltage, power","I still don't get Amperes, can someone please help with a simple analogy so I can understand better?","Think of a tank of water with a hole in it. The amount of water in the tank is the voltage, aka the potential/volts. The size of the hole is the resistance, aka the ohms. The amount of water that flows would be the amps in this example. If you wanted to add watts into this system, say you put a water wheel in that stream of water. The power produced would be watts."
"Basic electrical quantities: current, voltage, power",what is quantum mechanics ? please explain in brief,a body of principles that explains the behaviour of matter and it's interactions with energy on the scale of atoms and subatomic particles
"Basic electrical quantities: current, voltage, power",Can someone elaborate the formula dU/dt,I posted in tips if you are not familiar with derivatives.
"Basic electrical quantities: current, voltage, power","If water is a poor conductor of electricity, why do we get electrocuted if we stand in water and electricity is introduced?","Pure water is poor conductor of electricity but the water in your tap contains many minerals that  provide the ions for conduction of electricity. Similarly if you take pure water and dissolve a teaspoon of table salt (NaCl), it would become a good conductor because now it would have sodium and chlorine ions to help conduct electricity.

Do note that at very high voltages, even pure water starts to conduct electricity because water molecules become ionized and separate into H+ and OH- ions which results in increased conductivity."
"Basic electrical quantities: current, voltage, power","In the analogy for voltage, where you compare it to a ball rolling down a hill, does voltage increase as it rolls down the hill, i.e. does it build momentum with gravity?","nice question:

OK, so think about potential. : it means stored energy or energy capable of doing work...

So think about the ball, at which point does it have most potential energy? top of hill or bottom??

OK?"
"Basic electrical quantities: current, voltage, power",Why is I the symbol for current?,"intensité de courant, (current intensity) in French. It was used by André-Marie Ampère. You can guess who that guy was.

That is why we use I as symbol for current"
"Basic electrical quantities: current, voltage, power","what's the difference between charges and electron/proton? since in my mind, current is caused by the moving of electron, but the text says that charges cause it.","Current is the movement of charge.  Since electrons are particles with negative charge, their movement creates current."
"Basic electrical quantities: current, voltage, power","The electric power consumed by a device may be calculated by using either of the two expressions P=I^2 R or P=V^2 /R. The first expression indicates that it is directly proportional to R whereas the second expression indicates inverse proportionality


I Know, if you have a constant voltage, increasing the resistance decreases the current flowing in the system by Ohm's law and hence decreases the power consumption

However, if you have a constant current source, increasing the resistance increases the voltage dropped across the resistor and hence increases the power consumption. 


But more intuitively I wanna know about this, with some example....can anyone please explain me? Thanks is advance","Hello Leo,

CAUTION - this is an answer from an electrical engineer...

In my opinion the voltage source is relatively straightforward. Examples include a battery or wall outlet. As you stated as the resistance is decreased more current flows. With more current and a fixed voltage there will be more power.

The current source is a different animal. I'll give you a few examples to consider:

1) The current source is a mathematical construct that maintains a constant current. It will take on whatever voltage is necessary to do so including both positive and negative voltages. It has an infinite impedance. To my knowledge there are no perfect constant current sources. To make one you would need a device that could produce an infinite voltage (not possible).

2) Please search "Thevenin Norton Equivalent." Here you will find that a voltage source with series resistance can be modeled as a current source with parallel resistor. Note that there is no such thing as a perfect constant voltage source. Such a device would demand infinite current (again, not possible in this universe).

3) Please search "inductor kickback." Here you will find than an inductor acts as a constant current source for a limited amount of time. As the inductor is "turned off" it will act as a constant current source and do whatever is necessary to maintain the same current before and after the transition. 

4) Please search "transistor characteristic curves." Here you will find that a transistor appears to operate as an acceptable constant current source. 

I hope you like these examples. Know that it will take some time for the material to sink in. May I recommend you print this note and check things off as you have master the topics. 

Please leave a comment below if you have any questions.

Regards,

APD"
"Basic electrical quantities: current, voltage, power","This is more of a "dumb curiosity" question and is purely hypothetical, but if salt water is as good as copper and silver could it be used to help power most things we use today?","Good day dream question. Salt water happens to be NOT as conductive as copper and silver. Those two metals are _very_ good conductors compared to sea water.

Sea water has a conductivity of 5 x 10^6 S/m
Copper has a conductivity of 6 x 10^7 S/m, or 10 times higher.

But suppose these numbers were closer. Water is a lot cheaper than copper, so that's an advantage for water. Now all you have to do is figure out how to use the water to build the electronic gizmos we all love. That's where water becomes distinctly useless as an electrical interconnect. Can you imagine if all the phone lines and power lines you see going from pole to pole were garden hoses?"
"Basic electrical quantities: current, voltage, power",Is there a reason why proton's charge is called positive and electron's charge is called negative?,"A long time ago, Ben Franklin (the American statesman) proposed a theory of electricity where he thought electricity was a fluid. This was back when the only thing anyone knew about electricity were those static electricity experiments you can do with a comb through your hair or rubbing a balloon on your sweater. Nobody knew about atoms or electrons or protons. Anyway, Franklin proposed an object could have extra electric fluid or lack fluid, depending on what you rubbed it with, and that's what caused the static attraction, the different levels of electric fluid in two materials.  He called the "lacking" material negative, and the extra material "positive". About 150 years later the electron was discovered, and it turned out that the "lacking" materials actually had an excess of electrons. And that's how the electron got its negative sign."
Numbers in electrical engineering,how fast electricyti travel?,"The speed of electricity is not due to the individual speed of each electron but the combined movement of all the electrons in a circuit acting together. It's a bit like the links of a bicycle chain where each individual link does not travel that fast the but all of them move almost at once. An electron can only move a tiny distance called 'drift' but they all act as one field. The speed of electricity is really the speed of the electromagnetic field created in an electrical circuit, but this is something for study at a more advanced stage."
Numbers in electrical engineering,what are the scopes in Electrical engineering?,"A scope is designed to measure varying voltage signals, which is important when you want to find out if, for example, a particular component in a circuit is working properly. A scope can measure very tiny quantities which would be impossible by other means."
Numbers in electrical engineering,What is the difference between e-engineering and computer science?,Engineering  is building or inventing. Computer science is programing objects.
Numbers in electrical engineering,Why do electrical engineers have to deal with such small numbers when they have to build/invent things? You can't build something that you can't see.,"Probably the best reason we have for building things really small is that small transistors work better than big transistors. They are faster, and take less power to do the same thing. And every time you make a transistor half as big as the previous generation, you can pack four times as many of them in the same space on an integrated circuit. It's all good. The silicon electronics was invented in the 1950's and has been getting smaller ever since. When we want to make something too small to see, we don't give up, we invent better microscopes to see with!"
Numbers in electrical engineering,How long would it take for an electrical pole's circuit to blow out when it has an overload of half of its usual input/output of electricity?,"Let's clarify your question.  Do you mean that there is an electric circuit, like one on an outdoor pole, that is protected by a circuit breaker?  And is the question how long the circuit breaker will take to trip?  Also, when you say overload of half are you saying that there is 150% of the rated amps?  Many circuit breakers have a piece of metal holding the circuit closed.  The amount and type of metal is chose so that the metal strip will heat up if more amps of electricity pass through than the circuit breaker is rated for.  The heating takes some amount of time and then the piece of metal will deflect and then an internal spring will cause the circuit breaker to flip - meaning open up and no more electricity will flow.  The reason that this is important is that many electronic devices are sensitive to the type of voltage fluctuations that cause high current, but the heating is not instantaneous and so the high voltage can reach your computer (or stereo or TV) and destroy it well before the circuit breaker flips.   Among electricians there is an adage that circuit breakers protect the electric company, not the customer.  For your protection you need a surge suppressor.  I'm not sure this is what you asked, but it's important to know ;)"
Numbers in electrical engineering,I'm in fifth grade. Is it okay for me to be learning this type of material?,"This engineering topic is fairly challenging for a 5th grader. We use math ideas that you will learn about in Algebra in a few years. However, you will probably enjoy the first several videos that talk about the basic concepts of charge and current and voltage, and how we talk about circuits. In these videos it's perfectly ok to skip past any math parts you don't get just yet. You can learn anything."
Numbers in electrical engineering,"In engineering notation, what is the purpose of hopping 3 digits at a time? I noticed that the common prefixes are also 10³ apart from each other:

10⁻³ _milli_-
10⁻⁶ _micro_-
10⁻⁹ _nano_-
10⁻¹² _pico_-

Is this related, or just a coincidence?","The names and the group-by-3 are the same idea, and the same as putting commas every 3 digits in big numbers. The thought is that we have a good quick sense of arithmetic and comparisons for numbers between 1 and 1000. You can visualize $1 and $1,000 pretty easy. The same goes for component values, voltages, currents, frequencies."
Numbers in electrical engineering,"Does anyone know when and why it came to pass that we're seeing V replacing E in electronics math? Seems pointless, but would be interested to know why someone thought it was necessary. As something of a purist and originalist, it bothers me a bit. But perhaps there's a better reason than, "It's easier for greenies to learn."","Voltage is Energy, hence E can be used instead of V in electronics math. To me, E was helpful to understand definition of voltage during high school. I always found it easier to explain that how energy, i.e. E, (voltage) pushes electrons (current) in a circuit."
Numbers in electrical engineering,How far can we get through this course before calculus is required? Are there sections that would be better to work on at the same time as calculus?,You don't need calculus all the way through DC Circuit Analysis. When you get to Natural and Forced Response we have to solve a differential equation. That's where calc kicks in.
Real-world circuit elements,What are some real-life examples where "parasitic effects" become relevant?,"DC line loss is an example of a parasitic effect, When DC voltage is carried over a long distance it can lose voltage. If you had a DC power supply with +20V at the voltage source, and measured the voltage at the end of a 75 foot wire, It may show +19.5V. While marginal, it is a very real world example."
Real-world circuit elements,What is used in an integrated circuit to replace an inductor that takes too much space?,"Hello Thierry,

Good catch. Inductors are indeed hard to miniaturize.

For many applications a capacitors can serve the same function. Especially when combined with one or more op-amps. You can make filters of any type including low pass, high pass, notch, and bandpass. 

This is an interesting application https://en.wikipedia.org/wiki/Gyrator

Finally, there are some application where it is more efficient to keep the inductor. In this situation a discrete inductor will be placed along side the integrated circuit. This is very common in switched mode power supplies.

Regards,

APD"
Real-world circuit elements,"Can the parasitic effects of an inductor, a resistor, or a capacitator be useful in any situations?","Hello Jack,

Usually it's a nuisance. If we chose a capacitor we expect it to be a capacitor. Yet as the applied AC frequency increases it becomes an inductor. You read this correctly - at some high frequency a capacitor will appear to be an inductor with some resistance...  

Ref: http://www.murata.com/en-us/products/emiconfun/capacitor/2013/02/14/en-20130214-p1

One example of beneficial parasitics is seen in High Frequency (HF) radio circuits. In HF circuits an inductor plus capacitor may be used as a filter to select a radio station of interest. Having parasitic resistance increases the width of filter. If you are interested you can read about "Q" in the following link:

http://www.allaboutcircuits.com/textbook/alternating-current/chpt-6/q-and-bandwidth-resonant-circuit/

Regards,

APD"
Real-world circuit elements,How do you calculate "parasitic effects" in a given situation?,"Usually, you can't; being deviations from the ideal, calculable values, they have to be measured, not calculated. In some cases, such as when designing real components for manufacture, it is possible to calculate estimates for likely parasitic effects of the component resulting from a particular design, by a fairly lengthy analysis of the known (pre-measured) properties of the materials involved and the shapes and configurations of the pieces of those materials in the proposed design."
Real-world circuit elements,what would be a situation in which you would want to avoid your circuit having a sudden loss of current and an inductor could help ?,"When the electrical power lines are blown down, the resulting loss of power causes the current to drop and a switch is thrown to stop power surge.  If there is a generator on stand-by, the generator would start up and the power source would be switched to the generator.  When the power comes back on, a switch would senses the power change and switch back to normal.
There are numerous ways that current loss modifies how we use electronics."
Real-world circuit elements,"1. What is IC layer mean (under the example of a resistor in an integrated circuit)?
2. what is a bulk material and how is it different from just...material?
3. what is R,L,C (from the second paragraph)?",""IC" stands for "integrated circuit". These are the silicon chips inside all your electronic gadgets. We use the word "integrated" because a single little piece of silicon has many different components "integrated" into a single assembly. 

"Bulk" material is just .. material. The "bulk" word implies that we have a large amount of resistive material (like buckets full) that we are about to form into many separate small resistors.

R, L, and C stand for Resistor, Inductor, and Capacitor. These are the three basic "passive" components we use in electrical engineering."
Real-world circuit elements,How do you read a resistor from left to right if you can flip it over?,"That's a really good question. Sometimes it's very hard to tell which is the starting band of the color code. Your first step should be to figure out which band is the tolerance band so you can orient the resistor properly. 

4-band resistors have tolerances down to 5%. The colors for the tolerance (silver, gold) are supposed to look different than any of the regular "number-colors". But sometimes you can't tell brown=1 apart from gold=5%. When I can't tell the color for sure, I decode the resistor value both ways and pick the one I know is a standard manufactured value (there aren't that many different values, and you get to recognize them after a while). 

The 5-band resistor has a red band at one end and a brown at the other end. The tolerance could be 2% or 1%. Look at the gap between the last brown band and the previous brown band. That gap is ever so slightly larger than the other gaps. That's a tip-off that brown is the tolerance band, 1%. It's not much to go on, but that's all the info there is.

Instead of going blind reading colored bands, the real way to do it is  is to measure the resistor with an ohmmeter. If I'm building something and there are resistors all over my bench, that's what I always do."
Real-world circuit elements,"This might be a dumb question but...I often find it inconvenient to read the color bands on the axial resistors to determine the resistor value. Why can't the resistor value be labeled directly on the axial resistors (like most capacitors)?  Is it because the shape of the resistors makes it difficult to do so?

Thanks!","Resistors are really inexpensive, and cylindrical resistors don't have a flat spot to print on. Adding a printing step would have a significant effect on cost. 

Whenever I have axial resistors on my bench I also always have an ohm meter to check my color calculations."
Real-world circuit elements,Is it possible for resistors to heat up if there is too much current or voltage?,"Hello Dreamer,

You got it! 

In addition to resistance every resistor has a power rating. For example a resistor may be rated for 5 Ω and 3 W. If you put this "little" resistor across a 12 VDC battery you would have:

Current = V / R = 12V / 5 Ω = 2.4 A

Power = V * I = 12 V * 2.4 A = 28.8 W

Our example resistor is not rated to dissipate this power and will quickly self destruct.

Please leave a comment below if you have any questions.

Regards,

APD

P.S. Resistors also have a maximum working voltage. If you exceed this voltage the resistor could "flash over" (electrical arc) once again leading to self destruction!"
Real-world circuit elements,Can anyone explain how capacitors and inductors are used in real circuits and its purposes?,"Blackbird,

They are everywhere!

Motors, electrical power grid, power supplies, radio, computers. In fact, pick any electrical device and you will likely find an inductor or capacitor inside.

Unfortunately, Khan Academy is just starting this electrical community. You will have to look elsewhere to find your answers. May I suggest you start by researching and then building a crystal radio.

Happy soldering,

APD"
Ideal elements and sources,"The text articles are very interesting, however, they would be even more useful if they could be printed out. It there any way to make this possible?",I have an add-on for my Firefox browser called "Print Edit" which lets me delete portions of the page before printing.
Ideal elements and sources,What is the voltage across a ideal current source? Is it just the sum of voltage drops across every passive element in the circuit?,"Whatever it needs to be to make the current line up, as per Ohm's Law. An ideal current source adjusts its voltage constantly, as per Ohm's Law, in order to keep its current locked to the predetermined value despite whatever changes occur in the load's resistance or impedance. Likewise, an ideal voltage source will constantly match how much current it supplies, holding the voltage steady."
Ideal elements and sources,what is power? is energy always dissipated as heat?,"In an enclosed system (in this case, an electrical circuit), the amount of Energy is constant. 

Energy consumed over a period of time, is power. 
E = P x t   , Unit : E = joule or Watt-hrs , P = Watt or VA.

Or we can say, we have a circuit with 5V battery, and a 5 ohms bulb connected, how much energy needed to run (on) this bulb for 1 minute?

V=IR, P=VI, E=Pt. 
| solving for E, we get E = ( V x ( V / R ) ) x t = 5V x 5V / 5Ohm * 60s = 300 Joule. :)

-----
Is energy always dissipated as heat?

IMHO, for an ideal circuit, no. 
Heat is the rate of change of temperature, or measure of a structure lattice vibration. If we say it dissipate as heat, then we need to consider the whole physics surrounding it. :)

A water pipe that flows, doesn't just deliver water current at a constant volume per second, it also vibrate the pipe. it have friction with the pipe wall, it flows through pipes that have different diameters, the water also have friction with it's own water molecules. So, does the water circuit have a loss of energy? yes. 
Is it just heat/vibration? not really. 

Back to our concern, the electrical circuit. It really have a lot of similarities with the water pipe example. But instead of water flow circuit, it is a charge flow circuit. 
If the physical circuit is not built with superconductor, then there is almost always have internal resistance (from the wire/load/connections/change of conductor diameters).
The energy loss can be in the form of insulation capacitance, or conductors inductions, and ionization (charge exposed to atmosphere will charge the air). The rate is very minimal for small circuits, but in electrical transmission business, the energy loss can be very significant. :)"
Ideal elements and sources,"What is the difference between potential difference, voltage and electromotive force?","The term "voltage" is the honorary name given to "potential difference". They mean the same thing. I sometimes forget that "volt" and "voltage" are in honor of a person, and they only get their technical meaning because we say so. (Just like the physics term the newton means kg-m/s^2.) One interesting twist about the definition of voltage... it is defined to *be* a difference. So if someone asks, "What's the voltage difference between these to points?", it's kind of redundant (the same as saying "What is the potential difference difference?"). So the precise phrase would be, "What is the voltage between these two points?"

The term "electromotive force" (emf) is also a measure of potential difference. This term emphasizes what potential difference does: it impresses a "motive force" on an electron. EMF is the term used when talking about electric force generated by a moving magnetic field. The units of EMF are also volts (joules/coulomb), and the symbol is "E" or "e". You will see "e" all the time in circuits, used interchangeably with "v". Sal has a nice video on where the term EMF comes from: https://www.khanacademy.org/science/physics/magnetic-forces-and-magnetic-fields/magnetic-field-current-carrying-wire/v/magnetism-12-induced-current-in-a-wire.

At the beginning of EE it can get confusing to see all these terms thrown around. It's hard to tell if they mean the same thing or if there is some important difference that you don't quite get, yet. For PE, V, and EMF,  they are different ways to say "electric push"."
Ideal elements and sources,"At the end of capacitor and inductor, what is the long curly symbol right after " V= "
and after "i = " ?","The loopy symbol is from calculus. It is the "integral" sign.

In the capacitor equation above, v = ..., the integral sign tells you to add up the product of current, i, times a tiny interval of time, dt, for every t starting at time t = -infty and stopping at time t = T. Integration is the opposite of taking the derivative. You study integrals in integral calculus, https://www.khanacademy.org/math/integral-calculus.

Thanks for pointing this out. I added this response to the end of the capacitor section in the revised version of this article at http://spinningnumbers.org/a/ideal-elements-and-sources.html#capacitor."
Ideal elements and sources,"I don't know much about this ....so this may be weird. According to given;

P = (I^2)*R but also P = (V^2)/R

So is power Directly or Indirectly proportional to current?","Hello Abhishek,

There are a few relationships to consider.

From Ohm’s Law:

     voltage = current x resistance

Also power is defined as energy per unit time or if you prefer:

    P = voltage x current

As to your question, there are two scenarios to consider:

1) In the first case we do not know or care about the resistance. And so we say:

    P = voltage x current

2) In the second case we are given a fixed resistance. We then change the operating conditions of the circuit. Here is the important part - if we change the voltage the current must also change. For example if we assume a resistance of 2 Ohms and an initial voltage of 4 volts then we know the current is 2A. Consequently the power is 4 * 2 = 8 W. Now if we double the voltage to 8 volts the current will rise to 8 / 2 = 4A. The power is now 8 * 4 =  32 W.

When the voltage was 4 volts P = (V^2)/R = (4^2)/2 = 8 W also P = (I^2)R = (2^2)2 = 8W 

When the voltage was 8 volts P = (V^2)/R =  (8^2)/2 = 32 W also P = (I^2)R = (4^2)2 = 32W 

Recommend you Google “Ohm’s Law pie chart.” You will find a wheel with solutions for V, I, R, and I.  Work the equations voltage = current x resistance and P = voltage x current to solve for all items on the wheel.

Regards,

APD"
Ideal elements and sources,"How should I understand current sources? Let's say that I have a 1 A ampere current source: that source adds (reiforces, gives) a current of 1 A to the circuit or it means that the current in the branches is exactly 1 A? Thank you for support!","Gustavo - You asked:  for "a 1 A ampere current source: that source adds a current of 1 A to the circuit or it means that the current in the branches is exactly 1 A? The best answer is your second choice: The current source makes the current in its branch exactly 1A. The current source does not "add" 1 A to another current. 

In your comment to APD you described a 2-mesh circuit with a current source on the shared branch. If you try to use the Mesh Current Method, this configuration is a special case that requires extra care to solve. A current source in this position constrains two mesh currents to be the same value. You need to create another degree of freedom to solve the circuit. Search the web for the term "supermesh" to see what this means."
Ideal elements and sources,what is a Ideal circult  elements,All the components above are ideal circuit elements. Remember that there are 2 types real and ideal. Real components are the physical components we can test and apply actual power to the circuits. where as your ideal circuit components are in layman's terms "theory". all these formulas above are of ideal conditions where as in real the conditions are much more wide spread to cause voltage variation or current spikes or all sorts of things that may change the end result.
Ideal elements and sources,"In the section "Power as a resistor" - Aaron and Beth part, I have a question. What I understand is that voltage AND current are reduced by half each. 
Let's say 
new current(I) = I'    
new voltage(V) = V'

I' = I/2
V' = V/2

Then the new power is 
P'=I'V'=(I/2)*(V/2)= IV/4 = P/4
Hence I got that power is reduced by factor of 4. 

Where is the flaw in my solving process?
I used the equation P=IV, which involves both the changed variables in the question. I don't understand how it is 4*4=16. 
Thank you.","since the voltage cut by Aaron is cut across the resistor so,
p=v^2/r
i.e, v=1/2
     v^2=1/4
p1=v^2/r
or, p1=v'r 
where, v'=1/4  
now Beth also saw that she could also cut the current across the resistor by a factor of 2, 
p=i^2r
since i=1/2,
i^2= 1/4
so, p2=i^2*r or p=i'*r
here, i'=1/4
now on replacing the equations;
p=p1*p2
where r will cancelled out 
p=v'*i'
p=i^2*v^2
p=1/16"
Ideal elements and sources,What is a diode,"While there are several different diode types, each made from different materials, all diodes have one basic property, they allow current to pass in one direction only.  This property means that a diode operates, and can be thought of, as a "check-valve" on electron flow.  Alone, this property is rather underwhelming, but when combined with other diodes or with other ideal components, the property of a diode comes heavily into play.  Simply combining a diodes ability to rectify of AC to DC with the induction of a wound coil allows a radio to break a signal out from the EM spectrum, and many other rather amazing feats."
RLC natural response - intuition,"I'm tempted to presume that if the circuit was made up of real-world components, some energy would be lost as heat in the inductor as well, as the energy alternates between being stored in the magnetic field and being used to direct charge; is this correct? And if so, how efficient is the change between those states with real-world components (i.e. what percentage of energy is lost during a given transition)?","Hello Doctor,

You are correct there will be losses in a real inductor. There are three general reasons for this:

* The wire has resistance. There will be an I^2R loss causing the wire to heat up.

* It takes energy to flip the magnetic domains. This leads to heating of the core.

* There will be current flowing where it should not be. Please research eddy currents. Again this leads to heating of the core.

As a general statement a device such as a transformer (two coupled inductors) is in the neighborhood of 95% efficient.

Regards,

APD"
RLC natural response - intuition,"Regarding the mechanical analogue, 
    If we have: x~q;    v~i;    a~(di)/(dt);    k~(1/C);    m~L;    ~R;       
where force due to air resistance(damping)~v   
                                  (the ~ sign has been used to indicate analogousness)
then the math works out the same for both cases.
But if the damping agent is something like friction, its magnitude would be constant(unlike air resistance, which would be proportional to v). So I don't understand how both are same(in terms of the math involved).","Thanks for pointing this out. Friction is a complex phenomenon, so this analogy is something i should rewrite it in terms of air resistance, as you suggest."
N/A,"Under First Order Systems in the Introduction, would it be right to call the natural response of a first order an exponential decay in terms of the graph? Thank you!",Correct. All RC and RL circuits follow this curve. Don't forget there is another related curve to describe charging.
N/A,"After solving quadratic, we concluded that two roots are S1 and S2. But why did we are both to get general solution ? Isn't answer supposed to be one of the roots ?","You can't decide ahead of time what the answer is 'supposed' to be. You have to see what the math tells you. We proposed a very general solution, with terms that included S1 and S2. Then we proceeded to test the proposed solution by plugging it into the differential equation and testing to see if the equation came out true. Along the way we computed the leading constants. In the end we got a true solution, which makes us very happy and also makes us love the proposed solution.

What would have happened to the math if our fancy 2-term proposed solution was too fancy? The derivation would cause one of the terms to drop out. This would happen for example if K2 turned out to be 0. That didn't happen, did it?"
N/A,"Its stated that capacitor voltage can't change instantly, so v(0-) = v(0+) = Vo. But v(0-) is -Vo. Why were signs changed ?","Sorry for the confusion. I could have been clearer. The capacitor voltage has its positive sign at the bottom of the capacitor (to respect the passive sign convention). In the section on Figure out the Initial Conditions I started with this definition, but then in the second circuit diagram where the switch is closed I change over to calling the voltage just "v" and flipped it to be positive at the top. I mentioned "v" before showing you what it is. Sorry.

There's an improved version of this article at https://spinningnumbers.org/a/lc-natural-response-derivation.html."
N/A,Why can we write i(t) = K1 * e^jwt + K2 * e^-jwt? I would expect that we work out i(t) separately for each of s. Do I miss something?,"If you go down two parallel branches solving separately for each complex exponential term you eliminate solutions where both K's are non-zero at the same time. In fact, both K's can be non-zero, which results in the most interesting solutions."
Kirchhoff's laws,When I see the words "voltage on each resistor" - what does that mean? that voltage is getting eaten up or used by the resistor? Is it wasting energy?,"The phrases "Voltage on" and "Voltage across" mean the same thing. One end of the resistor is at a higher potential than the other end. The difference in potential is called the "voltage across" the resistor. It is the nature of resistors that when they have a voltage across them, a current flows. When current flows, there is energy being dissipated. If the circuit is doing something useful, then we say "Nice job using the energy! I like this song." If the circuit is not useful, then we might say "What a waste of energy, how sad"."
Kirchhoff's laws,"How is this affected if there are multiple batteries, and therefore multiple currents? What if the resistors are in parallel?","Kirchhoff's Laws work for every circuit, no matter the number of batteries or resistor configuration.  KCL tells you about the sum of currents at each specific node in the circuit. KVL tells you about the sum of voltage rises/drops around every loop of a circuit. KVL and KCL aren't fooled by multiple voltage or current sources, or parallel resistors. They always work."
Kirchhoff's laws,"Where does the current flow when it enters the node.? What if all the current (arrows) are pointing inward, how is the sum of current zero in that case?","good question.

If all the arrows are drawn as going into the node, then one of the currents going 'in' will have a negative value in your calculations.

Of course, there must be just as much going in as out"
Kirchhoff's laws,what is voltage?,"It is the electric potential between two points. You probably know potential energy, like when a bowling ball is sitting on a skyscraper it has the potential energy stored from gravity because it could fall. Voltage is the same thing but with electrons (negatively charged) that have potential because they will try and move to a postive (or "less" negative) area."
Kirchhoff's laws,is kirchhoff's law applicable for ac circuits?,"Hello Drakshaspodia,

Yes, both KVL and KCL apply to AC circuits. 

You will find AC circuit are more interesting than DC circuits as capacitors and inductors change impedance as frequency changes. Think of impedance as the resistance to an AC signal.

Regards,

APD"
Kirchhoff's laws,"In circuit diagrams for example the circuit diagram before KVL(having Vab,VR1,VR2...) how we can give + and - signs to a voltage I mean how we can give polarity signs to a component","When you apply voltage to a circuit and let currents start to flow, each component will have some current and there will also be a voltage appearing between/across the terminals of the component (by virtue of Ohm's Law). When we put voltage labels on components we are just giving names to those voltages so we can talk about them between ourselves and in equations.

You name a voltage by calling it something and putting + and - signs on it. You might be worried that the signs could be "wrong". Don't worry. We just give them names and signs so we have something to talk about. It's like saying that the top of a map is North. Just a reference direction. If (after we do the analysis) the voltage ends up being the other way around, it just gets a negative value. Just like if I'm walking South, I could say I'm walking -North."
Kirchhoff's laws,what is the algebraic sum?,"It's a fancy way of saying "total summation".
_Example: the algebraic sum of 8, -1, -2 is 5._"
Kirchhoff's laws,"what do we understand from the arrows in the voltage diagrams
what is voltage polarity","Hello 

Here is how you make the arrows. 

1) Assume a direction of current flow.

2) Walk around the loop in the chosen direction of current flow. For sake of argument lets start at the 200 Ω resistor. 

2)  As you walk along the circuit you will encounter a component. Ask yourself if the voltage as you enter this component is greater than or less than the exit terminal. 

3) If the voltage on the terminal you entered is greater than the exit terminal then the entrance terminal gets a “+”. And the other terminal gets a “-.”

For a resister you don’t need to think very hard. If you are traveling in the direction of the current then the voltage on the terminal you enter will be higher than the exit.

The battery is  more interesting. As we travel we will enter the battery on the negative terminal. When we look across we see the positive terminal. Consequently the entrance terminal gets a ‘-’ and the exit terminal gets a “+” symbol.

One last point - if you were tr travel all the way around this loop the sum of the voltages is equal to zero. This property is essential to you study of electronics. We give it the special name KCL (Kirchhoff's Voltage Law).

Regards,

APD

P.S. You could have assumed the opposite direction for the current and everything would have mathematically worked out..."
Kirchhoff's laws,Isn't the answer to the second question for i5 "-6 mA"? The answer key suggests "+6 mA" but this would give you a summation of +12 mA. I believe the description below the problem states the same.,"Hi cptlaurion,
the answer key says "-6mA" going into the node OR "+6mA" going out of the node, they have the same meaning. the "+ve" sign means that your arbitrary direction you suggested is true and the "-ve" sign means that your arbitrary direction you suggested is false and the true current direction is in the opposite one.
I hope you got what you need from my answer."
Series resistors,"what grade is this information for
i know its open to all grades but i want to know what specific grade this is for i am 13 years old am i behind  or what","You aren't behind at all! Electrical Engineering is university level material. But if you're interested, don't let that discourage you! It's never too early to play around and start learning some circuitry. Some of the math might be a little daunting (we're talking calculus and higher), but a lot of circuitry can be designed and analyzed with just a bit of algebra and determination.

If you're really interested in engineering, talk to a physics teacher at your school. I'm sure they'd love to walk you through building a couple circuits. Some high schools have electronics classes or even robotics clubs that are a lot of fun. 

Engineering is fun, challenging, and extremely rewarding, whether you want to study it professionally or if you just want to build gadgets to mess with. Good luck!"
Series resistors,There's an error while calculating I for R2. R1 is written twice. Thanks for your great article.,Thanks for catching this typo. It has been fixed.
Series resistors,Why in series current is not the same?,the current is always the same in series no matter what
Series resistors,"I'm completely new at this. Could someone explain why we know that "The three resistor voltages have to add up to ​Vs"? I don't understand this. Couldn't you  just take out a resistor, in which case the other resistors would have less voltage across them than at the battery?","Think about the properties of the voltage source and the resistors. 
The voltage source says, "No matter what, the voltage at my terminals is Vs. I will provide whatever current is required by my connections."

Resistors are not so rigid. They obey the much more flexible Ohm's Law, which says, "The ratio of my voltage to current is a constant ratio, determined by my value R."  v/i = R. 

You remove one of the three resistors and just have two resistors connected in series to the voltage source. The voltage source still says, "My voltage is Vs." The two resistors are connected across Vs. The two of them have to split up that voltage such that Ohm's Law is still obeyed for each of them.

I like analogies. Suppose you have three rubber bands of different stretchiness (resistance). Tie them together in series and stretch out the chain of rubber bands a fixed distance apart (Vs). Each rubber band will adjust to some different length to take up the stress (voltage on each rubber band).

Now remove one rubber band. Stretch out the remaining two to the same distance. They will stretch to a different longer length to span the same distance. Series resistors sort of do the same thing."
Series resistors,can you wach a VIDEO!/!/!/!,"Here's one. I found it in the Physics section on circuits. Hope it helps!

https://www.khanacademy.org/science/physics/circuits-topic/circuits-resistance/v/circuits-part-2"
Series resistors,"I would like to understand how to apply Ohm's law even with just single resistor but given a constant maximum mA current. I have a device that is giving off a maximum of 5V, 44 mA and it's sinking into a device which can a accept up to 40 mA. How do I size the resistor to arrive at a maximum pull of 20 mA or 10 or 40 exactly?  

- H","That depends on the voltage that you want to be dropped across the load when the current is 40mA and how the current through the load varies with applied voltage. Using a resistor to limit current through a load implies some voltage is dropped in that resistor, the larger the resistor the larger the voltage drop.

If I take the common example of an LED, which will have a certain maximum current rating and forward voltage drop at that current. For example, 20mA at 2V, in this case, to power the LED from a 5V supply you could use a resistor to drop the difference. The resistor's value would be (5-2)/0.02 = 150 ohms. If the supply voltage decreases however, the current through the LED will go down, the LED will get dimmer. To keep current constant you would need a device whose resistance varied depending upon output current, a constant current source, these usually take the form of an integrated circuit of some sort but can be made using discrete transistors."
Series resistors,"It seems like two of the problems show the wrong answer. In problem 2, doesn't the largest resistor (1200 ohms) have the largest voltage (6V)?  The answer shows the opposite.  In problem 4, don't all the resistors share the same current?  The answer is showing the middle one??","When you click on your favorite answer, it becomes green. Then click on the button underneath that says "check". If you have the right answer, it stays green, if you selected the wrong answer it turns red."
Series resistors,Hi! I understand the voltage goes from negative to positive. I'm confused on why in the diagrams the battery has one orientation of negative to positive while the resistors have the opposite orientation. Shouldn't they be in the same direction? Thanks!,"When someone hands you a circuit it has no labels. 

Your first step is to scribble labels for voltage and current on the diagram. The direction of those labels (both current arrow and voltage polarity) is arbitrary (there is no "right" way to do it). 

Usually you will annotate a voltage source with a voltage name that's in the same polarity as the source (so the + of the orange voltage label lines up with the black + on the voltage source). For the resistors, there is no "natural" starting polarity, so your choice of how you draw the voltage labels is up to you. 

Your best bet is to think about the current arrow and the voltage label together. They should be chosen so the current arrow flows *into* the + voltage terminal of the battery (this is the "Sign Convention for Passive Components"). It makes Ohm's Law easier to apply. 

Other than this tip you can orient the resistor voltage labels any way you want. When you work out the answers for V and I you will get positive or negative values. Your original labels tell you which way is positive."
Circuit terminology,"What does the voltage of a node measured against ground do to the voltage across other circuit elements in a circuit? If the voltage of a node measured against ground is 1 volt, will it increase the voltage across all circuit elements in a circuit by 1 volt?","Yes, if the voltage supply in the circuit featured in "A schematic puzzle" is one volt, each resistor (R1, R2, R3) will have 1 volt across it with respect to ground. All of the resistors are connected to the same "place" on the voltage source, so they all have equal potential across them with respect to ground. Using Ohm's law (V=IR) you can then calculate the current through each resistor and solve the circuit."
Circuit terminology,"I'm a bit confused about the second answer the the equivalence concept check.  C,F and H each have  one node connected to 3 resistors and another connected to 1 source and one resistor. However the third node of C and F are connected to 2 resistors and the source, whereas the third node on H is connected to three resistors and the source. Maybe I've misunderstood :)","Check circuit H one more time. The + terminal of the voltage source is connected to two resistors, just like C and F. When I trace out circuit puzzles like this, I like to pick one or two distinctive features of a specific element to start tracing from. In this case, the terminals of the voltage source. This works better for me than keying off a node, because the shape of a node is arbitrary and changes for each version of the schematic."
Circuit terminology,What is the concept of ground ?,"The article states that ground is, "the reference point from which voltages are measured (1), the return path for electric current back to its source (2), or a direct physical connection to the Earth, which is important for safety. (3)"

(1) It's like a reference frame for one/two dimensional motion in physics. It also is 0 volts

(2) Usually in schematics, you can see the ground part of the circuit right before the source in the bottom left corner."
Circuit terminology,"I had trouble understanding what a short was when i read it until i sat for a minute. I want to know if my thought process is right before i continue. I know that it is when there is a lower resistance somewhere where it shouldn't be. That lower resistance raises the current (ohm's law) because the voltage is the same, which damages what the current was originally going through (in your example, the resistor). That's why water messes up electronics. It runs through the conductive particles in the water, lowering the resistance.","You are very close. When you "short out" a resistor, you are adding a really small-valued resistor (like 0.001 ohms) right next to the original resistor. All the current that flowed in the original resistor now starts flowing through the "shorting wire". Ohm's Law says the current changes from i = v/R before the short to i = v/0.001 after the short. That tiny denominator makes i really big. 

The thing you didn't quite get right is what gets damaged. The original resistor doesn't mind a bit. The big i current isn't flowing through the original resistor. The thing that suffers is the battery. It is being asked to provide a really big i, and it might not be able to. 

The other thing that happens is that huge i generates a lot of heat. In a cell phone, the battery is connected to a special chip that regulates (keeps steady) the voltage for the rest of the phone. If you drop your phone in the "puddle," the water can short out either the battery or that special chip. In both cases the battery and the regulator chip fight like mad to keep the voltage where it is "supposed" to be, and they can die trying because of the internal heat they generate."
Circuit terminology,"I am a bit confused about short circuits, it says current is diverted away from its intended path, but then where does it go?","Consider an appliance such as vacuum cleaner plugged into an outlet at your house. Normally the current would flow out one terminal do some useful work in the appliance and return back on the other terminal. Let's call this the “normal” flow of say 10 A. In this article the appliance is the vertical resistor.

A short circuit is an “abnormal” flow of current. Lets assume the power cord leading to your appliance is damaged. Perhaps it was caught in a door or an animal gnawed away the insulation. The wire has been damaged and current flows somewhere it shouldn't. We now have a short circuit. The current is no longer 10 A but something much higher. To clarify, the appliance was the intended path, the crossed wires in the power cord is the short circuit.

These short circuits can be dangerous as the high current flow can cause heating – sometimes hot enough to start a fire. All homes should be equipped with a circuit breaker or fuse box to detect the short circuit and remove power from the faulty section."
Circuit terminology,A battery (source of charge) has what two terminals?,"One positive terminal, one negative terminal."
Circuit terminology,difference between short circuit and overloading,""Short circuit" refers to a wire placed between two points in a circuit, usually between the two terminals of a component. For example, if you connect a wire between the two ends of a resistor you have "shorted out" the resistor.

If you "overload" a circuit that means you are forcing it to do more work than it is capable of. Just like if you go on a camping trip and put too much stuff in your pack. Your pack is overloaded and you can't hike very far, or you might not even be able to pick it up. A common way to overload a circuit is to connect a shorting wire between its two output terminals."
Parallel resistors,"Physically, what is the difference between a voltage source and a current source?  Don't they both supply a current and voltage in a circuit?  Why use one over the other?
Thanks
NK","Voltage and current sources generate both voltage and current. The difference between them lies in which parameter (voltage or current) is being controlled. 

A constant voltage source (like a battery) is designed to generate a controlled voltage. When you put a constant voltage source in a circuit, the voltage across its terminals is always a constant value. Depending on what it is connected to, a voltage source provides (generates) whatever current is needed to keep the voltage on its terminals constant. Example: a 1.5 V battery connected to a 100 ohm resistor will generate a current of 1.5/100 = 15 mA. If you change the resistor to 10 ohms, the voltage will still be 1.5 V but the voltage source will now generate a current of 1.5/10 = 150 mA.

Current sources may seem a little strange, but they behave exactly like a voltage source, but with current being controlled. A constant current source is designed to generate a controlled current. When you put a current source in a circuit, the current through the source is always a constant value. Depending on what it is connected to, a current source provides whatever voltage is needed to keep the current on its terminals constant. Example: suppose you have a constant current source set to current = 1 mA. If you connect a 100 ohm resistor across the current source, the voltage will be V = 1 mA x 100 ohms = 0.1 V. If you change the resistor to 1000 ohms, the current will still be 1 mA and the voltage generated by the current source will rise to V = 1 mA x 1000 ohms = 1 V. 

Most transistors (MOSFET, Bipolar) and the old vacuum tubes have a region of operation where they act just like a current source. As beginning engineers, current sources are not familiar because they are buried inside integrated circuits."
Parallel resistors,If I make a circuit with 5 resistors of 30 ohms each in series and a battery of 24 volts and if I connect a 23W led bulb will it glow ??,"If I guess that the 23 watt LED lightbulb you have is designed for home lighting, then the circuit you describe may not light the bulb. Home LED lightbulbs are designed to work with 110 VAC or 220 VAC connected to them. There is a lot of circuitry inside an LED lightbulb to make it work with high voltage. It's packed with a lot more stuff than just an individual LED semiconductor device."
Parallel resistors,What is the reason behind the largest share of current going through the smallest resistor and the smallest share of current going through the largest resistor ?,"When given a choice, current will always go through the path of least resistance, literally in this example."
Parallel resistors,"If I have a more complicated circuit, do the resistors still have the same voltage?","If the ends of the resistors are connected to each other, then they share the same voltage and they are for sure in parallel. It does not matter that other complicated things are connected as well. The resistors are still in parallel."
Parallel resistors,"Is it the resistance of a resistor that determines the current flowing through it, or is that as more resistors are added, there is less current to go through to the next resistor? (By Kirchhoff's Laws, the current flowing into a system equals the current flowing out. So if the resistors in the "do it yourself" questions were switched (500 ohms first, and 50 ohms last) how would it be different?)","Current wants to "get away" from resistance, so the lower your resistance, the more current will pass through. If you switched those two resistors absolutely nothing would be different. This is one of the most fundamentally important concepts in Electrical Engineering, and there are a few things to be learned from this:

1. Things that are in parallel have the same voltage. Think of voltage as the height of a cliff. Think of the wires as a water slide down the cliff. One slide may be steeper than the other (so water flows down more easily, it has less resistance) but they start at the same height on the cliff. Same voltage, but could be different current depending on the resistances.

2. There are only two nodes in that diagram, see his previous lesson on this. Name the top node "A" and the bottom node "B". Mark each side of your circuit elements "A" and "B" as well. As long as the "A" side of the element and the "B" side of the element touch the "A" and "B" node respectively, you can redraw this diagram ANYWAY you want. This is because this is an ideal circuit where the wiring has absolutely no resistance. All of the circuit elements are practically touching each other.

3. You asked if more resistors are added, would there be less current to go around. The answer is maybe. Let's say all the resistors in his example were 1 Ohm. They would each get 1/3 of the total current. Let's say he adds another 1 Ohm resistor in parallel-- now each resistor gets 1/4 the total current. You could add a resistor with a really high resistance in certain places of the circuit  to make the current want to go somewhere else. You could add a resistor with a really low resistance in certain places of the circuit to make the current want to go there instead."
Parallel resistors,does an equal current pass through all branches at a node in a circuit?,"Definitely not. The only thing you know for sure is that all the currents flowing into a node add up to zero (Kirchhoff's Current Law). Other than that one rule, the currents can have any value."
Parallel resistors,Is it counted as parallel is they are connected vertically on the diagram?,Resistors are in parallel if their terminals are connected to the same two nodes. It doesn't matter if the resistors are drawn vertical or horizontal.
RLC natural response - variations,"how to get the equation for i=
​V0/W0*e−αt*t in crirically damped?","Jonathan is correct. The expression for current should be i = V0/L t e^(-at). This has been corrected in the article. The article still just states the result, without derivation.

Inspired by Jonathan's solution in this clarification, I wrote up this more complete derivation of the Critically Damped case: 
http://spinningnumbers.org/a/rlc-natural-response-variations.html#critically-damped  
This website is a continuation of the EE contributions I made at KA."
RLC natural response - variations,"why do you get barely any questions, tips, or thanks on your electrical engineering section?
on other sections, i see over 100 questions but on this section, i hardly ever see 10","There are lots of questions scattered throughout the EE subject area. You can see them if you add a /d at the end of the url, like this: https://www.khanacademy.org/science/electrical-engineering/d"
RLC natural response - variations,"If I add a SPDT switch in the circuit, I can charge the capacitor. But if there is one way to charge without the switch. (For exmaple, I add a battery and it will work and form same-frequncy wave until battery does not have any energy)","Providing an initial charge to a capacitor or initial current to an inductor is a tricky bit of work in a circuit simulator. It is difficult to implement a mechanical switch. They are usually not part of the simulator's primitive elements. 

It's possible to mimic a mechanical switch using very large transistors. I show an example of this on my web site, spinningnumbers.org. This is a follow-on to my work at KA where all the articles are updated. If you navigate to the Natural and Forced Response topic, find the article on RLC Variations. The simulation models have giant MOSFETS acting like mechanical switches to initialize the voltage. Remove the spaces and try this URL,

https : //spinningnumbers . org/a/rlc-natural-response-variations.html#under-damped

(Scroll down to the end of the Under Damped chapter to find the simulation model.)"
RLC natural response - variations,"The article begins by telling:
( α         > ωo )   implies overdamped circuit. Or,
( R/2L > ωo )   implies overdamped circuit..................... (1)

But at a later point, the article also tells:
"A circuit will be overdamped if the resistance is high relative to the resonant frequency."
This means,
( R         > ωo )   implies overdamped circuit..................... (2)

If ( R/2L > ωo ) and ( R > ωo ), both implies an overdamped circuit, this means both are equivalent statements.

How can ( R/2L > ωo ) means the same thing as ( R > ωo )?","Equation (1) is correct. 
For equation (2) you are taking a very qualitative statement and trying to turn it into an equation, but this doesn't work. The units are all wrong... ohms > radians/sec. I'm just trying to say you end up with an over damped circuit if the resistance is high. In technical terms, a circuit is over damped when equation (1) is true."
Loop current method,The loop current method and node voltage method are both pretty universal. So how do we determine when to utilize which one?,"Great question. The first thing I do is compare the number of nodes to the number of meshes. If one of them is smaller, that method will produce the fewest independent equations to solve. It the numbers come out close, I choose the method I like best (that's usually the one I'm less likely to make a mistake.)"
Loop current method,When analyzing a non planar circuit is there a method to determine what would be the best spanning tree that we can select.,"I'm not aware of a way to pick a "best" set of loops for a non-planar circuit. Any set that gives you a system of independent equations is "good" enough to solve the circuit. 

On a practical note, you might attack a small circuit with a by-hand analysis, in which case any system of equations you develop will not be much worse than the "best" (if there is one). Any circuit complex enough to merit searching for a "best" spanning tree would be complicated enough that you would be unwise to attack by hand. You would instead resort to simulation tools that sort themselves out according to their own internal logic."
Loop current method,"If you wanted to solve the current source problem without using a supermesh then how would you do the KVL equation through the current source? 

The two equations I have are: 
1) V_bat - R_1*i_1 - ? = 0
2) -R_2*i_2 - R_3*i_2 + ? = 0

I'm unsure of what to put for the "?".","The "?" term is the voltage across the current source. Make up a name for it, like VS or anything else.

When you insert the made-up voltage name and add equations 1) and 2) the made-up voltage vanishes. What is left is a single KVL equation going all the way around the outside. You've basically derived something like the supermesh equation from first principles.

But this leaves you with 1 equation in 2 unknowns (i_1 and i_2). You need one more equation to solve the circuit. Do you think you can create a KCL equation at the node above the current source? Does that give you the second equation you need?

As you can see from this, the shared current source is a trouble maker. You end up falling back on your wits to come up with a system of equations. That's okay. You have the wits to succeed."
Loop current method,If a loop had an independent current source in it would that be the current for the loop? For example if loop 1 had a 2mA current source would the I equal 2ma,"You are correct. If you are using the Mesh Current method and you have a current source participating in one of the meshes, that current source defines that mesh current.

You have to be careful with circuits that have current sources. If you have a current source participating in two meshes then the Mesh Current Method is not the best choice for solving the circuit.

If you are doing the Loop Method the same answer holds. If one of your loops passes through a current source, that defines the loop current."
Loop current method,"when we consider a loop like a single loop , do we take it that the loop current is the same across all elements in the loop, i.e its as if that loop is a mini series circuit?","If you have a circuit with a single loop, the current in every element is the same. In a single-loop circuit, all the elements are in series."
Loop current method,is there an example of how this method works with a non-planar circuit? e.g. what would the loops and meshes look like in the non-planar graph above?,"With a non-planar circuit the Mesh method does not work, but the Loop method does work. If you want to apply the Loop method to the non-planar circuit example shown above, follow the two rules in the Selecting Loops section.
* Draw enough loops so every circuit element is in a loop.
* Check that every loop has at least one element that isn't part of another loop. (This keeps you from drawing too many loops and assures you that all loop equations are independent.)

If you want to do a fun little research project, draw that non-planar circuit and give the elements a value (voltage and resistance values). Analyze the circuit on paper to derive voltages and currents. 

Then redraw the circuit in this simulator: https://spinningnumbers.org/a/circuit-sandbox.html and do a *DC* simulation. Compare your calculation to the simulator's answer."
Number of required equations,"Why are IV, V, and VI a valid set in the last example? IV and V already contain every element, so VI doesn't have any element that isn't in another loop, which was stated to be a requirement?

Or is that not a requirement, but simply one way of generating independent equations with certainty?","You have a very sharp eye. This one puzzled me as I was writing the article. If you specify loops IV and V you do indeed have every element in the circuit represented in some equation. But! These two loops don't touch. It's like you have two independent circuits semi-tangled with each other. The loop currents don't have a relationship unless it is forced by the inclusion of another loop, say loop VI. This is a case where the E - (N - 1) rule saves us from writing too few equations."
Number of required equations,What do you mean by independent equations? what's the difference with a just equation?,"If you have two equations and you say they are "independent" of one another, that means you can't transform one equation into the other one.  Here's an example of dependent equations,

x + y = 4
2x + 2y = 8

You can derive the second equation from the first by multiplying both sides by 2. In the example here, the dependent equations mean you can't solve for x and y, even though you have two equations.  

Here's an example of independent equations,

x - 2y = -1
4x + 3y = 7 

There are no scaling operations you can do to transform one into the other. That's what independent means. When you are asked to solve a system of equations, this is the property you need that allows you to get a unique answer for each variable. In the case of circuit analysis, we are careful to gather up enough independent equations to match the number of unknown variables (voltages and currents)."
Number of required equations,"When writing the KCL equations for node a,b and c the conclusion is that you get N-1 independent equations.

But the equation for node a is trivial. The equation for either node c or b is redundant (linear transformation).

So shouldn't we get N-2 independent equations?","The KCL equation at node A may be trivial, but it still has to be accounted for. This node provides the path for i1 to find its way between node B and node C. Without it, we would lose track of where i1 went. You can make a small change to the circuit to see why N-1 KCL equations are needed in general: Sketch in a resistor connected between node A and node C (in parallel with the voltage source). This doesn't change the number of nodes in the circuit, but it does add one more branch. The KCL equation at node A becomes non-trivial, and it needs to be included as an independent equation. 

Some textbooks have a term for nodes with 3 or more connections: "essential nodes". The nodes in the circuit with only two connections are called "non-essential", (or "trivial", in this article). You are told to write KCL equations for the essential nodes and don't bother writing the non-essential node equations. Node A is included in a subtle way: when you write the equations for B and C you use the knowledge that i1 is the same current in both nodes. See how node A sneaks in there? It really does provide an independent equation."
Inductor i-v equation in action,Why closing the switch (open circuit to close circuit) is not a sudden change in current,"Closing the switch causes a sudden change in *voltage*. The inductor current just after the switch changes is always the same as just before. This is true for both directions of switch movement (open-to-close, and close-to-open). 

Starting with the switch open... The current right *before* the switch closes is 0, and it is 0 the moment *after* the switch closes, too. Ideal switches are perfectly happy to carry 0 current in either the open or closed state.

When we open the switch, we use the same reasoning, BUT, in this case there is an epic clash of concepts: The inductor model goes to battle with the ideal switch model. 
The inductor says: the current is the same before and after, no matter if current is 0 or non-0. The ideal switch model says there can be any current when closed, but only 0 current when open. Who wins when these ideal superhero models clash?  In Ideal Land, the answer is a momentary infinite voltage across the switch. In Real Life, the inductor wins (the current stays the same), and the switch gets a spark between its contacts as a reminder of who's the boss in real life."
Inductor i-v equation in action,How long does it take for an inductor current to dissipate around the diode-inductor loop once the switch is opened (is it an inverse logarithmic rate)? Is the rate of dissipation correlated to the magnitude of the current? How much does the dissipation rate vary based on the quality of the diode?,"Hello Dr. 

It depends on the inductance, current, voltage drop across the diode, and the resistance of the circuit. Resistance includes the intrinsic resistance of the inductor as well as the remainder of the circuit. 

This is an important question because inductors are often found in electromechanical devices such as relays and solenoids. These devices will not turn off until the current has be reduced to some minimum. Know that there are tricks to speed up this process...

Regards,

APD"
Inductor i-v equation in action,"If inductor is connected to constant voltage source, will current keep on increasing forever ?
I thought that inductor resists change in current, but it itself is increasing current by 300 A per second. I don't understand, how these concepts work together ?","An inductor resists _sudden_ changes of current (instantaneous di/dt implies the existence of infinite voltage, which doesn't happen). It tolerates gradual changes. 

Think about inductor current as an analogy to inertia or mass. If you set a bicycle wheel spinning fast and you try to grab it with you hand and bring it to a stop instantaneously, it will give your hand a giant jolt and it will still rotate a little more. That experiment is analogous to trying to stop and inductor current in zero time. If you put your hand on the tire and let it rub against you the tire will slow down and eventually stop."
Inductor i-v equation in action,Does same phenomena also happens with capacitors ?,"There is this article describing how a capacitor behaves in a similar fashion:
https://www.khanacademy.org/science/electrical-engineering/ee-circuit-analysis-topic/ee-natural-and-forced-response/a/ee-capacitor-equation-in-action"
Inductor i-v equation in action,"We can resolve the ideal case, right? (Release the switch: What happens in an ideal circuit?) In an ideal world, an open circuit is just an infinite resistor. It becomes an RL circuit. The voltage graph isn't exactly an exponential curve because R=∞, so V approaches Ie^Rt/L = 0. There is no contradiction because of infinity.","Hello Alexander,

Capacitors keep voltage constant. Inductors keep current constant.

Suppose the inductor has been in circuit a long time. The flowing current has caused energy to be stored in the inductors magnetic field. Now lets open the circuit. Release the switch! 

The circuit will attempt to make R = ∞. The current will attempt to go to zero. But wait, the voltage across an inductor  = Ldi/dt. This is a problem. Know that voltage wind every time. The voltage will instantaneously rise until it finds a way to make the current equal to what it was before the switch was opened. Remember inductors keep current constant.

This is usually seen as an arc. The plasma between the switch contacts will maintain the current. If the "switch" is a semiconductor device such as a  transistor it will arc internally leading to its destruction.

Keep reading and you will be introduced to the "flyback diode." This device provides a non destructive bath that allows the current ton continue.

Regards,

APD"
Inductor i-v equation in action,I have a question to the little quiz in the text. "What is the voltage across the diode when the switch is closed?" The right answer: 3V. The second question: "What is the approximate diode current?" The right answer: almost 0. I do not understand how can a diode have 3V with almost no current flowing through it?,That happens when the diode is reverse biased. The 3 volts is applied in the reverse direction (3V on cathode side).
Inductor i-v equation in action,"What happens if we opened push button by keeping gap fair enough. Voltage is high, but gap too is more, so spark wouldn't take place. In that case will voltage stay in wire, stored as magnetic energy in inductor, as it has got no way to release that energy...","The energy in an inductor is stored in its magnetic field, which released its energy back into the circuit in the form of current (not voltage). If the gap is bigger than a millimeter, the voltage will be forced higher until it's high enough to form an arc (spark), thereby allowing the current to keep flowing. 

Remember this sparking happens when the switch goes from closed to open. So the gap starts at 0mm (full contact across the switch) and changes to open something like 2-3mm. In between you visit all the gaps between 0 and 3mm, so there is always a narrow gap for part of the time."
Inductor i-v equation in action,"i don't quite understand how is it possible for the diode to get forward biased voltage? In this case, the upper side voltage of the inductor is way above the bottom, and i agree Vpb could reach high level due to air-resistance, yet that doesn't mean the direction of VL is upside down. so, how does this diode perform protection function? thank you.",Check how you are thinking about the inductor voltages. The *top* terminal of the inductor is stuck at +3 volts. The *bottom* terminal of the inductor is the one that shoots up to some very high voltage. That mean the diode becomes forward biased because the diode symbol arrow is pointing in the direction from the high voltage (bottom of inductor) towards the low voltage (top of the inductor).
Inductor i-v equation in action,"When calculating the inductor current in the example above gave 300A/sec. I work in a factory where we have several DC motors with their field windings supplied from an unregulated 3 phase full-wave rectifier with a smoothing capacitor on the output. There is a bit of ripple on the supply, but it is effectively DC and is pretty stiff. The current through our field windings is constant, so where does the theoretical depart from the reality in this case. I should mention that there is a resistor in series with each field, with a wiper so field current can be adjusted. Thanks!",A DC motor accepts a DC power supply and converts it to AC using either a _commutator_ (for a DC motor with brushes) or a _motor controller_ (for a "brushless" DC motor). In both cases the current going through the windings of the motor are periodically turned on and off (or reverses direction) depending on the rotational speed of the motor.
Inductor i-v equation in action,"Why is there no extreme rise in voltage when we connect the current source to the inductor? Considering the equation for the voltage across the inductor, a sudden change in current provided by the source will drive the voltage to a high number.","The first thought experiment in the article is a Current Source connected to an inductor, with the question "what is the voltage?". Very intentionally there is no switch in this circuit. That's because I would have to deal with your valid question at the very beginning of the article (and I didn't want to do that yet). The issue of suddenly switching an inductor current is covered in the following section where a voltage source and switch are connected to an inductor. There, it shows that a sudden change of current indeed drives the voltage to a high number."
Application of the fundamental laws,"At the point  where  KCL  is   calculated  at  node b  ,  why  is  the  voltage  same  for  currents  i2  and  i3 ?","i2 flows through the 6-ohm resistor. i3 flows through the 5-ohm resistor. The terminals of both of these resistors are connected together (both top terminals connect to node b, and both bottom terminals connect to node c). That means they have the same voltage. The voltage has been named v2. (The "2" in the voltage name is not related to the "2" in the i2 name.)"
Application of the fundamental laws,"How is it that current flows "up" through the current source in this example, from lower voltage to higher voltage?  What am I missing here?  Is it magic?","The current source in this circuit creates a current flowing up from node "c" to node "b". Like a battery, a current source is a power *generator*. Something is going on inside the current source that makes it able to force current to flow "up" against an increasing voltage. (A battery can do the same thing, it forces current to flow out its positive terminal because of a chemical reaction going on inside.)  Voltage sources (batteries) are familiar to us, since we can go to the store and buy them. Current sources are not made from a chemical reaction. They are some sort of complicated electronic circuit that you don't run across at the grocery store. They are unfamiliar, but not magic. Pretty much every analog integrated circuit has circuits that act like a current source over a limited range of voltage."
Application of the fundamental laws,Why isn't there a voltage over the 5 ohm resistor?,"The voltage across the 5 ohm resistor is v2.
v2 is the voltage between nodes b and c, so this is the voltage appearing across both resistors and the current source."
Application of the fundamental laws,"excuse-me, at the lesson " step3- KCL at node B" <<-- how and where to get that i1 + is = i2 + i3;
i2, i3 and iS have the same node. I still don't understand it. Please help.","The KCL equation for node b is: ( i1 + is = i2 + i3 ). This is the form of Kirchhoff's Current Law where all the currents flowing *into* the node ( i1 + is ) are set equal to all the currents flowing *out* of the node ( i2 + i3 ).  The blue current arrow for i1 is drawn on the left side of the 20-ohm resistor, but that same current flows out the right end of the resistor and goes into node b. So node b has two currents flowing in, and two flowing out."
Application of the fundamental laws,"Please, could any of you recommend me web site for practising such exercises","Here's a suggestion: This article and the following videos/articles on Node Voltage and Mesh Current methods all have example circuits. For each different circuit, see if you can solve them with more than one method. 

Another very realistic way to practice is to make up simple circuits on your own and analyze them by hand. To check your work, draw your circuit in this simulator and run a *DC* analysis.  http://spinningnumbers.org/a/circuit-sandbox.html

This simulator is part of a web site I've been working on since my EE Fellowship at KA completed. The articles are all updated and improved, and circuit simulation is incorporated as part of the learning process."
Application of the fundamental laws,"please can i get help with how the line that follows "and crank the algebra" in the solution came about.
ho did we get -540/30? please help.",The first term on the right side of the equation as a 30 in the denominator. The second term is -18. -18 is equal to -540/30. Now both terms have a 30 in the denominator.
Application of the fundamental laws,"How would one label the current flow in node c? I see that it is unimportant for solving the circuit, but I can't yet wrap my head around _why_.  Particularly, I don't know how I would label the current on the node between the voltage source and the 6 ohm resistor, and then the branch between the two resistors (on node c).","The thing that's causing confusion is the definition of node c. Node c is the *entire* bottom horizontal wire in the circuit. So the two segments you identified (between voltage source and 6ohm, and the segment between two resistors) are both included as part of node c. Review the definition of node and "distributed node" in this article https://www.khanacademy.org/science/electrical-engineering/ee-circuit-analysis-topic/circuit-elements/a/ee-circuit-terminology.  When you account for the currents flowing into node c you will draw arrows on the vertical wire segments feeding into node c. You won't be drawing current arrows on the horizontal bits and pieces of node c. It's all one single junction."
Application of the fundamental laws,"by my calculations the Vdrop over R1 is equal to: 

( (  Vss / (R1 + ( ( R2 * R3 ) / ( R2 + R3) ) ) * R1

(  ( 140v / ( 20 + ( ( 6*5 ) / ( 6 / 5) ) ) ) * 20

Rtot = R1 + Rp

Itot (voltage side) = Vss / Rtot

Vdrop over R1 = Itot (voltage side) * R1

And this results in a Vdrop over R1 equal to 123,18 V
This is ofcourse unless you count the "Current Source" as a Voltage source also which would interfere with the "voltage source given".
Am i totaly wrong here?","Here's a good way to check your work. Simulate the circuit by copying this entire URL into a web browser.  Then tap on **DC** to run a simulation. Compare your calculations to what the simulator thinks is happening.

http://spinningnumbers.org/circuit-sandbox/index.html?value=[["v",[104,96,0],{"name":"VS","value":"dc(140)","_json_":0},["2","0"]],["i",[320,144,6],{"name":"IS","value":"dc(18)","_json_":1},["0","1"]],["r",[120,72,3],{"name":"R1","r":"20","_json_":2},["2","1"]],["r",[200,96,0],{"name":"R2","r":"6","_json_":3},["1","0"]],["r",[256,96,0],{"name":"R3","r":"5","_json_":4},["1","0"]],["w",[104,96,104,72]],["w",[104,72,120,72]],["w",[200,72,200,96]],["w",[200,72,256,72]],["w",[256,72,256,96]],["w",[256,72,320,72]],["w",[320,72,320,96]],["w",[320,144,256,144]],["w",[200,144,256,144]],["w",[200,144,104,144]],["g",[200,144,0],{"_json_":15},["0"]],["w",[168,72,200,72]],["view",7.200000000000003,-5.259999999999998,1.953125,"50","10","1G",null,"100","0.01","1000"]]"
Application of the fundamental laws,"In step 1, you don't treat any part of the circuit as a parallel circuit. So there is no difference in how you analyse the parallel circuit in comparison to the series circuit? Is this a standard in Kirchoff's Laws? Is the reason for this because, in a round about way, we have already resolved the currents (or voltages) accordingly so that Ohm's law, as it pertains specifically to parallel and series circuits, doesn't apply anymore?  For example (still in step1) i(3) = i(1) - i(2). Does that make sense?","In the simple example circuit there are two resistors in parallel, so there is an opportunity to simplify the circuit by combining them. However, in this lesson I wanted to leave those two resistors in place so I could focus on the method of solving the circuit. I didn't want the circuit to become too simple before getting to the point of the lesson. This wasn't meant to suggest a standard method of applying Kirchhoff's Laws."
Circuit analysis overview,"Hey, pretty new here, but does the Khan Academy Electrical Engineering 'faculty' cover Thevenin and Norton equivalent circuits, or offer an explanation for how to use the SPICE/PSPICE circuit simulators? Love the stuff on here, and for some reason I find it way easier to follow than what's going on in uni right now.","I will put Thevenin/Norton on my list of things to do.
Here is a peek at a circuit simulator I've been working on: 
https://willymcallister.github.io/circuit-sandbox/index.html

EDIT!! April 2018. It took a long time, but here is Thevenin/Norton Theory
Thevenin's Theorem is fully described in articles I prepared for spinningnumbers.org. This is the site I created as a follow-up to my EE contributions at KA:

http://spinningnumbers.org/a/source-transformation.html
http://spinningnumbers.org/a/source-transformation-example.html
http://spinningnumbers.org/a/thevenin-proof.html
http://spinningnumbers.org/a/thevenin-howto.html"
Circuit analysis overview,Does anybody have any good sites that have circuit analysis practice problems?,"I guess this site may help you :- http://www.allaboutcircuits.com/worksheets/series-parallel-dc-circuits/
Also, try searching for sample papers for practice in some Indian sites, they may have some standard questions at times. For example:- http://www.indiabix.com/electronics/rlc-circuits-and-resonance/
Hope these help."
Circuit analysis overview,dosn't AutoCad have a circuit simulator??,"Yes. The company that brings you AutoCad is AutoDesk. They offer a free simulator: https://circuits.io/

Another simulator you can try out is Circuit Sandbox, at my new web site: http://spinningnumbers.org/circuit-sandbox/index.html
No installation, no signup, just click on the link and draw a schematic."
Circuit analysis overview,Where can i find the assignments ( circuit mathematics ) and practice it ?,"Each of the articles on the different circuit analysis methods has an example circuit. If you want to construct a set of exercises, gather all those circuits and solve each one using all the different methods (Node Voltage, Mesh Current, Fundamental Laws, Superposition). If you can do that you will have a good grasp of the topic."
Circuit analysis overview,"I am having a problem solving circuits that include 3D shapes, like, there's a cube and you have a resistor on each side, if all resistors are equal, what is the equivalent resistance? ( in terms of the first resistance)","yup. for a cube there is 8 nodes and 12 resistors. 
use y to delta to reduce the number of nodes. leaving only the nodes that you need (to connect to other circuit or the 2 nodes that you want to measure). :)

Eg : 

3D cube circuit : 8 nodes and 12 resistors.

Node1 = [ 0 , 0 , 0 ]
Node2 = [ 0 , 0 , 1 ]
Node3 = [ 0 , 1 , 0 ]
Node4 = [ 0 , 1 , 1 ]
Node5 = [ 1 , 0 , 0 ]
Node6 = [ 1 , 0 , 1 ]
Node7 = [ 1 , 1 , 0 ]
Node8 = [ 1 , 1 , 1 ]

R01 = [ Node1 - Node2 ]
R02 = [ Node1 - Node3 ]
R03 = [ Node1 - Node5 ]
R04 = [ Node2 - Node6 ]
R05 = [ Node2 - Node4 ]
R06 = [ Node3 - Node4 ]
R07 = [ Node3 - Node7 ]
R08 = [ Node5 - Node6 ]
R09 = [ Node5 - Node7 ]
R10 = [ Node4 - Node8 ]
R11 = [ Node6 - Node8 ]
R12 = [ Node7 - Node8 ]

Assume 2 final nodes is Node1 & Node8. In other words, we are looking for Rfinal. Or Rfinal = [ Node1 - Node8 ]



[Step 1]
   Do y to delta transform on R03, R08 & R09. This will eliminate Node5, and results in Ra,Rb,Rc.
   Do y to delta transform on R02, R06 & R07. This will eliminate Node3, and results in Rd,Re,Rf.
   Do y to delta transform on R01, R04 & R05. This will eliminate Node2, and results in Rg,Rh,Ri.

Where the new set up will have 5 nodes and 12 resistors.

Node1 = [ 0 , 0 , 0 ]
Node4 = [ 0 , 1 , 1 ]
Node6 = [ 1 , 0 , 1 ]
Node7 = [ 1 , 1 , 0 ]
Node8 = [ 1 , 1 , 1 ]

R10 = [ Node4 - Node8 ]
R11 = [ Node6 - Node8 ]
R12 = [ Node7 - Node8 ]

Ra = [ Node1 - Node6 ] = (R3*R6 + R3*R8 + R6*R8 ) / R6
Rb = [ Node6 - Node7 ] = (R3*R6 + R3*R8 + R6*R8 ) / R3
Rc = [ Node7 - Node1 ] = (R3*R6 + R3*R8 + R6*R8 ) / R8

Rd = [ Node1 - Node4 ] = (R2*R7 + R2*R6 + R7*R6 ) / R7
Re = [ Node4 - Node7 ] = (R2*R7 + R2*R6 + R7*R6 ) / R2
Rf = [ Node7 - Node1 ] = (R2*R7 + R2*R6 + R7*R6 ) / R6

Rg = [ Node1 - Node6 ] = (R1*R5 + R1*R4 + R5*R4 ) / R5
Rh = [ Node6 - Node4 ] = (R1*R5 + R1*R4 + R5*R4 ) / R1
Ri = [ Node4 - Node1 ] = (R1*R5 + R1*R4 + R5*R4 ) / R4

As u can see, there are some resistors that are parallel now (connectted to the same node). Rj, Rk, Rl is equavalent.

Rc || Rf @ [ Node7 - Node1 ] > Rj = ( Rc || Rf ) = 1 / ( 1/Rc + 1/Rf )
Ra || Rg @ [ Node1 - Node6 ] > Rk = ( Ra || Rg ) = 1 / ( 1/Ra + 1/Rg )
Rd || Ri @ [ Node4 - Node1 ] > Rl = ( Rd || Ri ) = 1 / ( 1/Rd + 1/Ri )

Simplifying it, we'll have 5 nodes and 9 resistors.

Node1 = [ 0 , 0 , 0 ]
Node4 = [ 0 , 1 , 1 ]
Node6 = [ 1 , 0 , 1 ]
Node7 = [ 1 , 1 , 0 ]
Node8 = [ 1 , 1 , 1 ]

R10 = [ Node4 - Node8 ]
R11 = [ Node6 - Node8 ]
R12 = [ Node7 - Node8 ]

Rb = [ Node6 - Node7 ]
Re = [ Node4 - Node7 ]
Rh = [ Node6 - Node4 ]

Rj = [ Node7 - Node1 ]
Rk = [ Node1 - Node6 ]
Rl = [ Node4 - Node1 ]



[Step 2]

  Do delta to y transform on Re, Rb & Rh. This will introduce new Node9. This will results in Rm,Rn,Ro.
   
Rm = [ Node4 - Node9 ] = Re*Rh / (Re + Rb + Rh )
Rn = [ Node7 - Node9 ] = Re*Rb / (Re + Rb + Rh )
Ro = [ Node6 - Node9 ] = Rb*Rh / (Re + Rb + Rh )

Now 6 nodes and 9 resistors.

Node1 = [ 0 , 0 , 0 ]
Node4 = [ 0 , 1 , 1 ]
Node6 = [ 1 , 0 , 1 ]
Node7 = [ 1 , 1 , 0 ]
Node8 = [ 1 , 1 , 1 ]
Node9 = [0.5,0.5,0.5]

R10 = [ Node4 - Node8 ]
R11 = [ Node6 - Node8 ]
R12 = [ Node7 - Node8 ]

Rj = [ Node7 - Node1 ]
Rk = [ Node1 - Node6 ]
Rl = [ Node4 - Node1 ]

Rm = [ Node4 - Node9 ]
Rn = [ Node7 - Node9 ]
Ro = [ Node6 - Node9 ]



[Step 3]

  Do y to delta transform on R10, Rl & Rm. This will eliminate Node4, and results in Rp,Rq,Rr.
  Do y to delta transform on R11, Rk & Ro. This will eliminate Node6, and results in Rs,Rt,Ru.
  Do y to delta transform on R12, Rj & Rn. This will eliminate Node7, and results in Rv,Rw,Rx.
   
Rp = [ Node1 - Node9 ] = (Rl*R10 + Rl*Rm + R10*Rm ) / R10
Rq = [ Node9 - Node8 ] = (Rl*R10 + Rl*Rm + R10*Rm ) / Rl
Rr = [ Node8 - Node1 ] = (Rl*R10 + Rl*Rm + R10*Rm ) / Rm

Rs = [ Node1 - Node9 ] = (Rk*R11 + Rk*Ro + R11*Ro ) / R11
Rt = [ Node9 - Node8 ] = (Rk*R11 + Rk*Ro + R11*Ro ) / Rk
Ru = [ Node8 - Node1 ] = (Rk*R11 + Rk*Ro + R11*Ro ) / Ro

Rv = [ Node1 - Node9 ] = (Rj*R12 + Rj*Rn + R12*Rn ) / R12
Rw = [ Node9 - Node8 ] = (Rj*R12 + Rj*Rn + R12*Rn ) / Rj
Rx = [ Node8 - Node1 ] = (Rj*R12 + Rj*Rn + R12*Rn ) / Rn

Now, its 3 nodes and 9 resistors.

Node1 = [ 0 , 0 , 0 ]
Node8 = [ 1 , 1 , 1 ]
Node9 = [0.5,0.5,0.5]

Rp = [ Node1 - Node9 ]
Rq = [ Node9 - Node8 ]
Rr = [ Node8 - Node1 ]

Rs = [ Node1 - Node9 ]
Rt = [ Node9 - Node8 ]
Ru = [ Node8 - Node1 ]

Rv = [ Node1 - Node9 ]
Rw = [ Node9 - Node8 ]
Rx = [ Node8 - Node1 ]

Simplifying the parallel resistors, we have..

Rp || Rs || Rv @ [ Node1 - Node9 ] > Raa = ( Rp || Rs || Rv ) = 1 / ( 1/Rp + 1/Rs + 1/Rv )
Rq || Rt || Rw @ [ Node9 - Node8 ] > Rbb = ( Rq || Rt || Rw ) = 1 / ( 1/Rq + 1/Rt + 1/Rw )
Rr || Ru || Rx @ [ Node8 - Node1 ] > Rcc = ( Rr || Ru || Rx ) = 1 / ( 1/Rr + 1/Ru + 1/Rx )

Now, it's 3 nodes and 3 resistors.

Node1 = [ 0 , 0 , 0 ]
Node8 = [ 1 , 1 , 1 ]
Node9 = [0.5,0.5,0.5]

Raa = [ Node1 - Node9 ]
Rbb = [ Node9 - Node8 ]
Rcc = [ Node8 - Node1 ]



[Step 4]

Since our Rfinal = [ Node1 - Node8 ]

So,

  Rfinal  = ( ( Raa + Rbb ) || Rcc  ) = 1 / ( 1/( Raa + Rbb ) + 1/Rcc ) = Done!"
Simplifying resistor networks,I've just watched a video about the direction of the current and now I am confused. The first image of this article shows the current "i" going out of the positive side of the battery? shoundn't it be the other way around? Can someone explain it to me?,Whoever posed the problem (me) chose to ask a question about current and pointed the current arrow as given.
Simplifying resistor networks,where can i find questions related to finding  resistors and currents from circuits for class 10 from,"Hello Hemant,

I have found these books to be good. If you dig you can find pdf copies for download:

https://www.allaboutcircuits.com/textbook/

If you are interested in electronics I recommend you get a copy of "The Art of Electronics" by Horowitz and Hill. It's one of the most used books in my collection!

Regards,

APD"
Simplifying resistor networks,What would happen if you added a five ohm resister in between the 12 ohm resister and the 4 ohm resister?,"Hello James,

The overall resistance of the circuit would be lower with a resulting increase in current flow.

Recommend you work the problem with the additional resistor and see the results. It may be useful to first work the steps from in the animation...

Regards,

APD"
Simplifying resistor networks,How do you simplify a complex circuit with diagonal paths that cut off multiple resistors?,"Sometimes you run into a resistor network and you get stuck because of diagonal connections. The usual version of this is called a Delta-Wye network. 

Check this article... https://www.khanacademy.org/science/electrical-engineering/ee-circuit-analysis-topic/ee-resistor-circuits/a/ee-delta-wye-resistor-networks?modal=1

or an improved version here... https://spinningnumbers.org/a/delta-wye-resistor-networks.html"
Simplifying resistor networks,"R1 is a 3 ohm resistance connected in parallel to R2, a 6 ohm resistance.  Both resistances are connected with a 4 ohm resistance, R3. Current of 0.8A flows through R1. THEN find the potential diffrence across R3.",This sounds a lot like a "voltage divider" problem. Check out https://www.khanacademy.org/science/electrical-engineering/ee-circuit-analysis-topic/ee-resistor-circuits/a/ee-voltage-divider
Simplifying resistor networks,For which applications the DC and AC current is used. Describe the devices to convert AC into DC voltage and vice versa with working function for each.,This sounds like a homework problem. What ideas do you have so far?
Superposition,"For the example two, the equation rearranges part on how to get V is kind confusing to me. Can someone please simply explain to me? Thank you very much!","When I did this algebra I took a shortcut I will share it with you. (I should have written out the full derivation like Sal always does, sorry.)
Starting with the second equation in Example 2 Conventional Solution: 
- Separate the first fraction into separate numerators. Vs/R1 - v/R1
- Group together the two fractions with v in the numerator.  v/R1 + v/R2
- Factor out v. v (1/R1 + 1/R2). 
- Here's the trick: You might recognize that resistor expression from two parallel R's 
     Rparallel = 1/(1/R1 + 1/R2) = (R1 R2)/(R1+R2)
- Substitute the last term for the resistor reciprocals, flipping it over the right way:
    
  v ( R1+R2)/(R1 R2) = Is + Vs/R1   

Finish up by moving the big R fraction over to the right side.

This substitution I did with the resistor expression is fully worked out in
https://www.khanacademy.org/science/electrical-engineering/ee-circuit-analysis-topic/ee-resistor-circuits/a/ee-parallel-resistors where it says Special Case - Two Resistors In Parallel. It's a good one to memorize."
Superposition,To be honest I was searching for the detailed information about Superposition topic which includes questions like two given point charges separated by a distance and you determine the location where the electric field is zero.I was wondering whether I am able to find it or some different topic which helps me to understand it better because I dont see this topic at school and I will be really appreciated If someone helps,"This topic is covered in the physics section, under electric fields. This video might be helpful for your particular example. https://www.khanacademy.org/science/physics/electric-charge-electric-force-and-voltage/electric-field/v/net-electric-field-from-multiple-charges-in-2d"
N/A,Are differential equations truly necessary? Couldn't this material become more accessible (to lower math backgrounds) if things were introduced in the frequency domain rather than the time domain? Then we would be using only algebra and not calculus. The transformations back to time domain could be introduced later.,I like your style and thinking.Keep up the good thinking and you could be an amazing engineer!
N/A,Why was the current in resistor and current in capacitor taken in opposite directions in derivation of RC natural response ?,"Good question. This is one of the tricky parts of the analysis that most textbooks skip over.

In the section titled "Model the components" I define two current arrows for the resistor and capacitor currents.  I use two current arrows because I want to be sure I get the signs right when I use Ohm's Law for the resistor and i = Cdv/dt for the capacitor. Notice that these equations do not have a negative sign. That's because both of them respect the Sign Convention for Passive Components. (Resistor current flows _into_ the positive voltage terminal of the resistor. Capacitor current flows _into_ the positive voltage terminal of the capacitor.)

If I had defined a single current arrow, I would have to write one of those equations with a negative sign. I find it awkward to insert negative signs into i-v equations, so I did it the two-arrow way.

But now I have two current arrows I have to deal with... In the next section, "Model the circuit", the two currents participate in a KCL equation that gives us the differential equation to be solved. It is a pretty simple KCL equation. The signs on the two terms in the resulting equation came out correct, which is the reward for doing the two-current-arrows-then-KCL method.

You should try this: Define just a single current arrow named i. Then model the components with i-v equations, then model the circuit. This time you equate i in the resistor to i in the capacitor. When you derive the differential equation do you get the same thing? It takes some care to get this right. If it works for you, make that your favorite method."
N/A,If we are asked to find the current in the resistor of Example 1 . What to do ?,"In example 1, we solved the voltage across the resistor, v(t). Since you know the voltage, and you know the resistor value, you can use Ohm's Law to get the current, i(t). Incidentally, that's also the answer for the current in the capacitor. The same current flows in both R and C. 

Before t=0, the current in the resistor depends on the details of how the "helping" circuit (the switch) was operated. In the case of the specific circuit we started with, the current was 0 before the switch flipped."
N/A,How to find equivalent resistance of a complex circuit,"There are several different ways to to do this. I would recommend that first you should convert any Inductors and capacitors in your circuit into impedances. For inductors use Z = jwl. (Where j represents the imaginary impedance, similar to i in mathematics). w is the angular frequency. l is the inductance. For capacitors use Z = 1/jwc (also, -j/wc which can be obtained by multiplying both the numerator and the denominator by j). c is the capacitance.  Resistors stay the same (the ohms are purely real). Now combine all of these impedances as if they were a large resistor network. You will likely need a calculator that is capable of doing complex numbers. Good Luck and I hope that helps!"
N/A,"In the first part of the lecture, we are asked what is Vc before the switch is flipped up, after the switch is flipped up, and finally after the switch is flipped back down, For the second part (What is Vc after the switch is flipped up) it states that the capacitor voltage(Vc) will rise to the same voltage as the battery. This is incorrect because there is also a voltage drop across the resistor so Vc would be Vbatt - Vr. KVL equation would be Vbatt - Vr - Vc = 0.","As the capacitor is charging, current is flowing and there is some voltage drop across the resistor. But, the longer the current flows, the more charge accumulates on the capacitor. Eventually, the charge on the capacitor reaches the point where the voltage of the capacitor (q/C) is equal and opposite that of Vbatt. At that point (time), current stops flowing. There is no voltage drop across the resistor because there is no current when the capacitor is fully charged. Vr = IR, but I = 0. The charging behavior of capacitors is just the opposite of the discharging behavior that is illustrated so well in this lesson. Another good resource is Prof. Nave's Hyperphysics site. There are pages that show both the charge and discharge behavior of capacitors, along with the math."
N/A,"Regarding the circut with the battery (constant voltage source).
How can I calculate the *time* it takes to charge a capacitor? Just rearange the final RC response equation to find t? What about in a circuit without a resistor? What role does a resistor play when charging a capacitor, anyway (max. current perhaps)?
Thanks","Hello Nejc,

Yes, you can solve by manipulating the equation as you stated. You could use a rule of thumb and assume 66% charge in one time constant and fully charged in about 5 time constants.

In the real world there is no such thing as "no resistance." All wires have some resistance, the capacitor has an internal resistance, the voltage source (battery) has an internal resistance.

You are correct about the max current. As an example consider a lithium ion battery storage system connected to a DC to AC inverter. In many of these systems you will find a capacitor on the DC side between the battery and the inverter. Connecting this capacitor directly to the batter would cause an excessive current flow. A "current limiting resistor" is used to charge the capacitor. After the capacitor is fully charged to the DC batter voltage it can be directly connected to the battery.

Please leave a comment below if you would like to continue the conversation.

Regards,

APD"
N/A,"Why did we chose constant current source in RL natural response, but constant voltage source in RC natural response ? Can we do other way round ? What is reason for picking these sources in such manner ?","For RL and RC natural response we want to start the circuit off with some initial energy. A resistor doesn't store energy, so that means we place the energy in either L or C. An inductor's energy is stored in its magnetic field, which comes back out of the inductor as a current (the magnetic field pushes charge through the wire). For a capacitor, its energy is stored in the form of charge. That stored charge causes a voltage to appear on the capacitor, as in q = C v, or v = q/C. 

So in setting up to analyze natural response we pick the type of source that directly injects the energy into L or C."
N/A,"Excuse my ignorance, but why is the KVL VL+VR=0 instead of VL-VR=0?","It is somewhat tricky to set up the KVL equation for this RL circuit (and the RC circuit as well). You have to be careful with the sign convention for passive components. 

Look at the circuit in section "Model the Components". The starting point is to add the current arrow pointing up out of the inductor. That means it is flowing down through the resistor. 

The second step is to add voltage labels to L and R, while respecting the sign convention for passive components. For the L, the current flowing up means the positive polarity of the voltage is at the bottom of the inductor. For the R the current is flowing down from the top, so the positive polarity of the resistor's voltage is at the top of the resistor. Admittedly, the voltage on the resistor looks "right" while the upside down voltage on the inductor seems a bit odd. That's not because it is wrong, but because it is unfamiliar. 

The last step is to write KVL around the loop. I chose to start on the top node and circle down through the L and then up through the L. That results in two positive voltages being added together."
N/A,"Under the heading
Write expressions for i(t)i(t)i, left parenthesis, t, right parenthesis and v(t)v(t)v, left parenthesis, t, right parenthesis after t=0t=0t, equals, 0.

I found that we used s in equations for i(t) and v(t)
s = R/L

But when the values were used, we don't get the answer we should from 200 ohms / 16 micro-Henrys. Instead, I think the time constant (T or Tao) was used to get 80 nano-seconds.

Should we use s times t in the exponential or the time constant?
We got s from the integration, so where does the time constant come in?","Natural frequency s = -R/L is closely related to the time constant tau = L/R.

We found a solution to the differential equation by solving for s in the equation sL + R = 0. This gave us s = -R/L and we were able to assemble a solution for i(t). 

What are the units of s? If the exponent is -st, the units of s have to be 1/time. (exponents can't have units, so all the quantities in an exponent must cancel out.)

When you talk about the time constant you ask a slightly different question. Given the solution for i:

i = I_0 e^{-Rt/L}      

what value of time makes the exponential term equal -1?   Another way to ask the same thing is to ask, what value of time makes the exponential term equal to 1/e?

The answer is at t = L/R the exponent is -1. That special time is called the _time constant_ and we use the Greek letter tau. What are the units of tau? Since tau is a particular value we chose for t, the units of tau are seconds."
LC natural response,"In the predict the natural response section it says "(Current does not abruptly drop to 000 when the voltage reaches 000.)"
How is this true since Ohm's law states I=V/R?

Also, do the electrons on one side of  the capacitor simply run through the inductor to the other capacitor plate? and then back again? So the inductor just acts as a spring that pulls the elctrons back and forth from one plate to another?  

I hope this makes sense, if there is a video on inductors please point me in the right direction I'm having a hard time understanding.

Thanks","Hi KCThomas,

Notice that we are transferring energy between the inductor and the capacitor. There is no resistor in this circuit! Consequently, Ohm's law does not apply. In fact, as described, the energy will slosh back and forth between the components forever...

Personally I had a hard time understanding inductors. After all, an inductor is just a coil of wire. Let me tell you a story. One day I was measuring the current flow though an inductor. I had a 12 VDC battery, an ammeter, and large inductor. To save time I held the wires in my hand. The test went well and I got a good current measurement of 0.5 A.

--Did I mention I was hold both end of the inductor one with my right and one with my left hand? --- 

Anyway, all was well until I went to disconnect the circuit. That was the day I learned that an inductor is not a simple piece of wire. I assure you it was a painful lesson!

An inductor stores energy in a magnetic field. The amount of energy is related to the construction of the inductor and the amount of current flowing in the device. This energy is released when the current flow is reduced. Back to my story. There was energy stored in the inductor. And I had foolishly placed my hands across the device. When I disconnected the circuit I released the stored energy. It manifested itself as a high voltage shock that brought a tear to my eye.

Inductor and capacitors both store energy but they do is in different ways. One magnetically and the other electrostatically. When connected in the circuit as described in this article the energy constantly transfers back and forth between the two devices.

A mechanical analogy that may help is the mass and spring. Both store energy, one as kinetic and the other as tension. Please take moment to consider how this analogy relates back the capacitor and inductor. 

BTW, if we add a damper to our mechanical system we will have the equivalent of a resistor.

Regards,

APD"
LC natural response,"Is the pendulum system only an analogy or both system are equivalent? I mean, in the pendulum system we have a relationship between kinetic and potential energy  in a conservative field, ( we simplify by doing air resistance, torsion of rope and so on equal to zero). 

Is the magnetic field some kind of potential energy of the electrical system?

My ask have his source in this problem : I can't to reach an intuition about electromagnetic fields... Gravitational fields, instead,  are so easy to "imagine"!

Thank you very much for this course!","The pendulum system is a mechanical analog of the LC circuit. Voltage on the electric side corresponds to position away from 0 on the mechanical side. Current corresponds to the velocity of the pendulum. The two systems can't be "equivalent" because they are made of totally different things. However, we can use the same mathematics to solve both systems to derive sinusoidal motion. That's what makes this such a powerful and useful analogy, (more interesting than "just an analogy"). 

If you dig deeper, you can find other relationships in this analog. The magnetic field in the inductor causes the current to keep flowing even after the voltage goes to zero. The inductance (L) is analogous to the inertia of the mass at the end of the pendulum. 

This is a great analogy because you can visualize something you've seen before (a swinging pendulum) to help you understand something you are just learning about (LC)."
Node voltage method,"If current flows from higher(+) terminal to lower (-)terminal, then how come the direction of current in upper mesh (mesh with floating voltage source) is in anticlockwise direction? How does it satisfy the current flow from higher to lower potential concept?","When you assign the direction of current arrows at the beginning of a problem (before you know the actual current directions), you can choose either direction. When you do this, you are counting on the subsequent analysis steps to produce the correct sign of the current by the time you get to the end. I did not assign resistor values in the Floating Voltage Source circuit, but if I did the current will probably end up with a negative sign. That means it is actually flowing in the opposite direction of the arrow. Given my confidence in the methods of analysis, I'm not going to worry at the beginning if I've assigned the current arrows "right". It all comes out correct at the end."
Node voltage method,"Stupid questionI am sure, but why do you multiply the first equation (node b) by 15/10 to get rid of Vc?",I'm able to find where in the article you are seeing this. Perhaps give me a nearby text string to help locate the equation.
Node voltage method,"In general I thought I understood the node method but then I was looking at the text book Agarwal and Lang 2005 Foundations of Analog and Digital, Figure 3.41 where they show this example. I drew it below. There is just a current source. 

`
ei----2ohm-------
|               |
1ohm           I ^ 1 amp
|               |
|               |
-----------------
_|_
`
There is a statement in the text:
" Then, since the 1-A current flows through each of the resistors, the voltage across the 1-ohm􏱼 resistor is equal to ei. In other words ei = 1amp * 1ohm = 1"

That statement confuses me. If the current flows through each resistor, then ei is also equal to 2*1 isn't it? 

Can't I use the node method for this circuit? With the node method, (I always assume the current flows away from the node, and the sign usually works itself out) I get:

ei/1 + ei/2 - 1 = 0
3/2 * ei = 1 => ei = ⅔ v, which of course is wrong, but I'm not sure why. 
I am missing something, there is something I am not intuitively seeing. How would you write the node equation for this trivial circuit.","Lucky for me I have this exact text. The circuit in words is a single loop, with 1ohm on the left side, 2ohm across the top, and a 1A current source pointing up on the right side. Node voltage "ei" is the upper left corner, between the two resistors. The bottom edge of the circuit is ground. 

Finding voltage ei is actually very easy. The current everywhere in the loop is 1A. The 1ohm resistor is connected between ei and ground. It has 1A flowing through it. Therefore the voltage at ei is 1V. 

You want to apply Kirchhoff's Current Law at node ei, but you didn't get it quite right.

The currents flowing *out* of node ea are
- Down through the 1ohm resistor = 1A.
- Right through the 2ohm resistor = -1A. 

The KCL equation at node ea is
+1A + (-1A) = 0

It is a common error to use the current of the current source (1A) as the voltage across the current source (which is not 1V). You don't know the voltage across a current source until you consider everything connected to it.

If you want to draw schematics, try this... https://spinningnumbers.org/circuit-sandbox/index.html
Draw what you want. Click on the link icon and copy/paste a text version of the circuit. Try out this huge URL,

https://spinningnumbers.org/circuit-sandbox/index.html?value=%5B%5B%22i%22%2C%5B256%2C128%2C2%5D%2C%7B%22value%22%3A%22dc(1)%22%2C%22_json_%22%3A0%7D%2C%5B%220%22%2C%222%22%5D%5D%2C%5B%22r%22%2C%5B144%2C80%2C0%5D%2C%7B%22r%22%3A%221%22%2C%22_json_%22%3A1%7D%2C%5B%221%22%2C%220%22%5D%5D%2C%5B%22r%22%2C%5B224%2C64%2C1%5D%2C%7B%22name%22%3A%22%22%2C%22r%22%3A%222%22%2C%22_json_%22%3A2%7D%2C%5B%222%22%2C%221%22%5D%5D%2C%5B%22w%22%2C%5B144%2C80%2C144%2C64%5D%5D%2C%5B%22w%22%2C%5B144%2C64%2C176%2C64%5D%5D%2C%5B%22w%22%2C%5B224%2C64%2C256%2C64%5D%5D%2C%5B%22w%22%2C%5B256%2C64%2C256%2C80%5D%5D%2C%5B%22g%22%2C%5B200%2C128%2C0%5D%2C%7B%22_json_%22%3A7%7D%2C%5B%220%22%5D%5D%2C%5B%22w%22%2C%5B144%2C128%2C200%2C128%5D%5D%2C%5B%22w%22%2C%5B256%2C128%2C200%2C128%5D%5D%2C%5B%22view%22%2C98.6424%2C40.20688%2C3.814697265625%2C%2250%22%2C%2210%22%2C%221G%22%2Cnull%2C%22100%22%2C%220.01%22%2C%221000%22%5D%5D"
Node voltage method,"Floating voltage source example - what if we remove the R1 resistor?
I assume we then eliminate node C. How do we determine the branch (V2) current? I'm guessing we can calculate it, but when trying to do so, I get somewhat counterintuitive results. 
If someone bothers to check: Let A be the ref. node.
Why is there no current flowing through R3 (and subsequently V1) if *V1=V2*? What does that mean? Why is it so?","Congratulations on imagining a really goofy circuit. Last question first... If V1 = V2, the voltage across R3 is 0 volts. The two batteries combine to go up by V volts and down by the same V volts. So the top of R3 is at 0 volts, just like the bottom of R3. 

That also means the current in R3, by Ohm's Law, is i = v/R = 0/R = 0. No current flows in R3. 

That in turn means no current can flow in source V1. 

Which then tells us the current in R2 ALL comes from source V2. 

Here's a simulation. Copy and paste this entire URL into a browser.

http://spinningnumbers.org/circuit-sandbox/index.html?value=[["v",[232,24,1],{"name":"V2","value":"dc(1)","_json_":0},["2","1"]],["r",[128,104,0],{"name":"R3","r":"1000","_json_":1},["1","0"]],["v",[288,104,0],{"name":"V1","value":"dc(1)","_json_":2},["2","0"]],["r",[232,88,1],{"name":"R2","r":"100","_json_":3},["2","1"]],["g",[288,152,0],{"_json_":4},["0"]],["w",[128,152,288,152]],["w",[128,104,128,88]],["w",[128,88,184,88]],["w",[232,88,288,88]],["w",[288,88,288,104]],["w",[232,24,288,24]],["w",[288,24,288,88]],["w",[184,24,128,24]],["w",[128,24,128,88]],["view",47.66,-5.207999999999998,2.44140625,"50","10","1G",null,"100","0.01","1000"]]"
Delta-Wye resistor networks,"Why we can assume that terminal z isn't connect to anything?
I mean, in the example, it clearly show that terminal z did connect to something and must have a current flow through.","Hello Fasteric,

Try to think of each circuit as a black box - assume you don't know what is inside. When you "look" from terminal A to B you see a certain resistance. When you "look" from terminal B to C you see a certain resistance. Finally when you "look" from terminal C to A you again see a resistance. It's important that you "look" at the circuit in isolation. If it was connected to other things it would be difficult to do this thought experiment. 

Please give it a try you should be able to convince yourself that the wye and delta look the same. If it helps try calculating the resistances when the delta has three resistors each with a value of 3 Ohm. Then try the wye with three resistors each having a 1 Ohm value.

Regards,

APD"
Delta-Wye resistor networks,Can you provide the work for solving the 3 simultaneous equations that was not shown?,"This is awesome. Thank you for explaining. It's very hard to find a straightforward, detailed explanation of the transformations on the web, but you've presented one here. You should do a YouTube video. It would blow people's minds!"
Delta-Wye resistor networks,I want u to ask a full way to derive R1 and Ra plz give a derivation how we get R1 and Ra ?,"since,

(resistance between X&Y in Y) = (resistance between X&Y in delta)
(resistance between Y&Z in Y) = (resistance between Y&Z in delta)
(resistance between Z&X in Y) = (resistance between Z&X in delta)

so,
(R1 + R2) = ( Rc || Ra+Rb ) .. [1]
(R2 + R3) = ( Ra || Rb+Rc ) .. [2]
(R3 + R1) = ( Rb || Rc+Ra ) .. [3]

To get R1, we do ([1] + [3] - [2]) / 2, at the left hand side :

( (R1 + R2) + (R3 + R1) - (R2 + R3) ) / 2 = (R1+R2+R3+R1-R2-R3)/2 = (2 x R1)/2 = R1 ..[4]

Do the same for right hand side :

( ( Rc || Ra+Rb ) + ( Rb || Rc+Ra ) - ( Ra || Rb+Rc ) ) / 2
=( (Rc x (Ra+Rb))/(Rc+(Ra+Rb)) + (Rb x (Rc+Ra))/(Rb+(Rc+Ra)) - (Ra x (Rb+Rc))/(Ra+(Rb+Rc)) ) / 2
=( ((Rc x (Ra+Rb)) + (Rb x (Rc+Ra)) - (Ra x (Rb+Rc)) / Ra+Rb+Rc ) / 2
=( ((RbRc+RaRc) + (RaRb+RbRc) - (RaRb+RaRc)) / Ra+Rb+Rc ) / 2
=( (2 x RbRc) / Ra+Rb+Rc ) / 2
=(RbRc)/(Ra+Rb+Rc) .. [5]

Since, left hand side = right hand side, or [4] = [5],

R1 = (Rb x Rc)/(Ra+Rb+Rc)

Done, we got our R1. :D

ref : previous question @ 
https://www.khanacademy.org/science/electrical-engineering/ee-circuit-analysis-topic/ee-resistor-circuits/a/ee-delta-wye-resistor-networks?qa_expand_key=kaencrypted_ad2413cde556298b64a98d41d01fd684_cd6a16e8a8a657a21f768c0ff04804160d977a939ac691b3ecd6f7ee4a7f3b908c3a74bcab01337d6533d3b2cd73bf8f6ff245d796c6ba5cd4935e7434b49ff5a41f9fde6e3e3b40568f65d949ebef1c2069c478d967b52cc4b9a4782497244937b838cd8908e0ad3a3a524e87a524e6f816e4f6f1312d1554b5f5586074aab1f7d6c61e4d62263fecf53eb29522e61469af6deb96ff91ae7303c04481bb2de0"
Delta-Wye resistor networks,why would we want to go from y-delta,"Hello Professor,

They can be used to simplify the occasional circuit as shown in this video. They really come in handy when working with three-phase system. The transform simplifies the math :)

This link may help: http://www.belden.com/blog/datacenters/3-Phase-Power-Wye-It-Matters.cfm

Regards,

APD"
Delta-Wye resistor networks,so if they delta and y are then transformed into a combination circuit.. why have those??,One of the common places a Delta resistor configuration shows up is in a "bridge" circuit. If you search for "Whetstone Bridge" on the web you will see deltas in the resistor bridge. This circuit is used to make very sensitive differential voltage measurements.
Delta-Wye resistor networks,"I can derive R1, R2 & R3 easily, but I can't derive Ra at all. I can't figure it out !",Scan down through the comments here and find a response by learner _phidot_. There's a derivation in two separate comments.
Delta-Wye resistor networks,"If we used these configurations for inductors instead of resistors, would that create a magnetic field in the shape of the configuration?","In an inductor most of the magnetic field is concentrated on the inside of the coil. The field is much weaker around the outside of the inductor. If you tuck three straight inductors tight together in a triangle you pretty much get three magnetic fields in a triangle shape. But, if you curve the inductors into a circle the magnetic fields get together to make one more powerful field. See the second to last image of a circular-wound inductor in this article: https://www.khanacademy.org/science/electrical-engineering/ee-circuit-analysis-topic/circuit-elements/a/ee-real-world-circuit-elements"
Delta-Wye resistor networks,I didn't understand the derivation of the three simultaneous equations. Can someone please explain them.,I found this video to be very helpful: https://youtu.be/igvqOyJYAoA
Linearity,"Under the subheading Adding (additivity) you claimed:

All linear functions have the form of a line with scale factor (slope) _a_:

_f(x) = ax_

Could you give us a rigorous proof of this claim? By definition, a linear function has the following property:

_f(ax) = af(x)_

Could you show us how the statement _f(ax) = af(x)_ implies the statement _f(x) = ax_ ?","I will use different variables for the given function and the linearity test.

Is f(x) = ax a linear function?

Linearity test:
f(x) is linear if f(bx) = bf(x)   

Evaluate both sides of the linearity test and check to see if they are the same.

Left side: f(bx) = a (bx)
Right side: b f(x) = b (ax)             

abx = bax

The linearity test passes, so f(x) = ax is a linear function."
Linearity,"Let's analyse the equation of a line, for example `y=2x+3`. A _line_ should be _linear_ by definition. But, if I were to test it by the numbers, I would get strange results. For example, let's plug `x=3` and its double, `x=6` into the function. The linearity principle states that `f(2x) = 2f(x)`. So, let's try with our linear function `y=2x+3`.
(1) For `x=3`, `f(3)=2*3+3=9`
(2) For `x=6`, `f(6)=2*6+3=15`
15 is not the double of 9. What am I getting wrong?
Thank you for your help!","The term 'linear' has an everyday meaning and a different meaning in mathematics. In everyday language it means "Hey, that looks like a line." In math, it means those two properties in the article (scaling and additivity). Many, but not all, lines have the mathematical property of linearity. Only those lines that pass through the origin (lines whose y-intercept is zero) are linear in the mathematical sense. This particular restriction is what gives rise to all sorts of really good properties of linear circuits."
Linearity,A diode is a non-linear device. Elaborate.,"A diode is non-linear because it's i-v curve does not have the properties of scaling or additivity. The last illustration in this article shows a typical diode i-v curve. If you apply the tests for scaling or additivity to this curve, they both fail. If we drive a diode with a controlled voltage, the resulting current is *not* a scaled version of the voltage. That's why we say a diode is non-linear."
Mesh current method,"All the currents is defined going around in the same direction (clockwise). It must be defined all clockwise? I mean, can I define one of them, let's say i1, counter-clockwise?","You may define the current directions as you wish. The best practice is to choose one direction for all loops, either clockwise or counterclockwise. This advice is intended to reduce the chance of making a sign mistake as you write the loop equations. Components sharing two loop currents will always have the pattern of  (i1 - i2) because the loop currents will flow in opposite directions. However, you are perfectly free to assign directions as you wish, but stay alert for current direction!"
Mesh current method,Could you show an example of where there is a loop that only consists of resistors please. I'm struggling on how to set the polarities,"When you begin studying circuit analysis there is often a strong desire to set the problem up (label the voltage polarities) so they are "right". It is important to let go of this desire. Instead, realize that, at the beginning of the problem, the voltage assignments have only one job: to help you create the independent mesh equations. There is no "right" and "wrong" way to label the different resistor voltages. You can do it any way you want. The critical skill is the following step, where you write the mesh equations using the polarity assignments you just made. If you do that step right, all the voltage signs will come out right at the end of the problem.

One way to test your understanding is to solve a simple circuit twice with different voltage polarity assignments. During the process you will see how each polarity assignment generates a slightly different mesh equation. In the end you should get the same answer both ways. After all, it's the same circuit both times."
Mesh current method,what if we could guess the direction of one of the  currents?  should we continue with our guess or let it go and use the clockwise direction for all?,"If you want to start off with a guess for one of your mesh currents, you can do that. I recommend you start with that mesh, and then use the same direction for all the rest. Your guess (assuming it is correct) will earn you a + sign for that mesh current. 

The Mesh Current Method is set up as a robotic recipe for solving circuits, with the emphasis on consistency and getting the signs correct. It does not need a good guess to get the right answer. This won't take too long: solve your circuit two ways, with your guess, and with all clockwise. Notice how you get a few sign changes in the set of equations that emerge. And notice if it is easier or harder to write the terms where two mesh currents flow in one element."
Mesh current method,"How would one solve a more complicated loop such as the following :
https://s3.postimg.io/gfw569zjn/IMG_20160824_023012_1.jpg
I know I could start with using Ohms Law and hence start writing KVL but I don't get how to assign polarity to the obtained V.","Hello Anshuman,

I'd like to help but the drawing is unclear. From what I can tell you will need three loop equations. It looks like you have three voltage sources. I can't make out if the thing in the middle is a meter or a constant current source...

Please leave a comment below.

Regards,

APD"
Mesh current method,"why should we write the loop III equation above,and then we use just two loops(I and II)?",Loop III is never written out as an equation in this article. It was mentioned at the beginning to distinguish meshes from loops.
Mesh current method,Sir can i know what is the relationship between mesh current and branch current?,"The relationship between mesh and branch (also called element) current is described above. Search for the phrase "Let's take a close-up look at R3 in the middle branch of the circuit." In the illustration you see the element current is the combination of the two mesh currents that flow through R3. 

Element currents seem more "real" than mesh currents. Mesh current is a very clever computational trick at the heart of the Mesh Current Method for solving circuits. I actually enjoy using the Mesh Current Method because these currents seem so weird, and yet they always work."
Mesh current method,"Doesn't current flow from the positive terminal to the negative terminal? So, shouldn't the currents be going in the same direction through the middle resistor?","You are citing the Sign Convention for Passive Components. In the circuit above there are two mesh currents iI and iII. The oddball one is iII because it is flowing UP through the middle resistor. 

The Sign Convention is not saying you _can't_ have that; what its telling you is you better be careful when applying Ohm's Law to that resistor and iII. Because iII is flowing "backwards" through the resistor (coming in the - voltage terminal), the Ohm's Law equation has to include a negative sign in the product of (iII R)."
Parallel conductance,"In the example problem, I'm confused about the use of the variable G vs the variable S. What are the meanings of these two variables, and are they interchangeable?","Hello Alexis,

Electrical conductance (G) is measured in units of Siemens (S). This is the inverse of resistance (R) which is measured in units of Ohms (Ω).

Personally, I prefer the old unit unit called the mho abbreviated ℧. Note that mho is ohm spelled backwards. This older definition always made the inverse relationship between resistance and conductance easier to understand.

Please leave a comment below if you have any questions.

Regards,

APD"
Parallel conductance,What about conductance in series?,"Conductances in series have an equation very similar to resistors in parallel.
1/Gs = 1/G1 + 1/G2 + ... 1/Gn

See if you can derive this equation on your own, by combining what you learned in this article along with the theory in the Series Resistor article."
Parallel conductance,"hi, if one branch of parallel circuit were to open circuit what would happen to total current ? i'm assuming because it's parallel ( other branches are still connected to nodes) and current are usually divided in parallel series, the current would increase and as a result power would increase (power = current times volt)  Can you confirm?","If you remove a resistor from a parallel arrangement, the total current through the remaining resistors goes down. By removing a resistor, the overall equivalent parallel resistance goes UP, so the current goes DOWN."
Parallel conductance,"So for conductance, is basically the inverse of resistance? you can calculate resistance and just inverse it?",Yes. Conductance is the inverse of resistance. The main reason we talk about conductance is the equation for parallel conductance. That equation (sum of conductances) looks just like the formula for computing series resistance (sum of resistances). That is a nice observation to make and understand. In electrical engineering this kind of relationship between two equations is called a "dual".
Parallel conductance,"greetings 
I would like to know more about conductance G which weren't given a full understandable explanation",""Conductance" is defined near the beginning of the article. Conductance is the reciprocal of Resistance. It is not a new type of component or a new idea, it is simply a different point of view of a resistor."
Parallel conductance,"In which situations is it more useful to use conductance intstead of resistance, when they essentially describe the same thing?","Conductance might be helpful when a circuit is dominated by parallel connections. Adding conductance is simpler than an endless string of reciprocals of reciprocals for resistance. 

I just wrote this article on Delta-Y transformation equations. One of the derivations uses conductance in a really elegant way. http://spinningnumbers.org/a/delta-wye-derivations.html.  Look down at the last third of the article, the second derivation of Y-to-Delta."
Parallel conductance,""...specified in units of mhos, which is just "ohms" spelled backwards." Wouldn't that be smho instead of mhos??","ohm --> mho
ohms --> mhos

Although I do like your spelling, too. It's fun to say. Too bad it's an old unit we don't use any more. That would be a pretty funny debate."
N/A,"Is there a topic i can study here regarding the math on ohms law?
Better yet, can someone walk me through the part where it said:
v = −20μA⋅10kΩ
to
v = (-20 x 10^-6) x (10 x 10 ^+3)","If you are having trouble with the transformation from letter prefixes like 20 uA changing to 20x10^(-6), check the article on Numbers in Engineering: https://www.khanacademy.org/science/electrical-engineering/introduction-to-ee/intro-to-ee/a/ee-numbers-in-electrical-engineering.

There are other articles in the Introduction to Electrical Engineering that cover the symbols for current, voltage, and resistance."
N/A,"I don't fully understand the current direction and voltage polarity for two-terminal components. First, don't electrons move from negative to positive, so why does the current enter from the positive terminal? Also, why does the voltage polarity face the opposite way from the current?","Check out this video on how we define the direction of current: https://www.khanacademy.org/science/electrical-engineering/introduction-to-ee/intro-to-ee/v/current-direction

The definition of current direction used by all electrical engineers is to point the current arrow in the direction *positive* charge would move. Since electrons have a negative charge, they move in the opposite direction the current arrow is pointing. This quirky definition of current direction was created long before anyone knew that electrons existed, and that they carry the current in wires. There are no plans to change this definition, and, once you get used to it, it starts to feel normal."
N/A,"Maybe a stupid question, but why would one need a "voltage arrow"? Voltage is the energy per charge... so how can it have a direction? I'm so confused. Feels like these tutorials assumes that I know stuff that I don't know...","Hello David,

Instead of direction let's call it polarity. You could also call it a rise or fall in potential. From a practical perspective it tells you if the voltmeter will read a positive or a negative voltage.  

Yes, I understand your confusion. At first glance this passive sign convention seems completely useless. However, as you continue on it will start to be more and more important. You will appreciate the concept when you learn about Kirchhoff's Voltage Law (KVL). 

Ref: https://en.wikipedia.org/wiki/Kirchhoff%27s_circuit_laws

Regards,

APD"
N/A,What is the difference between current source and voltage source? I think they are the same because both of them produce electricity.,"Both sources create voltage and current. A voltage source creates a constant voltage, and the current adjusts to whatever is required by the attached circuit. A current source outputs a constant current, and the voltage adjusts depending on what is connected."
N/A,"How did you get from "i=+2V/250Ω" to "i=+8mA"
I got "i=1V/125Ω" = 1A/125","And if you divide 1 by 125, you will get 0.008 Ampere, which is 8 milli-Ampere (milli = one thousandth)"
N/A,Why would the label not match the actual?,"In general the label is like a vector in mechanics, if you assign it going up and then run through the math but find your answer is negative it means it's actually going down. The direction is so you have a clear idea of which way things are actually moving when all is said and done."
N/A,"Example 1: "What is i?"
i = +8mA
Example 1X: "What would happen if we labeled the resistor with the wrong sign convention?"
i = +8mA
"We got the wrong answer."
Did we though? Because those two answers look awfully similar to me, despite one using the wrong convention. If one of those examples could be i=-8mA due to being misled somehow, then that ambiguity should be pointed out and explained. However, even if the math does work out to be the same for both examples somehow, comparing the two examples is not useful for justifying the use of the correct convention. Also, we're talking about a resistor in these examples, and AFAIK it doesn't actually matter which way they're oriented, mathematically or practically, so again maybe not the best illustration to justify convention? If what you're trying to say is that +8mA IS the wrong answer for a diagram labeled with current flowing the other way, then that is not clearly stated and it also implies that the actual direction of current should be changed instead of fixing the label, which is where the real problem is here. Either way, something needs to be clarified or corrected.","The answers look similar, but one of them gives you the wrong current direction. 

In both Example 1 and 1X there is +2 volts on the resistor, with the + voltage applied to the resistor's upper terminal. In both cases the resulting current will be 8 mA flowing from top to bottom in the resistor. 

The sign convention tells us to draw a current arrow pointing _into_ the positive voltage terminal of the resistor. With this convention, Ohm's Law gives you i = +8mA, which is the correct answer. If you accidentally draw the current arrow pointing the other way (coming out of the positive voltage terminal, or equivalently, pointing into the negative voltage terminal) when you apply Ohm's Law you again compute i = +8mA. BUT, since the arrow is pointing up, that says the current is flowing up, which it is not (it is flowing down). 

Part of the challenge here is that current direction is indicated by mingling two signs. First you have the arrow symbol, which can point in two directions. Then you have the sign of i, as in i = +8mA or i = -8mA. The arrow direction and the arithmetic sign combine to give you the overall direction of current."
N/A,"If the convention is to have current flow into the positive terminal of a battery, as this article states, then why are most circuit schematics modeled with the current flowing out of the positive terminal? To me this seems explicitly contradictory.","Hello Sean,

Yes is is contradictory. Shrug - It's just the convention we use - positive to negative. It is regrettable that this is the first lesson electronics. It's not just here but in just about every electronics and physics textbook.

I think Randall Munroe said it best in his comic https://xkcd.com/567/

Regards,

APD"
N/A,I am confused with the labeling of voltage sources. I thought the convention is to have the conventional current flow from the positive terminal to the negative terminal. But the 3rd illustration is contradictory to the illustration of the wrong way of labeling the current.,"We use the word "convention" a lot. So first, let's calm that down a little. Whenever we say "current", all we have to say is "current", since we no longer need to be long-winded with "conventional current". 

The first part of the article is about how to assign current and voltage directions to passive components (R,, L, C). The reason we have this convention is so when you have a positive current you know the direction of the corresponding positive voltage.

The next part we talk about putting signs on an active component (voltage source). Active sources are a bit quirky when you apply signs, because they generate power (that's why they are so different from passive components.)  I offer three choices for doing this, along with some reasons to help you make your own choice. You may be thinking the third choice is wrong, but it is ok. In fact it's my second favorite. There is no "wrongness" here because it is not an attempt to distinguish between conventional current and electron current. The choice is just a matter of controlling and making sense of where you get positive current and positive voltage."
Capacitor i-v equation in action,"Would you walk us through the UNITS issues for this example? Specifically, how Amps per Farad becomes volts per second. I keep getting lost somewhere in the middle.","Here's one path to an answer. I'll start with the basic capacitor equation: q = Cv.   
   (q = charge, C = capacitance, v = voltage)
Now convert the variables to unit names. The units of q are Coul (Coulombs), units of capacitance are F (farads), v stays volts.
Substitute in the unit names and you get the definition of a farad,
    F = Coul/V 
Now modify Coul so we can talk about current. Multiply the right side by sec/sec.
    F = (Coul/sec) / (V/sec)
Coul/sec is the definition of current, so Coul/sec has units of Amps,
    F = A / (V/sec)
Now one last step to rearrange this into the form you asked for,
   A/F = V/sec

(By the way, congratulations on 4 million points on Khan Academy. You have possibly learned nearly everything!)"
Capacitor i-v equation in action,How could you know what is the current value that the capacitor is charging at(which is represented by i in the equations) when you don't have a current source but rather a voltage source?,"Good question. You have curiosity, a great trait for a learner.

If you replace the current source with a voltage source in the schematic at the top of this article you end up a circuit that does not make much sense. Say the voltage source produces a voltage pulse with very very sharp transitions. The capacitor equation says i = C dv/dt. The sharp transition means dv/dt will be a very large value for a very short time. If the voltage transition is instantaneous the equation predicts a pulse of infinite current in zero time. The reason this simple circuit is troublesome is because no resistor is involved.

When you add a resistor in series with the capacitor you get what is called the Natural Response of an RC circuit. That is covered in great detail in the sequence of videos and articles here,
https://www.khanacademy.org/science/electrical-engineering/ee-circuit-analysis-topic/ee-natural-and-forced-response/v/ee-rc-natural-response-intuition
or try this revised version: https://spinningnumbers.org/a/rc-natural-response-intuition.html

Simulate this circuit by copy/pasting this big fat URL into a browser:
https://spinningnumbers.org/circuit-sandbox/index.html?value=[["r",[224,72,1],{"name":"","r":"0","_json_":0},["3","1"]],["c",[256,88,0],{"name":"","c":"1u","_json_":1},["2","0"]],["w",[256,72,256,88]],["g",[200,136,0],{"_json_":3},["0"]],["w",[256,136,200,136]],["a",[232,72,0],{"color":"magenta","offset":"0","_json_":5},["3","2"]],["w",[224,72,232,72]],["w",[256,72,248,72]],["w",[200,136,88,136]],["v",[88,88,0],{"name":"Vin","value":"pulse(0,1,0,1n,1n,10m,20m)","_json_":9},["1","0"]],["w",[176,72,88,72]],["w",[88,72,88,88]],["view",38.928,33.1336,3.0517578125,"50","10","1G",null,"100","0.029","1000"]]

Click on *TRAN*. The current spikes are huge. Double-click on the resistor and change it to 1000 ohms. Do *TRAN* again and you are looking at the Natural Response of an RC."
Capacitor i-v equation in action,Can someone please post the answer for the end question? I feel it's kind hard and I wish I can check with the answers...thank you!,Have you grabbed the green dot in the last plot and dragged it around?
Capacitor i-v equation in action,"I am confused between t and T. What is difference between both of them, what quantites are specified by them ? Aren't both time itself ?","I admit this is a tricky notation. Little t time represents the time axis. Big T a specific time, it is the duration of the current pulse.

You may want to check out this revised version of the article: https://spinningnumbers.org/a/capacitor-iv-equation-in-action.html"
Capacitor i-v equation in action,"Why would no charges flow after pulse ? Capacitor has voltage of 6 volts, and won't it force electrons to flow around wire ? How can we decide that current is zero. We stopped current from current source, but won't capacitor cause current ?","Think of a capacitor as a bucket. It can hold charge, it can let charge flow in, or flow out. If the current pulse goes to a value of zero, that forces the value of current everywhere in the circuit to zero. The charge on the capacitor does not "have to" flow out. It just sits on the cap.

The analogy is filling a bucket with a garden hose. If the hose is on water current flows into the bucket and the water level (voltage) goes up and up. If you shut off the hose what happens? Easy! The water sits in the bucket. All the water is static, it does not flow anywhere because there is no path for water current. It's exactly the same for a capacitor."
Capacitor i-v equation in action,Isn't it i=C​dv/dt because the it says di instead of dv,Alejandro - Thank you for catching the error. It has been fixed. - W
Capacitor i-v equation in action,"*Voltage before the pulse*:
"Before the current pulse (t < 0), no current is flowing, so no charge accumulates on C. Therefore, v_(t<0) = 0. We didn't even have to use the equation."

Isn't this wrong? Wouldn't the fact that no current is flowing just mean the voltage is _constant_ and not necessarily zero? Wouldn't it be more correct to say that we _assume_ that v_0 = 0, and calculate v(T) _relative_ to v_0?

C*(dv/dt) = i
C*(dv/dt) = 0

For i to be equal to zero, then (dv/dt) must be equal to zero, thus the voltage must be constant, but not necessarily zero?","There is an assumption, stated at the beginning of the section, "We'll assume the initial voltage across the capacitor is zero."

If we don't make that assumption then yes, you are correct. The voltage starts at some constant v_o."
Voltage divider,"in problem 2 and problem 4, suggest that 20k and 50k can be seen as correct answers, since the questions already use k and μ for avoiding too many 0s.","Since this is the first time an answer is used in this course where "k" is part of the answer (20k), perhaps it is worth while putting in a mention of the possible notation in the text.  Anyway, nice course, I am enjoying it.  Thanks!"
Voltage divider,"Regarding Problem 4 - Challenge

Shouldn't the power be equal to P = I x Vout instead of Vin if it asks for the power dissipated by the divider? I was thinking that every element dissipates power and if it specifies the divider power it should be calculated using Vout. If not, why do we use Vin?","The voltage divider is made of two resistors, so the "power of the divider" has to account for both. You can compute the power a few different ways. 

Assuming i_out = 0...
 
If you know the current i flowing through the two resistors, then p = i^2 (R1 + R2).

Or, you could compute power based on the voltages,
p_total = p_R1 + p_R2
p_R1 = (Vin - Vout) / R1
p_R2 = Vout^2 / R2

Or, you could compute power based on both i and v,
p_total = p_R1 + p_R2
p_R1 = i (Vin-Vout)
p_R2 = i Vout

Or, simplest of all, 
p = i Vin"
Voltage divider,What is the difference between a 'Voltage Divider' and a 'Voltage Regulator'?,"Good question. A Voltage Divider is the simple 2-resistor circuit we talk about here. Remember the caution that a voltage divider only behaves itself when the current leaving the center node is practically zero? That limits where you can use a voltage divider. If you need to pull a lot of current at the new lower voltage, you use a Voltage Regulator.  This is an integrated circuit with 10-50 transistors specially designed to take a higher voltage and provide current at a very well-controlled lower voltage. 

The original IC voltage regulator is the LM317. It's been around forever. https://en.wikipedia.org/wiki/LM317.  If you scroll down a little you will see the typical circuit for using the LM317. Notice part of the circuit is a 2-resistor voltage divider that let's you adjust the output voltage. The divider determines the voltage. The regulator provides the robust current."
Voltage divider,"When evaluating the expression 
R1 || RL = R2 * 10R2 / R2 + 10R2 you get 10/11R2 = 0.91R2
Was this accomplished by factoring out R2 from the numerator and denominator?
R2(1 * 10) / R2(1 + 10) = 10/11 but wouldn't the R2/R2 just equal 1 or just cancel out? So how is it that it equals 0.91R2? We don't know the value of R2 so we just leave it in as a factor of the result?

When evaluating the expression
V-out = V-in(0.91R2/R1+0.91R2). You stated that R1 = R2 So they cancel out. leaving V-in(0.91/1+0.91) = 0.91/1.91=0.48V Assuming these computations were accomplished via factoring out the R2 this would assert the same computation as the first expression, but in this case R2 cancels out, whereas in the first expression it was left in. So how do I determine when I need to keep an a variable tied to a result, as in the first case of 0.91R2, and when to cancel it out, as in the second case 0.48v?

Thank you for your time.","The numerator of the resistor expression is R2 * 10R2 = 10 R2^2.
The denominator of the resistor expression is R2 + 10R2 = 11R2
When cancelling R2's you eliminate the one on the bottom but you still end up with one on top. 10R2/11.

In the voltage equation, _all_ the R2's cancel out."
Voltage divider,So can this be used for a DC circuit? I am trying reduce the voltage of a battery from 9v to 3.7v. what is the best way to do this?,"Hello Swag,

It depends on your application.

I assume you are using a 9 VDC battery. If you use a voltage divider over half of the battery's energy will be lost in the resistors. It turns out that this simple circuit is very inefficient.

From an energy perspective you would be better off using a a “switching Regulator.” For an example see: 

http://power.murata.com/data/power/dms-78xxsr.pdf 

For an explanation of how the circuit operates see:

https://en.wikipedia.org/wiki/Buck_converter

Regards,

APD"
Voltage divider,"If we put RL in the circuit, does that make any change to power dissipated by voltage divider ?","Hi  Mogbulumide,

This is a hard question to answer without knowing your background. I am assuming you have some knowledge of electronics but have not yet studied AC circuits. 

There are two answers to this question:

1) For Direct Current circuits - with DC an inductor acts as a short circuit. In reality you will "see" the resistance of the inductor's winding. In general you will not find inductors in pure DC circuits.

2) For Alternating Current circuits - yes the inductor can be part of the voltage divider. Although, we wouldn't call the circuit a voltage divider anymore. We would instead call the circuit a filter. The "voltage divider's" output would change depending on the frequency of the input signal.

This is where electronics gets interesting. You may be interested in this site:

http://sound.westhost.com/lr-passive.htm 

Happy soldering,

APD"
Voltage divider,"In Problem 3, it's intuitive to follow the previous formatting convention and give an answer of 20k ohms. The answer box however refuses to accept anything other than "20000". Is it possible to add 20k as a possible answer?",Sorry. No k. I wish it was possible. The automatic answer-checker just looks for numeric answers (it was originally developed to check math problems). I'm glad you got the answer right!
N/A,Why is the voltage across the capacitor (vc(t)) equals to the integral of the opposite of the current ? where does this minus sign come from ?,"Because, in this article, it is assumed that the positive sign of the capacitor is on the top, so, the direction of current that it used is different from the current that supposed to be in the circuit... so that's why it got the minus sign...

If you flip the sign of the capacitor, it could be also worked though... so we don't get the minus sign, but in the KVL equation, it will be regarded as voltage rise, and it will get the plus sign... and in the end... it gets the same equation..."
N/A,How do you get the simpler s equation (the one with the variables α and ω​naught) from the quadratic formula?,"Review the definitions of alpha and ωo. This happens right after it says, "We can make the notation a little more compact by replacing parts of the expression with two new variables, alpha and ωo:"

Now look at the equation right after the sentence, "We can revise the quadratic formula by mashing the 2L denominator up into each term of the numerator:".  

The first part of the equation, before the +/- sign, looks like -alpha. 
The second part of the equation, under the square root symbol you find two terms, they look like alpha^2 and ωo^2.

Please let me know if this helped you understand. This is a spot where the article needs to be really clear."
N/A,"Do we have to do all this calculus everytime we make a RLC circuit, And this will get more complicated with complicated RLC circuits. There is no general formula for the RLC like-LR or RC circuits?
I wanted to make a function generator using a buck-boost converter, To predict the values of current and voltage at the given continuously changing PWM signal will be hell lot of work!","Most RLC circuits are analyzed with Laplace Transform theory. That topic is beyond the scope of this introductory KA class, but it is the standard method for working with frequency filters and control systems.

The RLC circuit analyzed here is the parallel form. The solution to the natural response emerges from this long analysis. The answer is not a simple single exponential equation like we get for RC, but rather a choice of three different responses ("variations") depending on the value of R, L , and C. I did an improved writeup of this at spinningnumbers dot com. Look for the RLC articles in the Natural and Forced Response section."
N/A,"What role does s(natural frequency) play here ? What it determines, can you please explain about it ?","In the RLC derivation we found that s could have real or complex values. We described s in terms of alpha and omega, and found there were three general classes of behavior (under-damped, critically-damped, and over-damped). The solutions are rich and wonderful and varied. You get a drooping behavior from the real parts, and a wiggly behavior from the imaginary parts. 

If you want to think about the meaning of s, it is a parameter (a complex number) that captures both the natural droopy and wiggly aspects of current and voltage as they change with time. The units of s are 1/t, which is the unit of frequency. The real part of s specifies the rate of droop while the imaginary part of s tells you the rate of wiggle."
Diode as a circuit element,"Will there be any future semiconductor video, mabye about ICs or transistors?","GMB,

Perhaps but it will take some time. On its current trajectory this website is still in the early parts of what would be considered Electrical Engineering I01. Traditionally there is another class called linear circuits that come after EE1. Sorry, no IC or transistors there either. We will need to wait and see where KA takes us next.

In the interim may I recommend two books:

"Practical Electronics for Inventors" By Scherz and Monk

"Art of Electronics" by Horowitz and Hill

Regards,

APD"
Diode as a circuit element,From the graphical solution  of the diode it is shown that  if the voltage is increased then the diode current will not increase that much but at the same time current through the resistor will increase . But diode and resistor are both sharing the same current . Isn't this a contradiction ?,"Yes, the diode and resistor share the same current. The goal of the graphical solution is to find points on both the diode curve and resistor curve where the current is identical in the two components. The currents are the same where the two graphs intersect. 

But the first sentence is backwards. The horizontal axis is voltage and the vertical axis is current. If you increase the voltage on a diode a little (above 0.6v) the current will go up A LOT. You can turn that statement around... If you change the current through a diode (move up/down on the vertical axis) the voltage across the diode does not change very much. That's one of the key properties of a diode, above about 0.6v, the voltage drop across the diode doesn't change very much for any reasonable current, it stays in the range 0.6 - 0.9 v."
Diode as a circuit element,Can increasing the electric field of an intrinsic semiconductor increase the generation of electrons or conductivity?,"Hello Dzifa,

Sure, as a rule increasing the voltage on a semiconductor will cause more current. It's hard to give a more precise answer:

Yes: forward biased diode

Yes: more leakage current on a reverse biased diode - but keep going and you get all the current plus dead diode...

Sort of: for a transistor - here a transistor acts as constant current source.

Regards,

APD"
Diode as a circuit element,Can't you use indium and antimony to make a diode?,Yes. This would be an example of what is called a III-V semiconductor (named after the column's of the Periodic Table. These semiconductors are used to make thermal imagers.
Diode as a circuit element,Don't you damage a diode if you get past the breakdown voltage?,"Not necessarily. Damage happens if too much heat is generated. If you can control that, the diode survives. A type of diode called the Zener diode is intentionally operated in reverse breakdown."
Diode as a circuit element,"Answer to question # 1.  If the voltage across the diode is zero, there will be no current. Why is the load line of the resistor used to answer the question, instead of the diode equation line?  ","You do use the diode equation:
    i = Is (e^(qv/kT)−- 1)
so for v=0,
   i = Is (e^0 - 1) = 0"
Diode as a circuit element,did you use a 9v battery to light the led light,"Hello Jay,

You certainly can. BUT you must select an appropriate resistor to limit the diode current. Without a proper resistor the diode will be damaged.

Regards,

APD"
Diode as a circuit element,"Why are most transistors made of silicon? Why not lead? sure the farther away the valence electrons, the easier it is to acquire holes.","Choosing a material to make transistors is a balancing act. You want to modify the material (add impurities) to get a wide spectrum of semi-conducting properties (ranging from almost insulating to nearly fully conducting). If you choose a really big atom like Lead because it is easy to take away electrons, you won't be able to modify it with impurities to make it more like an insulator. The element Silicon sits in the "just right" spot in the periodic table so it can be manipulated to get a full range of conduction properties. Another neighboring element used for making diodes is Germanium. A lot of high speed transistors are made from a combination of Gallium and Arsenic. All these elements are nestled close to each other in the periodic table."
Diode as a circuit element,What is in the center of the glass diodes pictured above?,"Hello GMB,

The heart of the diode is a PN junction made of highly refined silicon (with a few controlled impurities). 

This link may help: https://en.wikipedia.org/wiki/P%E2%80%93n_junction

You may also want to take a look at Adafruit's tutorials: https://www.youtube.com/watch?v=ap7edIKkykA

Regards,

APD"
Diode as a circuit element,So what is the basic difference between an LCD and LED monitor?,"Liquid crystal diodes block light. 
Light emitting diodes emit it."
Electric force,"in the first sum with three charged points where 
​​∠​F​⃗​2​​ =−30​∘​​ +36.9​∘=+6.9∘
​​over here i don't understand why 30 is given -ve sign and 36.9 given  a +ve sign","First, draw a coordinate plane with q0, the body with charge +4 C, as the origin and the distance "line" between q0 and q1 as the x-axis. Then draw the line connecting q0 and q2 onto the plane, then you would see that the angle of that line, which would also represent the repulsive force between q0 and q2, is 30 degrees below the x-axis, or -30 degrees from the terminal ray +x-axis. Similarly, if you move the coordinate plane to now center over q2 (do NOT turn the graph, x-axis should still be parallel with the auxiliary line between q0 and q1) and draw the line that represents the attractive force between q2 and q1, then the attractive force "line" should be 36.9 degrees above the +x-axis, or (+)36.9 degrees from the terminal ray.

From this point, we can assume that the direction of force F12 is 36.9 degrees from the terminal ray, and the direction of F02 is -30 degrees from the terminal ray. The direction of resultant force F2 should thus be the sum of the direction of the component vectors (a property of vectors) and direction of F2 = -30(of F02) + 36.9(ofF12) = (+)6.9 degrees."
Electric force,"In the equation:
∠F->2=−30+36.9=+6.9∘
How did you get the number -30 and 36.9 degrees?​​​​",Right above that equation there is a link [Triangles]. Open that up to see where the angles come from.
Electric force,"Why they are adding -30+36= 6.9 make no sense to me . 
Please Help","The geometry of this example problem can be a bit overwhelming. I rewrote the example with simpler triangles here: https://spinningnumbers.org/a/three-point-charges.html

There are two triangles involved in a 3-charge problem. A charge triangle, and a force triangle. They are both shown right after the text "Interior angles of our two triangles,".

The -30 angle comes from the line in the charge triangle sloping down from horizontal.

The +36.9 degree angle is derived from the force triangle. It slopes up. 

The sum of -30 + 36.9 is +6.9 degrees. 

If this still gives you problems please check out the article at spinningnumbers.org. Then come back here. Let me know if I can help you out."
Electric force,What do you have to have to be one of those people who make robots for space missions and stuff like that?,"Hello Dipesh,

Passion, dedication, and hard work to become a mechanical or electrical engineer.  Check out this link for my favorite electronics celebrity from down under. He recently had a lunar rover on his blog.
 
https://www.eevblog.com/

Regards,

APD"
Electric force,In the first example shouldn't the direction of F12 be from q2 to q1? Why have they shown it from q1 to q2?,"Your question is about the subscript notation on Force vectors. The notation I use is the first subscript is the "from" charge and the second subscript is the "on" charge. So F_12 means the force ON q2 coming from q1. The force happens to be an attraction between the two charges, so it is pulling q2 towards q1. In this problem, I'm only interested on the forces on q2 because q2 was identified as the test charge in the example."
Electric force,"Willy McAllister wrote "The 30∘ angle gets a negative sign because it is rotating clockwise, while the 36.9∘ angle adds with a positive sign because it is rotating counterclockwise."

How do u say that it's rotating in clockwise and in anti-clockwise direction? pls somebody tell me",The reference for measuring angles is the positive x-axis. that is defined to be 0°. Positive angles are measured upwards (counterclockwise) and negative angles are measured the other way (clockwise).
Electric force,how is dQ=Q/L*dx?,"The whole line contains a charge of Q. 
The amount of charge in 1 meter of line is Q/L, where L is the length of the line in meters.
Q/L is called the *linear charge density* of the line. It could be a value like 2 coulomb/meter.

What if you want to know how much charge there is in 1 cm of the line? How would you figure that out? 

You take the linear charge density  and multiply it by the length you want to know about.

Q(in 1 cm) = Q/L * .01m = .02 coulomb

If you imagine a little short section of the line, dx long, the charge in that little section is,

Q(in dx) = Q/L * dx       

We give this tiny bit of charge contained in a tiny bit of line a name: dQ.

dQ = Q/L * dx"
Inverse square law,Why do we use the surface area of a sphere to relate to the inverse square law? And Hyperphysics says source strength of gravity is 4piGM. Where does this come from? Here is the illustration from Hyperphysics I'm talking about http://hyperphysics.phy-astr.gsu.edu/hbase/forces/isq.html#isqg  (I'm asking this question because I'm doing universal law of gravitation and I don't understand the inverse square law so please answer my above questions),"Hello Sam,

Before we start consider a flashlight. Let's shine the light on a 1 cm^2 target on a wall. If you hold the light 5 cm from the wall the target  will be very bright. As you move away from the wall the brightness of target is reduced.

Regarding the inverse square law. There is usually a theoretical point at the center. It has zero volume and produces whatever we want. This could be light, gravity, RF energy, etc.

This point source is usually surrounded by a sphere. As you recall the sphere has a surface area:

4*pi*r^2

Visualize the point source painting the inside of the sphere with light. In fact, let the point source produce one unit of light (intentionally ignoring the units). 

Now we must shift gears and talk about the amount of light per surface area – remember the flashlight and target. The inside of the sphere has a surface area. We know the formula from above. 

Done -  that's it. If we merge the stuff originating from our point source with the equation of a sphere we have the Inverse Square law:

source_strength / (  4*pi*r^2 )

The name inverse square law describes the r^2 in the denominator. As the diameter of the sphere grows the amount of light falling on each  square meter on the inside of the sphere is reduced by r^2.

Regards,

APD"
Inverse square law,"This does not apply when we are shining a laser light on a wall and increase the distance between the wall and the laser light, as the light rays here do not scatter. Correct me if I am wrong.","The light from a laser pointer does not spread out (at least not very much). If the laser light was butter, the toast would be buttered in one little spot.  

If you point your butter laser at the moon, however, the butter beam would be spread out, and you could butter toast there."
Inverse square law,"Hi Willy,

I don't get "Is the 2 a coincidence? A trick of nature?".
Please explain.","Students often ask why the denominator is r^2. The 2 in the exponent seems 'too perfect' to some people. Like why isn't it 2.1, or 1.9? The Fable of the Butter Gun shows why the exponent is exactly 2."
Inverse square law,does inverse square law valid in matter also??,"No, we use Newton's law of Gravitation for matter."
Inverse square law,Why in coulomb law's formula r become r square,See if this article on the "inverse square" law helps... https://www.khanacademy.org/science/electrical-engineering/ee-electrostatics/ee-electric-force-and-electric-field/a/ee-inverse-square-law
Inverse square law,why is the gun like that,yes. This is what you should be taking from the video. Not the concept but the illustration of the gun lol.
Plane of charge,Why the K be instand by 1/4πϵ​?,just to make the expression shorter and easy to remember
Plane of charge,have we taken point charge dQ in the hoop part explanation??,"Ashley, I don't quite understand your question. Could you rephrase it?"
Plane of charge,where did the sigma came from? dQ​hoop = σ⋅(2πr⋅dr),"Lower case "sigma" represents the amount of charge per area of the plane, in units of coulombs/meter^2. This parameter is called the "charge density"."
"Electric potential, voltage","I can't understand why we have a section of absolute voltage, I mean voltage itself means potential difference so then what do we mean by "absolute voltage" and "voltage"?","Go back to the equation for Electric Potential Energy Difference (AB) in the middle of the section on Electric Potential Energy. That equation tells you how electric potential energy changes when you move a test charge from point A to point B. For example, you could be moving your test charge towards or away from some charged object. To use this equation you have to put in two locations, A and B. There are just a few oddball situations that give us some trouble... What if I told you where B was but did not mention A? I might say it this way: "What is the potential energy of a test charge when you place it at B"? Well, you need an A to answer that question. If I don't give it to you, you have to make one up. A common choice that lots of engineers and scientists make is "A is infinity away from the charged object." When we make that choice, we say we are determining the absolute potential energy, or the absolute voltage. It's the same voltage as usual, but with the assumption that the starting point is infinity away. In almost all circuits, the second point is provided and this absolute idea isn't needed."
"Electric potential, voltage","Willy said-"Remember, for a point charge, only the difference in radius matters", WHY??",You would have had to have followed along the derivation to see that the component of length is cancelled out by a reciprocal in the integration. Check out Plane of Charge in this section called "Electrostatics."
"Electric potential, voltage","In the 'Doing work in an electric field section',
The equation we get for the small amt. of work done is
dW=−qE⋅dr 
I get that F(ext.) is -ve since it acts opp. to the electrostatic force on q. But then why isn't 'dr' also -ve?

Also, for the movement of q for that small distance 'dr' is in the same direction as that of the F(ext.). So, shouldn't 'dW' be +ve?

Please do reply.","Work is positive if the force is in the same direction as the displacement, negative if it's not. 
You have to pay attention to which force you are talking about: The force by the field or the force by an external force. 
It's really better not to try to handle this by manipulating a bunch of signs.  Just calculate the amount of work that's done and then ask yourself if the force was pushing in the direction of the displacement or opposite to the displacement."
"Electric potential, voltage","Sir just for shake of awareness Does moving charge also create  Electric field ?
                                                     &              Does static charge also create  Magnetic field ?","Yes, a moving charge has an electric field.   
No, a static charge does not create a magnetic field.

A moving charge creates a magnetic field. You can see this if you pass a current through a wire (moving charge) and hold it near a compass. The compass will tip to the side. 

The science of moving charges is called electrodynamics  or electromagnetism."
"Electric potential, voltage",how much voltage is there in a electric fence.,"It depends on the fence... 

Agricultural fence chargers are designed to produce several thousand volts. It is important to note that the voltage is NOT continuous. Instead the voltage is pulsed for short amount of time. The result is akin to a static electric shock.

Regrettably there are some fences in the world designed to deliver lethal shock. I'd rather not think about those...

Regards,

APD"
"Electric potential, voltage","So, basically we said that Fex=-qE=Fe because the difference between them is negligible, but actually speaking, the external force is a little greater than the the electrostatic force ? Am I getting this right?
Got another question, what's exactly this "external force" that does work on the charge to move it, in case of charges moving in a circuit, what causes these  charge to move from the source in the first place ?","If you want to actually move a charge, you have to apply an ever-so-slightly greater force to the charge to get it to start moving. It is important not to push too long or too hard because we don't want the charged particle to accelerate. (If it accelerates then all sorts of new physics starts to happen involving magnetism, which at the moment is way over our heads.) For now we make our charges sit still (static) or we move them super slow where they move but they don't accelerate, a condition called "pseudo-static". 

In this general definition of of electric potential you can imagine any external force you want pushing the charge. If I do the experiment with a charged balloon, I can use my hand to push the charged object towards another. In a circuit, charges move because they are repelled from like charges and attracted to unlike charges. A chemical reaction near the negative terminal of a battery releases an excess number of electrons in the vicinity (in the attached wire). Electrons in the wire are repelled from this concentration and move away, towards the positive battery terminal. There is a different chemical reaction happening at the positive terminal that absorbs electrons, creating a deficit of electrons for a net positive charge in the region near that terminal. Nearby electrons are attracted and move toward the positive terminal."
"Electric potential, voltage","I understand the term of electric potential difference between two particles , but how do we define the electric potential difference between two charged plates that are fixed ? Like I know  the equation Delta V = Ed , but can someone explain it ? Thanks","We can find the potential difference between 2 charged metal plates using the same formula V=Ed.

Consider 2 infinite metal plates fixed with distance 'd' between them( this situation can be approximated in real life as the areal dimensions of metal plates are large compared to distance between them). To find the potential difference the plates find the net electric field between them and multiply it with distance between the plates.

Electric field due to infinite charged metal plate using integration method:-
 https://www.khanacademy.org/science/physics/electric-charge-electric-force-and-voltage/electric-field/v/proof-advanced-field-from-infinite-plate-part-1

https://www.khanacademy.org/science/physics/electric-charge-electric-force-and-voltage/electric-field/v/proof-advanced-field-from-infinite-plate-part-2

Electric field due to infinite charged metal plate using Gauss law:-
https://www.youtube.com/watch?v=r-j0vE8rHYE

https://www.youtube.com/watch?v=yOv4xxopQFQ"
Line of charge,can someone explain how can we substitute d( theta ) / a  for  dx / (r squared) ?,The steps of the change of variable are described in the explanation link at the end of the paragraph just above where you are looking. The paragraph that starts with "The most suitable independent variable for this problem is the angle theta." Let me know if that explanation needs improvement.
Line of charge,I did not understand why you changed the variable !!,"The equation we built up from Coulomb's Law prior to the change of variable is based on the independent variable x, the distance along the line of charge. 

Somebody, a long time ago, (it wasn't me) tried to finish the problem using x and dx as the independent variable. They realized it was hard math. Then, it a flash of brilliance, whoever it was realized the best way to represent the problem was to use the angle Theta as the independent variable, and dTheta as the infinitesimal change of angle. 

Rather than going back to the beginning and starting over, the shortcut is to do a "change of variable". You figure out Theta in terms of x and do a swap.

This is a good example of setting up the equations in the natural variable for setting up (x and dx), and then for finishing the problem you switch to a different natural variable for finishing the problem (Theta and dTheta).   I can't say I would have ever thought of this myself, but this is the classic method of solving the line of charge."
Line of charge,"Hi, could anyone explain the butter gun in 1/a pattern?",In my simple mind it is like this:  the butter analogy hold as stated all the way to infinity in X as well in Y.  Which would be equivalent to integrating from -Pi/2 to Pi/2.  Only in the charge example here as "a" increases we are only expanding the field (bread) by only one dimension thus no longer a spread relative to 1/r^2 but just 1/r.
Line of charge,"What if the angles made from the charge q to the two ends of the rod are unequal. So what limits should i apply then in order to get the general equation? I tried it, and can't figure out which angle to take negative.","If you break the beautiful symmetry of this problem it gets much harder to solve. If the line of charge has finite length and your test charge q is not in the center, then there will be a sideways force on q. 

I think the approach I might take would be to break the problem up into two parts. Break the line of charge into two sections and solve each individually. One section symmetric with respect to the test charge, and another separate section for what's left on the longer side. 

Solve the symmetric problem as in this article, with symmetric angles on the integral limits.
For the chunk off to the side, you have to solve a nasty vector integral, but at least all the angles have the same sign.
The final answer is the superposition (vector sum) of the forces from the two parts."
Line of charge,How  did you integrate the integral cosθ dθ ? I dont understand it. Iam new to integration . How it converted to sinθ  when we apply the limits? Help me Willy....,"Check out Sal's video on the integral of cosine. (He refers to it as the "anti-derivative" of cosine, which means the same thing.) https://www.khanacademy.org/math/ap-calculus-ab/ab-antiderivatives-ftc/ab-common-indefinite-int/v/basic-trig-and-exponential-antiderivatives. Integration is the reverse process of differentiation, so "anti-derivative" is an appropriate term.

He covers the derivative of sine and cosine here: https://www.khanacademy.org/math/calculus-home/taking-derivatives-calc/ex-and-lnx-derivatives-calc/v/derivatives-of-sin-x-cos-x-tan-x-e-x-and-ln-x. One problem is Sal just gives the answer without showing why.

A great exercise to understand the derivative of sine is to draw a sine wave on paper. Then set up a separate graph a little lower on the page, with the y axis lined up with the sine graph. For each point along the sine curve, plot the slope on the graph underneath.   

For example, at x = 0, sin x = 0, and the slope is steep. On the lower graph, plot a number you guess for that slope at coordinate (x=0, y=somenumber). Do that for a bunch of different x values. What you should get should look like a cosine curve.  

Here's the finishing touch. Draw a third graph underneath the second one. Plot the slope of the second graph.  It should look like a sine curve, but with a twist. What is the twist?"
Line of charge,"In the general solution it seems to me that test charge q is symmetric to the line?
Also the solution L>>a is applicable only when the test charge  q symmetric to the line otherwise not? 
For example L=100 cm    and a=1cm  here L>>a
Will the same formula apply if we put the test charge q near to the end of the line (say at 97cm from one end of the line )
Am i correct?? 
Please help 
Thanks","You are correct. The solutions presented here assume the test charge q is straight across from (or near) the middle of the line of charge. 

For a long line (your example was 1cm away from a 100cm line), the test charge q should be somewhere in the vicinity of the 50cm mark on the line, say something like +/- 10cm. The long line solution is an approximation. It assumes the angle looking from q towards the end of the line is close to 90 degrees. If you are standing at 40cm and turn your head to look at one end, you pretty much turn 90 degrees.

If you want to solve the harder problem of an asymmetric line, (example: a 10 cm line, with q 1cm away opposite the 3cm point) you can break the line up into two sections. If you cut the line at 6 cm you get a symmetric problem (6cm line with q at 3cm)  plus an asymmetric chunk off to one side (4cm line with q positioned 3cm off the end).  The first symmetric line we already solved in this article. The second asymmetric line looks a lot like a similar example problem we did about half way through this article: https://www.khanacademy.org/science/electrical-engineering/ee-electrostatics/ee-electric-force-and-electric-field/a/ee-electric-force      
or an updated version of the article here: https://spinningnumbers.org/a/line-of-charge1.html

The total electric field is the vector sum of the two parts."
Line of charge,This article helped me a lot; I was curious if the plus C from integrating would have any relevance or explanation?,"The first integral appears just before the section titled "Useful Case: Long line of charge". If I add a "+ c" to that integral expression the c would represent extra electric field coming from somewhere besides the line of charge. Maybe I left some bits and pieces of charged lines laying about on the bench nearby. Or, there's some electric field existing in my laboratory. Both of those sources would be sensed by an e-field measuring device placed at the location of test charge q. 

In the simple analysis of the line of charge it is assumed that the only source of electric field is the line of charge."
Line of charge,what is d in change in variables dx/d(theta)=a*d/d(theta)*tan(theta)?,"The d is the calculus notation for a _differential_, so it always stays stuck to either dx or dtheta. 

The diagrams have a non-italic d whereas the text has italic d, which is a small but  unfortunate flaw."
Line of charge,I don't understand the integral calculation where sin θ is converted to 2!!How is it evaluated??,"Right after the sentence, "and evaluate the integral," the equation includes a sin θ term. The long vertical bar is the symbol for "evaluate at the limits of the integral". The vertical bar means subtract sin(lower limit) from sin(upper limit).


The upper limit is +pi/2 (90 degrees), the lower limit is -pi/2 (-90 degrees).

sin(pi/2) = +1
sin(-pi/2) = -1

The difference is +1 - (-1) = 2."
Electric field,Why electric feild is more stronger then magnetic field and gravitational field ?,"Hello Rajeshk,

This is an unsatisfying answer but it just is... These are fundamental forces of nature. 

As a consolation for my poor answer may I share my favorite video on the topic:

https://www.youtube.com/watch?v=1TKSfAkWWN0

Enjoy,

Aaron"
Electric field,"what is meant by "If charges are smeared out in a continuous distribution, the summation evolves into an integral."?","There are two ways to think about charge. We know that charge is the property of two atomic particles, electrons and protons. This makes it convenient to think about charge as particles, or like a bunch of sand. You can count sand particles (if there are not too many). Coulomb's Law treats charge this way, there's a q1 and a q2.

Another way is to think of charge as a continuous substance, like peanut butter. Peanut butter isn't a collection of particles, it's something different. You charge something by slathering it with peanut butter charge. The charge is uniformly distributed throughout the peanut butter.
If you see a problem statement like "assume a uniformly charged rod," that's an example of the continuous peanut butter version of charge. Continuous charge will include a density specification like 2 coulombs per meter, or 3 coulombs per cubic inch.

If you are presented with a problem based on peanut butter charge you have to figure how to apply particle-based Coulomb's Law. In this blob of charge we have to somehow identify a charge particle. The trick is to use calculus to focus down on a tiny tiny bit of the charged structure, a bit so small it can be considered a particle.

So in the article you see the equation for the electric field from multiple charges

F = 1/4pieo SUM (q_i/r^2)

In peanut butter charge q_i becomes the differential charge dq, and the SUM turns into (evolves into) an INT (integral). 

F = 1/4pieo INT (dq/r^2)

These two equations mean the same thing. In the second we rely on calculus notation to do the bookkeeping for adding up all those infinitesimal dq's."
Electric field,What is an equatorial line?,"That's a line around the equator of an object. You are probably looking at a problem that includes a sphere, and the sphere has an obvious "up" and "down" axis. The equator is the line half way between the north and south poles of the sphere, just like the Earth."
Electric field,"In the denominator of the equation given in "Electric field near multiple point charges", what is r? Considering we sum over multiple point charges, and our point might not be equidistant from all of them, shouldn't it be r_i?",You are correct. The r in the denominator should probably have a subscript of i.
Electric field,Sir i'm not saying about electric field strength or intensity.I am asking that can we measure how much area an electric field surrounds.?or it is spread to infinity?,"The strength of the electric field weakens with the square of the distance. So if you double the distance it's only 1/4th of the strength, if you increase the distance ten-fold the strength becomes 1/100th, and so on. Much the same as gravity. So, while it might not be "cut off" at a certain point it obviously diminishes quite fast into trivial strengths. Perhaps we could view it as being "cut-off" when the strength goes below Planck sizes."
Electric field,"1. What is 1/4πϵ0? Is it the same as k?
2. Is Coulomb's Law the same as the electric force equation which is Fe=k(q1q2/r^2)?
3. Could anyone explain where [ F = (1/4πϵ0)(Q times Qi/r^2)(ri) ]?","1. Yes. 1/4pie_o = k. It is just two forms of an arbitrary constant. The 1/4pi comes from a theory you study later in electromagnetics, Gauss's Theory, which deals with the surface area of a sphere (that's where 1/4pi comes from). Since Gauss's Theory is so important and is naturally written with the 1/4pi notation, some teachers bring that form all the way back to Coulomb's Law.

2. Yes. Coulomb's Law IS the electric force equation.

3. Coulomb's Law arises from a real-world experiment. It is not something you can derive from first principles. Coulomb himself designed and performed the experiment to measure electric force, and used the data he recorded to create the Law named for him. The little ri at the end is a vector notation to indicate the force lies along the line between the two charges."
Electric field,how is electrostatics related to transformers?,"Hello Cassiecsy,

Nearly every electronics and physics textbook begins with a discussion of electrostatics. There is talk about charge, charge carriers, and the transfer of charge. These concepts lead an understanding of voltage and current. 

Electrostatics helps us understand how we move these charge carriers (electrons in a wire). How to describe the concepts and how to perform measurements. 

Since in all cases we are talking about the movement of charges electrostatics has everything to do with transformers.

On the other hand, transformers are electromagnetic devices. Only the vocabulary of electrostatics is used. Unlike capacitors which store energy in electrostatic fields...

Sorry, it's not a simple answer. Please leave a comment below if you would like to continue the conversation.

Regards,

APD"
Electric field,electric field is also written in volts/metre. how is it similar to newtons/coulomb and why is volts/metre appropriate.,"The two representations for electric field are "equivalent", meaning you can derive one from the other.

The volt is the unit of electric potential, which is energy (joules) per unit charge (coulombs). That means 1 volt is a nickname for a potential of 1 joule/coulomb.

One joule of energy is the energy required to accelerate a mass of one kilogram using one newton of force over a distance of one meter. The newton is the unit of force and has units of F = ma or kg*m/sec^2. 

So, 1 newton of force is 1 joule of energy applied over 1 meter, or 1 joule/meter.

Imagine you are measuring electric field in the air gap between two capacitor plates. You know the voltage of each plate. V/m would be an appropriate unit to pick. Express volts as joules/coulomb and you get an electric field measurement in joules/(coulomb*meter). 

Another way to measure electric field is in terms of newtons per coulomb. You might pick this set of units because you are measuring an electric field by inserting a test charge into the field and measuring the force on the test charge. When you divide newtons expressed as (joules/meter) by coulombs, you get an electric field expressed in joules/(coulomb*meter). That's the same units as volts/meter!

[To create this answer I used Khan Academy's experimental AI tutor, "Khanmigo" to get a starting point. Then I revised the response to (hopefully) make it more clear. This is my first experience using an AI.]"
Electric field,does a force exists and shows its effect around an isolated charge present in free space,"An isolated charge creates an electric field in the free space surrounding the charge. There isn't a force in free space because there is no other particle in the vicinity. Force only exists if there is a physical body present to experience it. 

When you introduce a small test charge to the neighborhood of the first charge, the test charge will experience a force. 

You can say the force comes from Coulomb's Law "acting at a distance", or you can say the force is caused by the electric field that exists in the space surround the first charge."
Parts list for Spider,Is it super hard to make a robot?,"It all depends on how much motivation you have.  If you are motivated enough to create an advanced piece of technology, it should be easier to put together a robot.  If you don't believe you can do it, then you can't.  So the question isn't how hard it is to make a robot, its how motivated you are to accomplish a goal."
Parts list for Spider,I'm on an iPad and do see a parts list only a blank page.,you should use a computer or laptop because it is faster and more powerful. Computers tend to work better with google
Parts list for Spider,Is there a good way to improve the battery life,"There is a few tricks, but they are extremely difficult and provide only a little more battery life. If it was easy then battery producers would already be doing it."
Programming Spider,Can you program it to a remote?,"You probably could, but Karl doesn't give us the information to do that here."
Programming Spider,"It says Arduino is only available in the US I don't live in the US. Does it mean the Arduino software or actual Arduino brick?
Cos that would be REALLY annoying if I can't get it","Hi Dan,

Arduino originated in Italy. You should be able to purchase a kit anywhere in the world. Also, there are many clones available.

Regards,

APD"
Programming,But.... How about in the I pad or phone? Does it work?,Arduino is not available for download on mobile.
N/A,do you have to have a license to make them,"I am a big fan of arduino and unless you are using an arc furnace or spot welding to make your project, THERE IS NO LICENSE REQUIRED."
N/A,can you send me how to make it?,"The videos explain the parts you need, show how to make it, and show how to program it."
N/A,Why is it called the GOAL of spout ?,Hello sir .Can you make a remote controlled  beetle bot?
N/A,"Hmm.  This parts list is not really detailed enough for someone just getting started.  I've been to digikey, mouser, and many others, and the information given here is not really sufficient to correctly identify the bewildering array of parts on offer at those sites.  Can you please be more specific by including part numbers?","Hello Lazysndvl,

This would be very difficult as the available parts are constantly changing.

Recommend you look to Adafruit, Sparkfun, and Instructables for tutorials and parts.

Please don't look at the robot as the end goal. Instead, consider the journey, the lessons learned, the successes, and the many failures we have along the way. Know that I have let the "magic smoke" out of many components! Now it's your turn.

Regards,

APD"
Tool list for Spout,How much does it cost to make a spout bot?,"So far, it's cost me under$13, including shipping to Australia. I've not bought the motors, the batteries or the glue gun, but think this should be around AUD20, so total cost is going to be under $40, including shipping."
Challenge: drum partner,Is the sound sensor the lego motor?,No it is its own module from the NXT kit
N/A,Can the ant bot be modified?,yes! the idea here is that the ant is a starting point for you to jump off from.
N/A,Where can I find everything to make this?,"In the Nxt Lego kit, which can only be found online I'm pretty sure.  \/('_')\/"
Bonus points,Can Lego Robotics be a challenge to make?,"yeah, but you can work with other people and it gets easier."
Warm up: ultrasonic vision,what does the sensor have inside it?,"I'm not sure about other ones, but the ultrasonic sensor works like echolocation in bats. The sensor sends ultrasonic sounds that are unhearable by humans and then measures the echo to tell how far the object is."
Warm up: ultrasonic vision,I tried doing line following with my robotics team that this week is going to go to the states competition but the robot keeps wobbling can you tell me how to line follow without the robot wobbling? or can you post a video?,"If the robot is wobbling but still following the line, your program is working properly. If you don't want it to wobble, try making a more complicated line following program. Here's an example:

http://www.nxtprograms.com/NXT2/line_follower/steps.html#Program

the first program is probably similar to what you have.

A simplified version of what the link would show you:
If your program is wobbling, then it's probably something like this: "If black, turn right. Else, turn left". If you make your program detect the level of black and factor into your motor motions it will be much smoother. For example: "Left motor power = Color sensor reading. Right motor power = (100 - Color sensor reading)". This will need a lot of tweaking but if done properly it will be very smooth.

Also, make sure your color sensors are properly calibrated, and if possible use two sensors right next to each other. Making the robot move slower, and insuring that it approaches parallel to the line will decrease wobble too. Using these tips should make your line follower much smoother. Keep in mind that every line follower will have at least a tiny bit of wobble just because there will always be a delay in the robot reacting to its motion. 

Hope this helps, good luck!"
Warm up: ultrasonic vision,were do you get the robo legos,You could find it on Amazon or Lego.com.
Warm up: police siren,Can you make a actual city (life sized) out of Legos,Five or six have already been built. They are called legolands.
Warm up: police siren,how much does a new Mindstorm cost?,"You ant buy new ones on LEGO.com anymore... But, you can buy the Ev3(3.0) kit for 349.99USD"
Warm up: police siren,If you make a robot how are you going to make it move?,Program it. If you started the "JS: Drawing and Animation"  course it said that programming controls even Google's self-driving cars.
Warm up: police siren,Do you wire your Lego device into the computer?,"yes, you need to wire it. Or you can use bluetooth or wifi"
Preparing to study biology,Do you have to know chemistry to learn biology?,"Depends on up to what level you would like to learn Biology and all its related sciences (ecology, genetics, etc. to name a few.

You should be able to get away with "normal" high school bio without learning chemistry, although a general understanding of chemistry does not hurt. Other biology courses with more complex curriculae (think AP Bio, IB DP Bio, A-Level Bio, etc.) will require chemistry knowledge.

University level biology is another whole game. Chemistry is required to such a point, that most biology programmes have chemistry courses and credits built into them."
Preparing to study biology,so you used basic and algebra in the same sentence and basic was reffering to algebra now i am confused!!,For applying some concepts in Biology you need to know basic algebra.(Punett Square)
Preparing to study biology,Is there a specific grade range to start learning biology? For I have little experience with middle school subjects and less with High school subjects.,"Lol I'm still in middle school and I'm already learning biology. To answer your question, there probably isn't an age range."
Preparing to study biology,I feel like Khan Acadamy can make anything fun!,definitely agree!
Preparing to study biology,Are there any parts of the human body that get oxygen directly from the air and not from the blood,In human lungs. Alveoli get exchanged for oxygen.
Preparing to study biology,"Hi, I'm an adult and want to learn biology! I have a very basic understanding of the field and so I was wondering if I should start back at middle school biology or do you think starting here will be best?","I would recommend brushing up on intro of bio for middle school and if it’s too easy go to intro of bio high school. Once you finish learning the ropes of biology, I recommend Campbell Biology books."
Preparing to study biology,"I've been wondering which one I should start of with, biology, physics, chemistry, or something else in science ( I'm in 7th grade).","Before you go into science, I must suggest that you work up your math a bit. Math is basically the foundation for all of science and it will _definitely_ come in handy. So make sure you're ready to add and subtract first. Once you've done that, I'd recommend chemistry."
Preparing to study biology,What is a biological phenomenon? And which are some examples of it?,"A Biological phenomenon is the biological processes, properties, and characteristics of the whole organism in human, animal, microorganisms, and plants, and of the biosphere.     

An example would be the concept of metabolism."
The scientific method,"I thought a hypothesis was an "if, then" statement, and not a prediction?","Well, you could consider it to be both.  If you say, "If I do X then Y will happen" you are predicting what will happen if you do something."
The scientific method,"a hypothesis is supported (likely correct), a theory has lots of evidence to support it. What then Makes a theory become a LAW. Such as the Law of Gravity? Only difference i see is a law has a mathematical proof. Is this a correct assumption? or what Constitutes a law?",Theories don't become laws. Here is a good resource for defining how these scientific concepts relate: http://ncse.com/evolution/education/definitions-fact-theory-law-scientific-work
The scientific method,What if one time an experiment works and the next it does not?,"Exactly, like others said if you do more experiments, then you will be sure to find out which info is credible. When I did experiments, my teacher asked us to write a summary about the results we got, so I tested out our hypothesis 3 times to find the average out of all of them, and I got pretty good info out of my experiment. I hope this helps you out!"
The scientific method,"I've been told that the proper way to compose a hypothesis is by using an if/then statement. But in the example above, it doesn't use an if/then statement. My question is, is there a proper way to write a hypothesis? If so, what is it? Thanks in advance:)","I think that there is no definite format to writing a hypothesis, but as you said, yes there is a 'proper' and appropriate way to writing a hypothesis. 

Like the article says, a hypothesis must be testable, meaning we can do experiments with it to see if it is supported or not. I think usually non-testable hypothesis are something that are not exactly 'measurable' or 'observable', such as "Many people may think that red apples are attractive". There is no accurate way of measuring if people think that red apples are attractive.

Yes, an if/then statement is a very safe way to write a hypothesis. One of the things that we must be careful when writing a hypothesis is that we should not make it a conclusion (an actual 'statement'!); for instance, "Red apples cause pimples." is a conclusion that could be obtained from an experiment, while "Red apples _may_ cause pimples" might be a hypothesis. 
However, yes the best way is to write an if/then statement, because it is formatting your prediction in a very testable way. You are saying 'IF I do this..' - which is  the experimental portion- that 'THEN this will happen'- which is the prediction or 'educated guess' portion."
The scientific method,"I am using a new account now, so I’ll ready my question.
I was looking at the last step, iteration. At my school, they have taught us an extra step, which would be conclusion and analyze/share data. Could someone specify the definition of the conclusion and analyze/share data? I get the analyze/share data part, but I always get stuck on conclusions, especially so when I have to write lab reports.","Why do you think you get stuck at conclusions? Are you afraid to say what you mean? Have you ever taken Logic classes?

I haven't but after quite a year it became habitual and 'easy' to conclude.

Maybe you lack the theoretical part or you are just scared of those lab reports (my personal opinion but I may be wrong).

Do not be afraid, and keep practicing.

If you read dozens of Scientific articles you may get an idea of what 'Conclusions' look like. Also, analyze and share means what it says. Analyze the best way you can do (don't be too hard on yourself) and share with others (peers, professors, online, scicomm, etc).


Good luck :D and keep asking questions :D"
The scientific method,Can a hypothesis be wrong.,"You can't be expected to come up with an accurate hypothesis every time, this is why you have to do observations and/or experiments to test the hypothsis."
The scientific method,Can a hypothesis always be right?,A hypothesis does not always have to be correct. The scientific method aims to prove or disprove the hypothesis and continue from there.
N/A,do we have dna same as our parents?,"It's not exactly the same, we take roughly 50% from each. Also the expression of those genes can vary and some may be changed by factors such as DNA from viruses, or may not be expressed (shown) due to environmental factors."
N/A,why are viruses hard to cure,"Because, most of the antibiotics, infect the bacteria through destroying their cell wall. Whereas Viruses insert their genetic material into a human cell's DNA in order to reproduce. Antibiotics cannot kill viruses because bacteria and viruses have different mechanisms and machinery to survive and replicate. The antibiotic has no “target” to attack in a virus"
N/A,What are examples of Unicellular organisms?,"There are five groups of unicellular organisms:
bacteria, archaea, protozoa, unicellular algae, and unicellular fungi"
N/A,"How does the ability to evolve define whether one living thing is alive?  Evolution only occurs because living things with less beneficial traits die.  Species evolve because they are alive; they are not alive because they evolve.  The individual organism itself does not evolve; it simply lives and dies.  Can anyone help explain why evolution is necessary for a species to be considered living?  As for right now, I would say that "evolution" shouldn't be on that list.","The qualities of living things are  synthesis, transport, excretion, regulation, nutrition, growth & development, respiration, and reproduction. I agree with you that evolution is not included in this, and Caleb has a point in saying that individuals that reproduce will evolve. Evolution is a result of life, not a cause."
N/A,"In the "Is this the definitive list?" section, if the offspring of a female horse and a male donkey is a mule, what is the offspring of a stallion and female donkey?","Hinny is a stallion and a female donkey
Jenny is female horse and a male donkey"
N/A,"If viruses are not considered alive organisms, how can they be so dangerous and reproduce them  so fast?","Viruses can hijack our cell's DNA to program it to make more copies of the virus. Though viruses themselves contain no DNA and are technically not alive, they can re-engineer our cells to help them proliferate."
N/A,Do we know for sure that we are the only conscious organism?,"It is a matter of debate.

No, we are not the only species which could think, dream or feel, https://www.nationalgeographic.com/news/2015/07/150714-animal-dog-thinking-feelings-brain-science/
but we are the only species that are *self-aware*.

There are other conscious animal species as well, but human consciousness is different than animal consciousness.
Non-human primates are used for studies of the human model of consciousness.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3814086/

You can say that animals have consciousness:
' Human consciousness emerges on the interface between three components of animal behavior: communication, play, and the use of tools. These three components interact based on anticipatory behavioral control, which is common for all complex forms of animal life'

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5924785/

But humans have 'human awareness' - the ability to experience one's own “internal states” as intentional states. That's not something animals can do. 


You may find this interesting. Some Scientists theorize even Universe has consciousness.
https://bigthink.com/philip-perry/the-universe-may-be-conscious-prominent-scientists-state"
Controlled experiments,"In the case of environmental effects on children and how it affects their health, it being unethical to actually try an experiment, then from what I gather the best way to test a hypothesis would be to say, "When children are exposed to X, Y will happen." and then to collect data. Would legitimate studies only research this from children that are enrolled in such a study at birth with doctors/scientists/researchers taking blood samples or personally investigating the home environment for these factors? Or could this data be reported by parents? How would you account for people who are dishonest on their reports (as Gregory House states in nearly every episode, "Everybody lies.")? Is a retroactive study considered legitimate if children aren't entered into the study until they are older in age? Or if the researcher only relies on the parents' reporting data from birth to the current age that the child is involved in testing a hypothesis?","A lot of researches are done through surveys. Although it wouldn't be the most accurate, if having someone to check if children are exposed to X or if Y is happening is not possible due to financial, privacy, etc. reasons, survey would be the alternative method.

there is even a section on wikipedia of this:
https://en.wikipedia.org/wiki/Survey_(human_research)#Reported_behavior_versus_actual_behavior"
Controlled experiments,"when the coral reefs are bleached does that mean they have died, if not do they stay white forever or return to their original form?","When a coral is bleaching, it expels symbiotic algae (zooxanthellae), which supply food for the coral, get rid of metabolic byproducts, protect it from pathogens and also create its bright colors. Bleaching results in starvation, which is indicated by loss of color. This doesn't mean that they have died - if the corals find a different nutrient-supplying species, they can regenerate and stabilize again. If they don't find new symbionts and the factors which contribute to bleaching persist, then the coral might die of starvation or disease.
A colony of corals might regenerate if corals or their polyps from other colonies migrate and reproduce successfully elsewhere, where the conditions for growth are more favorable."
Controlled experiments,"So hypotheses are like conditional statements?

Thanks to anyone who answers,
Jack.",Yep! That's a great way of thinking about it. You could write your hypothesis as an if-then statement. :)
Controlled experiments,"How many times do you need to repeat an experiment in order to see if your  hypothesis is nearly true or not? 
Also how big does the sample size need to be to conduct the experiment? 10,20,100?","There are no official rules about how many times experiments should be repeated to be reliable. However, the replication level of your experiments will have an impact on the statistical tests you can perform on your dataset (parametric or non-parametric tests, which do not have the same power).

If the aim is to determine whether an event has occurred (for example, whether a pathogen is present in a colony of animals), the number of animals that need to be tested or produced is given by

Image p20007f55g177001.jpg
where β is the probability of committing a Type II error (usually 0.10 or 0.05) and p represents the proportion of the animals in the colony that are not infected.

*Sample size depends on type of experiment.*

Here is paper with formula:
https://www.ncbi.nlm.nih.gov/books/NBK43321/"
Controlled experiments,What is another example of an everyday use of controlled experiments?,"if you planted different types of seeds in each of the pots, trying to determine if soil type affected germination, you might find some types of seeds germinate faster than others."
Controlled experiments,"Isn't taking coral reefs from their environment unethical since corals are disappearing? Why not create an experiment that would remove co2 levels by adding plants that sequester carbon near the bleached corols? The corols in the water that do not have plants that sequester carbon would be the control group, while the others would be the experimental groups. The independent variables would either be the co2 or pH levels. The dependent variable would be the degree of bleaching from the corals. You would do a side-by-side comparison of each of the waters that have different co2 levels. Then, you could do large/repeated sample sizes by testing waters with high/medium/regular co2 levels that have corals in the water.","Adding plants would disrupt the ecosystem. It is much safer, and efficient, to study coral in a controlled environment."
Controlled experiments,why not test different acidity levels with different temperatures?,"If each one had different temperatures, then you have too many variables. Let's say you did the same experiment as the Australian researchers, but also had each sample at a different temperature. Let's say you get the following results:

Low acidity with cold temperature: 10% bleached

Medium acidity with mild temperature: 30% bleached

High acidity with hot temperature: 50% bleached

Now that you have your results, you know what causes bleaching in coral. But, do you? Is it temperature that causes it? Is it the acidity of the water? Is it the combination of both? How can you tell? This causes confusion and possibly false claims. If you want to know both, it is better to have two seperate tests. One for "Is Acidity Causing Coral Bleach" and another for "Is Temperature Causing Coral Bleach".

At the end, you will have two results, two claims, and zero variable confusion.

I hope this answers your question!

-Colin"
Controlled experiments,How do the sprouting seeds know to go up if they don't know which way the light is?,"Plants are PHOTOTROPIC I.e, they sense light and act accordingly. Some plants are negatively phototropic ( go against light) while others are positively phototropic (go towards light).

There is also GEOTROPISM, there plants that are negatively geotropic, go against gravity (upwards) while some others are positively geotropic ( the go towards the gravity). 

These phenomenons come under the topic TROPISM"
Controlled experiments,how come a prediction is not the same thing as a hypothesis? isn't a hypothesis what your predicting will happen?,"Yes, but the hypothesis has to be backed up by your experiment, and predicted outcome.

If you start frok predicted outcome and do nto know how to back it up: how to end upo getting those results and why presumably that happened, then it is not hypothesis.


You need scientific hypothesis to make a research proposal (this is an example)."
Controlled experiments,how do platns grow,"They grow by doing photosynthesis.(The taking in of carbon dioxide and water where the water is oxidised and when the carbon is reduced, causing a reaction where the carbon dioxide turns into glucose and the water turning into oxygen.)"
Lesson summary: Water and life,So water is a covalent or ionic bond?,"Water has a polar covalent bond, in other words, it is covalent but oxygen is more electronegative than hydrogen so it pulls the electrons to it, giving oxygen a slight negative charge and hydrogen a slight positive charge. Good question!"
Lesson summary: Water and life,What is diffusion and give some examples,"Diffusion is a type of molecular movement that brings water particles from places of high concentration to low concentration. There really are 4 different types. Simple Diffusion, Osmosis, Facilitated Diffusion and Active transport."
Lesson summary: Water and life,I think water is a covelant bond,"Yes, it is a polar covalent bond. That means that while the atoms are "sharing" the electrons, the oxygen hogs them a bit closer, creating a partial negative charge on that side of the molecule, and a partial positive charge on the Hydrogen side"
Lesson summary: Water and life,why is O electronegative?,"To say that oxygen is electronegative fails to grasp the whole picture here. This is because ALL elements (except for the noble gases) are electronegative to some degree or other; ELECTRONEGATIVITY IS A PROPERTY OF THE ELEMENT which basically says "how strongly does it attract electrons?"

An element's electronegativity value is determined by a mixture of different factors, but the general rule is that it increases as you move right and upward across the periodic table. (Copy-&-paste this link for a visual: www.chemteacher.chemeddl.org/joomla/index.php?option=com_content&view=article&id=91)

So as for oxygen, (which was the subject of your question) it's electronegativity would indeed be one of the highest among all the elements because of where it is positioned in the periodic table (but more specifically because the factors that I alluded to earlier are manifest for oxygen in such a way as to make it such)."
Lesson summary: Water and life,"I still don't quite get the meaning of adhesion and cohesion, and the difference between them. Can somebody help me out?","adhesion is an attraction to unlike molecules, and cohesion is an attraction to like molecules."
Lesson summary: Water and life,which property allow solid ice to flot in liquid water,"One property of water is that it crystallizes when it freezes, that is it arranges itself in a particular formation whenever it freezes. This formation happens to be less dense than its structure when it is in liquid form. It is this property that allows ice to float. Hope this helped!"
Lesson summary: Water and life,"I'd like to know about the different types of bonds, like Sal mentioned Ionic Bonds, Covalent Bonds and Hydrogen Bonds, but what exactly are they?","A Covalent Bond is where atoms share eletrons, A ionic is an atom steals an eletron from another atom, giving it to the opposite charge, thus the atoms are attracted to each other. A Hydrogen Bond: A weak bond betweeen to molecules resulting from an electrostatic atrraction between a proton in one molecule and an electronegative atom in the other.   Hope this helps,"
Lesson summary: Water and life,"I have a question, what will happen if acids, fire and water combine together?","Its not as exciting as you think it would be. if you put something like lemon juice on a fire, it will most likely go out, same with water. I hope this helps."
Lesson summary: Water and life,what exactly is an ion,"an electrically charged atom or group of atoms formed by the loss or gain of one or more electrons, as a cation (positive ion), which is created by electron loss and is attracted to the cathode in electrolysis, or as an anion (negative ion), which is created by an electron gain and is attracted to the anode."
Chemical bonds,"In the third paragraph under "Ionic Bonds", it says that there is no such thing as a single NaCl molecule. Why can't you have a single molecule of NaCl?","This is because sodium chloride ionic compounds form a gigantic lattice structure due to the electrostatic attractions between the individual ions. In this case, each sodium ion is surrounded by 4 chloride ions and each chloride ion is surrounded by 4 sodium ions and so on and so on, so that the result is a massive crystal. This particular ratio of Na ions to Cl ions is due to the ratio of electrons interchanged between the 2 atoms."
Chemical bonds,"Regarding London dispersion forces, shouldn't a "dispersion" force be causing molecules to disperse, not attract?",dispersion is the seperation of electrons
Chemical bonds,"What is the typical period of time a London dispersion force will last between two molecules? 
To me it seems it last far shorter than a second. If so, has it got time to do anything productive with the molecules? Do this London dispersion forces come in bursts? Electrons rapidly moving back and forth between two atoms in a molecule creating many London dispersion forces so fast it acts like a long-lasting bond between molecules?",The London dispersion forces occur so often and for little of a time period so they do make somewhat of a difference. In my biology book they said an example of van der Waals interactions is the ability for a gecko to walk up a wall. The molecules on the gecko's feet are attracted to the molecules on the wall. You could think of it as a balloon that sticks to a wall after you rub if on your head due to the transfer of electrons. The bond is not long-lasting however since it is easy to break.
Chemical bonds,"If enough energy is applied to mollecular bonds, they break (as demonstrated in the video discussing heat changing liquids to gasses).  Usually, do intermolecular or intramolecular bonds break first?  Is there ever an instance where both the intermolecular bonds and intramolecular bonds break simultaneously?","Intermolecular bonds break easier, but that does not mean first. Statistically, intermolecular bonds will break more often than covalent or ionic bonds. Yes, they can both break at the same time, it is just a matter of probability. Water, for example is always evaporating, even if not boiling. But, then, why no hydrogen or oxygen is observed as a product of pure water? Because water decomposes into H+ and OH- when the covalent bond breaks. The concentration of each of these ions in pure water, at 25°C, and pressure of 1atm, is 1.0×10e−7mol/L... that is: covalent bonds are breaking all the time (self-ionization), just like intermolecular bonds (evaporation). By the way, that is what makes both pH and pOH of water equal 7.

Note that even though H+ and OH- are naturally produced in water, they also recombine back into H2O. The speed of bonds breaking and the speed of recombination "fight" one another, until they are in chemical equilibrium, that is when both speeds are the same. See https://en.wikipedia.org/wiki/Chemical_equilibrium

For instance, this kind of "fight" also happens with evaporation inside a closed recipient. The equilibrium is reached when the number of molecules escaping from the liquid phase is the same as the number of molecules entering it."
Chemical bonds,what determines a molecule's electronegativity?,"The electronegativity of an atom depends on its effective nuclear charge (the positive charge experienced by an electron in the atom's outermost shell) and the distance between the outermost shell and the nucleus. Elements with a high effective nuclear charge and a small atomic radius tend to have high electronegativities. Fluorine, which has the highest electronegativity value of 4.0 on the Pauling scale, has a small atomic radius and a high effective nuclear charge."
Chemical bonds,Are hydrogen bonds exclusive to hydrogen?,"A hydrogen-bond is a specific type of strong intermolecular dipole-dipole interaction between a partially positively-charged hydrogen atom and a partially negatively-charged atom that is highly electronegative, namely N, O, and F, the 3 most electronegative elements in the periodic table."
Chemical bonds,"In the section about nonpolar bonding, the article says carbon-hydrogen bonds are relatively nonpolar, even though the same element is not being bonded to another atom of the same element. 

How is one supposed to know which bonds are nonpolar if the same atom isn't being bonded to the same atom (e.g. O2)","Look at electronegativities, and the difference will tell you."
Chemical bonds,what are metalic bonding,"Metallic bonding occurs between metal atoms. In this type of bond, the metal atoms each contribute their valence electrons to a big, shared, cloud of electrons. Because the electrons can move freely in the collective cloud, metals are able to have their well-known metallic properties, such as malleability, conductivity, and shininess."
"Atomic number, atomic mass, and isotopes","So for radiometric rating to work, you have to assume that the element has been decaying at the same rate the entire time?","@Sean Collin: the amount of carbon isotopes can be determined for each geologic era by analyzing glaciers, because they imprison atmospheric gases. The geologic era can be determined by the depth of the extracted sample from the ice, because the rate at which it forms is predictable. That can also be done with other kinds of natural formations such as rocks, soil, and anything that captures carbon atoms, and that have predictable rates of formation."
"Atomic number, atomic mass, and isotopes","If everything is actually 99.99% empty space, that means that the ground is too... Why aren't we falling through all that empty space? Also, If everything is 99.99% empty space, why can we only feel the NOT empty space?","Similar charges present in electrons of atoms repel each other. So, we don't fall through that empty space."
"Atomic number, atomic mass, and isotopes",How did they know that it takes 5730 years for it to decay? How can we measure such a thing?,"The half-life of carbon 14 is 5730 years, this means that 50% of it will undergo radioactive decay in 5730 years.  Or another way of looking at it a single atom of C14 has a 50% chance of undergoing radioactive decay in 5730 years.  

The decay of an individual atom of c14 is random so if you have 12 grams of carbon 14 you have about 6 * 10^23 atoms so there will be some that decay within seconds and other that will decay in 10,000 of years.  We know that the rate of decay is random but on average a constant so if 3*10^23 atoms in the 12 grams will decay in 5730 years we know that 5*10^19 will decay in a year or 1.62*10^12 atoms decaying in a second.  

This rate is measurable and from the decay rate you can determine the half life."
"Atomic number, atomic mass, and isotopes",How do you compute for their half-life?,"You can refer to the answer by Charles LaCour - it basically states that by measuring the rate of decay at smaller amounts of time, we can leverage the fact that the rate of decay is often a constant (a certain number of atoms decays within a certain amount of time). Then, we can use this constant to apply to larger amounts of time, finding the half-life of a complete sample.

Mathematically, you can use the half-life formula to determine the half-life period:

N(t) = N0 * (1/2) ^ (t/h), where
N(t) is the amount remaining,
N0 is the original amount,
t is the time elapsed,
and h is the half-life period.

You can rearrange the variables to solve for the half-life."
"Atomic number, atomic mass, and isotopes",How is possible carbon 14 atom convert to nitrogen 14 gradually ? I thought that can not be possible and if it does i guessed somehow in years the carbon can convert to some elements which has less proton numbers not opposite way,"A neutron decays into a proton by one of the constituent down quarks decaying into an up quark, emitting a W⁻ boson, which decays into an electron and anti-neutrino."
"Atomic number, atomic mass, and isotopes",this sounds hard to do 😂,same. i think i might faint
"Atomic number, atomic mass, and isotopes",How do you calculate the natural abundance of an isotope?,"You can't  directly calculate it you have to measure the amounts 
 of each isotopes found in nature and calculate the relative abundances."
"Atomic number, atomic mass, and isotopes",so if the atomic number of a element is given you know what the proton is; the same as the atomic number. if that element is neutral you also know that the number of electrons is the same. but if you are only given the atomic number is it possible to find out what the atomic mass is?,"No. The atomic mass is a laboratory-measured value, so you cannot determine it from the atomic number. 
 
You can *approximate* the atomic mass of a single isotope (not the element in general) by guessing that the atomic mass in atomic mass units is numerically the same as the mass number (the number of protons + the number of neutrons). However, that is only an approximation."
"Atomic number, atomic mass, and isotopes","There is any better way to find the age of a very very old object ?? Like with what we mesure if carbon-  14 ,potassium-40 and uranium-235 concentration test fails ? And one more question: how accurate those carbon  dating is? Can the fossils be infested whit those isotopes when the test is made ?","Carbon dating is, maybe surprisingly, very accurate and otherwise you can use other isotope dating methods. These are in fact very reliable :-)"
Chemical reactions,can radioactive elements set on fire?,"Sure, they pretty much act the same chemically as their stable isotopic counterparts."
Chemical reactions,Why do atoms come together?,Do you mean why several atoms come together in a molecule? They are more stable this way because when a bond is formed(by sharing electrons between atoms) energy is released.
Chemical reactions,Where are Hydrogen and Oxygen atoms found as single atoms?,"Oxygen and Hydrogen atoms are diatomic, meaning they can never be found alone in nature. If they fail to find another element to bond to, they are forced to bond with themselves."
Chemical reactions,Are two atoms of the same element identical?,"They do not have to be.  An element can have what are called isotopes.  The element is defined by the number of protons in the atomic nucleus but there may be different numbers of neutrons.   

For example the all of the isotopes of carbon have 6 protons but there are isotopes with 6, 7 and 8 neutrons."
Chemical reactions,Are all Hidrogen atoms equal to each other? Like totally equal no diference?,"Being as they are the same thing, if there is a difference, it would be so minuscule. But yes, There really isn't a genuine difference between multiple hydrogen atoms."
Chemical reactions,when water gets boiled by fire that is an example of a chemical reaction?,"No, it is a physical reaction because you still have water. However, the flame itself is a chemical reaction because the fuel no longer exists once burned.
A chemical reaction occurs when you no longer have the same substance or substances, but have some new substance or substances. Changing the state (such as boiling, freezing, melting, or grinding up) still leaves you with the same substance or substances, so such things are physical reactions.
 
While boiling or freezing water is just a physical reaction, cooking food is a chemical reaction. When you bake dough, you no longer have dough but bread -- cooling the bread back down does not turn it back into dough -- so that is a chemical reaction."
Chemical reactions,why does there always have to be two sets of reactments to form a proper chemical reaction?,"Think about it like this, a woman or man cannot simply "create" a baby by themselves. You need both the sperm and the egg! If there was only one reactant.. it would just stay as it was... as soon as it was to change (chemically speaking) then it would have reacted with something."
Chemical reactions,How can we tell which reactions are reversible or irreversible?,"It comes with experience, but even then it is not always easy or possible to decide just by looking. As you study more chemistry, you will come across equilibrium constants and thermodynamics, both of which help to determine reversibility.

One simple pointer is to see if a gas is liberated. For example, if oxygen is released (as shown in the H2O2 example above) the reaction will be irreversible if the gas escapes into the atmosphere."
Chemical reactions,"I understand that one of the ways to speed up a chemical reaction is to slice the solute into smaller pieces, this way it is more exposed to the solvent. However, what i fail to comprehend is how this method INCREASES the surface area of the solute. Wouldn't making the solute smaller DECREASE the surface area?","It increases the surface area : volume ratio--there's the same amount of matter but more surface as more of it is exposed. 
The apple example above is a good one--cutting something in half means new surface is exposed that was previously on the inside.

Surface area is the area of all the surfaces added together. A cube with length 1, width 1, and height 2 has 4 2x1 rectangles and 2 1x1 rectangles, which is 10 in total. Cut it in half and you have two cubes, each with 6 1x1 rectangles (half the height, same length and width). 2 x 6 = 12 so you now have a surface area of 12 instead of 10."
N/A,"The first sentence of the section "The structure of an atom" reads: "An atom is the smallest unit of matter that retains all of the chemical properties of an element. For example, one gold atom has all of the properties of gold and is still a solid metal at room temperature."

My question is, how can just one atom be a liquid or sold or gas, etc? won't it still look and act the exact same no matter what state it's in? It still has electrons and a nucleus. What would the change look like on the atomic level in these different states?","Thanks very much to everyone who noticed this problem and upvoted or commented on it. You're absolutely right that there is no meaningful way to classify an individual atom as a solid, liquid, or gas, as these terms are based on interactions between atoms or molecules.

I've corrected that paragraph to reflect that the gold atom is still considered gold because it has the same chemical properties as a larger quantity of gold (thanks to having the set of subatomic particles, specifically protons, that define gold at the atomic level). The correction should be live on the site later today.

If that section is still unclear, or if you have any other comments or suggestions, please don't hesitate to ask here (or to report issues with the "Report a mistake" button).

Thanks again for noticing this!"
N/A,"In the fourth paragraph, it says "There are 118 elements, but only 92 occur naturally. The remaining elements have only been made in laboratories and are unstable." Why are the elements made in laboratories unstable?","There are several forces at work inside the nuclei of atoms. The electromagnetic force of the protons wants to push them away from each other. Fusion allows these protons to get close enough together for the stronger, yet short ranged, nuclear force to overpower the electromagnetic force. Neutrons will help add to this nuclear force, but they tend to become unstable when they get into too great of concentration and the weak force will cause them to decay into protons. 

With all of that to consider, as you get larger and larger nuclei with more protons, the electromagnetic forces increase, as well as the distances in the nuclei, putting more strain on the nuclear forces holding it all together. The ratio of neutrons to protons gradually increases to try to compensate, but this results in the neutrons getting more unstable themselves, resulting in more opportunity for weak forces to destabilize them. Hence, larger atoms become more unstable. 

There are believed to be certain numbers/ratios that are inherently more stable. These are called magic numbers. It's thought that another one of these magic numbers lies just beyond the range of currently known elements, which means we could potentially discover some new elements that are relatively stable and extremely massive."
N/A,What is the specific difference between atoms and molecules?,Molecules are made up of two or more atoms.
N/A,The last paragraph said that the electrons will repel each other if they get too close and resulting in our perception of solidity...what does that mean..can someone explain to me thx a lot,"Since electrons have like charges,they repel each other (much like a magnet).This results in our idea of solidity."
N/A,"The only thing that has always confused me about atoms, is, how can nonliving atoms make up living things? If you look at the world at the subatomic viewpoint, does that mean nothing is alive? I mean, I get how living things are living and the defining properties of a living organism make sense to me, but if you talk about atoms, doesn't that mean we are living, but only to a point?",How can atoms form a computer or an Egyptian pyramid or a novel? These are examples of what is known as an emergent property -- a property possessed by a group that is not present in any individual making up that group. Life is an emergent property.
N/A,I'm very interested in the whole idea of our perception of solidity (last sentence).  Does this mean that the reason I cannot punch through a wall is because the atoms making up the elements of matter in the wall are repelling the atoms making up my body (more specifically my fist)?,"Exactly! It sounds surprising (I couldn't believe it when I first learned about it), but it's true."
N/A,What do you mean by perception of solidity  and explain with an example?,"Imagine a stack of books, the atoms of the books aren't able to pass through each other because of the electron clouds that surround their nucleus. The electron clouds repel each other because the forces aren't attracted to one another.

Since they don't pass through each other, this gives us our perception of solidity, and why solid objects won't pass through each other."
N/A,So water is a main element in our body right?,"Water is not an element but a molecule but it is the most common molecule in our bodies. 
Oxygen is the most common element _by mass_ (43% of all weight; carbon is 16% and hydrogen is 10%) in the body. The most common element _by number_ is hydrogen (62% of all atoms; water is only 24% and carbon is 12%)."
N/A,What's smaller: A proton or a neutron?,"Proton, by very little, is smaller."
"The periodic table, electron shells, and orbitals","If the Bohr model is an inaccurate representation of electron's movement, why is it so universally accepted?","Because in Bohr’s model for hydrogen atom we consider only Coulombic interactions between one proton and one electron.

It cannot be extended for other atomic species containing more than one electron. Because in this case in addition to the interaction between nucleus and electron there arises the interactions between electron and electron of the same species. Bohr couldn't solve this problem and this problems are successfully explained on the basis of later developed quantum mechanics.o

But Bohr's model can be applied successfully for hydro genic species like He+, Li2+ etc……."
"The periodic table, electron shells, and orbitals","I'm kinda also confused on what an electron shell is and what an electron subshell is. Is the elctron subshell the s, p, d and f orbitals? And is it a probability function describing where an electron is likely to be? What's the difference between an electron shell and subshell?
Thanks c:","All atoms are made up of energy levels (called shells) that hold 1 or more subshells.
Each subshell holds a certain type of orbit.

Each individual subshell has slightly varying energies from its "shell" energy level, depending on the distance from the nucleus.

Every subshell has a # of orbits s/p/d/f that can each hold 2 electrons each (one has the opposite spin of the other).

The first shell (of all atoms) has 1 subshell of s-orbitals containing 1 s orbital. This means that the first shell can hold 2 electrons.
The second shell has 2 subshells: 1 s-orbital and 3 p-orbitals. This means that the second shell can hold 8 total electrons.

Every orbital is a shape (that can be determined by a trigonometric function I believe). This shape tells us where it is likely to spend most of its time, so in a sense it is a probability function.

Hope this helps someone. :-)"
"The periodic table, electron shells, and orbitals",How can you determine the number of outer shell electrons based on the full electron configuration?,"I'll try to explain with the help of an example. Consider Sodium (Na)
Its electronic configuration is 1s2, 2s2, 2p6, 3s1
The largest value of the Principle Quantum Number (n) is 3, so that is the outermost orbital.
Counting the number of electrons, we find that only the s orbital is present and it has only one electron. So Na has one electron in its outermost orbital.

Another example that I'll use is Fluorine (F).
Its electronic configuration is 1s2, 2s2, 2p5.
Since the largest value of n is 2, we count all the electrons in the s and p orbitals that have n = 2. So we get 2 + 5 = 7. So fluorine has 7 electrons in the outermost shell.

Basically, count the number of electrons in the orbitals with the highest principle quantum number, and that'll give the number of electrons in the outermost shell."
"The periodic table, electron shells, and orbitals","I'm confused about all the 1s2 2s2 and 2p6.  It's hard for me to understand, I was wondering if you could help out with that?","The 1s is the first orbital electron shell and it is closest to the nucleus. The 2n is the second shell. It consists of the 2s and 2p shells. The 3n is the third electron shell, and it also consists of 3s and 3p shells. The number after it stands for the amount of electrons in each orbital."
"The periodic table, electron shells, and orbitals","In the second last paragraph, I don't really get why because of the d subshell having more energy, argon is stable with 8 valence electrons? Thanks",I am not sure where the confusion is. Argon has a full outer shell of electrons already. It will not have a d-subshell
"The periodic table, electron shells, and orbitals",How do scientists figure this out? Do we have microscopes powerful enough to view atoms and observe this behavior or is there some other method?,"No, it can't be figured out using microscopes. Most of it is based on theory worked out using a lot of maths. Experimental observations, such as the energy released or absorbed when electrons move from one state to another, corroborate the theory.

Experimental observations, using techniques such as X-ray crystallography, provide information on the shape of molecules which, in turn, corroborates the theoretical shapes of the orbitals."
"The periodic table, electron shells, and orbitals",How much space does electrons take up,"Overall, the electrons are much smaller than the protons and neutrons. But, they take up more space when you think about how they move. They are constantly moving, and at different wavelengths and frequencies. And, they also move fast and they act like gas particles, in a way."
"The periodic table, electron shells, and orbitals",Can Hydrogen lose its only valence electron? Can an element exist without electrons?,"Hydrogen can lose its one electron and became an ion, or the hydrogen cation H^(+). However, it is so reactive that it does not exist for long before reacting with other atoms.  

Hope that helps."
Solvent properties of water,why cant oil spread evenly there water?,"Well... There are 2 reasons for this...
1) Oil has a density less than water, so it just sits there on the top, not spreading out into the more dense water below.
2) Oil is very nonpolar, meaning that a polar molecule like water doesn't get attracted to it. Oil is a covalent bond, and doesn't dissolve into ionic bonds like water. Because of this, the oil just keeps to itself, repelling all the water molecules causing it to be so independent and for it to not spread evenly in the water."
Solvent properties of water,Im still can't wrap my head around hydrogen shells how are those formed?,So since water is more positive on one end and more negative on the other end compounds like NaCl start to dissolve because one of them is attracted to the partial positive side of the water and the other is attracted to the partial negative side. Then this process continues until the water kind of coats each of the atoms.
Solvent properties of water,"If ionic bond is stronger than hydrogen bond, why does "Dissociation" happen?","The accumulation of several partially polar H2O molecules overpowers the singular charge of the ionic bond. So when you have one ionic bond vs one hydrogen bond, ionic wins, but one ionic bond vs several hydrogen bonds, that leans towards the hydrogen bonds."
Solvent properties of water,"so does our saliva dissolve stuff because of its water content, enzymes (such as amylase) or both?",Water is the solvent and enzymes help to degrade larger molecules into smaller ones. I would not call degradation of starch into maltose dissolving.
Solvent properties of water,Even though oil doesn't have a positive and negative charges. How do you "make" oil blended with water like what happens to our gasoline?,"Gasoline is made from crude oil, which contains hydrocarbons – organic compounds made up entirely of hydrogen and carbon atoms. So this "Oil" is made with h2o and carbon"
Solvent properties of water,"Why do things dissolve? For example why wouldn't the NaCl just stick together? They are attracted by an ionic bond, so is the "pull" from the hydrogen and oxygen stronger than what they have to offer one another?

does this only happy with ionic bonds?

If I understand correctly.. electronegativity determines a molecules polarity. So does hexane not dissolve because it has a low or no electronegative number?

And another question about breaking ionic bonds. What is salt was suddenly in the presence of some molecule or element of that has the same charge as the Na or Cl. Could it forgo its ionic bond with one another and bond with an equally satisfying atom? Why or why not?","To answer the first question, a molecule must have a charge to dissolve in water, because for a substance to dissolve, it has to form bonds with the solvent, and it cant do that unless it is polar

2. It happens with polar molecules (like methanol), as well as ionising molecules (like any acid)

3. Hexane does not have an charge because the electronegativity of the carbon and hydrogen is negligible. 

4. When like 3 H2O molecules bond to the Na or Cl, they overpower the ionic bond between the Na and Cl, which allows them to dissociate. 

Hope that helps, if it doesnt, please ask away :)"
Solvent properties of water,"If non polar substances are not soluble in water, how does oxygen get dissolved in water,which supports marine life?","Oxygen as gas can dissolve in water but there is no reaction between oxygen and water. 

Oxygen and water both retain their molecular form. So that is the way how aquatic animals perspire, by using dissolved oxygen. :D"
Solvent properties of water,"Is water being a good solvent a chemical or physical property? Also, is adhesion a physical property, as it is due to waters polarity?","I think it's a chemical property. Also, I believe adhesion is a physical property. Did this answer your question?"
Solvent properties of water,Isn’t the oil floats due to low density ?,"You are correct that oil floats on water because its density is lower than water. However, the reason that the oil separates from the water rather than dissolves into it is because oil is nonpolar and water is polar. If a denser nonpolar substance was mixed with water, water would float instead."
"Acids, bases, pH, and buffers",so how does having more H+ per molar make a liquid able to burn a hole in a wall?,"The H+ are super reactive. The more of these you have in solution, the more reactive your solution will be. If it is highly acidic, then the H+ ions may react with the paint on the wall and otherwise disintegrate materials that make up the wall too."
"Acids, bases, pH, and buffers",why does the human blood need to be at a certain Ph,"Enzymes in the body are very specific, so they can only operate at certain pH and temperature. If the pH levels go up or down too much in the body, the enzymes will start to denature (unfold), and will no longer work properly, which would have disastrous effects on the human body."
"Acids, bases, pH, and buffers","In our class we "made yogurt", the milk's pH was 6.The final pH with the yogurt was 4.  What happened to the pH of the milk as it turned into yogurt, and why did this change occur?","Bacteria digest the sugars in the milk, producing lactic acid as a waste product. This is one reason yogurt tastes tangy."
"Acids, bases, pH, and buffers",Why does cytoplasm have a lower pH compared to blood?,"Because the cells maintain an ionic gradient between the inside and the outside of the cell as part of how it uses energy from different molecules to do work. Organic molecules such as proteins help to maintain this gradient. Some are too large to go diffuse through the membrane and hold a charge (like an ion), and others actively pump ions one or both ways to maintain the gradient."
"Acids, bases, pH, and buffers","In the video "Definition of pH," (https://www.khanacademy.org/science/biology/water-acids-and-bases/acids-bases-and-ph/v/introduction-to-definition-of-ph) Sal draws a diagram of the logarithmic scale number line with bleach at 12. The image of the same type of number line (https://ka-perseus-images.s3.amazonaws.com/7ca9aecccf7e9d5caaf1ea10d2835c81f4036708.png) has bleach at 13. So does bleach have a pH of 12 or 13?","Bleach has a PH of 12.6, so neither one is far off."
"Acids, bases, pH, and buffers","I have a question. 
If I added Bleach with Gastric acid, would the ph be back to 7??
*Just curious and wanted to break the logic of science*","First of all for safety when combining any chemicals you need to know what the reaction is going to produce.  

Adding bleach to an acid will produce chlorine gas which is toxic and very hazardous to breathe.  

To answer your question, yes initially the pH of the gastric acid (primarily hydrochloric acid) will lower but depending on the other chemical reactions it may not stay lower.  Adding bleach to hydrochloric acid you get water, salt and chlorine gas."
"Acids, bases, pH, and buffers","I know that, say, 7.0 is 10 times more acidic than 8.0 (although it isn't acidic). If that's the case, then how much more acidic is, say, 8.0 than 8.2? Thanks!","Since pH is based on base-10 logs (log₁₀) you just need to do the inverse function.

That means 10⁰⋅² or approximately 1.58 times more acidic.

If this seems mysterious, you might want to review the material on exponentials and logs — for example:
https://www.khanacademy.org/math/algebra2/exponential-and-logarithmic-functions

Does that help?"
"Acids, bases, pH, and buffers",Is water an acidic or a basic solution?,"Pure water has a pH of 7, which is considered perfectly neutral because it is neither acidic or basic, but rather right in the middle. However, that is water in its purest form, and the water you come in contact with is rarely, if ever, that pure.

Water found in nature has substances dissolved in it that influence its pH. These substances produce ions when dissolved in water. When the water has extra H+ ions, it is considered acidic. If it contains OH- ions, it is basic. Rain water is acidic, with a pH of around 5.0 - 5.5, and sea water is basic with a pH of roughly 8.1. So water in and of itself is neither acidic nor basic. However, when it becomes a solvent in a solution, its pH is affected by the solute(s) that is/are dissolved in it.

Many factors can affect the pH of water, natural and human. Carbon dioxide dissolving in water (and being removed through photosynthesis), temperature changes, organic decomposition, soil, and the presence of calcium carbonate (limestone) are all natural factors that affect its pH. Pollution is a major human-influenced factor that affects the pH of natural water.

I hope this helped!"
N/A,"In this paragraph of heat of vaporization I got a bit confused by these numbers: "Water’s heat of vaporization depends on the temperature: it's around 540 cal/g at 100 °C (water's boiling point) and around 580 cal/g at 25 °C (room temperature)." 
So in room temperature it needs only (?) 40 calories more to heat up 1C as it takes in the boiling point?  How come there is such a tiny difference, or is it actually a huge difference?","Yes, that part is not very clear. How come only 40 calories can increase the water temperature by 75 degrees to its boiling point, if the specific heat property tells us that 40 calories can only increase it by 40 degrees?

The relationship is non-linear. Remember that when you apply energy to water, some of it will increase the avg kinetic energy of the molecules (related to the temperature) and some will be spent to break off all hydrogen bonding and send the molecules flying away (related to heat of vaporization at a GIVEN temperature). 

You don't need to wait until 100 degrees for vaporization to begin. It occurs more and more as you near towards it. And as more molecules fly off, less energy is needed to break off the remaining bonds. That's why the difference between heat of vaporization at 25C (energy required to break all H-bonds between 1 gram of initially slow moving molecules) and at 100C (energy to break all H-bonds of 1 gram of fast molecules) is LESS then the energy required to make all of those 1 gram of molecules faster."
N/A,"In the last paragraph it says: "In lakes and ponds, a layer of ice forms on top of the liquid water, creating an insulating barrier..."

How does ice provide an insulating barrier?","Awesome question. Part of the answer is that less dense materials conduct less heat, and thus slow down heat transfer. If you think about using a metal vs wooden spoon in a hot pan of water, it's the metal one that will burn you, because it is more dense and a better conductor of heat. So the transfer of heat from water to air is slowed down by the layer of ice. Another part of the answer is the ice prevents evaporative cooling, the liquid water molecules become physically trapped and so the ones with the highest kinetic energy can't escape, which would reduce the overall average kinetic energy and thus temperature of the water (see Sal's video on evaporative cooling). Because this doesn't happen with the layer of ice in the way, water can stay warmer for longer."
N/A,"But why is the distance between molecules in ice bigger than in water? They are still, but why not close enough to each other to make a dense body?","This is because when water goes lower than 4 degrees celsius it expands. Meaning the molecules are further apart. So when water reaches 0 degrees celsius it is frozen at an expanded state. And since it is frozen at an expanded state with molecules further apart, it is less dense than water which has it's molecules closer together."
N/A,Why do the fastest-moving molecules leave the liquid?,"The higher the speed, the greater the movement, the larger the likelihood that the particle will ricochet off the container or another particle in just the right way to escape."
N/A,What if you drop a solid into a liquid and they both have the same density. Will the solid float or sink?,The solid would be suspended in the middle of the liquid without moving.
N/A,what is the difference between heat and temperature?,Heat is how fast the molecules are moving in a given object. Temperature is the way we measure heat.
N/A,Why is water’s high heat of vaporization important?,"Water's high heat of vaporization is important because it helps to moderate the temperature of the ecosystem. When water goes through the water cycle (evaporation, condensation, precipitation), at the stage of precipitation, heat is released, and rain falls."
N/A,"At the surface of a liquid, why do some molecules evaporate but others do not?","The layer which is most closer to the air, interacts with air molecules.


Rest of molecules cannot eadily evaporate because cohesion forces are *stronger* than cohesion forces."
N/A,do these relate to adhesion?,it would be cohesion as its talking about water molecules only and not an external body like glass.
Hydrogen bonds in water,what is used to break hydrogen bonds in water?,"In addition to heating water, you can use an electric current. Check out splitting water experiments online."
Hydrogen bonds in water,What is a partial positive or partial negative charge ?,"When one atom "shares" an electron with another atom to form a molecule, the atom with higher electronegativety (electron-greedy) will keep the shared electrons closer to itself than to the partner-atom. Since one atom gained an electron and keeps it near itself, the atom receives a "partial negative charge." It isn't fully charged because the molecule is neutral due to its balance of negative and positive regions. 
p.s. More electrons = negative charge, fewer electrons = positive charge."
Hydrogen bonds in water,"Could someone explain what a polar molecule and bond are? I'm not great at science in general, so I don't understand what a polar molecule is and why water is a polar covalent bond is.","a bond is when 2 or more elements combine chemically and create a molecule. Elements bond either by sharing or transferring electrons. When a bond is formed by sharing electrons, it's called a covalent bond. sometimes the electrons in a covalent bond are shared unequally which causes some parts of the molecule to be partially positive and other parts to be partially negative. When this happens, its called a polar molecule. In water, the oxygen atom gets the electrons more frequently than the two hydrogens because of unequal sharing. This causes the side of the molecule with the oxygen to be partially negative and the side with the hydrogens to be partially positive, making water a polar covalent molecule. hopefully that helps  :)"
Hydrogen bonds in water,Is every hydrophilic molecule polar?,"That is generally a safe assumption, but should not be regarded as a "law".  

An example that doesn't fit this rule perfectly is `CO₂`, which is non-polar, but still somewhat soluble in water — this is in part because it reacts with water, but also because of weak effects due to the presence of polar bonds within this non-polar molecule.

Also, note that hydrophilicity and polarity are both continua, so there are many molecules that are in the middle of both of these scales.

There are also many polyatomic ions (not formally molecules since they have charges) that are very hydrophilic, but also completely non-polar because they are symmetrical.  Examples include: ammonium (NH₄⁺),  sulfate (SO₄²¯), carbonate (CO₃²¯), and oxalate (C₂O₄²¯).

It is also worth remembering that single atom ions (e.g.s `Na⁺`, `Cl¯`, `Mg²⁺`) are hydrophilic but not polar."
Hydrogen bonds in water,what is the reason to bond,"Polar molecules, such as water molecules, have a weak, partial negative charge at one region of the molecule (the oxygen atom in water) and a partial positive charge elsewhere -(the hydrogen atoms in water). Thus, when water molecules are close together, their positive and negative regions are attracted to the oppositely-charged regions of nearby molecules which makes it bond! and even the answer- to become neutral is also correct! for more information visit-http://www.biology-pages.info/H/HydrogenBonds.html"
Hydrogen bonds in water,Every Organism is 60 to 70 percent water . Then Why am I not fluid? Why my bones Are Solid?,"Most of your cells are filled with cytosol, which is water. Your bones are made from cells called osteoblast, they arent cells, but a type of cement made by these cells. Your epidermis (skin) holds all the water in you together. Your blood cells have water, your muscles have water, your neurons have, water. Most of you is water. I hope that makes sense and helps :)"
Hydrogen bonds in water,how does water come around  the cycle,"The water cycle, in the simplest form, is evaporation, condensation, and precipitation. 
Evaporation: When the temperature raises high enough, the water particles begin to move faster and gain more kinetic energy. As they move faster, the particles spread out in all directions. This spreading converts the water into a gas, or water vapor.
Condensation: The temperature slowly or slightly drops to where the water vapor's particles begin to slow. The decrease in speed makes the particles come closer together, making small droplets.
Precipitation: When the droplet or cloud gets full with water, the density makes the water fall, making it rain. If the temperature is cold enough, the rain droplets will freeze as the particles slow, making snow.

I hope that helps!"
Hydrogen bonds in water,How many Hydrogen bonds can water theoretically form at one time and why?,"Have a look at the Lewis structure for a water molecule — in how many places do you think a hydrogen bond could form?

It may help to remember that hydrogen bonds typically form between a hydrogen atom that is covalently bonded to F, O, or N and a lone-pair of electrons on an electronegative atom.  

For details see this free online book chapter:
https://en.wikibooks.org/wiki/Structural_Biochemistry/Chemical_Bonding/Hydrogen_bonds

Does that allow you to answer your question?"
Hydrogen bonds in water,am confused why is oil hydrophobic?,"Oil is hydrophobic, because it is a nonpolar molecule. Thus, they will not have the same attraction, as a polar molecule."
Carbon and hydrocarbons,How do people actually look and measure the angles of bonds if we haven't actually seen an atom?,"I think it's just maths, based on the knowledge we already have. If a molecule has 4 hydrogens and 1 carbon (methane, as in the example above), and we know that electrons repel each other, then there's only one set of angles that allow those electrons to all be as far apart from one another as possible. The lower the number of electrons, the greater the angle, presumably."
Carbon and hydrocarbons,"is there a program in which a person can mix and match different elements together and see what compounds they come up with, what compounds they form. then when the compound is formed the program gives a backstory o how that compound is used throughout life",Check out materialsproject.org they have so much info on different elements and compounds.
Carbon and hydrocarbons,Why is oxygen electronegative?,"Oxygen is electronegative because it only needs 2 electrons to complete it's valence shell. Instead of losing an electron (like sodium, in sodium chlorine), it simply attracts to those 2 electrons. The more a atom wants an electron, the more electronegative it is and visa versa. 

To imagine whats more electronegative, simply look at the periodic table. At the far bottom left  to the top right is the scale for how electronegative an atom is. The closer to the bottom left, the less an atom is electronegative. Closer to the top right, the more electronegative the atom is.

Hope this helps ;)~"
Carbon and hydrocarbons,Is it possible to artificially create diamond using huge hydraulic presses with super hot base plates such that all conditions to create diamond are fulfilled ?,"While I'm not sure if it's possible through the means at which you said, I know that it is possible to artificially create diamonds.  Some pet owners have made their pets into diamonds because all earth life is based off of carbon."
Carbon and hydrocarbons,"If the bonds in methane are repelled to each other, then wouldn't the bonds be too far apart that it would break the bonds?","The force that repels the pairs of electrons in the bonds in not as strong as the force that attract the electron to the protons of the carbon and hydrogen atoms. Thus, the best the electron bonds can do to stay away from each other is to form a tetrahedron. :)"
Carbon and hydrocarbons,"Here it says that carbon can bond with 4 other atoms because it has 4 electrons on its outermost shell, while oxygen can bond with only 2 but yhe outermost shell has 6 electrons why can't it bond with 6 atoms.","The octet rule means that atoms tend to prefer having eight electrons in the outside valence shell. Since carbon has 4 valence electrons, it can bond with 4 hydrogen atoms (that have 1 valence electron) to reach the preferred 8 valence electrons. Since oxygen has 6 valence electrons, it only needs to bond with 2 hydrogen atoms in order to reach the preferred 8 valence electrons."
Carbon and hydrocarbons,How do people die?,"People can die from various causes, and the scientific study of death is known as thanatology. Some common scientific explanations for death include:

1. Cardiovascular events: Heart attacks, strokes, or other conditions that disrupt blood flow to vital organs can lead to death.

2. Respiratory failure: Illnesses such as pneumonia, chronic obstructive pulmonary disease (COPD), or severe asthma can result in the inability to breathe properly, leading to death.

3. Infections: Bacterial, viral, or fungal infections can overwhelm the body's immune system, causing organ failure and ultimately leading to death.

4. Trauma: Severe injuries, including those from accidents, falls, or violence, can damage vital organs and cause death.

5. Cancer: Uncontrolled growth of abnormal cells can invade and destroy healthy tissue, impairing essential bodily functions and eventually leading to death if left untreated.

6. Neurological disorders: Conditions like Alzheimer's disease, Parkinson's disease, or amyotrophic lateral sclerosis (ALS) can progressively affect the brain and nervous system, leading to death.

7. Organ failure: When one or more vital organs, such as the heart, liver, kidneys, or lungs, stop functioning properly, it can result in death if not treated or replaced through transplantation.

8. Metabolic disorders: Conditions like diabetes, kidney failure, or liver disease can disrupt the body's normal metabolic processes, leading to complications that can be fatal.

It is important to note that this list is not exhaustive, and each case of death is unique. Scientists and healthcare professionals continually study different aspects of death to better understand its causes and find ways to prevent or treat the underlying conditions."
Carbon and hydrocarbons,What is a carbon monoxide and what does it do?,"Carbon Monoxide (CO) consists of one carbon atom and one oxygen atom. It is often formed through combustion reactions, and is a toxic compound. This is why you may see carbon monoxide detectors."
Carbon and hydrocarbons,what is a Hydrocarbons and what does it do?,"Hydrocarbons are organic molecules composed solely of hydrogen and carbon, hence the name. There's a number of uses for hydrocarbons, but the main purpose of them in human society is a source of energy through their combustion, or burning them for energy.

Hope that helps."
Hydrocarbon structures and isomers,"The second picture in the article, showing various ring formations, and how they compare includes pyridine. From what I have previously seen here on Khan Academy, it was my understanding that one aspect of hydrocarbons is that they are comprised of chains made up of only carbon and hydrogen. Because of this, wouldn't pyridine be discluded from the hydrocarbon classification because it contains an atom of nitrogen? Thank you much for the clarification!","Good question! Pyridine is not a hydrocarbon, as hydrocarbons can only contain hydrogen and carbon atoms, by definition. I think the point he was trying to make by showing that molecule is that hydrocarbons can take on ring-shaped forms to form more diverse molecules, which could potentially include other atoms. I hope that makes things more clear! :)"
Hydrocarbon structures and isomers,how many carbons can be bonded in chain ( maximum) ?,"When carbon bonds to itself to form a matrix, there is no limit. Organic molecules formed from a carbon chain can grow quite large and complicated, forming the basis for the complex machinery of living organisms."
Hydrocarbon structures and isomers,What can determine an atoms stability?I mean that it was written that Benzene is exceptionally stable. I am speaking general.,"Stability suggests than an atom is very unreactive. For this to happen, the atom needs to be completely neutral. For example, Neon is a nobel gas that rarely reacts with anything else because it has a fully complete outer shell of electrons (which is what every atom "wants".) Sodium however has only one electron in its outer shell, so it would "like" to donate that electron to get rid of it. Chlorine has seven outer electron, so it wants to gain an electron to be stable. Therefore, Sodium and Chlorine easily react together to make table salt."
Hydrocarbon structures and isomers,"In the paragraph after the heading Cis-trans (geometric) isomers, it says that linear molecules have single carbon-carbon bonds and can rotate freely. This kinda conflicts with the video that goes with this pdf because I thought linear carbon-carbon bonds were triple bonded and does not allow rotation. Only tetrahedrons can do that. Is this a mistake?","Linear is being used two different ways here, which I agree is a bit confusing.  

The first use doesn't really mean linear in a geometric sense, but it is intended to mean "unbranched and not circular".   

Note that this is analogous to how we often use line — e.g. "The line for tickets was so long it went around the block!"."
Hydrocarbon structures and isomers,"How do we know what shape these molecules take and second - How can we control, or is it possible to control the shape of the molecules?","The configuration of the bonds around each carbon can be easily determined - this is known as the geometrical configuration and depends on the electron hybridisation (sp, sp2, sp3)  of the carbon and other atoms. What can be harder to predict is the overall shape of a large organic molecule because there is rotation around single bonds so a large number of different shapes are possible and a molecule can cycle through all the different configurations, although some will be energetically more stable than others.

Interactions between different parts of the molecule (e.g., hydrogen bonds, ionic interactions, lone pair repulsions, steric hindrance, etc) are responsible for some configurations being more energetically favourable than others."
Hydrocarbon structures and isomers,"Is the psa isomers reference Prostate Specific Antigen? If not, what is it?","Perhaps it was an error that was removed, because I can't find the item you are referring to."
Hydrocarbon structures and isomers,"I don't get what _planar_ is. If you mean that the molecule is symmetric when you divide it into half, why isn't Ethane planar?","planar or trigonal planar, it's due to hybridization, an alpha carbon in ethene has a hybridization of sp2 due to three sigma bond pairs resulting in in 2-dimensional geometry(the shape of molecule doesn't have height),there's an angle of 120 between the bond pairs ,
 whereas an alpha carbon in ethane forms four sigma bonds resulting in sp3 hybridization and 3-dimensional geometry(the shape of molecule has height now), that's why ethane is tetrahedral not planar."
Hydrocarbon structures and isomers,"hey! I got a bit confused when it comes to the rotation of the tetrahedral, the planar, and the linear models. So what is correct? The tetrahedral has possible rotations around the bond when the other two do not? Or does the triple bond of the linear model prevent more possible movements when compared to the planar model?","yeah, you are quite right, the single bond between ethane let's it rotate however the molecule wants but in case of ethene and ethyne which have 1 pi bond and 2 pi bonds in addition to 1 sigma respectively these pi bonds restrict their moment of rotation that's why only ethane is able rotate freely whereas other two can't."
Hydrocarbon structures and isomers,"Why cannot we superimpose enantiomers of L and D? In the example, carbon with F, H, Br, and Cl, if you superimpose back to back it exactly aligns.","Try to think of this in terms of laying your left hand on top of your right hand. They may seem to line up, but your left palm is showing. Therefore, your hands still wouldn't be the same. Also, keep in mind that most Carbon Enantiomers are 3 dimensional in a tetrahedral shape with some of the atoms revolving."
Functional groups,"There are many more functional groups,any tips for remembering there names?",You could try active recall where you watch a video or read and then you close it and try and write down as many things as you can remeber. (This works because it is more difficult at first telling your brain that it needs to focus on it creating connections between your brains nerves)
Functional groups,"In the table, what is the difference between a functional group being polar and being charged?",A charged group is either positive or negative (gains or loses an electron) and a polar group contains atoms that have a difference in electronegativity.
Functional groups,"Can someone please elaborate on what makes a molecule or atom,      polar/non-polar or acidic/basic?","Sure thing! An atom is the smallest building block of life, it cannot be broken down further (like Carbon). A molecule is a group of atoms chemically bonded in a fixed proportion (like CO2), which can be further broken down. An atom is polar molecularly if it is asymmetrical (in terms of bonding, it is polar when its electronegativity difference is >0.6). An atom is nonpolar molecularly if it is symmetrical (in terms of bonding, it's EN difference is <0.6). An atom is acidic when there are more positively charged hydroniums than negatively charged hydroxyls (same vise-versa)."
Functional groups,How can you tell if a functional group is acidic or basic just by looking at the functional group?,well determining by its ability to loose or gain a proton
Functional groups,"Are aldehydes and ketones (carbonyls) significantly soluble in water like alcohols and carboxylic acids? If not, why not?","The short molecules are soluble in polar substances like water because they are relatively polar. The longer the carbon chain is however, the greater the non-polar tail is, and the less soluble aldehydes and ketones become."
Functional groups,"In what year in school do we learn this? I am home schooled and i want to learn 11th grade, but i am not sure if this is near grade 11 or is it for 9th graders or for collage. What grade do you learn this?",this would be basic chemistry so you could learn this is 9th or 10th or even 11th grade if you take biology or chem
Functional groups,"is it normal that in the video, it written. that an Amino group is N-H-H,  while here its R-N-H-H","Well first thing is that we don’t write condensed structural formulas like that. The formula is written in a specific order so we know what is bonded to what. So if you write N-H-H or R-N-H-H, it looks as if nitrogen is bonded to only one hydrogen and that there’s a bridging hydrogen joining the nitrogen to the other hydrogen. If we have multiple atoms bonds to the same central atom, we use subscripts. 

If it’s an amine, we need that ‘R’ part of the formula to show that the nitrogen is bonded to a larger organic molecule. Otherwise it looks like a lone nitrogen molecule, like ammonia. So it’s properly written as R-NH2 (where the 2 is a subscript). 

Another thing to point out that we can have slightly different types of amines depending on how many carbon atoms are bonded to it from the rest of the organic molecule. An amine is essentially an ammonia molecule where a hydrogen has been replaced by a carbon atom. But since ammonia has a formula of NH3, we have the possibility of replacing all three hydrogen atoms with carbon atoms. 

An amine with only one carbon atom is called a primary amine (symbolized 1°) with a formula of R-NH2.
An amine with two carbon atoms is called a secondary amine (2°) with a formula of R2-NH.
An amine with three carbon atoms is called a tertiary amine (3°) with a formula of R3-N.

Hope that helps."
Functional groups,how alkanes are less reactive. why?,"Alkanes are less reactive than alkenes.
This is because alkenes have double bonds (C=C).

It is easy to break just one of these bonds in the double bond and make a reaction happen, but breaking the C-C single bond in an alkane is difficult"
Functional groups,Does anybody know whether there is a difference between O-H and OH?,There is no difference. OH has an imaginary bond between them (seen in O-H). We assume it is there. It is a common group so we do not have to draw the bond every time.
Functional groups,is phosphate group polar or non-polar?,"The phosphate group is non-polar, it is made up of a polar head but three non-polar tails, making the overall charge, non-polar"
Introduction to proteins and amino acids,"N-terminus and C-terminus. What terminates extension of peptide linkage? Are they guaranteed not to react with other amino acids? If so how?...is it like how there aren't any random amino acids beside those 23 mentioned above, because i.e. for Lynsine, any more hydrocarbon backbone added to the hydrocarbon backbone of lynsine makes it unstable and is actually impossible or something?

And would they be in zwitterion at physiological pH? Could this be why the terminus ARE terminus?","To answer your first question, you need to look at the process of creating a peptide during Translation in the Ribosome. Messenger RNA is a sequence of nucleotides, three nucleotides is a codon, and codons code (go figure) for certain amino acids, codons also code a "start" and "stop". So in a example the ribosome will read a start codon and start building a peptide until it reaches a stop codon. There is your termination. I'm not sure how to explain the reasons for the differences in the 23 amino acids. Ribosomes are almost like computers robotically doing what the inputted code commands it to do. 

Also, I wanted to add that this isn't the end of the story. Things happen to the peptides after transcription within the cell. For example, insulin isn't transcribed fully functional but has to undergo several processes (cutting of pieces, adding) within the cell before it lives up to it's essential functions."
Introduction to proteins and amino acids,how are proteins and phenotypes related to one another,"Provided that a protein has been transcribed and translated or "expressed" by the genes, that is the direct expression of phenotype. Large scale that may be seen in an organism as eye color, hair color, etc., as each protein has a different function."
Introduction to proteins and amino acids,"Should I make any distinction between the qualities: non-polar and hydrophobic or polar and hydrophilic? Can I use these terms interchangeably; which is to say, am I allowed to say non-polar instead of hydrophobic?","Yes, you should make a distinction.  While it is definitely true that most of the time they are the same, it is a good idea to keep in mind the individual definitions of polar, non-polar, hydrophobic, and hydrophilic."
Introduction to proteins and amino acids,"Hi, I remember that in the lipids lesson it said that a specific macromolecule (I don´t remember its name) was considered to be a lipid just because it was hydrophobic and in this article, I found this: "For example, amino acids such as valine and leucine are nonpolar and hydrophobic." So my question is what is the difference between the other macromolecule that was called a lipid because of its being hydrophobic and these proteins?","It is the presence of amine group and a carboxylic group with a specific configuration that makes a macro molecule to be classified as an amino acid. If you watch the video again, I am sure you would understand."
Introduction to proteins and amino acids,"If enzymes are proteins, and they can function as a part of the digestive system, doesn't that mean that the enzymes will be breaking down other proteins in the eaten food? So proteins can break down other proteins?","Yes, you are right the digestive enzymes in your stomach do break down other proteins."
Introduction to proteins and amino acids,"Do ribosomes make amino acids or do they just synthesize proteins? If so, where are amino acids made?","No, ribosomes don't make amino acids. They are just the sites where amino acids get linked together to form polypeptides. 
Of the 20 amino acids, 9 are essential, i.e, cannot be made by our body. We obtain them from the food we eat. The protein in the food is digested and broken down to release the amino acids. The essential amino acids are :
=Leucine
=Isoleucine
=Valine
=Histidine
=Methionine
=Threonine
=Phenylalanine
=Tryptophan
=Lysine
The remaining amino acids are non-essential, i.e, they can be produced by our body. They are produced by modifications of some of the essential amino acids. For example, Tyrosine is produced from Phenylalanine. This process occurs in the cytoplasm of cells, but it can also occur in the mitochondria as some enzymes and reactants (like alpha-keto glutarate) are found there."
Introduction to proteins and amino acids,"In the picture with the peptide bonding near the end, why are the hydrogens replaced with "R" groups?",ig Rs refer to alkyl groups
Introduction to proteins and amino acids,Distinguish between proteins and amino acids,proteins are polymers of amino acids whereas amino acid is a monomer of protein
Introduction to proteins and amino acids,""Some amino acids, such as lysine and arginine, have side chains that are positively charged at physiological pH and are considered basic amino acids"
"Aspartate and glutamate, on the other hand, are negatively charged at physiological pH and are considered acidic"

What is going on? Positive charge means that it has excess of H+ protons, so why is it basic and vice versa?","Lysine and arginine accept a proton and, in so doing, they act as bases and become positively charged. (Compare them with ammonia, which is a base and which becomes protonated in water to give NH4+ and OH- ions.)

Aspartate and glutamate, on the other hand, lose protons and become negatively charged. They act as acids. (Compare them with acetic acid, which dissociates in water to give acetate ions and H3O+.)"
Nucleic acids,How do mRNA and tRNA communicate with eachother during the formation of the proteins?,"mRNA is like a recipe from a cookbook; a list of ingredients to make a protein. mRNA is a chain of nucleotides (A, U, C, and G, not T since this is RNA). A group of three nucleotides is called a codon. A codon matches with three nucleotides, called an anticodon, on a single tRNA molecule while in a ribosome. The tRNA carries an amino acid, our ingredient to make the protein.
So mRNA is the recipe, tRNA matches to the recipe bringing an ingredient, and the line of ingredients become a protein."
Nucleic acids,"If A-T bonds have 2 hydrogen bonds and G-C bonds have 3... Would it be true that longer periods of A-T bonds in DNA (so like: AATAATTATTTTAATTAAAA) are less stable parts of the DNA helix than parts that have more (or only) G-C bonds in them? And if this is true, are these parts (AT only parts) more prone to mutations?","The first part is true, T-A bonds are less stable and more likely to come apart. The A-T bond strands also signal where DNA needs to separate for commonly transcribed genes, such as the TATA Box commonly found just before the beginning of gene sequences.

I'm not sure if they are more prone to mutations though."
Nucleic acids,"DNA is common to all organisms, all organisms use the same 4 nitrogenous bases, A T, C G

is that right?","Entirely true. Also, AT/GC are found in DNA while RNA is made from AU/GC. Just keep in mind that, even though all life forms have DNA, not everything that has DNA is alive: viruses can have DNA but are not living."
Nucleic acids,"Why do some nitrogenous bases have two fused carbon rings while other have one? Would it be possible for there to be nitrogenous bases with more than two fused carbon rings? Could there ever be an instance where there are more than just five kinds of nitrogenous bases (Adenine, Thymine, Guanine, Cytocine and Uracil)? If it could be possible how would DNA and RNA have to rearrange themselves? Would it be possible for DNA and RNA to use other sugars aside from Deoxyribose and Ribose? If so, like what? If not, why?","https://www.khanacademy.org/science/organic-chemistry/aromatic-compounds/aromatic-stability/v/aromatic-heterocycles-i

https://en.wikipedia.org/wiki/Heterocyclic_compound

https://en.wikipedia.org/wiki/Abiogenesis

https://en.wikipedia.org/wiki/Nucleic_acid_analogues

Hope this helps!"
Nucleic acids,Are the functions of nucleic acids guided only by molecular forces and just appear to have intention or are there other forces at work that I'm not aware of? How do these macromolecules "know" what to do?,"A creationist would say that this is part of the intelligent design. An evolutionist would say it's all down to chance. Two spanners to consider - 1) one molecule of hormone, once recognised by the cell, leads to prduction of thousands of times more molecules, and types of molecules, than a mere chemical would suggest, and such secretions can be brought about by tiny changes in brain activity. 2) DNA is just for storage. It is a molecularly inert form for the passing on of genes without having a massive effect upon the rest of the body - and so the active form is the sticky stuff of RNA and these determine how the proteins are folded together."
Nucleic acids,"When transcription takes place and the DNA is broken into two, and then mRNA is formed with one of the DNA strands or for BOTH the DNA strands?","Within a gene *usually* only one strand is transcribed, but there are many examples where transcription happens from the both strands. This is especially common in viruses.

Also, the strand that is transcribed for one gene may not be the same as the strand being transcribed for a neighboring gene.

Finally, the whole DNA double helix is not separated - just a small bubble is opened around each RNA polymerase as it works its way along the DNA."
Nucleic acids,"In the first paragraph of the section "Regulatory RNA (miRNAs and siRNAs)" it says "They bind to specific mRNA molecules (with partly or fully complementary sequences) and reduce their stability or interfere with their translation, providing a way for the cell to decrease or fine-tune levels of these mRNAs."

Does this mean that the purpose of microRNAs (miRNAs) and small interfering RNAs (siRNAs) it to make sure that there are not too many mRNA molecules producing proteins? They are regulating the amount of protein produced by the cell? Am I understanding this correctly?

Please help! Thanks. :)","Yes, miRNA regulates protein synthesis in a way it binds to mRNA transcript and 'silence' it."
Nucleic acids,how are DNA and RNA different and alike to each other?,"As stated in the summary at the end of the article, DNA and RNA have different functions. While DNA stores genetic information, RNA is involved in protein synthesis and gene regulation, as well as storing genetic information in some viruses. DNA and RNA also have different structures; DNA's phosphate-sugar backbone contains deoxyribose, while RNA's contains ribose. While DNA is double-stranded and has the nitrogenous bases adenine, thymine, cytosine, and guanine, RNA is usually single-stranded and contains uracil instead of thymine.

As for the similarities between DNA and RNA, they are both important biological polymers and contain four bases and a phosphate-sugar backbone."
Carbohydrates,"Why are galactose and glucose isomers, when the hydroxyl group that is "flipped" is linked to the chain by single bonds only? I thought only double+triple bonds forced atoms to stay where they are. According to the previous lesson about ethene/ethane, galactose and glucose should be the same thing because the flip happens around single bonds.","Well, single bonds allow the actual atom/molecule to rotate. However, in this case, when the article is talking about "flipped" molecules, the molecules are not able to rotate, they are just upside-down in relation to the neighboring molecules."
Carbohydrates,"Confused about differences between beta-glycosidic and alpha glycosidic linkages. Are beta-glycosidic linkages inherently stronger due to some chemical property, or is it just that humans lack the enzymes to digest it? Whatever the answer, this is not to be confused with the reason cellulose is so strong (which is due to the hydrogen bonds acting between different polymers of glucose, forming thin fibrils), am I correct?","Well from what I learned beta-glycosidic linkages are stronger due to the way bonds criss-cross between every alternate glucose molecule such as cellulose making it both physically and chemically stable. 

These beta-glycosidic linkages can be broken down by enzymes stored by the bacteria stored in a cow's gut for example which why cow's can ingest complex carbohydrates like cellulose and as you suggested humans cannot digest such carbohydrates as we do not have the enzymes that can specifically break beta-glycosidic linkages."
Carbohydrates,"How can you identify a carbohydrate? Are all molecules with a carbonyl group (C=O) and hydroxyl group (OH) carbohydrates? Or is it so that ONLY carbohydrates have one carbon (C) atom to one H2O? If the latter is true, why is deoxyribose a carbohydrate with a formula C5H10O4?","Unfortunately there isn't a universally accepted definition for what makes up a carbohydrate.

A very restrictive definition is as follows:
Carbohydrates consist of carbon, hydrogen, and oxygen — with the hydrogen and oxygen occurring in a 2:1 ratio.  There also must be at least three carbons.
In other words, these are organic molecules that incorporate multiple water molecules and have at least three carbons.


However, derivatives of molecules that meet the above definition are still generally thought of as carbohydrates.  
(In addition, some molecules that fit these parameters aren't generally thought of as carbohydrates.)

For example: deoxyribose is a sugar (carbohydrate) found in DNA that has had an oxygen removed.

Other modifications including addition of groups containing nitrogen and sulfur are also commonly found.


I recommend the wikipedia article on this subject:
https://en.wikipedia.org/wiki/Carbohydrate


Does that help?"
Carbohydrates,"With the glucose and galactose isomers, can't glucose's 3rd carbon spin around if it  doesn't have a double bond? Then it would be exactly like galactose. Does this happen or is there a reason why it can't?","Because it requires breaking off the bonds.

If you want to turn H, and OH into one another, you will have to break bonds and reattach them. This does not happen spontaneously in water. 

You _cannot_ turn one into another through mere rotations of a bond. :)"
Carbohydrates,"What is the advantage of polysaccharides, storage wise?","To add to the excellent reply from Okapi, another reason why glucose is stored as glycogen is that if it were stored as free glucose, this would cause osmotic pressure to increase such that cell membranes would rupture.  Even the elevated glucose level (hyperglycemia) seen in uncontrolled diabetes cause changes in osmotic pressure that are responsible for some of the symptoms, such as increased urination and excessive thirst."
Carbohydrates,Is fructose sugar healthier than glucose sugar?,It depends on the context of how its used.
Carbohydrates,What is the difference between a monomer and a monosaccharide?,"A monomer is the smallest unit of a polymer.
A polysaccharide (carbohydrate) is a polymer. A monosaccharide is the monomer that makes up a polysaccharide.
In short- Monomer is a general term, while monosaccharide is a specific term for the monomer that makes up a carbohydrate.
A monosaccharide is a single sugar molecule. This includes glucose, fructose, and galactose.
Disaccharides are double sugars, such as sucrose (table sugar).
Polysaccharides are long chains, such as plant and animal starches."
Carbohydrates,if single bonds can rotate freely do the stereoisomers become each other interchangeably ?,"No, single bonds stereoisomers such as some enatiomers are not interchangeably because they are stuck in the three dimension world"
Introduction to macromolecules,Can you have a polymer made of different macro molecules? Like a carbohydrate bonded to a protein?,"You mean like a _glycoprotein_? Yes, but then it is just one (even larger) macromolecule"
Introduction to macromolecules,Don't you just love biology?,Yes! It's wonderful and fascinating!
Introduction to macromolecules,Why are lipids polynomials,Do you mean polymers?
Introduction to macromolecules,Are glycogen molecules stored in every cell of the body or only in liver cells or other cells specialized for storing it? If it is only stored in certain parts of the body then is it broken down into glucose before it is transported to other cells for use?,"Glycogen is also stored in skeletal muscle cells for use by those cells. Muscle cells can break down glycogen but lack glucose-6-phosphatase, the enzyme that is needed if glucose is to enter the blood stream to be used by other cells.

Glycogen is also stored by other tissues in amounts smaller than in muscle."
Introduction to macromolecules,How are Hydrocarbons related to Macromolecules? Are they considered to be macromolecules or are they closely related?,"A hydrocarbon is a type of macromolecule. Basically a macromolecule is a "big molecule". Hydrocarbons are just a chain of carbon atoms with hydrogens bonded to all the carbons (hence, hydro-carbon). So, a big chain of carbons and hydrogens is a type of macromolecule. There are other types of macromolecules, but since most are organic (consisting of mostly carbon), hydrocarbons are used as an example."
Introduction to macromolecules,"The article states that "Dehydration synthesis reactions... generally require energy, while hydrolysis reactions... generally release energy." However, in chemistry we were drilled that breaking bonds requires energy and creating bonds releases energy; how would these guidelines mesh?","The breaking of bonds does require an input of energy, while the formation of bonds results in a release of energy. This is true for all reactions. But then we also have to concern ourselves with the magnitude of these energy inputs and outputs. It’s possible for a reaction to release more energy in bond formation than was put into it for bond breaking, and vis versa. 

We formalize this phenomenon in chemistry with the idea of enthalpy, or specifically the change in enthalpy. Reactions which release more energy than they take in are referred to as exothermic, and reactions which release less energy then they take in are referred to as endothermic. 

Hope that helps."
Introduction to macromolecules,what are macromolecules?,"There are four classes of macromolecules that constitute all living matter: carbohydrates, lipids, proteins, and nucleic acids. While they have different structures and functions, they are all composed of long complex chains of molecules (polymers) made up of simpler, smaller subunits (monomers). They are joined together in a process known as dehydration synthesis, in which a covalent bond is formed between two monomers by releasing a water molecule."
Introduction to macromolecules,"are there any other macromolecules apart from carbs ,fats,protiens and nucleotides","To some extent that depends on how you choose to define macromolecule, but those are (representatives of) the four groups that are usually considered to be biological macromolecules.

The second group is actually lipids, which includes compounds like steroids that are not fats.

The last group is nucleic acids — nucleotides are the monomers that make up nucleic acids.


Other than these there are many biological macromolecules that contain parts from two (or more) of these types.  Some examples are:
• glycoproteins — proteins with attached carbohydrate chains
• lipoproteins —  proteins with attached lipids
• lipopolysaccharides — carbohydrates with attached lipids


There are also many (usually) synthetic (i.e. artificial or "man made") macromolecules such as plastics, and allotropes§ of carbon (e.g. graphene and carbon nanotubes).

§Note: see — https://en.wikipedia.org/wiki/Allotropes_of_carbon"
Introduction to macromolecules,So lipids are macromolecules but not polymers? Is that even possible?,"Yes, macromolecules are large molecules that are formed by the joining of smaller units. Lipids fit that description, but they aren't polymers because they are made up of smaller units of different kinds (like glycerol and fatty acids) rather than monomers that repeat themselves."
Introduction to macromolecules,What are the four macro-molecules in living things?,"Proteins, lipids, carbohydrates, and nucleic acids."
Orders of protein structure,"When we digest meals rich in protein, are we denaturing the proteins and "re-naturing" them through the help of chaperonins, or breaking it down to it's base amino acids and re-creating proteins using those?","Oftentimes, we are breaking them down to their amino acid bases and creating new proteins. This is because many of the proteins that are found in the human body are not obtained directly from food, rather we need certain proteins in the food so we can use their amino acids to build the necessary proteins. The human body does not produce all 23 required amino acids, so we need to get them from our food, by eating proteins that contain those amino acids. :)"
Orders of protein structure,What is the N-terminus and C-terminus mentioned in primary structure?,"The N-terminus refers to the amino end of the amino acid with the nitrogen and hydrogens, and the C-terminus refers to the carboxyl group."
Orders of protein structure,"In the Primary Structure section when they're talking about Hemoglobin and sickle cell:

"What is most remarkable to consider is that a hemoglobin molecule is made up of two α chains and two β chains, each consisting of about 150 amino acids, for a total of about 600 amino acids in the whole protein."

What do they mean by two Alpha chains and two Beta chains? Do they mean two polypeptides in an Alpha helix shape and two polypeptides in a Beta pleated sheet shape? Or are they just calling two of the polypeptides "alpha" because they're both identical and the other two "beta" because they're also identical. 

I thought polypeptides could contain both Alpha helix's and Beta pleated sheets, if so you won't be able to call one polypeptide chain specifically one or the other.","Your second guess is correct – the two alpha chains are identical (as are the two beta chains).

This nomenclature is confusing and the designation of alpha and beta chains has nothing to do with alpha helices and beta sheets!

In fact, alpha- and beta-hemoglobins have very similar structures both of which are dominated by alpha-helices and have no beta sheet at all (see for example: http://www.rcsb.org/pdb/explore/jmol.do?structureId=2HHB&bionumber=1). 

And yes, many proteins have both alpha helices and beta sheets."
Orders of protein structure,"A question that came to mind as I was reading this and watching the previous videos is:
How do we know what amino acids look like? For example, we learned that there are two amino acids switched out which causes sickle cell anemia. How did we learn that and how do we know which amino acids that is?
We don't see the letters "C", "H", "S", "N", etc when we look through microscopes at proteins, so how did we get so advanced to understand protein interactions? It's fascinating!! Thanks!","This is a great question, but actually quite complicated so I'm not going to try to give a complete answer — I have given some useful links below if you wish to learn more.

Each amino acid has unique chemical properties that can be used to tell them apart.  
There are also methods that have been developed to remove amino acids one at a time.  
By combining theses techniques it is possible to directly determine protein sequences.

There are many different techniques for directly determining protein sequences — this wikipedia article is a decent introduction:
https://en.wikipedia.org/wiki/Protein_sequencing

The very first protein sequence (bovine insulin) was determined by Fredrick Sanger in 1951-2 (note that this was more than a decade before the first nucleotide sequence).

However, it is now relatively rare to directly determine protein sequence!
Instead, since it has been worked out (mostly) how DNA codes for protein, we usually infer the protein sequence from the DNA sequence.  This is because it is now *much* easier to sequence DNA.

Note that because of processes such as the post-translational modifications to proteins we still need protein sequencing and I believe that we currently rely too heavily on DNA sequencing."
Orders of protein structure,"It goes in depth about the structures, but lacks in explaining function. Besides holding other primary structure proteins, what does a tertiary and quaternary structure even do?","The function of tertiary and quaternary structure varies depending on type of protein, but in enzymes, the specific shape and configuration of the protein allows the formation of active sites. For example, catalase, an enzyme that breaks hydrogen peroxide into hydrogen and oxygen gas, has its proteins and amino acids configured in a certain way to create an area where the charges are so strong that spontaneous reaction occurs, by lowering the energy needed to break intermolecular bonds."
Orders of protein structure,"I am slightly confused with secondary structures. If the backbone determines the structure, how is it different from the tertiary structures? In other words, what are the main difference between each structure?","The secondary structure is formed by hydrogen bonds between carbonyl and amino groups that make up the *polypeptide backbone* and causes the molecule to either bend and fold (beta pleated sheet) or spiral around (helicase).

The tertiary structure is formed by many different bonds between R groups that make up the *side chains*, that make the strand of molecule bend and loop around in a more complicated three dimensional form."
Orders of protein structure,In the last paragraph they begin to talk about Proteins "folding" but they don't explain what this means.,"Proteins can fold into various structures/sizes (secondary, tertiary, quanternary) for various biological tasks. Think of it literally as proteins folding into smaller, more condensed forms."
Orders of protein structure,"In the sickle cell anemia example, is it the case that a key amino acid difference may cause catastrophic results or is it the case for that all amino acids are that important and changing any of them may cause similar catastrophic results?","Sickle cell anaemia is caused by a single point mutation of the gene coding for haemoglobin. As a result, a hydrophobic amino acid (valine) replaces the usual hydrophilic amino acid (glutamic acid). This very small change in sequence affects the outside of the protein and results in haemoglobin molecules sticking together, changing the shape of the cell.   

There are lots of other known mutations in the haemoglobin gene, some which affect health and others which have no impact.

In summary, for any particular protein, some amino acids are far more important than others."
Orders of protein structure,What duos it mean by denatured?,"In biochemistry, denaturation is a process in which proteins or nucleic acids lose the quaternary structure, tertiary structure, and secondary structure which is present in their native state, by application of some external stress or compound such as a strong acid or base, a concentrated inorganic salt, an organic solvent, agitation and radiation or heat. If proteins in a living cell are denatured, this results in disruption of cell activity and possibly cell death.

But in the "Denaturation and protein folding", I think they were talking about if the pH or temperature of a proteins environment was to change, the shape of the protein (I think) would change also, and when that happens, the protein is going to turn back into an unstructured string of amino acids. And when a protein loses it's high order structure (but not the primary one) it is called denatured."
Lipids,How do saturated and unsaturated fats affect the fluidity of cell membranes?  How do the length of fatty acid tails and the presence of cholesterol in cell membranes affect fluidity?,"unsaturated fats and shorter fatty acid tails increase the fluidity;
the presence of cholesterol basically adds structure and keeps the cell from being squished, but doesn't keep it super firm and rigid either. (which is a good thing)"
Lipids,"When a micelle is formed, are the hydrophobic tails packed together just because they don't want to touch the water or is there also bonding happening between the tails?","There is bonding too (van der Waals forces) although these are very weak. The packaging happens primarily because of the hydrophilic parts being attracted to each other and reducing the entropy of the system (=reducing the surface area, and forming a sphere with the hydrophobic parts in the center)"
Lipids,Do the number of carbons in a fatty acid affect the properties of the fat?,"Yes, it does. You can use penguins as an analogy to this concept. Penguins contain warmth (energy, thermal energy) in a cold environment by clumping together. The more penguins, the more energy conserved and not lost to the environment. Let's say one penguin equates one carbon. In the context of a fatty acid, the more carbons you have, the more "stabilized" the fatty acid is. The net energy needed to break the carbon bonds would be higher, and the molecule will therefore have higher melting point (and less water solubility)."
Lipids,""Sequestering the fatty acid tails on the inside of a micelle frees up the water molecules, allowing the system to take on a greater number of microstates (that is, increasing its entropy)." But I would think that the water molecules aren't "freed up" because they'll just form a bond with the phosphate group...(the head group)

Or am i wrong? Thanks!","The bonds between H2O and phosphate are not permanent and not strong either. They are simply polar interactions. If micelle were not formed then more space is taken up by the hydrophobic parts which actually reduce entropy because water cannot do anything (bond) with unipolar things. With the micelle formation, there are more water molecules together which can rotate, move, and hydrogen bond to nearby water molecules, and this increases the entropy."
Lipids,"Are saturated fats in plants and unsaturated fats in animals, or the other way around?","Both plants and animals contain both saturated and unsaturated fats and the relative amount can vary depending on the species, tissue, and growth conditions of the organism.

In general, plant fats tend to be more unsaturated, while saturated fats are more common in animals.

You may find this wikipedia article to be a useful introduction to this subject:
https://en.wikipedia.org/wiki/Saturated_fat"
Lipids,Where does lipolysis fit into this?,Because fats are capable of being oxidised far more times than carbohydrates the majority of energy stores are kept in lipids throughout the body. Adipose tissue and adipocytes is an example of this.
Lipids,Out of curiosity are the "oils" secreted by your skin and hair also made up of fats?,And due to their oily nature most likely unsaturated/ short fatty acids!
Lipids,"what is the biochemical functions of all the soluble fats, that is vitamin A,D,E and K","Vitamin A
-you can get it from carrots, it's incredibly important for the photoreceptors in your eyes, without it you can't see.

Vitamin D
- necessary for proper bone and tooth mineralisation, your body can produce it if you have adequate UV/ sunlight intake otherwise you need to supplement it or you will get bone resorption which is not a good time.

Vitamin E
- shown to improve the reproductive system in rats, in humans however it is a very important antioxidant, takes radicals that would otherwise be harmful to the cells in the body out of circulation.

Vitamin K
- a very important clotting factor, helps you mitigate bleeding etc."
Lipids,Why do fatty acid tails provide us with so much energy when we eat them?,"This is a good question, but one that I think you have enough information to answer on your own.  Therefore, I'm going to ask you some questions in response to help you figure out (some of) the answers yourself.

*Answer #1*
What is the oxidation state of the carbons in the fatty acid tail?

How does this compare with the oxidation state of the carbon in carbohydrates (the other group of macromolecules that are often used to store energy)?

How would you expect this to affect a oxidative process like cellular respiration?


*Answer #2*
How many moles of carbon are present in a gram of tetradecane — a 14 carbon alkane (a reasonable comparison for the tails of the fatty acids found in food)?

How many moles of carbon are present in a gram of glucose (a "typical" carbohydrate)? 


Do the answers to those two sets of questions help you answer your question?


If you are not familiar with reduction and oxidation states, then I encourage you to start working through the Chemistry material on KhanAcademy: 
https://www.khanacademy.org/science/chemistry

That may look like a lot of work, but you've probably watched many of the videos already under "Chemistry of life". A deep understanding of chemistry is essential to anyone interested in modern biological sciences or medicine, so I really encourage you to take the time to work though all of the chemistry material."
Biological macromolecules review,"After reading the key terms, I am a little bit confused.. to my understanding, monomers are the makeup of polymers... is that correct? If so, are the terms "polymer" and "biological macromolecules" synonymous?","Hello,
As I understand it, polymers are a subdivision of biological macromolecules. 'Polymer' is the branch of macromolecules that is made up of ONLY ONE monomer that repeats itself.

For example, a carbohydrate is a macromolecule that is classified as a polymer because it is made up of repeating monosaccharides, but a fat (lipid) is a macromolecule that cannot be further classified because if you look under the 'monomers' column, it is built up by more than one monomer.

Hope this helped!"
Biological macromolecules review,Isn't protein an energy molecule for muscles?,"Rather than providing energy for muscles, they are structural components, which means they build and repair muscles. Protein is only used as energy if carbohydrates and lipids aren't available for energy (side note: breaking down protein for energy is unhealthy and dangerous!). 
Hope this helps, - Layla"
Biological macromolecules review,Are phospholipids polymers?,There is considerable interest in the polymers bearing phospholipids in the main chains as the structures of these polymers are similar to biological tissues. Several polymers containing a phospholipid in the polymer backbone have been synthesized and characterized
Biological macromolecules review,how can lipids act as a chemical messenger?,"Some lipids such as steroid hormones serve as chemical messengers between cells, tissues, and organs, and others communicate signals between biochemical systems within a single cell."
Biological macromolecules review,"Are monomers and monosacchrides the same thing? Also, what is a polypeptide?","Monomers are the building blocks of the four basic macromolecules of life- monosaccharides are the monomers of carbohydrates, amino acids are the monomers of proteins, glycerol/fatty acids are the monomers of lipids, and nucleotides are the monomers of DNA.

Polypeptides consist of a bunch of amino acids bound together- so in a way it's a monomer of proteins!"
Biological macromolecules review,Why aren't minerals a macromolecule?,"What are the characteristics of a macromolecule?

Can you think of a mineral that meets all those criteria?

Does that help you to answer your question?"
Biological macromolecules review,why are vitamins not digested in the body,"Vitamins are not digested, whereas, they are absorbed.

Vitamins are organic compounds that are required for normal animal metabolism but are either not created in the body or are created in insufficient amounts and must be received through your diet. Almost all of vitamin absorption goes to the small intestine.

Vitamin absorption in the intestine is important for avoiding deficiency disorders, and it can be limited by a variety of factors, including intestinal disease, genetic abnormalities in transport molecules, excessive alcohol use, and drug interactions."
Biological macromolecules review,"which would be the differences between DNA and RNA were not very clear to me, they seem technically the same and I cannot differentiate them very well","If you are asking what the difference between the two is, here you go.

There are several differences. To start, DNA stands for deoxyribonucleic acid, while RNA stands for ribonucleic acid. These names describe the sugar that makes up their backbone--DNA = deoxyribose and RNA = ribose.

Second, while each has four nucleiotide bases, there is one difference. You probably know that DNA has guanine, cytosine, adenine, and thymine, and that guanine links to cytosine and adenine links to thymine. But RNA doesn't have thymine. Instead, it has uracil, a nucleiotide base with a slightly different chemical makeup. Thymine had the chemical formula C5H6N2O2 and uracil is C4H4N2O2. Uracil links to adenine in RNA just like thymine does in DNA

Finally, DNA is double-stranded and forms a double helix structure. RNA is single-stranded and is generally straight. DNA is a complete set of instructions needed for life (unless you're a virus, but that's a whole different story/debate) and RNA is used to copy DNA and to synthesize proteins. I know this is a lot to take in, but there are several videos and articles on Khan Academy to help. Here are a few.

https://www.khanacademy.org/science/high-school-biology/hs-molecular-genetics/hs-rna-and-protein-synthesis/v/molecular-structure-of-rna

https://www.khanacademy.org/science/high-school-biology/hs-molecular-genetics/hs-rna-and-protein-synthesis/v/rna-transcription-and-translation

https://www.khanacademy.org/science/high-school-biology/hs-molecular-genetics/hs-rna-and-protein-synthesis/a/hs-rna-and-protein-synthesis-review

Anyway, this is probably a lot, but I hope it helps!"
Biological macromolecules review,How should I remember all these terms?,You gain familiarity through repetition. Practice is key.
Biological macromolecules review,whats the main difference between saturated and unsaturated fats,"From a chemistry perspective, saturated fats have no double bonds between carbon atoms, while unsaturated fats have one or more double bonds. 

From a state of matter standpoint, saturated fats are solid at room temperature, while unsaturated fats are liquid or soft.

From a nutritionist's point of view, saturated fats can increase the risk for heart disease (because it stays as a solid at room temperature and can lead to atherosclerosis) and unsaturated fats can help maintain proper bodily functioning (because they stay as a liquid at room temperature and are less likely to clog your arteries.)

I know you asked for a main difference, but I included three because there are many differences between saturated and unsaturated fats. I hope you have a better understanding of saturated and unsaturated fats."
Basics of enzyme kinetics graphs,""Conversely, for a competitive inhibitor, the reaction gets never reaches its normal V{max}" it's noncompetitve right?","Yes, you are absolutely right, I just fixed that and it should be reflected on the site soon. Thanks for your good eye!

Also, if you find other errors in the future, please don't hesitate to report them through the "report a mistake" button.

Thanks again!"
Basics of enzyme kinetics graphs,""An uncompetitive inhibitor reduces Vmax, but increases the apparent Km"... doesn't the uncompetitive inhibitor bind to the enzyme and enhancing its binding to the  substrate (higher affinity means lower Km)?","You're right, and it should be changed in the article. The apparent Km decreases in uncompetitive inhibition because by binding to the enzyme-substrate complex, uncompetitive inhibitors are "pulling" that complex out from the reactions. This removal of substrate decreases its concentration, and allows the remaining enzyme to work better. In general, a lower Km indicates better enzyme-substrate binding."
Basics of enzyme kinetics graphs,"Can someone please clarify why Km is always the same?  If i were to add more enzyme Vmax would increase and since Km is just 1/2 of Vmax, wouldn't Km increase as well?","Km is not 1/2 Vmax!

Km is the substrate concentration at which the initial reaction rate is equal to 1/2 Vmax.

One way to avoid this type of confusion is to note that the units are completely different."
Basics of enzyme kinetics graphs,"Super helpful article!!
Why does the Vmax occur at the same determined time interval each time in a reaction?","Because every enzyme has its kinetics and speed it can operate with.

Cars also take always the same time to reach Vmax if starting from zero speed (start)."
Basics of enzyme kinetics graphs,"I don´t understand the graphs.   What the curves show is a minimum rate of reaction   at minimum  substrate concentration ,  and maximum rate at higher concentrations, which is the opposite of the theory. If I want to plot rate vs concentration the curve should be a  kind of decreasing exponential function, with 0 rate at maximum concentrations. Im I wrong?","If I'm understanding you correctly I think you've got things backwards ...

You seem to be saying that according to theory the maximum reaction rate would occur when there was no substrate.  
Does that really make sense?"
Basics of enzyme kinetics graphs,"An irreversible inhibitor, wouldn't the number of enzymes available decrease, thus making it a noncompetitive inhibitor?","Yes, I believe you're right about that. I didn't think about that before!"
ATP and reaction coupling,Is it possible to run out of ATP?,"The cell also has in place mechanisms to stop this from happening. Like the enzyme phosphofructokinase (crazy name, I know) which is involved in the beginnings of glycolysis. Glycolysis is one of the early stages of making ATP from ADP. So, when there's more ADP around phosphofructokinase will work harder (which allows to the whole cycle to go faster, regenerating more ATP).  When there's a lot of ATP, though, phosphofructokinase (and other enzymes like it) will slow down. So basically, the cell has things set up carefully so that the right amount of ATP will be available (unless, as Laurent said, the cell is dying)."
ATP and reaction coupling,What happens with those -3kJ/mol from the formation of sucrose? Does it transform on heat?,"Yes, this 3 kJ/mol is released as heat that dissipates in the environment."
ATP and reaction coupling,"Where does the energy come from to synthesis ATP from ADP and P ?
is it when you couple the reaction that turns it back into ATP",It comes from oxidative phosphorylation at the end of the electron transport chain.
ATP and reaction coupling,"Why just ATP though? Why not TTP, CTP, or GTP as well? If it is possible with one nucleotide, why not the others?","All eukaryotic proteins use ATP for their respective energy requirements not TTP, CTP, or GTP. Also because ATP donates a phosphoryl group."
ATP and reaction coupling,Why do energy released by ATP under standard conditions at 25 °C is important if human body temperature is 36.5–37.5 °C ?,"It is used for standardization, 25°C is called "room temperature" and is used for lab experiments in test tubes rather then inside of your body."
ATP and reaction coupling,"Wouldn't ATP be more stable when the middle phosphates' charged oxygen was located above the phosphates, so the charges are further apart?","Single bonds rotate along their axis, so any drawing you might see of a molecule is, by all means, NOT set in stone. Yes, like charges move away from each other, when permitted, but we usually don't draw it like that, for the sake of consistency."
ATP and reaction coupling,"When it is said "ATP releases energy", I would imagine something imaginary (kinda like a wave) travelling to help in creating another bond.

Energy is not created nor destroyed. At the end of the reaction above:
3K. energy transferred as heat.

The reaction glucose + fructose requires 27K.
As I said I used to imagine some imaginary wave, instead I'm thinking now that when ATP gives this 27K. it does this by creating instability, and we classify it as giving energy. Is this true?

If true, then theoretically can't phosphate, without being part of ATP, just 'run' around the cell and just keep creating instability (sounds like unlimited free energy). Why does it have to be reattached to ADP to form ATP again? Is it because inorganic phosphate is not unstable enough?

If not true then what is this 27K. energy represented by?","It is not ATP itself that releases energy, and also not the bond to the final phosphate bond being broken. If you think about it, you actually need energy to break any bonds, including that one (otherwise it would fall appart and not be a bond that keeps atoms together!). The energy is actually from _hydrolyising_ ATP, ie breaking that bond, but also forming new ones. The products ADP and inorganic phosphate are lower in (potential) energy than ATP. (This has several reasons, and isn't as simple as counting bonds and expecting them to have the same energies as in other molecules, but also that having a solvated inorganic phosphate is more entropically favourable). So, the ATP reaction wants to move in the ADP+ Pi direction. But you can't just do that and hope it magically drives another reaction in reverse/uphill. What often happens, is that ATP will react with the reactants of the other reaction, some steps occur converting reactant to product, and in the end ADP and Pi are released. Each step turns out energetically favourable, driven forward by a loss in free energy, and by the end you have converted reactants to products in a reaction that would not normally go forwards on its own by allowing ATP to drop from a high energy to low energy. Does this help explain?"
ATP and reaction coupling,"Could someone explain what "ΔG" is? I know it means something like "free energy", but I can't find any good articles about what it really is.","Delta G is really Gibb's Free Energy. If Delta G is less than 0, the reaction is spontaneous. If not, the reaction is not spontaneous. I encourage you to watch https://www.khanacademy.org/science/biology/energy-and-enzymes/free-energy-tutorial/v/gibbs-free-energy-and-spontaneous-reactions"
Types of energy,"ummmm i'm still a little confuse with "thermal and kinetic energy" so thermal is a form of kinetic energy,so thermal and kinetic are the same?!","Thermal energy is energy in disorderly motion - everything is moving in random directions. When people talk about "kinetic energy", they usually mean energy in orderly motion - everything moving in the same direction. The meaning of "orderly" can be a bit subjective, usually depending on how closely you're looking at the particles."
Types of energy,does ATP have kinetic or potential energy ?,"ATP has potential energy in the bonds between the phosphates. If an ATP molecule is used, one phosphate is 'broken' off and so the bond between the phosphates is broken. There was energy stored in this bond, which is then used to do numerous kinds of things in your body. This energy can be used to move things (kinetic energy).

Hope this helps!"
Types of energy,"In cameras, the chemical potential energy (battery) is converted to electrical energy (camera circuit). Then, what is this electrical energy converted to when I take a photo?

Thanks!","In the camera, as well in many machines you don't use the electron energy, but only the energy that pushes the electrons on the pathway. The electrons are only the carriers of the energy. But the internal energies of the electrons are not used (yet). Many persons don't fit on this: electric energy is not the energy of the electron: is the kinetic energy that is transformed from waterfalls (hydrelectric), thermoelectric generators, etc, that put potential energy and the potential energy difference (Volt) to electron movements. So, the machines uses that energy transforming into its uses (mechanical movement of the obturator, the digital LCD that guide you to take a best picture, etc. But the image reception occur with other source: the photossensitivity of many microLEDs with special features of transform photonic energy into voltage (potential energy diference), and that send to the microprocessor to calculate the spatial position of each microreceptiveLED, its voltage intensity  to bright. Color is a more complex understanding and I will not explain here :)"
Types of energy,If I light a candle but the flame isn't moving will it have kinetic or potential energy?,A flame is chemical energy caused by rapid oxidation of a fuel.
Types of energy,"Sorry I don't understand this line "Another example of kinetic energy is the energy associated with the constant, random bouncing of atoms or molecules" how it is kinetic and constant ?","Kinetic energy basically means movement. As the particles are in motion (which is perceived as pressure or temperature), it is considered as kinetic energy. The second part of your question can be explained by taking our own example. You and I are surrounded by air (hopefully ;)  ). This air vibrates, unevenly, or evenly to produce sound in the form of kinetic energy which our ears feel. The pressure can be felt underwater or if we are in a falling motion, that is, the wind hits your face. Hope this helps ;)"
Types of energy,Why can chemical energy be kinetic and potential?,Potential energy arises from the electrostatic energy in chemical bonding. Kinetic energy of molecules in chemicals arises because molecules are always constantly jiggling around.
Types of energy,I am a bit lost. I'm looking for how to find the kinetic and potential energy of something. Does anyone know where to find that?,"Kinetic energy: 1/2*m*v^2
GPE: m*g*change in height(delta h)
and theres also spring potential energy, which i forgot the formula for
Sal explained this in the work and energy chapter. watch his videos to learn more"
Types of energy,"Are there other types of energy? If they are, what are they?","Yes, there are, here are some I know: Potential energy, kinetic energy, rotational kinetic energy, radiant energy, thermal energy. There are more though."
Activation energy,what is the defination of activation energy?,"The official definition of activation energy is a bit complicated and involves some calculus. But to simplify it:
 
Activation energy is the minimum energy required to cause a process (such as a chemical reaction) to occur."
Activation energy,"I thought an energy-releasing reaction was called an exothermic reaction and a reaction that takes in energy is endothermic. In the article, it defines them as exergonic and endergonic. Are they the same?",Exothermic and endothermic refer to specifically heat. Exergonic and endergonic refer to energy in general.
Activation energy,"When mentioning activation energy: energy must be an input in order to start the reaction, but is more energy released during the bonding of the atoms compared to the required activation energy? Can the energy be harnessed in an industrial setting?","In an exothermic reaction, the energy is released in the form of heat, and in an industrial setting, this may save on heating bills, though the effect for most reactions does not provide the right amount energy to heat the mixture to exactly the right temperature. Often the mixture will need to be either cooled or heated continuously to maintain the optimum temperature for that particular reaction. For endothermic reactions heat is absorbed from the environment and so the mixture will need heating to be maintained at the right temperature. By right temperature, I mean that which optimises both equilibrium position and resultant yield, which can sometimes be a compromise, in the case of endothermic reactions."
Activation energy,"I don't get this. If a molecule has more activation energy, shouldn't it be more likely to reach the high barrier required and complete the chemical reaction faster? If I have more energy when I wake up, it is easier to get out of bed and it takes me less time to do so. Shouldn't chemical reactions be the same?","yeah, like amathakbari said-activation energy is the amount of energy needed to activate the complex that ocurrs at the transition state. it isn't energy you have"
Activation energy,What is the activation energy of the reaction?,Activation energy is the amount of energy needed to initiate a reaction.
Activation energy,can a product go back to a reactant after going through activation energy hump? (sorry if my question makes no sense; I don't know a lot of chemistry),"Theoretically yes, but practically no.
So this concept can be visualized with combustion or fire. While wood does not spontaneously burst into flame, if you add additional energy, with a match for an example, to the pile of wood, it starts a fire. What happens is that the energy in the match pushes the wood over the activation energy hump and starts the fire. Afterwards, the fire is self-sustaining because the fire creates enough heat to activate the rest of the wood.

Chemically, wood is composed of mostly carbon, which reacts with the oxygen in the air when 'activated' to create carbon dioxide.
So, for this reaction, carbon is the reactant and carbon dioxide is the product, which can be converted back into carbon (like photosynthesis) but requires more energy to do so.

The bottom line is that while it is possible, it will (in general) require additional energy to go back from a product to a reactant"
Activation energy,"Is there a difference between the terms endothermic/exothermic reaction and endergonic/exergonic reaction?

I only learned endothermic and exothermic as a reaction that stores energy and a reaction that releases energy.","Endothermic and exothermic refers to sign of the enthalpy of a reaction. Whether the net enthalpy change is positive or negative respectively. Where enthalpy is equivalent to heat.

 Endergonic and exergonic refers to the sign of the Gibbs free energy of a reaction. Whether the net free energy change is positive or negative respectively. Free energy taking into consideration both the enthalpy and entropy change of a reaction. 

Hope that helps."
Enzyme regulation,Allosteric regulation confuses me a lot. I don't really get it even after I watched the video on Khan Academy (MCAT) . Can anyone explain it to me briefly?,"I'll try an analogy — let me know if this helps.

Imagine that an enzyme is like tiny sculpture made from a wire twisted into a very complicated, but somewhat loose structure.  
The substrate is another much smaller sculpture that fits into a gap in the first sculpture — let's say it fits perfectly.
 Now think of hanging a weight off another part of the sculpture — the whole structure shifts a bit under the strain and now the substrate sculpture doesn't fit!   In this situation the weight would be analogous to an allosteric inhibitor. 

You could also imagine a similar scenario, but with the substrate fitting poorly until you added a weight — in this case the weight would be analogous to an allosteric activator."
Enzyme regulation,whats the difference between non competitive inhibition and allosteric regulation(involving inhibitor)? .its all so confusing,"Allosteric regulation and noncompetitive inhibitor bind to site other than active site but allosteric regulation change the conformation of enzyme and making the reaction less effective while the noncompetitive inhibitor, like mention in the reading just poison the enzyme so reaction does not take place at all."
Enzyme regulation,"In school, we conducted an experiment where a small piece of paper dipped in a liver solution was dropped into a test tube filled with hydrogen peroxide. After a few seconds, the liver juice coated paper rose to the the top. Why did it act in that way?","This is because the liver cells contain enzymes called catalase which speed up the breaking down of hydrogen peroxide into water and oxygen. When the reaction happens, oxygen is released and it pushes the piece of paper up to the surface along with it. This reaction happens faster or slower depending on the concentration of the liver juice you soaked the paper with."
Enzyme regulation,"if a allosteric inhibitor casues distortion of the enzyme's shape so that it cannot function, is it non-competitive or competitive?
(i looked up many resources ,such as princeton review AP bio,Barrons, internet, but they all weren't clear)","Being *allosteric* lets you know that the inhibitor binds somewhere other than the *active site*, where the substrate binds. The location that the allosteric inhibitor binds is called the *allosteric site*.

Because it isn't "competing" for the same binding site as the substrate, you can tell that it is non-competitive as the substrate will still be able to bond at the active site."
Enzyme regulation,what would happen if our bodies do not have inhibitors?,"*Good question*

Than uncontrolled cell divisions, uncontrolled sugar breakdowns, uncontrolled and unlimited phosphorylations (until the moment of using up all resources) and ultimately leading to energy depletion and death.

It may cause a ruckus in the body and high dysregulation which would end up fatal."
Enzyme regulation,What is an allosteric activator?,"A molecule that attaches to the enzyme at a site (not the active site), changing the configuration of the enzyme, which allows the substrate to attach to the active site easier."
Enzyme regulation,"Life is a process regulated by enzymes. What might be the sources of these enzymes? If particular enzyme is not available in person's cells, what sequence of events might result to produce it?","Enzymes are encoded as genes in the DNA — these genes are then transcribed to produce RNA and (for most enzymes§) then translated† to make a protein that has a catalytic activity (i.e. is an enzyme).

Typically enzymes found within a cell are encoded by the DNA of that cell.  However, multicellular organisms are colonized by many different microbes (these may be prokaryotes or other eukaryotes such as fungi) — these microbes often supply enzyme activities that aid the organism.  The digestive system of animals is one example of this.  In fact, most multicellular organisms depend on their microbiota for survival!

The process of regulating gene expression is highly complex, but there is KhanAcademy material on this is several places — I recommend starting here:
https://www.khanacademy.org/science/biology/gene-regulation

§Note: Some enzymes are make of RNA and these RNAs do not get translated.

†Note: Many proteins undergo post-translational modifications that are essential for them to function."
Enzyme regulation,"The information about noncompetitive inhibitors contradicts what Sal said in his videos: "Competitive Inhibition" and "Noncompetitive Inhibition"

What is described here as noncompetitive inhibition, Sal explains as allosteric. Sal has an entirely new definition for noncompetitive inhibition, describing it as a phenomena where the inhibitor and substrate can both bind.

I'm confused, someone please clear this up for me.","I think Sal is right about Competitive Allosteric Inhibition. In CAI, the inhibitor binds to an allosteric site (somewhere on the enzyme that is not an active site) and PREVENTS the substrate from binding in the first place. In non-competitive inhibition, the binding of the inhibitor still allows the binding of the substrate - the catalysis just doesn't work. 
The short answer is: CAI is competitive because only one thing, be it substrate or inhibitor, can bind to the enzyme.Non-competitive inhibition lets two things bind to the enzyme.
(I think Sal didn't write this article.)"
Enzyme regulation,How do you determine whether an enzyme's activity is enhanced or inhibited by regulatory cell binding?,"You follow up with the next steps. If reactions proceeds - it was activation, otherwise it must be some kind of inhibitor. :D"
Overview of metabolism,"I'm curious about how ATP ended up being the energy currency for both plants and animals, why the same molecule? Is because of a common ancestor?
Is there any cell that doesn't use ATP as its "energy currency"?","Yes, it is because of the common ancestor. If there was a different, more efficient molecule then this would have been used instead. Keep in mind that in the long run only the most effective processes and molecules can transferred by generations."
Overview of metabolism,Why is it that ATP happens to resemble an adenine base in DNA? Are they related in any way beyond structure? Is the adenine base special? Is there another energy currency molecule like ATP? Can we artificially create another energy currency molecule?,"Both ATP and DNA are nucleic acids. All nucleic acids have 3 parts.
1. A pentose sugar(A sugar with 5 carbon molecules)
2. Phosphate group(s)
3. A nitrogen base. DNA and ATP have the same nitrogen base- Adenine, present.

ATP is specially called an energy currency because it has an easily breakable bond between 2 of its phosphate groups. There are several other triphosphate molecules present in cells like GTP and CTP that play various roles, but ATP is the main 'energy trading' molecule. 
Triphosphate molecules can be synthetically created under the right conditions, our cells will still rely on ATP."
Overview of metabolism,What is ADP (adenosine diphosphate)? How is it different from ATP?,"ADP is adenosine diphosphate 
and
ATP is adenosine triphosphate

In ADP there is 2 phosphate molecules
In ATP there is 3 phosphate molecules"
Overview of metabolism,"How can a molecule be "worn out"...? Does he mean they've outgrown their usefulness, or that they actually lose hydrogens or their groups come apart somehow over time?","Good question... they don't truly mean "worn out" as I think you are thinking... I think what they mean is that a molecule such as glucose gets broken down a few times to harvest some energy in the form of ATP... and then another molecule such as pyruvate, for instance, enters another metabolic process for recycling, harvesting both energy, and the use of the carbons for other purposes. See the citric acid cycle and this will start to make more sense ( https://www.khanacademy.org/science/biology/cellular-respiration-and-fermentation/pyruvate-oxidation-and-the-citric-acid-cycle/v/krebs-citric-acid-cycle )... but you are right... "worn-down" is confusing wording."
Overview of metabolism,"Does metabolism vary widely between people? I have heard that it does not, but it would seem that it would be highly dependent on the weight of an individual.","yes, it does, because you could have an illness and because of this illness one of your hormones gets produced more or less. And so your metabolism would be regulated as faster or slower."
Overview of metabolism,"Are ADP/ATP reusable? What I mean is, once ATP released its energy, does it transform back to ADP? If yes can this ADP be used again to form back ATP?","This is an essential cycle that never stops until you die: ADP gets phosphorylated in the mitochondria, storing energy in ATP, and the ATP gets used to perform cellular work, releasing its energy in coupled reactions, and transforming back to ADP."
Overview of metabolism,"So basically, Metabolism is the core of a cell. It's where all the work happens right?",Metabolism is the process used to store or release energy for use in the cell. It allows other essential chemical reactions to happen. it is the basis for all the work in cell. Try to think of it as a process not an area where reactions happen
Overview of metabolism,How energy is transfered from cellular respiration to the process that formats ATP. Is it in heat? If so doesnt it affect other molecules in the area? Thanks,"The majority of ATP is generated through ATP synthase at the end of the electron transport chain. In this process, a concentration gradient of protons (H+) is what is used to drive ATP synthase, not heat."
Overview of metabolism,Is the convergence of glucose to glycogen considered anabolism ?,"Yes - this is an anabolic process, promoted by the action of insulin on the hepatocyte or myocyte. The reverse - i.e. the hydrolysis of glycogen back into glucose-1-phosphate - is a catabolic process."
The laws of thermodynamics,I still can't understand why heat is considered unusable energy? Why cant heat which is the kinetic energy of particles be transformed to another type of enegry that can be used?,"There is a device called a thermocouple which converts heat to electricity. However, you do have to have one end of the thermocouple in something colder than the heat source."
The laws of thermodynamics,Friction leads to entropy?,Yes. This generates heat (thermal energy) that in turn leads to a increase in entropy.
The laws of thermodynamics,"When it is said that some o the energy converts to unusable energy, it means unusable right know due to limited tecnology? or is it never going to be usable? (I'm not sure why molecular kinnetic energy could no be used)","That heat(that is no more in a closed system) is not usable because it can not be converted to other form of energy, and this is because it can not be ''captured/collected''.
  The heat is not kinnetic energy itself, Its what causes kinnetic energy (the movement)."
The laws of thermodynamics,"This might sound a bit gruesome, but do dead organisms also increase entropy of the universe?","Yes, actually. There’s a related thermodynamic concept known as equilibrium which all reactions, including biological reactions in organisms, try to reach. Going to equilibrium means a reaction is trying to maximize the increase in entropy to the universe. Organisms spend their whole lives trying to fight this equilibrium since maximizing entropy runs counter to a functioning complex living thing. 

It is possible for an organism to decrease the entropy in itself by using an input of energy because it corresponds to an increase in the entropy of the environment and a net change is an increase of the universe’s entropy. That’s really the main thermodynamic reason all organisms have to eat and consume energy, to obstruct all the life sustaining reactions from going to equilibrium. Once an organism dies, it can no longer resist equilibrium and all of the matter and energy of the once living organism disperses which causes an increase to the entropy of the universe. 

Hope that helps."
The laws of thermodynamics,"Everything posted has been very helpful and I thank you all . Since energy cannot be created or destroyed and it can only change form or be transferred from one object to another, can we not consider the sun as the "factory" of energy and if not where does the sun receive his energy from?","Nuclear fusion, the forces in the nucleus are transformed into energy. https://www.euro-fusion.org/faq/how-is-it-that-both-fission-and-fusion-produce-power-if-splitting-a-large-atom-into-two-smaller-atoms-releases-energy-it-seems-that-combining-two-smaller-atoms-into-one-larger-atom-would-require-ene/"
The laws of thermodynamics,Is there a formula or unit of measurement for entropy? Can we measure it in Joules or Kelvin/unit area?,"joules per kelvin
and it can get really tricky bc im pretty sure enthalpy is kilojoules/kelvin :)"
The laws of thermodynamics,Is computer considered as a closed system?,"No, a computer gives off heat. Think of it this way: when the computer whirrs, that means the fan is going. If you put your hand near the fan, you can feel the heat. Therefore, the computer is giving off heat. Not to mention it's gaining electrical energy from the outlet or whatever the computer is plugged into."
The laws of thermodynamics,"Regarding Entropy, do we know what is order is and where it comes from, or is it like Energy (we know what it does but as Feynman says that no one knows what energy is)?","I'm assuming you're asking about the opposite of entropy.  Technically, order can be measured as negentrophy (literally _negative entropy_), but it essentially just the reverse measurement of the entropy of a system and is of limited use.
   In regard to the origin of order, it can be assumed that since entropy increases as you follow the arrow of time, it must decrease as you follow it in the opposite direction. Since the universe is believed to have begun with a "big bang" resulting in a massive amount of entropy, it could hypothetically be assumed that the closest the universe has ever come to "order" was at same point before that. However, that is purely hypothetical. Assuming the currently popular model of a random universe, we would not expect order anyway, presumably negating the need for a real measurement of it. 

Hope that helped!"
The laws of thermodynamics,Can heat be turned back into usable energy?,Heat can be used to produce energy if there is a lower temperature system to transfer that energy to.
Enzymes and the active site,What would happen if the shape of the enzyme's active site were changed?,"If the active site were changed, possibly by a large change in temperature or pH, the enzyme would most likely not be able to catalyze the same reactions. This is because temperature and pH can denature (or change) and enzyme's shape and therefore make it unable to bind with the same specifically shaped substrates as before."
Enzymes and the active site,Which type of bond exists between enzyme and the substrate in enzyme substrate complex?,"Generally, they are ionic bonds or van der Waals forces (hydrogen bonds, London dispersion forces, and dipole-dipole interactions). They can occasionally be covalent bonds."
Enzymes and the active site,"Hi, I think there's a mistake in the text. Or perhaps I don't understand it. There's written "Instead, enzymes lower the energy of the transition state, an unstable state that products must pass through in order to become reactants". Products become reactants? Isn't it supposed to be the other way around? That reactants become products. I don't know.",yeah its probably a typo
Enzymes and the active site,what exactly are activated co enzymes,"(Activated) Coenzymes are small molecules. They cannot by themselves catalyze a reaction but they can help enzymes to do so. Enzymes are biological catalyst that do not react themselves but instead speed up a reaction.
So, a coenzyme activates the enzyme to speed up a (biological) reaction."
Enzymes and the active site,How does RNA catalyze a reaction?,"RNA molecules that can function as enzymes are known as ribozymes. RNA can have 3 dimensional structure because it can hydrogen-bond with itself and form loops. Some of the bases in the RNA have special functional groups which can add specificity to the shape. The RNA can also hydrogen-bond with other nucleic acids to create an even more specific shape.
 
One example ribosomal RNA, which can catalyze the translation of mRNA in ribosomes. In ribosomes, rRNA and proteins come together and form a space for messenger RNA to be read and for transfer RNA to bond to the ribosome and attach the correct amino acid. The specific shape of the rRNA allow the mRNA to be translated properly."
Enzymes and the active site,"Can you give me an example of a catalyst that is not an enzyme?
Many thanks!","Metals like rhodium and platinum are used as catalysts in catalytic converters, which lower dangerous emissions from cars. In the presence of these catalysts, nitrogen oxide, a dangerous substance, is broken into nitrogen and oxygen, both harmless."
Enzymes and the active site,enzymes have an active site that does all the actual work. but what is the function of the rest of the molecule? why it still exists? what is the evolutionary role of it?,"In general terms, the rest of the enzyme molecule is there to ensure that the active site contains the right amino acids in exactly the right orientation relative to one another.

Let's say that the active site needs three specific amino acids lined up in a very defined way. The rest of the molecule provides a framework (scaffolding, if you like) that ensures the active site is properly set up. Without this framework there would be no way of fixing the key amino acids into the correct positions.

Also, the critical amino acids may be a long way apart from one another in the primary sequence of the protein and are only brought together through the secondary and tertiary structuring of the protein.

What's more, with the induced fit model, the rest of the molecule can be involved in changing the confirmation of the enzyme. Related to this is enzyme regulation where modification of an amino acid remote from the active site can control the activity of the enzyme. Furthermore, in some enzymes there is a second binding site and when something, such as an inhibitor, binds to that site it changes the shape of the active site, also controlling the enzyme."
Enzymes and the active site,How do enzymes enable chemical reaction to take place rapidly ?,"They offer an alternative reaction pathway that has a lower activation energy i.e. less energy is required for the reaction to occur. Therefore, more particles will have the required energy, and more particles can react at the same time, thus increasing the reaction speed."
Enzymes and the active site,How do inhibitors stop enzyme activities?,"There are four different kinds of inhibitors; *competitive inhibitors, noncompetitive inhibitors (allosteric inhibitors), irreversible inhibitors*, and *feedback inhibitors*. 

*Competitive inhibitors* compete with the _substrates_ of an enzyme at its _active site_. When they bind to the active site of the enzyme, they prevent the enzyme from breaking or creating molecules. 

*Noncompetitive inhibitors*, also known as *allosteric inhibitors*, do not compete with substrates for the active site. Rather they bind to a different area on the enzyme. This area is known as the _allosteric site_. When the inhibitor binds to the allosteric site, it causes a _conformational shape change_, preventing the enzyme's substrates from attaching to it. Thus preventing the breakdown or formation of a molecule.

*Irreversible inhibitors* have two forms; *irreversible competitive inhibitors* or *irreversible noncompetitive inhibitors*. These inhibitors either bind to the _active_ or _allosteric site_ of an enzyme. 

*Feedback inhibitors* are the end products of reactions. They interfere with the enzyme that helped produce them. They bind to the _allosteric site_ of the enzyme changing the shape of the enzyme. They usually help in _regulating_ and _coordinating the products_ of an enzyme."
Enzymes and the active site,Rather than the environmental pH. Does the pH of the substrate also causes a change in it's active site?,"Okay, so pH is actually defined based on the concentration of H+ in a given volume. So the substrate doesn't have a pH. Many molecules of the substrate dissolved in water do have a pH, but an individual molecule? Nah. The substrate does have different polarities (positive and negative charged areas) but the enzyme is built to handle that. These differently charged regions help the substrate lock in place."
Free energy,"Why is it that in Spontaneity of Forward and Reverse Reactions, the change in G for both the forward and reverse reactions is equal to +7.3 kcal/mol? Aren't the signs supposed to be opposite? And isn't the change in G supposed to be positive for endergonic and negative for exergonic? Wouldn't a positive change in G for an exergonic reaction go against the Laws of Gibbs Free Energy Change?","I thought the same as you. Think it's an error. The second part of explanation (i.e. ATP + H2O -> ADP + Pi) is exergonic, so it should be -7.3kcal/mol"
Free energy,Why is it called free energy instead of available energy?,"It is the amount of work a thermodynamic system can perform. It is _free_ to do any work, i.e. the internal energy minus any energy that is unavailable to perform work."
Free energy,Is Gibbs Free Energy a type of potential energy?,"Nope! Gibb's free energy is the fancy name for a calculation that tells you if a reaction will go spontaneously, and if not, the amount of energy you'd need to put into a system to get that reaction to happen."
Free energy,What is the definition of Gibbs Free Energy?,""A thermodynamic quantity equal to the enthalpy (of a system or process) minus the product of the entropy and the absolute temperature."

Origin
named after J. W. Gibbs (see Gibbs, Josiah Willard)."
Free energy,"When the reaction is an endergonic one, does it mean that it will not happen? And do reactions which decrease entropy(with the change of entropy <0) increase the overall entropy of the surroundings and the universe? Thank you!","When a reaction is endergonic, it means that the reaction will not happen _spontaneously_, but may happen if there were some changes in energy. 

Reactions that decrease entropy, if spontaneous (meaning that if they are exothermic and happen at a low temperature), will increase the overall entropy of the universe because heat is released. This is because  of the second law of thermodynamics, which states that the entropy of the universe increases with any spontaneous process. 

Think of it like this: The universe includes both the system's disorder and the disorder of the surroundings. Thus, a spontaneous process can occur, in which the system becomes more ordered (meaning entropy decreases), only if the entropy increase in the surroundings is greater.  For example, when ice freezes below 0 degrees Celcius, the liquid water goes to a more ordered solid state.  That is, the system loses entropy. However, as the ice freezes, heat is given off the surroundings.  This heat flow increases random motion of molecules in the surroundings and increases the entropy of the surroundings. So in the system, even though entropy decreases, the entropy of the surroundings and universe increase. 

However, just to reiterate, this is only for reactions that are spontaneous. A non-spontaneous reaction that is decreasing the entropy of the system will decrease the entropy the universe because the reverse reaction is spontaneous (and will therefore increase the entropy of the universe)."
Free energy,Is free energy useful energy that can do work and don't include the heat ? Because heat is not as useful like other energy ( potential energy in chemical bonds... ),"Heat can be useec to do work. For example, a steam engine can use heat energy in steam to move pistons. However, heat is transferred to the surroundings and so the general entropy is increased.

Some say that this release of heat will lead to the `heat death of the Universe', as there is no more general movement for the heat to go. Thus you are partly right."
Free energy,"What does Sal mean by the term "spontaneous"?
Is the scientific meaning different to the everyday meaning?",In german we call this process 'unsolicited'. That means the process needs no specific catalyst or starting event to occur. It just happens by itself once the conditions are right.
Free energy,"hi all, I am very confused by is the standard temperature here 25°C? shouldn't "standard" be strictly 0°C?

Thank you all!","Standard conditions for biochemistry refer to a set of specific conditions that are used as a reference point to ensure consistency and accuracy in biochemical experiments. These conditions include a temperature of 25°C, pH of 7.0, and a concentration of 1.0 M of all ions present in the reaction. By using these standard conditions, scientists can compare and replicate results across different experiments and laboratories, which is crucial for advancing our understanding of biochemistry and developing new treatments for diseases."
Free energy,"Uma reação bioquímica onde o delta G é igual a zero, é considerada endergônica ou exergônica? Por exemplo a oxidação da Succinato à Fumarato pela succinato-desidrogenase, o delta G é igual a zero, essa reação é considerada uma reação endergônica ou exergônica?","Just so you know translated (to English it comes out to...) "A biochemical reaction where delta G is equal to zero, is it considered energonic or exergonic? For example, the oxidation of Succinate to Fumarate by succinate dehydrogenase, delta G is equal to zero, is this reaction considered an energonic or exergonic reaction?""
Free energy,what is free energy,"free energy is energy that can do work when temperature and pressure are uniform, as in a living cell"
Prokaryotic cells,Are red blood cells considered to be prokaryotic since they don't have a nucleus?,They are considered Eukaryots. They loose the nucleus when they mature and many non-vertebrates have erythrocytes with a nucleus.
Prokaryotic cells,How do prokaryotes get rid of waste?,"Prokaryotes use the process of diffusion, to either take in (endo) or release (exo), materials through their semi-permeable plasma membrane. Now you might say, what about their cell wall, the cell wall must be stopping these materials. Well actually, the cell wall (made of peptidogylcan in bacteria) is fully permeable, as it's role is not to stop materials from going in or out. It's function is to give support to the cell, which is why it is rigid but fully permeable, thereby allowing exchange of materials. Hope this helps!"
Prokaryotic cells,Do humans have prokaryotic cells in their bodies,"Humans do have bacteria in their saliva and stomach that we use to break down things we need, but we can't make that ourselves. So technically there is some in our bodies, we just didn't make it."
Prokaryotic cells,What makes Trichodina different from all prokaryotes?,"Trichodina is considered Eukaryotic protozoa -meaning it has a nucleus.


That sets its apart from all Prokaryotes.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3750665/
https://elps.eastlongmeadowma.gov/files/9214/3525/7686/MCAS_review_packet_1.pdf"
Prokaryotic cells,"From paragraph 10 to 16, I still don't get idea of surface-area-to-volume.","If you're still confused, you can watch the video "cell size""
Prokaryotic cells,Why is the flagellum only in the prokaryotic cells and not in the eukaryotic cells?,Eukaryotic cells they do have flagella (only one: Sperm cells) but they have a different composition
Prokaryotic cells,are there are any multi celluler prokaryotic,"No, there are not known multicellular Prokaryotes. Distinguishing characteristic among Eukaryote and Prokaryote Domains is being unicellular or multicellular."
Prokaryotic cells,what cell is used by prokaryotic cells and some other single celled organisms for movement.,"Flagella:
 are whip-like structures that act as rotary motors to help bacteria move.
Pili:
Rod like structures
 Fimbriae :
are numerous, hair-like structures that are used for attachment to host cells and other surfaces."
Prokaryotic cells,How does the eukaryotic cell size impact the cell's ability to tranport materials into and out of the cell?,"Cell size does not have much impact on the transport - what really has impact is proximity to the next cell, the junctions between cells in the epithelial tissue and the shape of the cell (the more circular cell the greater surface vs volume ratio)."
Prokaryotic cells,Do I have to memorize all of this or just stick up with the -Prokaryotes and eukaryotes review-,"*You can do whatever you want to do when it comes to your learning*. If you want to study the major highlights of the unit, then go look at the Prokaryotes and Eukaryotes Review. If you want to have a better understanding of prokaryotes in a more detailed sense, then I guess "memorize all of this" in this article. Or if you want to understand prokaryotes a little bit more and then look at an overall review, then do it! 

But *please* don't make it about energy points. Even though the perks are nice (or was nice--I still miss backgrounds) and it's soo satisfying to see that blue check mark after you read a long article or watched a long video, that's a secondary priority. Your first priority on this website (I hope it's your first priority) is to learn.

I want you to know that *no one* is stopping you from *doing what you need to do* when learning. After all, learning all of this information on Khan Academy is for _your benefit_, not someone elses's. So learn however you want to, as long as you feel like _you're_ learning! I wish you *all the best* in your learning journey. :)"
Plasma membrane and cytoplasm,What is meant by fluidity of cell membrane? How is it regulated?,"Nice question!
A membrane is not a rigid structure. It is fluid and is able to move which actually gives it more stability. As an analogy, think of your skin that is solid but is still able to move.
As for regulation: there are far too many pathways and factors to list. Heat and pressure for example can increase the fluidity, drugs and medication can do the same, cholesterol can be a bidirectional regulator, etc..."
Plasma membrane and cytoplasm,what is chemistry behind each function of cytoplasm?,Colloidal solution
Plasma membrane and cytoplasm,are the organelus full of the same cytosol as the rest of the cell?,"Partially. The ion ratios are usually the same (except for sarcoplasmic reticulum which stores Ca and results in high concentrations of Ca inside). Also it depends what the function of organelle is.

Peroxisomes are known to have lower pH and lots of peroxidase enzymes since they catalyze oxidation reactions."
Plasma membrane and cytoplasm,Is cytoplasm the same thing as cytosol?,Cytosol is the specific liquid  within the cytoplasm. Cytosol is a component of the cytoplasm like lysozymes and cellular structures are part of the cytoplasm.
Plasma membrane and cytoplasm,Why do polar molecules have more trouble getting through the phospholipid bilayer than non-polar molecules? Wouldn't the hydrophilic head mean that it attracts polar molecules?,"The hydrophilic head does interact with polar molecules, but the double layer of non-polar lipids between the heads prevents the polar molecules from passing through easily."
Plasma membrane and cytoplasm,Does nucleoid have a membrane ?,"No, the nucleoids of prokaryotic cells do not have membranes. In fact, prokaryotic cells do not have membrane-bound organelles whatsoever."
Plasma membrane and cytoplasm,"If any of you guys know freeze fracturing, can you help me:
Why are the pits and mounds of the membrane interior significant in understanding the structure of the membrane","The cell membrane is composed of 3 types of lipids. One of the chemicals which make up phospholipid heads is alcohol glycerol.


That glycerol is so important in case of the freezing cell because it acts as antifreeze.

So why, do our cells freeze, why humans die if left in cold environment?

Because _our_ cells have minimal content of glycerol, not enough to protect us. Usually, ice crystals form in our cells from all the water content in it."
Nucleus and ribosomes,Are translation and protein synthesis the same thing?,"Not quite, translation is part of protein synthesis"
Nucleus and ribosomes,What does RNA do?,"1. Messenger RNA (mRNA) carries the genetic information copied from DNA in the form of a series of three-base code “words,” each of which specifies a particular amino acid.

2. Transfer RNA (tRNA) is the key to deciphering the code words in mRNA. Each type of amino acid has its own type of tRNA, which binds it and carries it to the growing end of a polypeptide chain if the next code word on mRNA calls for it. The correct tRNA with its attached amino acid is selected at each step because each specific tRNA molecule contains a three-base sequence that can base-pair with its complementary code word in the mRNA.

3. Ribosomal RNA (rRNA) associates with a set of proteins to form ribosomes. These complex structures, which physically move along an mRNA molecule, catalyze the assembly of amino acids into protein chains. They also bind tRNAs and various accessory molecules necessary for protein synthesis. Ribosomes are composed of a large and small subunit, each of which contains its own rRNA molecule or molecules.

Translation is the whole process by which the base sequence of an mRNA is used to order and to join the amino acids in a protein. The three types of RNA participate in this essential protein-synthesizing pathway in all cells; in fact, the development of the three distinct functions of RNA was probably the molecular key to the origin of life. How each RNA carries out its specific task is discussed in this section, while the biochemical events in protein synthesis and the required protein factors are described in the final section of the chapter.

All credit goes to: https://www.ncbi.nlm.nih.gov/books/NBK21603/"
Nucleus and ribosomes,can we compare nucleoplasm to cytosol ?,"Yes, but there are some differences to keep in mind. Cytosol has enzymes, fatty acids, sugars, and amino acids, all dissolved within it. It is the area of the cell in which organelles are suspended. On the other hand, the nucleoplasm in the nucleus only contains chromatin and the nucleolus. It lacks any of the other macromolecules that could be found in the cytoplasm. Also, there are small differences between the chemical formulas and structures of the two substances."
Nucleus and ribosomes,"What does the 'deoxy' prefix to the full name of DNA signify, in contrast to RNA?",The deoxyribose (DNA) and ribose (RNA) are the 2 different sugar components to the structure :)
Nucleus and ribosomes,"This has always been a bit confusing for me: Do human cells have 46 chromosomes (2 of each) in resting state, or only in duplication states (while mitosis is happening) (so 23 in resting state). 
I always thought it was the second one, but why would we state everywhere that we have 46 chromosomes, while this would only be for the shorter period of the cells lifecycle?","We do have 46 chromosomes, 22 pairs of homologous chromosomes + sex chromosomes. Many cells are in G0 stage, so mitosis doesn't happen (somatic cells that don't divide anymore, just do their job), if mitosis happens then each chromosome would have 2 identical chromatids (homologous chromosomes aren't 100% identical, they may have different alleles), we could say that some cells have 92 chromosomes, while some 46 and gamettes 23, but it would be a bit confusing.
And I don't think chromosomes are resting, they are actively transcribed into RNAs."
Nucleus and ribosomes,"In one of the pictures above,we can observe a huge amount of ribosomes on the surface of the endoplasmic reticulum.Why?","The picture you are referring to is an image of a section of the endoplasmic reticulum known as the "Rough ER". The ribosomes there create proteins to be transported to their respective destinations by the Golgi Body. 

As for your second question, there are, in fact, ribosomes floating freely in the cell. The reason for having both bound and free ribosomes is that the bound ribosomes make proteins that will be transported elsewhere, while the free ones make proteins that will be used for the cell itself.

Does this help?"
Nucleus and ribosomes,"When the article says that ribosomes can be bound to the endoplasmic reticulum, does that mean that ribosomes are actually in between the two phospholipid bilayers of the nuclear envelope? And if so, how would the finished proteins exit the endoplasmic reticulum?","The ribosomes are reversibly attached to the outer surface of the membrane rather than being inserted into the membrane.


The proteins produced by ER-bound ribosomes start with what are known as a signal sequence§ and are initiated within the cytosol — the signal sequence then directs the complex of peptide, mRNA, and ribosome to dock with the ER. 

The ER-bound ribosomes are thus tethered to the ER by the growing polypeptide during its synthesis.  These proteins will eventually be exported, sent to some types of organelles, or remain associated with a cell membrane. 

In contrast, if a protein lacks a signal sequence it will (usually) be translated in the cytosol — many if not most of these proteins will remain in the cytosol, but some will end being imported into mitochondria, chloroplasts, peroxisomes, or the nucleus.


This process is covered in more detail here:
https://www.khanacademy.org/science/biology/gene-expression-central-dogma/translation-polypeptides/a/protein-targeting-and-traffic 


Does that help?



§Note: these signal sequences get cleaved and will not be part of the mature proteins."
Nucleus and ribosomes,"what is role of rRNAin protein synthesis?
and is there only three types of RNA or more?","rRNA forms rybosomes, which are organieles that put mRNA and tRNAs close enough so peptide can be made (it's just a factory). And yes, there are many more kinds of RNA, like snRNA, snoRNA, miRNA, whose function is mostly regulatory, or involved in some modification of other RNAs."
Nucleus and ribosomes,Is a protein an enzyme or is an enzyme a type of protein?,"An enzyme is a type of protein, there are also other types of proteins that aren't enzymes."
The cytoskeleton,Do prokaryotes also contain cytoskeltal fibres?,"Actually, prokaryotes most definitely DO have a cytoskeleton. For a long time it was though that they did not, but that view has changed over the past 20 years.  That said, the prokaryotic cytoskeleton  is not made of tubulin or actin, but of proteins that resembles these eukaryotic proteins.

I refer you to the primary review article: "The evolution of the cytoskeleton" in the Journal of Cell Biology (Published August 22, 2011 // JCB vol. 194 no. 4 513-525) by Bill Wickstead and Keith Gull. 
From their article:
"The view that the cytoskeleton was a feature unique to eukaryotes was dramatically overturned about 20 years ago by the discovery that bacteria possess homologues of both tubulin (de Boer et al., 1992; RayChaudhuri and Park, 1992; Mukherjee et al., 1993) and actin (Bork et al., 1992). Since that time, a combination of bioinformatics, structural data, and advanced cell imaging has cemented the idea that both bacteria and archaea have active and dynamic cytoskeletons.""
The cytoskeleton,Could someone explain the difference between the centrosome and the centrioles?,Think of it this way: Centro *some* = Organelle composed of/containing *2* (*some*) _Centrioles_
The cytoskeleton,What is the difference between polarity and directionality?,"Polarity is where electrons want to be to be stable, directionality is where atoms want to be on a molecule to be stable."
The cytoskeleton,"Flagella an cilia has 9 pairs of microtubules arranged in a circle plus 1 pair in the middle, so Why it's called 9+2 array ?",It is actually not 1 pair in the middle. They are 2 individuals as you could observe from the pic. 9+2 (9 pairs + 2 individuals).
The cytoskeleton,"I am a bit confused regarding the last paragraph. I am doing research for a presentation about centrosomes. This was extremely informative, but the last paragraph mentions that plant cells do not have centrosomes and that centrosomes may not actually be essential to mitosis, though when present, they do play an organizational role. However, when looking elsewhere on the internet, I keep coming across various articles and whatnot which say that plant cells DO have a centrosome, and instead the debate focuses around the centriole. Could someone please clarify? Thanks!","I know this is a little late but this is what I can find:     The centrosome, or MICROTUBULE ORGANIZING CENTER (MTOC), is an area in the cell where microtubules are produced. Plant and animal cell centrosomes play similar roles in cell division, and both include collections of microtubules, but the plant cell centrosome is simpler and does not have centrioles. https://www.cellsalive.com/cells/cell_model.htm. 

 From what I can tell plant cells do have a centrosome, they are just much less complex. I hope this helped."
The cytoskeleton,How do the dyneins on the microtubules 'know' to alternately 'walk' and then relax to let the other side have a go?,"They probably don't know, but just try, if they can reach the ground (and get their energy), they walk. Or there may be something else that tells them, or blocks them, when they are not supposed to walk."
The cytoskeleton,How does the presence of a cytoskeleton allow a eukaryotic cell to be larger?,"That is an _inetersting_ question.

The first and foremost known function of the cytoskeleton is to stop deformations of the cell. That way cytoskeleton helps to have an internal environment that is separated from the environment (actually that function is associated with membrane) but also helps mechanics, movement and better survival fo the cell.

Eukaryotic cells, apart from the cytoskeleton, are distinctive than Prokaryotic cells for having membrane-bound organelles. Organelles speak of a higher level of organization. That _requires_ more space, because there are more and more organelles which need to be able to fit into one cell while not being squashed tightly into each other. There also has to be free space for the cytoplasm. I mentioned cell movement and mitosis.

I do nto knwo whether mitosis is possible in Eukaryotic cells thanks to cytoskeleton or cytyoskeleton developed because of Mitosis (similar to what is older an egg or a hen?) but it defintiely goes hand in hand.


This paper may be interesting to you:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2851742/"
The cytoskeleton,Why don't prokaryotes have cytoskeletal fibers,"Well, prokaryotes do have some cytoskeletal fibers, just not the same ones found in eukaryotic cells (https://en.wikipedia.org/wiki/Prokaryotic_cytoskeleton). Presumably, the reason that prokaryotes don't have _the same_ cytoskeletal components as us is that eukaryotic cytoskeleton evolved after the divergence of prokaryotic and eukaryotic lineages from a common ancestor.

Hope that helps!"
The cytoskeleton,"In cell division, why does the cell use microtubules instead of microfilaments and intermediate filaments to pull chromatids  to the cell poles?
Thank you!",Maybe because microtubules are the strongest and biggest diameter so far among those three?
Cell-cell junctions,What sorts of cells does the blood/brain barrier consist of? I believe chemotherapy molecules are often too big to get through to treat the brain.,Each nerve cell in the brain must be fed by blood or the cells will quickly die of oxygen deprivation.  I believe you are perhaps reffering to a cappilary system that sustain these cells in a way that compartmentalise them as much as possible. It is also possible because of the late hour that my mind makes me write b.s. and I'm sorry if the answer is misleading or not helping...
Cell-cell junctions,Could someone thoroughly explain to me what desmosomes are?,"A desmosome, also known as a *macula adhaerens*, is type of cell-to-cell adhesion.

Desmosomes resemble plasmodesmata in plant cells because they also provide little space through which membranes of to adjacent epithelial cells are connected. Hiwever, in the case of desmosomes, intermediate filaments of cytoskeleton are connected. How?


First, desmosomes, have its connecting proteins (just liek the other types of cell-to-cell connections in animal cells). Their proteins are called _cadherins_.

Cadherins are attached to both cells and they protrude the cell enterior and anchor on intermediate filaments (cytoskeleton). Precisely, they attach to cytoplasmic plaque, which connects to intermediate filaments.

Is it clearer now? :)"
Cell-cell junctions,Do desmosomes and cadherins depend on one another?,"Yes, the cadherins are a big part of the desmosomes"
Cell-cell junctions,Can bacteria form junctions with each other in order to exchange genetic material?,"Bacteria can form junctions with each other to exchange genetic material. This is known as conjugation. Genetic material is exchanged between bacteria through conjugation tubes or sex pilus. One bacterium usually donates its DNA while the other receives it.
For more information check out this link:
https://www.quora.com/Does-hydrogen-atom-prefer-to-lose-or-gain-an-electron"
Cell-cell junctions,What is the difference between desmosomes and tight junctions?,"Like aria said in the comments, desmosomes allow stretching and are in more complex organisms. This is because with desmosomes, cells link up together, and the intermediate filaments have a connection in between. This allows for strength, tightness, and flexibility in the tissue. Tight junctions prevent water from leaking out of the cell and are present in the bladder."
Cell-cell junctions,"What are the functions of Cadherin ? Can you help me to answer this question by writing in points, not descriptive pattern? Thanks!","cadherins are basically proteins attatched to the cytoplasmic plaque of animal cells. They act as a sort of tie that prevents cells from seperating under pressure. 
This is probably a really dark way of putting things but think of it as two scenarios like this:
1) you bind two people together by their wrists or bodies with a rope.
2) you bind two people by skeletons. 
its harder to seperate the two bound by their skeletons no matter how far away they stretch, ryt?. its something like that. it connects two cells, say cardiac cells, by their adjacent cytoplasmic plaques which are in turn connected to the cells' cytoskeleton, which holds them together as they stretch.
Hope you got an idea:)"
Cell-cell junctions,What is cytoplasmic plaque and what are intermediate filaments and how exactly do they work with the cadherins to anchor the junction between epithelial cells?,"Cytoplasmic protein plaque is protrusion of cytoplasma which from luminal side binds intermediate filaments (ctoskeleton) and from the other sides binds cadherin. Cadherin binds to another cadherin which holds cytoplasmic plaque and binds to another intermediate filament in lumen of second cell adhering to the first cell.


Cytoplasmic plaque plays scaffolding role.


https://www.histology.leeds.ac.uk/cell/assets/desmosome_diag.gif"
Cell-cell junctions,"Is the "junction" between the nuclear membrane and the E.R. considered a junction?
If yes, what kind of junction is it?
If no, it is not a junction, what is it?
Many thanks!","I don't think there is _any_ junction since endoplasmic reticulum membrane is _continuous_ with the external nuclear envelope. When something is continuous means it is attached directly, we are speaking of one bigger entity."
Mitochondria and chloroplasts,Would it be possible for a modern day cell or organism to capture one of these cells and start a new symbiotic relationship with the host cell?,"That is an intriguing question. The origin of mitochondria is thought to have been a very rare event. The mitochondria seem to have their origin from one particular family of bacteria (the alpha-proteobacterium ) which are related to some existing bacteria. There are people trying to build cells so I guess maybe someone could try to create a modern endosymbiosis event.

There are many theories as to how eukaryotes came about. If you want to know more; see this paper: Endosymbiotic theories for eukaryote origin http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4571569/"
Mitochondria and chloroplasts,It would be so cool if we could recreate endosymbiosis and incorporate chloroplasts in human cells so we could photosynthesize,"i hate to ruin your guys fun but i think we would die, if you put chlorophil into our bodies."
Mitochondria and chloroplasts,"1) Are there any animals that have chloroplasts? Or are they only in plants?

2) If they are only in plants, would it be possible for an animal to have chloroplasts, chemically speaking?","Well according to modern classification, the organisms which have chloroplasts in them and have an advanced nucleus are called plants. Those organisms which show both plant and animal features(like Euglena) are kept in Kingdom: Protista
As for your second question, as Biology is science of exceptions we cannot publish any definite law. So in future, due to evolution, there may be animals with chloroplasts."
Mitochondria and chloroplasts,is peroxisomes needed in a cell,"Before the ancestor of mitochondria entered the eukaryotic cells, Peroxisomes were asource of power to the cell. They used to break down H2O2(Hydrogen Peroxides) and would form water and and energy. But now, there only function is detoxification as the energy produced by mitochondria is much more than the energy produced by the peroxisome. So, peroxisomes are sort of vestigial organelles which had a major function in the past but aren't so useful in the present age.."
Mitochondria and chloroplasts,"If mitochondria and chloroplasts evolved from bacteria, what did the cells use for energy before?  Isn't this a case of you can't have the one without the other?  Wouldn't the cell/animal/plant die without the energy from the chloroplast or mitochondria?",Before mitochondria and chloroplasts became part of cells they had their own ways of producing energy from metabolizing food around them. These older methods of producing energy were lost along the way because the mitochondria and chloroplasts were better at it and it was a waste of resources to have the two ways of producing energy so the cells that eliminated the older way were more efficient and survived better that the ones that didn't.
Mitochondria and chloroplasts,"In the endosymbiotic theory, what was the factor that decided that the chloroplast wouldnt converge with the other cells present on earth, so that there would be two types of cells, 
1. plant cells
and 
2. animal cells","It just happened this way. Some phytoplankton probably merged with chloroplasts prokaryotic cells and absorbed them and formed a symbiotic relationship with them and also with mitochondria (they have both organelles), and some zooplankton probably got the short stick and managed to form symbiotic relationship only with mitochondria prokaryotic cells and from them out ancient common ancestor was created..."
Mitochondria and chloroplasts,"Most antibiotics inhibit bacterial ribosomes... so, would antibiotics have an effect on mitochondria when taken?","Some of them may, if the antibiotics manages to get all the way through all the membranes to the mitochondria itself (which is not an easy way). 
If they do get into mitochondria, it may not be a big deal since most of mitochondrial proteins are made by eucariotic cell and then transported into mitochondria, only few proteins are made by mitochondria itself.
Actually it seems that some antibiotics do harm mitochondria, so these usually aren't used as long as there is some harmless alternative."
Mitochondria and chloroplasts,Do stand-alone chloroplasts and/or mitochondria still exist in nature as prokaryotes (Outside of a eukaryotic cell)?,"Yes§, this is part of the evidence supporting the theory that these (and possible some other organelles) arose through endosymbiosis (aka symbiogenesis).

The group of bacteria from which mitochondria seem to have evolved are the Alphaproteobacteria.

Chloroplasts appear most closely related to the cyanobacteria.

You can read more about this here:
https://evolution.berkeley.edu/evolibrary/article/_0_0/endosymbiosis_01 _

You might also find these interesting:
https://biologos.org/blogs/dennis-venema-letters-to-the-duchess/evolution-basics-endosymbiosis-and-the-origins-of-mitochondria-and-chloroplasts
https://biology.stackexchange.com/questions/43372/origin-of-the-double-membrane-of-mitochondria-and-chloroplasts

§More correctly, there are other descendants of the progenitor of these organelles that have remained as free-living organisms."
Mitochondria and chloroplasts,"Does this mean that when you eat vegetables, you are you eating light energy?","Yes, pretty much. In fact you could say you're eating the energy produced in the fusion reactions occuring inside of the Sun's core."
Mitochondria and chloroplasts,"Have they proven endosymbiosis to be the reason why mitochondria and chloroplasts contain their own DNA and ribisomes? I am very blown by the idea that the mitochondria in our bodies were once bacteria and, if they really are bacteria before,we now have a gazillion of them.","Proof is an elusive concept in science, but this theory is now generally accepted as the best explanation for multiple observations.  

Another piece of evidence supporting the theory that these (and possible some other organelles) arose through endosymbiosis (aka symbiogenesis) is that if you make an evolutionary tree of the DNA within either of these organelles and bacteria, you find free-living bacteria that are closely related.

The group of bacteria from which mitochondria seem to have evolved are the Alphaproteobacteria — many of them are intracellular parasites, which suggests how they originally ended up inside the first eukaryotic cell.

Chloroplasts appear most closely related to the cyanobacteria.

You can read more about this theory here:
https://evolution.berkeley.edu/evolibrary/article/_0_0/endosymbiosis_01 _

You might also find these interesting:
•https://biologos.org/blogs/dennis-venema-letters-to-the-duchess/evolution-basics-endosymbiosis-and-the-origins-of-mitochondria-and-chloroplasts
•https://biology.stackexchange.com/questions/43372/origin-of-the-double-membrane-of-mitochondria-and-chloroplasts"
Microscopy,"i was reading a question about where human samples come from,  and i was wondering why the cells die when they get into the vacuum.","Cells die upon entering a vacuum because a vacuum is a void.  This means that there is nothing there.  There is no air, just the absence of matter.  In the absence of matter, a cell cannot survive.  Plus, a cell in a multicellular organism cannot survive on its own for long, anyway."
Microscopy,When Was The Electron Microscope invented ?,"The electron microscope was invented in 1931 by  German physicist Ernst Ruska, and an electrical engineer, Max Knoll."
Microscopy,Why is an objective lens called that?,The lens closest to the object it is observing is called the objective lens. Get it? Object / Objective. It focuses light directly from the object to observe it.
Microscopy,what is a light microscope,"A light microscope is the typical microscope you would use at home: you simply observe something as it is using regular ilght. 
Other more specific and advanced microscopes might use electro-magnetic radiation that is not in the visible spectrum, such as electron microscope, but these images are not something you can detect by eye without proper machinery assistance."
Microscopy,"How many microscopes are made per year, both types of the electron microscopy. Who produces and, or make them with what foundation.","The production and distribution of microscopes, especially electron microscopes, can vary from year to year and depend on several factors. While I don't possess the exact figures for the current year, I can provide you with some general information.

Electron microscopes are typically produced by various manufacturers around the world. Some prominent companies known for manufacturing electron microscopes include JEOL, Thermo Fisher Scientific, Carl Zeiss AG, Hitachi High-Technologies Corporation, and FEI Company, among others.

These manufacturers often collaborate with various foundations, research institutions, and academic organizations to develop and manufacture electron microscopes. Additionally, there are government-funded initiatives and independent research institutes that contribute to the advancements in microscope technology and their wide availability.

It's important to note that the production numbers may vary significantly each year due to market demands, technological advancements, and research funding. To get specific figures for a particular year or detailed information about the production and distribution process, it would be best to consult industry reports, companies' annual reports, or contact the respective manufacturers directly."
Microscopy,which is the world's smallest cell?,"World smallest cell: SAR11 micro-organism (found in sea water). Length 1 micrometer.
while Mycoplasma gallisepticum has 10micrometers in diameter.

Human smallest cell: sperm cell.
While granular cells of cerebellum is 10micrometers (soma), sperm cell head is 5micrometers."
Microscopy,how much can the most powerful electron microscope magnify?,"A light microscope can only magnify up to 1000-2000 times, an electron microscope can magnify something up to 2 million times."
Microscopy,does time exist in perfect void?,"The void contains no space, no time, no mass, and no charge.

I see it kinda like this:

On Earth, one minute is 60 seconds. But on Mars, it is different. Same as all the other planets, because we tell the time via how we revolve around the sun, and how fast our planet is spinning. So if there were no sun and you weren't on a planet, there would be no time.

Time is a relative concept with no absolute, and is used as a guide to measure events in various ways. With gravity and possibly voids, all they do is slow the event down, not time.

So if you were an astronaut in space, you would only know how "old" you are if someone Earth were to tell you what the time is!"
Microscopy,Why is wave length the limiting factor?,"Correct me if I'm wrong, but according to the formula for resolution, the smaller the wavelength the better the resolution. That being said the shortest wavelength for visible light is blue at 450nm. Anything shorter our eye cannot capture."
Microscopy,can they still use the dead cells and can they get living cells from dead people?,"And for the second question, it would depend on how you classify a "dead" person. Some countries pronounce a person dead if their heart stops, whereas others have it as when there is no activity in the frontal lobe (of the brain). Any sample from a dead person would have to be taken very shortly after their "death", as the cells start to die (or are already dead) within minutes. You may, depending on the circumstance and whether they are "dead" when their heart ceases functioning, be restricted to what sample of living cells you can retrieve. If you somehow access the heart very soon after "death", you may stand a chance at getting a sample, although I do not recommend trying to do any of this as it is a: rather suspicious, and b: you may be required to commence cardiopulmonary resuscitation (CPR). This is all quite hypothetical, and don't try any of this, please."
Intro to cells,What is the main function of a typical cell in the human body?,"Cellular biology is a pretty in depth field, but cells basically break down sugars into usable energy, they regulate growth through cellular division, and synthesize different proteins to perform a variety of essential biological functions depending on what type of cell it is."
Intro to cells,"in the second paragraph, when you cut a cell in half, what do you see, and are any  cells the same?","When cut a cell in half you will see a cell membrane, cell wall (in some cells), cytoplasm- the jelly-like substance in the cell, mitochondria- the energy supplier to the cell, the nucleus-  which is the brain of the cell which tells the cell what it should become for example a blood cell or nerve cell. There are other components in the cell but this is as simple as I can remember."
Intro to cells,"Is it actually possible to cut a cell in half (as mentioned in the second introductory paragraph)? If so, how? If not, how do scientists know what the inside of a cell looks like?",they use staining agents do dye the cell. Staining agents include Methyl Blue and Safrannin
Intro to cells,how many cells is an egg made of?,"When you say that, do you mean it in an "embryonic egg, inside of the womb" context or an egg that has been laid?"
Intro to cells,Does number of the cells in our body always remain the same ?,"Not really: cells continuously die and split so that they keep getting destroyed but the body replaces them too. Also, children have fewer cells than adults (adults are larger and therefore need more cells)."
Intro to cells,Are cells in the human body more reliant on other cells than unicellular organisms?,"We are looking at it on a different scale.

An unicellular organism does not even have 'other cells to be reliant on' since it is unicellular. In a unicellular organism, interacting with other cells would mean intra- or inter-species interactions.

In those terms, the answer is _yes_."
Intro to cells,"if all cells come from cells, where did that first cell come from?",That is a huge gray area.
Intro to cells,how would that first cell survive?,"Most likely because of the lack of competition. If you were the only organism alive, with lots of resources around you, why wouldn't you be able to survive?"
Intro to cells,are cells made out of cells,"Lol that's not possible! Cells are instead made out of various biomolecules and cell organelles, which are made out of various other molecules bonded together."
N/A,What's the difference between a vesicle and a vacuole?,vesicles function is to transport proteins etc. while vacuoles store things
N/A,What's the difference between a lipid and a phospholipid? And why are proteins so important?,"A lipid is composed of glycerol and three fatty acid chains. A phospholipid has a phosphate group attached to it. 

And proteins are so important because they do all the key activities to make a functioning human. When an embryo is growing, it is because of proteins. When the muscles send and receive signals from the brain,  it is because of proteins. When cuts heal, it is because of proteins. When we digest food, it is because of proteins. You get the idea. They essentially do everything to make you able to live."
N/A,"i know there are vacuoles in plants and animals cells, are there any major differences between the two other than the size? location maybe. like characteristics or different functions? both vacuoles in each type of cell store energy.","The central vacuole of a plant has a crucial role. As mentioned above, the water  there pushes the cytoplasm outward against the cell wall. This creates  hydrostatic pressure - turgor. The mechanism keeps the plant from wilting and plays a key role in the water balance. Generally this central vacuole has a lower pH, witch help digesting substances; it can also be used as a storage room  - citruses have their juice in these vacuoles; it also  keeps the cell wall rigid and thus keeps the plant in upright position and so on. It also pushes every other cell organelle against the wall and to the surface of the cell. This a very clever way to push the chloroplasts closer to light and ''promote'' photosynthesis. Animal cells do not have a cell wall (they can have a similar thing , called a cell cortex). So the vacuoles here play a more subordinate role - they still help with endo- and exocytosis. Also the are quite smaller than plant vacuoles and greater in number. And of course, there are some animal cells with no vacuoles at all. Hope that helps :)"
N/A,""single-celled eukaryotes"?
isn't that wrong ?","No, that is not wrong. While most eukaryotic organisms are multicellular, there are some unicellular eukaryotes as well, though not many."
N/A,Why is the inner membrane of the lysosome not affected by the enzymes present inside it?,"The inner membrane of a lysosome is made up of proteins with an 'unusually' large number of carbohydrate groups attached to them. This prevents the breaking down of the proteinaceous membrane, ergo protecting them from the hydrolytic action of the enzymes."
N/A,"Why are mitochondria, choloroplasts, and peroxisomes not included in the endomembrane system?",I believe that they are not included into the endomembrane system because none of them receive anything from the Golgi apparatus. Hope this will help you:)
N/A,"Hey, everyone!
I'm having a rather hard time grasping some of the concepts in this article; specifically, how are the "shipments" between organelles (I.E. the ER and the Golgi) made? What structure connects them? Or do they just sort of float over?
I would appreciate some help on this. Thanks!","I'm reasonably sure the cytoplasm moves them. It's kind of flowing, and catches the "shipments" in its "current" and floats it over. I think the ER prepares them to flow through the cytoplasm to the next organelle,."
N/A,"If plant has no lysosomes, than how do they defend themselves from bacteria? Or bacteria simply do not attack plants?","Yes, bacteria do attack plants but plant cells have a different defense mechanism.

They have proteins which defend the plant from being infected. If a pathogen attacks a plant cell, then the proteins first try to prevent the pathogen from entering the plant cell. If that strategy fails and the pathogen manages to enter the cell, then the cell(or cells) have to sacrifice themselves, i.e, they die and prevent the pathogen from spreading further into the plant."
N/A,Do plant cell contain lysosomes?,Both plant and animal cells contain lysosomes.
N/A,Why are plant cells typically square (if they are) and why do they have a much larger vauole than animal cells?,"They are squarish because they have a stiff cell wall that forces them into that shape. If you meant vacuole, I think they have a larger vacuole because they have more need to store food than animals. In case of drought or famine, animals can move on to somewhere else if they need to get food or water, plants can't."
N/A,In the above diagram the author gives us an example of what a plant cell looks like and I noticed that the cell has an abnormally thick cell wall. What is the reason for thick cell walls in plants?,"Cell walls not only provide structure, and protect from mechanical damage, they also prevent the cell from bursting as plant cells need to continually absorb water to survive."
N/A,how come animal cells don't have a cell wall,"An animal cell needs to allow mobility for that animal so only has a cell membrane, a plant cell however has a cell wall to give the cell ridged structure and a plant doesn't move by itself so doesn't need mobility but rather it have protection."
N/A,Why don't plant cells have lysosomes?,"Plant cells don't have lysosomes, because their cell walls are tough enough to keep out foreign substances that lysosomes would have to digest out of the cell."
N/A,"The Endoplasmic Reticulum in a eukaryotic cell is the transport network of the cell and it extends from and connects the nuclear membrane to the plasma membrane of a cell. But then whenever we draw a diagram of a typical plant or animal cell, we never extend it to the plasma membrane- we always leave it somewhere in the cytoplasm. So, it should be extended, shoudn't it? And in that sense all our diagrams are theoretically wrong?","Well, from endoplasmic reticulum vesicles are formed and transport things to Golgi apparatus, where it may be modified somehow, sent back to ER or further to cell surface. So the whole network is: ER -> vesicle -> Golgi -> vesicle -> cell plasma membrane"
N/A,Procaryotic cells lack vacuoles too then?,Yes. Only eukaryotes have vacuoles.
N/A,Does the nucleus have a phospholipid bilayer?,Actually it is surrounded by a double membrane which has 2 phospholipid bilayers each.
N/A,Why is there a nucleolus? Shouldn't the production of DNA just be spread evenly around the nucleus?,The nucleolus is a region from the nucleus where the different RNAs are found. It is also the site where ribosomes are joined. It´s important to mention that ribosomes are made 1/3 from proteins and 2/3 from RNA. Proteins for the ribosome are exported from the cytoplasm  to the nulcleus trough the nuclear pores.
N/A,what is the function of a peroxisome?,"it is main function is to break down long chains of fatty acids and to detoxify substances, 

it produces H2O2 as a result, which can be harmful to the cell as a whole if not regulated, which is why it contains enzymes that is able to break down H2O2 into water and oxygen."
N/A,"are there any unicellular eukaryotes? if there are, names ?","Yes, there are many unicellular eukaryotes. In fact, they have their own kingdom in the standard five kingdom classification scheme in biology called Kingdom Protista. Kingdom Protista is divided into subkingdoms of Protozoa and Algae. In Subkingdom protozoa, you have organisms like amoeba, euglena, volvox, paramecia, even plasmodia (the microorganisms that causes malaria), just to name a few. Most types of algae are also unicellular eukaryotes."
The extracellular matrix and cell wall,How is this related to cell signaling? Does the extracellular matrix act as receptors?,"The integrins, which connect the ECM to the cytoskeleton, act as receptors in the sense that they receive signals from the ECM and modulate the cell signaling pathways."
The extracellular matrix and cell wall,The ECM and cell wall are used for support. Then what are cytoskeleton for?,ECM is outsideof cell Cytoplasm-like material and cytoskeleton isinside of cells structural material
The extracellular matrix and cell wall,Where are collagen synthesised and how does it reach its destination,"Proteins that get exported are (typically) synthesized by ribosomes bound to the ER (i.e. in the rough ER) and this is true of collagen.

The collagen precursor polypeptide then gets processed in the ER and Golgi before being exported via. exocytosis (vesicles bud off from the Golgi and then fuse with the plasma membrane).

Once outside the cell, collagen undergoes further modification by enzymes that are also secreted by cells.


To start learning more about the ER, Golgi apparatus, and exocytosis on Khan Academy:
•https://www.khanacademy.org/science/biology/structure-of-a-cell/tour-of-organelles/v/endoplasmic-reticulum-and-golgi-bodies
•https://www.khanacademy.org/science/biology/membranes-and-transport/bulk-transport/v/exocytosis
(You can also find other material on this by searching for various keywords such as "rough ER", "Golgi", or "exocytosis".)


Wikipedia also has an article on collagen that describes these steps in more detail:
https://en.wikipedia.org/wiki/Collagen#Synthesis


Does that help?"
The extracellular matrix and cell wall,"What is a polysaccharide? Is this the sticky goo that bacteria produce and nestle in, when a biofilm forms on a surface? What makes a molecule sticky? Sorry - 3 questions.",1) Multi sugar/carbohydrate molecule. 2) Bacteria usually lives in colonies and sometimes due to overpopulation can kill itself with their own waste byproducts. 3) It usually depends on the type of molecules. Polarity matters as well. Polar wise molecules ( such as water) will attract same affinity molecules. Fats are non polar molecules and attract similar affinity molecules. Thisis also why soap has both polar and non polar sides so it will attach to both fats and water so it can remove fats when rinsed with water...
The extracellular matrix and cell wall,why animals have extracellular matrix not a cell wall ?,This allows us to bend and be flexible! With a cell wall our skin would be rigid and we might break if we bend our arm for example!
The extracellular matrix and cell wall,"What is the difference between Proteoglycan and Glycocalyx?
Many thanks!",Glycocalyx is what surrounds a bacteria cell while Proteoglycan is what surround animal cell
Prokaryotes and eukaryotes review,"I thought some prokaryotic organisms could be multicellular;such as blue green algae, isn't that a multicellular prokaryotic?",There are some cyanobacteria that form filaments with a differentiated cell type that fixes nitrogen and 'normal' photosynthesising cells. It's a form of symbiosis that could be classified as multicellular.
Prokaryotes and eukaryotes review,How can eukaryotes be multicellular? Aren't they cells on their own?,"A eukaryote is an organism with complex cells, or a single cell with a complex structures. In these cells the genetic material is organized into chromosomes in the cell nucleus. Animals, plants, algae and fungi are all eukaryotes. There are also eukaryotes amongst single-celled protists.  Unlike unicellular archaea and bacteria, eukaryotes may also be multicellular and include organisms consisting of many cell types forming different kinds of tissue. Prokaryotes are  singled cell organisms."
Prokaryotes and eukaryotes review,"I read on another article here on Khan Academy that prokaryotic cells can organize to form something that resembles a multicellular organism, and that it can be discussed if that's multicellular or not. So how can prokaryotes "always" be unicellular?

Source: https://www.khanacademy.org/science/high-school-biology/hs-cells/modal/a/prokaryotic-cells

"In general, prokaryotes are single-celled organisms. However, there's increasing evidence that some groups of prokaryotic cells can organize to form structures that resemble multicellular organisms. Whether this counts as "real" multicellularity is a question hotly debated by researchers today."","I believe that the debate is continued, so we should still agree to the previous answer that prokaryotes CANNOT be multicellular. Bacteria might be an interesting exception, but further research shows that the cells might work together, but they lack the organization that other multicellular beings have.

Hope this helps!"
Prokaryotes and eukaryotes review,"So chromosomes/chromatin can be floating around anywhere with DNA inside the cell and that it doesn't need to be around a nucleus? 
I'm sorry if I seem dumb I'm new to this.","No worries! We were all new to this at one time or another! To answer your question, yes, it doesn't need to be inside a membrane-bound nucleus in the case of prokaryotes

Hope this helps!"
Prokaryotes and eukaryotes review,are biofilms made with _prokaryotes_ or _Eukaryotes_ cells?,Biofilm Structure A microbial biofilm is made up of many prokaryotic organisms that combine to form a colony. The colony is adhered to a surface and coated with a polysaccharide layer (or slime layer).
Prokaryotes and eukaryotes review,do eukaryotes cells live longer than prokaryotes,"The answer really lies in whether or not the cells combine to form a multicellular mass or if they prefer living by themselves. Ones that form together tend to live longer.

Hope this helps!"
Prokaryotes and eukaryotes review,How Can a cell be multicellular?,It is not saying that a cell is multicellular. When it says eukaryotes can be multicellular it is referring to an organism made of eukaryotic cells.
Active transport,"Questions:
1. How is the energy from the sodium ions transferred to the sodium/glucose symporter?

2. Does the energy from the sodium ions increase the affinity of the symporter to actively collect glucose? or does the symporter simply wait for a glucose to fall into place in its own time?

3. Can the symporter be activated by two sodiums without a glucose present? if not, does the symporter store energy from sodium ions until a glucose arrives? or do the sodium ions and glucose need to interact with the symporter simultaneously?","1) The "sodium/glucose symporter", known as SGLT (sodium glucose linked transporter), receives the energy needed to perform its transport from the electrochemical gradient established by the sodium/potassium pump. Because of the difference in sodium concentration (between the inside and outside of the cell) and due to the electrical potential difference (between the inside and outside of the cell), the SGLT is able to perform its function.

2) The affinity of the symporter to collect glucose is not dependent on the sodium concentration, but rather the concentration of glucose (you can imagine there would be a higher probability of glucose being able to cross the system if more glucose was near the system). The purpose of the sodium ions is to establish the electrochemical gradient which provides the energy for the SGLT to perform its function.

3) The exact mechanism for the transporter is not fully understood - the diagram, which indicates 2 sodium ions and 1 glucose ion, is meant for gaining a conceptual understanding of the system. If you're curious about the topic, I have linked an article and a video below. SGLT is typically seen in action in the intestines and kidneys.

http://physrev.physiology.org/content/91/2/733
https://www.youtube.com/watch?v=jCdJyUHqJhM"
Active transport,"how does the antiporter provide energy for molecules to go in the "opposite" direction? in a symporter it makes sense that the flow of one ion should cause other molecules to go along with it, however in an antiporter, what causes the other molecule to move up its conc. gradient?","In an antiporter it uses the energy of the ions flowing down their concentration gradient. Imagine this just like a hydroelectric power station uses the energy of water flowing down the waterfall to create electricity. This electricity can do work.
In case of the cell the energy is used directly to move the other molecule out of the cell against it´s concentration gradient."
Active transport,"if there are more Potassium ions in a cell, how is the cell negatively charged? shouldn't it be positively charged? this is in relation to the electrochemical gradient section. thank you","There are certainly more numbers of potassium ions in the cells, but remember that there are greater numbers of sodium ions outside the cell (since for every three sodium ions moved out of the cells, two potassium ions enter the cell), therefore, resulting in a net positive charge outside the cell and net negative charge inside the cell."
Active transport,"Hi, I'm just a little curious, why can't 3 potassium ions be pumped out and 2 sodium ions pumped in(the other way around)? Can't that serve the same role?","No, because the potassium is highly concentrated in the cell, and so that's where the molecules must go(based on active transport going low concentration to high concentration). And sodium is highly concentrated outside of the cell, so that's where it goes during active transport considering it is low to high concentration.
Hope this helped:)"
Active transport,"why wouldnt cells use atp for primary active transport of glucose directly, why go through a second step?","Because it is faster to utilize already available ATP through the electrochemical gradient. Also, it is spatially more available than in the case of ATP."
Active transport,i dont quite understand the secondary active transport. how does the carrier protein "harness" energy from another molecules concentration gradient? does the glucose molecule just randomly attach itself to the protein when it's about to transport a sodium ion to the other side?,"If for example there are alot of sodium ions outside, their positive charges will repel and like atoms don't like being near eachother so they flow to the other side if there's a way to. Active transport works by using a phosphate group from ATP to change the shape of the protein and thus do work."
Active transport,"what is the main difference between active transport using a carrier protein, and passive transport using facilitated diffusion?","Main difference: In facilitated diffusion, the solute moves down the concentration gradient, from regions of higher to lower concentration, relying on the specificity of the protein carrier to pass through the membrane. This process does not require energy. Conversely, in active transport, the solute moves against the concentration gradient, from regions of lower to higher concentration. This process requires some form of chemical energy."
Active transport,why do cells need membrane potential?,"Hi, your question is about to be answered after 2 years.
Cells need electrochemical gradient because that's what powers secondary active transporters, such as symporters or antiporters.
I hope you're still on Khan academy, because the key to success is to never stop learning ;)"
Active transport,what's the difference between the primary and secondary active transport?,Primary active transport uses energy that comes directly from ATP hydrolysis. Secondary active transport uses the energy from another chemical gradient that was itself created through active transport and ATP hydrolysis.
Active transport,can I be lost?,"I don't understand what you mean. I mean, yes, you could be lost if you wander off on your own in a mall or museum or so forth, but I'm pretty sure that's not what you mean."
N/A,"excuse me, can you tell me an example for pinocytosis ?",Cells in the kidney can use pinocytosis to separate nutrients and fluids from the urine that will be expelled from the body.Hope this helps!
N/A,Amino acids are monomers of proteins and proteins such as receptor proteins are involved. Does that mean that individual amino acids can enter a cell through receptor-mediated endocytosis?,"I am not fully sure, but I believe Receptor Mediated endocytosis means that the proteins act like an enzyme, meaning that only a specific macromolecule can fit into the receptor. An individual amino acid means that it cannot bind to the receptor because it does not fully meet the qualifications of the specific receptor. Imagine a password that scans your body to verify your entry. If you come one day without an arm(missing some amino acids), then the scan won't recognize, thus you won't enter. Similarly, receptor mediated endocytosis works this way. Hope this helps"
N/A,"in the first paragraph, a white blood cell's "work" is described. What happens when there are not enough white blood cells?","The body wouldn't be able to fight of infections and diseases, mainly because the white blood cells are the main line of immune defense. Thus causing illness disorders and in some cases death."
N/A,what is a real life example of endocytosis?,"Let me give you a biological example of endocytosis :
1.   Absorption of nutrients in the intestine.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1353524/
http://www.ncbi.nlm.nih.gov/pubmed/7226201
These two pubmed articles might give some insight.
Just check the abstract ."
N/A,How exactly do pathogens use receptor mediated endocytosis to enter the cell?,"The specifics are different for each pathogen, but in general a pathogen will have surface molecules that interact with the host cell receptors and "trick" the cell into initiating endocytosis.  Once the pathogen is inside a vesicle within the host cell it will sometime be able to break out of the vesicle§ and enter the cytoplasm where it can begin exploiting the host cell.

§ for example, enveloped viruses like the influenza viruses can fuse with the vesicle membrane to escape.

*References and further reading*:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4107984/ — very technical, but the figures give a decent overview

_Viruses:_
http://jcb.rupress.org/content/195/7/1071
https://www.nature.com/scitable/topicpage/how-viruses-hijack-endocytic-machinery-14364991

_Bacteria:_
https://www.frontiersin.org/articles/10.3389/fcell.2018.00001/full"
N/A,Are all the vesicles used in all bulk transport all coated in clathrin (or clathrin coated) or is it only in receptor-mediated endocytosis?,"The formation of the clathrin-coating is vital in vesicle formation, clathrin causes the vesicle to form while SNARE proteins make sure that the vesicle will arrive in the right place. 

Vesicle formation without the clathrin mechanism seems possible (I found a paper discussing the possibilities from 1994: ''Endocytosis without clathrin'' by Sandvig and Deurs, you'll hit a paywall if you can't use a university proxy).

That said however, clathrin does play a vital role and will be involved in (almost) all bulk transport."
N/A,What is a transmembrane protein?,"A transmembrane protein goes across the cell membrane, from the cytoplasm to the outside of the cell."
N/A,Can a plant cell undergo endocytosis?,"Off course! Think of roots. How can they absorb nutrients from the ground, if not through endocytosis?"
N/A,"If macrophages devour pathogens, how do they make sure that they win the fight? What if they themselves get infected by the virus since penetration seems to be so easy?","Macrophages are a type of immune cell that plays a crucial role in the body's defense against pathogens, including viruses. While it is true that macrophages can be susceptible to infection by certain pathogens, they have developed several mechanisms to minimize the risk and maximize their effectiveness in fighting off invaders. Here are some key aspects:

Recognition and Phagocytosis: Macrophages have surface receptors that can recognize specific molecules present on pathogens, such as viruses. Once a pathogen is detected, the macrophage engulfs it through a process called phagocytosis. This allows the macrophage to physically encapsulate and internalize the pathogen.

Degradation: Once inside the macrophage, the pathogen is targeted for destruction. Macrophages have specialized compartments called lysosomes that contain enzymes capable of breaking down the internalized pathogens. This helps to neutralize and eliminate the infectious agents.

Activation of Immune Response: Macrophages are capable of presenting antigens—fragments of the pathogens—to other immune cells, such as T cells. This presentation activates a more specific and potent immune response, coordinating the elimination of the pathogens.

Antiviral Defense Mechanisms: Macrophages can release antiviral molecules, such as interferons, which can inhibit viral replication and spread. They also produce reactive oxygen species and nitric oxide, which have antimicrobial properties.

While macrophages have these defense mechanisms, some highly adapted viruses can still evade or manipulate these responses, leading to macrophage infection. However, the immune system as a whole has multiple layers of defense. Other immune cells, such as T cells and natural killer cells, work together to eliminate infected macrophages and control the infection.

Additionally, macrophages can activate a process called apoptosis, which is programmed cell death. If a macrophage detects that it is heavily infected and unable to eliminate the pathogen, it may undergo apoptosis to prevent the further spread of the infection.

It's important to note that the immune response is a complex and dynamic process. The outcome of the fight between macrophages and pathogens depends on various factors, including the specific pathogen, the virulence of the infection, the overall immune status of the individual, and the coordination of the immune response.

Hope that helped!"
Diffusion and passive transport,Why no energy is spent on switching the carrier proteins?,"These carrier proteins are gated trans-membrane proteins and do not require ATP (adenosine triphosphate) to function. The gate is activated due to the concentration gradient of its target molecule. The target molecule binds to the gated carrier protein and, in response, the carrier protein opens up - this allows the target molecule to enter. The carrier protein then changes shape and releases the target molecule into the cell. It waits in its closed position, once again, until it is activated by the binding of its target molecule (outside of the cell). Therefore, no energy is spent switching shapes. The shape change only occurs due to the binding of the carrier protein's target molecule, in accordance with a concentration gradient."
Diffusion and passive transport,What is the difference between simple diffusion and facilitated diffusion?,Simple diffusion is the movement of molecules through a cell membrane without using the channels formed by integral membrane protein. Facilitated diffusion is the movement of molecules through those channels.
Diffusion and passive transport,"Can carrier proteins move molecules from the inside to the outside? Also, is it possible to replace carrier proteins with channel proteins that are specific to the same molecules? Channel proteins is faster, and you can still precisely modulate how much goes in and out by gating.","Yes and it depends but generally yes
the big thing to keep in mind is that many of these gates are evolving randomly. So getting the most efficient solution while inevitable is not going to happen quickly so if it works it works. Also keep in mind that for larger molecules (think an enzyme or a long carbon chain) the channel would have to be very large meaning that a lot of things could flow out on accident due purely to the size of the pipe. So using a gate instead keeps internal pressure while also heavily regulating the release of the molecules."
Diffusion and passive transport,"I noticed that according to the quiz (Practice: Passive transport) sodium, potassium, and calcium can't move through the channel proteins. In this article mentioned nerve and muscle cells in which channels can pass sodium, potassium, and calcium. Maybe it was about active transport, but this article about passive transport. It is strange, I had some troubles in the quiz because of it. Can somebody explain this stuff?","Yes , i also think that question is wrong. There are channel proteins in the body for transport of those ions.
Sodium : Voltage gated Channel Proteins in Neurons for propagation of nerve Impulse.
Potassium : There are Leaky Channels inside nerve cells ...refer Nerve trnsmission videos of Khan Academy itself.
Calcium : In smooth muscles of the Body...there are Voltage Gated Calcium Channels Present."
Diffusion and passive transport,the topic states above that "a concentration gradient itself is a form of stored (potential) energy" please explain this?,"A concentration gradient will cause movement of molecules from high concentration to low concentration. Therefore, it is a driving force for the movement and thus can be considered as energy."
Diffusion and passive transport,"If a molecule wanted to diffuse across the plasma membrane, but wasn't able to make it all the way through,  what would happen to it? Would it eventually work its way in, or would it get stuck in the membrane?","Interesting question, I don't know if anyone has looked into whether membranes might get "gummed up" by material getting stuck part way through.  

One interesting example I was able to find are the persistent organic pollutants known as PCBs (polychlorinated biphenyls) — these bioaccumulate and at least in some cases are known to disrupt membranes:
https://academic.oup.com/toxsci/article/80/1/54/1674897

Membranes are incredibly dynamic.  Vesicles are constantly leaving and joining each membrane.  In addition, membrane molecules (e.g. phospholipids) move between the two layers§ — for example the lipid composition of the inner and outer layer of the plasma membrane is quite different on most cells .  This very tight control of membrane composition suggests to me that there are probably mechanisms for clearing out bad/contaminated sections of membrane.

If this sort of thing interests you, you might want to consider going to grad school :-)

§Note: This is done by enzymes called flippases and floppases, just in case you were wondering if biologists had a sense of humor!"
Diffusion and passive transport,"What is faster, a simple diffusion (of oxygen, for example), or a facilitated one (of water through aquaporines)?","I don't think there is a general rule (leaning toward facilitated but I have counter examples too).
However, you cannot use passive diffusion to move things from low concentration to high concentration but you can do this with facilitated/active. Depending on the difference in concentration, the simple/passive diffusion will vary while facilitated diffusion can move against concentration gradients and if affected by other conditions too."
Diffusion and passive transport,What is osmosis,The movement of water across a concentration gradient.
Diffusion and passive transport,if particles moves from low concentration to higher concentration can we call it the concentration gradient of that substance as the concentration changes?,"Careful: it moves from HIGH to LOW, not the other way around.
That said, this is also the definition of a _gradient_: it changes as you move from high to low. 
Using a real life example of gradient: lets say you are in a dark room and then you turn on one lightbulb. The light will have a gradient too because the closer to are to the lightbulb, the brighter it becomes (high concentration of light) and the further you move away, the less light there is (low concentration of light). The differences in light intensity is a gradient."
Diffusion and passive transport,Which of these cells can help to move and transport blood,"Blood is a cell, not a particle. That means that it could not be diffused. It actually gets transported by blood vessels, which are long chains of muscle cells."
Osmosis and tonicity,"Why doesn't the pressure of the cell (even a red blood cell that isn't rigid), balance out the net inflow in a hypotonic solution? The net inflow doesn't work with energy, but because their is room to slide around!?",I think this is the case with a plant cell that has a rigid cell wall thus in a fixed volume hydrostatic pressure will increase until osmotic pressure is opposed. But with an RBC the volume is not fixed (due to lack of cell wall) so osmotic pressure increases unopposed until the cell lyses.
Osmosis and tonicity,What could be an example of solute in a plant cell?,"eg of solute in a plant cell - Mineral nutrients like Na , K , Ca ."
Osmosis and tonicity,what is ion and molecule? and how do elements become positive / negative charged?,"An Ion is basically a charged atom. The atom can be either positively charged (by losing one electron) or negatively charged ( by gaining one electron).
Molecules are groups of electrically neutral atom/s which are chemically bonded.
Charge is due to loss or gain of an electron in an atom."
Osmosis and tonicity,"My group and I are making lab project by estimating the osmolarity in tissues by bathing the blood samples from the 3 members of my group with hypotonic and hypertonic solutions and observing it by using our microscope. Since we are done with observations, we are assigned to do a group lab report, and my individual task is to basically do the data analysis. However, I do not know which type of graph should I create regarding the observation and its results of the osmolarity of the blood samples in all three solutions. Should it be line graph, bar graph, pie graph, or, etc.?",I might recommend using a line graph because it will clearly show the difference between the three blood samples.
Osmosis and tonicity,What are some factors that affect Osmosis?,great question
Osmosis and tonicity,Why does the cells of stomata becomes flaccid instead of shrinking when they loss water from them?,"First cells become flaccid. If enough water is lost they will plasmolyse, which is where they shrink away."
Osmosis and tonicity,so essentially the cell is trying to keep the ratio of solute to solution the same both inside & outside of the cell? is that why water moves out?,"Yes, you got it exactly right!"
Osmosis and tonicity,I keep on getting hypertonic and hypotonic mixed up any suggestions?,"Maybe you could think of the *e* as standing for excess, while the *o* stands for low?"
Structure of the plasma membrane,what is between the phospholipid bilayer?,"Since the polor ends of the phospholipids face the outer/ inner surface of the cell. They are in contact with the inter/outer cellular fluid predominantly water, glycoproteins,glycolipids, However the hydrophobic tails inter twin with each other forming the enter space between the polor heads. The space between the polor heads would contain saturated and unsaturated fatty acids which forms these tails. This gives them a slight negative polarity. With these fatty acid tail ( bent or straight) we would find a mosaic of integral proteins, cholesterol,. and yes,  water molecules passing threw!"
Structure of the plasma membrane,"So with that example of the pinhead touching the fluid membrane (and the membrane flowing out of the way), I'm wondering how a person can bleed if all cell membranes do this. As in why don't sharp objects like pins and needles go straight through (I know it sounds silly) our skin without drawing blood?","Bleeding occurs when veins are torn out. When you pass a pin through your skin ,the pinhead is literally much bigger than the individual cell for the pinhead to pass through the said cell membrane.So you can guess the pin must torn out some small veins on its way into your skin,not into an individual cell.Moreover there is no blood inside a cell or cell membrane for it to come out.Hope this clears your doubt"
Structure of the plasma membrane,"What is meant by "Transmembrane proteins may cross the membrane just once, or may have as many as twelve different membrane-spanning sections." I don't understand the twelve different membrane-spanning sections part.",I think it looks like three-pass transmembrane protein (in the first picture about proteins) only having 12 sections instead of 3.
Structure of the plasma membrane,Why do we have proteins in the cell membrane?,http://www.sparknotes.com/biology/cellstructure/cellmembranes/section2.rhtml
Structure of the plasma membrane,Would I need all of this information for regular High School Bio?,Yes.
Structure of the plasma membrane,"What are lipid rafts, what are they made of and whats their function? and where in the plasma membrane are they located?
thank you!","Lipid rafts are regions within the plasma membrane that are more rigid than the surrounding membrane.  

They are made of the same components as the rest of the membrane, but in differing amounts — for example they contain much more cholesterol. 

AFAIK their function is not completely clear, but they may help concentrate certain membrane proteins in a way that makes some cell processes more efficient.

There is an extensive wikipedia article on this that you may find interesting:
https://en.wikipedia.org/wiki/Lipid_raft

This article might also be worth reading:
http://www.jlr.org/content/44/4/655.full"
Structure of the plasma membrane,fluid mosaic model is cell of ??,"That's not correct .... the fluid mosaic model is a model of the plasma membrane which is present in ALL cells, both eukaryotic and prokaryotic, single-celled and multi-cellular organisms."
Fluid mosaic model: cell membranes article,"The article says the cell membrane has 2 types of proteins but it's missing the lipid bound protein (in-between the two phospholipid leaflets) mentioned in the "cell membrane proteins" video.

The article says there are 5 types of molecules but only 4 are listed.

The article says "The kinked shape of cis-unsaturated fats make it more difficult to pack tightly." What about trans-unsaturated fats?","I think lipid bound proteins are excluded because they do not play a role in transport or signaling.

In part 4 of the 5 types of molecules, there are two different categories lumped into one: large, polar; and ions.

Trans-unsaturated fats can pack more tightly than cis-unsaturated fats but less tightly than saturated fats."
Fluid mosaic model: cell membranes article,"How does phospholipid movement (flipping, flopping, scrambling) in the bilayer contribute to the survival of a cell?","This is actually a super cool question, never thought of it. I can think of several possible answers:
1) Signaling: though these videos don't mention it much, there are many different kinds of phospholipids and they can be useful for signaling and telling other cells what type of cell this is.  e.g. some phospholipid types are only on the outside membrane. One type of phospholipid, phosphatidylserine, is usually present more on the outside than inside. We know from observation that if it's present in equal numbers on the outer and inner leaflets, the cell is dying. So there might be some signaling going on.
2) To remove potentially dangerous molecules. Sometimes atoms or molecules generate radicals which are highly reactive. Maybe switching a radical from the outer to inner leaflet allows for safe removal or modification of the radical by the cell. It's better to contain a danger inside a cell so the cell can just die instead of losing the cell (in cases that the cell can be regenerated like in skin).
3) To increase the size of the membrane. Maybe phospholipids are produced inside the cell and they need to be flipped to the outer membrane to increase its size. The opposite could also be true, moving phospholipids into the inner leaflet to decrease the overall size of the outer membrane."
Fluid mosaic model: cell membranes article,"The article asks what makes a cell membrane fluid and then talks about three points that influence the fluidity of the cell, one of them being cholesterol.  Towards the end of the paragraph it says that without cholesterol, the phospholipids get closer together, then a sentence or two later it says that without cholesterol phospholipids get farther apart.  Is this a typo, or will phospholipids do both depending on the environment and condition they are in?","The key is temperature. Without cholesterol, the phospholipids will get closer together in a cold environment. The cholesterol acts as a kind of spacer to prevent them from getting too close. Conversely, in hot temperature, the phopholipids spread too far apart without cholesterol. The phospholipids want to be near the cholesterol molecules, causing them to be closer together."
Fluid mosaic model: cell membranes article,How might a phospholipid bilayer's tail become unsaturated?,"The unsaturation of the phospholipid bilayer's tail refers to the presence of double bonds in the fatty acid chains that make up the tails of phospholipids. These double bonds create kinks or bends in the fatty acid chains, affecting the overall fluidity and properties of the membrane.

The unsaturation of phospholipid tails can occur through two primary mechanisms:

Biosynthesis: Phospholipids are synthesized by cells through various enzymatic reactions. During the biosynthesis of fatty acids, the cell may introduce double bonds into the fatty acid chains through an enzyme called desaturase. Desaturase enzymes catalyze the insertion of double bonds between specific carbon atoms in the fatty acid chain, resulting in unsaturated fatty acids. The extent of unsaturation depends on the specific desaturase enzymes present in the cell.

Dietary intake: In certain cases, the degree of unsaturation in the phospholipid bilayer can be influenced by the dietary intake of unsaturated fatty acids. When organisms consume foods containing unsaturated fats, these fats can be incorporated into newly synthesized phospholipids, increasing the level of unsaturation in the membrane.

Hope that helped!"
Fluid mosaic model: cell membranes article,are all membranes made of phospholipid bilayers,"Mostly yes, but some archaea that live at high temperatures us a monolayer, basically the lipid tails go through the whole membrane and are attached to head groups on either side. If you google it, some diagrams will make it clear.
Maybe other exceptions also exist, but that is the only one that comes to mind."
Fluid mosaic model: cell membranes article,Is cell membrane different than plasma membrane? If so what are the differences and the similarities between cell membrane and plasma membrane?,"No difference, they are different terms for the same thing."
Fluid mosaic model: cell membranes article,How can you master this topic if you have trouble with it?,"Repetition and practice. Something else that may help is using different sources. Here's a link to the Amoeba sister's youtube video on the subject:https://www.youtube.com/watch?v=qBCVVszQQNs
But there is also crash course:https://www.youtube.com/watch?v=dPKvHrD1eS4 and the organic chemistry tutor.
Try looking for resources that work best for you, these all helped me and I hope they help you too :) :D"
Fluid mosaic model: cell membranes article,Can someone tell me the nitty gritty bits of the role cholesterol has on the membrane?,"Cholesterol is important because it controls the fluidity of the membrane.

*At low temperatures*: due to the limited movement, the membrane would become less fluid without cholesterol. However, because cholesterol is there, it does not. Why? I like to think of it as cholesterol "gets in the way" of the phospholipids packing together, since it is hydrogen bonded to them. 

*At high temperatures*: Without cholesterol, the membrane could become too fluid. However, cholesterol raisings its melting point, thus preventing this.

Cholesterol has these properties because it is a special type of lipid known as a *steroid*.Therefore, it has a rigid 4-ring structure. These rigid rings interact with the phospholipids around them and limit their movement due to their rigidity, thus preventing the membrane from undergoing any exxtreme changes in fluidity.

Hope this helps! :)"
Fluid mosaic model: cell membranes article,Can anyone also please provide some info about the saturated and unsaturated tails? Thanks.,"Saturated means that the tail does not have double bonds (the carbons are *saturated* with hydrogens) while unsaturated means that there are some double bonds and the carbons are not fully saturated with hydrogens. There are varying levels of unsaturation depending on the amount of double bonds present in the tail. Double bonds in the tail introduce bends and kinks that prevent the lipid tails from stacking as closely together and as such will increase the fluidity of the membrane. Conversely, a membrane with mostly saturated lipids will have lower fluidity because the tails stack closer together."
The cell membrane review,"Does the phospholipid bilayer of the cell membrane, make the membrane "water resistant," due to inward hydrophobic tails and the outward hydrophilic heads?","Yes,  it does, even though water can still get through the bilayer into the cytoplasm via the integral proteins in the bilayer"
The cell membrane review,How can water pass through the phospholipid bilayer if it has aquaphobic tails? Won't the water molecules get repelled out?,"I think another article said that some water molecules can sneak past the hydrophobic tails because they are very small (the water molecules, that is)."
The cell membrane review,how many cells in my body,About 37 trillion cells
The cell membrane review,Do u like whoppers? How many cells are in one?,More than 1.
The cell membrane review,i have a question i do not understand the word phobia can anyone comment to explain a bit more thanks.,phobia is greek for fear >
The cell membrane review,"what does a skin cell membrane look like? they aren't semipermeable, are they?",Look anywhere in lesson 3 and you will find a cross picture of cell membrane. And they ARE semipermeable.
The cell membrane review,why is a cell membrane semipermeable?,"The cell is kinda like an exclusive concert. It can't let just anyone in.  There are all sorts of free radicals and harmful metals that could invade the cell, not to mention those bacteria and viruses that constantly try to attack the cell. The cell needs a membrane to protect itself - to some degree - and establish an environment where it can do its job. You wouldn't want some stranger to randomly pop into your house, and neither does the cell. It does need some things from the outside world, though. That is why it allows certain particles to pass through the membrane. Hope this helps!"
The cell membrane review,What is the big difference between plasma membrane and cell membrane.,"there is no big difference, it is the same thing. another name for a plasma membrane (or a cell membrane) is a fluid mosiac model. again there is no big difference between these names, they are the same thing."
The cell membrane review,how many cells in  my body,"It's an estimated answer, but scientists predict around 37.2 trillion cells."
The cell membrane review,"So, is the plasma membrane the same thing as the cell membrane?","Yes, the plasma membrane and cell membrane are the same things."
Active transport review,is sweating a form of active transport,I think that sweating is a form of passive transport as heat that is generated in the cells inside your skin is moving WITH the concentration gradient from hot (inside) to cold (outside). I think that's right. I haven't yet studied the videos on perspiration.
Active transport review,What is the difference between facilitated diffusion and active transport?,Facilitated diffusion is a type of passive transport and along the gradient. Think of a pipe connecting a full tank of water to an empty one. Active transport is against the gradient. Think of a pump moving water from a nearly empty tank to an almost full one.
Active transport review,Are the largest molecules moved by only active transport or also by passive?,"No, actually both facilitated diffusion and active transport occur. When the molecules moving from high to low conc. like Glucose is very large, then we need channel proteins to move them into the cell, and channel protein only because they have the shape and structure to do so, so that the movement is only unidirectional (into the cell). Active transport transports or moves materials against the concentration gradient, that is, from low to high, and the size doesn't matter here like facilitated diffusion, only the concentration."
Active transport review,What is importance of active transport ?,Active transport is important because it allows substances to move against the concentration gradient. This helps it maintain the appropriate balance of substances in the cell.
Active transport review,"How do carrier/channel proteins select which particles to pass through and when?
More specifically,
How do aquaporins only let water in? How can the cell control the amount of water that can diffuse through aquaporins? How come the channel protein will not bring in potassium ions when it needs to bring in sodium ions?","Hi ! The shapes of the channels is very specifically adapted to letting only one type of molecules through. For example, aquaporins are shaped in a way that only water can pass through (because water has a specific structure and charge). Sodium and potassium do not have the same size nor shape and therefore one cannot use the channel of the other as well. 
The cell can control the amount of water that it lets in or out, by controlling the amount of aquaporins in its membrane. This is done by exocytosis/endocytosis of aquaporins, that can be controlled for example by antidiuretic hormons (that tend to provoke endocytosis of aquaporins)."
Active transport review,"How does the carrier protein change shape? Can the protein somehow bend, or does it chemically change?",The protien changes shape by using ATP energy. And no it cannot bend
Active transport review,I don't understand active and passive transport i need help.,Active transport uses energy to transport molecules across the plasma membrane. This uses energy from ATP. They also use pumps to get molecules in or out of the cell. Passive Transport does NOT use energy to transport molecules across the membrane. This can also just be molecules diffusing across the permeable membrane or a direct channel which they can enter or exit.
Active transport review,"what actually makes particles move down the concentration gradient? as in, why are particles by random motion able to passively move into an area of low concentration?? how can random motion lead to an overall non-random outcome??","The movement of particles is random, but even with that randomness, particles have a high probability to move from the area with high concentration to an area of low concentration. 

A good example would be if you get some small objects and assign them into two groups (A and B for example). However, you add more objects to group A than you do to group B. Then, for each object flip a coin. If the coin comes up as heads, keep the object in its assigned group. If the flip is tails, move the object to the opposite group. Once you're done, no matter how many more objects you put in group A then B, you should have a roughly equal distribution in each. 

This isn't a non-random outcome, it's just how probability works. The chance of an object moving from group A to group B is greater only because there are more objects in group A and therefore more chances to move to the other group."
Active transport review,"What are the differences between a carrier and a channel protein? Also, what are some examples?","Channel proteins are proteins that create hydrophilic holes in cell membranes, facilitating the transport of molecules down the concentration gradient. Carrier proteins are integral proteins that transport chemicals across the membrane both down and up the concentration gradient
 Some examples of channel proteins include chloride, potassium, calcium, sodium ion channels, aquaporins, etc. Examples of carrier proteins are sodium-potassium pump, glucose-sodium cotransport, valinomycin, etc."
Active transport review,what is hydrophillic and hydrophobic? Please answer,"Hydrophilic means a molecule or part of a molecule is _attracted_ to water. Hydrophobic means the opposite, it _repels_ water."
Passive transport review,"Hi, what exactly is facilitated diffusion?",When the molecules pass through the membrane via protein. (passive/active transport) Usually large and charged molecules use facilitated diffusion.
Passive transport review,How can water pass through the hydrophobic part of the cell without breaking the cell membrane?,I think they have passage ways so the water doesn't touch the hydrophobic parts of the cell membrane.
Passive transport review,"so if I understand, channel proteins do not require ATP. Am I right?",Yes. Channel protein is passive transport and doesn't use energy.
Passive transport review,can cholesterol pass?,"Cholesterol is part of the phospholipid bilayer membrane, it doesn't pass through because it is part of the membrane"
Passive transport review,What direction in a gradient does passive transport go?,From higher concentration to the lower concentration.
Passive transport review,What are the differences between osmosis and diffusion? are osmosis a part of diffusion?,"Osmosis is a type of diffusion, but it is specifically the diffusion of water,H2O. Diffusion is a term for any movement along a gradient"
Passive transport review,what is osmosis and what are some examples for it?,"Osmosis is the flow of water or other fluids across a semi-permeable membrane to balance chemical concentrations on both sides of the membrane. Try these Khan Academy videos and articles for more information.

https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/mechanisms-of-transport-tonicity-and-osmoregulation/v/diffusion-and-osmosis

https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/mechanisms-of-transport-tonicity-and-osmoregulation/v/osmosis

https://www.khanacademy.org/science/ap-biology/cell-structure-and-function/mechanisms-of-transport-tonicity-and-osmoregulation/a/osmosis

If you really want to understand osmosis, try this experiment. Take a normal egg. submerge it in vinegar for 24-48 hours, or until the shell has dissolved. Then, take your egg without a shell and submerge it in syrup for 24 hours. Observe. Then, take your egg and put it in distilled or bottled water for 24 hours. Observe again.

I know that this is a very vague answer, but I suggest going back and re-reading the article to try to understand why this is happening. I've found that sometimes knowledge gained by oneself when possible is better than getting an answer. Also, the practical application of osmosis in the experiment also helps understand it better."
Passive transport review,When water passes through the hydrophobic how does it get the water to go through the body and give it energy?,"Water passes through the membrane in a diffusion process called osmosis. During active transport, energy is expended to assist material movement across the membrane in a direction against their concentration gradient. Active transport may take place with the help of protein pumps or through the use of vesicles. hope that helps"
Passive transport review,Why does the hydrophobic center of a cell membrane prevent polar substances from diffusing through it?,Because they are to large to pass through without breaking it apart. (I think)
N/A,how does the nadh from glycolisys gets into the matrix so its electron could be used?,"It says above that NADH can't't cross the mitochondrial membrane, so there is some sort of shuttle protein."
N/A,"if the volume of the intermembrane space  was increased, what effect would this have on the function of a mitochondrion?","Hm.... A cell stays small to allow easier transport of molecules and charged particles from organelles. If the intermembrane space of the mitochondria was increased, I would think that respiration would be less efficient, because now the electrons have to cross a larger space and lose much more energy. So.... That's my guess and it would probably be wrong,"
N/A,What does substrate level phosphorylation means?,"Substrate level is the 'direct' formation of ATP in glycolysis and the Krebs cycle, basically any ATP not formed during the electron transport chain."
N/A,"Where did all the hydrogen ions come from? If NADH becomes NAD+, it releases H+ and if FADH2 becomes FAD and would release 2H+. So are the hydrogen ions released by those electron carriers are going to be used for the gradient and also for the water formation? Or are the Hydrogen ions that just came back through the ATP synthase going to be used for forming H2O??","The individual reactions can't know where a particular "proton" came from.  

Remember that all aqueous solutions contain a small amount of hydronium (H₃O⁺) and hydroxide (OH¯) due to autoionization.  

This means that processes in cells can use water to get rid of or grab "protons" (H⁺) as needed.  

This does have a small local effect on the pH, but forming that NADH or FADH₂ used protons so it all balances out in the end."
N/A,"I don't quite understand why oxygen is essential in this process. I get that oxygen serves as an electron acceptor at the end of the electron transport chain, but why is having this electron acceptor so important? Why would ATP not be able to be produced without this acceptor (oxygen)?","It is sort of like a pipeline. If you block the exit, the flow through the entire pipeline stalls and nothing moves. Oxygen is what allows the chain to continue and keep producing ATP."
N/A,"Where do the hydrogens go? I mean in glycolysis, one glucose is oxidised into two pyruvic acid and two NADHs. But technically there should be net two protons left in cytosol and that's where I am puzzled. Are the protons tansported into mitochondria matix and later pumped out by ETC or intermembrane space to form electrochemical gradient, or are they left in cytosol? According to the amont of water molecules generated in chemiosmosis, all the hydrogen from the glucose should be used to  form water, so do protons go into the mitochondria or mitochondria has extra protons itself?","Remember that all aqueous solutions contain a small amount of hydronium (H₃O⁺) and hydroxide (OH¯) due to autoionization.  

This means that processes in cells can use water to get rid of or grab "protons" (H⁺) as needed.  

This could have a small local effect on the pH, but cells are well buffered.  Also, in the end the various processes that create and use H⁺ end up balancing each other out.

The only situations where we really need to keep an account of H⁺ are processes involving membranes (e.g. oxidative phosphorylation) where H⁺ gradients are created and used."
N/A,How much H2O is produced is the electron transport chain?,"`C6H12O6 + 6O2 → 6CO2 + 6H2O + energy`


6 molecules of water :D


This is the overall formula for cell respiration, however, you ask how many water molecules are produced _specifically_ during electron transport chain?

Knowing that in the end, you get 6 molecules of water from *one* glucose molecule.
In the electron transport chain, hydrogen atoms are being added to available oxygen in order to produce water.


So you are confused about 6Co2, too? well, you know that after glycolysis, you get 3C molecules and bot undergoes Krebs cycle. Now, what you get from one Krebs cycle and proceeding ETC is doubled.

While it is true that via Krebs cycle we get 2 CO2 (giving 4 in total), do not forget decarboxylation prior to entering Krebs cycle (in between Glycolysis and Krebs cycle) there are is 1CO2. 1x2 = 2, 2+4 = 6

only 2NADH are reduced during ETC, giving a total number of 2, and also one FADH2 giving 1. It is 3x2 =6

*as for Oxygen*, it comes from the red blood cells which carry oxygen to absolutely every cell. Once in the cell, it enters mitochondria and acts as final acceptor of electrons. if not, water would not be produced.


http://www.dbriers.com/tutorials/2012/04/the-electron-transport-chain-simplified/"
Connections between cellular respiration and other pathways,Is there a difference in pathway between normal cells and cancerous cells?,"Yes, cancer cells tend to favor lactic acid fermentation and this is known as the Warburg effect.

The following is a link to get you started on learning more about this subject:
https://www.researchgate.net/figure/Metabolic-differences-between-normal-and-cancer-cells-are-shown-In-normal-cells-glucose_fig1_266086485

A recent review article on this:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4928883/

And a "webinar":
http://www.sciencemag.org/custom-publishing/webinars/metabolic-changes-cancer-beyond-warburg-effect"
Connections between cellular respiration and other pathways,"Do nucleotides ingested from the cells we eat, say in the cells of  a tomato, enter in the cellular respiration pathway? What happens to them?","They may be incorporated into our own nucleic acids, used as energy carriers within cells, or enter cellular respiration.

The biochemistry is somewhat complex, but to learn more you could start with this wikipedia page:
https://en.wikipedia.org/wiki/Nucleic_acid_metabolism#Degradation_of_nucleic_acids"
Connections between cellular respiration and other pathways,"I'm just wonder whether the use of proteins and lipids in cellular respiration is unhealthy, or does the body needs to do this too?","Proteins and lipids can also be used by the body to  create ATP. However, the body prefers glucose(carbs). Therefore, glucose is first taken before lipids and proteins,"
Connections between cellular respiration and other pathways,"Do molecules from a specific functional group produce more ATP or go through cellular respiration faster than another functional group? For example starches vs. proteins. Would barley (containing mainly starch), and mung beans (containing mainly protein) have a different rates of respiration? Which would be faster?","Catabolism of polysaccharides is fastest of the three macromolecules. Fats are second, and probably a fairly close second at that. Catabolism of protein is going to be much slower due to being a chain of polypeptides, a more complicated molecule than polysaccharides. In fact, about 25% of the total energy gained from breaking down proteins into amino acids for energy is used simply in breaking down the protein because the process is so intensive."
Connections between cellular respiration and other pathways,"How long does it take for completion of cellular respiration and also the individual metabolic pathways (glycolysis,tca,etc) to occur?","It is very hard to quantify and say exactly how long it takes for one round of cellular respiration. We do know that it occurs very quickly. Cells do not stockpile ATP which means that as soon as ATP is used up more needs to be made. Cellular respiration, more than likely, occurs in milliseconds.

But usually, it is hard to estimate how fast metabolism occurs because all reactions are connected and metabolites from anabolic reactions enter catabolic reactions. It is a big network never stopping, never making a break. Highly dynamic."
Connections between cellular respiration and other pathways,can lactose be used for cellular energy?,"In general yes, but it may depend on the organism.

For mammals, lactose is present in milk and so young mammals will typically produce the enzyme lactase to allow this sugar to be metabolized.  

Other organisms (e.g. some bacteria) will also be able to metabolize lactose — for example the gut bacteria _E. coli_ has a well studied ability to use this sugar.

Khan Academy has material on this in a few places — for example see:
https://www.khanacademy.org/science/biology/gene-regulation/gene-regulation-in-bacteria/v/lac-operon

Does that help?"
Connections between cellular respiration and other pathways,Could fat molecules be used for cellular respiration instead of glucose? and why?,"I do not think lipids could be used for cellular respiration _instead of glucose_.

Why?

Because it relies on the chemistry of bonds and beta-oxidation of fatty acids.

Sugar is the primary source fo energy, being as starting reactant in cellular respiration, or the final product of photosynthesis.

Also, lipid synthesis or beta-oxidation is a much slower process plus no stage requires phosphate.

Relying on entirely different pathways and molecules would require a change of the cell's energy molecule ATP and the mechanism of phosphorylation and dephosphorylation."
Connections between cellular respiration and other pathways,Some muscle cells can switch between aerobic respiration and fermentation. What's the advantage of this capability?,"The better adaptation, preparedness, effectiveness and better efficiency of using energy."
The citric acid cycle,Explain why citric acid cycle can't operate in the absence of oxygen?,"Cooper is right...

Once the ETC stops oxidizing NADH to NAD+ there is no longer any NAD+ available for the Krebs cycle to reduce back to NADH and the cycle comes to a halt. Therefore, the Krebs cycle is actually regulated by the availability of NAD+

It is true that the Fermentation process an contribute to NAD+ regeneration but remember that under anaerobic condition most of the cell's pyruvate is being sent to the Fermentation pathway... and even when NAD+ is regenerated during Fermentation, there will be much less Pyruvate (I'm trying to avoid words like "none") entering the Kreb's Cycle.

All this being said, yes technically it can but it would not be contributing to the overall goal (ETC) so the ATP production will be significantly less."
The citric acid cycle,Is there a difference between ATP and GTP?,"ATP is adenosine triphosphate, or adenine (the DNA base) with a ribose (the sugar) attached which makes it adenosine, then with three phosphate groups added. GTP is all the same stuff, except for Guanine substituted in for Adenine."
The citric acid cycle,"Which provides more energy output, 1 ATP molecule or 1 GTP molecule?","The difference between ATP and GTP is not on their energy output, but on their relative abundance in cells. There are far more ATP than GTP in cells to provide energy, because of evolution."
The citric acid cycle,How kerebs found this cycle?,"Krebs was working on the problem of finding the chemicals that act as intermediaries in cellular respiration. He discovered that when he added certain chemicals to pigeon breast muscle cells, their oxygen consumption would increase, thus indicating that more respiration reactions were taking place. These chemicals are the same ones we now identify as those making up the Kreb's Cycle. :)"
The citric acid cycle,Going from Malate to Oxaloacetic Acid 2 hydrogen ions are hydrolyzed but only one NADH is formed. Where did the other Hydrogen Ion go?,"NAD+ needs 2 electrons en 1 proton to make NADH.
The oxidation of malate transfers these products to NAD+. There is indeed a remaining H+ ion that is released in the matrix as a proton. That way the charge is kept on both ends of the reaction. 
This also happens with the other times that NADH is formed (releasing a proton) but there the proton was released beforehand when the carboxyl group was created."
The citric acid cycle,"In the picture "Oxidation of pyruvate and citric acid cycle", in step 3 and 4, I saw there are 2 H+ ions produced but I'm not sure where they came from. I think there should be no spare H+ ion in step 3 and 4.","They are not spare, that's the way NAD+ is reduced. Those H+ ions are used in generating proton gradient later for ETC."
The citric acid cycle,I was wondering whether it's necessary to remember the formula of each compound? Thank you! :),"Most basic biology classes, even AP bio don't require you to know the exact structure, although you might want to know their basic structure such as oh this is glucose with a phosphate group attached, this is a molecule with an extra proton, since most questions in that topic will revolve around that."
The citric acid cycle,Can GTP serve the same functions as ATP?,"They are both energy carriers and there are even enzymes that will exchange high-energy phosphates among ribonucleotides§.

However, these molecules are not interchangeable at a molecular level — most enzymes can only use one or the other as a source of energy.

For example, ribosomes use GTP (never ATP) to drive the correct decoding of the codons in mRNA — in contrast, aminoacyl-tRNA synthetases can only use ATP to couple amino acids to the correct tRNA‡.

Does that help?


§Note: Nucleoside-diphosphate kinases (NDKs) — for details see:
https://en.wikipedia.org/wiki/Nucleoside-diphosphate_kinase


‡Note: Khan academy has more about these processes here:
https://www.khanacademy.org/science/biology/gene-expression-central-dogma#translation-polypeptides"
The citric acid cycle,If using this for CLEP bio should I memorize this cycle and equation?,"Having taken the CLEP Biology exam, I would recommend it. You may not come across it, but it can't hurt. I had a few questions regarding this, but I can't remember whether I needed the equation memorized. I still memorized it though, because I would rather know it and not need it than not know it and need it."
The citric acid cycle,Why doesn't it produce hydrolisis when water added in the step 7?,"One thing that determines which reactions happen in a cell is which enzymes there are, since they are the catalysts that increase the rate of feasible reactions so that they actually happen at a useful rate. So enzymes are often responsible for deciding at exactly which position in a large molecule a reaction will happen, where in a test tube, the chemicals might slightly prefer to react at a different position.

That being said, from a chemical point of view, fumarate and water reacting the way they do makes sense, whereas I don't see how a hydrolysis reaction could take place. In hydrolysis reactions, the negatively charged oxygen of water 'attacks' some partially positive charged atom on another molecule and shares its electrons with it in a new bond, and a 'leaving group', which is happier to take its electrons with it, is displaced and leaves. It then picks up the spare H+ from the original water. In this way an OH- has been added to one part of the original molecule, and a H+ to the other, and the molecule has been split (lysed) into two by water(i.e _hydrolysed_).

But in step 7, fumarate has a double bond across which the water is added (in a 'hydration' reaction). So the molecule is not split in two, because a bond remains linking the two atoms that got either the H+ or OH- added to them.

Does this help?"
Regulation of cellular respiration,"So this page and the entire section is on cellular respiration and how it works but what I’m curious is: With all these many tiny molecules bopping into each other and performing all these different and variable reactions inside of a tiny cell, how did biologists / chemists figure this out?

(Hoping for a detailed technical answer…)",You can follow up through reading his paper on it. http://www.nobelprize.org/nobel_prizes/medicine/laureates/1953/krebs-lecture.pdf
Regulation of cellular respiration,Why is it essential that the enzymes that catalyze steps 1 and 2 are not inhibited when ATP concentrations are high?,"No, it is not that they are _obligated_ to stay active, the point is that by inhibiting those enzymes you _do not_ affect rates of glycolysis.

Regardless of ATP levels, hexokinase and phosphoglucoisomerase can or cannot be inhibited but it won't affect levels of produced ATP."
Regulation of cellular respiration,"In this entire Cellular Respiration section, I haven't been able to figure this out: If the anaerobic glycolysis occurs, does pyruvate oxidation and the krebs cycle continue? Or are the last 3 steps only able to occur with aerobic glycolysis?","If anaerobic glycolysis occurs,  pyruvate oxidation and the Krebs cycle does not occur. The lactate produced is transported to the liver where it is converted to pyruvate again."
Regulation of cellular respiration,how does citrate come out of the mitochondria ?,"*Citrate - pyruvate shuttle*


Citrate can exchange for malate. The citrate in the cytoplasm can act as a regulator of phosphofructokinase, or as a substrate for ATP citrate lyase, an enzyme that reverses the citrate synthase reaction, and produces acetyl-CoA and oxaloacetate.

The oxaloacetate produced in the ATP-citrate lyase reaction can be converted to malate. Both the oxaloacetate and malate can be used for a variety of reactions; for malate, one additional reaction, catalyzed by a malic enzyme, results in the formation of NADPH and pyruvate and carbon dioxide. The pyruvate produced by the malic the enzyme can return to the mitochondria to complete the cycle."
Regulation of cellular respiration,How do the various stages of cellular respiration work together and utilize enzymes to reduce or oxidize molecules to efficiently create ATP energy for the cell?,"If the environment is rich in oxygen then aerobic cellular respiration will take place, in some oxygen deprived scenarios, like when exercising, the cells might switch to anaerobic cellular fermentation due to the fact it will produce some readily available energy but albeit much less versus the aerobic pathway."
Regulation of cellular respiration,"I thought ADP was too stable to lose another phosphate group. So, does the cell mistakenly use ADP in place of ATP when it's low on the latter?","ATP is the most common energy carrier for the cell.  Each phosphate that you remove conveys energy but less each level.  ATP has more energy than ADP for example.  The cell sometimes doesn't need all the energy from ATP -> ADP and thus, ADP -> AMP can be used to drive a reaction.  This is why the cell might use ADP.  Our enzymes are pretty good at choosing the right energy carrier that leads to the best efficiencies.  ADP usually doesn't carry enough energy to power a reaction requiring ATP."
Regulation of cellular respiration,"Biochemistry question: We use citric acid in industry to increase self life etc. of foods. Instead of utilizing citrus fruits scientists have learned we can use microganisms (Asperigillus niger) and harvest their citric acid (that is produced as an intermediate during cellular respiration). These microorganisms are grown in "fermentation tanks". But, these fermentation tanks must supply oxygen to the microorganism so that it can go through cellular respiration (or part of it).  So, my question is: why is this process considered fermentation if it includes using oxygen?","Certain micro-organisms, such as the Clostridium Botulinium can only use fermentation, and oxygen is actually dangerous to them. A lot of other micro-organisms can perform both aerobic and anaerobic respiration. The type of respiration will depend whether oxygen was supplied to the mixture or deprived of it when the situation mandates itself... I hope that helps..."
Regulation of cellular respiration,"Cells uses biochemical pathways for it's anabolic processes, which there are more steps to create the end product. Can someone tell me why making your process longer be more beneficial to the cell?","That's not the point we are looking at it.

If you set it that way it looks like making process longer is more beneficial, which usually *is not* in the cell.

Cells use longer biochemical pathways for anabolism because usually intermediates of catabolism or anabolism are substrates for _other_ reactions.

Literally, every molecule has its own place in the network of metabolic reactions. :)

comment if you have more questions."
Regulation of cellular respiration,Can someone tell me if cellular respiration is similar to photosynthesis?,If anything I would say they are both close to being opposite of one another. Cellular respiration takes in carbohydrates for example and break them down to their oxidized form CO2 and harvest the energy stored in the carbs by breaking their bonds to drive our physiological functions (Catabolism). Photosynthesis on the other hand is the process of creating chemical energy from light energy emitted from the sun. In plants another process known as the Calvin cycles uses this chemical energy to reduce a whole bunch of CO2 molecules to generate carbs/sugar/glucose (Anabolism).
Steps of cellular respiration,if glycolysis requires ATP to start how did the first glycolysis in history happen?,"You must remeber that life on this planet has been evolving for billions of years, it is highly unlikely that the originating system resembles the current system. The development of celluar respiration began as a simple inefficient system progressing to it's current incarnation."
Steps of cellular respiration,What is the role of NAD+ in cellular respiration. Why is the role NAD+ plays so important in our ability to use the energy we take in?,"Hello Breanna! 
NAD+ is an electron transport molecule inside the cristae of a cell's mitochondria. In glycolysis, the beginning process of all types of cellular respiration, two molecules of ATP are used to attach 2 phosphate groups to a glucose molecule, which is broken down into 2 separate 3-carbon PGAL molecules. PGAL releases electrons and hydrogen ions to the electron carrier molecule NADP+. Each PGAL molecule has a phosphate group added to it, forming a new 3-carbon compound. These phosphate groups and the phosphate groups from the first step are then added to adenosine diphosphate or ADP, forming 4 ATP molecules. This also produces 2 molecules of pyruvic acid."
Steps of cellular respiration,"When it states in "4. Oxidative phosphorylation" that the NADH and the FADH2 return to their "empty" forms NAD+ FADH2, the author meant FAD when referring to the "empty" forms, right?","the empty state of FADH2 is FADH, after oxidation it loses 1 h+ ion and elctron."
Steps of cellular respiration,I have a question... Which part of the body will most likely use the cellular respiration? Is it lungs?,"Cellular Respiration happens in your cells and you entire body is made up of cells, it goes on all throughout your body including your lungs and brain."
Steps of cellular respiration,"When the electron carriers NAD+ and FAD gain electrons, why are 2 hydrogen ions also being added?","The free energy from the electron transfer causes 4 protons to move into the mitochondrial matrix. 


In other words, electrons provide energy for hydrogen atoms. Electrons fuel movement of protons. :)"
Steps of cellular respiration,Does the glycolysis require energy to run the reaction?,Yes glycolysis requires energy to run the reaction. 2 ATPs  are used up by glycolysis this then begins the oxidative process of glycolysis.
Steps of cellular respiration,Aren't internal and cellular respiration the same thing?,"Cellular respiration is oxidative metabolism of glucose which takes place in mitochondria and in the cell. 

Internal repsiration is gas exchange between blood and tissues.


https://med.libretexts.org/Bookshelves/Anatomy_and_Physiology/Book%3A_Anatomy_and_Physiology_(Boundless)/21%3A_Respiratory_System/21.9%3A_Gas_Exchange/21.9B%3A_Internal_Respiration"
Steps of cellular respiration,"In the Citric Acid Cycle (Krebs Cycle),  would the four-carbon molecule that combines with Acetyl CoA be Oxaloacetic acid?",Yes. Acetyl CoA and Oxaloacetic Acid combine to form a six-carbon molecule called Citric Acid (Citrate).
Steps of cellular respiration,"I was taught that it was Glycolysis, Pyruvate Oxidation, Krebs cycle, Electron Transport, and then Chemiosmosis. Which is correct? or is it saying the same thing in different terms?","It is the latter...the same thing is being said in different terms.
- Glycolysis and pyruvate oxidation are directly mentioned.
- Citric Acid cycle is also known as Kreb's cycle (Discovered by Hans Kreb).
- The Oxidative Phosphorylation step as mentioned above can be broken into these two steps: 
a. Electron Transport Chain helps in creating a proton gradient i.e. as the electron travels through the electron transport chain, its energy is used up to transport hydrogen ions into the intermembrane space.
b. Chemiosmosis: As a proton gradient is achieved, the hydrogen ions pass into the mitochondrial matrix through the ATPase (FoF1 complex) embedded in the mitochondrial membrane, and ATP is produced. these two steps together are known as oxidative phosphorylation since the energy and electrons are obtained by oxidizing (taking electrons from) NADH and FADH2."
Steps of cellular respiration,"After oxidative phosphorylation, the ATP created is in the mitochondrial matrix, right? If so, how does it get out of the mitochondrion to go be used as energy?","Just like the cell membrane, the mitochondrion membranes have transport proteins imbedded in them that bring in and push out materials."
Pyruvate oxidation,Is this considered anaerobic or aerobic?,This is aerobic as it involves the Mitochondria where pyruvate oxidation occurs.
Pyruvate oxidation,"I'm a little confused, it says a carboxyl group is snipped off, which would make sense because then the NAD can be reduced. However it shows no hydrogen in the carboxyl group","I was confused about this too, but now I know:
The carboxyl group *does* give the acetyl group a negative charge, *but* this is not why the NAD+ comes. If you look at the illustration, it shows the CoA attached to sulfur and Hydrogen in step 2.  The NAD+ comes to snatch up a H ion that the CoA-SH left."
Pyruvate oxidation,"What exactly is NAD+ and NADH? And what are they made of, I have asked my bio teacher but he doesn't really answer in depth. Sorry I know it may seem like a stupid question but I find myself confused on this stage.","https://upload.wikimedia.org/wikipedia/commons/thumb/b/b5/NAD_oxidation_reduction.svg/250px-NAD_oxidation_reduction.svg.png  NADH is a molecule that can donate a hydrogen atom and the electrons to go along with it, NAD+ can accept a hydrogen atom and its electrons."
Pyruvate oxidation,Does the pyruvic acid required for krebs cycle come from glycolysis??,"Yep, the pyruvate becomes Acetyl CoA after losing a carbon molecule. Then it joins with Oxaloacetate to get into citrate cycle."
Pyruvate oxidation,"Why is NADH formed when NAD+ is reduced, gained electrons? Shouldn't it be NAD with no charge or NAD- with a proton kicked out? Furthermore, where did the hydrogen to build NADH come from?",The bicarbonate buffer system is what creates H ions.  Our body recycles 70% of CO2 by hydrolysis.  CO2 and H2O convert into carbonic acid H2CO3 and immediately get broken down into H and HCO3
Pyruvate oxidation,What causes the carboxyl group of the pyruvate to be removed?,"The enzyme 'pyruvate dehydrogenase' pulls away the carboxyl group, resulting in the release of Carbon Dioxide, leaving the Acetyl group behind for binding with CoA."
Pyruvate oxidation,What general key things do I need to know for each step of the Krebs cycle?,"usually the enzymes and intermediates are most important, and also the by-products released, ie, the NADH, FADH, and GTP"
Pyruvate oxidation,"My textbook states that the pyruvic acid is first converted into acetic acid before being oxidized. This conflicts with what is being presented here. What is going on?

Furthermore, my textbook states this occurs in the cristae of the mitochondria — while this site claims it happens in the matrix...",Definitely happens in matrix. This site is correct.
Pyruvate oxidation,What does the structure of Co-enzyme A look like?,"CoA consists of an adenine nucleotide base attached to a ribose 5 carbon sugar, from which is attached a chain of 2 phosphate molecules (as in ADP). The enzyme protein comes next on the chain, followed by a covalently bonded sulphur molecule, which is then lastly attached to the removable functional group, the acetyl group -COCH3"
Pyruvate oxidation,"Is this process also called the link reaction?
if it is, according to my teacher, the process occurs in the mitochondria inner chamber..","Yes, it's also called the link reaction. The matrix is in the inner chamber."
Fermentation and anaerobic respiration,Is there a reason why Flourine can't be used in place of oxygen as the final acceptor in the electron transport chain? Wouldn't it produce more ATP due to its higher electronegativity?,"There are a few reasons that spring to mind. The first is simply to do with availability. Oxygen makes up 21% of our atmosphere and is stable in both air and water whereas fluorine is much rarer. In addition fluorine is very reactive so would not exist by itself for very long. Also if fluorine were used as the terminal electron acceptor it would form HF, hydrofluoric acid in solution which is hard for the cells to deal with and would affect pH in the cytosol affecting enzyme function whereas oxygen just forms water. Finally fluoride is known to be damaging to the body above certain concentrations affecting things like the nervous system and hormone secretion as well as protein synthesis.
Please bear in mind these are just my thoughts.

P.S remember oxygen is not producing the ATP itself it is merely keeping the transport chain unblocked so the electrons keep flowing. A more electronegative element wouldn't necessarily have any effect on the rate of electron flow down the ETC and therefore wouldn't affect the rate of ATP production."
Fermentation and anaerobic respiration,Would Balsamic Vinegar be an example of lactic acid fermentation since the grape bypasses the alcohol?,"To make vinegar, grapes are first made into wine via fermentation. The next step in the process is the introduction of an Acetobacter bacteria strain. Acetobacter in the presence of oxygen will feed upon ethanol and release acetic acid (vinegar) as a byproduct."
Fermentation and anaerobic respiration,"In the diagrams there write, "NADH regeneration," wouldn't it be more accurate to say "NAD+ regeneration?"",its kind of like regenerating nad+ so that they can accept electrons to *become nadh again*
Fermentation and anaerobic respiration,"Okay, this is actually really interesting... if the lactate isn't what's causing the soreness of muscles after exercising, then what is it?","It is associated with damage to the muscle fibers, but the details don't appear to be well studied.

This article seems to be the source for much of the information currently available on the internet:
https://www.ncbi.nlm.nih.gov/pubmed/7830383"
Fermentation and anaerobic respiration,Where is the electron transport chain in an anaerobic respiration found?,"The electron chain is not found in anaerobic respiration. Anaerobic means "without oxygen". The electron transport chain requires oxygen, therefore it cannot be present in anaerobic respiration.

I hope this helped! Comment if you have any questions; I'll answer to the best of my ability."
Fermentation and anaerobic respiration,Why can't human undergo ethanol fermentation? is there an enzyme that is required which we don't have?,"Exactly.

We lack alcohol pyrivate dehydrogenase.

Also, it would be lethal for humans to produce ethanol. Ethanol is very toxic, causing: drowsiness, cognitive impairment, liver failure, liver cirrhosis, and eventually death."
Glycolysis,"when NAD is turned into NADH, G3P(5H) loses two electrons and "two" protons. but in the next step, 3-bis..., theres still 4H. not sure how this happens.",The other H comes from HPO4 with a 2- charge which eventually turns itself into inorganic phosphate.
Glycolysis,"In the Investment phase, where did the 2 atps come from that were used up? was it taken from somewhere else? if the goal is to produce atp in glycilysis, where do we get atp to begin the process?","The ATPs originally came from your mother through parental nutrition, while you where developing in the womb. When you are born you will have a stock pile of ATP in your body, which must be replenished to stay alive. The body has many ways to make ATP, which can be seen by looking at the vast amount of metabolic reactions that occur with the body.  This is also why we can survive for a long time without any additional consumption of food as the many catabolism pathways in the body that breakdown larger molecules and transfer the energy from the breakdown to ATP. When food is abundant the breakdown of glucose by glycolysis and the Krebs cycle will produce much more ATP than the 2 ATPS required in the investment phase.  Additionally, this investment phase aids in regulating the metabolic reactions that occur in our body/cells."
Glycolysis,"In step 6, where does the second phosphate group come from?","By my understanding, phosphates are often freely floating throughout the cell. This is because they're used for tons of processes, and enzymes like phosphatase clip them off of ATP and various other molecules during reactions, and then just leave them to float around."
Glycolysis,Why the 1st phase are same in aerobic and anaerobic respiration,This is because oxidation in glycolysis doesn't involve oxygen atoms. It's just movement of hydrogen. So it's behaving in the same way with or without oxygen.
Glycolysis,"In the highlight glycolysis part,in the second last paragraph,why fructose-1,6-bisphosphate is unstable?
Can you explained more detail on what is means by speeds up or slows down glycolysis?I still dont understand.
Thank you.","One important note is that the enzyme that catalyzes the reaction phosphofructosekinase is what actually speeds up or slow downs glycolysis. Once fructose-1,6-bisphosphate is formed it will be broken down to the two carbon molecules at the same speed. The way it is speed up or slowed down is due to phosphofructosekinase the enzyme that catalyzes the reaction to create fructose-1,6-bisphosphate is regulated by both ATP and ADP, when ATP levels are high it is inhibited and less fructose-1,6-bisphosphate will be created when ADP levels are high it will be activated and more fructose-1,6-bisphosphate will be created. This allows the cells a way to regulate the breakdown of glucose depending on the energy needs of the cell as stated by Chris."
Glycolysis,"in step 6 in the detailed payoff phase... how after NAD+ is reduced, gained 2 H+ and converted to NADH, H+ is still produced ? 
Thanks in advance.","I think you have two very subtle differences mixed. Note that one H radical is [H]+ with one electron, and the reason why I write this is because when you add the proton, the H+, then you actually also need to add additional electrons, so for every one H you also have one electron. You would write:
1.  The NAD+ gains 2H (free radical) to become NADH (free radical) & [H]+. 
2.  Alternatively, you could say that the NAD gains 2H (free radical) to give NADH2 (free radical)"
Glycolysis,What is unusual about fructose being metabolized in the liver vs other tissue types?,"There are several reasons. Simply put, the liver is really well equipped and prepared to metabolise it and also fructose, as opposed to glucose for example, seems to be a better substrate for glycogen synthesis in the liver. 
Fructose and glucose both seem to be very similar, they have almost identical structures but even a tiny change in a molecule can affect how it is metabolised in the body. I recommend reading up on it further since that's a fascinating question worth exploring."
Glycolysis,"The steps 5&6 are confusing me 
In step 4 the aldolase enzyme break up the "Fructose-1,6-phosphate" into GAP & DHAP
What's after that ?

without structures please.","DHAP gets converted to G3P (glyceraldehyde-3-phosphate) by the enzyme triosephosphate isomerase and then you get 2 G3P molecules which get converted to 1, 3 bisphosphoglycerate by glyceraldahyde-3-phosphate dehydrogenase and at the same time you have 2 NAD+ being reduced to 2 NADH by a hydrogen ion and 2e- going to each NAD+"
Glycolysis,what is the difference between aerobic and anaerobic glycolysis?,Aerobic is within an oxygen filled environment. and anaerobic there is no oxygen present in the environment.
Introduction to cellular respiration and redox,What is the difference between nadph and nadH,"It is just one extra phosphate group in NADPH, the rest of the molecule is identical. Both act as proton donors although for different sets of biochemical reactions."
Introduction to cellular respiration and redox,What is the difference between NADPH and NADH,NADH is used in cellular respiration whereas NADPH is used in photosynthesis; NADPH has an extra phosphate group.
Introduction to cellular respiration and redox,Is NAD+/NADH primarily involved with glucose (entering ETC via complex1) & FAD/FADH2 primarily (exclusively?) involved with fats & amino acids (entering ETC via complex2)?,"Not that I know of. They are both carriers for hydrogen ions (H+) and their purpose is to get those electrons/ions to the ETC where they can be used to make ATP. Since the NADHs are dropped at the first protein complex, the hydrogen ions that it brings in go through active transport in 3 proteins, making 3 ATP for every NADH. The FADH dropps off the H+s at the second protein complex, and since the H+s it brings in only go through 2 proteins, it only makes 2 ATP for every FADH molecule.

So to answer your question, where the molecules enters, to my knowledge, has nothing to do with whether it is involved with glucose or amino acids. Could you possibly be getting it confused with something else?"
Introduction to cellular respiration and redox,"I still can't comprehend the notion of electrons' energy levels. I thought that it had to do with which orbital the electron was in, being the furthest away from the nucleus the ones with higher energy levels. But then, why are electrons at a higher energy level when associated with a hidrogen than when associated with an oxygen?","Yes, further apart orbitals are associated with higher energy levels.

Look, if an element is more electronegative than it attracts other atoms and makes electrons scroll down to the lower energy states. More electronegative element hogs electrons stronger than a less electronegative element."
Introduction to cellular respiration and redox,What is the purpose of Cellular Respiration??,"Cellular respiration is an absolutely essential process for any cell because it's how it produces energy. 

Cells need energy for all kinds of things: moving things around, producing substances, getting nutrients, etc.

For cells, this energy typically comes in the form of a molecule called ATP. Cellular respiration is a series of steps by which fuel molecules (such as glucose from your food) can be used to produce ATP that the cell can use. 

Does that help?"
Introduction to cellular respiration and redox,"Do all catabolic processes occur under anaerobic conditions, while anabolic process occur under aerobic conditions, or is that just a coincidence?","Did you mean the opposite of what you wrote?

In any case, things are not nearly that simple.


Catabolism (the breakdown of complex molecules to simpler components) can be anaerobic or aerobic.  In fact both types happen in our bodies all the time — in most tissues we typically use oxidative respiration (an aerobic process) to maximize the amount of energy we extract from food.  However, during vigorous exercise our muscles run out of oxygen and switch to an anaerobic process called lactic acid fermentation.  This is also the process that powers our red blood cells.

You will learn more about some forms of anaerobic respiration later in this section:
https://www.khanacademy.org/science/biology/cellular-respiration-and-fermentation#variations-on-cellular-respiration


Anabolism (building complex molecules from simpler components) in most cases isn't directly influenced by oxygen availability, but since it requires energy it will be hampered by anaerobic conditions (at least in aerobic organisms like us).

However, there is at least one hugely important anabolic process that is poisoned by oxygen — nitrogen fixation.
(For more information on this see:
https://www.nature.com/scitable/knowledge/library/biological-nitrogen-fixation-23570419)"
Introduction to cellular respiration and redox,Why is it that O is more electronegative but when a carbon based molecule loses O it becomes reduced?,Because it gains an electron.
Introduction to cellular respiration and redox,i still cant understand the concept of oxidation and reduction in term of NAD+ and FAD.. when NAD+ oxidise or reduce to NADH? why ?,"NAD+ --> NADH is reduction (because it's gaining a hydrogen). It's being reduced because NAD+ is made up of carbon, hydrogen, nitrogen, oxygen and phosophorus atoms and all of these are very electronegative except for hydrogen. When the NAD+ bonds with a hydrogen the electrons are hogged by the very negative atoms like when Sal was talking about glucose. This is the same for FAD I think because it's made up primarily of those electronegative atoms. Hope that helps :)"
Introduction to cellular respiration and redox,Is the action/movement of ATP synthase passive or active?,Overall functioning of ATP synthase is 'passive'. It requires a proton gradient in order to work. it does not require dephosphorization of another ATP molecules.
Introduction to cellular respiration and redox,Can you explain how 36 ATP is forned in cellular respiration in eukaryotes?,"Actually, the amount of ATP produced in cellular respiration actually varies. It depends on the cell's efficiency and therefore fluctuates in the maximum production of ATP. So it can be any whole number of ATPs, probably 34, 36, or 38 ATPs in a eukaryotic cell. Usually, that number varies in the oxidative phosphorylation step, depending on the amount of NADH and FADH2 available for the process. NADH produces 3 ATP while FADH2 produces 2 ATP via chemiosmosis. Glycolysis produces 2 ATP and 2 NADH, Krebs Cycle produces 2 ATP, 6 NADH, and 2 FADH2. Then, you have a net total of 36 ATP. Sal explains this much better than I could :P."
N/A,can we say that global warmimg will result with more photorespiration in c3 plants if precautions are not taken?,"I'm not sure about this, because CO2 levels in the atmosphere are increasing... which might indicate that there would actually be LESS photorespiration because of increased CO2 levels. Curious to hear what others think."
N/A,In the last paragraph. How can photorespiration support plant immune defenses?,"Plant defense mechanisms include different kinds of cell signaling pathways and cascades. Certain membrane-spanning receptors react to pathogens and activate gene expression. However, in order to proceed with those mechanisms, photosynthesis has to be disrupted.

As we know, photorespiration is that 'salvage' way which occurs once photosynthesis is disrupted."
N/A,what are plant pigments?,"There are many types such as Chlorophyll A, Chlorophyll B, Xanthophyll, Carotenoids, etc. They function to lengthen the absorption spectrum. Some, like the last two pigments listed, also function to increase photoprotection. The Chlorophyll A is what is most prevalent in the leaf, and therefore, gives the leaf its color."
N/A,When C3 plans are in a hot environment what do they first die of? Because their ability to produce glucose is significantly reduced and they will eventually use up all their H2O ?,I think of take in CO2 during day whicc CAM plants doesn't and en up losing (not use up) H2O.
N/A,Why do the numbers of carbon in the diagram for Photorespiration not match up,"They do, There are 6 5-carbon RuBP molecules (30C), which are broken into 6 3-carbon PGA molecules (18 C) and 6  2-carbon phosphoglycolate molecules (12C). These 2-carbon phosphoglycolate molecules are further broken up into 3 3-carbon PGA molecules (9C) and 3 1-carbon CO2 molecules (3C). The CO2 is released (3C), the 9 total PGA (9x3=27C) are used to regenerate some, but not all of the RuBP. Total product being 9 PGA and 3 CO2 (27C+3C=30C) which is the same amount as we started with in the 6 RuBP"
N/A,"If alternative systems exist to solve this problem, why don't all plants use those systems? Is it less efficient?","It isn't really such a big enough deal to completely wipe out RuBisCo. Remember, back when plants were first starting, there was WAY more CO2 than oxygen. Plus, scientists are beginning to research if there are hidden benefits that haven't been identified yet."
N/A,"Concerning the last part of the text above... How exactly can plants get light-induced damage, how does this damage the plant and how does the redox balance help against this (Does this have something to do with reactive oxygen species?)?","Yes, exactly! It has to do with reactive oxygen species! It was also mentioned in the videos prior to this.

Photorespiration is some kind of 'salvage' and protective pathway which avoids the accumulation of unnecessary 02 which could potentially elicit great damage in cells in the form of reactive oxygen species."
N/A,"why is photorespiration taking place in three different places chloroplasts, leaf peroxisomes and mitochondria?",This is because the different enzymes needed for amination and oxidation of different intermediates are present in the above said 3 organelles. The detailed diagram of the cycle ought to clear your doubt.
The light-dependent reactions,"Ok so from what I am understanding from this article is that the electrons for the electron transport chain come from the splitting of water, but I am having trouble grasping that? Specifically, are the electrons moving on up and down the chain by themselves...without protons and neutrons?","You are correct. When we split the H2O, our 2 protons in the hydrogen (the h+ ions, basically just a proton floating around), the waste product of oxygen, and then our 4 electrons. Since we have these 4 electrons removed, they allow the hydrogen to be positively charged, as the hydrogen now only has a positive charge in it. 

A simpler way to think of it is to relate this to a circuit - only electrons flow through circuitry of say, a light bulb, not entire atoms."
The light-dependent reactions,How does ATP release energy?,"ATP consists of adenosine - itself composed of an adenine ring and a ribose sugar - and three phosphate groups (triphosphate). The phosphoryl groups, starting with the group closest to the ribose, are referred to as the alpha (α), beta (β), and gamma (γ) phosphates. The system of ATP and water under standard conditions and concentrations is extremely rich in chemical energy; the bond between the second and third phosphate groups is loosely said to be particularly high in energy. Strictly speaking, the bond itself is not high in energy (like all chemical bonds it requires energy to break), but energy is produced when the bond is broken and water is allowed to react with the two products. Thus, energy is produced from the new bonds formed between ADP and water, and between phosphate and water. 
The net change in energy at Standard Temperature and Pressure of the decomposition of ATP into hydrated ADP and hydrated inorganic phosphate is -12 kcal / mole in vivo (inside of a living cell) and -7.3 kcal / mole in vitro (in laboratory conditions). This large release in energy makes the decomposition of ATP in water extremely exergonic, and hence useful as a means for chemically storing energy. Again, the energy is actually released as hydrolysis of the phosphate-phosphate bonds is carried out. 
This energy can be used by a variety of enzymes, motor proteins, and transport proteins to carry out the work of the cell. Also, the hydrolysis yields free inorganic Pi and ADP, which can be broken down further to another Pi and AMP.
I Hope This Helps."
The light-dependent reactions,"May I ask about the source of hydrogen ions for reduction of NADP+? I am reading some articles that say that the hydrogen ions derived from the photolysis of water are used to reduce NADP, but in my understanding, photolysis and NADP reduction occur on opposite sides of the thylakoid membrane, photolysis contributes to the proton gradient, and that the uptake of hydrogen ions to form NADPH occurs in the stroma (and thus also indirectly contributes to the size of the proton gradient through consumption of stromal hydrogen ions). Can you make this any clearer for me? Thanks!","Remember that all aqueous solutions contain a small amount of hydronium (H₃O⁺) and hydroxide (OH¯) due to autoionization§. 

This means that processes in cells can use water to get rid of or grab "protons" (H⁺) as needed.

Does that help?


§Note: If you are not familiar with this concept, I suggest watching:
https://www.khanacademy.org/science/chemistry/acids-and-bases-topic/acids-and-bases/v/autoionization-water
and then reading the article following that video for details."
The light-dependent reactions,I am still confused whether the hydrogen ions are pumped from lumen to stroma or from stroma to lumen or both?,"at first hydrogen ions are pushed into lumen, but as the concentration increases inside the lumen , it is going to activate the ATP synthase enzyme which synthesis ATP by pulling 2 hydrogen ions out to the stroma"
The light-dependent reactions,"i just thought of this, would it be possible to genetically engineer a plant that can use light in the infared wavelengths (heat) for photosynthesis?","Quite interesting question!

I do not think it would be possible.

Plant cells are not designed to accept/tolerate infrared or UV light (which is destructive to plants).
BUT

there are some speculations about engineering plants to harvest infrared light to perform photosynthesis more effectively and produce more sugar.

Since there are algae which can do photosynthesis in low light conditions, why wouldn't it be possible for plants too?

We have to be patient and see where this is going. :)


https://undark.org/article/can-better-photosynthesis-help-feed/"
The light-dependent reactions,"photosynthesis involves the 
a. oxidizing of carbohydrates
b produces all the earth oxygen gas
c reduction of carbohydrates
d. oxidation of carbohydrates",？？i am so screwed for AP bio
The light-dependent reactions,"My textbook says that ATP is made as electrons move along the electron transport chain. It this referring to the contribution of pumping protons across the membrane for chemiosmosis, or is there another method of synthesising ATP entirely?","Electrons move down the transport chain, which creates a proton gradient, and then that gradient is used to make ATP"
The light-dependent reactions,"In paragraph 13 you say that the ATP and NADPH produced from the light dependent part of photosynthesis are used to fuel the Calvin Cycle. I'm wondering if ALL of the ATP and NADPH get used this way, or if some are used as fuel for other immediate cellular processes. Thanks!","Some must get used within the chloroplast for other metabolic processes, but my understanding is that most gets used to fix carbon — this uses a lot of ATP, which is part of why cyclic photophosphorylation exists.   Chloroplasts even have a mechanism for exchanging ADP for ATP to support their basal metabolic processes in the dark.

In particular ATP isn't very stable, so it makes sense to use it to make sugars (and other macromolecules) before exporting the "energy".

You might also find this discussion interesting:
https://biology.stackexchange.com/questions/42888/why-is-atp-produced-in-photosynthesis-used-to-synthesize-glucose"
The Calvin cycle,Do  plants move,"Yes, they can. For example, morning glories and Venus flytraps move. Some other plants also have reflexive movement, as in a response to being touched."
The Calvin cycle,if a plant is in drought conditions i.e. wilting does chloroplast activity slow down?,"Yes. Because the plant can no longer absorb more H2O through its root structure, the plant will use what water it has stored. The wilting occurs because it is undergoing plasmolysis which reduces the turgor pressure on the plant's cell wall."
The Calvin cycle,Why is the O2 not counted in the calvin cycle? In light reaction plant takes H2O and uses the H but releases the O. In calvin cycle plant takes CO2 and uses the carbon but my gues is that the O2 is not lost. Is it also released to the atmosphere?,It gets added to the glucose molecule( C.6 H.12 O.6 )
The Calvin cycle,"Where did the Oxygen removed from 1st Carbon in 3PGA  went? 
In the reduction process 3PGA(Carboxylic acid)--> G3P(aldehyde), 1 O is missing? Where did it went?","actually the O is in between of  C-1 and P. when 2H are added by NADPH2 , the bond between C and P  breaks. 1H is used to reduce C. other H togather with O combines with P forming phosphate group.          hope you understand"
The Calvin cycle,"To clarify, one cycle of the Calvin Cycle would produce 1/6 of a glucose molecule, hypothetically speaking?","Not quite. It is true that you need to fix six CO2 molecules for each glucose molecule you produce, and you need 6 ribulose-1,5-bisphosphate to do so, however the reactions need 3 of each to produce phosphoglyceraldehyde. ie. the cycle does not produce 1/6th of a glucose molecule 6 times and join the units together. Instead, it takes 3 of each reactant to produce PGAL, which happens *two times* to lead to production of 1 glucose molecule. This is why it takes *2* cycles to produce one glucose molecule."
The Calvin cycle,Where does the sugar go after being produced from the compounds leaving the Calvin Cycle?,"Sugar goes into plastids to be stored or being actively utilized for plant growth, flowering and seeds."
The Calvin cycle,Does calvin cycle produces oxygen as a by product too?,"No it does not.

All the oxygen released comes from "splitting" of water by photosystem II during the light-dependent reactions.  

The "extra" oxygen in CO₂ gets used during the hydrolysis of ATP during the Calvin Cycle."
The Calvin cycle,Why does it take 6 turns of the Calvin Cycle to form 1 molecule of glucose?,"because three carbons bond with 3 RuBp to make 3 molecules. This splits into 6PG or 6 phosphoglycerate. 6 phosphoglycerate is changed into 6 biphsophoglycerate, which is changed to 6G3P. 5 of those goes back into the cycle to make RuBp so that it can do it all over again, and one is put aside to make glucose. But you need 6 of these to make glucose, so it will take you 6 turns. Hope this helps!"
The Calvin cycle,in the last line why does it say that it takes 6 cycles to make one molecule of glucose? is only one CO2 and one RuBP used in each cycle?,"One cycle takes in one CO2. Three cycles, after many smaller steps, creates six G3P (three-carbon); here, five goes back into the cycle, and only one is used for glucose. Glucose is a six-carbon molecule, so two G3P are needed. The math, then, is 3X2=6."
The Calvin cycle,What's the formula of the calvin cycle?,"3 CO2 + 6 NADPH + 6 H+ + 9 ATP + 5 H2O → glyceraldehyde-3-phosphate (G3P) + 6 NADP+ + 9 ADP + 8 Pi   (Pi = inorganic phosphate)
Taken from wikipedia article on it"
Intro to photosynthesis,"Okay, if the light dependent reactions can create the ATP itself, then why not just transport that ATP everywhere instead of forming Glucose then spending a lot of other time in transforming back that Glucose into ATP?","Excellent question.

The major reasons that I know of:
1) The high energy bonds in ATP are (by definition) unstable, so for long term storage of energy ATP is not a good choice.
2) In many situations phosphate is a limiting nutrient, so needing to make more ATP could severely limit the plants ability to store energy.
3) Fixed carbon (e.g. glucose) can be converted into other molecules the plant needs including:
• cellulose for structure
• lipids for long term energy storage, cell membranes, etc.
• proteins for structure, catalysis, etc."
Intro to photosynthesis,what is hydrolysis,"When you add water, you can separate a compound into two. For example in hydrolysis of an ester,  when you add water you get alcohol and carboxylic acid."
Intro to photosynthesis,Why is the first photosystem depicted in photosynthesis diagrams called "photosystem II" and the second photosystem called "photosystem I"? Are the names arbitrary or do they tell us something about the nature of how the photosystems work?,"The reason for this is simply because Photosystem I was discovered first, and Photosystem II was discovered second.  You're right, it is confusing because the Photosystem II process occurs first, followed by Photosystem I."
Intro to photosynthesis,"The reactions occur without any dependence on light...so can it run during night time?...if so,in night time, the guard cells of the stomata close, so how can it take in carbon-dioxide to continue the cycle?...","Both reactions, the light-depended reaction and the Calvin's cycle OCCURS ONLY in the light (and out of color spectrum, mainly blue and red colors are used thus green reflected into your eye).  
1. Light-depended reaction gives you the NADPH
2. You need NADPH in Calvin's cycle 
And you don't get the NADPH without light.
EDIT after a comment brought up by Safwan: to be exact, The Calvin cycle needs light to start, but can continue for a while even without the light."
Intro to photosynthesis,"You, along with the rest of the human population, owe your existence to plants and other organisms that capture light: FALSE!",Do you care to give some supporting information for that statement?
Intro to photosynthesis,What happens after the plants form glucose and oxygen? What happens to the oxygen when it is released?,"Glucose is utilised in respiration and excess glucose is stored  in the form of starch....
The o2 released might be utilised by humans etc"
Intro to photosynthesis,What does the Pi stand for in the pictures describing light reactions and the Calvin cycle?,"Pi stands for inorganic Phosphate... It is described in chemistry as the phosphoryl group, i.e. PO3 with a 2- charge.... This phosphate bonds with the adenosine group to form AMP, ADP, ATP, and the like. Hope this helps"
Intro to photosynthesis,Why would you consider photosynthesis important ?,"Photosynthesis is extremely important! It is the process in plants that allows it to harness energy from sunlight and convert it into chemical energy that can be used by plants and other organisms. In fact all the energy we get from food is derived from the energy we get directly from plants or indirectly from animals that ate plants. Hence without the sun or plant's ability to carry out photosynthesis, there would be no energy to sustain most of the life on earth."
Intro to photosynthesis,"Wait, so:ATP=Three Phosphates. ADP=Two Phosphates. What if there is only one Phosphate?
What would it be called? And what would happen if there was only one phosphate?","ATP is Adenosine TriPhosphate, with three phosphates, and lots of energy stored in bonds.
ADP is Adenosine DiPhosphate, with two phosphates, and some energy stored in bonds.
AMP is Adenosine MonoPhosphate, with a single phosphate group. These do not have energy stored in the bonds between phosphates, as there is only one.
Biological processes add/subtract phosphates, changing these into each other.
A related molecule, cAMP (cyclic AMP), has a cyclic structure, and rather than an energy storage role, it functions as a messenger in cell signaling pathways."
Light and photosynthetic pigments,Is the lumen really space or does it just absorb all other wavelengths and appear empty? How would you tell?,"The lumen is very much so a space. Our Intestines have a lumen. By definition, the lumen is simply an internal body cavity encapsulated or enclosed by something. In this case, the thylakoid membrane (the 3rd membrane of chloroplasts)  encloses the lumen. The lumen would contain all of the reactants and intermediates of the light-dependent reactions. As the video displayed, water molecules are broken and the H+ protons are pumped into the lumen. So overall, the lumen is a cavity that contains the organic molecules (H+) that have diffused or transported across the thylakoid membrane. Hope this helps!"
Light and photosynthetic pigments,Why are leaves green even though other pigments are present?,Because chlorophyll is most _abundant_ pigment so it masks other pigments.
Light and photosynthetic pigments,Can we conduct photosynthesis under monochromatic light rays such as green?,"Interesting question! Whether the plant would be able to live or not depends both upon the plant itself and the wavelength of the light. Different types of pigments absorb different wavelengths of light, and some plants have more of one type than others. If a plant has more carotene, for example, it would better absorb orange light. No pigment really absorbs green light best, which is why its reflected and most plants are green or greenish. Scientists can create "action spectrums" that show what wavelengths of light result in the most oxygen produced (to measure the amount of photosynthesis). 
It turns out that green light is actually very useful for plants, and although it is the most reflected light it does serve a purpose, with the plant still managing to use most of the green light thrown at it. Green light, for some reason, penetrates better into lower-lying leaves and allows them to photosynthesize better. 
Under a monochromatic light source, the plants obviously wouldn't do as well. Red light is the most important, as chlorophyll a, the most common type, absorbs light best in the red area of the spectrum. The blues are second, and green comes in last. It's hard to tell for sure if the plant will photosynthesize enough to thrive under green light, but it definitely will at least a little."
Light and photosynthetic pigments,"For clarification, do all plants have both chlorophyll a and b (I presume in the leaves?), or do all plants have chlorophyll a and only some have chlorophyll b? Thanks!","No that'she not right. In algae and cyanobacteria there is chlorophyll a and chlorophyll b occurs in green algae and plants. 

Source: www.ucmp.berkeley.edu/glossary/gloss3/pigments.html"
Light and photosynthetic pigments,"Plants contain chlorophyll a which absorbs green lights but in the light dependent stage, 
light of wavelengths 680nm and 700nm which are red lights are absorbed why is that so please.","Chlorophyll looks green not because it absorbs green light, but actually because it doesn't absorb it. The green is left unabsorbed, so it can reach your eyes."
Light and photosynthetic pigments,How do carotenoids dissipate the excess energy as heat?,"The simple answer is that due to their structure carotenoids are able to convert chemical potential energy into vibrational energy.

This seems like a reasonably informative page:
https://biology.appstate.edu/fall-colors/hidden-colors-leaves-what-are-functions-those-yellow-and-orange-pigments-we-see-fall
• the portions most relevant to your question are about half-way down starting with "Carotenoids are More than Just Accessory Pigments""
Light and photosynthetic pigments,"Just asking a question here, when an acid interacts with chlorophyll, which part of the chlorophyll gets stripped off? Thanks!","The acid removes the magnesium ion replacing it with two hydrogen atoms giving an olive-brown solid, pheophytin-a."
Light and photosynthetic pigments,why are wavelengths and pigments important for photosynthesis?,They're responsible for what light is absorbed and what light is reflected.
Light and photosynthetic pigments,At which wavelength is chlorophyll a most effective? Is it when the line on the graph peaks? Or when it is at its lowest point?,"Chlorophyll a absorbs the maximum wavelength at the peaks indicated by its graph, i.e,at the blue and red regions(450-470nm and 660nm). So at the blue and red wavelenghts chlorophyll a is most efficient."
Light and photosynthetic pigments,what is the role of pigments during photosynthesis?,"I suggest you reread this article, since that is a big part of what it discusses.

e.g. the section titled "Pigments absorb light used in photosynthesis"."
"C3, C4, and CAM plants","This might be a bad question, but is there a difference in the equations for each path of photosynthesis?",This is not a bad question! The pathway and reaction is all the same but when/how it occurs varies.
"C3, C4, and CAM plants",what role does temperature have in this,"The high temperature will make the plant close its stomata to reduce water loss by evaporation. If the stomata is closed, the oxygen from photosynthesis will build up inside the leaf while the carbon dioxide will not get into the leaf.

This situation will make the concentration of oxygen inside the leaf higher than carbon dioxide. The rubisco will more likely bind the oxygen. So, the photorespiration happens.

For more details, you could visit the photorespiration article 
https://www.khanacademy.org/science/biology/photosynthesis-in-plants/photorespiration--c3-c4-cam-plants/a/c3-c4-cam-plants"
"C3, C4, and CAM plants","What would be the result of a competition between aCAM plant and a C4 plant in a hot, very wet, environment?","Many plants will not grow well in soils that are constantly moist or wet. However, several plants are tolerant of and have adapted to perform well under these conditions. 

both CAM and C4 plants are dominant in very hot, dry environments like deserts so thriving in very wet soil would not be an advantage for them.

However, there are epiphytic CAM plants in very moist forests during the rainy season.
_Bromeliaceae_.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4242292/"
"C3, C4, and CAM plants","In the C4 diagram, ATP is used and results in the formation of 'AMP'. What is AMP?",adenosine monophosphate. It is like ATP that has lot two phosphate groups.
"C3, C4, and CAM plants",Which enzyme is involved in the breakdown of malic acid to CO2 and pyruvate (in C4 pathway)?,"Malate dehydrogenase — you can start learning more about two different forms of this enzyme in the following wikipedia links:
•https://en.wikipedia.org/wiki/Malate_dehydrogenase_(oxaloacetate-decarboxylating)_(NADP%2B)
•https://en.wikipedia.org/wiki/NAD-malic_enzyme"
"C3, C4, and CAM plants",The plant in which water use efficiency is higher is,C4 have higher water efficiency than C3 plants. C3 grasses release 833 molecules of water per co2 molecule while C4 grasses release 277 molecules of water.
"C3, C4, and CAM plants",Which type of plants are most efficient,"It could be argued that CAM plants are the most efficient because they create the most amount of energy from the least amount of water. However, these plants won't do very well in a very wet environment because they're used to opening their stomata for only small amounts of water. It really all depends on the environment, each plant adapts to be the most efficent for where they are!"
Homeostasis,Can someone explain what is negative feedback?  I didn't understand the concept from the article....,"From what I understood, negative feedbacks is your body's response to keep things normal or stable, whereas positive feedbacks exacerbate certain effects on the body by repeating functions deliberately.  In essence, negative feedbacks preserve your body's original or 'set' condition and positive feedbacks do the opposite and change you body more by constantly pushing certain types of growth or development in the same direction until something has been accomplished. The example they used was a fetus's head constantly putting more and more pressure on the cervix until birth. Since this is very necessary and important, a positive feedback loops is run: the substance that  pushes the fetus' head towards the cervix, oxytocin, is released as a cause of contractions from the uterus, which are themselves a cause of pressure from the fetus' head on the cervix. So the pressure essentially causes contractions in the uterus which stimulate nerve impulses in the brain to release more oxytocin, which further increase the pressure of the fetus' head. Clearly the goal isn't to maintain the fetus' current state but rather push it to the point where it is primed for birth."
Homeostasis,"Is the system that regulates pH, homeostasis?","To be precise, homeostasis is a process/phenomenon not a system.

Homeostasis is actually the process of maintaining a stable internal environment despite changes in the external environment. 

There are mechanisms in organisms that regulate pH and this regulation is an example of homeostasis.  For example, if you have learned about buffers, then it may help to know that essentially all organisms use buffers (and other mechanisms) to maintain control over the pH — for example the different organelles within eukaryotic cells will consistently have different pHs:
http://book.bionumbers.org/what-is-the-ph-of-a-cell/

Does that help?"
Homeostasis,what is pH guys and how does it relate to homeostasis.,"pH is a measure of how acidic or basic a solution is. More specifically, pH=-log[H+], which essentially means that the more positively charged hydrogen ions you have in a volume of solution, the lower the pH is and the more acidic the solution is. You can also check out this video (if you haven’t already seen it): https://www.khanacademy.org/science/high-school-biology/hs-biology-foundations/hs-ph-acids-and-bases/v/introduction-to-ph

pH matters for homeostasis because it’s part of the chemical environment in which biochemical reactions have to take place. For example, enzymes (which help speed up chemical reactions in living things) have ranges of pH where they work best. Because these molecules’ proper functioning is necessary, pH is very important for maintaining homeostasis. 

Hope this helps!"
Homeostasis,what is the control center in temperature homeostasis hot?,The control center for temperature is the hypothalamus.
Homeostasis,How can very low temperatures be fatal?,"Low temperatures would mean that the enzymes would be inactive or they may not be able to catalyse as much. This slows down reactions in the body (lowers metabolism), meaning that you may be deprived of essential things such as energy etc, which can eventually lead to complications such as death."
Homeostasis,How does Blood clot relate to Homeostasis?,"Blood clotting is considered part of the Positive Feedback (PF) Loop. This is defined as an effector that will AMPLIFY the effect of the Negative Feedback (NF) Loop. For instance, when there is a hemorrhage (loss of blood), it will cause a sequential activation of clotting factors. Here, a single clotting factor results in the activation of many more clotting factors. This is also known as a PF cascade. This overall process will give the completion of the NF Loop because blood loss was prevented with the clotting factors, resulting in Homeostasis."
Homeostasis,How can blood vessels dilate result in heat loss？,"This is because the dilation of blood vessels increases their surface area making it easier for the blood to interact and transfer heat with cooler parts of the body, generally the more surface area, the more heat loss."
Homeostasis,can someone please tell me which organ in the body controls homeostasis?,"Homeostasis is mainly controlled by the organs in the central nervous system and the endocrine system (hormones). Organs in the two systems send commands to other organs in other systems to allow them to carry out certain functions. 

Example for the nervous system: You have stepped outside into some snowy weather. It is cold outside, and your body temperature is dropping. The nervous system sends signals to the muscles that tell them to shake. The shaking of the muscles generates heat, keeping you warm.

Example for the endocrine system: Unfortunately, your have not eaten anything for hours. This results in a low blood sugar level. To maintain homeostasis, cells from the pancreas release a hormone known as glucagon, which raises your blood sugar by decreasing the storage of sugar in body cells.

Does this help you?"
Homeostasis,What system controls homeostasis?,"There are *many* different systems that organisms use to maintain homeostasis.  

For example, the processes used for thermoregulation in mammals and birds are very different from the methods used to keep pH relatively constant."
Homeostasis,"I understand how homeostasis happens in our bodies, but why does it occur? Furthermore, why do we need it? Why do we try to control the internal functions of our bodies rather than the external stimuli that cause them? Why are there not more uses of positive feedback loops?","1. It occurs so our body can function.
2. (See number one)
3. It is much easier to control our bodily functions than the weather and climate.
4. What do you mean?"
Ligands & receptors,"Why don't hydrophobic ligands get stuck in the membrane? If they're passing through the membrane, then they encounter the hydrophobic space that is the inside of the membrane. If they are also hydrophobic, why do they leave that to continue on into the cell?","I think one reason is diffusion due to the ligand's concentration gradient.  Typically more than one signaling molecule gets released into the environment. If they make it to the hydrophobic portion of the membrane, the next lowest area of concentration would likely be the inside of the cell."
Ligands & receptors,took me 1000 yrs to read,🤣 i tried just putting the face and it said it was too brief
Ligands & receptors,wouldn't lipid ligands generally be hydrophobic??,"You are correct in the notion that only hydrophobic molecules can ''touch'' eachother for interaction; in a cellular environment however, you usually deal with proteins that contain both hydrophylic and hydrophobic patches due to the characteristics of the amino-acids constituting the protein in question. These patches, together with 3D-structural constraints usually determine possible interactions.

An interesting fact is that the hydrophobic/hydrophylic patches of proteins can be influenced by pH changes (protonation of amino-acids in low pH environments and de-protonation in high pH-environments); this can play an important role in experiments."
Ligands & receptors,"So do hydrophobic ligands only bind to intracellular receptors or do they also bind to trans-membrane receptors even though they can diffuse passively across the membrane? Same question for hydrophilic ligands, do they only bind to trans-membrane receptors or do they also bind to intracellular receptors?","Good question — there are few absolute rules in biology!

For hydrophobic ligands I'll give you examples for steroid hormones — many steroid hormone receptors are found in the cytoplasm and then move into the nucleus once bound by their steroid, while others are always found in the nucleus.

However, recent research has revealed that there are also steroid hormone receptors in the plasma membrane.

I recommend this wikipedia article as a place to start learning more:
https://en.wikipedia.org/wiki/Steroid_hormone_receptor


While uncommon, there are some hydrophilic ligands that bind to intracellular receptors.  One example is the neurotransmitter epinephrine, which also acts as a hormone.

You may find this free online textbook chapter helpful in learning more:
https://www.ncbi.nlm.nih.gov/books/NBK9924/"
Ligands & receptors,"What happens to the ligands after they are received? Do they dissolve and become energy, are released back into the extracellular fluid, or something else entirely?","Usually they can be re-absorbed and used again. In the case of Calcium, it is reabsorbed.

Nothing in our body is wasted. It either binds reversibly< or become converted to metabolic intermediate."
Ligands & receptors,what are considered kinases: an RTK receptor or an RTK's specialized ligand?,You find the kinase activity in the receptor itself. But you need a ligand to trigger the dimerization (2 receptors molecules share one ligand) of 2 receptors which only the can act as a proper kinase on each other
Ligands & receptors,"since water-soluble messengers bind to receptors situated on the outside of the cell membrane, is it possible for these messengers to influence gene transcription in the cell nucleus","Yes, it is, by activation of for example MAPK pathways. Cell signaling always includes some cascade and rarely ends up on just one action step.

:)"
Ligands & receptors,"In this, it says 'They [hormones] must bind to carrier proteins in order to travel through the (watery) bloodstream.' The fact that they must bind to carrier proteins implies that otherwise they would repel water. However, hydrophobic molecules are just nonpolar and should still be able to go through water. Why do they [hormones] need to bind to carrier proteins?","Hydrophobic molecules will most likely precipitate in the watery bloodstream. This way they will accumulate in, obstruct bloodvessels or accumulate in fatty tissues. They also won't be transported as efficiëntly and thus have little to no effect. By binding to carrier proteins they won't precipitate or accumulate in specific places and can do their thing in cells where they are supposed to do their thing.
Hope this helps!

PS. I am not sure if you understand the polar-apolar principle, so here it is in short: polar molecules dissolve in other polar molecules. apolar molecules dissolve in other apolar molecules, but polar molecules generally don't dissolve (or in very, VERY tiny amounts) in apolar molecules (same for apolar in polar)."
Ligands & receptors,what would happen if it was nonpolar ligand that was binding?,"What do you mean by *nonpolar* ligand?

Here we are not talking about polar and nonpolar substances and covalent bonds."
Response to a signal,"(Third paragraph in Example: Growth factor signaling)
What do you mean saying that MNK1 help to translate folded mRNA? Can it translate even hairpins?
Thank you :)","Yes, you've got it right! MNK1 helps to translate certain mRNAs which form, hairpins.


However, the accent is on the _certain_ meaning that it cannot help _every_ singular hairpin,l but _some_ hairpins. :)"
Response to a signal,"About Gene Expression, do the transcription alterations of factors such as c-Myc pass on the daughter cells of future generations? or is there a reversion mechanic before the cell goes into mitosis? Thank you.
P.S: in the last paragraph of "cellular metabolism" you wrote "moelcules"","Alterations to the genetic sequences that code for transcriptional regulators such as c-Myc may be inherited from a parent cell, assuming it isnt imprinted(genomic imprinting). The ability of a daughter cell to retain a memory of the gene expression patterns that were present in the parent cell is an example of epigenetic inheritance: a heritable alteration in a cell or organism's phenotype that does not result from changes in the nucleotide sequence of DNA."
Response to a signal,What are two examples of a response (or end result) of a cell signalling pathway?,"Let's say you are bleeding and lost lots of blood. And then you immediately stand up. Ending result of a signaling pathway is falling unconsciousness (blood pressure drop).

You just finished oyur meal. Your stomach is full and stretching receptors. The ghrelin hormone suddenly drops in its concentration in your blood. Why? Because Ghrelin is the hunger hormone and you do nto need it anymore. You are not hungry.


I can tell you anything happening in your body and nature is cell signaling influencing physiology."
Response to a signal,"Biochemically, what triggers the adrenalin gland to pump a high number of adrenalin signals?","Adrenaline is released mainly through the activation of nerves connected to the adrenal glands, which trigger the secretion of adrenaline and thus increase the levels of adrenaline in the blood. This process happens relatively quickly, within 2 to 3 minutes of the stressful event being encountered. When the stressful situation ends, the nerve impulses to the adrenal glands are lowered, meaning that the adrenal glands stop producing adrenaline.

 http://www.yourhormones.info/hormones/adrenaline/


Meaning that biochemically, the electrical signal from nerves activates the release of adrenaline. 
High level of stress also activates the release of ACTH which stimulates the release of cortisol."
Response to a signal,"I'm confused about something, Is EPGFR  a tyrosine kinase receptor while RAS is a G protein?","Nice observation!
Ras is a subfamily of G-proteins while EPGFR is tyrosine kinase receptor.

https://www.ncbi.nlm.nih.gov/pubmed/11129168
http://pathwaymaps.com/maps/398"
Response to a signal,How could activating a transcription factor cause long-term cellular changes?,"Activating factor activated transcription of certain DNA. Usually RNA transcript is unstable and that's how transcription is controlled. Where transcription factor takes place, that mRNA is 'preserved'. That way certain genes are 'turned on'."
Response to a signal,how are things possible i mean like how will people know this type of stuff what if scientist don't know about these things ?,"Could you clarify, I am sorry I don't fully understand the last part of your sentence?"
Response to a signal,Why do different cells respond differently to the same signal?,"In many cases, the same signal molecule binds to identical receptor proteins yet produces very different responses in different types of target cells, reflecting differences in the internal machinery to which the receptors are coupled.


Meaning that based on the architecture and organisation fo the cell (not just the receptor per se, the response depends on).


https://www.ncbi.nlm.nih.gov/books/NBK26813/"
Introduction to cell signaling,"Wait, so then whats the feature of a target cell that makes it receptive to a particular signalling molecule? Would this be the shape of the receptor? Was that the second part spoken about in the overview video?","Yes, the shape of the receptor is due to its function.  A specific ligand will only fit into a specific shape of receptor protein."
Introduction to cell signaling,"Could someone give an example of a ```
gaseous plant hormone
```","The plant hormone ethylene promotes ripening, as seen in the ripening of dates. Ethylene is widely used in agriculture. Commercial fruit growers control the timing of fruit ripening with application of the gas."
Introduction to cell signaling,Can a ligand have more than one receptor?,"Yes, and a receptor can have more than one ligand.

You can read more about this here:
https://www.khanacademy.org/science/biology/cell-signaling/mechanisms-of-cell-signaling/a/signal-perception"
Introduction to cell signaling,How do these types of cell communications apply to the immune system?,"Cell signaling is essential for the functioning of the immune system.


The first line of defense, the humoral immune system relies on signaling. Leukocytes are being attracted with chemoattractants to come to the place of infection and pass blood barrier via diapedesis.


Later, when the second line of defense kicks in - B and T lymphocytes, again is influenced by signaling molecules.

B plasma cells recognize receptors on the surface of the cells of antigens so antibodies can bind to them and neutralize/kill them.

T killer cells need also receptor recognition in order to work properly and kill the pathogen, not a cell of host."
Introduction to cell signaling,"How autocrine signaling is important in cancer, I mean what's the mechanism?","That is way more advanced than can be covered in this introductory material and definitely not something I'm familiar with.

You might however find this section of the wikipedia article on autocrine signaling a useful place to start learning more:
https://en.wikipedia.org/wiki/Autocrine_signaling#Cancer"
Introduction to cell signaling,"Is there a distinction between Paracrine signaling and Synaptic signaling?
Some sources suggest the two are different, kindly clarify for me on that point.","Yes, they are different since *synaptic signalling* is more precise and _specified_ form of paracrine signalling.


So to clear out, both are types of paracrine signalling. But paracrine signalling is just broader term, while synaptic is specuiifc for synapses and neuronal tissue.


Paracrine signalling is any type of signalling where  signals bind to receptors and stimulate nearby cells. But in synaptic, those nearby cells involve synapses."
Introduction to cell signaling,what is the difference between cell signaling and signal transduction??,"Cell signaling is the broad multiple sets of pathways involved in how cells communicate. Signal transduction is one of those pathways. When a cell receives a signal, signal transduction is the multiple sets of processes that happen within the cell for that signal to reach its intended target and to then illicit a response."
Introduction to cell signaling,I don't understand the last sentence of synaptic signaling. Can someone please explain?,The signaling cell reabsorbs the neurotransmitters so that it can release it again later.
Introduction to cell signaling,"If a cell wants to signal itself by autocrine signaling, why does it release the substance to the surroundings? Wouldn’t it be better if the signaling molecule stayed inside the cell and affected the intracellular pathways directly. What are the advantages of releasing a signaling molecule to the surroundings compared to making it signal directly inside the cell?","Autocrine signaling unlike intracellular signaling occurs outside of the cell. They bind to receptors on the outside of the cell, to initiate a response that is quick. Intracellular signaling, on the other hand, binds to receptors inside the cell to initiate responses that take a long time. An example of such a response is the transcription of DNA which leads to other processes that later produce a protein. So, it is much better for cells to send autocrine signaling outside especially if the response is needed quickly."
Cell-cell signaling in unicellular organisms,Are there any medical applications of quorum sensing yet?,"This video probably won't anwser your question, but you should definitely check it out!
https://www.youtube.com/watch?v=KXWurAmtf78"
Cell-cell signaling in unicellular organisms,Are bio films also involved in brain neurons since they are all connected?,"No. Biofilms are aggregates of microorganisms.

There is no place in neurons nor in blood for microorganisms."
Cell-cell signaling in unicellular organisms,Can someone explain the positive feedback loop? What does that have to do with the transcription factor of the gene for the enzyme that makes AHL? Says it amplifies the response for a positive feedback loop. Not sure what that means.,A positive feedback loop amplifies the response. Here is a link to the article on homeostasis.        https://www.khanacademy.org/science/biology/principles-of-physiology/body-structure-and-homeostasis/a/homeostasis
Cell-cell signaling in unicellular organisms,If AHL is hydrophobic doesn't it have to transport in some vacuole?,"Not a vacuole, I think you mean vesicle. I also don't think so. Water can't pass through, and it has to be polar to bond to water, so it's likely nonpolar, meaning it should be able to pass through the membrane unless it's too big."
Signal relay pathways,What regulates the distribution of fluid between interstitial and intracellular compartments?,"I was under the impression that this is due to osmotic pressure, so differences in solute concentration"
Signal relay pathways,What mechanism ampfily the signal ? and why they have to do that ?,"Many if not all of the steps described in this article can amplify a signal.  

For example each step in the section titled *Phosphorylation example: MAPK signaling cascade* involves a kinase phosphorylating downstream molecules.  For instance, if each time a RAF molecule gets activated it phosphorylates 20 molecules of MEK, then you've amplified the signal by 20 times.

Why questions are typically difficult in biology, but I'll give a slightly hypothetical example of why this is important.  One response a cell needs to divide is an increased rate of protein synthesis, so maybe at the end of the pathway ERK needs to phosphorylate the (up to) 10 million ribosomes to increase their activity.  This would take a very long time if only a few ERK molecules were activated!  In addition, there are 244 known direct targets identified for ERK in humans§, so even if you only had a few of each of those molecules amplification would still be needed to get a timely response!  
(Note: Those targets often need to modified in multiple locations — for example at least two ribosomal proteins are targets of ERK, one on two different amino acids.)

§Reference:
http://sys-bio.net/erk_targets/targets_all.html

Does that help?"
Signal relay pathways,How exactly does the cell signalling reverse?,"This differs per pathway. For pathways that release Ca2+ for example, the Ca2+ pumps pump the Ca2+ back into the ER, so there will be less and less Ca2+ in the cytosol. 
Also, in these messenger cascades, often at the end of the cascade a phosphatase is activated, which will deactivate the kinases. If only a very short, small signal is needed, the phosphatases will be activated earlier on in the cascade (depends on the pathway).
For the ligand/receptor interactions: a ligand often binds it's receptor for a short while, but not very long, so the initial signal won't be active for long.
Hope this helps you out a bit!"
Signal relay pathways,Do all signaling pathways simply turn on or turn off enzymes?,"No, they can also regulate the transcription of genes, the translation of proteins, the behavior of structural proteins, vesicle transport within cells, inhibitors of enzymes, and countless other processes.  You can probably assume that most processes in a cell are affected in some way by at least one signaling pathway!"
Signal relay pathways,"How does cAMP activate protein kinase A? If it's through phosphorylation, does the cAMP disappear after it has done its job (because it loses its only phosphate)?","No, not through phosphorylation. Note that the text says that it "activates" PKA and *the latter* then establishes a phosphorylation cascade. 
 
PKA is composed of 4 subunits - 2 Regulatory (R) and 2 Catalytic (C) subunits; and as the name suggests only the 2 C subunits have a further signaling role. The R-subunits feature _cAMP_-binding sites.

In the resting state when _cAMP_ levels are low, the C-subunits are in a deactivated state due to the R-subunits. What _cAMP_ does is that when it binds at the R sites, it causes a dissociation of the C subunits from this protein ("conformational change") making them now "activated" and thus eliciting downstream responses. 

And yes the _cAMP_ does "disappear" after it has done its job but not quite by losing its phosphate. The enzyme _phosphodiesterase_ converts _cyclic-AMP_ to _AMP_ (by hydrolyzing the _3'C-Phosphate_ bond) marking the termination of the pathway.


https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3504441/"
Signal relay pathways,can someone explain how this works with insulin and glucose? Along with GLUT2 and GLUT4 and their function in all of this? Is GLUT4 relevant for all body cells or just muscle and adipose? So confusing...,"*GLUT4* is an insulin-responsive glucose transporter that is found in the heart, skeletal muscle, adipose tissue, and brain.


*GLUT2* is expressed mainly in beta cells of the pancreas, liver, and kidney.

There are many more receptors:
Class I facilitative glucose transporters are represented by GLUT1 to GLUT4,
Class II has four members, namely, GLUT5, GLUT7, GLUT9, and GLUT11.
 Class III glucose facilitative transporters, namely, GLUT6, GLUT8, GLUT10, GLUT12 and GLUT13 (HMIT).

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5425736/"
Signal relay pathways,What does it mean to be a proto-oncogene? I have been having a hard time grasping what oncogenes are.,"Thank you for this question. I've recorded a video on this topic and will give you a link once I upload it.

So *protooncogene* is signalling molecule which acts as *green light* to form a tumour. It is switched on for tumour. If it is activated (or even mutated) tumour arise.

You may ask, how comes I am not having cancer? 

Because proto-oncogene has its antidote - *tumour suppressor gene*.
Tumour suppressor gene acts as a brake for cell cycle and sits between G0 and G1 phase of the cell cycle.

No matter that you have proto-oncogenes, as long as you have an unmutated version of tumour suppressor genes, proto-oncogenes won't harm you.


You can think of them both as antigen and antibody."
Signal relay pathways,Do signal transduction pathways require a source of energy? Might proteins involved have to be altered or modified?,There's usually an activation of some sort in the signal transduction pathway to incite a response. So for example the proteins involved might be enzymes that receive substrate from the previous protein/step and are thus activated to function. Hope this helps!
Signal relay pathways,How does the signal transduction mechanism works underlying mitosis?,"I'm not exactly sure what you are asking but I'll do my best to answer. When a cell receives the appropriate growth factor, a kinase is activated. For example, in the article above, MAP Kinase is eventually activated, which phosphorylates different proteins in the cytosol and nucleus. These proteins, once phosphorylated, begin causing reactions that cause the cell to enter the S phase of the cell cycle, where DNA is replicated. Once the cell enters from G1 to S phase, it will inevitably complete the cell cycle through G2 and M, or mitosis, phase."
Cell cycle checkpoints,"If cells who have broken DNA automatically die, then would it be possible for a chemical to be given to cancer patients, that would break or make the infected cells think their DNA was broken? Wouldn't this kill out the cancer?","There are many repair processes for DNA breaks — for KhanAcademy material on this see:
https://www.khanacademy.org/tag/dna-repair

Consequently, it is unlikely for a single break to kill a cell.

That being said, radiation treatment and (most?) chemotherapy drugs do exactly what you are suggesting — they cause large amounts of DNA damage and overwhelm the ability of rapidly dividing cells§ to repair themselves.   
This usually leads to cell death.

§This includes the cancer cells we want to kill, but also many healthy cells including those renewing the lining of the gut and in hair follicles.  Killing of healthy cells is a big part of why people undergoing cancer treatment often feel very ill and lose their hair."
Cell cycle checkpoints,Do the same checkpoints exist in meiosis? Thank you!,"Good question!

Yes, recent research has shown that regulation of meiosis is similar to that of mitosis (though somewhat more complicated).

References and further reading:
https://www.sciencedirect.com/science/article/pii/S153458070800172X

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4411289/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4080918/

http://rstb.royalsocietypublishing.org/content/365/1546/1653"
Cell cycle checkpoints,what happens to a cell if it does not “pass” the spindle checkpoint?,"In this case, the cell would not continue past metaphase, rather wait until the spindle fibers have all attached to the sister chromatids. If the fibers have still missed some chromatids, then either the cell will divide incorrectly with unequal genetic material in the daughter cells or it will have the proper checks in place to initiate cell death."
Cell cycle checkpoints,why would damage to a cell's DNA prevent it from doing it's job?,"The DNA is sort of like the instructions for building, operating, and maintaining a cell.  If those instructions get damaged then things start to go wrong.

Maybe this analogy will help?
Imagine you were trying to build a model by following written instructions.  Part way through you discover that something has damaged a section of the instructions.  You do your best, but at the end your project ends up being a bit messed up.  

Then someone makes a photocopy of your damaged directions, which end up even less clear than your original. They then try to build another copy of the model, which ends up even more flawed than your version ...

Does any of that help?"
Cell cycle checkpoints,How many strategies are there to increase the activity of checkpoints? I think it will be a great hypothesis for anticancer drug design.,"Quite interesting!

I found an article explaining the therapeutic potential and short backs of that approach. It turns out that targeting cell checkpoints may be a double-edge sword for cancer. 


https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5037895/


DNA- and mitotic spindle-damaging drugs are even mainstream in cancer therapy. While there is no something to 'increase' activity, there are things which target and damage points. 
Actually, drugs are inhibitors for checkpoints so it automatically leads to apoptosis. 
The drawback is that these inhibitors don't work in all types of tumors."
Cell cycle checkpoints,what happens if cells don't divide,It will kill itself if it can't fix itself. Cell suicide is called apoptosis.
Cell cycle checkpoints,"If there are checkpoints, then why are there still people with extra/missing chromosomes because the spindles do not attach/do their job (e.g. down syndrome)?","Alright well the most common form of down syndrome is known as trisomy 21, which is when a person has 47 chromosomes instead of 46 chromosomes in each cell. This is caused by nondisjunction, which gives a gamete an extra copy of chromosome 21. Nondisjunction would occur at the spindle checkpoint, and so the cell is supposed to be stopped and the error corrected there. However, if the spindle checkpoint isn't working properly, nondisjunction can occur and the cell will go on with the division even with that error present, resulting in conditions such as trisomy 23."
Cell cycle checkpoints,"Do the lines in the diagrams symbolize where in the cycle the checkpoint is occurring? If so, isn't the G1 Checkpoint supposed to occur *before* the G0 Phase?","No, because that would mean the cell passed the checkpoint. In other words, the cell is stopped before passing the line/ the checkpoint. Think of it sort of as luggage checking at an airport, so like making sure the cell has what it's supposed to have and nothing else before letting it pass, otherwise it goes to G0 phase."
Bacterial binary fission,can you please give me examples of bacteria that use binary fission?,"All bacteria go through binary fission, it is how they reproduce."
Bacterial binary fission,"Is there a certain number of times mitosis can happen to a cell, or its offspring?","Yes actually, there are things called telomeres within each cell's DNA, and each time they split it gets shorter and shorter, when it's too short to divide any further, it will likely die."
Bacterial binary fission,What does binary fission stand for?,The septum is forming by affixing of protein complexes and protein filaments can you explain that please and if you haves ome pictures will be better. Thank you
Bacterial binary fission,How do binary fission and conjugation differ?,Binary fission normally results in 2 identical daughter cells while conjugation occurs when one bacterial cell uses a sex pilus to inject DNA into another bacterial cell. Conjugation can lead to 1 bacterial cell sharing a gene that increases the fitness of the other cell (such as the ability to use a new nutrient or antibiotic resistance).
Bacterial binary fission,hi is parthogenesis also a part of binary fission,"Not really. Both are types of asexual reproduction where the offspring are genetically the same as the parent, but binary fission has to do with the organism itself splitting into two, whereas in parthenogenesis, the parent gives birth to a child, but its a form of asexual reproduction because there is no other gender to fertilize the egg. There's a Khan Academy article that goes over this more in depth: 
https://www.khanacademy.org/science/high-school-biology/hs-reproduction-and-cell-division/hs-types-of-reproduction/a/hs-types-of-reproduction-review"
Bacterial binary fission,Which of the following eukaryotic process is similar to the bacterial asexual reproduction?,"I can only come up with mitosis. Since both are 'division' of a cell. In the first case, it represents whole organism and in the latter, it represents one cell of many (multicellular organism). Then meiosis can be plausible too. That is division of germ cells."
Bacterial binary fission,Why is it typical for prokaryotes after fission to have their chromosomes circular?,"Having circular chromosomes allow prokaryotes(in this case bacteria) to divide/reproduce infinitely. This is because circular DNA lacks telomeres, a region of repetitive DNA used to prevent deterioration of chromosomes. Also, some prokaryotes have linear DNA like Agrobacterium tumefaciens, which has both linear and circular chromosomes."
Bacterial binary fission,"I have heard E. Coli divides every 20 minutes, and this could cover the surface of the Earth in 36 hours if left unobserved. So, is it common to see a E. Coli bacterium or is it rare. Since, if it was common it would have covered most of our planet's surface. But it being rare is not possible since its cell division is very quick? I hope you understand my question... Thanx","I'm sure it doesn't say 'if left unobserved'. Logically it doesn't work as most E. coli are unobserved. It is found pretty much everywhere, including in our bodies."
Meiosis,is there random orientation in metaphase 2?,"Good question!

I think that is assumed to be generally true, but it would be very hard to test in most organisms.

The only evidence for this being true that I know of comes from the fungus _Neuropsora crassa_ that makes a linear§ ascus (sac containing the meiotic products).  

This allows us to see that in this species independent assortment also occurs in metaphase II.

§Note: The order of the spores within the ascus reflects the meiotic divisions.

References:
•http://mcb.berkeley.edu/courses/mcb140/Syllabus/AmacherLecture/Lecture6.pdf
•https://link.springer.com/referenceworkentry/10.1007%2F978-1-4020-6754-9_16853"
Meiosis,In meosis 2 when did the chromosomes duplicate?,there was no chromosomal duplication in meiosis II only the centrosome duplicated. If there would have been chromosomal duplication cells would never have been able to produce haploid gametes the cell used in meiosis II are the product of meiosis I
Meiosis,"When the new nuclear membrane forms around the chromosomes, how does the cell make sure the centrosomes are outside the nucleus and ALL chromosomes are inside?","Well, it works based on patterns of nuclear defragmentation. On the places where old fragments of a nucleus are, new form. Also, thanks to cytokinesis, the cell splits exactly half its length."
Meiosis,Please specify if the number of chromosomes becomes haploid in meiosis I or meiosis II? And if does in meiosis I then how? In meiosis I chromatids are not separated then how come chromosome number reduces to half??,"The number of chromosomes becomes haploid in meiosis I, because the actual sister chromatids are not pulled apart by spindle fibers. For example, if a cell was undergoing meiosis, and had a total of 4 chromosomes in it, then 2 of them would go to one daughter cell, and 2 of them would go to the other daughter cell. That makes 2 haploid cells. 

Then, in meiosis II, each of the 2 sister chromatids in the daughter cells would be split apart by spindle fibers, giving each cell 2 chromosomes. As you said, the fact that in meiosis I chromatids are not separated means that the entire chromosome is moved to one cell; if there were 4, then they would be moved to each daughter cell equally. I hope that helps; if you still have trouble please say so!"
Meiosis,"If the starting cell has 46 chromosomes, then how can it produce four cells with 23 chromosomes?","Remember that when replicating in interphase, the chromosome number DOES NOT CHANGE 

in interphase before S (replication phase) we have 46 single stranded chromosomes: 23 are from mom and 23 are from dad (they code for the same things meaning chromosome 1 of mom codes for the same thing as chromosome 1 of dad. Likewise chromosome 5 of dad is similar to chromosome 5 of mom)

after replication how many chromosomes do we have? 
answer: still 46, but what's different?
the single strand chromosome (1 chromosome) became two stranded yet attached identical sister chromatids (still 1 chromosome)

it is only when the sister chromatids separate are they each considered separate chromosomes.

This means that in meoisis II when we split the sister chromatids:
the parent cell starts with 23 chromosomes (EACH double stranded=two sister chromatids, so there are 46 chromatids. Anaphase II splits the sister chromatids which now separate (23 chromatids go to one pole and 23 chromatids go to other pole). When the chromatids are separated they are now called chromosomes 

so a haploid parent cell of 23 chromosomes (double strand) just created two haploid daughter cells of 23 chromosomes (now single strand).

The above is also how a 46 chromosome (double strand) cell in mitosis can result in 2 daughter cells each with 46 chromosomes (single strand). 

Even Sal admits how confusing this is, but he explains all this visually in a separate video differentiating the terms chromatid, chromosome, and chromatin."
Meiosis,why is interphase not included as a stage of cell-division in both mitosis & meiosis?,"Interphase _is_ stage of the cell cycle, but _not_ a stage of _cell division_ (meisosis).


Interphase is that gap phase (exactly G0) where cell cycle stops, DNA and organelles grow and synthesize."
Meiosis,"So meiosis is just to make a zygote? What happens after that? Also, why are there different processes of meiosis for sperms and eggs if they only have to join. Someone help, I'm really confused","Yes, meiosis's goal is to make a zygote. This zygote will (hopefully) turn into an embryo, then a fetus, which eventually becomes a human if everything works out. Meiosis in sperm and eggs is different because, well, sperm and eggs are different. A spermatocyte needs to split into four cells, while an oocyte needs to split into only one because many sperm are needed to fertilize a single egg. Once a sperm reaches the egg, it is only then that they join."
Meiosis,The male transfers sperm to ovaries then sperm is spreading in the ovaries then ultimately it becomes offspring. Am I right?,You're almost correct. Males transfer sperm to the female and only one of the many sperm ends up fertilizing the egg. Then the fertilized egg becomes a zygote that ultimately grows into a baby. I hope this helps!
Meiosis,Different between karyogenisis and dikaryogenesis,"Karyogenesis is the formation of a nucleus. Dikaryogenesis is almost non existent on the Internet, but supposedly it has to do with the formation of 2 nucleuses, and there may be a preference in the expression of one of them."
Meiosis,"will you please explain me all the stages of prophase-1 in meiosis

how can we find the order of stability of covalent compounds by inductive effect","1. Chromosomes condense and homologs loosely pair along their lengths, aligned by gene.
2. The paired homologs become physically connected along their lengths through a process called synapsis.  This forms a synaptonemal complex.
3.The random rearrangement of corresponding genes occurs between the non sister chromatids (because at this stage each chromosome consists of two sister chromatids).  
4. Synapsis ends, and the homologs move slightly apart, no longer bonded along their lengths like in the synaptonemal complex.  
5.  Some of these homologs have one or more chiasmata, an X shaped region where a genetic rearrangement has occurred.  This formation occurs because of sister chromatid cohesion, where a gene that has been given to the homologous pair in synapsis is still bonded to the corresponding part on the sister chromatid of its former chromatid.  
6. Centrosomes move to opposite ends of the cell, and the nuclear envelope dissolves.  
7. Microtubules from one centrosome attach to the kinetochore (protein structures at the centromeres) of one chromosome from each of the homologous pairs, while the other centrosome connects to the kinetochore of the other chromosome in each homologous pair, and each homologous pair moves towards the metaphase plate (where they line up before anaphase)."
Sexual life cycles,what happens to the offspring if the number of chromosomes from parental cells are not halved,"This leads to a condition known as polyploidy (more than two sets of chromosomes).

Assuming this only happened for one parent, what you are describing would result in triploid§ offspring (organisms with three copies of each chromosome).   In many cases (particularly in animals) a zygote that has the wrong number of chromosomes will die.   Even in plants, which are much more tolerant of polyploidy, this would likely result in the offspring being sterile – in fact, many "seedless" fruits (e.g.s bananas, oranges, and many other citrus fruits) come from triploid plants.

Further reading:
https://en.wikipedia.org/wiki/Polyploid

§Note: This is assuming that the parents are diploids."
Sexual life cycles,Why zygosporangium contain multiple haploid nuclei from the two parents.(fungus),"A zygosporangium contains multiple haploid nuclei from the two parents within a single cell. The haploid nuclei fuse to form diploid nuclei, which are equivalent to zygotes. The cell containing the nuclei is called the zygospore."
Sexual life cycles,"For a haploid cell, they take 1 chromosome from each set of chromosomes. Is it random for each one? For humans there are 46 chromosomes(2n) and the gamete has 23 chromosomes(n). So, how are the chromosomes picked per set? The cell has 2 choices, is it random which one is picked?","Yes, the selection of chromosomes is random — this is known as independent assortment.

Furthermore, whether the paternal or maternal allele is picked for any given gene also occurs somewhat randomly.

This is because during meiosis there is recombination (exchange of DNA between the maternal and paternal chromosomes) — this means that each chromosome in a gamete will contain sections from both parents.

This leads to an essentially infinite number of possible genetic combinations within the gametes of a single individual!

Does that help?"
Sexual life cycles,"Does the sperm cell that fertilizes the egg cell differ genetically from the egg in the life cycle of mosses? I'm unsure because I know that (1) the eggs and sperm are produced by female and male gametophores, respectively and (2) the male & female gametophytes are produced from spores. 
I suppose that the answer to this question depends on whether or not the egg and sperm come from the offspring of the same parent or not. What do you guys think?","First all first, there is no sperm in mosses. 

Mosses mostly reproduce by spores. 

As for gametogenesis, there are archegonia and antheridia, not ovum and spermatozoid. Bryophyte sperm is called *antherozoid*."
Sexual life cycles,"In the paragraph 'Alternation of Generations', it is stated that seed plants exhibit alternation of generations. I don't quite understand how this differs from the diploid-dominant life cycle of an animal - after all, a plant comprised mainly of diploid cells creates haploid gametes that fuse to create a diploid zygote, which is similar to the process seen in animals. Why is it that seed plants are said to exhibit 'Alternation of Generations', while animals are said to be diploid-dominant?","The key is the last sentence from the first paragraph of the Alternation of Generations section — "Species with alternation of generations have both haploid and diploid *multicellular* stages."

This is easiest to see in non-vascular plants and ferns where you can have separate diploid and haploid organisms during the lifecycle.  In most vascular plants the gametophytes (haploid phase) are very reduced and totally dependent on the sporophytes (diploid phase), but they are still multicellular.

These videos may help make this clearer:
https://www.khanacademy.org/science/biology/crash-course-bio-ecology/crash-course-biology-science/v/crash-course-biology-135
https://www.khanacademy.org/science/biology/crash-course-bio-ecology/crash-course-biology-science/v/crash-course-biology-137"
Sexual life cycles,i dont understand y do we under go mitosis,This will help: https://www.reference.com/science/mitosis-important-96e816484e66be44
Sexual life cycles,"In the plant life cycle, are gymnosperms and angiosperms a gametophyte and is physically and physiologically dependent on its sporophyte? Or do mosses/ferns fit this description?",Gymnosperms and Angiosperms do not have gametocyte and sporopgyte phases - it only applies to Mosses and Ferns.
Sexual life cycles,how long is a gamete cell cycle time,"Sexual cells are sexually active (undergoing meiosis) once the meiotic division II is triggered in puberty until the age of 50 approximately for women, and for the men it is going in later decades of life.

IF you ask how long one cycle persists it depends on whether we are speaking of men or women. In men it is 55 days https://pubmed.ncbi.nlm.nih.gov/19745218-spermatogenic-cycle-length-and-sperm-production-in-a-feral-pig-species-collared-peccary-tayassu-tajacu/

in woman in it one month (menstrual cycle)."
Cancer and the cell cycle,How does DNA get damaged in the first place?,"A number of factors, radiation, carcinogens, mutagens, and oxidative stress all contribute."
Cancer and the cell cycle,"Could you make a cancer-like cell, or rather a cell that has a mutation that makes it and its offspring grow into a neoplasm, and have their mutation be GOOD? The article says that cancer cells are known to be immortal, so if that's the case, could you use "good" neoplasms to fight cancerous ones that would later form tumors? Thanks to anyone who can understand my question :-)","It is feasible, however the main issue is you don't want to introduce some foreign type of human mutated and immortal cancer without the full ability to knock it out and rein it in. Probably there will be treatments that revolve around this whether is be putting drug producing genes in cells that surround a cancer, although it wouldn't exactly be wise to use a cancer cell to fight a cancer cell by definition, since there are better cell options out there. However if such a cell was discovered tomorrow that didn't grow very fast, only grew near tumors, somehow produced weapons to fight it, no doubt it would become a very popular therapy, however a non-cancerous cell may do the trick better without the risk of it turning into actual cancer."
Cancer and the cell cycle,"Why not engineer a retrovirus to insert an extra copy of the P53 gene? First as a treatment for people with a dangerous cancer, then try it on people who have only one working copy of P53?",I think there are several reasons why this isn't a treatment (yet). I'm sure there's a lot you have to figure out before you can get a virus to successfully insert a copy of the gene. There may be some epigenetic factors that would make this technique not work very well and nobody has figured out how to get around that yet.
Cancer and the cell cycle,"It might not be directly related to this topic, but I have a question. Can cancer be inherited? or does it just depends on your normal habits?","Some people are born with a gene mutation that they inherited from their mother or father. This damaged gene puts them at higher risk for cancer than most people. When cancer occurs because of an inherited gene mutation, it is referred to as "hereditary cancer."
Although this is often referred to as inherited cancer, what is inherited is the abnormal gene that can lead to cancer, not the cancer itself."
Cancer and the cell cycle,"So, I was wondering what could happen if P53 is introduced to cancer cells, once they have mutated. May be, introducing a functional P53 to cancer cells before they progress so far, could prevent them. Is it possible ? What do you say? Please answer","I was thinking the same thing! except maybe giving immunization shots to fix the DNA in earlier stages like when you are just born. But it would definitely be interesting to see if it worked after the patient had cancer. I think it could possibly work afterwards, but the only problem is, if the cancer is already affected large parts of the body, and the P53 activates the apoptosis, then you could kill of a large amount of cells in your body, too much to live. Other than that, I think this would completely work."
Cancer and the cell cycle,"Besides chemo and radiation, what other cures are there for cancer?","here is a website that can show you more examples and what they mean
http://www.cancer.org/treatment/treatmentsandsideeffects/treatmenttypes/treatment-types-landing"
Cancer and the cell cycle,"So, how long does cancer cell cycle take compared to normal cell?","That depends if it is a benign tumor (not to bad) or a bad tumor (I cannot spell its name). If the tumor is benign the cells it contains will split only slightly faster than a normal cell.  If it is a dangerous cancerous tumor, then the cells in it will split much faster and more uncontrollably than a normal cell would.  

If a normal cell takes a second to divide and then waits a week and divides again (this is just an example, this is not accurate information) a bad cancer cell might take a second to divide and then wait an hour. If this is the case you will have two good cells from one good cell and 168 bad ones from the cancerous cell. NOTE: this is just an example I made up, real cells divide much quicker and can wait much shorter or longer amounts of time before dividing again, some cells never even divide again."
Cancer and the cell cycle,""In general, human cells can go through only about 40-60 rounds of division before they lose the capacity to divide, "grow old," and eventually die" what factor defines which cell is the old one, and which on is this the new one when the cell divides? if one cell was not younger compared to the original cells, wouldn't all the cells just die at the same time?","There are A Caps (long strings of adenosine nucleotides) at the end of chromosomes, and as the cell keeps replicating, it starts to wear off. These are what the checkpoints in previous articles talk about. If there is not enough A cap to safely replicate the DNA without it wearing off, then the more important DNA could be damaged irrevocably and could be damaged and the cell would permanently go into G0 stage or apoptosis."
Cancer and the cell cycle,Can cancer become so cancerous that kills itself? Could so many mutations accumulate that it would not be able to divide anymore?,"_Interesting question!_

Definitely, yes. But do not rely on that. Once there are too many mutations accumulated it is too late and it will affect healthy cells as well. You mean, mutations which trigger apoptosis, right? In that case, cancer would resemble an auto-immune disease.


Other than that it is not possible for cancer to just 'kill itself', moreover it thrives really well and always finds a way to grow and spread."
Cancer and the cell cycle,"Is it possible to completely reverse the damage done by cancer cells to the host's DNA? Few form of cancers, which occur due to mutation in DNA, leading to uncontrollable growth of cells, may be treatable by gene therapy by targeting the mutated gene.","That sounds like a nice idea but in reality, many mutations cause cancer. Plus there is that variability among cancer cells. What do I mean by that?


I mean that even within cancerous tissue not all of them are clones. there are genetic variants among them.

If you prepare gene therapy, how do you know which one to traget? Let's suppose you know which one, - cell variant A. Then you are left off B, C, D.
If there is left the only one of let's say D, that's enough to regrow and reoccur - several years later. Without you even knowing you left that one cell."
Apoptosis,If cells undergo Apoptosis to get rid of default or harmful cells why do we have diseases of the cell like sickle cell anemia or cancer?,"Maybe the DNA of the cells is so damaged to the point where it can't go through apoptosis, So cancerous cells continue dividing, leading to disease. But today we can use radiation therapy or special treatment to render many types cancerous cell harmless. (I'm  learning about this region of biology right now, so keep inquiring and maintain a fresh curiosity about how your world works!)"
Apoptosis,"Could you please clarify the role that calcium plays in programmed cell death? I understand it has some purpose, but I'm very unsure otherwise.","Ca is known to plays a role in necrosis, and high levels of Ca usually lead to necrosis of tissue.


However, Ca plays a role in apoptosis as well. Cell concentration of Ca triggers the contraction of myofilaments, secretion of hormones, etc.

the increases of [Ca2+]c occur, both at early and late stages of the apoptotic pathway. Ca2+ release from the endoplasmic reticulum (ER) and capacitative Ca2+ influx through Ca2+ release-activated Ca2+ channels have been proposed to be apoptogenic. 

the proteins of the Bcl-2 family, are localized in organelles deeply involved in Ca2+ handling (the mitochondria and the ER).

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2844952/"
Apoptosis,Is autolysis and apoptosis same?,"NO, autolysis is when enzymes kill a cell, but apoptosis is when a cell kills itself. Think of it as homicide vs. suicide."
Apoptosis,What is the difference between apoptosis and necrosis?,"Apoptosis is a physiological driven process while necrosis is a pathologically driven process.

Apoptosis is control by the cell (suicide) while necrosis is end product of being sick (external damage, either physical-chemical or biological)."
Apoptosis,How could the process of Apoptosis hurt a multi-cellular organism?,"Apoptosis mainly prevents hurting a multi-cellular organism, but i guess if the apoptotic signal is mutated (certain enzymes or receptors in the apoptotic pathway working not the way they should) it could result in mass apoptosis in tissues. This would result in tissue damage."
Apoptosis,"For multicellular organism we have things like apoptosis and necrosis,what about organism with only one cell?
In this essay,"eliminating bad cells" function of apoptosis is mentioned.Can we kill cancers and infections by expanding this function of apoptosis?
Mentioning"cells of adult organisms may be eliminated to maintain balance",what about teenagers?Do we have this function,too?","Actually, cancer treatments are in fact triggers of apoptosis. Radiation treatment mutilates cancer cells in a way that causes the immune system to detect them and make them commit apoptosis."
Apoptosis,Do all cells contain the proteins necessary to undergo apoptosis?,"By default yes. Until something goes wrong - and that is how cancer arises.

I mean, _one of mechnisms_ for cancer is *faulty apoptosis*.


If one gene mutates or miRNA does post-translational modifications, or even if alkylating agents change DNA, you end up with a complete lack of or faulty nonfunctional proteins. In that case, apoptosis is not possible and continual cell division takes place which slowly grows into pathological growth."
Apoptosis,Can you explain how apoptosis leads to cancer when a failure occurs?,https://www.khanacademy.org/science/ap-biology/cell-communication-and-cell-cycle/regulation-of-cell-cycle/a/cancer
Cell cycle regulators,In the first section you mention a graph of cyclin levels over the expression cycle throughout mitosis. Why is G1 Cyclin required throughout the entire cyclin expression cycle of mitosis?,"G1 cyclins levels are _not_ required throughout mitosis. In fact, the concentration of G1 cyclin drops during mitosis. 

Don't confuse the cyclin expression cycle with mitosis. The cyclin expression cycle refers to the levels of cyclins throughout the eukaryotic cell cycle, which includes interphase (G1, S, and G2) and mitosis (M phase). 

I think the question you meant to ask is: "why do G1 cyclin concentrations span the entirety of the cyclin expression cycle?"

Short answer: Mitogens 

Long answer:  Most eukaryotic cells only divide in the presence of _mitogens_.  Mitogens stimulate cell division by increasing the amount of _G1 cyclins_, which trigger cells to enter _Start_ (i.e., the point in G1 which cells commit to divide). 

G1 cyclins regulate entry into _Start_ by turning on expression of G1/S and S cyclins. Thus, G1 cyclin concentrations are elevated during the phases that require G1/S and S cyclins. This explains why the levels of G1 cyclin span a large portion of the cyclin expression cycle. 


At what point in the cell cycle would cells no longer require mitogens for division?

As mentioned above, at  _start_, cyclin G1/S is activated by G1 cyclin and through a positive feedback loop, G1/S cyclin is able to maintain its own activity and G1 cyclin and mitogens are no longer needed to drive the cell cycle. This explains why the levels of G1 begin to plateau. 


Yet, G1 cyclin is still needed for S cyclin activation, so G1 cyclin concentrations does not rapidly fall after the activation of G1/S cyclin.  
 

Sources: Yale School of Medicine
http://medcell.med.yale.edu/lectures/cell_growth_control.php"
Cell cycle regulators,Do cyclins and cdks have a role in meiosis too or just mitosis?,"Good question!

Yes, recent research has shown that regulation of meiosis is similar to that of mitosis (though somewhat more complicated).

References and further reading:
https://www.sciencedirect.com/science/article/pii/S153458070800172X

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4411289/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4080918/

http://rstb.royalsocietypublishing.org/content/365/1546/1653"
Cell cycle regulators,"G1/S cyclins move the cell from G1 phase to S phase, so what does the G1 cyclin (relatively abundant throughout the cell processes in the diagram) do?",G1/S is activated by G1 cyclin. Look at the answer above. It is positive feedback loop.
Cell cycle regulators,How do the presence/absence of Cdk inhibitors affect (or result in the formation of) cancer cells?,"CDK inhibitor inhibits binding of cyclin to Cdk. 
If that is prevented, the cell cycle stall.


However, in the absence of *inhibitors* cell cycle is continually proceeding and happening (circulus vicious) ending up in cancerous growth."
Cell cycle regulators,Why are cyclin/cyclin-dependent kinases important for our understanding of the biology of cancer?,Cyclin/Cyclin-dependent kinases (CDK) prevent the cell from moving on to the next phase until everything is checked and is confirmed to be working properly. Cancer is when the cyclin/CDK is unable to do its job so the cells divide rapidly
Cell cycle regulators,I tutor AP biology students and a teacher has asked students to find the size of Cdk vs cyclin. The students and I have not been able to locate this specific information.  Your drawings indicate that Cdk is larger which is what I would presume but do you know this from some reference source?,"Size in what units§ and of the individual polypeptides or of the complex? 
(For example CDKs typically make a dimer and are often found in a complex that includes regulatory subunits and a cyclin)?  
(Note that the answer will also change for the many different forms within and across species ...)

Thus there is no one "size" — possibly the intention is to get a feeling for relative sizes?

§Note: This could be molecular weight, length in amino acids, or dimensions in angstroms (Å). 

Two resources for answering this type of question are Uniprot (for protein information) and PDB (for structural information including 3D visualizations) — e.g. for Cdk1s:
https://www.uniprot.org/uniprot/?query=cdk1&sort=score
http://www.rcsb.org/pdb/results/results.do?tabtoshow=Current&qrid=1D52EF2E

Links for a specific (yeast) Cdk1 protein, which is known as Cdc28p:
https://www.uniprot.org/uniprot/P00546
https://www.rcsb.org/structure/3LJ1"
Cell cycle regulators,How does p21 regulate p53? How does the thresh hold level of p53 work?,"p21 is a cyclin-dependent kinase inhibitor. 

p21 induces cell-cycle arrest by binding and inhibiting CDK4 and CDK6/cyclin D complexes, resulting in de-phosphorylation and activation of the retinoblastoma (RB) pocket proteins that function together with E2F transcription factors to repress the transcription of cell cycle-related genes.

 p53-mediated repression has also been implicated through activation of its direct transcriptional target, p21.

p21 expression is necessary for the downregulation of p53-repression targets.



https://www.nature.com/articles/onc2013378"
Cell cycle regulators,Is the protein APC/C destroys that holds the sister chromatids together the synaptonemal complex mentioned in meiosis?,"Exactly!

In mouse oocytes, APC/CCdh1 mediated degradation of substrates appears to be required for maintaining prophase I arrest and preventing entry into meiotic divisions.


https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4070676/"
N/A,When are mutations more likely to occur in the cell cycle? Is there a specific stage in mitosis  or phase that leaves the DNA extremely susceptible or vulnerable to mutations? Or can mutations occur at any given moment? When is the DNA most vulnerable to external factors that could create mutations in the genetic code?,"Interesting question!

I'm not sure how well studied this is, but the consensus seems to be that mutations mostly happen during DNA synthesis — i.e. S phase.  A major reason for this is that DNA synthesis introduces many errors — some of which are not corrected."
N/A,what is the difference between DNA & RNA?,"to be more specific, there are 3 main RNA types: mRNA (matrix) - is copied from DNA, to later copy proteins off it, rRNA (ribosomal) - is what ribosomes are made of, and it makes proteins, using mRNA, tRNA (transport) - holds amino acids, which are later brought to rRNA with mRNA to make proteins.
To sum up, DNA holds information on how to make all proteins, and all the RNA work to make them."
N/A,Why do cells divide than grow,"I think they grow to accommodate for the doubling of new organelles and the split of DNA in later stages. After that, then they split. I hope it helps :-)"
N/A,"in other words, you go from a     cell to a    cell.","Not necessarily. You go from a cell to two cells, or even four during meiosis."
N/A,What is the DNA inside a cell called? genetic material or chromosome?,"DNA is genetic material, and the way it is physically present in our nuclei is by being condensed into chromosomes."
N/A,"How long does it take for a cell to fully grow? Days, weeks?","It really depends from cell to cell. Division and growth of cells take 24 hours for many human cells, but liver cells take more than a year and neuronal cells take many years and once they fully develop they never re-enter the cell cycle.

For example, sex cells, spermatozoids take 74 days to fully finish the cycle, while oocyte sometimes takes 40 years. (meiosis starts when the female embryo is in mom's uterus and stops until puberty, then that same oocyte may not be 'unlocked' until the age of 40+)."
N/A,"In my textbook, it says the chromatin fibres condense into chromosomes in prophase. However, here it says the chromosomes already existed in interphase, but in the form of chromatins. Which one is correct?","Right after the cell is born, the DNA is in the form of chromosomes, but in early G1 phase, the chromosomes break apart into chromatids and are only reformed as chromosomes in early prophase, in preparation for division. Pretty much once the  nuclease is formed in the young cell, the chromosomes are free to break apart into the thinner strands called chromatins. But once prophase starts, the DNA has to be collected and organized for division so they regroup/bundle up as chromosomes."
N/A,How does a cell copy its DNA?,"Hi Thandeka, 

The way a cell copies its DNA is actually a pretty complex (but very interesting!) process. There are quite a few steps to this, but the main process that copies the DNA of a cell is called transcription. Khan Academy has some fantastic videos about transcription, you can watch one using the following link: 

https://www.khanacademy.org/science/biology/gene-expression-central-dogma/central-dogma-transcription/v/rna-transcription-and-translation

Happy learning!"
N/A,"About the mitosis. Why does a cell have to divide? Is it because our body needs more cells because others die? For example if you make a cut onto your finger. If that's the case, what about the inner cells, say, cells of liver or heart?","Many cells have a limited life span, so mitosis needs to occur so that healthy, living cells can be maximized."
N/A,Can you give a short summary of mitosis using the steps??,"The cell goes through 4 steps (prophase, metaphase, anaphase, and telophase.) The cells at the end of the process also have the same amount of chromosomes as the parent cell. At the end, 2 cells are produced. Mitosis is used to make body cells, and occurs in the body."
N/A,So is mitosis the same as asexual reproduction?,"Asexual reproduction = formation of one or multiple genetically identical individuals from one parent. Mitosis = duplication of the cell's chromosomes, after which two identical cells are formed, so not whole individuals. ... Asexual reproduction involves only one parent. All the offspring are identical to the parent"
N/A,"In the last paragraph, it's said that you end up with 2 "new" cells, but wouldn't one of those new cells be the parent cells? The diagram could be read like that too.","The 'original' cell, before it divides, is called the parent cell. Both new cells are called daughter cells. (The 'parent' cell ceases to exist after mitosis.)"
N/A,"In plant cells the "celll wall" separates the cell into two daughters at the end of mitosis right? then they split into two or they remain together?
(sorry if there's a mistake my native language is not english)","In plant cells, the first part of mitosis is the same as in animal cells. (Interphase, Prophase, Metaphase, Anaphase, Telophase). Then, where an animal cell would go through cytokineses, a plant cell simply creates a new cell plate in the middle, creating two new cells. The cell plate later changes to a cell wall once the division is complete."
N/A,why does nucleolus disappear during cell division and then reappear again?,"The nucleolus is a region in the nucleus where the genes encoding rRNA (for ribosomes) are found. In fact, the structure of the nucleolus relies on transcription of these genes. The rRNA genes are found on several chromosomes. During mitosis, the chromosomes each condense and separate, so clearly the nucleolus can't stay around the whole time during mitosis. I would guess that there is more control to its disassembly though than just the surrounding DNA being pulled away during condensation."
N/A,Is actin in cytokineses also the same protein as the actin which plays a role in our muscle fibers and their contractions.,"Yes, it is, you are exactly right! Actin is an important part of the cell's "skeleton" and is used in many different cellular processes that need strong fibers."
N/A,Are motor proteins found in all living creatures? Do they all serve a similar function or can they have many varied or specific roles? Examples?,"Yes motor proteins are essential proteins for all organisms - they have lots of important roles such as muscle contraction, transporting cargo around the cell and cell motility (e.g. enabling sperm to swim!). Nice question. https://en.wikipedia.org/wiki/Motor_protein"
N/A,How does the cell "know " to carry out Mitosis ? Is it directed by its DNA ?,"The details of what causes this or that to happen is probably still being studied. Whereas we know how proteins are made from genes, many questions remain in other areas like mitosis. Like, how does the mitotic spindle system know that all chromosomes have been connected?"
N/A,What would happen in anaphase if one or more of the chromosomes didn't pull apart?,"Good question!

Under normal circumstances this is relatively rare, but if the sister chromatids from a chromosome fail to separate during anaphase they will typically both end up in one daughter cell.  

This mistake is known as mitotic _nondisjunction_ and results in the daughter cells being aneuploid (having an incorrect set of chromosomes).  

Aneuploidy is often associated with severe developmental defects, cancer, or death.

You can start learning more about nondisjunction and aneuploidy here:
https://www.khanacademy.org/science/biology/classical-genetics/sex-linkage-non-nuclear-chromosomal-mutations/a/aneuploidy-and-chromosomal-rearrangements"
N/A,What is the purpose of mitosis?,Mitosis allows organisms to grow and it repairs damaged cells. This is because it creates more identical cells.
Probabilities in genetics,What is the probability of having 5 boys in a roll,"Probability for sex ratio is always 1/2, but since we are speaking of having 5 boys in a row, probability changes.

1/2 x 1/2 x 1/2 x 1/2 x 1/2 = 1/32"
Probabilities in genetics,"If monohybrid crossing is something like this Aa x Aa and dihybrid  crossing is something like this AaBb x AaBb, then is this AaBbCc x  AaBbCc called trihybrid crossing and this AaBbCcDd x AaBbCcDd called tetrahybrid crossing? 
Or is there a specific word for crossings that involve more than one pair of alleles?
Perhaps polihybrid crossing?","Not really, but I agree. We need a word to group all these together."
Probabilities in genetics,Why do possible outcomes change? Why can you not guarantee the total outcome in a punnett square?,"There's still chance involved. It's like if you tossed two coins. Each has a 50% chance of landing heads side up, but you can't say that there will definitely be one that lands heads up and one that lands tails up. 

The same goes for genetic probabilities. In the article's example with the dogs' fur color, there might be a litter of eight puppies in which five puppies have the lighter color. Even though each puppy only has a 1/4 probability that it would have light fur, it's not like the genes are sorting themselves out and saying "Well we already have two puppies with light fur, so we have to stop allowing those genotypes to happen now." Each is an independent event.

Hope this helps!"
Probabilities in genetics,I'm still a little confused about the whole probability thing could somebody explain it in a more understandable way please?,"basically, you use the punnets squares to determine all the different possible combinations u have. u line them up and cross them to tell the combos. and then u look and see: how many times does, lets say, AA occur? u look and it occurs 2/4 times in the box, so u know there is a 50% chance of the cross producing an AA set. do u understand the whole punnett square thing, or...?"
Probabilities in genetics,What's an example of an "or" situation (either Event X or event Y) that is NOT mutually exclusive?,"If two events are not mutually exclusive, it would be the same as "and" situation."
Probabilities in genetics,"If I am given 50% of AD and 30% of BC and 30% of AC and 10% of AB, (not precise percentages). How can I figure out the alleles of the "parents" that have ABCD combinations? Or work the math backwards?","If both parents had ABCD alleles, then it would be equal percent for all combinations, which is not given by this task.


Also, I see no CD combination.

Since there is no CD, my projection is it is 0% that both parents have ABCD alleles."
Probabilities in genetics,"If the baby came from the mom , would we have more of the moms genes?","No, as the genes are formed from a 50% contribution from the genes of both male and female gamete."
Probabilities in genetics,what is the reason for the 9/16 probability,"Because, 3/4*3/4=9/16. You get multiply these due to the probability rule of multiplication."
Probabilities in genetics,how do solve all recessive traits?,"It 0% since in every possibility of getting CC and Cc, there will be a dominant trait.  If you multiply that by anything, the answer will still be 0%.

If you want to know for any case that does not come out to be 0%, then you would make a punnet square for each trait separately and multiply the probabilities. For example, if you have AaBb and aabb, you would make a punnet square for Aa and aa and another punnet square for Bb and bb. Then you calculate the probability of a recessive trait coming up and multiply them. In this case, there is a 2/4 chance for a recessive trait for the first one and a 2/4 chance for a recessive trait for the second one. 

2/4 * 2/4 = 4/16 = 1/4 

In this case, there is a 1/4 chance for all recessive traits."
Genetic linkage & mapping,Is 50% always the highest recombination frequency or could it theoretically be exceeded if a small enough population of flies were used?,"If you draw out a punnett square, you will see that it is impossible to exceed 50%. You see, when you perform a punnett square you are assuming independent assortment. You are already assuming that the alleles will distribute themselves completely randomly. Even when you make that assumption, you get only a 50% maximum rate of recombination. If I could go through a punnet square with you it would be easier to see. Go through yourself and try to design a scenario where you get greater than 50% recombination."
Genetic linkage & mapping,what percentage or map units is considered close? is anything lesser than 50 map units considered close??,"Anything below 25 map units is considered close. The lesser the distance, the lesser the crossing over, and the more the chances of the gamete being parental."
Genetic linkage & mapping,How do we know if alleles are on the same chromosome?,"Alleles are different versions of the same gene, so they will always be at the same locus. If you mean how do we know that genes are on the same chromosome, it has to do with recombination frequency. If the frequency is 50% they are not on the same chromosome and therefore assort independently of one another. If the frequency is less than 50%, they are being assorted into the same gametes at a higher frequency because they are physically attached to the same chromosome."
Genetic linkage & mapping,"If RF is 0.5, how can I find out if genes are on the same chromosome far apart or on different chromosomes?","Based on _RF value alone_, you cannot obtain that kind of information.
Because it could be either 0.5 value for genes on the same chromosome, or 0.5 value for two genes on different chromosomes. (as it is stated in the article below how is that possible).


You need to have more RF values (e.g. for A-B, A-C, B-C) to calculate and guess their position."
Genetic linkage & mapping,"How can you create a tester to test if the trait is sex-linked? Eg. White eyed fruit fly could only be produced as a male, wouldn't it be impossible to breed a tester?","A cross between a female fly that is heterozygous for white eyes and a male that is white-eyed could produce female progeny with white eyes, because the mother makes two kinds of gametes: one X chromosome that encodes red eyes, and one X chromosome that encodes white eyes. If the gamete encoding for white eyes is fertilized by the X chromosome from the father, then female white-eyed flies result."
Genetic linkage & mapping,"In the finding recombination frequency section it showed the formula as Recombination frequency (RF)= 
Total offspring/Recombinants ×100% I tried doing the equation myself but I could not get the final answer I kept getting 0.1074321 instead of the answer which is 10.7 where did I go wrong?",0.1074321 x 100% is 10.74321%. Rounded down to one decimal place = 10.7%
Genetic linkage & mapping,What if I were to do an F1xF1 cross (Both parents are heterozygous for both genes)? I know the expected phenotypes should be 9:3:3:1 but how would I calculate the recombination frequency then if the parental phenotype prevails disproportionately? Would it just be all the recombinants / total offspring * 100 again? Or is that ONLY for a test cross with a homozygous recessive parent?,"Interesting question — I've never done or seen anyone else work out recombination frequencies for an F1xF1 cross and I suspect it would be a nightmare — its giving me a headache just trying to work out whether this could even work theoretically.

One significant problem is that both parents are undergoing recombination, so when those gametes combine the recombinations will sometimes cancel out (e.g. if the F0 parents were AB/AB and ab/ab, the F1 generation would produce parental (AB, ab) gametes, but also recombinant (Ab, aB) gametes.  AB x ab and Ab x aB could only be distinguished by a test cross!
 
I think you are safe in assuming that this is only done for test crosses!

However, I think it would be a great exercise to try working this out by starting with a range of known recombination frequencies and seeing how they would affect the 9:3:3:1 ratio.  If you do try this exercise, please share your results in a comment!"
The chromosomal basis of inheritance,What is another definition for "hemizygous?","A chromosome in a diploid organism is hemizygous when only one copy is present. The cell or organism is called a hemizygote. Hemizygosity is also observed when one copy of a gene is deleted, or in the heterogametic sex when a gene is located on a sex chromosome."
The chromosomal basis of inheritance,"What if a white eyed male fruit fly (genotype XwY) is crossed with a heterozygous (i.e. with genotype Xw+Xw) female fruit fly?
Don't we get a white eyed female fruit fly?","You may get a white female with a XwXw genotype or a red-eyed female with a XwXw+ genotype. Morgan used this to verify his hypothesis further.
Open the hidden experiment tab under the "Confirming the model" subheading above.
Hope this helped. :)"
The chromosomal basis of inheritance,"Hello! I dont understand why the mutant is on the X chromosome if we said that it is defining by the sex chromosome?? if it's only for male (XY) and female has both XX, I would predict that the mutant would be on the Y chromosome, which only the male has.
thnks!","If the white eye trait was linked to having the Y chromosome, then you would expect that:
a) all male offspring of white-eyed males had white eyes, because they should all inherit their father's Y chromosome. In actual case they had red eyes though.
b) It would not be possible to have white eyed females, because they don't have a Y chromosome. However, in the actual case, Morgan performed experiments by crossing females which were offspring of a white-eyed male with another white eyed male, and found you can get white eyed females, so the trait is not linked to the Y chromosome. This suggests the white eyed trait is X-linked but recessive, so females only show this phenotype when they have two copies of it, and no red-eye version. 
Hope that helped!"
The chromosomal basis of inheritance,"It is stated in the second to the last paragraph that Bridges showed more detail about Morgan's findings wherein he showed that rare male or female flies with the unexpected eye colors were produced through nondisjunction of sex chromosomes during meiosis, and since it is meiosis they should bed divided. What then is left in the cell? Does it have both X and Y? If so what about the other cell that was supposed to inherit the other sex chromosome.","Bridges found rare flies with surprising inheritance patterns: daughters that inherited X-linked traits (like eye colour) only from their mother, and sons that inherited their X-linked traits from their father. Due to these inheritance patterns he suggested that these daughters were XXY, and the sons were XO (unlike in humans, in drosophila, sex is determined by how many X chromosomes are present, rather than depending on the Y chromosome). His explanation was that nondisjunction had occurred during meiosis in the mother, producing egg cells with XX or no sex chromosomes. When these rare eggs were fertilized by sperm carrying either X or Y, the offspring were the XXY daughters with 2X chromosomes from the mother, and X0 sons inheriting an X from the father (those with XXX and Y0 combinations died). He also looked under a microscope and saw that these were indeed the chromosome combinations that the flies had. This work provided further evidence that inherited traits, which could be studied using the breeding experiments of genetics, are linked to physical chromosomes, that were being studied for example with dyes and microscopy. 

There is more information where I read most of this, here: https://embryo.asu.edu/pages/calvin-bridges-experiments-nondisjunction-evidence-chromosome-theory-heredity-1913-1916
And here is another interesting article on the chromosome theory, Bridges' contribution, and its impact http://www.genetics.org/content/202/1/15"
The chromosomal basis of inheritance,"Is this a mistake in the text? Emphasis mine.

_Morgan did lots of other experiments to confirm an X chromosome location for the eye color gene. He was careful to rule out alternative possibilities (for instance, that *it was simply impossible to get a white-eyed female fruit fly*).

By mating the F2 files [sic] from the cross above, *Morgan was able to obtain white-eyed females*, which he then crossed to red-eyed males. All the female offspring of this cross were red-eyed, while all the males were white-eyed._

Other comments suggest readers are getting thrown off by the contradiction. Personally I can see how a white-eyed female can be born to two parents carrying the recessive allele.","There is no mistake or contradiction. Note the statement preceding it: "He was careful to rule out alternative possibilities"

He ruled out that it was impossible to get white-eyed females by obtaining white eyed females."
The chromosomal basis of inheritance,Why was the idea initially controversial? What did it initially lack?,Gregor Mendel's work didn't explain co-dominance and so many other factors but was later found out to be the basic building block of genetics.
The chromosomal basis of inheritance,"where did the first white eyed fly come from?
if there were no white eyed flys to begin with where did he get the white genotype? Please help.","The first mutant white allele isolated (called w1) arose spontaneously because of transposon insertion.
There are now many strains of flies with different mutations in the white gene (you can find a long list here: http://flybase.org/reports/FBgn0003996.html).
Some of these have far smaller mutations, such as just one amino acid change like described here: https://www.sciencedirect.com/science/article/pii/S0005273699000644"
The chromosomal basis of inheritance,so whats the role of the cromosome y in the eye color here?,"The role of the Y chromosome is to determine the sex. As for eye color, nothing."
The chromosomal basis of inheritance,I thought it wasn't possible t obtain a white-eyed female because of the differing chromosomes in the two sexes?...,"If you breed a homozygous red eyed female with a white eyed male, the female offspring will be heterozygous and have one copy of the mutant allele, even though the eyes are still red. Then if you breed such a female with a white eyed male, some of the female offspring will receive an X chromosome from the mother containing the white mutation, as well as the white mutant allele on the X chromosome from the father. Such females have two mutant copies and no 'normal' alleles to compensate, so would have white eyes."
The chromosomal basis of inheritance,Couldn't we have a White EYE female fruit fly in the F3 Generation ?? PLEASE HELPP,"The previous comment is incorrect, the logic is flawed. If a white eyed female required a white eyed female, you would have an infinite regression. You can have a white eyed female in generation 3, by mixing a red eyed female with the white eyed gene with a white eyed male."
The law of independent assortment,"I understand this, but I still get confused on the Mendelian laws.
Here is what I think I know:
The law of segregation states that the two alleles of a single trait will separate randomly, meaning that there is a 50% either allele will end up in either gamete. This has to do with 1 gene.
The law of independent assortment states that the allele of one gene separates independently of an allele of another gene. This has has to do with 2 genes.
Is my understanding of these laws correct?","That is correct. But as an addition, there is also the concept of *linkage*, where the allele of one gene is very close to an allele of another gene in the same DNA strand, that it is very unlikely for the two allele to separate independently (in other words, they are inherited as one unit). This has to do with 2 genes. This concept is essentially independent assortment, but deals with *unit of multiple alleles*, rather than *just an allele*."
The law of independent assortment,Why is science soooo complicated??😩,Because Adults
The law of independent assortment,What is the difference between segregation and independent assortment? :),"Segregation means that the chromosomes or any gene present on chromosome did not lose its identity or get mixed up with other genes. During gametogenesis it keeps its identity. 
While independent assortment means that the chromosomes whether dominant or recessive after gametogenesis goes into any of the gametes i.e in simple language the movement of chromosomes is not affected by movement of other chromosomes"
The law of independent assortment,For the experiment of F1 generation how did Mendel know for sure that the tall parent's genotype is (TT) ?,"The pea plants he used self-fertilized, meaning that each parent ends up having the same set of genes as the offspring. (This is _before_ he crossed them.) This means that there were pure lines of descent from the original pea plants without variation. The genotypic variation of the offspring (heterozygotes) was introduced by Mendel, who crossed 2 plants of different traits."
The law of independent assortment,"The phenotypes are a 9:3:3:1 ratio, but what are the possible genotypes?","there are 9 different genotypes in a F1 dihybrid cross and the ratio is
1:2:1 :2:4:2: 1:2:1

in a monohybrid cross the phenotype ratio is 3:1 which gets compounded when doing a dihybrid cross into 9:3:3:1

the genotype ratio in a monohybrid is 1:2:1
and gets compounded to my answer in a dihybrid cross. I show the work below.

F1 generation is heterozygote for both traits: AaBb or Aa and Bb 
  A  a
A AA Aa
a Aa aa
and 
  B  b
B BB Bb
b Bb bb

here are the possible genotypes and ratios made from the squares above:
AABB(1) AABb(2) AAbb(1) AaBB(2) AaBb(4)Aabb(2)aaBB(1) aaBb(2) aabb(1)

this is nothing more than a 1:2:1 compounded to two characters."
The law of independent assortment,"Does this mean that any living organism (Pea plant, dogs etc.)
will show phenotypic ratio of 9:3:3:1 ? Where 9 plants have all dominant alleles and 1 plant has all recessive alleles ?",Just know that a 9:3:3:1 ratio happens when you cross TWO Heteroygous pairs. Also....Look over what a Dihybrid cross is. Dihybrid cross is when your crossingg 2 different types of Genes. So you should get an out come out of 16...
The law of independent assortment,"Can you explain to me what is the difference between linked and not linked. Also, how to identify if an allele is not linked.","Linkage or whether 2 genes are linked or not depends upon the distance between them. If the distance between 2 genes are small or if they are next to each other in a chromosome, most probably when meiosis occur these genes remain together. So genes that remain together and almost never segregate are called linked genes.  
Hope this helps."
The law of independent assortment,Does the law of independent assortment apply to two genes on different chromosomes or two alleles on different chromosomes?,"Law of independent assortment applies to two genes of different chromosomes _and_ two alleles of same genes.


What does it mean_ It means that alleles are inherited independently and do not affect alleles from _other_ genes."
The law of independent assortment,"If the genes are the same, then why is it that many people look different form their parents?
That's just if they were the same though.","In each of your parents, there are genes coding for their appearence, i.e bone structure, hair color, eye collar, that are shown. However, there are also genes that aren't expressed by your parent that they have, such as something different. Considering there are billions of genes that code for even one thing, there is an extremely high liklihood of you expressing a gene that wasn't expressed in your parents, (but was still there)"
N/A,What is multiple allele is one sentence that is easy to understand?,Multiple Alleles are three or more possible alleles for one individual trait.
N/A,isnt codominance the same as incomplete dominance in that case if both alleles can be expressed?,"Not really.
In codominance, both alleles are completely expressed.  If you crossed a red flower with a white one and the alleles were codominant, you might get flowers that are red and white in patches.  If the alleles were incompletely dominant, the flowers would be pink because the traits blend."
N/A,"I'm confused on why there are some "exponents" on the alleles. For ex, c^ch c^ch
what does that exactly mean?","It's to distinguish the alleles in an easier way, once you have to deal with different traits it will be useful since the base could specify the trait while the exponent specify the allele for that trait.

For example, if you were talking about the traits color and height with the alleles red and blue, and tall and short, respectively, you could express genotype as:
C -> Color
H -> Height 
R -> Red 
B -> Blue
T -> Tall
S -> Short

* C^R C^B H^T H^S (This would be heterozygous in both traits)
* C^R C^R H^T H^T (This would be homozygous for red color and tall height)

You can also use lower case to denote that an allele is recessive (although this is arbitrary)."
N/A,in case of pea plant tall is the dominant gene and dwarf is the recessive gene. does that hold good for other organisms as well? is dwarf always recessive gene and cant it be dominant in the presence of tall gene?,"What's dominant and recessive can change between organisms because species tend not to be able to breed with other species, so the gene pool for a species tends to be isolated to just that species."
N/A,Is multiple allelism the same as polymorphism?,"Not exactly — what is true is that genetic polymorphisms are responsible for the existence of (most) alleles.

Polymorphism (literally "many forms") means different things in different contexts, but in a genetic context it really just means that there are differences in the sequences. 

For example SNPs (pronounced "snips" — stands for single nucleotide polymorphisms) are a very common type of sequence polymorphism.

Having multiple alleles is (usually§) a consequence of multiple different sequence variants for a gene (i.e. genetic polymorphisms) being present in a population.  However, any two alleles are likely to have multiple polymorphisms (i.e. sequence differences) that separate them.  Furthermore, two alleles that appear to the same at a phenotypic level may have different sequences.  A good example of this is the ABO blood groups — traditionally we have identified three alleles Iᴬ, Iᴮ, and i, but it turns out that are multiple sequences that correspond to each of those alleles!
For more on this see:
https://en.wikipedia.org/wiki/ABO_blood_group_system#Subgroups

§Note: Sometimes alleles result from epigenetic changes (heritable changes that don't alter the sequence) — these can be referred to as epialleles and appear to be less common than alleles based on sequence polymorphisms."
N/A,Is the rabbit example also an example of epistasis?,"Epistasis occurs when the phenotypes associated with alleles of one gene are affected by what alleles are present for a *different* gene.

How many genes are involved in the rabbit example?

Does this help you to answer your question?"
N/A,"Where multiple alleles exist for a trait, anyone individual will have more than two alleles for that trait?","No, they will only have 2 alleles (unless something is wrong). Multiple alleles just means that more than 2 exist. For example, there are 3 alleles for blood type in existence, but healthy individuals will only inherit 2."
N/A,what is codominance i dont unerstand,codominance is when both parents are both homozygous dominant  and both traits show in the offspring like if a homozygous dominant yellow flower and a homozygous dominant red flower made a new flower the flower would have both red and yellow petals
N/A,"If the extra copy of X chromosome is inactivated by Barr bodies, why does XXX or XXY show an abnormal phenotype? Is the inactivation not perfect (i.e leaky)?","Excellent question. X inactivation happens in XXY males, as well as normal XX females. However, in XXY males, a few genes located in the pseudoautosomal regions of their X chromosomes have corresponding genes on their Y chromosome and are capable of being expressed. This means even though the extra X is deactivated, during recombination in Meiosis 1 there may be exchange of genes between X and Y and would result in expression of these traits."
N/A,"And about that, how will the inactivated X chromosome be when it undergoes meiosis to produce gametes?","@Junsang is right, the compact X chromosome winds open during meiosis undergoes gamete production normally."
N/A,"Given the explanations above, how does Swyer syndrome occur? (a person who is typically raised as female and has female external genitalia but also has a Y chromosome) I noticed this in the 2016 Olympics, as it was hotly debated with track and field.",hmm.. perhaps the Y chromosome is missing an SRY gene? would love to hear from an expert
N/A,"In Turner's syndrome, the individual has 45 chromosomes of the karyotype XO (only one X chromosome), and displays mental retardation and physical abnormalities, among other symptoms,while a zygote with two X chromosomes would develop as a normal female.Why is that? Wouldn't one of the X chromosomes be inactivated anyway?","Great question!

At least one factor that contributes to this is that the X (and Y) chromosomes have what are called pseudoautosomal regions (PARs).

The PARs allow crossing over between the X and Y — this allows for meiotic pairing, crossing over, and disjunction of the X and Y in males.

The PARs are not X-inactivated and so are thought to contribute to the defects associated with sex-chromosome aneuploidy including Turner's syndrome.

For example Turner's syndrome patients are usually short and one PAR gene, _SHOX_, is a transcription factor that promotes skeletal development particularly bone growth in the arms and legs."
N/A,"Can a malfunction happen in which both X chromosomes stay active somehow, and would that be lethal? Could that ever happen?","Good question. From what I've found so far:

The mechanism of inactivation is still not very well understood, but there are some theories.
In mice, there are 2 events of inactivation. It is known that inactivation happens in females and also in males and cases which have an extra X chromosome.
In the fisrt, the event of inactivation fraternal X (Xp) is inactivated, and in the late blastocyst, second inactivation event happens. This time fraternal Xp reactivates and now _random_ inactivation happens.

Meaning that it never catches _both_ X chromosomes.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2630377/

I guess mutations can happen. However, it is _hardly possible_ that in every single cell of the female body both X chromosomes are inactivated. If that happens I suppose it would be lethal and cause severe bodily malfunctions.

If both X chromosomes are inactivated in some cells, that female is a chimera.

Also, bear that:  X chromosome inactivation is not an all-or-none phenomenon. Of the 2000 or so X-linked genes on the X chromosome, about 10% are not inactivated by X inactivation of the chromosome on which they lie. Thus, these genes maintain two actives, transcribed and translated copies in individuals with two X chromosomes.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2885450/

May this photo help:
https://dev.biologists.org/content/develop/139/12/2085/F1.large.jpg?width=800&height=600&carousel=1"
N/A,"It's stated that the extra X chromosome in people with Klinefelter syndrome will be inactivated. Since it's been inactivated, by right, it'd virtually be the same as normal people, isn't it? But why is it people with Klinefelter syndrome still have abnormalities? Thank you.","As stated by Dr. Barry Starr, "the problem comes from the fact that X inactivation is not complete. X inactivation starts at the middle of the chromosome and spreads towards the ends. Apparently it peters out before it makes it all the way. The genes at the ends that are still on lead to Klinefelter's syndrome. In fact, many of the symptoms of Klinefelter's are really those of a feminized male."  Link to the full article: http://genetics.thetech.org/ask/ask141"
N/A,But my question is that some X. Linked dominant disorder like alpart syndrome etc if the defective allele come in heterozygous can cause problems what's about the other normal allele (recessive)??,"Well, normal allele cannot do much in that case since it is _recessive_.

What you ask is, what if X on which dominant allele is, gets inactivated? In that case, it is not heterozygous and the normal allele is only expressed.

But, there is a tricky part. What if during crossing over, dominant allele got onto X which will stay active? In that case, the syndrome will manifest."
N/A,"(Under Sex chromosome aneuploidies topic)
What about Just Y chromosome in male (relative to the non dis-junction of sex chromosome)? Will it result in fetal death as there's no X chromosome at all?","only Y will be spontaneous abortion, at least one X required to be viable. because X has more expressed genes than Y."
N/A,"Is there Y inactivation as well for when the genotypes are mutated into XYY, XYYY, etc.? If so, does it work the same way as X inactivation?",I don't think there is a y inactivation since there are usually just one y chromosome
Variations on Mendel's laws (overview),Is people with multicolored eyes (like one eye brown and the other blue) an example of incomplete dominance?,"No; genetic heterochromia is the result of a mutation on at least one gene that determines eye color (scientists discovered that eye color is controlled by at least eight genes in what is called polygenic inheritance). An individual may have also acquired it because of an injury, meaning that it had nothing to do with genetics at all.

Did this help?"
Variations on Mendel's laws (overview),what is lethal alleles?,"think about the word lethal it means something deadly and alleles means it is a specific form of gene, so lethal genes means alleles that preventing us to live"
Variations on Mendel's laws (overview),"How does epistasis relate to getting a 9:7 ratio? how does this concept work? is there an example we can relate this to?

also does complementary gene mean the same as principle of complementation? cos from what I understand of complementation, is when two mutant pure breeding parents cross and give rise to a progeny all with wild type phenotype. I don't get the explanation of recessive alleles of two different genes giving rise to the same phenotype.","You will get 9:7 fenotipe ratio in Duplicate Recessive Epistasis (DRE) for P: AaBb x AaBb, then the F1's genotipes will be 9:3:3:1 (9[A_B_], 3[A_bb], 3[aaB_], 1[aabb]). In DRE, any recessive homozigote is epistatic and they all give the same fenotipe. So we look for how many of the F1's genotipes that doesn't has any recessive homozigote then compare to how many of those that has recessive homozigote (epistatic gene, it means all of them have same fenotipe), then we got 9:7.

Example: Snail Shell Color
https://www.youtube.com/watch?v=0HfkCppZLfo&t=6m

Also, Complimentary genes are those genes in DRE. They are complimentary because for a hypostatic fenotipe to occure needs all of them to be homozigotely or heterozigotely dominant (which are also hipostatic to the homozigotely recessive genes)."
Variations on Mendel's laws (overview),"Is the Incomplete dominant same as the bleeding rule, which was proposed before the Mendel genetics?","No
In incomplete dominance, no blending takes place. It happens due to incomplete enzyme or no functional enzyme.
Basically, it is the enzymes that produce the phenotypic character. In the nucleus, mRNA is produced from the DNA. This mRNA goes into the ribosome, the protein synthesis house, wherein these enzymes are synthesized. Sometimes, the enzyme malfunctions or is produced in insufficient amount. Hence, the phenotypic character is affected.
This phenomenon is observed in the plant snapdragon or _Antirrhinum majus_"
Variations on Mendel's laws (overview),can a kid from two different parents look the same as your parents resulting to be more alike to your parents as if he/she was their child?,"The genetics of a organism like a human is far more complex than the genetic of peas that Mendel studied. 

The simple way it is usually explained you get the idea that a specific gene allele is directly mapped to a specific trait.  This is rarely the case in complex organisms.  

Often it is a set of genes (gene complex) is responsible for a trait and a specific trait may be caused by multiple combinations of the genes alleles.  

So just because someone may look more like someone elses parent  doesn't mean that they are more genetically similar."
Variations on Mendel's laws (overview),can humans also exhibit incomplete dominanace in their phenotypes.,"Yes. One of the most well-known examples of this has to do with the genes for straight and curly hair. If an offspring has inherited both a curly hair gene and a straight hair gene (they are heterozygous), they get wavy hair. Their hair does not curl, but it is not straight either."
Variations on Mendel's laws (overview),complementary genes mean that it is all the same right,No. It just means that different combinations give the same phenotype.
Variations on Mendel's laws (overview),what is the relationship between mendels law to genetics,"Gregor Mendel was basically the one who invented genetics, He documented his experiments with pea plants, and his findings are known as Mendel's law. So, without Mendel's law, we wouldn't have genetics."
Mendel and his peas,what is difference between geneotype and phenotype,"genotype = genetic code 
phenotype = physical appearance/properties/expression of the gene"
Mendel and his peas,what does it mean when it says that it "self fertilizes"?,Self fertilizing is when the pollen from one plant is put on the stigma of the same flower or another flower that is growing on the same plant.
Mendel and his peas,why the ratio  is always roughly 3:1 not exactly?,"It is correct that it won't be exactly half ,because as Alexander said, there would be slight imperfections (nothing is absolute ,I mean).
But , for this pea plant experiment ,I think it would be that tall and short are compound traits ,like they are made up from a combination of small traits."
Mendel and his peas,"What determines what gamete is chosen to move on? Or is it just random, and each gamete has an equal chance at being passed on to the offspring?","Does garden pea, Pisum sativum has a discontinue character on height, colour...? mostly those characters are continuous, they are controlled by many genes."
Mendel and his peas,How can we identify that after breeding multiple times we have got a homozygotic offspring and does multiple breeding results in a homozygote  offspring ?,"When 2 parents breed, they each have a genotype, let's say one is AA, the other is aa. Both are purebred and homozygous. In its offspring, they create a new genotype, one letter from each of the parent's genotype. This creates many outcomes, including the heterozygous, Aa."
Mendel and his peas,"why did he use pea plants, why not any other flower?",because pea was an annual plant and its was a self fertilizing plant and its easy to manually fertilize it
Mendel and his peas,what is difference between geneotype and phenotype,Genotype is the specific gene alleles where as the phenotype is the physical expression of the alleles.
Mendel and his peas,How it can be explained if Gregor Mendal studied eight character?,"Who knows, really depends on what 8 character was. What really important is that those traits are not linked (on the same chromosome) and that those traits are comparable (for example tall and short) and easily distinguishable.


All 3 Mendelian Laws would probably stay the same."
Mendel and his peas,"If a tall plant and a short plant bred together, how would all of the plants end up being tall? Wouldn't 75% become tall and 25% become short based on the 3:1 ratio?","All plants would end up being tall if the parents are homozygous for the traits controlling each character. 75% would be tall if and only if the p generation is heterozygous for the character while 25% would be short, which conforms to the 3:1 ratio."
Mendel and his peas,What does F1 generation mean? It doesn`t make sense.,"The F stands for filial, which comes from the Latin word _filius_, meaning son.  F1 means the first generation of children (or baby pea plants)."
Polygenic inheritance and environmental effects,how environment causes pku?,"The environment doesn't actually cause the PKU -- that is genetic. But the environment can cause it to express in the phenotype -- create symptoms -- based on the environment. The PKU gene simply causes a person to be unable to properly process phenylalanine (they lack an adequate amount of the necessary enzymes). If that person eats foods that are high in it, they can begin to express symptoms of that genetic mutation. If they limit or eliminate those foods, they often will have no symptoms."
Polygenic inheritance and environmental effects,"What's the difference between polygenic and epistasis?
It sounds like in both of them, multiple genes affect one trait.","While a polygenic phenotype can occur without epistasis, if you have epistasis you must be dealing with a polygenic phenotype.

Polygenic just means that there are multiple genes involved in a phenotype.  
Epistasis refers to situations where one allele masks the phenotypic effect of one or more alleles of another gene."
Polygenic inheritance and environmental effects,how are we able to walk on the earth,"Gravity. I personally wouldn't ask this question in the genetics unit, though."
Polygenic inheritance and environmental effects,Does anyone know anything about syndactyly and its genetic inheritance?,"Syndactyly is a mendellian dominant trait, so it is inherited much like any other gene."
Polygenic inheritance and environmental effects,"Can a disaster, natural or man-made, affect human traits?","Quite interesting question!

I can think of radiation which causes *mutations*.

Definitely causes of mutations can affect human traits and phenotype, but not in the form that it will _favor_ survival. Nonetheless, future generations may be less adaptable and degenerated (recall Chernobyl nuclear plant disaster or Minamata disease in Japan (caused by excessive mercury due to chemical industry).


My answer is *definitely yes*. *Negative impact*."
Polygenic inheritance and environmental effects,"So I am very short for my age , yet my mom and dad are both tall but my mom is a little shorter than my dad . Why is that? Do i have a disease or something that affects my growth ?","A short stature can be caused by a variety of causes. It could be genetic, a hormone known as growth hormone could be low in the body, or, in more serious cases, an underlying disease or condition may have contributed to your stature (I.E: tumors, malnutrition, mitochondrial disease). If you are otherwise healthy, it is most likely either genetic or hormonal.

Does this help?"
Nucleic acids,How do mRNA and tRNA communicate with eachother during the formation of the proteins?,"mRNA is like a recipe from a cookbook; a list of ingredients to make a protein. mRNA is a chain of nucleotides (A, U, C, and G, not T since this is RNA). A group of three nucleotides is called a codon. A codon matches with three nucleotides, called an anticodon, on a single tRNA molecule while in a ribosome. The tRNA carries an amino acid, our ingredient to make the protein.
So mRNA is the recipe, tRNA matches to the recipe bringing an ingredient, and the line of ingredients become a protein."
Nucleic acids,"If A-T bonds have 2 hydrogen bonds and G-C bonds have 3... Would it be true that longer periods of A-T bonds in DNA (so like: AATAATTATTTTAATTAAAA) are less stable parts of the DNA helix than parts that have more (or only) G-C bonds in them? And if this is true, are these parts (AT only parts) more prone to mutations?","The first part is true, T-A bonds are less stable and more likely to come apart. The A-T bond strands also signal where DNA needs to separate for commonly transcribed genes, such as the TATA Box commonly found just before the beginning of gene sequences.

I'm not sure if they are more prone to mutations though."
Nucleic acids,"DNA is common to all organisms, all organisms use the same 4 nitrogenous bases, A T, C G

is that right?","Entirely true. Also, AT/GC are found in DNA while RNA is made from AU/GC. Just keep in mind that, even though all life forms have DNA, not everything that has DNA is alive: viruses can have DNA but are not living."
Nucleic acids,"Why do some nitrogenous bases have two fused carbon rings while other have one? Would it be possible for there to be nitrogenous bases with more than two fused carbon rings? Could there ever be an instance where there are more than just five kinds of nitrogenous bases (Adenine, Thymine, Guanine, Cytocine and Uracil)? If it could be possible how would DNA and RNA have to rearrange themselves? Would it be possible for DNA and RNA to use other sugars aside from Deoxyribose and Ribose? If so, like what? If not, why?","https://www.khanacademy.org/science/organic-chemistry/aromatic-compounds/aromatic-stability/v/aromatic-heterocycles-i

https://en.wikipedia.org/wiki/Heterocyclic_compound

https://en.wikipedia.org/wiki/Abiogenesis

https://en.wikipedia.org/wiki/Nucleic_acid_analogues

Hope this helps!"
Nucleic acids,Are the functions of nucleic acids guided only by molecular forces and just appear to have intention or are there other forces at work that I'm not aware of? How do these macromolecules "know" what to do?,"A creationist would say that this is part of the intelligent design. An evolutionist would say it's all down to chance. Two spanners to consider - 1) one molecule of hormone, once recognised by the cell, leads to prduction of thousands of times more molecules, and types of molecules, than a mere chemical would suggest, and such secretions can be brought about by tiny changes in brain activity. 2) DNA is just for storage. It is a molecularly inert form for the passing on of genes without having a massive effect upon the rest of the body - and so the active form is the sticky stuff of RNA and these determine how the proteins are folded together."
Nucleic acids,"When transcription takes place and the DNA is broken into two, and then mRNA is formed with one of the DNA strands or for BOTH the DNA strands?","Within a gene *usually* only one strand is transcribed, but there are many examples where transcription happens from the both strands. This is especially common in viruses.

Also, the strand that is transcribed for one gene may not be the same as the strand being transcribed for a neighboring gene.

Finally, the whole DNA double helix is not separated - just a small bubble is opened around each RNA polymerase as it works its way along the DNA."
Nucleic acids,"In the first paragraph of the section "Regulatory RNA (miRNAs and siRNAs)" it says "They bind to specific mRNA molecules (with partly or fully complementary sequences) and reduce their stability or interfere with their translation, providing a way for the cell to decrease or fine-tune levels of these mRNAs."

Does this mean that the purpose of microRNAs (miRNAs) and small interfering RNAs (siRNAs) it to make sure that there are not too many mRNA molecules producing proteins? They are regulating the amount of protein produced by the cell? Am I understanding this correctly?

Please help! Thanks. :)","Yes, miRNA regulates protein synthesis in a way it binds to mRNA transcript and 'silence' it."
Nucleic acids,how are DNA and RNA different and alike to each other?,"As stated in the summary at the end of the article, DNA and RNA have different functions. While DNA stores genetic information, RNA is involved in protein synthesis and gene regulation, as well as storing genetic information in some viruses. DNA and RNA also have different structures; DNA's phosphate-sugar backbone contains deoxyribose, while RNA's contains ribose. While DNA is double-stranded and has the nitrogenous bases adenine, thymine, cytosine, and guanine, RNA is usually single-stranded and contains uracil instead of thymine.

As for the similarities between DNA and RNA, they are both important biological polymers and contain four bases and a phosphate-sugar backbone."
N/A,Why is Cesium chloride used? Why can't the centrifugation be done without it?,The density of the cesium chloride solution increased along a gradient down the tube.
N/A,what causes the double helix of the DNA to "unzip","During DNA replication, the enzyme helicase unwinds the DNA double helix by disrupting the hydrogen bonds that keep it together. Different proteins are also involved in the unzipping of the double helix such as single strand binding proteins that keep the two strands from reforming hydrogen bonds."
N/A,"What would have happened if they grew the bacteria in the light isotope and then introduced it to the heavy isotope?  What would the vial layers and densities look like? (Essentially, what would happen if you did the opposite of what they did.)","I think the exact same thing would have happened, but instead of the number of light 14N DNA increasing over successive generations, the heavy 15N DNA would increase with each generation."
N/A,"Could someone explain to me the results of the 3rd and 4th generation please? I don't quite understand that part, why isn't all DNA semi-conservative? Why is there a N^14 light strand?","1st we know: Bacteria is grown in N15 , 
then placed in N14 .
(remember N14 is the light isotope and N15 is the heavy one.)
So initially all nitrogenous bases of each nucleotide will have contained N15 isotope.
So once place in N14 medium ,DNA replication will use the N14 Isotope only.
No more N15 available.
Thats why in the 3rd and 4th generation , the N15 strand disappears over time
So what remains are DNA Strands that undergo Semi conservative replication  with the  fixed amount of N15 and an increasing amount of N14, as N14 is available in the medium.
The chart in Fig. 2 kind of explains it."
N/A,Would the results be different if they didn't use E. Coli but something else instead?,"No, because DNA replicates semi-conservatively. :)

Maybe the experiment would be set up slightly different but results must be the same.

Replication is semi-conservative in both: Eukaryotes and Prokaryotes meaning that it is the same for _any living organism_."
N/A,when its splitting is there every a case when it doesn't split correctly,"Absolutely! There are numerous syndromes, diseases and conditions based on the improper splitting. This is something that is easily googled and you can find tons of information on!"
N/A,"If it is concluded that each strand serves as a template for the synthesis of a new complementary strand, how come a hybrid strand does not produce two hybrid molecules. For example, one light and one heavy template strand, produces a complementary heavy and light strand respectively.",Good question! Keep in mind that the DNA is grown in N15 (heavy) but the next generations are in N14 (light). So a hybrid strand cannot produce hybrid molecules because there aren't N15-labelled nucleotides available! The question and response below might help clarify too :)
N/A,Why are bacteria like Escherichia coli good for studying DNA replication (as opposed to using other types of cells)?,"E. coli is *model organism* that's why.


Why E. coli model organism?
E. coli is a perfect model for several reasons: E. coli is a single-celled organism that can be manipulated and killed with no ethical concerns. It has a rapid growth rate and is very easy to culture and grow.

https://study.com/academy/lesson/escherichia-coli-e-coli-as-a-model-organism-or-host-cell.html

The main reasons why E. coli is the organism of choice extends and is not limited to its fast growth in chemically defined media; relative cheap culture media; does not form aggregates; industrial scalability; several molecular tools for manipulation; extensive knowledge of its genetics and genomics; extensive knowledge on its transcriptome, proteome, and metabolome, and several strains are considered biosafety 1, which renders it ideal even for teaching and school demonstrations.

In terms of ecology, E. coli is a facultative aerobe (either respiration takes place in the presence of oxygen or fermentation in its absence), which bears a sensor for oxygen presence (redox state in the quinone pool) and can activate or repress the required metabolic enzymes, depending on oxygen levels.

The building blocks of E. coli consists of about 55% protein, 25% nucleic acids, 9% lipids, 6% cell wall, 2.5% glycogen, and 3% other metabolites [16–18], which for biotechnological applications is important since carbon flux is often a problematic issue to address to generate a novel metabolic pathway or to enhance a current functioning pathway. 

E. coli is part of the normal microbiota of mammals, rendering the predominant facultative microbe of the gastrointestinal tract and is currently a hot debate on the impact on normal microflora establishment and their role in disease.

E. coli harbours a genome with particular features such as a strikingly organized structure, remnants of many phages, and insertion sequences (IS) and a high transport capacity toward the cytoplasm.

https://www.intechopen.com/books/-i-escherichia-coli-i-recent-advances-on-physiology-pathogenesis-and-biotechnological-applications/-i-escherichia-coli-i-as-a-model-organism-and-its-application-in-biotechnology"
N/A,It means the other two models don't exist?,"Models are proposed explanations for or descriptions of something.

All three of the models discussed in this article "exist", but one of them is a better description of how DNA replication actually occurs.

Does that help?"
Classic experiments: DNA as the genetic material,"it was good
 but i wanted to ask that why do twins have different dna structure??","It happens, because normally there is only one egg at the time of ovulation in the ovarian duct. And if a sperm is present there is more than enough of spermatozoids. So one lucky sperm fertilizes one egg. This way an zygote is produced which later becomes embryo and eventually a baby. 
But in some cases, there is two or even more eggs in the ovarian duct, and as we know there are hundreds of sperms, both can get fertilized. In this case two different zygotes form, hence the name "dizygotic" twins. In more simple way, it is like getting pregnant twice, when female body gives two eggs that can be fertilized. And different eggs have different sets of DNA (because of myosis, crossover and other things). So dizygotic twins are related as much as simple brothers (or sisters)."
Classic experiments: DNA as the genetic material,"Hi, 
I'm kind of confused on Avery's experiment on transforming factors. I understand the process of it, but I don't know what exactly was grown in the petri dish, or how it proved that DNA is the transforming molecule. 

Thank you,","There were three major components to their experiment: (1) separated, subcellular components of heat-kill virulent S. pneumoniae (2) non-virulent S. pneumoniae and (3) mice. To see which subcellular component (the "purified substance," as Khan refers to it) was the transforming principle (responsible for "passing on" virulence to non-virulent bacteria as shown in Griffith's experiment), they systematically injected _one type_ of substance per trial into non-virulent bacteria. This initially non-virulent bacteria then was injected into mice; if the mice lived, then the substance injected could not have been the transforming principle. They then noticed that one specific substance (which we now know is DNA) transformed the initially non-virulent bacteria and killed the mice when injected. 

The results of three other tests then gave these scientists additional evidence that supported DNA as the transforming principle, which are listed in the article. The first two should be self explanatory: the substance tested positive for DNA detection and negative for protein detection. Its chemical composition also matched that of DNA. The last one may be a little confusing without knowing about the experimental setup above. They essentially treated the substance with either (1) protein/RNA degrading enzymes or (2) DNA degrading enzymes. Injecting the substance treated with (1) showed that non-virulent bacteria were still transformed (became virulent) and mice still died. Therefore, the transforming principle could not be protein/RNA, which had been degraded by enzymes in that sample. Injecting the substance treated with (2) showed that non-virulent bacteria were _not_ transformed and mice _did not_ die. This suggested that DNA was indeed the transforming principle because when it was degraded, virulent bacteria were unable to "pass on" their virulence."
Classic experiments: DNA as the genetic material,I don't understand how the mice died with the smooth strain but not the heat killed smooth strain.,Because the heat killed smooth strain have been killed and so those dead bacteria can no longer grow and reproduce in numbers and overwhelm the mouse and kill it.
Classic experiments: DNA as the genetic material,"You know how DNA makes us different from any other person, well could it be so complex that we could have an attached mutation that makes us different from the human race?","Mutations are present in every individual. It is part of life, the older we get the more mutations we acquire. Mutations occur in our DNA, its a structural change (a mutation is not necessarily attached to our chromosome) that alters our DNA, these alterations can be large or small. So you can think of a mutation as a genetic change in the sequence of our DNA. For example, individuals with the disease Sickle Cell Anemia are still human (and part of the human race), but they have a mutation in their genome.
So to answer your question: mutations do not necessarily make us different from the human race-because you would still have the same human genetic makeup as everyone else. The only difference between you and other people is that your DNA is slightly altered (with a mutation)."
Classic experiments: DNA as the genetic material,What does the word transformation mean?,"Transformation in normal, everyday language, means to change something. 
In the bacterial transformation experiment, Griffith saw that the R strain of bacteria could be changed, or 'transformed' into S-strain bacteria when they were mixed with dead S-strain bacteria. 
Nowadays, 'transformation' has a very specific meaning in biology. It describes the process of bacteria taking up DNA directly from their surroundings, like in Griffith's experiment. There are also other ways DNA can get into bacteria, and they have their own names. 'Transduction' is when DNA is injected into bacteria by phage (like mentioned in Hershey and Chase's experiment above), and under certain circumstances, DNA can also be passed from one bacterium to another by 'conjugation'.

Also, another separate meaning of transformation in biology is when normal cells become 'transformed' to cancer cells."
Classic experiments: DNA as the genetic material,what evidence was there to lead hershey and chase to conclude that only DNA from the bacteriophage entered the bacterium leaving protein sheath behind,"Hershey and Chase attached atom tags to DNA and proteins from the bacteriophage. I believe it was sulfur and phosphorus. Then, they looked in the bacterium and saw only the tag they attached to the DNA, sulfur I think."
Classic experiments: DNA as the genetic material,I still do not fully understand how the rough strain bacteria kill the mice when there's heat killed smooth strain bacteria. Do they incorporate the dead bacteria's DNA into theirs and start replicating it and producing proteins based on that newly acquired sequence? how does that happen or why? Is that similar to what viruses do?,"When bacteria incorporate DNA outside of themselves into their genome, it's called transformation. This is what happened in the experiment, as the rough bacteria sucked up the still-intact DNA from the dead smooth bacteria. Yes, they did incorporate the dead bacteria's DNA into theirs and started replicating it to produce proteins from the newly acquired sequence. By the way, what viruses do is slightly different--they inject their own DNA into the bacteria which is called transduction."
Classic experiments: DNA as the genetic material,"How did Hershey found out the precise location of the radioactive source at the end? Is it like if you take your Geiger counter near the source, the count rate increases?","Probably something like that. Or you tip the supernatant to one place, and keep the pellet in your tube, and then you can detect them seperately. A geiger counter is one way, another way to detect radioactivity is using photographic film.

Edit: They did various experiments with the pellets, but in the end it looks like they dried their samples and used a geiger counter to measure how radioactive each fraction was"
Classic experiments: DNA as the genetic material,"What is the function of the enzymes protease, RNase, and DNase in relation to the mice experimentation?","RNase and DNases are not designed/used or connected specifically to the mice.


Mice are used as model organisms, but it means that the same DNase would have the same effect on Caenorhabditis Elegans (nematode model organism).

RNase is a type of enzymes that cut RNA molecules, and DNase is enzymes (endonucleases or exonucleases) that specifically cut DNA molecules. But it does not matter which organism is experimented on.

Proteases on the other hand, are used to cut proteins."
Discovery of the structure of DNA,What is a codon and how does it relate to a DNA function and structure ?,"A codon is the name for a group of three subsequent nucleotides in RNA. Since RNA is transcribed from DNA, the DNA sequence will determine the sequence of RNA, the codons, and ultimately what amino acids come together to form a protein. If a DNA sequence  (template strand) goes CTTAGG, the corresponding RNA will read GAAUCC. In this sequence there are two codons: GAA followed by UCC, which will code for amino acids."
Discovery of the structure of DNA,"well I have 2 doubts:
1) in the second para under the topic 'right hand helix'  i couldn't understand as to why DNA is a right handed helix
2) in the second para under the topic 'base pairing' how exactly is the bigger size of purines and small size of pyramidines affecting the bond length?","As far as the 2nd question is concerned , it is because the double helix should have a uniform diameter all throughout otherwise there might be problems during the supercoiling . Now if , purine is bonded to purine , both being bigger , would end up in a diameter that would be larger than that formed by the 2 pyrimidines and thus the diameter would be uneven . The fact that A will pair T and G with C was found experimentally ."
Discovery of the structure of DNA,"Am I understanding this correctly? The amount of the total bases in a cell's DNA is always the same in each organism in a species, but the amount of each type of base (A,T,G, and C) in a cell's DNA can vary between organisms in the same species.

And is the double-helix form of DNA its condensed or decondensed form? 

Thanks!","Not exactly.

The amount of each type of base in a cell's DNA is the _same in all cells in the whole organism_. Genetic code is the same, but gene expression is different.

What is different is proprotion of AG to CT for each species and defined as a different number (CHargaff's rule).


The condensed form is *chromosomes*. The double helix is always double helix, regardless of being part of Euchromatin or Heterochromatin.

So, in metaphase, you can only see the condensed form of chromosomes. But you can isolate DNA (extract) by various methods and see t by the naked eye as well.


Hope this helps :D"
Discovery of the structure of DNA,"I want to make sure I have these ideas true! 
It may have nothing to do with the article but I found it relevant.
Starting from zero:
We all have 2 copies of chromosomes; one from the mother and the second from the father.
Each chromosome is formed of DNA and proteins ( basically histamin) .
DNA is a double helix; 2 strands, each one has coding  areas ( which are 2% and maybe less) and non-coding areas . Within the gene itself there are non-coding sequences which their name is “ introns “. 
The non-coding area (outside the gene) of DNA strand has different types of sequences ; satellites and repeated sequencing . 
Is that true for now?","Seems mostly correct.

The one mistake I notice is that I think the word you were looking for was histones (not histamin).  
Chromatin is composed of DNA plus associated proteins and RNAs.  These other molecules organize, fold, protect, and control the DNA. 
A major component of chromatin are nucleosomes — a twist of DNA wrapped around an octamer of histones.

Note that the non-coding DNA between genes is *very* diverse and much of it is composed of many different families of repeated sequences including multiple types of transposons and inserted retroviral genomes."
Discovery of the structure of DNA,Why is adenine a purine base?,"I'm not sure it is the NH2 group which accepts protons most readily to make it a base. I think it could be the nitrogens in the rings, which I think also have lone pairs of electrons that could accept a H+. I think on the other hand the NH2 nitrogens the lone pair electrons are delocaslised so wouldn't make it very basic."
Discovery of the structure of DNA,How can you tell the helix is right handed?,"You can tell if if the helix is right handed or left handed based on the way it twists. Here's a link to an image that shows the difference between a right and a left. Hope this was helpful!  

https://www.google.com/imgres?imgurl=http://1.bp.blogspot.com/-a9mozeRTQ3M/VQ7VbFXcLfI/AAAAAAAAXpc/FLsA3yb63nU/s1600/right%252Bvs%252Bleftt%252Bhanded%252BDNA.jpg&imgrefurl=http://sandwalk.blogspot.com/2015/03/on-handedness-of-dna.html&h=357&w=222&tbnid=4six7X82OnMXYM:&tbnh=160&tbnw=99&usg=__3ts8S2DUkv-GCt810cHksqyLH48=&vet=10ahUKEwjiubHonbbTAhXkzIMKHXmRDe0Q9QEIJTAA..i&docid=bxjwHpzOd_V1PM&sa=X&ved=0ahUKEwjiubHonbbTAhXkzIMKHXmRDe0Q9QEIJTAA"
Discovery of the structure of DNA,What are the four different kinds of nitrogen bases?,"The four nitrogenous bases are as follows: Adenine, Thymine, Guanine, and Cytosine.
Cytosine and Thymine are pyrimidines
Adenine and Guanine are purines. 
Adenine and Thymine are a complementary pair.
Cytosine and Guanine are a complementary pair.
Hope that helps!"
Discovery of the structure of DNA,What is the order of the nitrogenous bases of the DNA if I have to put up a 3d model?,"There isn't a single order — all combinations along a strand are possible.  The only thing that is fixed in DNA is that A pairs with T, and G pairs with C.

The sequence of bases is a very complex code that we are still working to understand.  You can think of DNA as being the instructions for building, operating, and maintaining a cell.  The order of the letters is used to encode how, when, and where proteins and RNAs are made.  This affects every process within that cell and often in neighboring cells as well.

So, for a structural model of DNA the order doesn't actually matter, but if you could pick the sequence associated with something well known like the restriction enzyme _EcoRI_ ...

Does that help?"
Discovery of the structure of DNA,What is the difference between DNA and RNA,"I will answer you the way I have answered this question before with other users. I hope it is adequate.

There are several differences. To start, DNA stands for deoxyribonucleic acid, while RNA stands for ribonucleic acid. These names describe the sugar that makes up their backbone--DNA = deoxyribose and RNA = ribose.

Second, while each has four nucleiotide bases, there is one difference. You probably know that DNA has guanine, cytosine, adenine, and thymine, and that guanine links to cytosine and adenine links to thymine. But RNA doesn't have thymine. Instead, it has uracil, a nucleiotide base with a slightly different chemical makeup. Thymine had the chemical formula C5H6N2O2 and uracil is C4H4N2O2. Uracil links to adenine in RNA just like thymine does in DNA

Finally, DNA is double-stranded and forms a double helix structure. RNA is single-stranded and is generally straight. DNA is a complete set of instructions needed for life (unless you're a virus, but that's a whole different story/debate) and RNA is used to copy DNA and to synthesize proteins. I know this is a lot to take in, but there are several videos and articles on Khan Academy to help. Here are a few.

https://www.khanacademy.org/science/high-school-biology/hs-molecular-genetics/hs-rna-and-protein-synthesis/v/molecular-structure-of-rna

https://www.khanacademy.org/science/high-school-biology/hs-molecular-genetics/hs-rna-and-protein-synthesis/v/rna-transcription-and-translation

https://www.khanacademy.org/science/high-school-biology/hs-molecular-genetics/hs-rna-and-protein-synthesis/a/hs-rna-and-protein-synthesis-review

Anyway, this is probably a lot, but I hope it helps!"
Molecular mechanism of DNA replication,Is topoisomerase same as DNA gyrase ?,DNA Gyrase is a topoisomerase. There are several kinds
Molecular mechanism of DNA replication,How are the histone proteins taken care of during eukaryotic DNA replication?,The DNA is first unwound at origins of replication and the displaced histone proteins move onto to other parts of the DNA that haven't been unwound so that those parts can maintain their chromatin structure.
Molecular mechanism of DNA replication,"In the last section "DNA replication in Eukaryotes" it says that in eukaryote cells a little DNA at the ends of the chromosomes gets lost. If this is the case, will we eventually loose enough DNA to stop functioning properly?

You might say that this is indeed why we die eventually. Each time our cells divide and our DNA gets copied some of it gets lost placing a limit on how many times our cells could divide and still function properly. However, consider that DNA is also copied before meiosis. This means that the DNA that was lost when the ancestors of my cells (in my parents) divided was never passed on to me. And the DNA that got lost when my cells divided to form my germ cells will never get passed on to my sperm cells. Will humanity eventually loose its entire gene pool?",At the ends of DNA strands there is a section non-coding nucleotides that we call a telomere.  The telomere is what gets shorter every time a cell divides and when the telomere is gone is when the cell spontaneously dies.  There is no loss of coding DNA in this process so there is no loss of genetic information between generations.
Molecular mechanism of DNA replication,"The part of the article that deals with the Okazaki-fragments states that:

"DNA polymerase I and DNA ligase are also needed (more infrequently) for the leading strand. DNA polymerase I removes the primer at the very beginning of the strand, and DNA polymerase seals the remaining gap."

Shouldn't the gap between the Primerreplacement and the new Nucleotide chain be sealed by DNA-Ligase instead?","Yep, that was a typo! I've fixed it now and it should be corrected on the site shortly. Thanks for noticing!"
Molecular mechanism of DNA replication,""Many DNA have proofreading activity" mentions : "In most cases, the correct nucleotide is indeed added, because the DNA polymerization reaction won't usually occur unless the incoming nucleotide base-pairs correctly with the template." If the reaction cannot occur unless there is correct base matching, how then can the DNA polymerase still make an error?","The key word is the "usually." The reaction won't occur with a mis-paired base in most cases. However, about 1 in 10^5 base pairs will involve an incorrect pairing. This may not same like a high rate of errors, but it is high enough to cause a lot of mutations in a cell. The role of the proofreading is to fix these occasional but still problematic errors."
Molecular mechanism of DNA replication,Why are the DNA polymerases numbered here? (I/II/III) I though that Eu-k were named by alpha beta delta etc,"Prokaryotes have DNA polymerases I, II, III, eukaryotes have alpha, delta, epsilon and such."
Molecular mechanism of DNA replication,"In the paragraph 'DNA polymerases' it says that polymerase II has a DNA repair function, but in 'Many DNA polymerases have proofreading activity', it is stated that DNA pol. I and II have proofreading activity. Does DNA pol. II aid in a different repair mechanism than proofreading?","Great question! Yes, DNA polymerase II is involved in repair of damage that occurs outside the context of DNA replication, such as cross-links between strands caused by certain chemical agents. There is a little more detail in the Wikipedia article if you are curious: https://en.wikipedia.org/wiki/DNA_polymerase_II."
Molecular mechanism of DNA replication,"'A DNA molecule “unzips” as the hydrogen bonds between bases are broken, separating the two strands.' What makes this happen?","Helicase enzyme. It binds at replication initiation site and moves along DNA, in front of polymerase III, opening replication fork."
Molecular mechanism of DNA replication,"Genome refers to the haploid content of DNA in a cell, so how can it consist of  3 billion base PAIRS? Or is it the diploid content in any cell?","Most DNA exists as a double-stranded DNA in a double helix — the strands are held together by base pairs and we usually think of this as a single molecule (even though there are no covalent bonds between the two strands).

So, each haploid chromosome has at its core a (mostly) double-stranded DNA "molecule" and a human haploid genome contains ~3.2 billion base pairs.

A diploid cell has two of each haploid chromosome (each of which contains a double-stranded DNA "molecule"), so a diploid human genome contains ~6.4 billion base pairs.

Does that help?"
Molecular mechanism of DNA replication,"Topoisomerase works at the region ahead of the replication fork to prevent supercoiling.

What does it mean? I can not understand supercoiling.","Take a piece of rope and start twisting it — at some point it will begin to shorten and form a twist perpendicular to the rope between your hands.  

This is supercoiling!

See for example, this video:
https://www.youtube.com/watch?reload=9&v=BjcJu-o3YwY

There is also a relevant wikipedia article:
https://en.wikipedia.org/wiki/DNA_supercoil"
DNA proofreading and repair,why would cells ever apply non-homologous end joining if there is a cleaner and safer alternative? Do they only do that when there's no undamaged template available?,"In the absense of homologous chromosome (when DNA hasn't undegone replication yet) 
non homologous end joining is done."
DNA proofreading and repair,"Is there potential, during any of the above proofreading methods to "correct" the template DNA rather than the newly-formed strand?","By potential, do you mean that is mistakenly correcting the template strand possible? If so, then yes it is. The mechanism to determine which is the newly-formed and the template strand isn't perfect and relies on methylation and other epigenetic markers. These can fail. If the damage includes these markers, or the damage/defective piece is extensive so as to avoid these markers from being introduced, or if the damage doesn't allow the DNA repair machinery to sense these markers, it is very much possible the correction is faulty. Some repair machineries are anyway strand non-specific, and some are even sequence non-specific (see Non Homologous End Joining, which is the last resort at DNA stability)."
DNA proofreading and repair,Why is thymine in DNA and uracil in RNA?,Thymine is the nucleotide that DNA uses. RNA is not the same thing as DNA so it seems very natural that the two of them would have some differences. Uracil is one of them.
DNA proofreading and repair,"what happen if DNA have uracil instead of uracil ? how can DNA repair it ?
and what are the reasons that DNA contain thymine not uracil","In your question – "what happen if DNA have uracil instead of uracil ?"  — I am assuming your second "uracil" was supposed to be "thymine" ...

I'm not sure what you really want to know — as it says in the article, uracil in DNA is usually recognized as a mistake and removed by the `Base Excision Repair` pathway ...


There are a number of proposed reasons why thymine is used in DNA.

1) Cytosine residues in DNA undergo a spontaneous change that converts them into uracil.  There are enzymes that specifically recognize and remove uracil (but not thymine) from DNA and this helps suppress what would otherwise be a major contributor to the rate mutations.  

2) Thymine is chemically more stable (though slightly more expensive to make), so this again probably helps reduce the mutation rate.

An interesting and detailed discussion of these factors and more can be found here:
http://www.scienceinschool.org/2011/issue18/uracil

If you have further questions please leave a comment."
DNA proofreading and repair,"What occurs in cancerous cells when going through mismatch repair? Is the issue ignored? Or is it because the cancerous cell had gone through mismatch repair, then became cancerous?","In cancer cells, the mismatch repair has not happened. This leads to mutations. This is a classic example: https://en.wikipedia.org/wiki/Xeroderma_pigmentosum Without the nucleotide excision repair system, the individual develops melanoma and/or carcinoma at a very young age. Also recall that skin cancer metastasizes to the lungs, so this is a very bad prognosis indeed."
DNA proofreading and repair,How the proteins involved in DNA repair detect the fault?,"It depends on what is wrong. For example, some damage distorts the shape of the DNA helix, and there are proteins scanning the genome for this. Sometimes damage is detected when an RNA polymerase stalls. In mismatch repair, there are proteins involved that detect the mismatch, and proteins that detect which is the old and which is the newly synthesised DNA strand."
DNA proofreading and repair,Why is thymine in DNA and uracil in RNA?,"Uracil is the cheapest to produce energetically, and is therefore favored at the RNA level where fidelity is not as important and large quantities are produced."
Telomeres and telomerase,"A question I've had for a while is how are telomeres and the sections of DNA that they protect not worn our through the duration of human existence or life in general? Although the number of divisions from zygote to producing gametes may not be "many" in terms of cellular divisions, it seems to me that the damage should add up over time. Does anyone have an answer?","It does add up over time, but not as quickly as you are thinking. It adds up over the whole human lifetime and is actually believed to be a key factor in aging and death."
Telomeres and telomerase,"Since most somatic cells do not have the telomerase, I wonder how they will deal with the overhang?? Will the overhang just stay there? Or bein removed somehow??","This most probably is not true, as telomeres are actually a prevention mechanism from things like cancer. When our cells divide the original dna is mutated while copied. Most of these mutations are gradually damaging the function of the cell. After certain amount of division the dna is so damaged that the cell doesn't function normally and a cancer cell is born (Imagine the game "chinese whispers" played with dna). Most of these damaged cells die out naturally, but sometimes it happens that the telomere mechanism is broken and the cancer cells starts replicating even when it normally shouldn't anymore and forms a tumor (this is why cancer lines we extracted from dead people and use in labs are immortal - because the telomere mechanism is damaged while human cells aren't). So no "doping" telomerase to make human immortal most possibly would not work (which is kind of sad)."
Telomeres and telomerase,if telomerase can initiate a protective loop inhibiting the end of DNA damage then why is it inactive in most cells?,"Because most of our cells undergo controlled cell cycles and cell death - apopotosis.


Do you want tumours to grow all over your body and eventually metastaze?

Uncontrollable dividing is not evolutionary accepted trait for humans. We are not hydras or jellyfishes."
Eukaryotic pre-mRNA processing,"Why in the last example, using an actual RNA molecule, is methionine coded by the codon AUC? Methionine is referenced as being coded by the codon AUG in the table provided.",That was a mistake! Thank you for noticing and pointing it out. It should be fixed now :)
Eukaryotic pre-mRNA processing,Why are the introns referred to as "junk" (RNA splicing section)? Don't they play a role in gene expression regulation? Thank you.,"I think they are only considered "junk" in terms of what they contribute to the resultant protein. They do likely play a role in regulation, but because they are spliced out before translation, they will not effect the protein that results from translating the mature mRNA sequence."
Eukaryotic pre-mRNA processing,Is it possible that DNA introns/splicing exist so that bacteria can't copy eukaryotes' DNA and express the same proteins? As they are known to steal DNA that floats around in general..,"I am not aware of that but sounds interesting! 
That is interesting point of view because Prokaryotes do not have introns (and can't because of couples translation to transcription)."
Eukaryotic pre-mRNA processing,why does the introns exist at the first place just waiting to be splice ?,"Lim Pin Seng, 

Introns allow for alternative splicing; generating multiple proteins from a single gene. It adds a layer of complexity to an organism, without having to drastically extend the genome length. In return, it may also save energy as the cell does not have to replicate as long of a genome - a reasonable explanation as to why introns may be favored. 

Further, introns may possess regulatory processes or code for functional RNA products. In addition, introns may also be mobile elements, contributing to the overall variation of the genetic pool.

Hope this helps!"
Eukaryotic pre-mRNA processing,"In the little drop-section explaining more about spliceosomes, it states "Once the intron has been cut out, the spliceosome will "glue" (ligate) the flanking exons together." How would this work with alternative splicing? Additionally for alternative splicing, can only one exon be removed? More alternatives could be created through removing two exons or switching the exons around. Ex: 145 and 14235","Good question!

Control of alternative splicing is very complex — it often involves binding of proteins or small RNAs to the pre-mRNA in ways that favor or inhibit use of specific splice sites.

The wikipedia article on this seems like a good place to start learning more:
https://en.wikipedia.org/wiki/Alternative_splicing


While skipping an exon is very common, there are probably examples of almost any pattern you can think of!


An extreme example of how complex alternative splicing can get is the _Dscam_ gene of _Drosophila_ (a fly), which apparently has ~38,000 different splicing variants and roles in both the immune system and nervous system development†.


Does that help?


†Reference: https://www.cell.com/cell/fulltext/S0092-8674(00)80878-8"
Eukaryotic pre-mRNA processing,Why prokaryotes do not require these post trancriptional mechanisms as needed in case of Eukaryotes? Does it mean that Eukaryotes' trancripts are free of introns?,"Prokaryotes do have some post-transcriptional modifications, but introns are much less common and as far as I know are always self-splicing — i.e. don't require a spliceosome.

Mature mRNAs in eukaryotes generally lack introns, but note that alternative splicing means some sequences can act as either introns or exons,"
Eukaryotic pre-mRNA processing,"With so many mRNA molecules being manufactured all the time, shouldn't all that splicing create a build up of spliced out introns  in the nucleus?
Evolution wouldn't waste resources..What happens to them?","Good question!
As is often the case in biology the answer is "it depends".

Many introns are broken down to individual ribonucleotides by enzymes (ribonucleases) that are then reused.

However, some introns have second lives and can act as signaling or regulatory molecules.

This is still an area of active research and it is quite likely that more functions for introns will be uncovered in the future.

If you wish to know more, you could start with this section of the wikipedia article on introns:
https://en.wikipedia.org/wiki/Intron#Biological_functions_and_evolution

Does that help?"
502 Bad Gateway,where does tRNA form ( where does it come from) ?,"It is coded by DNA, then it's transcribed by special polymerase, spliced and there we have it."
502 Bad Gateway,"Hi, where does the Amino Acid comes from? The one the tRNA transports. Does it come from the Lysosome?","Amino Acids either come from exogenous origins (from the catabolism of ingested food), or anabolic from other precursors. 

These free amino acids are found in the *cytoplasm* and are brought to the ribosome."
502 Bad Gateway,What happens to tRNA molecules when they leave a ribosome?,"They attach to amino acids (that have been obtained from our diet) in the cytosol and return to the ribosome if the same codons appear in the mRNA sequence, for them to be translated."
502 Bad Gateway,Does the Wobble Position apply to START and STOP codons as well?,"From my understanding, it won't apply to the start codon, AUG, because there is only one possible codon available. If you look at the codons for an amino acid such as Leucine; CUU,CUC,CUA,CUG, there are multiple options available and the third letter varies, but all four codons code for Leucine. 

I think the wobble position will apply to the stop codons; UAA, UAG and UGA, because there is variation in the third letter.

Note - I got the codons from the genetic code table, on the article 'The genetic code'.

I'm not 100% sure that I am correct though"
502 Bad Gateway,"ATP is used to bind the amino acid to a tRNA.
How is the actual peptide bond formed during translation? Wouldn't that also need energy?","Another good question.

The bond in the aminoacyl-tRNA is higher energy than the peptide bond, so there is no new energy input required to form the peptide bond — the energy came from hydrolyzing ATP to AMP plus PPᵢ (pyrophosphate).  However, a GTP is hydrolyzed to ensure that the correct aminoacyl-tRNA binds to mRNA-ribosome complex and another is used to move the ribosome along the mRNA by one codon.

This discussion does a reasonable job of explaining the energetics of this process:
https://biology.stackexchange.com/questions/40964/how-much-nucleoside-triphosphate-is-required-to-form-one-peptide-bond-during-pro"
502 Bad Gateway,What is the difference between DNA replication and the process of DNA translation/transcription,"Replication is making more DNA, transcription is DNA to mRNA, and translation is mRNA to proteins!"
502 Bad Gateway,"So, a tRNA is is L shaped in 3D and clover leaf shaped in 2D?
That's a bit confusing..","You might find this exercise helpful to get a feel for how that works:
https://www.youtube.com/watch?v=lw41sO1myKw&feature=youtu.be

Basically two of the loops (D and T) are wrapped around each other, which converts the 2D clover leaf into an L-shape."
502 Bad Gateway,You have mentioned that the two subunits (both) come together for initiation. Isn't that only true for prokaryotic cells?,"You are correct, this article deals with prokaryotic translation. In eukaryotic translation, there are also ribosomal subunits which must come together around an mRNA, but the process is a whole lot more complex with lots of protein-RNA interactions and protein-protein interactions. The wiki article on eukaryotic translation has a nice overview diagram. I think people are still figuring out exactly how the process works in eukaryotes.
https://en.wikipedia.org/wiki/Eukaryotic_translation"
502 Bad Gateway,What does it mean when tRNA is charged?,when tRNA has bound amino acid on its end and carrying it to the A site of the ribosome.
502 Bad Gateway,What is meant by the third position in reference to the 'wobble binding' of tRNA?,"The third position refers to the third letter of the codon, reading from left to right (5' - 3' direction). If the codon was UUC, the third position would be C. There are some tRNA molecules that can bind with more than one codon, as in the example above. This is called wobble pairing, because the first position of the tRNA anticodon does not bind as tightly to the third postion of the codon, meaning the pairing between codon and anticodon is more flexible."
"One gene, one enzyme",How did Beadle and Tatum know that only a single gene had been changed when they exposed the bread mold to radiation? Did they just assume this would be the case because mutations were going to be rare anyway and having 2 at the same time would be even rarer? Or was there some way to check?,"You are correct. The best way to prove this would be to repeat the experiment lots of times. If it's always just one nutrient that's required to rescue the spores, then it's probably just one part of one pathway being altered.
If two or more genes were being mutated then you would expect more than one pathway to be disrupted and therefore more than one nutrient required to rescue the spores. That is, unless the multiple genes all just happened to be on the same pathway, but that would be rare given the huge number of biochemical pathways in an organism.
Nowadays we could confirm the number of mutations and where they are by simply sequencing the genomes!"
"One gene, one enzyme","What are some exceptions to the one gene, one protein hypothesis?","There are many exceptions. 

1) Alternative splicing: one gene makes multiple polypeptides
2) Transcription of ribozymes (not proteins)
3) A protein with quaternary structure such as haemoglobin requires multiple polypeptides, synthesized from different sequences.

Beadle and Tatum's hypothesis is very simplistic model and cannot account for the many ways in which DNA is used."
"One gene, one enzyme","So,one codon for one amino acid,and one gene for one polypeptide, and polypeptide(s) form proteins ! But what is alleles? Is it a codon? Gene?","Great question! An allele is a particular form or "version" of a gene. Two alleles of a gene might have different DNA sequences that specify slightly different polypeptides. You can learn more about alleles in this video: https://www.khanacademy.org/science/biology/classical-genetics/molecular-basis-of-genetics-tutorial/v/alleles-and-genes.

Hope that helps!"
"One gene, one enzyme",But what about splicing?,Alternative splicing can make more different proteins from one gene
"One gene, one enzyme",how can the deficiency of a single protein or vit can stop the growth of the organism??one gene one enzyme theory,"This isn't something that has a single answer — how the deficiency of an essential protein or vitamin might stop the growth of an organism will depend on the what is deficient, the organism in question, and sometimes even the environment!

An somewhat silly analogy might be to ask why removing the spokes from the front wheel of a bicycle is sufficient to make it unrideable vs. why removing the handlebars makes it unrideable — the answers are totally different.  Note also that the second question doesn't even make sense for a unicycle 😀"
The genetic code,"Are Glutamate (Glu) and Glutamine (Gln) interchangeable? or there is something wrong with the example on reading the codon table, because CAG codes for Gln, not Glu.","They are 2 different amino acids, so no they cannot be use interchangeably."
The genetic code,When does the tRNA know when to use AUG as a start codon and when to code Methionine? Are there other influencers,"Excellent question!

Translation is quite bit more complicated that this introductory material can cover.

The sequence of the mRNA around a potential start codon influences whether or not it will be used§.  These sequences are bound by proteins that help guide the ribosome to assemble at the correct place to start translation.
(In fact, codons other than AUG are sometimes used as start codons!) 

This is covered in a bit more detail in another article:
https://www.khanacademy.org/science/biology/gene-expression-central-dogma/translation-polypeptides/a/the-stages-of-translation

I also encourage you to look at some of the references for that section, which will help give you more detail on this high complex process that is still being actively studied.


§Note: The mechanisms are very different in prokaryotic and eukaryotic organisms — they can also vary between different species and even for different genes!"
The genetic code,would it be possible to use the "coding language" of RNA to synthesize chemicals?,"Yes, proteins are made of amino acids which are coded within the DNA sequence, so yes, recombinant DNA may be used.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2845543/


Also, there are already efforts to use DNA as a digital store of information:
https://www.youtube.com/watch?v=NsfuBSsF1Fk
https://www.ebi.ac.uk/research/goldman/dna-storage
https://www.nature.com/news/how-dna-could-store-all-the-world-s-data-1.20496"
The genetic code,"Why is `AUG` a start codon and `UAA` , `UGA` and `UAG` stop codons?",No one knows exactly why evolution chose which specific codons represent each amino acid.  This likely happened in an arbitrary manner very early in evolution and has been maintained every since.
The genetic code,I have heard that the 3' end of mrna is rich in stop codons so that in case of a mutation the peptide gets released but I am unable to find an article about that. Can someone confirm if this is true or not?,"You are correct.

Usually nucleotides present in mRNA channel downstream the A site help determining the future.
 The expected hierarchy in the intrinsic fidelity of the
stop codons (UAA>UAG>>UGA) was observed, with
highly influential effects on termination readthrough
mediated by nucleotides at position +4 and position
+8. 


https://watermark.silverchair.com/gkx1315.pdf?token=AQECAHi208BE49Ooan9kkhW_Ercy7Dm3ZL_9Cf3qfKAc485ysgAAAlcwggJTBgkqhkiG9w0BBwagggJEMIICQAIBADCCAjkGCSqGSIb3DQEHATAeBglghkgBZQMEAS4wEQQMiuKY1yQvGdfscjqKAgEQgIICCmJx0U3b-ecY2oxn1QYcqc6a6QXYNlX9FCUngn9zbbPC6TWDitK20Cl65tVkDb6ARGxakyB0TEEbjl2c5gg6rg2qBTOI7x9Vy8585GIls0cxO0YkUJjM5nl4tIHHoOTo9GSTyGAW827IJoH0xMHIBZC6tWuwCiR6jqOaN1HrKwsQVlraRvdQyJb9eCxJcVkE-No67IraffHateNr-8Xin1lgr4vGQAfQXU9PjGDIReo41KpdTVC4ROs0BWMsX5SiIrOq0CT2I_d8aPe3BoxnnN5Vwdb-tIzNAmBaBiIlyQa2NBwBvWioTTqoTIlkqhVX4USGtnaevTT72XcMrlPPZm-hY4KtVOzqRFEiJZvumj8GsYH5VL8XA-vT_ZHLfZxscDuS2AaEIts5h3YNsYXoB_VtpESmnQzfU8QXfocNOamKdN2HvESBttG-e1DGLH7er75hfzVjy99742-LR77NeJApSW8uphwYIJGkdiRMkKm33yLfYQi2FH7UjzzmPuBukRAYG9gDCtTozVMKGh25SeJhmtQ2ASplMszMGS0eHfdOEFXsP3xM7Y_qNU8Bp3Er0_1f-3QzZrvK4R0HBzKUFaBhBxzm36nDFx7kMyvupiurNRcLbGuj65jWL5ezK4Rel-eplBH3Zv087GDxgvSEss9ZFntFfyS1O0Ra3yW8F6OFRZNJY86-N0puzw

There are also cases where there are mutations non-stop codon so transcription cannot stop.

https://www.cell.com/cell/pdf/S0092-8674(16)30788-7.pdf"
The genetic code,"In the section, Reading Frame, frameshift  mutations are mentioned.

Point mutations will shift the frame of reference.
The insertion or deletion of three(or it's multiple )bases would insert or delete one or more codons or amino acids, without shifting the reading frame. But addition or subtraction of amino acids from a polypeptide would transform it..... How is this dealt with?","How small "in frame" indels (insertions and deletions) are dealt with depends on many factors including where in the gene the indel happens — so the short answer is "it depends".

For example, if you disrupt the catalytic site of an enzyme the effect will probably be the same as if the protein was never produced at all — this is likely to lead to a complete loss (assuming the mutation is homozygous) of that enzyme activity — the effect on the cell could be anything from fatal to unnoticeable (depending on how critical that enzyme activity is in that cell).

On the other hand, some proteins have loops of amino acid sequences on their surfaces that do not appear to be critically important and making those loops a little longer or shorter might have little or no effect on the protein function.

(Note that we only use "point mutation" to refer to mutations that change a base — not for deletions of a single base pair.)"
The genetic code,"So the genetic code is the mRNA sequence of bases and it starts from the 5' to the 3' and it is the coding strand. Now if we want to find the tRNA sequence, which is the template or the non-coding, for ACU, for example, we start at 3' to 5' and we write it as TGA? Is that the correct way or am I missing something?","Just one correction. You do not write it TGA but UGA.

There is no Thymine in RNA, but Uracil. Everything else is right. :D

화이팅!
같이 공부합시다."
The genetic code,Are proteins made at the same time as new DNA? Does DNA unwind when it makes proteins?,"The DNA that isn't being utilized is very tightly packaged, and contrarily, the DNA that is being utilized is unwound, so yes, in a sense, but your choice of words is slightly off... DNA unwinds to be transcribed into RNA, which eventually makes its way to a ribosome, which then gets translated into protein. So you are somewhat correct, just your word choice is off. Don't forget the central dogma: DNA->RNA->protein, that middle molecule is essential."
Stages of translation,"The part about mRNA shifting one codon, isn't it the ribosome that shifts one codon?",No. The ribosome is the workbench and the mRNA is being moved through the ribosome shifting downwards every codon.
Stages of translation,"What about Initiation factors? IF1, IF2 & IF3. Please could you explain their roles? Thanks","IF1, Binds to the 30S subunit to the A site, prevents tRNA binding
      IF2, Binds initiator tRNA (f-Met) and controls its entry to the ribosome at the P site
      IF3, Required for the 30S to bind mRNA"
Stages of translation,what about untranslated regions? such as the 5' and 3' UTR,"They don't get translated! 


The 5' UTR is everything 5' of the start codon.  

The interesting question is how does the ribosome know which start codon to start with?

The short answer to that is that the sequence of the mRNA around a potential start codon influences whether or not it will be used§. These sequences are bound by proteins that help guide the ribosome to assemble at the correct place to start translation.
(In fact, codons other than AUG are sometimes used as start codons!) 

This is covered in a bit more detail in another article:
https://www.khanacademy.org/science/biology/gene-expression-central-dogma/translation-polypeptides/a/the-stages-of-translation

I also encourage you to look at some of the references for that section, which will help give you more detail on this high complex process that is still being actively studied.


The 3' UTR is simpler to identify — it is typically† everything after the first in frame stop codon and before the polyadenylation signal (where the polyA tail gets added.


Does that help?

————————————————————————————————————

§Note: The mechanisms are very different in prokaryotic and eukaryotic organisms — they can also vary between different species and even for different genes!


†Note: As is often true in biology there are numerous caveats and exceptions.  A common example is found in eukaryotic genes — these genes often have introns, some of which are only spliced in some circumstances, so the in frame stop may be in different places for different transcripts from the same gene.  This is knowns as alternative splicing."
Stages of translation,what is the total atp or gtp utilised?,"It costs 4n high-energy bonds to make a peptide chain. n= the number of amino acids in the chain.

For example: 

How many high-energy phosphate bonds are required to make a 50 amino acid polypeptide chain?

Solution: 200.
-2 phosphate bonds hydrolyzed per amino acid to make the amino-acyl tRNAs (or 100 for the 50 AAs)
-2 phosphate bonds required for each elongation step (49 steps in a chain of 50, so 98 for the chain)
-1 GTP for initiation to position the first tRNA and mRNA on the ribosome
-1 GTP for termination

For a total of 200."
Stages of translation,"During translation, is the tRNA used up or can it be recycled?","Great question!
The tRNA is released into the cell and can again be joined with an amino acid.  (Details on the joining are in the previous section.)"
Stages of translation,"In eukaryotic mRNA, is the start codon always at the start of the first exon?","Yes, it is. 

It cannot be considered start codon if it is not AUG at the beginning of first exon.

What might confuse is that it does not have to be on the very strict beginning, there might be nucleotides before, but that is 5' untranslated region.

The first AUG is usually considered as a start codon, but probably GGC could take place in front of that AUG and be not translated by the ribosome."
Overview of transcription,The hairpin somewhat appears to look like a tRNA molecule. Am I wrong in saying that tRNA is formed from these hairpin structures?,"No, you're not wrong. A tRNA contains hairpins as well, though the hairpins play different roles in the two cases. In transcription termination, the hairpin causes the RNA polymerase to stall and the transcript to separate from the DNA. In a tRNA, multiple hairpins form and give the tRNA molecule the 3D shape it needs to perform its job of delivering amino acids."
Overview of transcription,"if introns are not important, why are introns are formed?","Good question!

Introns have multiple roles in biology including the regulation of gene expression.

Other introns have functions after they are spliced out from the transcript and can act as signaling or regulatory molecules.

Some relatively rare types of introns appear to be parasitic DNA molecules — they insert copies of themselves into genes and then splice themselves out from the RNA presumably to keep the host cell alive.  It is possible that the more typical introns originated from such parasitic DNA elements.

This is still an area of active research and it is quite likely that more functions for introns will be uncovered in the future.

If you wish to know more, you could start with this section of the wikipedia article on introns:
https://en.wikipedia.org/wiki/Intron#Biological_functions_and_evolution"
Overview of transcription,do the presence of introns indicate something related to evolution?,"Not really. Introns enable one gene to produce multiple polypeptide sequences, thereby creating a more efficient genome. This will make more sense if you look at the examples in the pre-mRNA processing article. I think you're thinking of pseudogenes, which are non-coding regions remaining in an organism's DNA from ancestral roots. You're correct in your conclusion that introns are non-coding, but just because a sequence is an intron in one pre-mRNA sequence doesn't mean that it can't be included in the exon sequence in another."
Overview of transcription,"Hi, this isn't mentioned in this article, but I would like to ask,
What is the difference between a gene and a cistron? Why do we need the term , cistron, in the first place?
And what do the terms monocistronic and polycistronic mean?","Really there isn't much difference — as far as I know the existence of the two terms is an accident of history — my advice would be to use gene.

Many prokaryotic (and a few eukaryotic) genes are transcribed together into a single mRNA and then translated separately from the single mRNA.  These situations are described as "polycistronic".  The more common condition of one transcript encoding a single protein is thus "monocistronic".

Confusingly, the entire multigene (polycistronic) unit will often be referred to as an operon.  Operons are typically made up of genes encoding proteins that work together in an organism and this structure ensures that they are all made at the same time and in similar quantities.

You can read more about this here:
https://www.khanacademy.org/science/biology/gene-regulation/gene-regulation-in-bacteria/v/operons-and-gene-regulation-in-bacteria

And for a bit more detail:
https://en.wikipedia.org/wiki/Operon"
Overview of transcription,I thought helicase was the enzyme that separates the DNA helix for the SSB to keep the DNA strands separated?,"Yes, helicase was the enzyme   that makes the DNA to unwinds its strands  by breaking the Hydrogen bonds between the nucleotides."
Overview of transcription,What I don't understand is: If the Promoter is located at the 5' end of a gene how does RNA polymerase start there if it reads from 3' to 5' and syntetase RNA from 5' to 3?,The RNA is actually synthesized using the antisense (complementary) strand as the template.
Overview of transcription,Are there other ways that the mRNA strand could detach from the DNA strand instead of the hairpin turn? And what would happen if the mRNA nucleotide accidentally gets changed instead of the normal one ie. a mutation?,"This is briefly covered in the next article — short answer: yes, but transcription termination is still being actively studied and is not completely understood.

Additional reading:
https://en.wikipedia.org/wiki/Eukaryotic_transcription#Termination
https://www.nature.com/scitable/topicpage/dna-transcription-426


I'm not completely sure I understand your second question — are you asking what would happen if the "wrong" base was incorporated into an mRNA?

If so, probably not much since each gene typically will make multiple transcripts and most mRNAs have a very short lifetime.  (Note that this is almost certainly something that happens all the time since all biological processes make errors.)  

While I've never see any evidence that any of this ever actually happens, it seems possible that in rare cases the change might make an mRNA encode a toxic protein that could kill a cell or worse yet trigger cancer formation.  I suppose if you were spectacularly unlucky it might even promote prion formation (a contagious toxic protein structure)."
Overview of transcription,"Won't the RNA have the wrong sequence if the introns are spliced, or is it predetermined to omit the codons in the introns in order to have the "perfect" code in the mature RNA?","Introns are actually noncoding DNA segments (in other words, they do not code for proteins), so splicing them out actually helps produce a functional protein rather than potentially disrupt protein function. However, this doesn't mean introns are useless either; in fact, they are actually very important for regulating gene expression. 

We've learned a lot about introns since their discovery but many questions about them and their functions still remain unresolved. You can learn more about them in the link below. Hope that helps!

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3325483/"
Overview of transcription,"Does the transcribed region always start with bases TAC, so that the RNA will start with bases AUG, which codes for methionine?","No, transcription starts upstream of the AUG, so the mRNA contains a 5' untranslated region. Then ribosomes translate starting from the AUG in the mRNA. The details of how they find the AUG is different in eukaryotes and prokaryotes."
Overview of transcription,does the hairpin structure come in to play in transcription?,"A hairpin loop is an unpaired loop of messenger RNA (mRNA) that is created when an mRNA strand folds and forms base pairs with another section of the same strand. The resulting structure looks like a loop or a U-shape.

Hairpins are a common type of secondary structure in RNA molecules. In RNA, the secondary structure is the basic shape that the sequence of A, C, U, and G nucleotides form after they are linked in series, such a folding or curling of the nucleic acid strand. mRNA hairpins can be formed when two complementary sequences in a single mRNA molecule meet and bind together, after a folding or wrinkling of the molecule. Hairpin loops can also form in DNA molecules, but are most commonly observed in mRNA.

There are many instances of the hairpin loop phenomenon among nucleic acid strands. One example of a hairpin loop is the termination sequence for transcription in some prokaryotes. Once a polymerase meets this loop, it falls of and transcription ends. Another more general example is tRNA, a central player in protein synthesis, which is partially formed by hairpin loops. The tRNA molecule actually contains three hairpin loops that form the shape of a three-leafed clover. One of these hairpin loops contains a sequence called the anticodon, which recognizes and decodes the mRNA molecule three nucleotides (one codon) at a time during translation. This clover-leaf structure supports the eventual connection between every codon, anti-codon and amino acid.

http://www.nature.com/scitable/definition/hairpin-loop-mrna-314"
Nucleic acids,How do mRNA and tRNA communicate with eachother during the formation of the proteins?,"mRNA is like a recipe from a cookbook; a list of ingredients to make a protein. mRNA is a chain of nucleotides (A, U, C, and G, not T since this is RNA). A group of three nucleotides is called a codon. A codon matches with three nucleotides, called an anticodon, on a single tRNA molecule while in a ribosome. The tRNA carries an amino acid, our ingredient to make the protein.
So mRNA is the recipe, tRNA matches to the recipe bringing an ingredient, and the line of ingredients become a protein."
Nucleic acids,"If A-T bonds have 2 hydrogen bonds and G-C bonds have 3... Would it be true that longer periods of A-T bonds in DNA (so like: AATAATTATTTTAATTAAAA) are less stable parts of the DNA helix than parts that have more (or only) G-C bonds in them? And if this is true, are these parts (AT only parts) more prone to mutations?","The first part is true, T-A bonds are less stable and more likely to come apart. The A-T bond strands also signal where DNA needs to separate for commonly transcribed genes, such as the TATA Box commonly found just before the beginning of gene sequences.

I'm not sure if they are more prone to mutations though."
Nucleic acids,"DNA is common to all organisms, all organisms use the same 4 nitrogenous bases, A T, C G

is that right?","Entirely true. Also, AT/GC are found in DNA while RNA is made from AU/GC. Just keep in mind that, even though all life forms have DNA, not everything that has DNA is alive: viruses can have DNA but are not living."
Nucleic acids,"Why do some nitrogenous bases have two fused carbon rings while other have one? Would it be possible for there to be nitrogenous bases with more than two fused carbon rings? Could there ever be an instance where there are more than just five kinds of nitrogenous bases (Adenine, Thymine, Guanine, Cytocine and Uracil)? If it could be possible how would DNA and RNA have to rearrange themselves? Would it be possible for DNA and RNA to use other sugars aside from Deoxyribose and Ribose? If so, like what? If not, why?","https://www.khanacademy.org/science/organic-chemistry/aromatic-compounds/aromatic-stability/v/aromatic-heterocycles-i

https://en.wikipedia.org/wiki/Heterocyclic_compound

https://en.wikipedia.org/wiki/Abiogenesis

https://en.wikipedia.org/wiki/Nucleic_acid_analogues

Hope this helps!"
Nucleic acids,Are the functions of nucleic acids guided only by molecular forces and just appear to have intention or are there other forces at work that I'm not aware of? How do these macromolecules "know" what to do?,"A creationist would say that this is part of the intelligent design. An evolutionist would say it's all down to chance. Two spanners to consider - 1) one molecule of hormone, once recognised by the cell, leads to prduction of thousands of times more molecules, and types of molecules, than a mere chemical would suggest, and such secretions can be brought about by tiny changes in brain activity. 2) DNA is just for storage. It is a molecularly inert form for the passing on of genes without having a massive effect upon the rest of the body - and so the active form is the sticky stuff of RNA and these determine how the proteins are folded together."
Nucleic acids,"When transcription takes place and the DNA is broken into two, and then mRNA is formed with one of the DNA strands or for BOTH the DNA strands?","Within a gene *usually* only one strand is transcribed, but there are many examples where transcription happens from the both strands. This is especially common in viruses.

Also, the strand that is transcribed for one gene may not be the same as the strand being transcribed for a neighboring gene.

Finally, the whole DNA double helix is not separated - just a small bubble is opened around each RNA polymerase as it works its way along the DNA."
Nucleic acids,"In the first paragraph of the section "Regulatory RNA (miRNAs and siRNAs)" it says "They bind to specific mRNA molecules (with partly or fully complementary sequences) and reduce their stability or interfere with their translation, providing a way for the cell to decrease or fine-tune levels of these mRNAs."

Does this mean that the purpose of microRNAs (miRNAs) and small interfering RNAs (siRNAs) it to make sure that there are not too many mRNA molecules producing proteins? They are regulating the amount of protein produced by the cell? Am I understanding this correctly?

Please help! Thanks. :)","Yes, miRNA regulates protein synthesis in a way it binds to mRNA transcript and 'silence' it."
Nucleic acids,how are DNA and RNA different and alike to each other?,"As stated in the summary at the end of the article, DNA and RNA have different functions. While DNA stores genetic information, RNA is involved in protein synthesis and gene regulation, as well as storing genetic information in some viruses. DNA and RNA also have different structures; DNA's phosphate-sugar backbone contains deoxyribose, while RNA's contains ribose. While DNA is double-stranded and has the nitrogenous bases adenine, thymine, cytosine, and guanine, RNA is usually single-stranded and contains uracil instead of thymine.

As for the similarities between DNA and RNA, they are both important biological polymers and contain four bases and a phosphate-sugar backbone."
Protein targeting,Can you explain all the initiation factors in both prokaryotes and eukaryotes. what their purpose is and how they function.,"Explaining all of the initiation factors is probably beyond the scope of this introductory article.

There are three initiation factors for translation in prokaryotes. For anyone who wants to know how they work, you can read a review paper here; http://onlinelibrary.wiley.com/doi/10.1046/j.1365-2958.1998.00893.x/epdf

As for eukaryotic translation initiation factors, that's even more complex! I'm not sure we even know exactly how they all work yet. You can view a summary table of them here:
http://www.nature.com/nrm/journal/v11/n2/fig_tab/nrm2838_T1.html

And there is a slightly longer explanation of how some of them work here:
http://bioscience.jbpub.com/cells/MBIO269.aspx"
Protein targeting,"Can you please tell more about adding sugars to the proteins, their purpose and functions. It would be wonderful if you'll explain chemical mechanism as well. Thank you))","The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycosylation. 

It helps in folding proteins.

Carbohydrate groups are added via glycosidic bonds."
Protein targeting,"First of all, thank you for the helpful article!
I have some questions considering this article:
1. What do you mean by molecular tags? Do you mean other signal peptides like the NLS which is on amino acids that are destined for the nucleus?
2. And what other factors except signal peptides determine the final destination of the protein in the cell?

Thank you for your time 
Konstantinos","1. Molecular tags are used in genomic sequencing as a method but also as a natural process in the cell. So you are correct, plasmid NL5 can be considered as used for molecular tagging.
2. Glycosylation, molecular chaperones..."
Protein targeting,Do proteins that are formed in the cytosol undergo further modification (e.g. folding)?,"Yes, proteins do undergo folding (some of them). Linear proteins not, but those with tertiary and especially quaternary structure (assembling of subunits) undergo further modifications and interactions depending on other signalling molecules in the cell.


That is considered as *post-translational modification*

https://www.thermofisher.com/me/en/home/life-science/protein-biology/protein-biology-learning-center/protein-biology-resource-library/pierce-protein-methods/overview-post-translational-modification.html"
Protein targeting,"In the second stage of translation in gene expression--elongation, ribosomes are said to provide tRNA as well as amino acids to bind to codons in the mRNA strand in chemical reactions with aminoacyl-tRNA synthetase.My question is, do the ribosomes provide the tRNA and amino acid materials themselves? (Since they are made up of 2/3 tRNA strands and 1/3 protein) If so, how do they replenish their storage of tRNA and proteins? Are some of the proteins made after translation used to replenish their storage?","Ribosomes are made of two subunits. Each of proteins and _rRNA_. Not tRNA.

Yes their role is to catch mRNA in sandwich structure and to attract tRNA, but they are composed of rRNA.

https://micro.magnet.fsu.edu/cells/ribosomes/ribosomes.html
https://www.pnas.org/content/104/50/19671"
Protein targeting,Does the signal sequence is cleaved off after entering the different organells to which it's targetted for?,"Yes, it is."
Overview of translation,You state that AUG is the start codon and also the codon for Methionine. Do all proteins made in cells start with MET?,"N-terminal initiating methionine, although being the first amino acid, is not present at N-terminus of all proteins. This is because of a process that is known as post-translational modification. There are more than a hundred post-translational modifications known, one of which is the removal of methionine from the N-terminus of a polypeptide. N-terminal methionine is removed from a polypeptide by the enzyme methionine aminopeptidase."
Overview of translation,where are the amino acids attached to the transfer RNA coming from? in the pictures it makes it seem like they just magically appear and float into the ribosome.,The amino acids are actually brought by the tRNA from the cytoplasm to the ribosome. These types of RNA "transfer" the amino acids to all these sites.
Overview of translation,"Hi there

I am curious - what stops a ribosome from attaching to another location that may be misread as an AUG when it might be uAU|Guu (Tyr + Val) for instance?","Excellent question!

Translation is quite bit more complicated that this introductory material can cover.

The sequence of the mRNA around a potential start codon influences whether or not it will be used§.  These sequences are bound by proteins that help guide the ribosome to assemble at the correct place to start translation.
(In fact, codons other than AUG are sometimes used as start codons!) 

This is covered in a bit more detail in a later article in this tutorial:
https://www.khanacademy.org/science/biology/gene-expression-central-dogma/translation-polypeptides/a/the-stages-of-translation

I also encourage you to look at some of the references for that section, which will help give you more detail on this high complex process that is still being actively studied.


§Note: The mechanisms are very different in prokaryotic and eukaryotic organisms — they can also vary between different species and even for different genes!"
Overview of translation,Why is an actual gene that codes for a protein likely to be longer?,"This is because when a gene is transcribed by RNA polymerase into pre-mRNA, it contains both coding (exon) segments and non-coding (intron) segments. After the complementary pre-mRNA strand has been synthesised, the intron segments which do not code for any part of the protein are removed from the sequence, and the remaining exon segments are spliced together via action of RNA ligase. The removal of the introns causes the mRNA strand to be shorter than it was originally, possessing less codons. However, the loss of introns ensures that the protein translation will not be interrupted by non-coding genes."
Overview of translation,"Is the tRNA made from DNA, or its a preexisting molecule?","The tRNA is a modified version of the mRNA , which is in turn made with the help of DNA"
Overview of translation,what is the open reading frame? how does that fit into all of this?,"An open reading frame (ORF) is a series of codons that begins with a start codon (usually AUG) and ends with a stop codon.  There can be no additional stop codons within that sequence. 

In genes that lack introns (e.g. most prokaryotic genes), an ORF in the DNA sequence will define the entire translated region.  If splicing occurs (i.e. in genes with introns), a final processed mRNA (transcript from a protein coding gene) will have a long ORF that directs ribosomes to produce a polypeptide.

Does that help?"
Overview of translation,What happens to the mRNA after being translated? Can it be translated again?,"Yes it can, although it has a very short lifespan (a few hours)."
Overview of translation,"After it goes through A P E sites, does the site migrate or does the mRNA move for new codons to be translated ?","In one of the previous sections, it was stated that the ribosome moves; since the A P & E sites are part of the ribosome, the sites move."
Overview of translation,"Are there any important enzymes involved in translation? In the article it says "the ribosome also acts as an enzyme, catalyzing the chemical reaction," but is the ribosome an enzyme or does it just ACT as an enzyme? Thanks.","Well, there is one enzyme which is crucial for translation and that is "aminoacyl tRNA synthetase".  This enzyme attaches an amino acid to the tRNA. There is a different version of this for every different amino acid (so 20 of these in human bodies).  

The enzyme is a "synthetase" because it creates a new structure called "aminoacyl-tRNA", which is the tRNA which has an amino acid linked to it. The word "aminoacyl" means that an amino acid is linked to something, in this case tRNA. 

This process happens BEFORE the tRNA enters the ribosome and it takes place in the cytosol. ATP is required for that reaction. 

I hope that helps ^^"
Intro to gene expression (central dogma),Why there are 61 codons? Why not 64??,3 of them are stop-codons which terminates translation (61+3=64).
Intro to gene expression (central dogma),what  happens to the mRNA after translation process i.e after proteins are produced?,"Hi Srinidhi,

After mRNA is translated, is either stored for later translation or is degraded. The eventual fate for every mRNA molecule is to be degraded. The process of degrading mRNA molecules happens at a relatively fixed rate.

Hope this helps!

Jonathan Myung"
Intro to gene expression (central dogma),"I'm still confused on two things. One, what is a TATA box? ANd two, what are the poly-a tails and 5' caps?",The TATA box tells where a gene begins so that it can be transcribed.  The Poly-A tail is a string of (mostly) adenines on the 3' end of the mRNA that gets eaten away by hydrolytic enzymes.  It is there so that the coding section of the mRNA doesn't get eaten.   (The hydrolytic enzymes themselves are there to protect from viruses.)   It is also recognized by the nuclear pore and allows the mRNA to leave the nucleus.  The 5' cap tells the ribosome where to begin translating.
Intro to gene expression (central dogma),What happens if a mRNA breaks? Will part of the protein be produced from the broken piece?,"Yes, most likely. If the context of the mRNA fits with the translational machinery (applicable  for the part of mRNA with the initiation codon only. The part without the initiation codon would not be translated), it might produce a truncated protein where the N-terminal part would be present but the C-terminal part (wrt to the original full length protein) would not be there.  However, most of these truncated proteins are recognized by the cellular repair machinery as abnormal and they are recycled. Sometimes though, such proteins can linger and may even participate in cellular functions (in a positive or detrimental way). Most likely source of truncated proteins is DNA rearrangement though, and mRNA breakage would not likely have a major effect (it might, depending upon the need of the original protein) as there would be other full-length mRNAs that would be translated into the protein of interest. Hope this helps."
Intro to gene expression (central dogma),Can a DNA end in 3' and the last molecule in this end is a phosphate? Why not??,"Phosphate is always attached to 5' end, and OH group to 3' end, because of the chemical structure of DNA."
Intro to gene expression (central dogma),It is essential that we need RNApolymerase for transcription. But to synthesize this enzyme we need transcription to happen .  So either RNApolymerase has to be present from the start or there should be another mechanism by which polymerisation of RNA happen. So how is it done for the First Time ??   How is it possible ?,"Some proteins and other molecules come from the previous cell, so the new cell can start its own production. Another thing is that some RNA can act as an enzyme and catalyzes reactions, though it occurs much less often."
Intro to gene expression (central dogma),Why do the number of A's on the poly-A tail vary?,"Each time a mRNA is read, an ''A'' of the poly-A tail is cut off, when there's no more ''A'' in the tail, the mRNA can be degraded. A mRNA (let's call it mRNA 1) can have more ''A'' in its tail than another mRNA (mRNA 2) depending on how much the cell needs that product  (1 instead of product 2)."
Intro to gene expression (central dogma),"It is mentioned in The Genetic Code, that,
One codon is a "start" codon that indicates where to start translation. The start codon specifies the amino acid methionine, so *most* polypeptides begin with this amino acid.

AUG codes for methionine, which contains sulfur. In the Hershey-Chase experiment, they made use of the fact that all proteins contain sulfur (because of the presence of methionine, I guess)
Are there proteins which do not begin with methionine?","There are, but this is (usually) due to removal or modification of the amino-terminal (start) methionine.  For example enzymes called "methionine amino-peptidases" cut off this amino acid from the beginning of some proteins — this is an example of what is known as a "post-translational modification".

It is also quite common for the first part of a protein (including the starting methionine) to be removed during processing — an example is secreted proteins that have their signal sequences removed during secretion or membrane insertion. 

Methionines can also be oxidized to form chemically related residues."
Intro to gene expression (central dogma),Why is amino acid sequence not directly read from a template DNA strand? Why do we need an intermediary mRNA ?,"This is an interesting question to think about, but "why" questions in biology are often very difficult to answer in a meaningful way.  

Below I've listed one possible evolutionary reason for the use of mRNA as an intermediary and then some advantages to this system.


One strongly supported hypothesis is that RNA actually came first — this known as the "RNA world hypothesis"§.  

This means that we use RNA because "life" has always used RNA and getting rid of it by evolutionary processes would be essentially impossible.  (You'd have to redesign life from scratch!)


Making mRNA also allows efficient production of proteins from a single gene.  

This is because many mRNAs can be transcribed from a gene and then each mRNA can be translated independently (and multiple times).


There are also multiple levels of regulation that can control how much mRNA is present, what parts of the mRNA get kept‡, and how frequently the mRNAs get translated.  

This allows cells to be much more responsive to changing conditions.


In addition, in eukaryotes DNA is kept in the nucleus, while translation happens on ribosomes (found in the cytoplasm).  

Having an RNA intermediate allows the information in DNA to travel from the nucleus to the cytoplasm.


There are probably more advantages that I haven't thought of — I encourage you to keep thinking about your question as you learn more about how cells work!


Does that help?



§Note: For more information see:
https://en.wikipedia.org/wiki/RNA_world


‡Note: For example alternative splicing in eukaryotes — to learn more see:
https://www.khanacademy.org/science/biology/gene-expression-central-dogma/transcription-of-dna-into-rna/a/eukaryotic-pre-mrna-processing"
Intro to gene expression (central dogma),What happens in a mutation where the Stop Codon is removed/altered? What does the cell do then? does it perform apoptosis?,"There are repair mechanisms. That one is called *Non stop Decay* that mechanism is able to detect mRNA which cannot be degraded because there is no STOP codon. It has to detach mRNA from the ribosome so it can translate the next mRNA sequence.

Nonstop decay is the mechanism of identifying and disposing aberrant transcripts that lack in-frame stop codons. It is hypothesized that these transcripts are identified during translation when the ribosome arrives at the 3′ end of the mRNA and stalls. Presumably the ribosome stalling recruits additional cofactors, Ski7 and the exosome complex. The exosome degrades the transcript using either one of is ribonucleolytic activities and the ribosome and the peptide are both released. Additional precautionary measures by the nonstop decay pathway may include translational repression of the nonstop transcript after translation, and proteolysis of the released peptide by the proteasome.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3638749/"
Stages of transcription,What is the benefit of the coding strand if it doesn't get transcribed and only the template strand gets transcribed? Please answer asap. Thank you!,"Having 2 strands is essential in the DNA replication process, where both strands act as a template in creating a copy of the DNA and repairing damage to the DNA. Additionally the process of transcription is directional with the coding strand acting as the template strand for genes that are being transcribed the other way.
In the diagrams used in this article the RNA polymerase is moving from left to right with the bottom strand of DNA as the template. If the promoter orientated the RNA polymerase to go in the other direction, right to left, because it must move along the template from 3' to 5' then the top DNA strand would be the template."
Stages of transcription,"During DNA replication ,DNA ligase enzyme is used alongwith DNA polymerase enzyme so during transcription is RNA ligase enzyme also used along with RNA polymerase enzyme to complete the phosphodiester backbone of the mRNA between the gaps?","*Great question*!

Not during normal transcription, but in case RNA has to be modified, e.g. bacteriophage, there is T4 RNA ligase (Prokaryotic enzyme).
(s the ability of bacteriophage T4 to rescue essential tRNAs nicked by host
nucleases, or in the more exotic RNA editing processes
seen in kinetoplastids, in which mRNA molecules are
cut, their coding sequence altered, and then the RNA
pieces spliced back together).

Nucleotidyl transferases share the same basic mechanism, which is the case of RNA ligase begins with a molecule of ATP is attacked by a nucleophilic lysine, adenylating the enzyme and releasing pyrophosphate.

https://www.cell.com/molecular-cell/pdf/S1097-2765(04)00089-9.pdf

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4234903/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1624903/"
Stages of transcription,Why does RNA have the base uracil instead of thymine?,"To add to the above answer, uracil is also less stable than thymine. RNA molecules are constantly being taken apart and put together in a cell, and the lower stability of uracil makes these processes smoother. In DNA, however, the stability provided by thymine is necessary to prevent mutations and errors in the cell's genetic code. :)"
Stages of transcription,"i heard ATP is necessary for transcription. Which process does it go in and where? (initiation, elongation, termination)","ATP is need at point where transcription facters get attached with promoter region of DNA , addition of nucleotides also need energy durring elongation and there is also need of energy when stop codon reached and mRNA deattached from DNA. There for termination reached when poly Adenine region appeared on DNA templet because less energy is required to break two hydrogen bonds rather than three hydrogen bonds of c, G. transcription process starts after a strong signal it will not starts on a weak signals because its energy consuming process."
Stages of transcription,"so there are many promoter regions in a DNA, which means how RNA Polymerase know which promoter to start bind with. what triggers particular  promoter region to start depending upon situation.","This is a good question, but far too complex to answer here.  In fact, this is an area of active research and so a complete answer is still being worked out.

There are many known factors that affect whether a gene is transcribed.  These include factors that alter the accessibility of chromatin (chromatin remodeling), and factors that more-or-less directly regulate transcription (e.g transcription factors).

Also worth noting that there are many copies of the RNA polymerase complex present in each cell — one reference§ suggests that there could be hundreds to thousands of separate transcription reactions occurring simultaneously in a single cell!

The following are a couple of other sections of KhanAcademy that provide an introduction to this fascinating area of study:
https://www.khanacademy.org/science/biology/gene-regulation

https://www.khanacademy.org/test-prep/mcat/biomolecules#gene-control


§Reference:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2926752/"
Stages of transcription,"According to my notes from my biochemistry class, they say that the rho factor binds to the c-rich region in the rho dependent termination, not the independent. Therefore, in order for termination to occur, rho binds to the region which contains helicase activity and unwinds the 3' end of the transcript from the template. However, if I am reading correctly, the article says that rho binds to the C-rich protein in the rho independent termination. I am still a bit confused with what is correct.","The article says that in Rho-independent termination, RNA polymerase stumbles upon rich C region which causes mRNA to fold on itself (to connect C and Gs) creating hairpin. That hairpin makes Polymerase stuck and termination of elongation.


I do not see the Rho factor mentioned in the text nor on the photo.

Probably those Cs and Gs confused you. 

:D"
Stages of transcription,""unlike a DNA polymerase, RNA polymerase does not need a primer to start making RNA. "
DOesn't RNA polymerase needs a promoter that's similar to primer in DNA replication isn't it?","it doesn't need a primer because it is already a RNA which will not be turned in DNA, like what happens in Replication."
Stages of transcription,Is the Template strand the coding or not the coding strand? My professor is saying that the Template is while this article says the non-template is the coding strand,"The template strand can also be called the non-coding strand. This strand contains the complementary base pairs needed to construct the mRNA strand.
The coding strand could also be called the non-template strand. This isn't transcribed and consists of the same sequence of bases as the mRNA strand, with T instead of U."
N/A,is the proteasome the same as a peroxisome? or is it a different organelle for breaking things down?,"no, they are different. a proteasome is a tube shaped protein that "chops up" other proteins tagged for degradation by ubiquitin, whereas a peroxisome is a cell organelle that processes peroxides."
N/A,Splicing occur after poly (A)tail and head attachment ??  Or first head and poly(A)tail then splicing  ? Im so confused .... plz explain and reference,"Capping takes place soon after the transcript is initiated. 

Tailing and splicing then happen more-or-less independently. For short transcripts this usually means the tail is added first. For long transcripts the introns near the 5' end will generally have been spliced before the tail is added.

You can read more about this here:
https://www.ncbi.nlm.nih.gov/books/NBK21563/"
N/A,What is the advantage of post‐transcriptional regulation vs transcriptional regulation?,"Good question, but too complex to answer completely here — I'll give you a few advantages, but I encourage you to read more about this subject on your own.

1) Biological systems are quite error prone, so overlapping mechanisms often are used to achieve tighter control.
For example, in the _E. coli trp_ operon the repressor is reported to decrease expression by about 70 fold.  Attenuation can add another 10 fold decrease in expression.  
Both mechanisms thus work together to give a better level of control.

2) Post-translational modifications (PTMs) have the additional advantage of often being reversible — you don't need to make new proteins a cell can just fine tune their activity as needed.

This has multiple advantages — for example, this saves cells energy and time (synthesizing new mRNAs and then proteins is energy intensive and slow compared with making PTMs).

PTMs are also important for allowing the recycling of proteins if they are no longer needed — a critical example of this is in the cell cycle where regulators for some the stages must be broken down to allow the next stage to proceed normally."
N/A,Can somebody explain more on the insulin part and how does it work? Thanks.,"Insulin consists of two poly-peptide chains connected but it doesn't start off the way. The first protein translated by ribosomes in pancreatic beta cells is preproinsulin (a single polypeptide chain). After creation, in its journey through the cell, that single polypetide is proteolytically(fancy word for breaking a peptide chain into smaller chains) cleaved forming proinsulin. Afterwards, proinsulin folds into the correct formation, some bonds are added, more cutting and it matures into insulin-the active chemical we use. So it seems there is a lot of places where the production of insulin can go awry."
N/A,Is a Proteosome similar to a Lysosome?,"What do you think?

Can you make a list of similarities and differences?  

What do you conclude from that?

There is information on lysosomes here:
https://www.khanacademy.org/test-prep/mcat/cells/eukaryotic-cells/v/lysosomes-and-peroxisomes"
Overview: Eukaryotic gene regulation,what is the difference between Eukaryotic gene regulation and Prokaroytic gene regulation,The two major differences have to do with the fact that there is no nucleus in prokaryotes and it is linear DNA.
Overview: Eukaryotic gene regulation,two exambles of epigenetic effects that control gene expression in eukaryotic cells,"Epigenetic inactivation of the X chromosome in females - from pharmaceuticals.

Honeybees are genetically identical but queen bees can produce as many as 2,000 eggs in a single day, whereas worker bees are sterile."
Overview: Eukaryotic gene regulation,"When it says that "almost all cells have the exact same DNA", does that mean that some cells have different DNA than the rest of the body? (are they talking about sex cells?)","Yes that is one example. Another would be red blood cells, when they are mature they no longer have a nucleus. Also in some immune cells, DNA is modified to make more variety so you can have lots of different antibodies. But in that case, only very small region of DNA is changed - most genes are left the same. Maybe there are a few more exceptions, but most cells have the same DNA."
Overview: Eukaryotic gene regulation,Is this the same or related to epigenetics?,"Epigenetics refers to changes that can be inherited by daughter cells (and sometimes even offspring), but don't involve changing the sequence of the DNA.

These changes typically involve alterations in chromatin accessibility, but some alterations in chromatin accessibility are not heritable (and thus aren't epigenetic).

So, I would classify epigenetics as one type of gene regulation.


Khan Academy has more material on this, which can be found by entering "epigenetics" into the search field found near the top of every page — this will lead you to these results:
https://www.khanacademy.org/search?page_search_query=epigenetics

Some additional resources for learning more:
• https://ghr.nlm.nih.gov/primer/howgeneswork/epigenome

• https://en.wikipedia.org/wiki/Epigenetics"
The trp operon,"I don't understand the point attenuation.
Attenuation of the operon allows the cell to stop (or not) the transcription of the operon before the genes coding for the enzyme, right?
But, if the levels of tryptophan are high in the cell, wouldn't the translation of the Trp genes be already regulated via the repressor fixed on the operator ?

What is the point in attenuation of the polymerase cannot fixe itself first? When is it used by the cell as a mean of regulation?","Great question!

In general biological systems are quite error prone — in the case of the _trp_ operon the repressor is reported to decrease expression by about 70 fold.  Attenuation can add another 10 fold decrease in expression.  

Both mechanisms thus work together to give a better level of control."
The trp operon,what is the product of trp operon?,"There are 5 structural components of trp operon as described above they produce different enzymes namely, trpE-anthranilate synthase component I, trpD - anthranilate synthase component II, trpC- N-(5'-phosphoribosyl)-anthranilate isomerase, trpB- tryptophan synthase β, and trpA- tryptophan synthase α. All of these enzymes have a combined role in production of tryptophan."
The trp operon,What is the co-repressor in the trp operon?,"Tryptophan.

I guess the section titled `Turning the operon "on" and "off"` could have made this a bit clearer ..."
The trp operon,"What does the tryptophan actually do when produced by the trp operon? If it is just produced to block the trp operon from producing more of the same substance, I don't see the point of tryptophan.","Tryptophan is an amino acid, and it is used to build some proteins."
The trp operon,"Why when the 1+2 và 3+4 hairpin is formed, the RNA Polymerase detaches? It's hard to understand this point...","Look. Compare photos above and photo below. In the photo above region 4 is free to bind to RNA polymerase. Why is it important? because it encodes attenuator and promotes translation.

However, when there is High TRp, mRNA folds and 3 and 4 region form loop. Loop makes it region 4 hidden and detaches from RNA polymerase. 

Just follow the photos and obserev them as long as you need. Tryto reproduce on paper (schematically).


Ask more specific which part does not make sense."
The trp operon,"What would be the easiest way to make large amounts of tryptophan, using a strain of E-Coli (through genetic engineering)? Could you please direct me in the right direction?","Hmm...I would say that you might want to use some of the components described in this article, but with modifications that would "break" the negative feedback loops that limit the amount of Trp produced.

For instance, you would probably want to express the _trp_ operon under a constitutive ("always-on") promoter, and you might also want to alter the sequence of gene encoding the gatekeeper enzyme (the one that is negatively regulated by feedback inhibition) to make it insensitive to tryptophan binding, i.e., by disrupting the tryptophan binding site. Finally, you would probably want to not include the leader of the _trp_ operon when making the version under the constitutive promoter, or else the attenuation mechanism would prevent the accumulation of large amounts of Trp in the cell.

I'm sure there are other ways to do it, but that would be my first thought (that you would basically need to reconstruct a version of the system that is no longer self-regulating). Hope that helps!"
The trp operon,why there are two codons trp? what happen if there is only one codon trp?,"Thank you for your help, now I think I may help you.

So, there are 2 pairs of regulating genes (GDCF) but that is less relevant here. We are interested in regulating starting sequence operon.
The operon is composed of *3* promoters (3 places for binding) *but* it has two Trp residues to bind two sensing signals.

It binds L- Trp, and the other codon binds tRNA trp (charged or uncharged).

The question arises about what would happen if only one is present (let's imagine mutation happened).

They can function without each other. That is a form of double control.

We can say that the principal promoter is the one binding L-Trp while Terminator is the one binding charged or uncharged tRNA Trp.

If Trp binds to L-Trp, then it activates corepressor and diminishes the production of TRp. (it is logic high Tryptophan = no need for a synthesis of Tryptophan). However, the synthesis does not simply stop. There is wehere another promoter (terminator) that comes into place. Uncharged tRNA Trp binds and termination stops at the leading place. Meaning now translation.

Now, what if the tRNA TRp terminator is missing? It means that translation will proceed but at a slower pace.

What if the first codon is missing? It could potentially impair the Trp operon regulation severely. Because cells would not be able to sense whether Tryptophan is present in the cell or not.



Hope this helps :D


For reference, click on the https://rnajournal.cshlp.org/content/13/8/1141.full.pdf+html 
page 2 figure 2."
The trp operon,What does the Trp stand for ?,"`Trp` is the accepted three letter abbreviation for the amino acid tryptophan.  

You might wonder why they didn't use `Try` – in addition to `Try` being a word, there is another amino acid called tyrosine, whose code is `Tyr`, so they decided to try something a little more different :-)"
N/A,"what is the evolutionary advantage of regulation of prokaryotic gene expression?
what are the drawbacks?","Great question. The upsides of gene regulation is a conservation of energy within the body, as it is not being used for unnecessary functions. The drawbacks could maybe be the possible mutations? If there was a mutation that were to transcribe a protein non-stop, it could satiate the cells or use up available resources for no reason."
N/A,What does it mean for there to be a negative and positive gene regulation? What's the difference?,Positive gene regulation controls the production of genes by turning them on while negative gene regulation controls the production of genes by turning them off.  Positive gene regulation allows for the production of a gene that is needed for use at a particular time/situation in a cell while negative gene regulation prevents the overproduction of a gene at a particular time/situation in a cell.
N/A,Can you give a couple examples of rare eukaryotic operons?,"The examples that I found for mammals are all bicistronic (operons with two genes):
LASS1-GDF1, SNRPN-SNURF, MTPN-LUZP6 and MFRP-C1QTNF5

You can search for those gene pairs, but there doesn't seem to be a huge amount of information available and in many cases one of the genes is almost completely uncharacterized.

Eukaryotic operons (aka polycistronic mRNAs) are apparently very common in nematodes (round worms) and also frequently seen in _Drosophila_ (a fly).

Unfortunately I have only found academic papers that cover this interesting phenomenon:
•https://academic.oup.com/bfg/article/8/1/68/219251

•https://pdfs.semanticscholar.org/24c6/239e22766cbf11e8a717d3beff6f69be594e.pdf

Does that help?


ADDENDUM:
Also, the mitochondrial genome uses operons (polycistronic genes), but since the mitochondria is descended from a bacteria it seems like cheating to count that ..."
N/A,Why is it beneficial for bacteria to be able to regulate the production of proteins?,So that they do not use energy to make something that they do not need.
N/A,How can the cell know that the genes in an operon are separate? Wouldn't the cell create all the genes in a operon as one gene and make them all as a whole protein?,"Good question!

Even though all the genes in an operon are transcribed together, they are *not* translated together.  There are untranslated sequences between each gene that contain a RBS (ribosome binding site).  When the mRNA is being translated, the RBSs for each gene will independently bind to different ribosomes and so they all make separate proteins.

This figure may help make things clearer:
https://en.wikipedia.org/wiki/Operon#Overview"
N/A,Are the operator and enhancer exist at the same time?,"Yes. there could be enhancer or silencer.

The operator is a place of operon where repressor binds while enhancer is a place where activator binds. They could easily be neighboring coding sequences on the same operon."
N/A,What's the difference between operons and other normal genes?,"Operons are groups of genes that are transcribed together as a unit, and share one promoter."
N/A,Is operator a kind of silencer?,"Not operator itself, it is just place where repressor binds. But when repressor binds it is *silencer*."
Transcription factors,Alright but I still don't understand what is the difference between a general transcription factor and a specific one.,"General, or basal, transcription factors simply assist in the binding of RNA polymerase to the promoter. Other types of transcription factors include activators and repressors. These transcription factors affect transcription in different ways; activators assist in the binding of RNA polymerase and repressors stop transcription."
Transcription factors,can a single mRNA strand be translated multiple times?,"Yes, it can even be read by several ribosomes at once."
Transcription factors,Are enhancers required for transcription to occur?,"Generally, enhancers can be bound by activators to increase the likelihood that a particular gene will be transcribed. Therefore, they are not strictly required."
Transcription factors,"does prokaryotes have any transcription factors?
if yes, kindly mention their names??","Yes, prokaryotes have transcription factors. Think about E. coli and the lac operon. The activator and repressor proteins involved in lac operon expression are the transcription factors. However, the mechanisms by which transcription factors work are simpler than those in eukaryotes."
Transcription factors,are all transcriptional factors  proteins? if not what are different transcription factors?,"Yes, all transcription factors are proteins. They are coded for by regulatory genes, which are genes that encode a protein involved in regulation of gene expression (such as a transcription factor). However, recently people are discovering that transcription factors can have bits of sugar and other non-protein stuff added to them to regulate their activity. But yes, all transcription factors are proteins."
Transcription factors,"Does general transcription factors always bind to proximal control elements, and specific transcription factors to distal?

Also, are the bindings to specific transcription factors essential for that individual gene to start transcription? 

I would very much appreciate the help.","Good question!

While I believe the pattern you describe (with the general transcription factors binding to proximal elements) is common, many promoters (possibly most) don't follow that pattern.

For example, according to a 2014 review† only ~20% of RNA polymerase II promoters contain a TATA box (which means that ~80% aren't bound by TATA binding protein) and ~30% have no recognizable promoter elements!

Another example is that many (but not all) genes transcribed by RNA polymerase III have promoters within the gene§.


†Note: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4214234/


§Note: See the first figure in this review for details:
http://genesdev.cshlp.org/content/16/20/2593.full


As for your second question, it appears that some "housekeeping"¶ genes  (including many of the TATA-less pol II promoters) lack specific factor binding sites.


¶Note: "housekeeping" genes (e.g. translation factors and ribosomal proteins) are expressed everywhere and at a so their expression doesn't require a lot of fine tuning."
Transcription factors,Which ways would you test if a mutant gene was affecting a transcription factor?,"Knock-out a gene.Targeted gene deletion in order to study the efefct of gene mutation.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4597246/"
Intro to biotechnology,"is it possible to become inhuman (superhuman, meta human) if biotechnology found traces of DNA that had a ability to have powers?","That is doubtful. If you are thinking about powers such as telekinesis this is not possible. on the contrary if you are thinking about powers which animals have (e.g., wings from birds or camouflage from octopi) this is a possibility."
Intro to biotechnology,"This is a really weird question, but if a zygote is cloned from birth, and both are grown at the same time at the same place such that when they are born, they look exactly the same, is there a way to tell which one is the original baby and which one is the clone? :)","I am hesitant to believe that cloning is so accurate, if you monitored them you would see differences I am sure."
Intro to biotechnology,is it possible to use gene therapy to make your body circulate a cell that can produce rapid regeneration of lost limbs or organs or wounds?,"It's not yet discovered, but who knows? :)"
Intro to biotechnology,Who's this Dolly the Sheep??,"Dolly the sheep is the first mammal that was successfully cloned from an adult cell in 1996 and lived for six years. Well, the process was done by using a somatic cell which contain 46 chromosomes or embryo  and placed in the surrogate mother egg cell with no information (DNA) in the womb. I hope this help!"
Intro to biotechnology,What is the difference between penicillin and penicillium?,"Penicillum is the antibiotic medicine, and penicillum is a genus of fungi, the mold that the article says penicillin is produced by. Members of Penicillum are also used to make cheeses like Blue and Brie."
Intro to biotechnology,If you decide to clone a live mammal with diseased the cloned one will have that disease too or there won't be any effect of that disease. Or you should present a healthy one not a diseased one?,"Well, it depends on the disease. 

If it was a genetic disorder causing the disease, then the cloned mammal should present with the same genetic disorder since the genome should be identical (excluding epigenetic variations). 

Things become more complicated regarding a viral and bacterial infection. For instance, certain viral infections like HIV can embed its genome into the host's cells, therefore in this case, the viral infection would hypothetically transfer into the clone because you are copying the genome (including the viral genome) from mammal. 

Still, mammalian cloning is in its embryonic stages (no pun intended), so much biological machinery and attendant effects are unknown."
Intro to biotechnology,who is dolly the sheep,Dolly was the first cloned animal.
Intro to biotechnology,summerize how gene threapy works,"On it! 

Suppose that a girl is affected by a genetic disease caused by a recessive allele (aa) that lowers the rates of production of a specific protein. What we are gonna do is take some somatic cells from her and alter their DNA so that she has the dominant (and healthy) allele (Aaa). Then we are gonna re-inject the cells in the girl. As a result, the girl will produce normal amounts of that protein because the expression of the dominant allele censors the one of the recessive!

Hope this helps!"
Gel electrophoresis,""All DNA molecules have the same amount of charge per mass. Because of this, gel electrophoresis of DNA fragments separates them based on size only."

I don't get it.
F=qE
ma=qE
a=qE/m
and (q/m) is a constant.
If all fragments have the same acceleration, then shouldn't they all move with the same speed?","Great question.
Your equations are correct but your model has assumptions. When you define that a=qE/m ,you assume that the only force acting on the DNA is the electric force from the electric field so that's why your calculation takes this as the resultant force since it is the resultant force which will accelerate a body according to Newton's second law. 

However, there's one more factor that comes in play. The DNA fragments move through the agarose gel so they are experiencing viscous drag as they move through the gel. This viscous drag is proportional to the mass of the DNA fragment . Let me explain why. 

The mass of the DNA fragment  depends on the length of the DNA fragment. The longer the DNA fragment ,the more atoms it contains so the more electrons it contains . The more electrons in the DNA fragment ,the stronger the intermolecular london forces of attraction between the DNA fragment and the gel molecules so the greater the viscous drag experienced by the DNA fragment. Yes all your equations are correct and they travel at the same acceleration but it's the viscous drag through the gel that causes heavier DNA fragments to move slower than the lighter DNA fragments .I myself once had the same question in my mind but realized that the viscous drag is the game changer of the scenario. Hope I answered your amazing question."
Gel electrophoresis,Is it possible to make gel electrophoresis determination machine in home ?,"I personally don't know, but if you Google search on "how to make your own gel box," some hits come up - maybe one of those would help you? Good luck! :)"
Gel electrophoresis,Which poles are known as the cathode and anode? Sorry I get a bit confused with these two :\,"In a *galvanic (voltaic) cell*, the anode is negative and the cathode is positive. However, in an *electrolytic cell* such as we have here, it's the reverse: the anode is *positive* and the cathode *negative*.
This is because the flow of electrons goes in the opposite direction in the second system."
Gel electrophoresis,Are there more recently devloped methods to measure DNA length?,I would also add that researchers almost always use gel electrophoresis to at least check that the PCR was successful as sending a failed PCR product to another lab for sequencing etc. would be a complete waste of money and it's not cheap yet!
Gel electrophoresis,why do the bands appear to be of the same size while the DNA fragments vary in their sizes?,"The bands that you see are as a result of loading dye, which helps scientists see the DNA they're loading into the gel. The DNA fragments are typically illuminated under UV light, and aren't visible in visible light."
Gel electrophoresis,"what does it mean to have multiple bands for same sample (for ex: sample#3 above). Also when two or more bands appear for the same sample, which band do we use to determine the size?","Multiple bands mean DNA fragments with different size and lengths. Realistically when doing   gel electrophoresis you'll see many more bands for the same sample. To determine the bp size, you estimate using the reference DNA."
Gel electrophoresis,I'm doing a lab in class on gel electrophoresis where a married lady was raped and she wants to find to whether her baby is from her husband or the rapist. The gel electrophoresis shows more shared bands between the child and the husband than the child and the rapist. I was wondering how accurate this procedure is and what more someone could do to be more certain that it is the husband. Can more DNA from these people be tested?,"I think this method is pretty accurate, but again, including more reference DNA would be more helpful. Let's assume that rapist and husband are not genetically rated - in that case, it is easy to distinguish them."
Gel electrophoresis,"I don't understand how the length of a DNA fragment can be used to identify a person. 

Here's how I'm guessing it happens and the questions I have about it. There's much that might be wrong, so please let me know:

Let's say you do PCR for a specific sequence on a hair cell from a crime scene. Firstly, how would you select the sequence to do PCR with?

Then, let's say you did gel electrophoresis and found out the DNA for the chosen sequence is 5000 bp long. (Side question: why wouldn't you know the length of your target sequence before doing PCR?)

Then, you take the hair cells of a few suspects (for simplicity, you know for sure that the culprit HAS to be one of them) and do PCR for the same sequence and gel electrophoresis. At this point, why would the different suspects have different lengths for that sequence? Doesn't a certain sequence have a fixed length?

Let's say, somehow, only one suspect has 5000 bp for that sequence. Why does this mean that they are a match for the crime scene hair? How does having the same length for a sequence indicate identical genomes?

Sorry about how long this was but I'm pretty confused so it'd be great if someone could explain.","For your first question:
You will do PCR of the entire sample. Then a restriction enzyme is used to cut the part you want. One restriction enzyme will make the cut on the same place in all samples. So you will have the fragment containing the same sequence."
Gel electrophoresis,"So when fragments of DNA are put in the gel electrophoresis box, do they keep moving toward the positive end until they reach a certain point where they stop, based on how many base - pairs long they are, indicated by the ladder? In other words, do they stop at a certain point that tells scientists how long they are? Because if they just kept moving toward the positive end (at different speeds), then the fragments would just pass each length interval on the ladder, and then scientists wouldn't know how many base - pairs long they actually are. Hope this makes sense.","Everything (including the ladder) gets loaded at the same time in separate wells (slots/holes in the gel).  

This is done with the power supply turned off so there is no electric field.  

After loading the samples into the well you turn on the power§.  

This allows the DNA from the standard(s) (usually referred to as a ladder) and sample(s) to migrate in parallel.

This means you can compare the sample(s) to the ladder(s) at any time.  

In general, the longer the gel is run the more separation you get, but the bands will also get fatter (more spread out).


We generally decide when to stop the gel (turn off the voltage) based on the migration of one or more dye molecules included in the samples.  

These molecules migrates at known rates similar to those of a small DNA molecule.


Does that help?


§If you're smart you also double check that the samples are moving in the correct direction! (ADDENDUM: not that _I've_ ever committed "retrophoresis", nope not me, I also didn't (re)invent a name for it ..."
Overview: DNA cloning,Why does the DNA need to be in the form of a plasmid when pasted in a bacteria and not just the string of DNA cut by the restriction enzyme?,"There are several reasons:

1) Linear DNA is unstable because there are enzymes present within all organisms (including bacteria) that degrade linear DNA molecules.

2) Vectors contain a sequence (known as the origin of replication) that causes the DNA to be replicated within the bacteria — this is necessary to maintain at least one copy of the new DNA per bacterium as the cells divide.

3) Vectors usually contain at least one sequence that allows selection for the vector (e.g. antibiotic resistance) — this is discussed in this article.

4) Vectors can also be used to do different things with the DNA.  A common example of this would be an expression vector — this causes the DNA to be transcribed and translated and would allow you to examine the protein encoded in the cloned DNA.

Does that help?"
Overview: DNA cloning,When the bacteria taking up the plasmid. How can we be sure that the bacteria used aren’t having any plasmid in it? To make sure that when we grow it on agar the bacteria got the recombinant DNA. What if. The original bacteria we use to take up the recombinant  plasmids are already having its own plasmid. So how can we differentiate them then?,"Good question :-)

It could be difficult to know if you were just using a random bacteria isolated from nature — especially since there are likely to be many thousands of different plasmids (1730 were present in a sequence database as of 2009).  We could sequence all the DNA inside the bacteria, but that is still a lot of work ...

However that doesn't matter as much as you might think.

For example, assume we are using a plasmid that contains a marker (selectable gene) encoding resistance to ampicillin.  All we need to know is that the bacteria were are transforming are not already resistant to ampicillin.  This is easy to test — we just try growing the bacteria in the presence of ampicillin, if they don't then we can use our plasmid.

In practice microbiologists have domesticated strains of bacteria (a favorite is _Escherichia coli_  — often abbreviated to _E. coli_) that have been studied for decades.  In almost all cases you would be using one of these well characterized strains and so would not need to worry about whether there were unknown plasmids."
Overview: DNA cloning,"Do the bacteria ever make mistakes in the replication process? If not, why? If they do, how can we still call Dolly the sheep a clone if the original sheep is actually slightly different?","This is DNA cloning, not the actual cloning of organisms. For more information on cloning, visit this webpage: https://en.m.wikipedia.org/wiki/Cloning. Hope you find it useful! :)"
Overview: DNA cloning,Are identical twins also clones ?,"The short answer is no. While they share a lot of DNA, there are also mutations that naturally occur within your cells, so no two people can share exactly the same DNA."
Overview: DNA cloning,How is the cutting and joining of DNA monitored?,"To assess whether a "digest" (restriction enzyme cutting reaction) is complete, we usually run a small sample of the digest on an agarose gel§ with a "ladder" sample containing fragments of known sizes and a small sample of uncut DNA.

This comparison allows us to see whether we got fragments of the expected sizes and how much uncut plasmid still remains.


We generally don't directly check whether a ligation has worked — ligation is very reliable and it is usually easier to just transform the DNA into a new host bacteria.  
We then purify plasmid DNA and use restriction digests, PCR †, or sequencing to test whether we got the desired outcome.


§For details see:
https://www.khanacademy.org/science/biology/biotech-dna-technology/dna-sequencing-pcr-electrophoresis/v/gel-electrophoresis-dna

†For details see:
https://www.khanacademy.org/science/biology/biotech-dna-technology/dna-sequencing-pcr-electrophoresis/v/the-polymerase-chain-reaction-pcr"
Overview: DNA cloning,How can we clone a gene that is unknown sequence ?,"You can use partial digestion method and expression in bacterial vectors and finally antibiotics to select your cloned vectors.

Look at this:
https://www.researchgate.net/post/How_do_i_clone_genes_with_unknown_sequence

particularly this paper has protocol:
https://www.researchgate.net/publication/10637344_Partial_characterization_of_a_transposon_containing_the_tetA_determinant_in_a_clinical_isolate_of_Acinetobacter_baumannii using tetA resistance gene as a marker on a plasmid (resistance to Tetracycline)."
Overview: DNA cloning,Why bacterias without plasmids will die?What are the functions of plasmid?,"*Plasmids* are usually present in bacteria, and plasmids can replicate its own DNA independently of the bacteria, which is why it is often used in DNA cloning. Plasmids usually have an *antibiotic resistant gene*, so the bacteria won't die in the antibiotic. For more information, visit this webpage: https://en.m.wikipedia.org/wiki/Plasmid. I hope this answers your question! :)"
Overview: DNA cloning,"Could you have a vector other than the bacterial plasmid
for instance a bacteriophage","Yes, though every case I know of involves a phage based plasmid (known as a "phagemid") that is manipulated as a bacterial vector before being converted into a bacteriophage.

I haven't personally used phagemids and suspect they are no longer commonly used, but you can learn more about this technology here:
https://en.wikipedia.org/wiki/Phagemid

Does that help?"
Overview: DNA cloning,"In "Steps of DNA cloning" step 2, how can a plasmid be transformed into bacteria? Shouldn't it be "Insert the plasmid into bacteria"?","Transformed with CaCl and heat - called heat shock.

Ca makes bacterial membrane porous and susceptible to the plasmid."
Overview: DNA cloning,"After you finish cloning the gene into the plasmid, how could you check to see if your gene is actually inside the plasmid? Could restriction enzymes be used to determine this?","Many scientist send their plasmid samples to a laboratory for sequencing, so  they do not have to do it by themselves."
DNA sequencing,"This might be a bit off topic, but I am a chemistry student and I want to get a tattoo of my father DNA. Now I know the human DNA contains too many basepairs to fit as a tattoo. But if a small segment of the sequence is used, how likely is it that that sequence also belongs to a different person?","Technically speaking, you could use the sequence from DNA fingerprinting (the method used to identify a person), but it would be still a lot of material for a tattoo, it's typically thirteen sequences of varying length... I think it would be pretty big tattoo.
Another option would be getting a tattoo of "DNA ladder" (the DNA fingerprinting pattern seen on electrophoresis), this is also unique for a person and DNA related. And add only two or three nice, detailed basepairs next to it."
DNA sequencing,"Why can't the die molecule be attached to a regular nucleotide, and then the entire DNA chain could be read as a single item?","you cannot read the entire dna chain as a single item, even if each base pair were to be dyed since you would be getting the four colours at once due to the small size of the molecule. you use ddntp to stop the synthesis for a strand and get fragments of all possible lengths that move in ascending order of length. this lets you to exactly know which base comes at what point."
DNA sequencing,How do we know the specific primer if we already don’t know the DNA fragment sequence ?,"If we want to amplify a fragment of DNA, but don't know the sequence a technique known as "Ligation-mediated PCR" can be used.  This technique starts by adding (ligating) the primer sequences to the ends of the DNA fragment."
DNA sequencing,"Are there two systems to sequencing?
one with light (laser) and the second with electric field?","In traditional (Sanger) sequencing, both electric fields and lasers are required for slightly different, but interdependent, purposes. The electric field is applied to the DNA in the capillary tube, and it pulls the DNA pieces through in order from shortest to longest. As the pieces pass the laser (moving through because of the electric field), they are excited and detected by the detector.

Some next-generation sequencing does not use lasers at all. Instead, it uses H+ ion fluxes to determine whether bases have been added. I'm not super familiar with this technique, but you can read more in this Wikipedia article: https://en.wikipedia.org/wiki/Ion_semiconductor_sequencing.

Hope one of those answers addresses your question!"
DNA sequencing,in a chromatogram why are the peaks of different heights?,The height of each peak is in proportion to the amount of the particular component present in the sample mixture injected into the chromatograph.
DNA sequencing,Does a 2000bp or a 500bp migrate faster throgh this agarose gell,"In other words, the 500bp would migrate faster."
DNA sequencing,Why do the nucleotides used here have 3 phosphate groups instead of 1?,"It's to provide it with energy. The regular DNA replication also uses 3phosphate groups because by removal of each one of them, it gets enough energy to bind to the previous nucleotide."
Bacterial transformation & selection,"How are the proteins bound to the antibodies, in the affinity chromatography, released?
And how are these antibodies formed or selected to match and pick up the proteins?","When you use the chromatography, you (always) need to use several buffers each with different salt concentrations to purify the protein. The proteins react to the presence of salt, so it would be whether the proteins would stick to the resin or not (this really depends on what protein you are using) or the proteins would unfold or not. Some of the main buffers that many labs use are:

Column Equilibration Buffer (2M) is to store all of the components in the columns so that they don't dry up. 
Binding Buffer (4M) unfolds the proteins so that the hydrophobic proteins stick to the resin and the hydrophilic proteins pass through the column. 
Wash Buffer (1.3M) releases the moderately hydrophobic proteins from the resin (lower salt conc.).
Elution Buffer (0.1M) releases the proteins (lowest salt concentration).

I hope this made sense..^^"
Bacterial transformation & selection,How does transformation ensure that a bacteria will get only one plasmid?,"Good question.

For a typical transformation (e.g. an insert ligated into a vector) you would have something on the order of 10⁹ to 10¹⁰ DNA molecules and maybe 10⁷-10⁸ bacteria. 

However, transformation is an inefficient process — you will typically get less than a thousand colonies (often many fewer).

Thus, the chance that any one bacteria would get two plasmids is extremely low (around 10⁻⁴ - 10⁻⁵).

Note also that in many situations you are only transforming one version of a plasmid, so it wouldn't matter even if you did get multiple copies of a plasmid.

Does that help?"
Bacterial transformation & selection,Can we use Calcium chloride in Solution to make bacteria more permeable instead of Heat Shock?,"There are certainly different methods of DNA sample preparation, and calcium chloride is one of them! Depending on the type of bacteria you use and the analysis methods you plan on using, certain methods are better than others (and most are used in parallel). Calcium chloride is typically used with heat shock to prepare what is called "competent cells." Competent cells are cells which have been treated (typically with calcium chloride) to improve the success of transformation. DNA is negatively charged, so the calcium cations in calcium chloride bond to the negatively charged DNA, creating an overall neutral charge. This reduces electrostatic repulsion and assists with the success of the heat shock!"
Bacterial transformation & selection,DNA lygase requires ATP but we ant providing any ATP in ligation reaction. then how it works??,"Correct, the DNA ligation reaction requires ATP. A typical ligation reaction involves incubating the *plasmid*, *DNA fragment* of interest and *DNA ligase* in a *ligation buffer*. We typically use a *ligation buffer* that contains ATP which allows the reaction to take place."
Bacterial transformation & selection,How can bacterial transformation can be used in the field of science? What are some real-life applications of this process?,"Real-life application is for the needs of the Biotechnology industry and research.


Whenever you need to develop new drug treatment, to test antibiotic resistance of bacteria, to use bacteria, for genetic engineering and _mainly_ for gene expression studies.

So you use bacteria to 'force' gene of interest into her and then grow on the medium. After selected colonies (those who have plasmid growing up on selective medium with antibiotic) you also use chromogenic colours to visualize the expression of certain proteins in those colonies.
https://edvotek.wordpress.com/2014/07/18/biotechnology-basics-bacterial-transformation/


In nature, bacterial transformation happens common, when developing antibiotic resistance and bacteria then sned their resistant even to another one (horizontal transmission)."
Bacterial transformation & selection,How can reporter genes be used to separate bacteria who have taken up the transformed plasmid from those who have taken up the non-transformed plasmid?,"That's why reporter genes exist - usually, antibiotic-resistant genes are used as markers (such as Tet - resistance to Tetracycline).

IN that case, all bacteria would be inoculated onto antibiogram including Tetracycline.

If Bacteria grow, it means that colonies carry transformed plasmid. If they do not grow they do not carry transformed plasmid.

Antibiogram is used to selectively separate bacteria."
Bacterial transformation & selection,Why cant bacterial plasmid vectors be used to transform plant cells?,"Well, they can...but it depends what kind of bacteria and what kind of plasmid. To transform a plant cell, you'd want a plasmid vector that could be replicated in _Agrobacterium tumiefaciens_. _Agro_ is a bacterium that can insert segments of DNA into the genome of a plant cell, and it's used to generate stably transformed plants. To transform a plant cell, you'd need to insert your gene into an _Agro_-compatible vector, between two sites in the plasmid that "tell" the bacterium which segment of DNA to transfer. Then, if you infected plant cells with the plasmid-carrying bacteria under the right conditions, you could get transformed cells with the gene of interest inserted into the DNA.

However, you couldn't use just any bacterial plasmid vector to make a transgenic plant. For instance, a plasmid that replicates in _E. coli_ (as described in this article) could not be used to stably transform plant cells.

Hope that helps!"
Bacterial transformation & selection,Wouldn't it be hard to find a restriction enzyme for a particular gene of interest because the desired gene must have the recognition site for the restriction enzyme on both ends?,"First, most vectors will have a region known as the "Multiple Cloning Site" (MCS) that can be cut with many different restriction enzymes† — this gives you more choices of enzyme and makes it more likely that you can find one that cuts near the ends of the region you wish to clone. 

Second, we often don't care if we clone a small amount of extra DNA , this means that we can search over a larger area than you might expect to find appropriate restriction enzymes.

Third, we don't need to use the same enzyme for both ends.  In fact, it is quite common to use two different enzymes and this allows us to do "directional cloning" — i.e. the different ends mean the insert can only be put into the plasmid in one orientation‡.  This again greatly increases the number of possible restriction enzyme sites.


If the regions flanking the sequence you want to clone don't contain any useful restriction sites you can instead use primers with restriction sites added to their 5' ends and then amplify the sequence using PCR§.  

This amplifies the insert you want and creates a copy of the insert DNA with whatever restriction sites you want added at the ends. 

There are many more tricks that have been developed, but adding sites at the ends of primers almost always works, so that is a very good one to know! 


Does that help?



†Note: There are hundreds of commercially available restriction enzymes recognizing many different sequences (many of which are palindromes, but not all).  

Among these the most commonly used are six-cutters (with 6 bp recognition sites — if you make a bunch of simplifying assumptions you can calculate that these enzymes on average will cut once every 4096 bp.


‡Note: For some applications this can be very important, for example if you are using an expression vector you need the insert to transcribed in the correct direction!


§Note: Polymerase chain reaction — you can learn more about this technique here:
https://www.khanacademy.org/science/biology/biotech-dna-technology#dna-sequencing-pcr-electrophoresis"
Bacterial transformation & selection,Wont some of the bacteria that didnt take up the recombinant plasmid have their own plasmids that have antibiotic resistant gene such as ampicillin so that even they survive and appear in the colony?,"Good question!

It could be difficult to know if you were just using a random bacteria isolated from nature — especially since there are likely to be many thousands of different plasmids (1730 were present in a sequence database as of 2009).  We could sequence all the DNA inside the bacteria, but that is still a lot of work ...

However this doesn't matter as much as you might think.

For example, assume we are using a plasmid that contains a marker (selectable gene) encoding resistance to ampicillin.  All we need to know is that the bacteria were are transforming are not already resistant to ampicillin.  This is easy to test — we just try growing the bacteria in the presence of ampicillin, if they don't then we can use our plasmid.

In practice microbiologists have domesticated strains of bacteria (a favorite is _Escherichia coli_  — often abbreviated to _E. coli_) that have been studied for decades.  In almost all cases you would be using one of these well characterized strains and so would not need to worry about whether there were unknown plasmids."
Bacterial transformation & selection,My textbook says small size vectors are preferred for cloning. Why?,"Larger vectors are more likely to contain duplicates of the restriction sites and so are harder to work with — you typically will cut at unique restriction site(s)§ when cloning, but these are harder to find in larger vectors. 

Larger vectors are also more likely to be broken by "shear" forces in a solution — e.g. when the solution is being pipetted.

Finally, the efficiency of ligation and transformation tends to decrease with larger vectors.

A typical plasmid can be up to total size of around 50 kb, but plasmids that are more than 20 kb are very difficult to work with and may require special transformation techniques. 

In particular, larger vectors are more likely to 

Does that help?


§Note: These are often found clustered together in a "Multiple Cloning Site" (MCS)."
N/A,Why do restrictive enzymes that do blunt cuts even exist if they are so inefficient?,"Restriction enzymes are found in bacteria and they have some biological role (explained below), but we are exploiting it in our way to use in experiment.

Biological role of restriction enzymes in bacteria: when restriction enzyme is present in a given bacterium, such bacterium can prevent (restrict) the growth of certain bacterial viruses (bacteriophages) and this is the reason also to call it as RESTRICTION enzymes. in this way it is the defensive enzyme that protects the host bacterial DNA from the DNA genome of foreign organism (bacteriophage) by specifically inactivating the invading bacteriophage DNA by digestion

Now one more question arises that WHY (& HOW) THESE RESTRICTION ENZYMES CAN CUT ONLY FOREIGN DNA BUT NOT THE HOST BACTERIUM'S DNA?
Explanation: if particular bacterium has restriction enzyme, it must have companion site specific DNA methylase which methylates DNA of host bacterium in site specific manner and methylated DNA is not the substrate for restriction enzyme. so host bacterium DNA is not cut by restriction but when new DNA is inserted by bacteriophage, it is not methylated and so it chopped by restriction enzyme and bacteria can survive (i.e. bacteria's innate immunity !)
Hope everything is clear..."
N/A,How long does the process of cutting DNA take?,"It depends on the enzyme and the lab that produces them, but the rule of thumb for digestions is 1 hour at the appropriate temperature: For example, SmaI works at 25C, while EcoRI works at 37C.

If you want to know more then know that enzymes are sold in certain 'sizes', which are the units present on the vial. A unit, according to NEB is:

"One unit is defined as the amount of enzyme required to digest 1 µg of λ DNA (HindIII digest) in 1 hour at 25°C in a total reaction volume of 50 µl."

Hope this helps"
N/A,what would happen if the gap never closes?,"Although the other answer is funnier, what would actually happen if the gap never closed during a ligation is that the DNA fragments would come apart again. The sticky ends will only hold them together briefly, and if ligase doesn't connect them during that time, they will go back to floating around and bumping into other pieces of DNA and enzymes in the reaction mix."
N/A,I did not understand how to differentiate between plasmids in which the gene of interest has been correctly inserted and those in which it isn't.,You can read this article for more info: https://www.khanacademy.org/science/biology/biotech-dna-technology/dna-cloning-tutorial/a/bacterial-transformation-selection. I hope this helps you! :)
N/A,How do scientists make sure that the bases of the plasmid are complementary to the bases of the inserted DNA?,"The easy way is to use the same restriction enzyme(s).  

Sometimes this won't be possible§ — in these cases you could try to find enzymes that leave the same overhang (i.e. have compatible cohesive ends).

There are other techniques that can be done if this isn't possible such as partially filling in the ends to create compatible ends or "blunting" where you fill in and/or chew of the overhangs and then do a blunt end ligation.

Another very common alternative is to use primers with restriction sites at their 5' ends and then PCR amplify the insert you want — this creates a copy of the insert DNA with whatever restriction sites you want at the ends.  

§For example there might not be restriction sites for the same enzymes in the correct places in both the vector and insert."
N/A,What happens to the restriction enzyme once the recombinant plasmid has been formed. Is it destroyed?,"You must remove or destroy the restriction enzymes (REs) before you ligate.  Otherwise the REs will just recut your newly ligated DNA.

This is often done by purifying the cut DNA — usually by running the digest (cut DNA) on an agarose gel and then cutting out the band of interest."
N/A,"I am quite confused as to the strand of the target gene, when we are cutting the gene are we pasting the whole gene into the plasmid or are we just pasting the part that the restriction enzyme has cut from the whole targeted gene?","We are not exactly "pasting" the whole gene, by which I mean that we are not applying ligase to the entire length of the gene. We are _inserting_ the gene, and to do that we are using ligase to paste the two ends cut by the restriction enzymes to the two ends of the plasmid."
N/A,What if there are not restriction enzymes on either side of the target DNA? Would it still be possible to use restriction enzymes?,"First, most vectors will have a region known as the "Multiple Cloning Site" (MCS) that can be cut with many different restriction enzymes† — this gives you more choices of enzyme and makes it more likely that you can find one that cuts near the ends of the region you wish to clone. 

Second, we often don't care if we clone a small amount of extra DNA , this means that we can search over a larger area than you might expect to find appropriate restriction enzymes.


If the regions flanking the sequence you want to clone don't contain any useful restriction sites you can use primers with restriction sites added to their 5' ends and then amplify the sequence using PCR§.  

This amplifies the insert you want and creates a copy of the insert DNA with whatever restriction sites you want added at the ends. 

There are many more tricks that have been developed, but adding sites at the ends of primers almost always works, so that is a very good one to know! 


Does that help?



†Note: There are hundreds of commercially available restriction enzymes recognizing many different sequences (many of which are palindromes, but not all).  

Among these the most commonly used are six-cutters (with 6 bp recognition sites — if you make a bunch of simplifying assumptions you can calculate that these enzymes on average will cut once every 4096 bp.


§Note: Polymerase chain reaction — you can learn more about this technique here:
https://www.khanacademy.org/science/biology/biotech-dna-technology#dna-sequencing-pcr-electrophoresis"
N/A,"If you put a same restriction enzymes to two samples of the same person's DNA. The resulting DNA strands after the restriction enzymes cutting should be the same size, right?

So, Can a forensic scientist use gel electrophoresis after this to determine if the DNA of the suspect matches the DNA found or to determine if the found DNA belongs to the criminal or the victim?","That is true, but for a typical restriction digest of human DNA you will get around a million different bands with a range of different sizes§ — on a gel this just looks like a smear of DNA and is of no use in identifying individuals.

In addition, two DNA molecules could be exactly the same size, but have different sequences — even if you isolated them (or detected them with a specific probe) you would probably not be able to distinguish them using any form of gel electrophoresis.

Individual humans are about 99.9% identical at the nucleotide level, so telling us apart by DNA requires relatively sophisticated techniques!

There are many different techniques to get information from this sea of DNA, if you want to know more about how this is currently done:
https://en.wikipedia.org/wiki/DNA_profiling


§ ~6.4 billion base pairs in a diploid human genome and a typically six cutter enzyme will on (a very rough) average cut every 4096 bp."
N/A,"Dystrophin is one of the longest genes, with 2.4 million base pairs. Does size have any impact on the size of the plasmid that needs to be used (does it have to be big enough to be able to cut a 2.4 million base pair section out of it?), does the plasmid simply expand to accomodate the gene? Isn't it quite likely that the gene itself would be cut up by the restriction enzymes? How could you assure that the gene would remain in tact and recircularize in the plasmid successfully with such a large gene?","A typical plasmid can accommodate inserts of any size up to total size of around 50 kb, but plasmids that are more than 20 kb are very difficult to work with and may require special transformation techniques.  The efficiency of ligation and transformation tends to decrease with extremely large inserts.

For large inserts there are different kinds of vectors (not plasmids) that can be used.

For an enormous insert like you are asking about you would need to use a type of vector known as an artificial chromosome.  These are specific to the type of organism in which you wish to grow the vector with insert.  For example you could use a YAC (yeast artificial chromosome) for the dystrophin gene.

To clone the entire dystrophin gene you would probably have to screen through a library of large fragments made by cloning randomly made fragments of genomic DNA (for example this can be done mechanically by passing the DNA solution through a needle).  

In practice you would probably get clones from an already made cDNA library (made by reverse transcribing mRNA) — this means you wouldn't need such a giant vector.  There are actually many different transcripts made from the dystrophin gene that produce different versions of the protein (known as isoforms) — the transcripts range from about 5-14 kb, much more manageable!

If you want to get an idea of the complexity of transcription from the dystrophin gene:
http://www.dmd.nl/isoforms.html"
Evolution of viruses,"I know this will most likely be impossible but is it possible for a virus to evolve rapidly enough to spread and wipe out life on earth, I mean the H1N1 pandemic looked bad enough right?","Viruses could never wipe out life on Earth. There are two reasons for that.

1) The more successful the host is, the more successful is the virus going to be. Humans are very widespread specie, which means that viruses that attack us have very good chances of spreading from one victim to another. But, as the population of their hosts declines, viruses will have more trouble in spreading. In the end, when there would be only a few isolated groups of people left, our imaginary deadly virus wouldn't be able to spread anymore.

2) Someone will be immune to virus. Those people will survive and continue the humanity. Their children will have their genes and they will all be immune to that specific virus. Spanish flu couldn't affect everyone, HIV can't affect everyone, none virus can affect everyone. It's just how things work."
Evolution of viruses,"If the HIV virus only has a lifespan of 52 hours, then wouldn't the HAART "cocktail" therapy be able to block the HIV virus for at least 52 hours, thus causing the death of the virus? Unless the HIV virus evolves and mutates within those 52 hours, which I highly doubt is always and/or mostly the case.","Good point. In that case, cocktail therapy would perfectly work and ensure no viruses escape."
Evolution of viruses,how does the virus affect human population?,"One virus can affect human population only if his infection becomes epidemic or pandemic.

Epidemic - a sudden increase in the number of cases of a disease to a level that is greater than the expected level in a given population in an area.

Pandemic -  an epidemic of world-wide proportions

https://www.infoplease.com/askeds/pandemic-vs-epidemic"
Evolution of viruses,What would happen if 3 viruses combined?,"Probably recombination of genetic material would happen.

Now, you may take 3 of the deadliest viruses in the world, but the resulting virus may be something harmless or low degree dangerous.

Or maybe each one may infect and cause disease on its own.

Genetical rearrangements can end up in any kind of results."
Evolution of viruses,How does the influenza virus affect the human body?,"Influenza virus has two different glycoproteins on it's lipid envelope called neuraminidase (helps the virus to leave the host cell)and haemaglutinin(aids the virus to enter the host cell).

In humans,haemaglutinin binds to (saliac acid) receptors on the epithelial cells in the upper respiratory tract and then the virus enters the cell through a process called 'endocytosis'.
Once in the cell , the negative sense Rna is replicated into positive sense ss rna which then helps in the process of progeny production.
Now viruses mutate very rapidly...Therefore the daughter viruses have slightly different glycoproteins than their parent and other progeny viruses.
This is why you can get flu every year or even twice or more in a year.

Now, neuraminidase is a receptor destroying protein which is why it aids the virus to elude from the cell by destroying saliac acid receptors."
Evolution of viruses,Why is it that the article says that the average human cycle is only 20 years?,When looking at generations of an organism you measure the average time between birth and having offspring.  For humans the figure of 20 years has been used but may very depending on the area and time period used.
Evolution of viruses,What does rna mean?,"RNA stands for RiboNucleic Acid.  It is described in the section on nucleic acids, over here:

https://www.khanacademy.org/science/biology/macromolecules/nucleic-acids/v/dna-deoxyribonucleic-acid"
Evolution of viruses,Can a virus wipe out the dinosaurs or cause a mass extinction event?,"I know there will be people who disagree with me, but i firmly believe the answer to both questions is no.

(Just as a side note, dinosaurs aren't extinct. Present-day birds are indeed dinosaurs.)

To cause a mass extinction, a virus would have to be able to infect a broad variety of species and cause disease with a mortality rate of 100 %. To my knowledge, no known type of viral disease has such a high mortality rate (even though some are close to that number!). The more lethal a virus is, the sooner it will run out of possible hosts. Earlier types of ebola virus were very lethal (the highest recorded mortality rate was 90 % during the 2003 epidemic in DR Congo), but those viruses didn't cause massive epidemics. Each outbreak had several hundreds of casualties.

Some scientists speculate that viruses could have caused several smaller extinctions in the history of life on Earth. Fossil records confirm that in between so-called mass extinctions, there were also smaller extinction events which happened during periods of relatively stable environmental conditions. So what was the cause? Even though some believe it was because of the viruses, as of now we have no evidence to support that claim.

That's just my opinion. The topic is still very controversial, and i would be interested to hear others' opinions."
Evolution of viruses,"Vaccines provoke the host's immune system to produce appropriate antibodies against the antigen in the vaccine. In relation to the section, Case study: HIV, why do vaccines for viral infections/viruses become ineffective over time? Is it because as viruses mutate, antigens develop on their surfaces which are different to the original antigens on the virus before mutation, and hence require the production of different antibodies to be granted immunity against the new, mutated virus?","A person's immune system is introduced to the protein on the surface of a dead or weakened virus so that it can be recognized as a foreign without the chance for the virus to overwhelm the immune system.  That person's immune system is primed to recognize and eliminate anything with that protein on it.  

If the virus mutates or is somehow changed so that the protein coat no longer has the same protein on its surface that person's immune system will not immediately recognize it as foreign and the virus has a chance to insert itself into a cell for replication before it is detected.  

A lot of research is needed to identify what parts of the virus protein coat are not likely to change over time so that a vaccine will continue to work even of the virus changes."
N/A,How can you tell if someone is a carrier?,"For Autosomal dominant and X-linked dominant, there is no question of a carrier since the affected allele will be dominant.
For *X-linked recessive*, the carrier will always be the mother/female. Since she has 2 X-chromosomes, one can compensate for the function of the other non-functional chromosome. The father/male can never be the carrier because he has only one X-chromosome, which, if affected, will be indicated on the pedigree chart.
For *Autosomal recessive* cases, it is a little tough to figure out the carrier without sufficient information. We can only know that the affected individual will be homozygous recessive, but we have no way to know if the unaffected individual is a dominant homozygote or a heterozygote (carrier). The only exception to this will be when one parent is homozygous recessive (affected). Then we can say that the offspring will definitely be carriers of the condition.
Hope that is helpful!"
N/A,"If a recessive trait shows up in all the generations, how can we figure out that the trait is recessive?","For autosomal recessive where there is no skipped generation, the other parent must be heterozygous for the trait, which would mean the children have a chance of having the recessive trait through inheriting the recessive chromosome from the carrier parent.
For X-linked recessive, the same is true, with one parent being a carrier. Ways to prove X-linked recessive are that if the trait is recessive, there will be mother-son and/or daughter-father links. This means that if the mother is affected, the son must be as he must inherit one of her affected X chromosomes. The same is true with daughter-father links. If the daughter is affected then the father must also be as she will inherit one of her X chromosomes from him.

Hope this helps someone."
N/A,how dow we know if it is autosomal?,Equal number of males and females affected i think
N/A,"So if a parent is a carrier but doesn't show, it has to be female as a male would have to express it. 
Am I correct?  
thank you for correcting me if it is required.","for sex-linked genetic disorders/diseases, you are correct. This is because the alleles expressing the disorder/disease are usually only present in the x chromosome, although some (few) genes are expressed in both x and y chromosome. This is due to the fact that the y chromosome is smaller.
If you are female, you have xx chromosomes, while you have xy chromosomes if you are a male. 
As mentioned earlier, genetic disorders/diseases are usually found only in the x chromosome. Hence, if the allele for the disorder/disease is recessive, to be a carrier, the person must be heterozygous. 
Because females have two x chromosomes, they can either get the disease (homozygous recessive), be a carrier (heterozygous), or just not have it at all (homozygous dominant). 
But for men, as they only have one x chromosome, only one chromosome can express it, so they can either have it (one recessive allele), or not have it at all (one dominant allele)."
N/A,whats the difference between x-linked and sex linked?,"Genes that are carried by either sex chromosomes are said to be sex linked.
Men usually have a combination of X and Y sex chromosome, while women have two X’s. since men inherit Y chromosomes, they are the only ones to inherit Y-linked traits.
Hope that helped 👍"
N/A,Can you have a male who is a carrier of an x linked recessive trait but doesn't express it?,"No that is not possible. Since males only get one x, it is impossible for them to be only carriers of a trait and not express them. Females, on the other hand, have two x chromosomes, which means they can be a carrier for an x-linked trait.




Hope this helps!"
N/A,how to understand whether a trait going within a pedigree chart is recessive or dominant,"If both parents do not have the trait and the child does, it is recessive. If one parent has the trait and the child does or does not, it is dominant."
N/A,"On a pedigree chart, how do you show that a person is a heterozygous carrier for a particular recessive allele that is not expressed in the phenotype? For example, how do you visually show that someone is an UNAFFECTED carrier for a genetic disorder?","I've seen carriers denoted by squares or circles that are half shaded, sort of like a full moon. 

Edit: What? Not a full moon, a half moon"
Overview of metabolism,"I'm curious about how ATP ended up being the energy currency for both plants and animals, why the same molecule? Is because of a common ancestor?
Is there any cell that doesn't use ATP as its "energy currency"?","Yes, it is because of the common ancestor. If there was a different, more efficient molecule then this would have been used instead. Keep in mind that in the long run only the most effective processes and molecules can transferred by generations."
Overview of metabolism,Why is it that ATP happens to resemble an adenine base in DNA? Are they related in any way beyond structure? Is the adenine base special? Is there another energy currency molecule like ATP? Can we artificially create another energy currency molecule?,"Both ATP and DNA are nucleic acids. All nucleic acids have 3 parts.
1. A pentose sugar(A sugar with 5 carbon molecules)
2. Phosphate group(s)
3. A nitrogen base. DNA and ATP have the same nitrogen base- Adenine, present.

ATP is specially called an energy currency because it has an easily breakable bond between 2 of its phosphate groups. There are several other triphosphate molecules present in cells like GTP and CTP that play various roles, but ATP is the main 'energy trading' molecule. 
Triphosphate molecules can be synthetically created under the right conditions, our cells will still rely on ATP."
Overview of metabolism,What is ADP (adenosine diphosphate)? How is it different from ATP?,"ADP is adenosine diphosphate 
and
ATP is adenosine triphosphate

In ADP there is 2 phosphate molecules
In ATP there is 3 phosphate molecules"
Overview of metabolism,"How can a molecule be "worn out"...? Does he mean they've outgrown their usefulness, or that they actually lose hydrogens or their groups come apart somehow over time?","Good question... they don't truly mean "worn out" as I think you are thinking... I think what they mean is that a molecule such as glucose gets broken down a few times to harvest some energy in the form of ATP... and then another molecule such as pyruvate, for instance, enters another metabolic process for recycling, harvesting both energy, and the use of the carbons for other purposes. See the citric acid cycle and this will start to make more sense ( https://www.khanacademy.org/science/biology/cellular-respiration-and-fermentation/pyruvate-oxidation-and-the-citric-acid-cycle/v/krebs-citric-acid-cycle )... but you are right... "worn-down" is confusing wording."
Overview of metabolism,"Does metabolism vary widely between people? I have heard that it does not, but it would seem that it would be highly dependent on the weight of an individual.","yes, it does, because you could have an illness and because of this illness one of your hormones gets produced more or less. And so your metabolism would be regulated as faster or slower."
Overview of metabolism,"Are ADP/ATP reusable? What I mean is, once ATP released its energy, does it transform back to ADP? If yes can this ADP be used again to form back ATP?","This is an essential cycle that never stops until you die: ADP gets phosphorylated in the mitochondria, storing energy in ATP, and the ATP gets used to perform cellular work, releasing its energy in coupled reactions, and transforming back to ADP."
Overview of metabolism,"So basically, Metabolism is the core of a cell. It's where all the work happens right?",Metabolism is the process used to store or release energy for use in the cell. It allows other essential chemical reactions to happen. it is the basis for all the work in cell. Try to think of it as a process not an area where reactions happen
Overview of metabolism,How energy is transfered from cellular respiration to the process that formats ATP. Is it in heat? If so doesnt it affect other molecules in the area? Thanks,"The majority of ATP is generated through ATP synthase at the end of the electron transport chain. In this process, a concentration gradient of protons (H+) is what is used to drive ATP synthase, not heat."
Overview of metabolism,Is the convergence of glucose to glycogen considered anabolism ?,"Yes - this is an anabolic process, promoted by the action of insulin on the hepatocyte or myocyte. The reverse - i.e. the hydrolysis of glycogen back into glucose-1-phosphate - is a catabolic process."
Intro to gene expression (central dogma),Why there are 61 codons? Why not 64??,3 of them are stop-codons which terminates translation (61+3=64).
Intro to gene expression (central dogma),what  happens to the mRNA after translation process i.e after proteins are produced?,"Hi Srinidhi,

After mRNA is translated, is either stored for later translation or is degraded. The eventual fate for every mRNA molecule is to be degraded. The process of degrading mRNA molecules happens at a relatively fixed rate.

Hope this helps!

Jonathan Myung"
Intro to gene expression (central dogma),"I'm still confused on two things. One, what is a TATA box? ANd two, what are the poly-a tails and 5' caps?",The TATA box tells where a gene begins so that it can be transcribed.  The Poly-A tail is a string of (mostly) adenines on the 3' end of the mRNA that gets eaten away by hydrolytic enzymes.  It is there so that the coding section of the mRNA doesn't get eaten.   (The hydrolytic enzymes themselves are there to protect from viruses.)   It is also recognized by the nuclear pore and allows the mRNA to leave the nucleus.  The 5' cap tells the ribosome where to begin translating.
Intro to gene expression (central dogma),What happens if a mRNA breaks? Will part of the protein be produced from the broken piece?,"Yes, most likely. If the context of the mRNA fits with the translational machinery (applicable  for the part of mRNA with the initiation codon only. The part without the initiation codon would not be translated), it might produce a truncated protein where the N-terminal part would be present but the C-terminal part (wrt to the original full length protein) would not be there.  However, most of these truncated proteins are recognized by the cellular repair machinery as abnormal and they are recycled. Sometimes though, such proteins can linger and may even participate in cellular functions (in a positive or detrimental way). Most likely source of truncated proteins is DNA rearrangement though, and mRNA breakage would not likely have a major effect (it might, depending upon the need of the original protein) as there would be other full-length mRNAs that would be translated into the protein of interest. Hope this helps."
Intro to gene expression (central dogma),Can a DNA end in 3' and the last molecule in this end is a phosphate? Why not??,"Phosphate is always attached to 5' end, and OH group to 3' end, because of the chemical structure of DNA."
Intro to gene expression (central dogma),It is essential that we need RNApolymerase for transcription. But to synthesize this enzyme we need transcription to happen .  So either RNApolymerase has to be present from the start or there should be another mechanism by which polymerisation of RNA happen. So how is it done for the First Time ??   How is it possible ?,"Some proteins and other molecules come from the previous cell, so the new cell can start its own production. Another thing is that some RNA can act as an enzyme and catalyzes reactions, though it occurs much less often."
Intro to gene expression (central dogma),Why do the number of A's on the poly-A tail vary?,"Each time a mRNA is read, an ''A'' of the poly-A tail is cut off, when there's no more ''A'' in the tail, the mRNA can be degraded. A mRNA (let's call it mRNA 1) can have more ''A'' in its tail than another mRNA (mRNA 2) depending on how much the cell needs that product  (1 instead of product 2)."
Intro to gene expression (central dogma),"It is mentioned in The Genetic Code, that,
One codon is a "start" codon that indicates where to start translation. The start codon specifies the amino acid methionine, so *most* polypeptides begin with this amino acid.

AUG codes for methionine, which contains sulfur. In the Hershey-Chase experiment, they made use of the fact that all proteins contain sulfur (because of the presence of methionine, I guess)
Are there proteins which do not begin with methionine?","There are, but this is (usually) due to removal or modification of the amino-terminal (start) methionine.  For example enzymes called "methionine amino-peptidases" cut off this amino acid from the beginning of some proteins — this is an example of what is known as a "post-translational modification".

It is also quite common for the first part of a protein (including the starting methionine) to be removed during processing — an example is secreted proteins that have their signal sequences removed during secretion or membrane insertion. 

Methionines can also be oxidized to form chemically related residues."
Intro to gene expression (central dogma),Why is amino acid sequence not directly read from a template DNA strand? Why do we need an intermediary mRNA ?,"This is an interesting question to think about, but "why" questions in biology are often very difficult to answer in a meaningful way.  

Below I've listed one possible evolutionary reason for the use of mRNA as an intermediary and then some advantages to this system.


One strongly supported hypothesis is that RNA actually came first — this known as the "RNA world hypothesis"§.  

This means that we use RNA because "life" has always used RNA and getting rid of it by evolutionary processes would be essentially impossible.  (You'd have to redesign life from scratch!)


Making mRNA also allows efficient production of proteins from a single gene.  

This is because many mRNAs can be transcribed from a gene and then each mRNA can be translated independently (and multiple times).


There are also multiple levels of regulation that can control how much mRNA is present, what parts of the mRNA get kept‡, and how frequently the mRNAs get translated.  

This allows cells to be much more responsive to changing conditions.


In addition, in eukaryotes DNA is kept in the nucleus, while translation happens on ribosomes (found in the cytoplasm).  

Having an RNA intermediate allows the information in DNA to travel from the nucleus to the cytoplasm.


There are probably more advantages that I haven't thought of — I encourage you to keep thinking about your question as you learn more about how cells work!


Does that help?



§Note: For more information see:
https://en.wikipedia.org/wiki/RNA_world


‡Note: For example alternative splicing in eukaryotes — to learn more see:
https://www.khanacademy.org/science/biology/gene-expression-central-dogma/transcription-of-dna-into-rna/a/eukaryotic-pre-mrna-processing"
Intro to gene expression (central dogma),What happens in a mutation where the Stop Codon is removed/altered? What does the cell do then? does it perform apoptosis?,"There are repair mechanisms. That one is called *Non stop Decay* that mechanism is able to detect mRNA which cannot be degraded because there is no STOP codon. It has to detach mRNA from the ribosome so it can translate the next mRNA sequence.

Nonstop decay is the mechanism of identifying and disposing aberrant transcripts that lack in-frame stop codons. It is hypothesized that these transcripts are identified during translation when the ribosome arrives at the 3′ end of the mRNA and stalls. Presumably the ribosome stalling recruits additional cofactors, Ski7 and the exosome complex. The exosome degrades the transcript using either one of is ribonucleolytic activities and the ribosome and the peptide are both released. Additional precautionary measures by the nonstop decay pathway may include translational repression of the nonstop transcript after translation, and proteolysis of the released peptide by the proteasome.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3638749/"
N/A,"And what about a cell/organism containing 2n - 2 chromosomes, supposing these two missing ones are paired up? Is this cell/organism considered aneuploid or euploid?","It is anueploid. The number of chromosomes for a species is fixed. For example, if a human cell had 44 chromosomes instead of 46, it is anueploidic in nature; nullisomic in fact (2n-2). Just because 44 is an even number doesn't mean it is euploidic! Hope this helped :-)"
N/A,How is chromosomal "rearrangement" different from "crossover"?,"Crossovers (recombination events) occur between homologous chromosomes (actually sister chromatids).  Meaning, recombination occurs between chr13 sister chromatid from Mom crossing over with sister chromatid of chr13 from Dad. 
Duplications and inversions can happen on a single chromosome. So, you can have a region of, let’s say, chr22 duplicated. Or that region might get inverted. Translocations can involve a region of (for example) chr13 swapping places with a region of chr22. 
I think the key is that crossovers are typically between homologous chromosomes whereas rearrangements are a broader category where they CAN be between homologs but there are also non-homologous chromosomal rearrangements."
N/A,"If there was an instance of a gamete with -1 chromosome and a gamete with +1 chromosome that joined together, would that individual be considered "normal"?",That’s a really good question. I think you’re right! Though the odds of that happening are extremely rare. Cool thought experiment though!
N/A,"If there's a diploid (2n) cell that went through the cell cycle but somehow all of the chromosomes stuck together and went to one daughter cell while the other daughter cell had no chromosomes, is the daughter cell with the chromosomes considered tetraploid (4n) at that point because there are now 4 chromosomes per homologous pair, or would it actually be considered 2n+2n? For instance, if n=12, then it would be 2n+24?","The likelihood of that actually happening is very rare. But that does not mean it's impossible, there's never a 0% (or 100%) of anything in science (in most cases). 
If that was to happen it would be called tetraploid a form of polyploidy. It's not likely to happen but it has happened a species of frogs (from the genus Neobatrachus) has been found where they actually contain 4n instead of the usual 2n. The probability of one of these mutations to occur is low, and then to have this happen [at least] twice and to find each other to mate was probably close to 0%."
N/A,does nondisjunction automatically lead to one monosomy and one trisomy?,"Mitotic nondisjunction can occur with the inactivation of either topoisomerase II, condensin, or separate. This will result in 2 diploid daughter cells, one with 2n+1 and the other with 2n-1.

If nondisjunction occurs during meiosis I, it is the result of the failure of the tetrads to separate during anaphase I. At the end of meiosis I, there will be 2 haploid daughter cells, one with n+1 and the other with n-1. Both of these daughter cells will then go on to divide once more in meiosis 2, producing 4 daughter cells, 2 with n+1 and 2 with n-1.

Nondisjunction in meiosis II results from the failure of the sister chromatids to separate during anaphase II. Since meiosis I proceeded without error, 2 of the 4 daughter cells will have the normal haploid number. The other 2 daughter cells will be aneuploid, one with n+1 and the other with n-1. 

_If meiotic nondisjunction, then yes. The result is monosomy and trisomy._


https://www.ncbi.nlm.nih.gov/books/NBK482240/"
N/A,Is translocation essentially formed from the process of crossing over?,"Good question!

Translocations can be the result of crossing over between sequences that are similar but located on different chromosomes.  

One source of these events are the repetitive elements§ that make up most of the genome in many species including humans.


Another way that translocations can happen is if the DNA is broken in multiple places — e.g. by exposure to radiation. 
 In some cases the DNA will heal, but with the "wrong" parts of chromosomes stuck together.


§Note: A major component of the repetitive DNA comes from the many different families of transposons — pieces of DNA that can copy themselves to new places within the genome."
N/A,"What happens if nondisjunction occurs during mitosis? I assume the cell would likely undergo apoptosis, but I'm not sure...","In many cases, polyploidy takes place and one cell ends up with zero chromosomes, while the other one has doubled garniture.

It leads to apoptosis of thew one cell without chromosomes."
N/A,I think the diagram for nondisjunction in meiosis I is incorrect. It looks like sister chromatids failing to separate during mitosis.,"Yes, it is correct. Maybe it looks like that but it is correct. Look at it again. :)"
N/A,"If you heavily breath on a plant, will it help growth considering it needs CO2, water, sunlight?","In an open environment, probably not by any noticeable amount. However, if you put the plant in a sealed container such as a greenhouse and sit in the greenhouse for a while then the CO2 concentration will rise. So in a sealed container the answer is yes but just a plant sitting in your house or outside breathing on it won't make a huge difference."
N/A,how does the plant reléase the oxgen,through stomata on the back of it's leaves
N/A,"Calvin Cycle: ATP is used to create sugars that the plant will use to grow and live.

My question is where does the ATP come from? Light-dependent reactions make ATP with the light energy, but the Calvin cycle seems to already have it so that it can convert into sugars... Does the Calvin cycle happen after the light-dependent reactions occurs or is the Calvin cycle independent? An example of my question:

Does photosynthesis happen like this?

LDR: Light energy + H2O = ATP + NADPH + O2 

And then after that:

Calvin Cycle: ATP + NADAPH + CO2 = sugar

? 
Sorry if I got some things wrong @~@","The Calvin cycle is dependent on the Light-dependent reactions, and almost in the same way Light-dependent reactions are dependent on "The Calvin Cycle".  The "light-dependent reactions" receive light, and provide energy for the Calvin cycle. After used by the Calvin cycle, the molecules go back to the thylakoids to be reenergized in a way. So it is almost like a constant cycle between the two areas. For clarity refer to the diagram given above."
N/A,what is NADPH?,the electron carrier for photosynthesis. NADH(without the P for photosynthesis :) ) is used in cellular respiration. They carry electrons to and fro and are subsequently oxidized or reduced. They need to carry the electrons because electrons are high charge substances
N/A,""Light energy is captured by chloroplasts and stored as ATP"
ATP is need to make sugar, BUT ATP is already compose of sugar. Where do this sugar come from?","ATP is not sugar, it is a nucleotide. The carbon atoms needed to build sugar molecules are taken from the CO2 that the plant absorbs. CO2 is converted into glucose during the Calvin cycle, which is an anabolic pathway and therefore needs ATP to actually build up the molecules."
N/A,during what stage of photosynthesis are ATP and NADPH converted to ADP + Pi and NADP+,"During the Calvin Cycle, the ATP and NADPH are broken down into ADP, Pi, and NADP+ to provide energy for the cycle. Then, after passing through, the used-up molecules react to bind together into ATP and NADPH again."
N/A,Why are *photosynthesis and cellular respiration* are not simply reversal of each other?,They are in a way. Photosynthesis uses carbon dioxide and water to make oxygen and high energy sugars like glucose. Respiration takes in oxygen and glucose and turns it back into carbon dioxide and water.
N/A,""Light energy is captured by chloroplasts and stored as ATP" 
ATP is need to make sugar, BUT ATP is already compose of sugar. Where do this sugar come from?","ATP itself is not composed of sugar.

When light energy is captured by the chloroplast, it, along with carbon dioxide and water, gets converted to ATP, NADPH, and oxygen (light-dependent reactions). The ATP and NADPH then enter the Calvin cycle and fuel the synthesis of molecules that _eventually_ become sugar molecules. 

These sugar molecules can then be sent to the plant cell's mitochondrion to undergo cell respiration, which produces even more ATP that can be used to fuel the plant cell's many complex processes."
N/A,How do trees survive when they lose their leaves in the winter? How can photosynthesis still occur without the chloroplasts in the leaves? Do they keep energy in storage to use during the season?,"Deciduous trees store energy and resources within their bark, which can be used during the winter months when they have no leaves. Additionally, their physiological process change and slow down, as to not consume as much energy compared to the warmer months. It's a bit like hibernation for trees, where they stock up on resources and decrease energy consumption to make it through the winter. 
Evergreen trees (like the firs you see during Christmas time) have special adaptations to the cold that negate the need for this period of dormancy.

Does this help?"
N/A,does bacteria have a Hayflick limit (limit of division) like normal human cells do?,"Okay, so this is very complicated question to answer and it requires a lot of molecular biology. If any part of my answer is incomprehensible, please let me know.

The main difference between our genome and bacterial genome is that our DNA molecules are packed into structures we called chromosomes and they are linear, meaning they have a starting point and an end point. Bacteria don't have chromosomes and their DNA is circular.

Due to the mechanism of DNA replication, our DNA isn't completely replicated. That is, "the mother" DNA and "the daughter" DNA (those are not official terms) aren't identical. "The daughter" DNA will always be a bit shorter.

What does that mean for us? How much of DNA do we use per one cell division? Well, on the both ends of our linear DNA there are what we call telomeric regions, or telomeres. Those are long repeated sequences that don't code for any protein. Their only purpose (as far as we know) is to save the important part of DNA from being lost during the replication process. Instead of losing important genes, we lose a small part of telomeres in every cell division. After 40 - 60 divisions telomeres reach critical length and they can't be sacrificed anymore. This is where DNA replication and hence cell division stop happening.

Because bacteria have circular DNA, they don't have those problems. Their polymerase can replicate an entire genome without losing one single part of it. They don't need telomerases and therefore they don't have any limits in cell division. If a bacterial specie had Hayflick limit they would stop reproducing after some number of divisions and that would be the end of the specie.

What you should ask now is: what about cancer cells? They seem to be immortal and divide without any limits. What about single celled eukaryotes, like amoeba? They have chromosomes too (linear DNA) but they don't have Hayflick limit. The answer to those questions is very interesting and rises a lot of possibilities for us. There is an enzyme called telomerase. This enzyme extends telomerases and prevents them from being lost after a number of replication cycles. It works forever in cancer cells, but for some reason it stops working in "normal" cells. Why? We don't know yet, but we're on our way to find that out. This means we could treat cancers with telomerase inhibitors - if we prevent telomerase from extending their telomeres, cancer cells will stop multiplying after reaching Hayflick limit. Could we treat our normal body cells with telomerase and prevent them from reaching the limit? The answer might be yes. Would that mean we could become immortal in such a way? We don't know yet, but we're certainly going to dig deeper into the problem.

Thanks for asking such an interesting question!

Alex"
N/A,Can bacteria get cancer if so what happens?,"No, bacteria cannot get cancer. Cancer is the uncontrolled growth of cells in a multicellular organism, and bacteria are single cellular."
N/A,what is the advantages of prokaryote with absence nucleus,"Essentially, prokaryotes are simpler than eukaryotes. This may not sound like an advantage, but it means that it's really easy to make new prokaryotes, which means that prokaryotic cells reproduce much faster than do eukaryotes. Also, this faster reproduction means that these cells can adapt faster as there are faster generations, which can be an advantage."
N/A,"how were the fossil of the prokaryotes found?
Here it says that fossils of prokaryotic were found, how was it understood that it was a prokaryotic?
i dont think that something so small like a bacteria could actually leave a imprint like a fossil.
thank you","Bacteria generally don't leave fossils, and at most we can infer their existence based on evidence of their effects on other fossilized creatures, such as infections. However, some bacteria have been known to create iron or clay sort of shells that survive after the bacteria has died, creating a sort of model of the bacteria. Bacteria have also been found in fossilized amber, and some cyanobacteria can create stromatolites, which are rocks created by cyanobacteria, calcium carbonate, and the surrounding sediments. Stromatolites can be fossilized, and when cut open, there are sometimes layers or fossilized cyanobacteria inside, protected by the stromatolite."
N/A,can eukaryotes have flagella and pilli? or is that only for prokaryotes?,"Yes, and the flagella of motile bacteria differ in structure from eukaryotic flagella. 


However, Eukaryotes do not have pili or fimbriae."
N/A,"Do Prokaryotes, specifically Archea, have ribosomes?","Yes they do.  Ribosomes in prokaryotes are similar to, but smaller than, those in eukaryotes."
Enzymes review,Do enzymes in the human body have the same optimal peak rate?,"No, the optimal peak varies across enzymes and is dependent on the enzyme in question.
For example, pepsin typically functions optimally in the acidic conditions of the stomach while trypsin prefers the more alkaline conditions of the small intestine"
Enzymes review,"So, an actual field question! But this section got me wondering.

I take lactase to assist in the breakdown of the few milk products I consume because it appears I'm lactose intolerant. I'm instructed to take one (or two, if one doesn't seem to be enough over time) every time I consume dairy.

Why do I need to continue to take these over time? Enzymes are reusable, right? They're not reactants. They should stick around after managing my lactose intake. So why do I need to keep taking these things every time I consume dairy? Isn't there a point after prolonged use where there should be a sufficient buildup of lactase enzymes present in the gut to address this issue long term?

Is my immune system doing away with the lactase for some reason?  Do I have really garbage gut pH? What's going on here?","Take this with a pinch of salt, but I am pretty sure that enzymes do not last forever. They will eventually wear out, and will be broken down into amino acids for other proteins. The supplements may also have to fight through the acidity of the stomach, and if you are warmer than usual, it is more likely that the enzymes will denature. Because they will wear out or potentially get damaged, you would need to replenish these enzyme stores to ensure that your body can break down the lactose found in dairy.

Like diabetes, you would have to keep taking the supplements in order to manage the condition. Again, though, please take my answer with a pinch of salt."
Enzymes review,Can an enzyme have more than 2 active site?,"Yes they actually can-- Here's a bit I found on Reddit ( any search will bring up a number of more reliable sources saying the same thing however ;D)

Yes. Some enzymes will bind a substrate and then there will be a change in its quaternary structure that could open up another active site for a different type of substrate. Other enzymes have more then one of the same active site and they can bind multiples of the same substrate.

Hope that helps!"
Enzymes review,where are enzymes created? in the cell?,"Like all proteins they are produced by *ribosomes*, which are in the cytoplasm (the part of the cell that is outside the cell nucleus). After an enzyme is synthesized it may be modified in the Golgi apparatus or elsewhere in the cytoplasm."
Enzymes review,What is the pH?,"In chemistry, pH is a numeric scale used to specify the acidity or basicity (alkalinity) of an aqueous solution. It is roughly the negative of the logarithm to base 10 of the concentration, measured in units of moles per liter, of hydrogen ions. More precisely it is the negative of the logarithm to base 10 of the activity of the hydrogen ion.

You can also learn more about it here, on KA:https://www.khanacademy.org/science/high-school-biology/hs-biology-foundations/hs-ph-acids-and-bases/v/introduction-to-ph"
Enzymes review,What are the different types of enzymes and what are the differences?,"If you are asking the types of enzymes by *how* they break reactant, there are *7 types* (some websites say there are 6 because after 2018, one type was added (-_-)). 
Oxidoreductases, Transferases, Hydrolases, Lyases, Isomerase, Ligases, and Translocase. (Maybe you don't need to learn them at this point.)

If you are asking the types of enzymes by *what* reactant they break, there are...well there are many (it is said there are about 2000 kinds). 
I have never counted but maybe there will be 20 ~30 enzymes you will see learning biology. One third of them will be about plants and the rest will be about human body. Don't worry, you will learn them step by step.

As you can see the above, basically the difference is determined by  how they break or what they break."
Enzymes review,"In the last paragraph it mentions that an enzyme is not a reactant.
What is a reactant?",A reactant is a substance that changes in a chemical reaction.
Enzymes review,Why can enzymes work again after being inactivates but may not work after being denatured?,"When they are denatured, the shape of the protein is changed permanently, thus the active site is changed permanently as well. Therefore the enzyme cannot work like it used to. But an inactive enzyme is caused when the temperature is too low for example, the enzyme is fine because it is really cold, there are virtually no collisions/very less collision, meaning that no reaction is taking place. As there is nothing wrong with the enzyme, if you just merely increase the heat, the enzyme will work as it should because there will be collisions."
N/A,"I'm sure RNA interference has been tried in the treatment of Covid-19. Is there a particular reason why the process worked for one virus, Ebola, but does not work for another virus, Covid-19? Granted, they are different types of viruses, but the idea is to interfere with the purpose of mRNA in general not a specific type of mRNA.",if it interfered with the purpose of mRNA in general we would all be dead.
N/A,"The 5'Cap G is different than a regular G found in the DNA or mRNA, right? It's methylated? Does that affect the function or reading at all? Does that stay on the mRNA for translation?",It is methylated so it would be a little different than DNA/mRNA. It does not affect the function/reading because the ribosome docks onto the Shine Dalgarno Sequence (in prokaryotes) and the Kozak Sequence (in eukaryotes). Once it docks here it will start transcribing at the start site (AUG). It does stay on the mRNA while translation happens and actually serves as a site for the docking of proteins but that is beyond the scope of the material on the test.
N/A,"Is there a reason that a deoxyribose and Thymine are changed, in order for mRNA to leave the nucleus? I can't see how that one hydroxyl or, moreso, that methyl group makes a difference; is this known?","This is kind of a basic explanation, and it would be hard to get into the nitty gritty details, but I hope it helps you understand.
Thymine is changed to Uracil because Uracil is easier to produce. DNA contains Thymine because it is more stable, but RNA does not need to be around as long.
The hydroxyl group on RNA is there for a similar reason. This group makes the molecule more susceptible to hydrolysis (to recap, the splitting of a molecule using water), so RNA can be more easily decomposed. DNA uses deoxyribose because, like Thymine, it is more stable.
Even though this question is 3 years old, I hope it helps people who might be wondering the same thing."
N/A,"If the introns are going to be removed anyways, what's the purpose of having them in the DNA?","Here is the awnser that I found in my textbook
Introns are crucial because the protein repertoire or variety is greatly enhanced by alternative splicing in which introns take partly important roles. Alternative splicing is a controlled molecular mechanism producing multiple variant proteins from a single gene in a eukaryotic cell."
N/A,is there videos and power points?,No unfortunately. But there is a transcript under the video
N/A,"In the mRNA processing, does the slicing of pre-mRNA goes before the Protection phase, or the other way around?  Thanks!","I've always understood that they are near simultaneous. The important fact is that the primary RNA transcript (pre-mRNA) must have the Introns spliced out (splicing phase), and have the 5' cap and 3' Poly-A tail added (Protection phase) to become true mRNA. Only once these changes have occurred can the mRNA exit the Nucleus to be translated into a protein."
N/A,"on the answer to the second question macias said that the ribosome attaches to the shine dalgarno sequence and then starts transcription  .
i was wondering if that is in both transcription and translation i though it was only translation can some one clarify please.
also the video on translation does mention it  but not on transcription.","Let's see if this helps:
(1) The *Shine Dalgarno sequence* is in a prokaryotic mRNA.
(2) *mRNA* and *ribosome* are only involved in the _*translation process*_
(3) Because of (1) and (2), *Shine Dalgarno sequence* does not apply to the _*transcription process*_"
Cell-cell junctions,What sorts of cells does the blood/brain barrier consist of? I believe chemotherapy molecules are often too big to get through to treat the brain.,Each nerve cell in the brain must be fed by blood or the cells will quickly die of oxygen deprivation.  I believe you are perhaps reffering to a cappilary system that sustain these cells in a way that compartmentalise them as much as possible. It is also possible because of the late hour that my mind makes me write b.s. and I'm sorry if the answer is misleading or not helping...
Cell-cell junctions,Could someone thoroughly explain to me what desmosomes are?,"A desmosome, also known as a *macula adhaerens*, is type of cell-to-cell adhesion.

Desmosomes resemble plasmodesmata in plant cells because they also provide little space through which membranes of to adjacent epithelial cells are connected. Hiwever, in the case of desmosomes, intermediate filaments of cytoskeleton are connected. How?


First, desmosomes, have its connecting proteins (just liek the other types of cell-to-cell connections in animal cells). Their proteins are called _cadherins_.

Cadherins are attached to both cells and they protrude the cell enterior and anchor on intermediate filaments (cytoskeleton). Precisely, they attach to cytoplasmic plaque, which connects to intermediate filaments.

Is it clearer now? :)"
Cell-cell junctions,Do desmosomes and cadherins depend on one another?,"Yes, the cadherins are a big part of the desmosomes"
Cell-cell junctions,Can bacteria form junctions with each other in order to exchange genetic material?,"Bacteria can form junctions with each other to exchange genetic material. This is known as conjugation. Genetic material is exchanged between bacteria through conjugation tubes or sex pilus. One bacterium usually donates its DNA while the other receives it.
For more information check out this link:
https://www.quora.com/Does-hydrogen-atom-prefer-to-lose-or-gain-an-electron"
Cell-cell junctions,What is the difference between desmosomes and tight junctions?,"Like aria said in the comments, desmosomes allow stretching and are in more complex organisms. This is because with desmosomes, cells link up together, and the intermediate filaments have a connection in between. This allows for strength, tightness, and flexibility in the tissue. Tight junctions prevent water from leaking out of the cell and are present in the bladder."
Cell-cell junctions,"What are the functions of Cadherin ? Can you help me to answer this question by writing in points, not descriptive pattern? Thanks!","cadherins are basically proteins attatched to the cytoplasmic plaque of animal cells. They act as a sort of tie that prevents cells from seperating under pressure. 
This is probably a really dark way of putting things but think of it as two scenarios like this:
1) you bind two people together by their wrists or bodies with a rope.
2) you bind two people by skeletons. 
its harder to seperate the two bound by their skeletons no matter how far away they stretch, ryt?. its something like that. it connects two cells, say cardiac cells, by their adjacent cytoplasmic plaques which are in turn connected to the cells' cytoskeleton, which holds them together as they stretch.
Hope you got an idea:)"
Cell-cell junctions,What is cytoplasmic plaque and what are intermediate filaments and how exactly do they work with the cadherins to anchor the junction between epithelial cells?,"Cytoplasmic protein plaque is protrusion of cytoplasma which from luminal side binds intermediate filaments (ctoskeleton) and from the other sides binds cadherin. Cadherin binds to another cadherin which holds cytoplasmic plaque and binds to another intermediate filament in lumen of second cell adhering to the first cell.


Cytoplasmic plaque plays scaffolding role.


https://www.histology.leeds.ac.uk/cell/assets/desmosome_diag.gif"
Cell-cell junctions,"Is the "junction" between the nuclear membrane and the E.R. considered a junction?
If yes, what kind of junction is it?
If no, it is not a junction, what is it?
Many thanks!","I don't think there is _any_ junction since endoplasmic reticulum membrane is _continuous_ with the external nuclear envelope. When something is continuous means it is attached directly, we are speaking of one bigger entity."
DNA structure and replication review,"What is the difference between:
Replication fork
Replication complex
Replication unit
Origin of replication 
Replication bubble","The replication fork is the branched (forked) DNA at either end of the replication bubble.

The replication complex is the group of proteins that help synthesize the new DNA strands.

A replication unit is any chunk of DNA that is capable of being replicated — e.g. a plasmid with an origin of replication (ORI) is a replication unit.  Alternatively, this can also mean a region of DNA that is replicated together.

An ORI is a DNA sequence at which replication is initiated.  ORIs are recognized by the replication machinery — specifically the pre-replication complex.

A replication bubble is the region of DNA where new strands of DNA have been or are being synthesized.  A replication fork is found at each end of a replication bubble.

You can find more details and (many) of these terms in this free online book chapter:
https://www.ncbi.nlm.nih.gov/books/NBK26826/


This seems like a reasonable source for quick definitions of terms:
http://dictionary.sensagent.com/"
DNA structure and replication review,What does it mean to have a 3' end as opposed to a 5' end?,"5' ends with the phosphate, and 3' ends with the deoxyribose sugar."
DNA structure and replication review,"1-Unwinding the (origin of replication) is done when certain proteins are attached to the site (which is AT rich) , I mean not by Helicase , right?


2-who removers the primers in the lagging strand?
Is it the same DNA pol ?

3-Why does polymerization rate in prokaryotes is faster than in eukaryotes?","1) My understanding is that many proteins are involved in unwinding the origin of replication including at least one helicase.  
Note that helicase is a type of activity, not a single protein — for examples and more details see:
https://en.wikipedia.org/wiki/Helicase

2) The primer is removed by an endonuclease that recognizes RNA:DNA hybrids (RNase H) and then exonucleases that remove the RNA nucleotides.  In _E. coli_ this exonuclease activity is performed by DNA polymerase I.

3) Eukaryotic DNA is generally much longer, more complex (typically multiple linear chromosomes with ends vs. usually circular DNA), and is highly packaged into nucleosomes (and higher order structures).  All of these factors mean that it takes longer to replicate eukaryotic DNA.


References and further reading:
https://www.ncbi.nlm.nih.gov/books/NBK9940/

https://sydney.edu.au/science/molecular_bioscience/PHAR2811/PHARlectures/PHARlecture5/PHARlecture5notes.pdf"
DNA structure and replication review,which enzyme breaks the h bonds?,"As enzymes breaks the hydrogen bonds that hold the double helix together,so the two strands unwind and separate and that enzymes is helicase"
DNA structure and replication review,is there any case in which primer exist in DNA after replication,"Usually, there is not because DNA Polymerase always replaces the RNA nucleotides with the DNA nucleotides. Unless for some reason, the DNA Polymerase fails to function, it may happen but proofreading should catch it. Otherwise, there should not be any errors."
DNA structure and replication review,lagging strand how to memorize it,"leading strand synthesized continually whereas lagging strand is synthesized in fragments(Okazaki fragments)
Memorize it this way: Lagging strand lags behind and does his homework(replicating dna) in bursts when he feels like it. Leading strand leads the way and is a good model. lol"
DNA structure and replication review,"I may be understanding this wrong, but when DNA separates, a new strand forms that is identical to the one it separated from. So, wouldn't those double helices of DNA be identical to each other?","When DNA separates to replicate, DNA polymerase (and the other enzymes) attach new bases to each strand, and those new bases are each complementary to the template strand, matching the other original strand that the template strand just broke off from. The end result of this is two completely identical DNA molecules, each having one strand from the original DNA and one strand of new DNA made from surrounding materials, put together by DNA polymerase and other enzymes."
DNA structure and replication review,isnt the leading and lagging strand different because when unzipping the DNA the halfs are pointing in oppisite directions of one another?,yes the leading strand goes towards the replication fork and the lagging strand goes away from the replication fork in okazaki fragments
Genetic variation in prokaryotes,How does a transposable element do the cutting and pasting? Does it use an enzyme from the cell or does it have its own enzyme?,"Many§ transposable elements will encode a transposase — an enzyme to catalyze its movement to another location.  The exact mechanisms vary among different types of transposons, but cutting and pasting is done by some of them.

You can read more about this in these wikipedia articles:
https://en.wikipedia.org/wiki/Transposase
https://en.wikipedia.org/wiki/Transposable_element

§Note that transposons can also have parasites — these are known as non-autonomous transposons.  They tend to be smaller versions of the autonomous transposons and "steal" the enzyme produced by autonomous transposons to move themselves."
Genetic variation in prokaryotes,Can you tell the enzyme how is catalyzes transformation,"Good question, but there is not one specific enzyme responsible for transformation. Transformation requires the expression of about 40 genes, each of which could express a unique protein. It's a complex process and people are still working out the details of how it actually works. Some of the proteins involved are probably enzymes but we don't know exactly what they all do."
Genetic variation in prokaryotes,"Why are the process of transformation, conjugation, and transduction “easy” to do with prokaryotic cells like bacteria, but much less commonly encountered in eukaryotic cells?",Because prokaryotes' DNA exits as a single loop and is relatively shorter than for eukaryotes due to the fact that multicellular organism have a greater need for a variety of proteins.
Genetic variation in prokaryotes,What is the relationship between a sex pilus and a mating bridge?,"A mating bridge is a connection between two bacterial cells that provides a passageway for DNA in bacterial conjugation.
A mating bridge is different from a sex pilus, which is a structure made by an F+ strain bacterium in bacterial conjugation

Sex pilus acts as an attachment site that promotes the binding of bacteria to each other. In this way, an F+ strain makes physical contact with an F− strain. Once contact is made, the pili shorten and thereby draw the donor and recipient cells closer together. A conjugation bridge is then formed between the two cells, which provides a passageway for DNA transfer."
The genetic code,"Are Glutamate (Glu) and Glutamine (Gln) interchangeable? or there is something wrong with the example on reading the codon table, because CAG codes for Gln, not Glu.","They are 2 different amino acids, so no they cannot be use interchangeably."
The genetic code,When does the tRNA know when to use AUG as a start codon and when to code Methionine? Are there other influencers,"Excellent question!

Translation is quite bit more complicated that this introductory material can cover.

The sequence of the mRNA around a potential start codon influences whether or not it will be used§.  These sequences are bound by proteins that help guide the ribosome to assemble at the correct place to start translation.
(In fact, codons other than AUG are sometimes used as start codons!) 

This is covered in a bit more detail in another article:
https://www.khanacademy.org/science/biology/gene-expression-central-dogma/translation-polypeptides/a/the-stages-of-translation

I also encourage you to look at some of the references for that section, which will help give you more detail on this high complex process that is still being actively studied.


§Note: The mechanisms are very different in prokaryotic and eukaryotic organisms — they can also vary between different species and even for different genes!"
The genetic code,would it be possible to use the "coding language" of RNA to synthesize chemicals?,"Yes, proteins are made of amino acids which are coded within the DNA sequence, so yes, recombinant DNA may be used.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2845543/


Also, there are already efforts to use DNA as a digital store of information:
https://www.youtube.com/watch?v=NsfuBSsF1Fk
https://www.ebi.ac.uk/research/goldman/dna-storage
https://www.nature.com/news/how-dna-could-store-all-the-world-s-data-1.20496"
The genetic code,"Why is `AUG` a start codon and `UAA` , `UGA` and `UAG` stop codons?",No one knows exactly why evolution chose which specific codons represent each amino acid.  This likely happened in an arbitrary manner very early in evolution and has been maintained every since.
The genetic code,I have heard that the 3' end of mrna is rich in stop codons so that in case of a mutation the peptide gets released but I am unable to find an article about that. Can someone confirm if this is true or not?,"You are correct.

Usually nucleotides present in mRNA channel downstream the A site help determining the future.
 The expected hierarchy in the intrinsic fidelity of the
stop codons (UAA>UAG>>UGA) was observed, with
highly influential effects on termination readthrough
mediated by nucleotides at position +4 and position
+8. 


https://watermark.silverchair.com/gkx1315.pdf?token=AQECAHi208BE49Ooan9kkhW_Ercy7Dm3ZL_9Cf3qfKAc485ysgAAAlcwggJTBgkqhkiG9w0BBwagggJEMIICQAIBADCCAjkGCSqGSIb3DQEHATAeBglghkgBZQMEAS4wEQQMiuKY1yQvGdfscjqKAgEQgIICCmJx0U3b-ecY2oxn1QYcqc6a6QXYNlX9FCUngn9zbbPC6TWDitK20Cl65tVkDb6ARGxakyB0TEEbjl2c5gg6rg2qBTOI7x9Vy8585GIls0cxO0YkUJjM5nl4tIHHoOTo9GSTyGAW827IJoH0xMHIBZC6tWuwCiR6jqOaN1HrKwsQVlraRvdQyJb9eCxJcVkE-No67IraffHateNr-8Xin1lgr4vGQAfQXU9PjGDIReo41KpdTVC4ROs0BWMsX5SiIrOq0CT2I_d8aPe3BoxnnN5Vwdb-tIzNAmBaBiIlyQa2NBwBvWioTTqoTIlkqhVX4USGtnaevTT72XcMrlPPZm-hY4KtVOzqRFEiJZvumj8GsYH5VL8XA-vT_ZHLfZxscDuS2AaEIts5h3YNsYXoB_VtpESmnQzfU8QXfocNOamKdN2HvESBttG-e1DGLH7er75hfzVjy99742-LR77NeJApSW8uphwYIJGkdiRMkKm33yLfYQi2FH7UjzzmPuBukRAYG9gDCtTozVMKGh25SeJhmtQ2ASplMszMGS0eHfdOEFXsP3xM7Y_qNU8Bp3Er0_1f-3QzZrvK4R0HBzKUFaBhBxzm36nDFx7kMyvupiurNRcLbGuj65jWL5ezK4Rel-eplBH3Zv087GDxgvSEss9ZFntFfyS1O0Ra3yW8F6OFRZNJY86-N0puzw

There are also cases where there are mutations non-stop codon so transcription cannot stop.

https://www.cell.com/cell/pdf/S0092-8674(16)30788-7.pdf"
The genetic code,"In the section, Reading Frame, frameshift  mutations are mentioned.

Point mutations will shift the frame of reference.
The insertion or deletion of three(or it's multiple )bases would insert or delete one or more codons or amino acids, without shifting the reading frame. But addition or subtraction of amino acids from a polypeptide would transform it..... How is this dealt with?","How small "in frame" indels (insertions and deletions) are dealt with depends on many factors including where in the gene the indel happens — so the short answer is "it depends".

For example, if you disrupt the catalytic site of an enzyme the effect will probably be the same as if the protein was never produced at all — this is likely to lead to a complete loss (assuming the mutation is homozygous) of that enzyme activity — the effect on the cell could be anything from fatal to unnoticeable (depending on how critical that enzyme activity is in that cell).

On the other hand, some proteins have loops of amino acid sequences on their surfaces that do not appear to be critically important and making those loops a little longer or shorter might have little or no effect on the protein function.

(Note that we only use "point mutation" to refer to mutations that change a base — not for deletions of a single base pair.)"
The genetic code,"So the genetic code is the mRNA sequence of bases and it starts from the 5' to the 3' and it is the coding strand. Now if we want to find the tRNA sequence, which is the template or the non-coding, for ACU, for example, we start at 3' to 5' and we write it as TGA? Is that the correct way or am I missing something?","Just one correction. You do not write it TGA but UGA.

There is no Thymine in RNA, but Uracil. Everything else is right. :D

화이팅!
같이 공부합시다."
The genetic code,Are proteins made at the same time as new DNA? Does DNA unwind when it makes proteins?,"The DNA that isn't being utilized is very tightly packaged, and contrarily, the DNA that is being utilized is unwound, so yes, in a sense, but your choice of words is slightly off... DNA unwinds to be transcribed into RNA, which eventually makes its way to a ribosome, which then gets translated into protein. So you are somewhat correct, just your word choice is off. Don't forget the central dogma: DNA->RNA->protein, that middle molecule is essential."
Polygenic inheritance and environmental effects,how environment causes pku?,"The environment doesn't actually cause the PKU -- that is genetic. But the environment can cause it to express in the phenotype -- create symptoms -- based on the environment. The PKU gene simply causes a person to be unable to properly process phenylalanine (they lack an adequate amount of the necessary enzymes). If that person eats foods that are high in it, they can begin to express symptoms of that genetic mutation. If they limit or eliminate those foods, they often will have no symptoms."
Polygenic inheritance and environmental effects,"What's the difference between polygenic and epistasis?
It sounds like in both of them, multiple genes affect one trait.","While a polygenic phenotype can occur without epistasis, if you have epistasis you must be dealing with a polygenic phenotype.

Polygenic just means that there are multiple genes involved in a phenotype.  
Epistasis refers to situations where one allele masks the phenotypic effect of one or more alleles of another gene."
Polygenic inheritance and environmental effects,how are we able to walk on the earth,"Gravity. I personally wouldn't ask this question in the genetics unit, though."
Polygenic inheritance and environmental effects,Does anyone know anything about syndactyly and its genetic inheritance?,"Syndactyly is a mendellian dominant trait, so it is inherited much like any other gene."
Polygenic inheritance and environmental effects,"Can a disaster, natural or man-made, affect human traits?","Quite interesting question!

I can think of radiation which causes *mutations*.

Definitely causes of mutations can affect human traits and phenotype, but not in the form that it will _favor_ survival. Nonetheless, future generations may be less adaptable and degenerated (recall Chernobyl nuclear plant disaster or Minamata disease in Japan (caused by excessive mercury due to chemical industry).


My answer is *definitely yes*. *Negative impact*."
Polygenic inheritance and environmental effects,"So I am very short for my age , yet my mom and dad are both tall but my mom is a little shorter than my dad . Why is that? Do i have a disease or something that affects my growth ?","A short stature can be caused by a variety of causes. It could be genetic, a hormone known as growth hormone could be low in the body, or, in more serious cases, an underlying disease or condition may have contributed to your stature (I.E: tumors, malnutrition, mitochondrial disease). If you are otherwise healthy, it is most likely either genetic or hormonal.

Does this help?"
Apoptosis,If cells undergo Apoptosis to get rid of default or harmful cells why do we have diseases of the cell like sickle cell anemia or cancer?,"Maybe the DNA of the cells is so damaged to the point where it can't go through apoptosis, So cancerous cells continue dividing, leading to disease. But today we can use radiation therapy or special treatment to render many types cancerous cell harmless. (I'm  learning about this region of biology right now, so keep inquiring and maintain a fresh curiosity about how your world works!)"
Apoptosis,"Could you please clarify the role that calcium plays in programmed cell death? I understand it has some purpose, but I'm very unsure otherwise.","Ca is known to plays a role in necrosis, and high levels of Ca usually lead to necrosis of tissue.


However, Ca plays a role in apoptosis as well. Cell concentration of Ca triggers the contraction of myofilaments, secretion of hormones, etc.

the increases of [Ca2+]c occur, both at early and late stages of the apoptotic pathway. Ca2+ release from the endoplasmic reticulum (ER) and capacitative Ca2+ influx through Ca2+ release-activated Ca2+ channels have been proposed to be apoptogenic. 

the proteins of the Bcl-2 family, are localized in organelles deeply involved in Ca2+ handling (the mitochondria and the ER).

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2844952/"
Apoptosis,Is autolysis and apoptosis same?,"NO, autolysis is when enzymes kill a cell, but apoptosis is when a cell kills itself. Think of it as homicide vs. suicide."
Apoptosis,What is the difference between apoptosis and necrosis?,"Apoptosis is a physiological driven process while necrosis is a pathologically driven process.

Apoptosis is control by the cell (suicide) while necrosis is end product of being sick (external damage, either physical-chemical or biological)."
Apoptosis,How could the process of Apoptosis hurt a multi-cellular organism?,"Apoptosis mainly prevents hurting a multi-cellular organism, but i guess if the apoptotic signal is mutated (certain enzymes or receptors in the apoptotic pathway working not the way they should) it could result in mass apoptosis in tissues. This would result in tissue damage."
Apoptosis,"For multicellular organism we have things like apoptosis and necrosis,what about organism with only one cell?
In this essay,"eliminating bad cells" function of apoptosis is mentioned.Can we kill cancers and infections by expanding this function of apoptosis?
Mentioning"cells of adult organisms may be eliminated to maintain balance",what about teenagers?Do we have this function,too?","Actually, cancer treatments are in fact triggers of apoptosis. Radiation treatment mutilates cancer cells in a way that causes the immune system to detect them and make them commit apoptosis."
Apoptosis,Do all cells contain the proteins necessary to undergo apoptosis?,"By default yes. Until something goes wrong - and that is how cancer arises.

I mean, _one of mechnisms_ for cancer is *faulty apoptosis*.


If one gene mutates or miRNA does post-translational modifications, or even if alkylating agents change DNA, you end up with a complete lack of or faulty nonfunctional proteins. In that case, apoptosis is not possible and continual cell division takes place which slowly grows into pathological growth."
Apoptosis,Can you explain how apoptosis leads to cancer when a failure occurs?,https://www.khanacademy.org/science/ap-biology/cell-communication-and-cell-cycle/regulation-of-cell-cycle/a/cancer
Frog development examples,Which part is the archenteron or coelom?,"This response is a few years late, but for those wondering... In late gastrula of figure. 6?, the archenteron is the space that forms from the blastopore lip. In blastula, you can see the blastocoel as the cavity at the top, it disappears shortly after the archenteron is formed."
Frog development examples,"How is the uneven distribution of the molecules in the egg kept like that? Wouldn't the molecules tend to spread out evenly, even if they were positioned on one side of the cell in the beginning?","What I recall, in fruit flies, all the chemicals are locked on one side of the egg, and unlocked/released by molecules provided by sperm at time of fertilization. Once unlocked, the chemicals diffuse producing a gradient. Overtime, the chemicals will be uniformly distributed like you mentioned, and no longer be useful as location marker."
Frog development examples,""In fact, I remember one of my professors telling us that you could squeeze a female Xenopus frog "like a tube of toothpaste" to get the eggs out for experiments!"

Wouldn't that hurt the frog? Or do scientists not care about that if they need something for their experiments? I'm sorry about how blunt this sounds, but I am vegan and a strong believer in animal rights, and was just wondering if some scientists use more humane methods to get what they need for their research.","I agree and am curious as well, as to the humaneness of the methods used. I believe that all living beings should be treated the most humane way possible. Are there ethics guidelines regarding the use of animals in research? What do these guidelines entail?"
Homeotic genes,I don't get how homeotic and hox genes are different. Why does the article start talking about homeotic genes and then forget about them and just talk about hox genes?,"The Hox genes are a subset of homeotic genes. There are other types of homeotic genes, as described in the article. The Hox gene is just a type of homeotic gene."
Homeotic genes,What are the similarities between animal and plant homeotic genes?,"Plants don't have Hox genes, but they have homeotic genes with a homeobox. They have the same base pairs, but they don't control the orientation of the "head" and "tail"."
Homeotic genes,Can ultrabithorax mutants still fly?,"Some alleles are lethal, so in those cases obviously not!

For non-lethal alleles this information is well-hidden, but at least one abstract seems to indicate that at least some viable mutants can still fly.  
Since other lineages of insects (e.g. moths and butterflies) retain two pairs of wings and can fly it makes sense that _Drosophila_ with the second pair wings derepressed would also be able to fly ..."
Homeotic genes,Do all Hox genes have the same functions in all animals?,"No, each Hox genes function for the vertebrate. For example, in a fly, there is a hox gene that functions for wings, which is not in humans."
Homeotic genes,"If Ultrabithorax is inactivated and causes mutations which leads to the second pair of wings, does the fly still develop halteres that help it to balance or does it become unable to balance?","No. Since ultrabithorax is inactivated, no halteres are present. Fly apart from being unable to fly also cannot balance off. That mutation is lethal."
Homeotic genes,What does it mean to duplicate a gene?,"To duplicate is to make a copy of something. Therefore, to duplicate a gene is to make a copy of a gene"
Prokaryote interactions & ecology,Related to the section on Mutualism...how does Ruminococcus get in the cow's gut to begin with?,Am not sure... but why not through the mother cow's placenta?
Prokaryote structure,does bacteria have a Hayflick limit (limit of division) like normal human cells do?,"Okay, so this is very complicated question to answer and it requires a lot of molecular biology. If any part of my answer is incomprehensible, please let me know.

The main difference between our genome and bacterial genome is that our DNA molecules are packed into structures we called chromosomes and they are linear, meaning they have a starting point and an end point. Bacteria don't have chromosomes and their DNA is circular.

Due to the mechanism of DNA replication, our DNA isn't completely replicated. That is, "the mother" DNA and "the daughter" DNA (those are not official terms) aren't identical. "The daughter" DNA will always be a bit shorter.

What does that mean for us? How much of DNA do we use per one cell division? Well, on the both ends of our linear DNA there are what we call telomeric regions, or telomeres. Those are long repeated sequences that don't code for any protein. Their only purpose (as far as we know) is to save the important part of DNA from being lost during the replication process. Instead of losing important genes, we lose a small part of telomeres in every cell division. After 40 - 60 divisions telomeres reach critical length and they can't be sacrificed anymore. This is where DNA replication and hence cell division stop happening.

Because bacteria have circular DNA, they don't have those problems. Their polymerase can replicate an entire genome without losing one single part of it. They don't need telomerases and therefore they don't have any limits in cell division. If a bacterial specie had Hayflick limit they would stop reproducing after some number of divisions and that would be the end of the specie.

What you should ask now is: what about cancer cells? They seem to be immortal and divide without any limits. What about single celled eukaryotes, like amoeba? They have chromosomes too (linear DNA) but they don't have Hayflick limit. The answer to those questions is very interesting and rises a lot of possibilities for us. There is an enzyme called telomerase. This enzyme extends telomerases and prevents them from being lost after a number of replication cycles. It works forever in cancer cells, but for some reason it stops working in "normal" cells. Why? We don't know yet, but we're on our way to find that out. This means we could treat cancers with telomerase inhibitors - if we prevent telomerase from extending their telomeres, cancer cells will stop multiplying after reaching Hayflick limit. Could we treat our normal body cells with telomerase and prevent them from reaching the limit? The answer might be yes. Would that mean we could become immortal in such a way? We don't know yet, but we're certainly going to dig deeper into the problem.

Thanks for asking such an interesting question!

Alex"
Prokaryote structure,Can bacteria get cancer if so what happens?,"No, bacteria cannot get cancer. Cancer is the uncontrolled growth of cells in a multicellular organism, and bacteria are single cellular."
Prokaryote structure,what is the advantages of prokaryote with absence nucleus,"Essentially, prokaryotes are simpler than eukaryotes. This may not sound like an advantage, but it means that it's really easy to make new prokaryotes, which means that prokaryotic cells reproduce much faster than do eukaryotes. Also, this faster reproduction means that these cells can adapt faster as there are faster generations, which can be an advantage."
Prokaryote structure,"how were the fossil of the prokaryotes found?
Here it says that fossils of prokaryotic were found, how was it understood that it was a prokaryotic?
i dont think that something so small like a bacteria could actually leave a imprint like a fossil.
thank you","Bacteria generally don't leave fossils, and at most we can infer their existence based on evidence of their effects on other fossilized creatures, such as infections. However, some bacteria have been known to create iron or clay sort of shells that survive after the bacteria has died, creating a sort of model of the bacteria. Bacteria have also been found in fossilized amber, and some cyanobacteria can create stromatolites, which are rocks created by cyanobacteria, calcium carbonate, and the surrounding sediments. Stromatolites can be fossilized, and when cut open, there are sometimes layers or fossilized cyanobacteria inside, protected by the stromatolite."
Prokaryote structure,can eukaryotes have flagella and pilli? or is that only for prokaryotes?,"Yes, and the flagella of motile bacteria differ in structure from eukaryotic flagella. 


However, Eukaryotes do not have pili or fimbriae."
Prokaryote structure,"Do Prokaryotes, specifically Archea, have ribosomes?","Yes they do.  Ribosomes in prokaryotes are similar to, but smaller than, those in eukaryotes."
Prokaryote classification and diversity,How did scientists do experiments on archaebacterias if they only live in extreme places?,They don't live only in extreme environments. Approximately 40 % of your own microflora are actually archaea. In the past few decades we found out that many prokaryotes that we thought were bacteria are actually archaea.
Prokaryote classification and diversity,Why mycoplasmas included in gram positif when it dont have cell wall?,"Because of the criteria used.
Mycoplasma is not classified under 'gram positive' based on Gram staining (which does not give results) but based on *genetics*.

Comparison of DNA sequences and 16s ribosomal RNA tend to support this idea and Mycoplasma are now categorized as gram-positive."
Prokaryote classification and diversity,"If bacteria and archaea are prokaryotes, why does figure 3, the lineage diagram near the top, indicate that archaea and eukarya have a more recent ancestor? Doesn't common ancestry dictate classification?","Excellent observation!

You are correct, prokaryote is not a good phylogenetic grouping — it really just means "not a eukaryote".

Prokaryote is an old term that is no longer considered valid in a phylogenetic context, but is too useful to give up.

The accepted explanation for the evolution of the Eukarya is that a Bacteria ended up inside (was eaten or infected) an Archaea — this is known as symbiogenesis, or the endosymbiotic theory.

This is the most fundamental example of a limitation in thinking of phylogenies as trees — sometimes the branches fuse!

The diagrams on the right in this wikipedia article may help you visualize the "true" relationship among the three domains:
https://en.wikipedia.org/wiki/Prokaryote#Classification"
Prokaryote classification and diversity,"Did Archea and Bacteria branch before or after Eukarya appeared? If before, from which of these domains did Eukarya branch?","Yes, Archea and Bacteria branched before the Eukarya appeared. Only after they branched did the Eukarya branch off from Archea. Evolutionists think this because Archea and Eukarya are similar, Archea and Bacteria are similar, but Eukarya and Bacteria aren't very similar. And using DNA hybridization and things they hypothesized this, though there really is no proof."
Prokaryote classification and diversity,to which kingdom do mold belong,"That depends on the mold!

Most molds are fungi — Kingdom: Fungi
https://en.wikipedia.org/wiki/Mold

Other things called molds include:
• "water molds" (Kingdom Chromista):
https://en.wikipedia.org/wiki/Oomycete

• "slime molds", which aren't Fungi, but whose classification is still uncertain: 
https://en.wikipedia.org/wiki/Slime_mold"
Prokaryote classification and diversity,What is the difference between Archea and Bacteria?,"Differences Between Bacteria and Archaea
•Different cell wall proteins
•Different lipids in plasma membrane
•Different ribosomal proteins and RNA
•Archaea ribosomal proteins resemble eukaryotic ribosomal proteins."
Prokaryote classification and diversity,what are Prokaryotes are found in,"Prokaryotes are found practically everywhere, from inside other organisms (like digestive bacteria) to in really extreme environments that have high heat or acidity, for example."
Prokaryote metabolism,How do organisms synthesise ATP using aerobic and anaerobic methods,"Anaerobic - glycolysis and fermentation
aerobic - electron transport chain and Krebs cycle"
Prokaryote metabolism,Why do obligate anaerobes die in the presence of oxygen?,"To some extent that probably depends on the organism in question, but in general they die because they lack the defenses against oxygen found in aerobic organisms.

Oxygen is actually quite toxic and most current life forms have multiple defenses against this "poison".  In fact, the first life on earth was anaerobic and when oxygenic photosynthesis was "invented" (about two and half billion years ago) it led to what is described as the first mass extinction on this planet§!

To begin learning more:
https://en.wikipedia.org/wiki/Obligate_anaerobe#Oxygen_sensitivity


§Sometimes referred to as the "The Oxygenation Catastrophe":
https://origins.asu.edu/blog/oxygenation-catastrophe
https://en.wikipedia.org/wiki/Great_Oxygenation_Event"
Prokaryote metabolism,in this there is only prokaryotic mater  only is there is no autotrophic matter please explain it,"I do not know what you mean. Here on Planet Earth, there are Eukaryotes and Prokaryotes. Also, we have autotrophs and heterotrophs."
Genetic variation in prokaryotes,How does a transposable element do the cutting and pasting? Does it use an enzyme from the cell or does it have its own enzyme?,"Many§ transposable elements will encode a transposase — an enzyme to catalyze its movement to another location.  The exact mechanisms vary among different types of transposons, but cutting and pasting is done by some of them.

You can read more about this in these wikipedia articles:
https://en.wikipedia.org/wiki/Transposase
https://en.wikipedia.org/wiki/Transposable_element

§Note that transposons can also have parasites — these are known as non-autonomous transposons.  They tend to be smaller versions of the autonomous transposons and "steal" the enzyme produced by autonomous transposons to move themselves."
Genetic variation in prokaryotes,Can you tell the enzyme how is catalyzes transformation,"Good question, but there is not one specific enzyme responsible for transformation. Transformation requires the expression of about 40 genes, each of which could express a unique protein. It's a complex process and people are still working out the details of how it actually works. Some of the proteins involved are probably enzymes but we don't know exactly what they all do."
Genetic variation in prokaryotes,"Why are the process of transformation, conjugation, and transduction “easy” to do with prokaryotic cells like bacteria, but much less commonly encountered in eukaryotic cells?",Because prokaryotes' DNA exits as a single loop and is relatively shorter than for eukaryotes due to the fact that multicellular organism have a greater need for a variety of proteins.
Genetic variation in prokaryotes,What is the relationship between a sex pilus and a mating bridge?,"A mating bridge is a connection between two bacterial cells that provides a passageway for DNA in bacterial conjugation.
A mating bridge is different from a sex pilus, which is a structure made by an F+ strain bacterium in bacterial conjugation

Sex pilus acts as an attachment site that promotes the binding of bacteria to each other. In this way, an F+ strain makes physical contact with an F− strain. Once contact is made, the pili shorten and thereby draw the donor and recipient cells closer together. A conjugation bridge is then formed between the two cells, which provides a passageway for DNA transfer."
Prokaryote reproduction and biotechnology,what are gram positive and negative bacteria,"Gram-positive bacteria are the ones which, when a stain is added (in the Gram staining technique), become purple. Gram-negative bacteria lose the purple stain easily, and they only retain a red or pink color. This is because gram-positive bacteria have a thick peptidoglycan (sugar and amino acid) layer which absorbs the purple stain very well, but gram-negative ones have a very thin peptidoglycan layer, so they are only weakly stained."
Prokaryote reproduction and biotechnology,Would E. coli be a gram negative bacteria or gram positive??,"It is gram negative, catalase positive (reacts with H2O2), MacConckey agar positive (ferments lactose), and Quellung positive."
Prokaryote reproduction and biotechnology,What is negative bacteria?,*Gram-negative* bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. So they color as red after Gram staining. E.g. E.coli.
Prokaryote reproduction and biotechnology,Has CRISPR largely replaced the method of transformation explained in this article?,"CRISPR followed by recombination can be an alternative to restriction followed by ligation.

It can't replace transforming DNA into bacteria.

In fact, we generally assemble the parts needed to make CRISPR work in a bacterial plasmid!"
Prokaryote reproduction and biotechnology,"Why does a heat shock trigger the bacterium to take the plasmid?
How does a bacterium take up the plasmid?
And what are some possible causes of bacteria not taking them?","Heat shock increases the permeability of the cell membrane so that the plasmids can move across it more easily, the bacteria will not immediately take up the DNA so the cell membrane has to be destabilized by the heat shock so that the plasmids move across it. This is not a perfect process so only some bacteria are transformed (take up the plasmid) because some of it is due to chance. The bacteria do not really choose whether or not to take the plasmid, it is more just if the cell membrane is permeable to the plasmid or if it is not."
Prokaryote reproduction and biotechnology,Whats the difference between eukaryotic reproduction and prokaryotic reproduction?,"The main difference is that mitosis requires microtubules to pull the chromosomes apart, whereas binary fission just needs the nucleoid to replicate then the bacteria can immediately divide."
Prokaryote reproduction and biotechnology,can PCR amplify prokaryotic cells?,"It does not amplify cells but isolated DNA, it does not matter where you take the DNA from."
Prokaryote reproduction and biotechnology,"Are plasmids something that humans create and they give them to bacteria?  From the article above, it sounds like humans create and give them to bacteria.","No, humans do not make plasmid DNA. All human DNA is found within our linear chromosomes. Plasmids are generally found only in bacteria (with the exception of some archaea and eukaryota). The plasmids can come from the circular bacterial genome - bits of DNA can be turned into plasmids and conversely plasmids can be integrated back into the primary genome. Plasmids may also have viral origins, meaning they are a relic of something that infected the bacteria in the past. The system is very fluid, allowing bacteria to share important genetic material easily and fast."
Intro to viruses,Can viruses be considered a separate kingdom from the main five kingdoms of living  organisms?,"No, because they are not living things. Good question, though."
Intro to viruses,Will science/medicine ever find a way to make us immune to every virus and bacteria?,"Another aspect is that we are constantly running into new viruses. Why? Viruses can be divided into two groups: one group of viruses spreads only between humans, and the other group mainly spreads between animals and may spread to humans. Drastic population increase and worldwide drought led to widespread deforestation, in order to acquire more farming land and wood. Naturally, many animals lost their habitats and were forced to move into lands where humans lived. Viruses that were originally spread only between these animals were able to spread to humans as well. So if the status quo continues, humanity is going to come across much more diverse viruses than ever before. It can be assumed that it won't be easy to find a cure for all these new viruses."
Intro to viruses,How did Viruses develop in the first place? Did they just evolve or something......,"This is an excellent question and is the subject of current scientific research!

Short answer — we don't know and the answer may be different for different viruses.

For a longer (more satisfying) answer I recommend this:
https://www.nature.com/scitable/topicpage/the-origins-of-viruses-14398218"
Intro to viruses,"If a surface, e.g., a table, is  contaminated with a virus, e.g., COVID 19, is the virus unit attached to some carrier unit such as inside a water vapor droplet or attached to dust, etc. or is it a separate chemical unit free to be moved about like a stone laying on the ground that can be kicked around?","I think "chemical unit" is the wrong phrase to use here. A simple stone or pebble at a microscopic scale can be compared to a rough mountain range on earth. At that scale, it's basically the same as any other similar surface. A small pebble or a giant boulder is the same at that level.

On all surfaces, there are a lot of places for germs to hang out, but it depends on the germ and the surface whether you can actually find anything there.

Usually, the answer is both. 
Viruses can most definitely stick around, even on smooth, dry surfaces for hours or even days, and water vapor and dust are great examples of where to find pathogens.

But again, it depends on the surface and the virus."
Intro to viruses,"Could there be a way to attract viruses to certain areas? Because it was noted in the article that a virus binds to receptors such as proteins.
Is it possible to get the virus out of the host cell without causing harm to the host cell?
Can some host cells be immune to viruses or unaffected by even the worst of viruses?","It would be possible, but not practical. Having free roaming proteins in your body to attract viruses is like having pools of acid in the ocean to digest plastic.
It works, but not particularly well and causes more harm than good.

Also it's worth noting once a virus is inside a cell, its not coming out until thousands of copies of itself are ready to burst out.

And as far as we know, a virus-immune cell isn't quite biologically possible.


Hope this helps"
Intro to viruses,"I know you told us about the life cycle of a virus in the above lesson. But I was wondering about the life cycle of a virus with growth (development) and death. 
Do viruses die? 
Do they grow/develop - along with reproducing?","No, viruses do *not* have that trait of living organisms - growth and development. 

Viruses only reproduce - if they find host (cell).

Do viruses die? No. They just don't reproduce in case they do not find a suitable host (meaning wasted proteins and nucleic acids.

Moreover, prions (just proteins) may cause a ruckus if in human body (thought to lead to Alzheimer disease).


Think of viruses rather as *machinery* not living organism."
Intro to viruses,can a virus be killed by freezing it,No the scientific community is split on whether a virus is alive or not but freezing a sample will actually preserve it. Researchers have found and analyzed ancient samples of viruses taken from glacial deposits. Hope this was helpful. :)
Intro to viruses,How is a viral infection treated?,"Viral infections are hard to treat because viruses live inside your body's cells. They are "protected" from medicines, which usually move through your bloodstream. Antibiotics do not work for viral infections. There are a few antiviral medicines available so far.
Hope this helps!"
Intro to viruses,Why are viruses smaller than their host?,So they can attach to the host as stealthily as possible. Too large of a pathogen could alert the immune system to a threat before the virus even gets anywhere.
Intro to viruses,"If a virus meets a hydrogen peroxide molecule, what happens?","From What I can gather, according to this:https://www.ncbi.nlm.nih.gov/pubmed/203115, Hydrogen peroxide can make viruses inactive."
Animal & human viruses,Why would viruses ever use RNA(-) if all it does is provide extra work to turn it into RNA(+)?,"Short answer: it works well enough to survive — note that some of the most pathogenic viruses are RNA(-).

Long answer (rampant speculation warning) — proposed advantages for RNA(-) viruses:

1) Allows the virus to make many mRNAs from a single infecting RNA(-) genome rather than being limited to transcription from a single RNA(+) genome, this is an extra step but it allows the virus to amplify its output of proteins and RNA as it takes over the cell

2) Increases viral efficiency by allowing the different viral genes to be expressed at different levels — genes near the 3' end get expressed at higher levels than those nearer the 5' end (see refs for details).

3) Since they carry their own replication machinery these viruses aren't as dependent on host factors and so may be able to infect a broader range of hosts — this also means they have more freedom to evolve.

You can read more about these hypotheses on the following pages:
http://www.bio.net/hypermail/virology/1994-October/000905.html
https://www.reddit.com/r/askscience/comments/2zu5eg/is_there_any_benefit_of_an_rna_virus_being/
https://www.quora.com/Do-negative-sense-RNA-viruses-have-an-advantage-over-positive-sense-RNA-viruses"
Animal & human viruses,Where do prions fit in the virus/bacteria/etc. classification?  For example the prion that causes Creutzfeldt–Jakob disease?,"Prions are an entirely separate class of disease from viruses, bacteria, fungus, and protists. When proteins are created, they are originally just a chain of amino acids which are then folded into a specific 3-dimensional shape. The primary theory at this point is that a prion is a mis-folded protein. When the prion comes into contact with a protein that is chemically but not structurally identical to itself, it causes the other protein to spontaneously re-fold into the shape of the prion. When the protein re-folds it becomes unusable for the cell. When this occurs enough times, the cell is unable to function properly and dies, releasing the prions to contact other cells where the process is repeated until the organism dies (usually from extensive brain damage). If you need further information I would recommend reading the book "Deadly Feasts" by Richard Rhodes."
Animal & human viruses,How does the viral genetic code know what to do once inside a cell?,The viral genome is actually much like a cookbook which contains all the instructions whereas the enzymes and proteins are the chefs that do the work.
Animal & human viruses,what the difference between eukaryocytes and prokaryocytes?,"1) Eukaryotes have a membrane-bound nucleus in which they store their genetic material, while prokaryotes do not. Prokaryotes store their genetic material in a cluster in the cytoplasm called a nucleoid.

2) Eukaryotic cells are much bigger than prokaryotic cells. For comparison, most prokaryotes are 0.2 - 2 μm (1 μm = 0.001 millimetres), whilst eukaryotes are generally 10 - 100 μm.

3) Lastly, prokaryotic cells lack organelles. For example, prokaryotes do not contain mitochondria or chloroplasts. Their ribosomes (organelles used for protein synthesis) are smaller than those of the eukaryote.

There are many more differences, however these are the most notable. To help understand the topic better, you could look at Khan Academy's "Bacteria and Archaea" section."
Animal & human viruses,"'To turn its host cell into a "virus factory," the virus must induce the cell to make viral proteins, and the only way to do that is by providing an mRNA for the cell's translation machinery to read.'
I couldn't understand this part. Please help. Thank you.","Some viruses have an RNA genome and before integrating their genome into that of a host cell, it must use the enzyme reverse-transcriptase to create DNA. I hope this helps :)"
Evolution of viruses,"I know this will most likely be impossible but is it possible for a virus to evolve rapidly enough to spread and wipe out life on earth, I mean the H1N1 pandemic looked bad enough right?","Viruses could never wipe out life on Earth. There are two reasons for that.

1) The more successful the host is, the more successful is the virus going to be. Humans are very widespread specie, which means that viruses that attack us have very good chances of spreading from one victim to another. But, as the population of their hosts declines, viruses will have more trouble in spreading. In the end, when there would be only a few isolated groups of people left, our imaginary deadly virus wouldn't be able to spread anymore.

2) Someone will be immune to virus. Those people will survive and continue the humanity. Their children will have their genes and they will all be immune to that specific virus. Spanish flu couldn't affect everyone, HIV can't affect everyone, none virus can affect everyone. It's just how things work."
Evolution of viruses,"If the HIV virus only has a lifespan of 52 hours, then wouldn't the HAART "cocktail" therapy be able to block the HIV virus for at least 52 hours, thus causing the death of the virus? Unless the HIV virus evolves and mutates within those 52 hours, which I highly doubt is always and/or mostly the case.","Good point. In that case, cocktail therapy would perfectly work and ensure no viruses escape."
Evolution of viruses,how does the virus affect human population?,"One virus can affect human population only if his infection becomes epidemic or pandemic.

Epidemic - a sudden increase in the number of cases of a disease to a level that is greater than the expected level in a given population in an area.

Pandemic -  an epidemic of world-wide proportions

https://www.infoplease.com/askeds/pandemic-vs-epidemic"
Evolution of viruses,What would happen if 3 viruses combined?,"Probably recombination of genetic material would happen.

Now, you may take 3 of the deadliest viruses in the world, but the resulting virus may be something harmless or low degree dangerous.

Or maybe each one may infect and cause disease on its own.

Genetical rearrangements can end up in any kind of results."
Evolution of viruses,How does the influenza virus affect the human body?,"Influenza virus has two different glycoproteins on it's lipid envelope called neuraminidase (helps the virus to leave the host cell)and haemaglutinin(aids the virus to enter the host cell).

In humans,haemaglutinin binds to (saliac acid) receptors on the epithelial cells in the upper respiratory tract and then the virus enters the cell through a process called 'endocytosis'.
Once in the cell , the negative sense Rna is replicated into positive sense ss rna which then helps in the process of progeny production.
Now viruses mutate very rapidly...Therefore the daughter viruses have slightly different glycoproteins than their parent and other progeny viruses.
This is why you can get flu every year or even twice or more in a year.

Now, neuraminidase is a receptor destroying protein which is why it aids the virus to elude from the cell by destroying saliac acid receptors."
Evolution of viruses,Why is it that the article says that the average human cycle is only 20 years?,When looking at generations of an organism you measure the average time between birth and having offspring.  For humans the figure of 20 years has been used but may very depending on the area and time period used.
Evolution of viruses,What does rna mean?,"RNA stands for RiboNucleic Acid.  It is described in the section on nucleic acids, over here:

https://www.khanacademy.org/science/biology/macromolecules/nucleic-acids/v/dna-deoxyribonucleic-acid"
Evolution of viruses,Can a virus wipe out the dinosaurs or cause a mass extinction event?,"I know there will be people who disagree with me, but i firmly believe the answer to both questions is no.

(Just as a side note, dinosaurs aren't extinct. Present-day birds are indeed dinosaurs.)

To cause a mass extinction, a virus would have to be able to infect a broad variety of species and cause disease with a mortality rate of 100 %. To my knowledge, no known type of viral disease has such a high mortality rate (even though some are close to that number!). The more lethal a virus is, the sooner it will run out of possible hosts. Earlier types of ebola virus were very lethal (the highest recorded mortality rate was 90 % during the 2003 epidemic in DR Congo), but those viruses didn't cause massive epidemics. Each outbreak had several hundreds of casualties.

Some scientists speculate that viruses could have caused several smaller extinctions in the history of life on Earth. Fossil records confirm that in between so-called mass extinctions, there were also smaller extinction events which happened during periods of relatively stable environmental conditions. So what was the cause? Even though some believe it was because of the viruses, as of now we have no evidence to support that claim.

That's just my opinion. The topic is still very controversial, and i would be interested to hear others' opinions."
Evolution of viruses,"Vaccines provoke the host's immune system to produce appropriate antibodies against the antigen in the vaccine. In relation to the section, Case study: HIV, why do vaccines for viral infections/viruses become ineffective over time? Is it because as viruses mutate, antigens develop on their surfaces which are different to the original antigens on the virus before mutation, and hence require the production of different antibodies to be granted immunity against the new, mutated virus?","A person's immune system is introduced to the protein on the surface of a dead or weakened virus so that it can be recognized as a foreign without the chance for the virus to overwhelm the immune system.  That person's immune system is primed to recognize and eliminate anything with that protein on it.  

If the virus mutates or is somehow changed so that the protein coat no longer has the same protein on its surface that person's immune system will not immediately recognize it as foreign and the virus has a chance to insert itself into a cell for replication before it is detected.  

A lot of research is needed to identify what parts of the virus protein coat are not likely to change over time so that a vaccine will continue to work even of the virus changes."
The biology of Zika virus,What country has the highest percent of people infected with the Zika virus?,"Brazil has been battling the largest Zika outbreak yet, with more than a million people infected."
The biology of Zika virus,"If an infected mosquito lays its eggs and dies, is the virus transmitted to its offspring genetically? In other words, can an infected mosquito pass the virus on to its offspring somehow, or does the virus within that infected mosquito, die with the mosquito?","Yes, the virus is transmitted to mosquito offspring.

https://www.sciencedaily.com/releases/2016/08/160830091524.htm"
The biology of Zika virus,What is the name of the tissue zika invades and what is the route of invasion?,Zika invades the central nervous system. Associated with Astrocytes as well.
The biology of Zika virus,What countries has the Zika virus not ''attacked''?,"Zika has not attacked any country ( This may not be up to date) In Europe, Australia, and Antarctica. It has attacked about half of the countries in the tropical zone, or countries south of Uganda, Congo, and Malaysia, and north of US, Italy, and China. Countries that it has attacked, are Brazil, Equador, Guiana, Mexico, Bahamas, Southern US, Central America, French Polynesia Indonesia, and South East Asia, and Central Africa,  but, don't take my word for it, I may be wrong, or outdated.
 Hope this helped :3"
The biology of Zika virus,why is it that only the genus Aedes is the vector?,"I presume it could be anything that can get infected.  It could be a tic.  I guess monkeys.  Since the original discovery was in a Rhesus monkey in the Zika Forest in Uganda in 1947.  If got bit by an infected monkey, its a vector.  Aedes is just the primary vector."
The biology of Zika virus,Is the Zika Virus still a danger?,"Viruses and pathogenic bacteria _always_ impose a threat to humanity. 

Especially if we do not have developed vaccine against the specific virus. Because even vaccines are not 100% effective plus it is hard to create herd immunity.

Zika virus is transmissed by viruses and affects oregnant women. 

If you are not in tropical areas near mosquitos and do not carry baby, maybe it is not a potential threat to you directly.

I am more concerned with the recently sequenced genome of the new respiratory virus in China (Coronavirus, related to SARS) which might become a global problem and potentially cause pandemic..."
The biology of Zika virus,Whenever a mosquito is infected with Zika does the appearance make it stand out from other mosquitos like swelling or change in color?,"No, unfortunately, no phenotypic, visible change in the mosquito.

There is no way you can distinguish whether than one mosquito standing on your arm is infected or not. That's why I encourage people killing mosquitos. :'D

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6305470/"
Bacteriophages,"If it's true that 8 percent of our genome were from viruses that merged with our eukaryotic ancestors, could that viral DNA be the seed for cancer in all of us?","That also made me think about mitochondrial diseases. There's this endosymbiotic theory where they said mitochondria and chloroplast were descendant of ancient prokaryotes organism that developed a symbiotic relationship with the progenitor eukaryotic cells. So, could it be that the ancient prokaryote cell infected with bacteriophage that causes what we have today the mitochondrial diseases? I'm still new to these topic so I don't know much."
Bacteriophages,When a phage injects its double stranded DNA to a host does it still remain a phage or does it still has some other DNA strands to qualify being a phage?,"Viruses usually inject their all genetic material into one cell, which helps to spread disease through is assembly and release of new viruses from the first infected cell.

Sometimes DNA (and RNA) viruses have more strands. For example, the Ebola virus (RNA VIRUS) has 8 strands of RNA."
Bacteriophages,i thought the antibiotic killing bacteria and viruses. but why the antibiotic kill only viruses? (that what i understood),Antibiotics only work on bacteria not viruses.  Antibiotics work on specific processes in the life cycle of the bacteria that either kill the bacteria or stop it from replicating.  Viruses use the host cells to replicate so the antibiotics do not affect the viruses life cycle.
Bacteriophages,what about the classification of bacteriophage? ..how is it classified and what are the differences between their kinds,"Bacteriophage is in essence, just another virus. It got it's name from the fact that people discovered it infects bacteria (I presume, could be wrong). 
Here's a wiki page about how they are classified.
https://en.wikipedia.org/wiki/Bacteriophage"
Bacteriophages,what potential dangers could phages even have? Will it accidentally evolve and target human cells?,"Eukaryotic cells (including humans) are very different from those of Bacteria, so it is very unlikely that a bacteriophage could evolve to target any eukaryotic cell.  

Most viruses are highly specific and bacteriophages are reportedly extremely specific and are used therapeutically in some countries. 

I don't know how effective this is in practice, but they potentially have some advantages over antibiotics.
https://en.wikipedia.org/wiki/Bacteriophage#Phage_therapy"
Building a phylogenetic tree,"One thing that I am unsure of is regarding the idea of a common ancestor. Is a common ancestor an individual or a population? Is the last universal common ancestor an individual or a population? Or is it impossible to know?
If the common ancestor of humans is two individuals, this would mean there is a theoretical 'Adam & Eve' type situation. But that would surely be too small a population from which to develop a species, there wouldn't be enough variation. So the common ancestor must refer to a population that split off to cause speciation - is that correct?","Good Question! A common ancestor is a species. This may consist of multiple populations. For example, our most recent ancestor with chimps was Australopithecus afarensis. There were multiple populations of this species, so there was enough genetic diversity to evolve into both humans and chimps. Some populations gradually became human while others gradually became chimps."
Building a phylogenetic tree,"In the phylogenetic tree, the finished diagram with maximum parsimony, in the last step, does it matter where you branch off the alligator and where you branch off the bald eagle?","It's personal preference. If you wanted, you could switch the two."
Building a phylogenetic tree,"Seven species ABCGEFG AND THREE ANCESTRAL TRAITS MEDIUM MOLAR ENAMEL, ROUND SHAPE OF THE ORBITS, CURLY TAIL  A= med,round,curly. B= med,square,curly C= med,round,none D= med,round,none E= thick,square,curly F= med,round,none G= thin,square,none. How would I construct a phylogenetic tree?","C/D/F-A-B/E-G coming off of B. My logic is C/D/F are the ancestral species. I than build the tree starting with the species with one derived trait, than two, and than three where they no longer share any of the specific ancestral traits."
Building a phylogenetic tree,"If a phylogenetic tree is meant to be a reconstruction of an evolutionary sequence, can there be more than one correct set of relationships among a group of species?",Usually the tree u can find in publication is said to have the best fit of the mathematical model in the background and its data. It is the most probable solution of a set of different solutions.
Building a phylogenetic tree,"Can a phylogenetic tree be illustrated as lines branching off of other lines, like in this example or can they be made from brackets connecting two groups and within those groups, more brackets connecting other groups together?",You can do it any way that illustrates the branching of the species from common ancestry points.
Building a phylogenetic tree,What is the difference between a cladogram and phylogenetic tree?,"A cladogram is a diagram that shows the relationship between different organisms based on their similarities. A phylogenetic tree is a diagram that shows the genetic history in which organisms evolve and adapt. So, basically the difference is that phylogenic trees have a time scale"
Building a phylogenetic tree,"If there is a change on the E lineage and the descendants of E, F and G, have no tails, since taillessness is also present in its most recent common ancestor with A, B, C, and D, should taillessness still be a derived trait? Which ancestor should I compare a species to when looking for a derived trait? Thanks in advance.","In that case, taillessness would still be a derived trait.  When looking for derived traits, the species should be compared with the species closest to it on the phylogenetic tree - in this case, it's D, so if D possesses a tail, tailless E has a derived trait."
Building a phylogenetic tree,Which gene we basically choose to create a phylogenetic tree?,If you want to compare species then you will chose a gene which you can find in all of them. Some genes can be found multiple times in each species' genome so to avoid taking the "wrong" one you should pick a gene which is only present once. This is an active area of research.
Allele frequency & the gene pool,"In this lesson, there was an explanation of what 'alleles were.  I am interested in historical population genetics, and am wondering if the HVR numbers that come with mTDNA are equivalent to the alleles that go with the Y Chromosome.  Thank you.","I assume mTDNA is shorthand for mitochondrial DNA - DNA inside mitochondria and HVR is short for hypervariable region or a place where base pairs are repeated, generally within the mTDNA, but also sometimes in the nucleus. mTDNA is always inherited from the mother and goes into mitochondria in each cell in the child. It does not seem to serve any function as far as I know. The alleles on the Y chromosome are different. They function to change certain processes in the human body to make the offspring male. 

In short, they are not equivalent."
Allele frequency & the gene pool,"If there are only 2 alleles at a locus and one is at frequency 0.3, what is the frequency of heterozygotes and how do you figure it out?","you can figure it out by making use of hardy-weinburg equation which is p+q=1.
let say p is the frequency of 0.3 and we are looking for the frequency of q.
p+q=1
0.3+q=1
q= 0.7 or 70%
i don't know maybe this is right but someone else can also answer it and you compare"
Allele frequency & the gene pool,Could you please further explain how to find allele frequencies of a new generation?,"To furtherly explain that, all you need to do is to repeat that same process you've used to solve for the old generation."
Allele frequency & the gene pool,"How does looking at all the copies of all the genes in a population, How can  we can see globally how much genetic variation there is in the population.","THat's why the Human Genome Project was so important.

PCR and other gene sequencing methods are now used. Everything is stored in databases so nowadays it is relatively easy to obtain wanted information and compare whole genomes."
Allele frequency & the gene pool,What is the difference between genome and genotype?,"The genome is the collective term for all the genetic material in a cell.

The genotype is what alleles are present for one or more genes.

Does that help?"
Mechanisms of evolution,What is the point of using the Hardy Weinberg equation if there is no population that fits the conditions anyways?,It provides a baseline and lets us compare populations and also monitor and differentiate factors that change those populations.
Mechanisms of evolution,"Shouldn't the allele frequencies technically be labeled as allele proportions? They are a proportion of the total amount of alleles. A frequency would not tell us anything about the total, simply how many alleles there are.","I think knowing how many alleles there are is quite a key to knowing how many total individuals there are. The alleles help identify the amount of homozygous recessive or dominants,and the heterozygous dominants, which is basically enough to know the total alleles of a population"
Mechanisms of evolution,"In the article there is the statement: "Non-random mating won't make allele frequencies in the population change by itself, though it can alter genotype frequencies." I was perplexed by this but then realized that I think the author must be using a narrow definition of "non random." If some individuals are so unattractive that that mate less often that would be a type of non randomness and would, obviously, lead to changes in allele frequency. Am I correct?","Yes you're right. In Sal's example, all of the organisms in the population get an equal opportunity to mate. For example if all the black beetles mate with other blacks, and whites with whites, then you wont get any 'mixed genotype', but all of the alleles are still passed on. However, if all beetles preferred to mate with black beetles, then the alleles for darker pigment would have a higher chance of being passed on. But in that situation there is an unequal opportunity to mate. In summary I agree with you - Sal is just pointing out a curious but unlikely situation where the allele frequence sticks to the HW equilibrium but the genotype frequency does not."
Mechanisms of evolution,How does evolution unify the biological sciences?,"It explains biological observations, considering evolutionary factors as reasons."
Mechanisms of evolution,"In the conditions for the Hardy-Weinberg Equilibrium , how does random mating stabilize the allele frequency?","It seems to me that rather than random mating stabilizing the frequency, it's non-random mating that destabilizes the allele frequency (or the genotype frequency). For example, if we are talking about a population of beetles, and the females prefer to mate only with larger males if they can, then the alleles present in the smaller beetles will be less likely to pass on than the alleles in the larger beetles. Therefore, the allele frequency will not be stable and the HW equilibrium will no longer be applicable.
In other words, the allele frequency can ONLY be stable if certain conditions are met including random mating (and all the other assumptions must be met too!)."
Genetic drift,"I still don't understand. How come that genetic drift is beneficial for endangered species, isn't genetic drift reducing the allele frequencies and thus creating less variation where natural selection could wipe out the entire population?",Genetic drift is random and doesn't decrease the genetic diversity of a species.  If anything it would increase the diversity since the genetic changes are not the same throughout the population.
Genetic drift,"How could genetic drift ever create some type of allele that hampers a species or organism from living or reproducing? Wouldn't natural selection kick in over a few generations and take out the gene hampering these actions, no matter the severity of the genetic drift, or bottleneck event? If so, such "bad genes" would not last long, even in extreme bottleneck scenarios. Am i right?","Genetic drift is more common in smaller populations.  Imagine an island where 5 white rabbits and 10 grey rabbits live.  Perhaps grey rabbits have better camouflage against the island's rocks.  If a storm randomly kills 10 grey rabbits and 2 white rabbits, only the white rabbits survived to pass on their genes.  Even though grey is preferred, it obviously would not give them an advantage against a storm.  

Natural selection is dependent upon variation.  If all the rabbits possessing the grey allele are killed, that gene (and that phenotype) could literally be lost forever in the small island population."
Genetic drift,"It may sound pedantic, but is there any sort of practical occasion where genetic drift acts as a truly random evolutionary mechanism? This article states that "allele benefit or harm doesn't matter" for genetic drift, but is this even possible? I mean even during virtually random events, like an asteroid hitting the Earth and causing a major extinction, natural selection can still act upon allele fitness for this post-apolytiptic scenario - as for non-avian dinosaurs during the K–Pg extinction event.

I can't really think of an event that creates that supposed "random" allele selection - and as such I can't see much of a pratical, tangible difference between genetic drift and natural selection. How can allele frequency, which heavily depends on genotype survival/fitness, not be dictated by natural selection?","In the scenario of the asteroid causing a mass extinction, the asteroid wipes out many of the alleles present in the gene pool, regardless of whether they are beneficial or not. The 'fitter' alleles of this reduced gene pool are passed down to the subsequent generation. Natural selection without the asteroid (i.e. genetic drift) would have produced significantly less alteration in the gene pool, (and subsequently allele frequency), at least for the same time period . This is not to say that genetic drift (here, the bottleneck effect) occurs independently of natural selection, just that in scenarios such as natural disasters, it has a much greater impact. Also, in some cases (e.g. color of fur and eyes) there really is no such thing as a 'beneficial' allele. Evolution in this case is solely dependent upon genetic drift."
Genetic drift,"lets say that there is a population of equal no.s of alleles of blue ,yellow and red. now 2of each alleles migrate to a different place . and the new population consists of 2 blue alleles ,2 yellow alleles and 2 red alleles.will it still be called a founder effect?","No, it would be called founder effect if you isolated *only one* allele. From what we can see, again, all types of alleles are present (regardless of the quantity of each)."
Genetic drift,why Genetic drift effect is strongest in small populations ?,"In small populations it is more likely that chance events will significantly change the frequencies of alleles in the population.

For example: 
Imagine a population of 4 organisms which have one gene for color with two alleles - lets say a dominant allele called `A` and a recessive allele called `a`.   
The individuals have the following genotypes:
#1=`AA` 
#2&#3=`Aa`
#4=`aa`
A storm happens and by chance a tree falls on individual 1 and kills it – so sad!

What has happened to the frequency of the alleles?

What would happen if the tree had fallen on #4?  How about #2 or #3?

Now imagine there were 40 organisms with the same mix of genotypes – even if something killed off 1/4 of the population what are the chances it would get all 10 `AA`s?

Does this help?"
Genetic drift,"In the above example for founder effect, 
_'It is believed that a single couple out of the original 200 founders carried a *recessive allele* for Ellis-Van Creveld syndrome. Genetic drift, in combination with reproductive isolation, caused *this allele* to increase in frequency in the population.'_
can someone please explain this.
how does recessive allele increase in frequency? is the dominant one having the syndrome or the recessive one?","if the couple has several has several children, then all of them would carry the recessive allele. if the other couples have an average offspring count less than that of the aforementioned couple, the allele would increase in freq. then if the children grow up and have offsprings, their children would also carry the recessive gene. the example is talking about the allele freq., not the actual number of people who have the syndrome (just to make that clear)
I think the recessive one would cause the syndrome."
Genetic drift,Some of this is right. See if a population continued to stay separated from each other (like in a colony as mentioned above) the chance for genetic drift could end up taking away bad genes or creating new ones. But if the population was already mostly wiped out it stands little chance of survival.,"but they would still be alive, and a smaller population means more resources for individuals. some creatures do not need to be in large groups to survive. also, as long as the remaining population has offsprings, then the populations won't die out."
Genetic drift,"What if the founding population say migrates to another environment and is not fit for that environment? Will they just die off? Is the case where beneficial alleles can be lost and harmful ones can be fixed only if the founding population is fit for its new environment, and therefore can survive and reproduce?","In that case, what has been labeled as 'beneficial' is no more beneficial and same applies for harmful alleles.

New environment dictates new mutations and new rate of survival.

No, not the whole population will die off."
Genetic drift,How can some phenotypic variations significantly increase the fitness of the population using sickle-cell anemia,Comparing sickle cell phenotype to normal phenotype says that their survival is lower. I do not see how that phenotypic 'change' can increase fitness since sickle cell phenotype is a priori destined for destruction.
Genetic drift,Does this mean that evolution can actually take a step back in cases were adaptive genes are lost and genes with harmful effects stay?,"Evolution doesn't go in a direction, it is a continuing process."
Phylogenetic trees,"Can a phylogenetic tree show which organism is more evolved, if they evolved at the same nod?","Look at (or make) a tree showing your family going back at least to your grandparents.

First question: What does this tell you about people in your family?

Phylogenetic trees are really very similar, but for species rather than individuals within a family.

Second question: What do you mean by "more evolved"?

Does this help?"
Phylogenetic trees,how to represent an extinct specie in a tree diagram,Ending a line before present day shows that a species is extinct
Phylogenetic trees,What phylogenetic trees can and can’t tell us,"One example that comes to mind is that a phylogenetic tree determines where two organisms diverged from their common ancestors but not specifically when. These diagrams are not chronological in a direct way, more so a before and after situation. (Hope I helped, correct me if I am wrong)"
Phylogenetic trees,how did a common whale evolve from a common ancestor?,"I'm not sure what you mean by a "common whale".

The following has information on whale evolution:
https://evolution.berkeley.edu/evolibrary/article/evograms_03

If that doesn't help, can you please clarify your question?"
Phylogenetic trees,how does phylogenetic classification related to phenetic  classification?,"Phenetic speciation means classification of species by appearance alone. For example if two frogs look similar they are called a species even if they cannot mate.
Phylogenetic classification does consider appearance and phenotype, but it also goes much further in terms of looking at functionality, and comparison of genomes. Phylogentics explains an organisms evolutionary history. This is a more rigorous system than phenetics."
Phylogenetic trees,What are the characters used to determine the most accurate evolutionary trees?,The most accurate phylogenetic tree will have the fewest nodes. It's something called parsimony which means that the best tree is the simplest.
Phylogenetic trees,Can someone explain to me the process when a new species will emerge on the tree? Thank you,"Speciation is a huge topic and still being researched — I recommend starting with the following material on KhanAcademy:
https://www.khanacademy.org/science/biology/her/tree-of-life/v/allopatric-and-sympatric-speciation
https://www.khanacademy.org/science/biology/her/tree-of-life/a/species-speciation

You can also browse through the KhanAcademy material on evolution to learn more:
https://www.khanacademy.org/tag/evolution"
Phylogenetic trees,"The fact that branches can be rotated and still remain true indicates that branching order (the order in which species are listed) doesn't matter. If that's the case, I don't understand the purpose of polytomy. This article says it's because we don't know the branching order, but why does that matter?","I think you may have misunderstood what branching order means — confusingly it doesn't mean the order of the branches!  

Rotation doesn't change the branching order — it rearranges the order of the branch tips, which we all agree isn't significant.

Branching order is being used to describe the sequence in which species split from each other.

Thus, a polytomy is a way of acknowledging that there is not yet enough information to say which of the species split off from the common ancestor first.

Take the example PQR polytomy — we know that the ancestral population ("PQR") probably first split into one of the following: 
P + "QR"
Q + "PR"
R + "PQ"

And then the second population split again.

This is what the article means by branching order.

Does that help?"
Phylogenetic trees,"In the phylogenetic tree containing A,B,C,D,E, what is the closest relative to E?","E's closest relative is whatever species is at the first node (the first 2 branches that extend from the root, or trunk)"
Phylogenetic trees,How would you draw a phylogenetic tree given simple DNA sequences between species?,"It is a difficult task. What you are asking is phylogenetic reconstruction from genomic sequence analysis. There are some ways to do this. One obvious way is to consider two species closest if they match at more base pairs. But what is difficult is to decide if one arose from the other or if they are at the same level, arising from a different common ancestor. 

All of this is very difficult and many algorithms are available, especially since genomic data itself is large, complex (different kinds of genomic data is available - RNA, DNA, Methylated DNA etc) and also based on what we know of the function of the genes (difference in functional gene is a more significant difference than the difference in non-functional genes).

If you are interested, look up maximum-parsimony methods of phylogenetic tree reconstructions."
"Darwin, evolution, & natural selection","In the example of the mice and hawks, what if due to natural selection the hawk's ability to spot out black mice increases? Will that cause the mice to 'counter evolve' and will this cycle of evolutions on the prey and predators' part continue?","Very good!  You've correctly deduced an important evolutionary process known as co-evolution.

This phenomenon is a key to understanding not just predator-prey interactions, but also many other ecological phenomena such as: host-parasite interactions (including disease evolution), and the interaction between many flowering plants and their pollinators (an extreme example being orchid flowers that mimic female insects to get their pollen transferred by male insects).  

More info:
https://www.khanacademy.org/science/biology/crash-course-bio-ecology/crash-course-ecology-2/v/crash-course-ecology-01

https://en.wikipedia.org/wiki/Coevolution"
"Darwin, evolution, & natural selection","How would have homo sapiens evolved from the apes , why did the characteristics of standing erect dominate over bending forward. would it be a transmission of the lifestyle of apes eating food from the ground to hunting ?","From the Homo Sapiens book, Yuval shared a very simple but reasonable concept that standing on 2 legs on the ground will give more broad and wide of view instead of 4 legs. 

Climbing on to the tree will give more advantage but more effort just to check the surroundings. So standing on 2 legs dominated over time for our species to become."
"Darwin, evolution, & natural selection",If natural selection is favouring traits which are beneficial for the environment then couldn't it be stated that as a human choosing to have less children is a trait which is favourable to pass onto your children?,"Natural selection favors traits that are better for the ORGANISM'S survival and reproduction not for the environment. So actually the inverse would be true. A human who has a gene (not conscious choice, as genes - not thought - are passed onto offspring) that makes him susceptible to having more children will pass on that gene (as it is likely that more of his children will survive than someone who has, say 1 child) to more offspring and will thus be selected for."
"Darwin, evolution, & natural selection","I have a doubt, is it possible for natural selection to reduce the size of an organism? If possible, are there documented cases of this?","Of course, natural selection just selects for the organisms that will be the most fit (have the most offspring) in a particular environment.  


One situation where selection can often favor being smaller is on islands and other isolated ecosystems where limitations in food supply and the inability to migrate can mean that smaller organisms are better able to survive famine.

This phenomenon is known as "insular dwarfism" — there is an entire wikipedia article on this subject including numerous examples here:
https://en.wikipedia.org/wiki/Insular_dwarfism

Perhaps the most dramatic example of this are the numerous (extinct) species of dwarf elephants:
https://en.wikipedia.org/wiki/Dwarf_elephant


Does that help?"
"Darwin, evolution, & natural selection",How does natural selection occur in both plants and animals?,"Natural selection is a mechanism that makes any species - be it a plant, animal, fungus, bacteria, you name it - better adapted to their environment. For herbivores (i.e. plant eaters), the plants are indeed part of their environment. In such a situation, the evolution of the plant may affect the evolution of the plant eater (which may in turn affect the evolution of the plant). This process (or feedback) is called coevolution.

Coevolution may also occur with predator and prey, parasite and host, and many other cases where two species are dependent on each other."
"Darwin, evolution, & natural selection",All theories must be testable with many pieces of evidence to back it up.  Is there any examples of famous experiments used to test this theory?  Or any sources the support this theory?,"That's not how science works. You can come up with any ridiculous theory and find as many evidences for it you please. What you should do is to create an experiment that can _overthrow_ the theory. If your theory falls, it's dead. If it survives, it lives as long as some experiment doesn't overthrow it.

As for the theory of evolution, Darwin and Wallace (and some people before them who are usually not given any credit whatsoever) came up with it after observations in the nature. Since then, theory of evolution has survived every attempt of overthrowing. Evolution is a long process, so it's not easy to come up with an experiment to test it. That's why there are still many people who are really skeptical about it.

Probably one of the most famous experiments (or projects...) that has anything to do with evolution is the domestication of red fox in Siberia. Check it out:
https://en.wikipedia.org/wiki/Russian_Domesticated_Red_Fox"
"Darwin, evolution, & natural selection","on the second to the last paragraph,i would like to ask if such heritable differences occur to the point that the groups can have different numbers of chromosomes? If so, how?","Not sure about animal species.

In-plant kingdom it occurs and helps the creation of new species or more 'potent' for agriculture, such as watermelons ets- Polyploidy (multiplying sets of chromosomes) do exist in plant kingdom.


As for animals, polyploidy is incompatible with life. Aneuploidy, on the other hand, is compatible but _always_ leads to errors and diseases in animals.


You propose some error/event occurring where two chromosomes fuse and it results in one less or 2n-2 chromosome garniture resulting in evolving species?

Not sure about genetic mechanisms, maybe that is possible in unicellular organisms."
"Darwin, evolution, & natural selection","How old was Darwin in 1831 when he set sail on the 
HMS Beagle?",22 years old
"Darwin, evolution, & natural selection",What are the three observations that Darwin's concept of natural selection was based on?,"Darwin's concept of natural selection was based on several key observations:

-Traits are often heritable. In living organisms, many characteristics are inherited, or passed from parent to offspring. (Darwin knew this was the case, even though he did not know that traits were inherited via genes.)

-More offspring are produced than can survive. Organisms are capable of producing more offspring than their environments can support. Thus, there is competition for limited resources in each generation.

-Offspring vary in their heritable traits. The offspring in any generation will be slightly different from one another in their traits (colour, size, shape, etc.), and many of these features will be heritable."
"Darwin, evolution, & natural selection",Is there other theory that doesn't agree with Darwin's theory of evolution,There have been other theories but they disagree with observations that the theory of evolution through natural selection explains.
Species & speciation,"There are now evidence showing that Homo sapiens interbred with Neanderthals and produced offspring. These offsprings seems to be fertile since the study found traces of Neanderthals DNA in modern humans. (see http://www.wired.co.uk/article/dna-analysis-humans-neanderthals-breeding)

So, if organisms which can interbreed to produce viable, fertile offspring means that they belong to the same species, does this mean we (modern day human, Homo sapiens) is the same specie as the extinct Neanderthals?","Hybridization is known to happen between what are generally accepted to be different species — sometimes this leads to new species, other times some traits from one species become incorporated into another species.  This second possibility is what seems to have happened with _Homo sapiens_ and _Homo neanderthalensis_.  However, some people now argue that Neanderthals were in fact just a subspecies.

Note that the definition of "species" is hotly debated among evolutionary biologists and none of the (numerous) proposed definitions seems to adequately cover all cases. (This is a lot like our attempts to define "life" — we can list characteristics, but they don't all apply in all situations.)

This website has an accessible discussion of some of the complications associated with trying to define species:
https://evolution.berkeley.edu/evolibrary/article/evo_40"
Species & speciation,Why haven't dogs undergone speciation yet? What major changes must one breed undergo in order that they become incompatible to mate to another bread?,"Dogs are currently undergoing speciation. However, because they have only recently have split into many breeds, it will take much more time for them to become different species. One breed must keep mating with it's own kind for a long period of time and must not mate with the other breed. Eventually the genetic information of the first breed will become so different from the genetic information in the other breed that the two breeds will become separate species and will be unable to have fertile offspring or offspring at all."
Species & speciation,"Suppose that two groups of animals are reproductively separated due to a mechanical barrier, but if we artificially fuse their gametes and implant the resultant zygote in a female womb, the zygote can develop into a healthy fertile organism. Now should we consider the two groups separate species or not?","No, because the offspring is able to reproduce which means that the two parents are of the same species.  Plus, just because organisms live in different places doesn't necessarily mean that they are of different species.  Hope that helped."
Species & speciation,What can speed up speciation process?,The biggest factor is with the rate of creating offspring.  The shorter the time between generations the faster that speciation can occur.
Natural selection in populations,"If disruptive selection occurs on a population, is it possible that it could result in two separate species where each specializes in a certain area based on it's phenotype?",It is possible but one of the things that need to happen for speciation to occur is for the two different populations to decrease or stop intermingling their DNA.  If the two populations are still breading with the other the gene pool will continue to have both phenotypes until one disappears form the gene pool.
Natural selection in populations,Can directional selection lead to allopatric speciation?,"That is an interesting question. Directional selection helps the survival of the most extreme phenotype. And now you are looking at it from a broader perspective.

I think it can. So you mean that the phenotype which survived creates new species? Possible."
Natural selection in populations,Why is it important to examine the fitness of each individual relative to others in the population?,To see what is possible fate of each individual and population itself. To follow the evolution and the process of speciation.
Natural selection in populations,"If disruptive selection of this type persisted for a prolonged period, what would be the likely outcome?","I Suppose that if disruptive selection persisted for a prolonged extent of time, this will lead to the extinction of moderate phenotypes."
Natural selection in populations,Why would the Disruptive selection not work fro the medium colored beetles?,"Because they have nowhere to hide. There is no "medium" colored shrub for them to hide in, whereas for the light and dark colored beetles they can hide in the moss and the shrubs, respectively. So the medium colored beetles would be quickly picked off by predators."
Natural selection in populations,"When applying the mechanism of natural selection, how does a population become suited to their environment?","Consider that natural selection will lean toward fitness-increasing alleles becoming more common in a population. _Fitness_ is a measure of reproductive success, so consider the following example: 

You have two organisms, organism A and organism B. Both organism A and organism B live in the same environment. The environment is subject to extreme heat throughout the year. Organism A handles extreme heat very well, while organism B does not have traits that contribute to handling extreme heat. 

In this case, organism A is more likely to survive than organism B, meaning that organism A will be the one to successfully reproduce. Therefore, organism A's genes that contribute to survival in a hot environment will be passed down and future generations will be better adapted to handle the hot environment.

The example above exemplifies one case where a population becomes better suited to their environment through natural selection. You can think of many such cases, so feel free to brainstorm!"
Natural selection in populations,"Using relative frequency and graphical analysis,  how do you determine whether or not a population is evolving","If you measure the allele frequencies in a population this year, then again next year; if they differ significantly, then allele frequencies have changed, the population has evolved"
Natural selection in populations,can natural selection have negative effects on an environment?,I do not think so. haven't seen any case so far.
Evidence for evolution,"If species share an unique physical feature e.g. a complex bone structure, they may have inherited it from a common ancestor. From background knowledge, all living organisms on Earth share a common group of ancestor (LUCA). Therefore, if all species share a common ancestor, is there the chance that they may all share a physical feature?","Yes, they share 'form' during embryonal development. But there is when the evolution of life becomes really interesting.

Embryonic stages of all chordates and even invertebrates are the same. As foetus grows it slowly develops different features."
Evidence for evolution,"In the summary, the first bullet point says that  Homologous structures provide evidence for common ancestry. Doesn't homologous structure also provide evidence that we all had a common Designer? Also, under the sub title Homologous Structures, in the last paragraph it talks about the vestigial organ of a boa constrictor. Doesn't that boa need that organ for reproductive reasons?","you can think for you that a designer is guiding evolution. we will just not speak in terms of a god/creator or something because there is no material sense.
and in your beliefs you can find evidence for anything..."
Evidence for evolution,is it possible to have a generation of organisms that have absolutely nothing in common with your ansestors,Probably yes. But offspring has to inherit at least some genes from some ancestor.
Evidence for evolution,What inference can you make about organisms having similar protein structures?,"Protein structure is crucial evidence in Bioinformatics because based on protein structures we can predict protein functions! It is believed that protein structures and protein (molecular) interactions can be predicted and based on that can easily classify organisms and make clusters.

The structure can tell us whether that was convergent or divergent evolution. It can talk about genetically connected organisms wich evolved in different niches or about unfamiliar organisms which ended up in the same ecosystem.


I can't tell you concrete, I'd need an example, but this is what whole phylogenetics is about and targeting proteins structure and protein-protein interactions."
Evidence for evolution,why is evolution so important to life,Evolution is the explanation for why the various species developed.
Evidence for evolution,"Between DNA sequencing and Fossils, which would you say is the most significant supporting evidence for evolution via natural selection?","Based on my limited knowledge, DNA sequencing is better evidence for Universal Common Descent (UCD) than fossil evidence.

This is mostly because intermediate fossils do not necessarily have to be ancestral, they just have to mix and match traits between the predicted relationships. For example, _Archaeopteryx_ has both reptile and bird characteristics, but it most likely is not an ancestor of modern birds. It's still evidence for UCD (a falsification would be if there only reptile fossils and only bird fossils, with no intermediates, OR intermediates occur between relationships not predicted, like a horse with wings), but it's not always as neat as we would like to be.

It's worth noting that on a psychological level, it's very visually persuasive.

DNA sequencing, on the other hand, automatically suggests a genealogical relationship, but it also confirms the prediction of relationships made by UCD in a more concrete way than fossil evidence."
Evidence for evolution,"Is it true that it takes about 1,000 generations for evolution to actually happen? How many generations would it take for evolution to occur in humans then?","No, evolution is continuously occurring. If a population is reproducing, it is evolving."
N/A,Where can you find a wild cow?,"Well, to answer your question it's pretty simple In the wild .w."
N/A,"Unless it provides a selective advantage, a heritable mutation would not, in most likelihood, persist. What kind of advantage does _lactose intolerance_ provide?","You have that backward.  

The ability to digest milk past infancy is not common in nature.  There is no benefit for a mammal to continue to produce the enzyme lactase past infancy unless milk is consumed later in life.  

For human populations that keep herds of animals the milk they produced things like cheese and yogurt that changes the lactose in the milk so it is slightly more tolerated and provided good storage of food.  This was a benefit so individuals that developed the ability to digest lactose after infancy had an advantage so that trait started to spread."
N/A,can artificial selection bring back extinct animals?,"It is definitely feasible; however, there are several things to consider:

-Is the climate suitable for this organism anymore?
-Why not spend the money protecting organisms that are going extinct right now?
-Will there be a suitable food source for the organism?
-Will the organism be healthy? Organisms that have been genetically altered in such a fashion are typically not in the best health. Clones like Dolly the sheep do not live for long, and hybrids like the mule are sterile.

Did this help?"
N/A,How does artificial selection help to prove evolution taking place in bacteria,"One thing to keep in mind is that in science no theory is ever proven.  

The genetic code for a organism can be different from the genetic code that is passed to offspring because of genetic damage or errors in the process of replication of DNA.  These changes are fairly random.  This is an observed fact.  

This difference in genetic code between organism and offspring leads to random changes in the genetic code of the gene pool of the organism and its offspring.  

Genetic changes in a gene pool of an organism can cause changes in the organisms that affect how an individual organism functions.  This is an observed fact.  

The natural or artificial selection based on these functional changes has been observed to cause specific genetic information to become more prevalent in a gene pool.  This is also an observed fact.

Based on these observation any many others is the basis of the modern theory of evolution.  

Artificial selection on bacteria is like a proof of concept of the theory of evolution.  It is a study of these changes in a controlled and simplified environment to understand the process before looking for these types of processes and influences in nature."
N/A,What different between human breed selection and artificial selection?,Artificial selection and selective breeding are the same. Humans chose desirable traits in a species and breed them together to pass on those traits.
N/A,Does artificial selection affect the species negatively?,"It depends on the situation. For example, pugs have been bred and inbred so much for many years to the point that they are born very unhealthy. Artificial selection can also be beneficial, for example with corn. Corn used to be very slim and did not look at all like how it does today. Thanks to selective breeding, corn is now plentiful and larger."
N/A,Do dogs get smaller I don't think so?,"Dogs started out as wolves before humans selectively bred them. Not all breeds are smaller now, but something like a Chihuahua definitely got smaller compared to its wolf ancestors. 

Does that help?"
N/A,My brother asked me to ask: Why do dogs have different size ball,"Female dogs mate with multiple males (often in a brief period). 
So there's a competition - among the males and among the plethora of sperms to fertilize the egg. 

More the number of sperms of a male, the higher are the chances that the offspring would be related to that male. Well, for producing more sperms, you need bigger sperm factories aka testes. And these sperms had a chance to carry the traits for large testes.

So, this trait of bigger testes, remained more and thus got selected.
If the dog belonged to a breed where female multiple-matings were less likely, it is possible there wasn't any advantage of larger gonads. So, there wasn't any selection in this aspect. 


P.S. Note that small testes trait wasn't wiped out at all.

https://www.sapiens.org/biology/sperm-competition-testicle-size/

Does that help?"
N/A,"I understand that a fossil not being found doesn't mean the organism didn't exist, simply that it hasn't been found yet (or never fossilized). But several fossils that do exist don't seem to fit in with the theory of evolution.  What about pollen from Cambrian or older sediments the Romairma formation in South America or in the Hakatai Shale in the Grand Canyon in North America? Flowering plants are highly advanced and wouldn't have existed in the Cambrian or Precambrian epochs.",There are multiple possible explanations for those examples you cite. The fossils or their age could have been misidentified. It is also possible that our current understanding of the sequence of events is incorrect. Hopefully future scientific inquiry will decrease apparent contradictions.
N/A,"This article admits, under Evidence For Evolution: Fossil Record, that the record is incomplete. So how is it that we can actually teach this as fact when there is no evidence for macro evolution. The tree shown that all species share a common ancestor is a hypothesis that remains unproven, why not also teach the idea of creation? Creation explains more of what we see than these hypothesis displayed as fact.","Scientific theories are never proven, proofs are for mathematics.  The theory of gravity and quantum mechanics are not proven but but you do not question them being taught.  

Evolution is a scientific theory and has a bunch of supporting verifiable evidence.  It is a theory that accurately describes observations and has made predictions that we have been verified.  

Gaps in the fossil record do not disprove evolution.  Fossils are rare events so there are are going to be gaps.  

There is evidence for macro evolution.  What you call macro evolution is just micro evolution over a longer period of time.  

There is no verifiable scientific evidence for creationism.  There is no more evidence for the world having been created 5,000 to 7,000 years ago than there is for it having been created last week."
N/A,the possible explanations for the examples you may cite not the fossils or the age you could also have been misidentified. and it can be possible that the current understanding of the process of events is incorrect.,"The identified age is counted as evidence for evolution. In the pictures showing the evolution of horses, there are dates shown. Why do you think those are more accurate then evidence against evolution."
N/A,"How did scientists estimate the percentage of species lost during these mass-extension events, if they don't know how many species are alive even today ?","Good question. I don't know a lot about the details of this, but my sense is that it's actually much easier to estimate what percentage of species die during a mass extinction than it is to talk about the total number of species on Earth (either in the past, or in the present). Percentages can be estimated by taking a sample of organisms from the fossil record just before the mass extinction, observing how many die out during the time of the mass extinction, and dividing the number that die by the number that were in the sample. If the sample is biased in some way (say, for example, your sample includes only organisms that live on land, and not in the sea), then the result you get might be misleading, and so the exact numbers are debatable. But determining the total number of species on Earth is an even harder problem, and isn't as straightforward to estimate using samples."
A brief history of mass extinctions,Is there any evidence that there were ever any epidemics plaguing dinosaurs? Like the bird flu?,"Yes, the dinosaurs were subject to the plague, but that's not the huge way they go extinct."
A brief history of mass extinctions,If the sunlight was blocked how the plants  survived ?,"Well first, sunlight wasn’t completely blocked out and prevented from reaching the Earth’s surface. The amount reaching the surface was greatly diminished, but still some sunlight made it through. 

Second, not all plants have the same demands. Some plant species adapted to life with limited sunlight. Some plant species surely died off, but the ones which evolved to be more hardy survived."
A brief history of mass extinctions,How did the mass extinction start?,by an asteroid
A brief history of mass extinctions,"So, did T-Rex go extinct?","T-rex itself is extinct.  There are no more T-rexs living anywhere at all.  However, modern birds are closely related to dinosaurs, based on biology, fossil records, and evolutionary studies.  That does not mean today's chickens and turkeys are dinosaurs like you would see in Jurassic Park or other dinosaur movies.  But it does mean our birds today have dinosaurs in their very ancient family tree, and so sometimes birds are considered "living dinosaurs"."
"Atomic number, atomic mass, and isotopes","So for radiometric rating to work, you have to assume that the element has been decaying at the same rate the entire time?","@Sean Collin: the amount of carbon isotopes can be determined for each geologic era by analyzing glaciers, because they imprison atmospheric gases. The geologic era can be determined by the depth of the extracted sample from the ice, because the rate at which it forms is predictable. That can also be done with other kinds of natural formations such as rocks, soil, and anything that captures carbon atoms, and that have predictable rates of formation."
"Atomic number, atomic mass, and isotopes","If everything is actually 99.99% empty space, that means that the ground is too... Why aren't we falling through all that empty space? Also, If everything is 99.99% empty space, why can we only feel the NOT empty space?","Similar charges present in electrons of atoms repel each other. So, we don't fall through that empty space."
"Atomic number, atomic mass, and isotopes",How did they know that it takes 5730 years for it to decay? How can we measure such a thing?,"The half-life of carbon 14 is 5730 years, this means that 50% of it will undergo radioactive decay in 5730 years.  Or another way of looking at it a single atom of C14 has a 50% chance of undergoing radioactive decay in 5730 years.  

The decay of an individual atom of c14 is random so if you have 12 grams of carbon 14 you have about 6 * 10^23 atoms so there will be some that decay within seconds and other that will decay in 10,000 of years.  We know that the rate of decay is random but on average a constant so if 3*10^23 atoms in the 12 grams will decay in 5730 years we know that 5*10^19 will decay in a year or 1.62*10^12 atoms decaying in a second.  

This rate is measurable and from the decay rate you can determine the half life."
"Atomic number, atomic mass, and isotopes",How do you compute for their half-life?,"You can refer to the answer by Charles LaCour - it basically states that by measuring the rate of decay at smaller amounts of time, we can leverage the fact that the rate of decay is often a constant (a certain number of atoms decays within a certain amount of time). Then, we can use this constant to apply to larger amounts of time, finding the half-life of a complete sample.

Mathematically, you can use the half-life formula to determine the half-life period:

N(t) = N0 * (1/2) ^ (t/h), where
N(t) is the amount remaining,
N0 is the original amount,
t is the time elapsed,
and h is the half-life period.

You can rearrange the variables to solve for the half-life."
"Atomic number, atomic mass, and isotopes",How is possible carbon 14 atom convert to nitrogen 14 gradually ? I thought that can not be possible and if it does i guessed somehow in years the carbon can convert to some elements which has less proton numbers not opposite way,"A neutron decays into a proton by one of the constituent down quarks decaying into an up quark, emitting a W⁻ boson, which decays into an electron and anti-neutrino."
"Atomic number, atomic mass, and isotopes",this sounds hard to do 😂,same. i think i might faint
"Atomic number, atomic mass, and isotopes",How do you calculate the natural abundance of an isotope?,"You can't  directly calculate it you have to measure the amounts 
 of each isotopes found in nature and calculate the relative abundances."
"Atomic number, atomic mass, and isotopes",so if the atomic number of a element is given you know what the proton is; the same as the atomic number. if that element is neutral you also know that the number of electrons is the same. but if you are only given the atomic number is it possible to find out what the atomic mass is?,"No. The atomic mass is a laboratory-measured value, so you cannot determine it from the atomic number. 
 
You can *approximate* the atomic mass of a single isotope (not the element in general) by guessing that the atomic mass in atomic mass units is numerically the same as the mass number (the number of protons + the number of neutrons). However, that is only an approximation."
"Atomic number, atomic mass, and isotopes","There is any better way to find the age of a very very old object ?? Like with what we mesure if carbon-  14 ,potassium-40 and uranium-235 concentration test fails ? And one more question: how accurate those carbon  dating is? Can the fossils be infested whit those isotopes when the test is made ?","Carbon dating is, maybe surprisingly, very accurate and otherwise you can use other isotope dating methods. These are in fact very reliable :-)"
Hypotheses about the origins of life,"Could another experiment much like the Miller-Urey experiment be conducted again with slightly different components today? If so, could we learn anything new from it?",Clicking on the expandable 'What about Nucleotides?' link revealed an answer to your question. It's noted that "one recent study using a different approach (not an approach similar to Miller and Urey) found that RNA nucleotides could be formed from inorganic components under conditions thought to resemble those of early Earth."
Hypotheses about the origins of life,"Does it mean that DNA is the evolution of RNA?
Is it possible that Panspermia and Abiogenesis happened at the same time ?","Hi, Bintia and thank you for your questions.

DNA evolved from RNA, that's our current belief. When i was a student i was constantly searching for some kind of info on that process (in other words, how did DNA became from RNA) but i found almost nothing. Some scientists believe that viruses "invented" DNA because they are the only "living" beings who have both RNA and / DNA for their genetic material.

I would say it is possible that panspermia and abiogenesis happened at the same time, however we can only speculate about that. Abiogenesis might be still happening in some obscure thermal vents somewhere in the depths of oceans, who knows."
Hypotheses about the origins of life,"Why is it that the RNA world hypothesis is more favored  over the Metabolism-first hypothesis? (In other words, how is the RNA hypothesis more reasonable?)","I assume that's because RNA molecules have many abilities and in general have more diverse functions than proteins. RNA can be a genetic molecule (like in some viruses), it can epigenetically control the expression of genes (like micro-RNA molecules), it can have enzymatic abilities (like ribozymes) and so on. Proteins, on the other hand are mostly known as enzymes.

So, from our current perspective, it looks like an RNA molecule had better chances of catalyzing its own replication because, in theory, it can do that. Proteins are good enzymes, but they can't serve as genetic material and therefore they can't make copies of themselves.

I should also note that the discovery of prions in 1980's dramatically changed our view on the topic. It happened in the moments when most people in the scientific community already declared RNA's as winners in the battle against proteins but then, all of a sudden, Stanley Prusiner discovered proteins that can turn other (but similar) proteins into their own clones.

Even though it still looks like RNA molecules are better candidates, the battle is still going on."
Hypotheses about the origins of life,Do you believe that the diversity we see around us comes from a single ‘origin of life’ event or multiple ‘origin of life’ events?,"All life on earth appears to be related — this is based on the presence of ancient genes that are found in (essentially) all living organisms.  

This progenitor of all known life is referred to as the "Last universal common ancestor" (LUCA).

You can start learning more about this here:
https://en.wikipedia.org/wiki/Last_universal_common_ancestor"
Hypotheses about the origins of life,"So how exactly, do the inorganic elements on early Earth turn into the organic maters that are the building blocks of life","The amino acids that are the base building blocks of life are simple to make.  In the 1950's scientists combined ammonia, hydrogen, methane, and water vapor and added energy in the form of electrical sparks and 11 of the common amino acids were formed."
Hypotheses about the origins of life,This is so confusing!!,i know it may look confusing but its how life works.Life keeps going and going and soon we have the animals today and cells help all life stay alive
Hypotheses about the origins of life,"Since there is so much diversity on Earth,is it more or less likely to have an ‘origin of life’ event today than 4 billion years ago? Is there a limit to mutations?","We think that any newly originated organism (or proto- organism) would be very unsophisticated and unlikely to survive competition with existing organisms.  This suggests that successful "origin of life" events (i.e. where the new organisms persist in the environment) are very unlikely.

Beyond that, we aren't sure exactly what needs to happen for an "origin of life" event to occur so it is difficult to know whether current conditions would enhance or inhibit these events.

We do know that the early earth's atmosphere was reducing (didn't contain oxygen) and it is quite possible that oxygen would interfere with the chemistry necessary for an "origin of life", so my _guess_ is that a new "origin of life" is unlikely on this planet ..."
Hypotheses about the origins of life,what is difference between Miller and Operian  hypotheses and who was right?,"The Operian hypothesis suggests that simple, inorganic molecules gave rise to more complex organic ones (such as amino acids), and then those combined to create the most complex molecules of life (such as proteins). Miller and Urey, on the other hand, performed an experiment in which they simulated an early earth environment and proved that small inorganic compounds can combine to create more complex organic ones under such conditions. In short, the Miller experiment provided scientific support for the Operian hypothesis."
Hypotheses about the origins of life,How is it that the RNA World hypothesis is still being considered?   See this article from retraction watch:  https://retractionwatch.com/2017/12/05/definitely-embarrassing-nobel-laureate-retracts-non-reproducible-paper-nature-journal/,"A quick search of pubmed for the phrase "RNA world" finds 914 papers:
https://www.ncbi.nlm.nih.gov/pubmed/?term=%22RNA+world%22

Why do you think retraction of a single paper (about one possible contributor to a protein independent RNA replication) invalidates this hypothesis?

If you are really interested in this subject I encourage you to start learning more by looking at some of the references at the bottom of this article.

Two examples:
•http://www.ncbi.nlm.nih.gov/books/NBK26876/

•http://evolution.berkeley.edu/evolibrary/article/ellington_03"
RNA world,What makes the fruit fly so suitable for research?,"it has short life span and few chromosomes, so it is much simpler to study them."
RNA world,So they say that the first organisms were RNA? Or not?,"Yes, scientists claim that RNA formed first (possibly at the bottom of the sea) and then fused into double-stranded DNA organisms. That's what the RNA Life Theory is. Hope that helped"
Ecological levels: from individuals to ecosystems,""An individual is one organism and is also one type of organism(species)"

If two species mated and some infertile hybrid was made that could not pass on its genes, would that infertile hybrid technically NOT be an individual because it doesn't belong to a species, being the only member?","Good question! The definition of what a species is--and to some extent, what an individual is--does not have a clear consensus among taxonomists. I will illustrate this with a genetic definition, a biological definition, and an evolutionary definition of species.

Being a genetically distinct species, regardless of fertility or species population, is sometimes enough for taxonomists to classify different organisms as separate species. Take Lonesome George for instance: he was widely considered to be the last individual of the species _Chelonoidis abingdonii_. However, he was still genetically distinct from the other Galápagos tortoises. George would therefore be considered a separate species by genetic standards. The same principle can be used for hybrids, who have a different genetic makeup than their parents (I.E: The mule).

However, some may use different definitions of species to draw the line between different organisms. Some use what is called the Biological Species Concept, which involves the ability to interbreed with other individuals. If two species cannot breed with each other, they are distinct. This definition breaks down with hybrids; with hybrids, you can have two genetically separate species with two different niches be considered the same species because of hybrid production. Applying this concept here, your infertile hybrid would be the same species as its parents.

If you look at the Evolutionary Species Concept, though, you'd be right. This concept is like the Biological Species Concept, but the offspring maintain their characteristics over time. For instance, look at Pakicetus, what is known as the most basal whale. Its remains suggested an aquatic lifestyle, and it also had an inner ear structure found in modern Cetaceans. All of these characteristics remained as the species evolved. Because the hybrid is infertile, it would not be able to maintain its characteristics, meaning that it is not a species under this concept.

I encourage you to explore more of these species concepts, as this question does not have a clear answer. Depending on your definition, the answer would be a yes or a no.

Did this help?"
Ecological levels: from individuals to ecosystems,How are niches related to these levels in ecology?,"Niche is the *role* an organism has in an ecosystem. For more info, click https://www.khanacademy.org/science/biology/ecology/community-ecosystem-ecology/v/niche-bozeman (video) or https://www.khanacademy.org/science/biology/ecology/community-ecosystem-ecology/a/niches-competition (article). I think the study of niche should be in *community*, because it is the *role* it has that impacts other populations. I hope you find this helpful! :)"
Ecological levels: from individuals to ecosystems,Can an ecosystem consist of two communities,"Yes, an Ecosystem can have two communities."
Ecological levels: from individuals to ecosystems,What are some of the "many definitions" of species?,A biological species is a group of organisms that can reproduce with one another in nature and produce fertile offsprings.
Ecological levels: from individuals to ecosystems,What would happen if there were no ecosystems/ if all the ecosystems died? Is there a theory for what would happen to all the living things?,Probably the whole Biosphere and Life would collapse. But I do not see shortly :D
Ecological levels: from individuals to ecosystems,"Could a community of animals slowly start collapsing on its self. For example they start to eat each other slowly, slowly eating there population away until they no longer exist. Basically eating each other to extinction.",Every population that experiences a spike eventually exhausts their food source and collapses. They don't usually resort to canibalism but it does happen sometimes. This usually causes a chain reaction across the food web that can increase and decrease other organisms in the community.
Ecological levels: from individuals to ecosystems,why is population bigger than ecosystem,It does not make sense. The ecosystem is a category above the population of individual species. An ecosystem comprises of many populations...
Ecological levels: from individuals to ecosystems,"In the second paragraph, individual and species are the same thing or different? Kinda need more information","Individuals and Species are different.. Look at it this way - 
Definition of Individual - A single organism, of a specific species. 
Definition of Population - All of that particular species in a given area.
So, species in this example,  is just an additional way to specify the  ecological levels. 
Hope that helps!"
Ecological levels: from individuals to ecosystems,Can an ecosystem consist of two communities?,"Yes, an Ecosystem can consist of two communities. :D"
Interactions in communities,"In the overview, they made mention of herbivory. is there any such ting as carnivory or omnivory? and if there was, what would have been the effect, considering the predator and prey relationship.","Yes, there are such things as carnivory and omnivory, the *predator-prey relationship* will still be +/-, because the predator benefits from eating the other organism but it harms/kills the prey. I hope you find this useful! :)"
Interactions in communities,"Is there a type of interaction for a plant eating an animal, like a Venus flytrap eating a fly? It doesn't seem like a predatory interaction, but it also doesn't seem like a herbivorous interaction.",That would be predation. One species is eating another.
Interactions in communities,Where do we draw the line between parasitism and predation. Would a mosquito sucking on our blood or lice eating our scalp be parasitic or predatory?,"The examples you have given are both parasitic but the way I understand it, the difference lies between host and prey.
A parasite can cause death but it's kind of counter-intuitive for them to do so. They usually want to live and continue to feed from a host for some time. Also unlike a predator which consumes the majority of it's prey, a parasite can only feed off a small part of it's host.
Hope this helped🍀"
Interactions in communities,"What about *0/0* relationships, where both species live in the same environment, but _do not affect each other?_","The definition of relationship is that two things have some effect or are connected in some way. If they both do not affect each other, then there is no relationship."
Interactions in communities,is (-/0) type of interaction not a thing?,"Technically not, but I think that this -/0 still exists. For example, stepping on an ant: You don't notice it, but the ant is killed."
Interactions in communities,why does the secondary consumer still depend on the producer despite consuming the primary consumer?,"It's a chain of interactions, where all levels can affect all other levels. For example, if all the producers died off due to a disaster, the primary consumer population would drop drastically, which of course would affect the secondary consumers."
Interactions in communities,"Can anyone give me separate examples of the various types of adaptations in preys (mechanical, chemical and behavorial)?","How about this:
Mechanical: something like antelope that can run fast to escape, or a tortoise hiding in its shell. Camouflage is very common, as is its inverse, aposematic (warning) coloration
Chemical: A skunk spraying! Many insects have similar chemical defenses
Behavioral: Parrots flocking, quail "exploding" into flight suddenly and noisily (maybe this is mechanical too?). Herds of ungulates stick together to make it harder for the predator."
"Population size, density, & dispersal","How can i measure the density of grass? I mean, in grass is hard recognizing an individual of another one.","setting up quadrats up staking out an area with sticks and string or by using a wood,plastic or metal place on the ground"
"Population size, density, & dispersal",What are patterns of distribution and density.,Patterns of distribution are how individuals in a population are distributed in space at a given time
"Population size, density, & dispersal",so whats exactly the diffrence between population density and size ?,"Population size means the total number of organismns in a given area like number of oak trees in a forest. 
Population density means number of organisms living per unit area like number of oak trees in say 1 sq km of the forest."
"Population size, density, & dispersal",I don't unederstand the mark-recapture method,"The Mark-recapture method is a method used by ecologists to estimate populations that are too difficult to count manually. For example, imagine yourself and two others manually trying to count all the people in New York. Impossible, right? 
The mark-recapture method has two parts: marking a group of animals, say deer, and recapturing a group of deer at a later date, say three months (the two groups of deer have nothing in common except they're captured in the same area and I assume are the same species). For an example with numbers, say we marked 20 deer and released them into the wild, then three months later we return to the same area and capture 50 deer, 5 of them marked. Since 1/10 or 10% of the deer were marked, we can assume that 10% of the deer are the deer we marked previously, or 20 deer. We then multiply 20 by 10 (to get 100%), and so we have an estimate of 200 deer.
This method is fallible though, as deer might be voluntary  captured to receive food (example)which would result in a underestimate, or that the marked deer might be more shrewd the next time the experimenters come along and escape quicker than the rest, resulting in an overestimate."
Intro to biogeochemical cycles,I didn't understand how can matter be recycled?,I agree. This article contains big words that many young adults my age cannot understand.
Intro to biogeochemical cycles,"explain which cycle (water, carbon, or nitrogen) relies mostly on physical changes to move matter through the biosphere.","To answer this, think about what a physical and chemical change are. Physical changes change the physical properties of a substance but don't change what it's made out of. Chemical changes involve chemical reactions and rearrange atoms in substances. Now we think, which of these cycles keeps the substance the same throughout? 
The answer to that would be the water cycle. Through evaporation, condensation, precipitation, etc, water just changes its state and some other properties. We don't take the hydrogen and oxygen and rearrange them in any way, or anything like that. 
If you take the carbon and nitrogen cycles, there you have carbon cycling between inorganic CO2 in the atomosphere and organic carbon-based compounds in organisms. There's a chemical change right there. The nitrogen cycle involves atmospheric inorganic nitrogen (N2) turning into organic ammonia (NH3). Another chemical change."
Intro to biogeochemical cycles,"Under the third title (Energy flows, but matter is cycled), in the third paragraph it mentions only the six most important biogeochemical cycles. But all bioelements undergo a biogeochemical cycle, right? Even oligoelements and trace elements? I mean, they must come from somewhere.","Carbon cycle.
Nitrogen cycle.
Nutrient cycle.
Oxygen cycle.
Phosphorus cycle.
Sulfur cycle.
Rock cycle.
Water cycle."
What is ecology?,Which level of ecology deals with the concept of "niche?","Niche is the *role* an organism has in an ecosystem. For more info, click https://www.khanacademy.org/science/biology/ecology/community-ecosystem-ecology/v/niche-bozeman (video) or https://www.khanacademy.org/science/biology/ecology/community-ecosystem-ecology/a/niches-competition (article). I think the study of niche should be in *community*, because it is the *role* it has that impacts other populations. I hope you find this helpful! :)"
What is ecology?,"In biotic and abiotic factor, why does dead skin cells fall under biotic instead of abiotic?","This is because they were once alive, and were created by a living thing. Take an abiotic rock, for example, it was never living, never part of a living thing, and will never be. Dead skin cells, however, were once living as part of a living thing such as you. So even though those cells are dead, they are still considered biotic factors"
What is ecology?,So Ecology Is basically how different things Interact with each other.,"Yes and no. Organisms interacting with each other are only part of Ecology. The formal definition of Ecology is the study of how life interacts with life/other living things and their environment. So, yes different things are interacting with each other, but they're also interacting with their environment, like the ocean or a forest, or a large rock."
What is ecology?,what is difference between ecology and environmental science ?!,"This is a great question, and I am so glad you asked! Ecology is the study of how living things interact with each other and their environment. Environmental science uses ecology, but falls on the more human end of the spectrum, focusing on conservation, sustainability, and basically how we can keep the environment going."
What is ecology?,"In a Food Web, can there be more than five in a chain to the top?","Sure, but really not practical since energy diminishes by about 90% as we move to each level.   0.001% is really slim and under most circumstances would not be adequate to support a 6th layer."
What is ecology?,"When studying organisms in ecology can it be any size, like some might study bacteria, but studying an elephant would also be studying an organism?",the list above is correct because it is in smallest to largest.
What is ecology?,What are examples of emergent properties?,"An emergent property may be the cycle of energy within a community that is made possible through the populations included in the community. An energy cycle would not exist in a population, but would exist in a community due to the presence of populations.

Hope that makes sense!"
What is ecology?,Does the Biosphere have to be the entire earth? Or can it be made up of multiple Biospheres depending on how you look at it?,"A biosphere does not necessarily have to be an entire planet.The Amazon forests or the Savannah grasslands,for instance,can be considered as biospheres. Earth has several such biospheres so when we consider all the biospheres on earth, our planet simply becomes the largest scale to look at biospheres.So yes,biospheres can be made up of multiple Biospheres depending on how you look at it."
What is ecology?,What is the difference between ecologists and environmentalists?,"I believe that the difference is so nuanced that they can be used almost interchangeably, but ecologists study the science of how nature evolves and lives and try to conserve that, while environmentalists study the effects of human actions on the environment and how to prevent any negative outcomes."
What is ecology?,is dead plant biotic or aboitic,"Something that is biotic is a living or once living component of a ecosystem, so a dead plant is biotic."
Energy flow & primary productivity,"My name is Jannah, my question is are the decomposer's the main part of the food chain/ the food web?","@Jannah  Hello, Hope you're having a great day!
 here is a close answer to what you were questioning....
Actually, in some cases, They may be considered the main part of a food chain/ food web because they recycle elements (minerals) which help plants grow and plants transfer their energy to the consumers and so on....."
Energy flow & primary productivity,Why is productivity an important factor when considering the stability of an ecosystem?,"Because without productivity there is no consumerism. :D


The stability of the ecosystem lies in the fact that productivity and consumerism constantly happen without disruptions."
Energy flow & primary productivity,"Hi! I need some help reconciling the reasons why energy is "lost" between trophic levels. In paragraph 3 of the section titled, "Producers are the energy gateway," you talk about how "(energy is) dissipated as heat as it moves through the ecosystem" and then explain in the "Energy pyramids" section that "(An energy pyramid's upright) pattern reflects the laws of thermodynamics, which tell us that new energy can't be created, and that some must be converted to a not-useful form (heat) in each transfer." However, the penultimate paragraph of the section titled, "How does energy move between trophic levels?" lists the reasons for inefficient transfer of energy, and it isn't clear to me how the previously described heat dissipation factors into this list. Can you clarify? Thanks!","Okay so basically, imagine a human and you're eating food. Not all of that energy gets put into your biomass, some of it goes to maintaining homeostasis (like your blood temperature and stuff.) If you eat a human (which you probably won't...), the energy you get is going to come from the biomass and the temperature of blood wouldn't give you any energy. Therefore, the energy is lost."
Energy flow & primary productivity,"Hello! Where do decomposers fit in on the energy pyramid, and what percent of the energy of which level do they receive (i.e. tertiary consumers receive 10% of the secondary consumer's energy)? Thank you!","Decomposers are placed in *separate trophic level*.

A separate trophic level, the decomposers or transformers, consists of organisms such as bacteria and fungi that break down dead organisms and waste materials into nutrients usable by the producers.


You see that they work entirely different than producers or consumers."
Energy flow & primary productivity,"In the graphics, particularly the energy, biomass, and number pyramids, why do the authors feel the need to label the producer a primary producer? Is there a such thing as secondary producer?","*Good question*


Occasionally, terms such as 'secondary producers' and 'tertiary producers' are used. Animals that consume plants are considered secondary producers since they 'produce' the biomass for their predators.

So yes, there is a thing such as secondary and even tertiary producers. Regarding the length of chain of food.

https://biologydictionary.net/producer/"
Energy flow & primary productivity,"If energy level decreased as the trophic level increases, doesn't this mean plants and other primary consumers are more energy dense than secondary and tertiary consumers? Then why is it that animal based foods are more energy dense than the plants we eat?","*Total* energy decreases, but as you noted energy density tends to increase.  The difference is because organisms in lower trophic are typically much more numerous!

If you weighed all the plants in an ecosystem and compared that to the mass of herbivores what would you find?

Think about a grassland — how much grass is there compared to grazing animals?

Does that help?"
Energy flow & primary productivity,Is there a way to increase/maximize the transfer efficiency of energy between trophic levels or in general?,"In general, only about 10% of energy is transferred from one trophic level to the next, and this number can vary from 5-20% depending on the ecosystem. This means that 90% of obtained energy is lost at each trophic level, greatly affecting the maximum number of possible levels in the ecosystem.

A crucial component of this ecological efficiency is the trophic assimilation efficiency: the proportion of consumed resource biomass that is converted into consumer biomass. Theoretical work predicts trophic assimilation efficiency to be in the range of 13–50%, depending on the predator-prey mass ratio. Which means that it relies on mass-ratio.

We cannot do much to increase it though but to create different food chains. https://royalsocietypublishing.org/doi/10.1098/rspb.2015.3043


which is not something we can do in nature. People a lot of tackle into that problem and our nutrition is really interesting. We produce things such as antibiotics, food supplements, proteins, probiotics. which all can _highly increase_ transfer energy because almost ll we eat is used. (especially in case of proteins and vitamin supplements).

https://globalchange.umich.edu/globalchange1/current/lectures/kling/energyflow/highertrophic/trophic2.html
https://courses.lumenlearning.com/boundless-biology/chapter/energy-flow-through-ecosystems/"
Energy flow & primary productivity,"So I was wondering when you find NPP, you do GPP - Respiration Loss, right? But I now I get the respiration loss in a percent (For example: 20%) If you were trying to do the subtraction, how would you subtract 20% from 0.012 grams/cm2/day if 0.012 is the GPP and 20% is the respiration loss. The question also gives that 1 gram of rice is 1000 calories.","First of all, find the real value based on percentage.

If it says respiration loss is 20%, you find what 20% of NPP 0.012grams, right?

After you get value in grams you can subtract it."
What is an ecosystem?,"Is biodiversity something that can be artificially encouraged? Like, if biodiversity is important for promoting resistance/resilience, how can an ecosystem increase their biodiversity? Is that something that only comes about after long periods of equilibrium (species are allowed to mutate, occupy specialized niches, etc)? Or can humans speed up the process, perhaps by introducing species from similar ecosystems and allow them to spread and take hold, thus increasing biodiversity in an ecosystem?","I do not think we can artificially boost it or promote successions biodiversity abundance etc.

All we can do is to try to interfere as less as possible and to eliminate human impact factor which destroys habitats.

People have been changing it for millennials! By introducing species, hunting for species and making them extinct, etc, but there is no way I think we can artificially boost and enhance it.

Even the idea of zoos is utterly dumb (in my opinion) and does no good. Safaris can let it slide."
What is an ecosystem?,What makes up an eco-system?,"Biotic factors, such as producers and consumers, and abiotic factors, such as the temperature, soil, water and physiographic factors."
What is an ecosystem?,why is this so long to read bruh like fr,Because this article is about ecosystems and many different things happen when you learn science.
What is an ecosystem?,why decidous forest are so called?,"yes during fall the leaves start to fall off the trees, and thy grow back on untill summer."
What is an ecosystem?,Why is it that all the ecosystems are so different? Can you find the same species in different ecosystems?,"Yes, you can. But what makes an ecosystem is not just plenty of species but habitat and their interactions as well."
What is an ecosystem?,"On the 2nd key point, it was mentioned that  "Broad categories of terrestrial ecosystems are called biomes." I looked up "biome" on google and read that a biome is not an ecosystem.

So, are biomes ecosystems? Thanks.","No,It is not an ecosystem because it (biomes) is based on climate"
What is an ecosystem?,Is climate change part of ecosystem.,"Yes, it is.

Just like evolution is part of life and even the individual life of species. that way climate change is part of an ecosystem."
What is an ecosystem?,what do biomes and ecosystem have in common,"Biome can be also called biotic community. It is the biotic environment of an ecosystem, as we know that ecosystem include living things (biotic factors) functioning together with the physical envionment (abiotic factors)."
What is an ecosystem?,why are biomes and climate so important for ecosystems?,"Biomes are extremely important to continue life on Earth as it is known today, as each one helps to balance other biomes through climate and variation, and provides unique necessities to both biome and human. Climate is an important environmental influence on ecosystems. Changing climate affects ecosystems in a variety of ways. For instance, warming may force species to migrate to higher latitudes or higher elevations where temperatures are more conducive to their survival."
Life history strategies,Insects come under semelparity or iteroparity?,"I think it depends on the insect. Most insects, such as praying mantises and some moths would fall under semelparity, because they die right after reproduction. (some moths don't even have mouths!) But other insects, like the monarch butterfly, can come back year after year, so that would be iteroparity."
Life history strategies,How can you tell from a life table that the population of the organism is iteroparous or semelparous?,"You might not be able too,  but if you look at multiple tables over week periods, you will notice how a ton of elderly die and the base widens in *semelparity*. When it is *iteroparous*, the pyramid tends not to fluctuate as much."
Life history strategies,"Is there a connection between semelparity/iteroparity and fertilization? Could it be that when the female egg is fertilized frequently throughout an organism's lifetime, iteroparity will occur?",Exactly. The sexual behavior of an animal is intertwined with their parity.
Life history strategies,"Is it true that the more offsprings of one organism survive, the more fit one organism is?","Yes, that is the accepted definition for fitness in evolutionary biology.

To learn more:
https://en.wikipedia.org/wiki/Fitness_(biology)"
Life history strategies,How can you maximize the number of plant species (richness) in the smallest area you can?,To give area with many factors and different niches so plants are not in competitive relations to each other.
Population regulation,is  Population stays under carrying capacity logistic or exponential.,"logistical population growth has a carrying capacity, exponential doesn't."
"Life tables, survivorship, & age-sex structure",Why is Japan's population shrinking? Isn't it a developed country with good medical care?,"Those things are true, but Japan has an extremely high population density, due to being confined to the nation's islands. High population density puts a negative pressure on growth because there is less space and fewer resources to accommodate higher numbers of population."
"Life tables, survivorship, & age-sex structure",why are the developing countries shrinking while the 3rd world countries populations are growing shouldn't it be the other way around?,"Because they have better-controlled fecundity and fertility.

Many countries such as China even have restrictions to shrink their population on purpose because they are overcrowded.

As for underdeveloped countries, they are not controlled. The poorer the country the less control and different mindset."
"Life tables, survivorship, & age-sex structure",Can a population pyramid be used for animals?,"Yes, yes they can. Population pyramids can be used for any organisms. They could be used for bacteria if you wanted."
"Life tables, survivorship, & age-sex structure","Someone please explain it to me, in the Dalla mountain sheep survivorship curve, the x-axis represents no. of individuals. Fair enough. 
But, in the second survivorship curve, the x- axis says "percentage of maximinum life expectancy". What does it mean, and how does it help us?
Thanks.","That's not the Dalla mountain sheep curve. It's a Species survivorship curve with different species such as: human, bird and tree. It gives us a big picture about how many individuals survive over time. For instance, for trees: many seeds are dispersed, not many find good conditions to sprout, and even less may grow. However, one they reach adulthood, it is likely that they continue living. They have a continuous curve at the "life expectancy" axis. It is the reverse case for humans. Babies are likely to survive their first years and they carry on living. However, after adulthood, their life expectancy is declining. Birds are the average between these two extremes. This information is very relevant. Let's suppose you intend to make a conservation programme for a rare tree species. You would have to protect (from logging) the mature and old trees and, in the meantime, you should make a nursery to grow young ones and plant them constantly. In this was you could ensure that the species would not die out."
"Life tables, survivorship, & age-sex structure",Im still confused as to how the fourth age structure pyramid shows a shrinking population growth,"The population pyramid is smaller at its base, meaning that there are fewer young individuals: fewer people who are able to reproduce. Also, there's a spike around the middle-aged section - people who are about to retire and can't reproduce - which will lead to a shrinking population, because there are less people able to reproduce.

tl;dr: There are fewer children than adults."
"Life tables, survivorship, & age-sex structure","In population growth, wouldn't disease also play a key role in an animal surviving?","Diseases are one possible death factor, but not the only one. Therefore death rates are a more accurate measure to describe population growth.
Try to think of it through a money analogy: the total amount of money you have in your wallet is the population, your income is the birth rate and your expenses represent the death rate. If you wanted to know how much money you have, you wouldn't care about _how_ you had spent it, just about _how much_ you spent. It is the same with population growth: you care about _how many_ individuals died, not about _how_ they died."
"Life tables, survivorship, & age-sex structure",Insects will have which type of survivorship curve?,"Type III. Spiders for example, lay thousands of eggs that mature on their own without parental nurturing."
Exponential & logistic growth,Why can we just say that the carrying capacity of the seals is 7500? Just because the data seems to imply that?,"Yes! It's an interpretation of field observations. When someone analyzes real world data, the trends that appear can usually be fit to a known mathematical function. In this case, the logistic curve of the data had a carrying capacity of 7500 so that is the inferred capacity for that population. It's a great question though, and considering the spread of that data it might have a significant standard deviation (so 7500 might not be the "exact" carrying capacity)."
Exponential & logistic growth,My textbooks says that "The intrinsic rate of natural increase is biotic potential." what does it mean?,I believe "biotic potential" refers to the availability of resources.
Exponential & logistic growth,Is there any way to include the bounces into an equation? I am talking about the bounces in the last graph.,"You could add error bands to the graph to account for the deviations of the observed values from the values the model predicts. These would not tell the viewer whether a given observation was above or below the predicted value, but they would remind the viewer that the equation only gives an approximation of the actual values."
Exponential & logistic growth,"In Exponential growth there is a line:
"the number of organisms added in each generation—increases as the population gets larger" and
"In exponential growth, a population's per capita (per individual) growth rate stays the same regardless of population size, making the population grow faster and faster as it gets larger." 
Aren't these contradictory?","No, if you have a growth rate of 1 per every 10 people.  If you have a population of 100 people then the number of people added to the next generation is 10 giving a population of 110, the next generation no adds 11 people for a population of 121.  If you continue this table you get this:
```
# added  Total
         100.00
10.00    110.00
11.00    121.00
12.10    133.10
13.31    146.41
14.64    161.05
16.11    177.16
17.72    194.87
19.49    214.36
21.44    235.79
23.58    259.37
25.94    285.31
28.53    313.84
31.38    345.23
34.52    379.75
37.97    417.72
41.77    459.50
45.95    505.45
50.54    555.99
55.60    611.59
```
Each of these generations adds  1 person for every 10 people of the previous generation but since the generations get larger the number of people added get larger as well."
Exponential & logistic growth,My textbook mentions "Geometric Growth" in addition to Exponential and Logistic growth. Could you explain this? Thank you!,"Geometric growth is a situation where successive changes in a population differ by a constant ratio. So while exponential growth is a drastic amount of growth in a short amount of time and logistic is growth that practically stops at some point, geometric growth would be a growth rate that almost never changes. For example, a growth of 2x per hour is geometric growth; every hour, a population doubles, with that rate never changing. So if that population starts with 2, the next hour is 4, then 8, then 16. Exponential growth would be more like 2x^y of growth. Does that make sense? That's the clearest I can think to explain it. Sorry if it's a little confusing."
Exponential & logistic growth,how is a carrying capacity of an ecosystem affected?,"humans have used technology.  When the idea of food as a limitation was providing part of the capacity of a smaller ecosystem, technology that harvested and grew food more efficiently increased how many people the ecosystem could support"
Predation & herbivory,If you refer to the linked reference material. It distinguishes between true predation and general predation as it has been defined.,Yes with mosquito bloodsucking being an example of _general predation_ and lions being true predators. Because predator eats all parts of organisms and kills it.
Predation & herbivory,So what exactly is herbivory and what is predation?,"The name itself says - herbivory is eating plants and predation is being a predator (meaning carnivore).

Herbivores feed on plants, carnivores feed on meat (other animals). To eat or to be eaten. :D"
Predation & herbivory,""A mosquito sucking a bit of blood  can be a form of predation." quoted above  I believe is a wrong statement because it's only a mode of nutrition -Saguivorous and it can be more a part of parasitism , a facultative ectoparasite. 
if the above statement made is true ,do you mean to say that the mosquito is the predator and we  are the prey? 
Need an explanation justifying the statement, made above.",If you refer to the linked reference material. It distinguishes between _true predation_ and general predation as it has been defined.
Food chains & food webs,Which has largest population in food chain ?? If answer is Decomposer please mention the authentic source to prove this statement correct means any book where it is written like so.,http://www.saralstudy.com/study-eschool-ncertsolution/biology/ecosystem/123-which-one-of-the-following-has-the-largest-populat
Food chains & food webs,What type of consumer eagal is ?,"Eagles are considered apex predators, or tertiary consumers.

http://www.biology-online.org/dictionary/Consumer"
Food chains & food webs,What are the limitations of food webs?,"Nutrient limitations. This paper explains how plants can be limiting since they are sources of food for herbivores and higher trophic levels are based on herbivores.

https://link.springer.com/chapter/10.1007%2F978-94-011-2342-6_8"
Food chains & food webs,what will happen when predators died,There will be an increase in the prey population
Food chains & food webs,Is there a difference in the way autotrophs and heterotrophs are decomposed?  Do different functions need to be used by the decomposers for each?,"Sort of, but this mostly depends on the composition of the extracellular matrix of the organisms rather than whether they are autotrophs or heterotrophs.

Some examples:
Fungi have cell walls made of chitin and insects have an exoskeleton made of chitin.  Chitin is resistant to degradation and so requires specialized enzymes to breakdown.

Plants (mostly autotrophs but some heterotrophs) have cell walls containing cellulose, which again requires specialized enzymes to break down.

Woody plants have other compounds (e.g. lignin) that are even harder to break down."
Food chains & food webs,why food chain and food web are important to biologist,they wanted to protect the species and help them.
Food chains & food webs,Why are we (Humans) part of the Consumers? How Did it happen?,"We were always part of the consumers because we are *heterotrophs*, which means that we *cannot make our own food*; *we need to eat other organisms for energy*, or else we die, unlike *autotrophs*, which can use photosynthesis or chemosynthesis to *make their own food*, and they *don't need to eat other organisms*, so *all autotrophs are producers* and *all heterotrophs are consumers*. Note: *Autotroph* means _self-feeding_, while *heterotroph* means _other-feeding_. *Examples of autotrophs or producers*: *all plants* and *some bacteria*. *Examples of heterotrophs or consumers*: *all animals*, *all fungi*, *some bacteria*. I hope this helped you! :)"
The water cycle,"I am wondering, how can we empty aquifers faster than they replenish? Shouldn't they be filled up continuously since it's all a cycle? Or is the water that we use from these aquifers raining down, or flowing down, into other areas or the ocean?","it's all a cycle, but there are factors influencing precipitation such as global warming or deforestation etc, pollutants can also be another way of disrupting the fresh ground water."
The water cycle,Can water pollutants and air pollutants interfere with the water cycle and the ecosystem around it?,"Yes. Air pollutants such as sulfuric acid can acidify precipitating rain water, causing acid rain. Water pollutants can render clean drinking water undrinkable, affecting many animals and especially humans who need the most water for uses such as cooking and bathing."
The water cycle,why is clouds white colour?,because vapor is kind of white and combined with dust i guess it pretty much makes a white thing
The water cycle,how do aquifers help the water cycle ?,"Aquifers show up as springs in some places. Sometimes, they even form underground rivers which eventually may join a surface river. In this way, they contribute to the water cycle. Sometimes, they may choose to stay confined in the underground regions."
The water cycle,what's the difference between permeability and porosity?,"*Porosity* is a measure of how much surface is open space.

*Permeability* is a measure of the ease with which a fluid (water in this case) can move through a porous surface."
The water cycle,How is aquifer faster then they replenish.,Groundwater can become depleted if we use it at a faster rate than it can replenish itself. The replenishment of aquifers by precipitation is called recharging. Depletion of aquifers has increased primarily due to expanding agricultural irrigation
The water cycle,What process contributes to the formation of groundwater?,"In the soil there are small holes that get filled with air and are also useful for plant roots. So when it rains, some water seeps into the soil and flows into those small holes."
Tolerance ranges of species,How do scientists tag animals? Do they literally put a tag on them or do they insert some sort of chip in their body?,"There are many ways to tag animals, and inserting a tracking chip (like one might to a pet) is one of them. This article gives several examples of ways that animals are tagged and tracked: http://mentalfloss.com/article/63777/10-animals-we-tag-and-what-we-learn-it
You see, it really depends on what the tag will have to do, and what environmental pressures that the animal (with the tag) experience."
Tolerance ranges of species,What exactly is the definition of an optimal range?,"'Optimal Range' - is the climate conditions an organism (or concept) thrives at. Ex, I can live in 20-degree weather, but I am much better suited for 75-degree weather. 

 It's the small part of the total tolerance range where an organism performs best. 

https://answers.yahoo.com/question/index?qid=20100526210858AAEgzJu&guccounter=1&guce_referrer=aHR0cHM6Ly93d3cuZ29vZ2xlLmNvbS8&guce_referrer_sig=AQAAAIXZ6BqD1eNYAudgzEwZ6QzagpDKNtCymwxBgqkZATdyMMYntae783ZtW8cmH85jCIIVr3Hq76N9rrZxjeEkjkLhvIhCghJiAcUXX0BvSsERvKk6OORWkh1NC72dve8N5rxgMYkAfzCv2BTNUHk-D-HiMtV2gTzBhOG91bCooOcq"
Tolerance ranges of species,Soooo... what is the optimal range of a tolerance graph?,"That completely depends on what organisms and what environmental conditions you are interested in!

An example is the temperature ranges ideal for penguins will be different than those for parrots. 

Similarly, the range of salinity (saltiness) best for marine organisms will be very different than what is even survivable for fresh water organisms."
Tolerance ranges of species,Can tolerance graphs be formatted a different way?,"I do not think so, but others might think it might be possible."
Tolerance ranges of species,What is an example of an organism with a low tolerance?,The polar bear was a great example. They can only survive in the cold.
Niches & competition,What makes a niche an ecological functional role rather than just ecological space,"The majority of species exist in a standard ecological niche, sharing behaviors, adaptations, and functional traits similar to the other closely related species within the same broad taxonomic class, but there are exceptions."
Niches & competition,Why is it not possible for two organisms to occupy the same niche at the same time?,"If two species occupied the same niche, they would be competing for the exact same resources. The competitive exclusion principle states that one of the species would drive the other to extinction. 
NOTE: You probably mean a "species," not "organisms." A species is composed of many organisms, and since those organisms are part of the same species can share the same niche and coexist."
Niches & competition,What are ecological parameters?,"A variable, measurable property whose value is a determinant of the characteristics of an ecosystem."
Niches & competition,What is a Niche? How is it different from habitat? I don't understand.,A habitat is where organisms live (their "house"). A niche is like the organisms "job" they do in the environment.
The nitrogen cycle,I heard that lightning also helps in nitrogen fixation so is it teue or not?,"during lightning   the high temperature and pressure in the air , convert nitrogen into its oxides which dissolve in water to give nitric and nitrous acids.these are used by various life forms. so  its true"
The nitrogen cycle,"Can ammonia be directly converted into atmospheric Nitrogen? Or does it have to be first nitrites or nitrates and then converted into atmospheric Nitrogen?

Thanks to anyone who answers this question.","It has to go through the process of becoming a nitrite, then a nitrate, before it can become atmospheric Nitrogen. All parts of the cycle are needed, and you cannot skip a step of the cycle."
The nitrogen cycle,"If an animal consumes a plant that contains nitrogen, is the animal getting the nitrogen from the proteins in the plant?","Yes, around  half of the nitrogen in a plant is incorporated into proteins.  These will be broken down to amino acids (or small peptides) during digestion and absorbed.

A significant amount will also be incorporated into nucleic acids (RNA and DNA), which will also be broken down and absorbed.

REFS:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC541224
http://www.oswego.edu/~balko/bio203/Digestion.htm"
The nitrogen cycle,What kind of cycle is the nitrogen cycle? Gaseous or sedimentary?,"Both! As you see from the diagram, the nitrogen cycle goes both airborne and underground!"
The nitrogen cycle,how does amino acids fit into this,"In general, the nitrogen cycle has five steps:
Nitrogen fixation (N2 to NH3/ NH4+ or NO3-)
Nitrification (NH3 to NO3-)
Assimilation (Incorporation of NH3 and NO3- into biological tissues)
Ammonification (organic nitrogen compounds to NH3)
Denitrification(NO3- to N2)

Nitrogen assimilation is the formation of organic nitrogen compounds like amino acids from inorganic nitrogen compounds present in the environment. Organisms like plants, fungi and certain bacteria that cannot fix nitrogen gas (N2) depend on the ability to assimilate nitrate or ammonia for their needs.

https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/nitrogen-assimilation"
The nitrogen cycle,"why are the dead zone full of nitrogen and phosphorus , and why do we still us nitrogen rich soils?","Nitrogen and phosphorous from agricultural runoff are the primary culprits, but sewage, vehicular and industrial emissions, and even natural factors also play a role in the development of dead zones.

Increased nutrient concentrations lead to blooming of algae which cause depleted oxygen levels. Ending up with eutrophication.


https://www.scientificamerican.com/article/ocean-dead-zones/?redirect=1"
The nitrogen cycle,Why is it that normal Nitrogen is "N" while Nitrogen in the atmosphere is "N2"?,"because nitrogen atoms tend to bond with other nitrogen atoms to form nitrogen molecules, which are N2."
The carbon cycle,"The article says in the section entitled "Human Impacts on the Carbon Cycle" that more carbon dioxide dissolving in water is not a good thing because it produces bicarbonate along with H+ ions which can in turn reduce the levels of bicarbonate. Am I missing something? The only way increased carbon dioxide will lead to more H+ ions in the water is through producing bicarbonate. All that will happen is that same bicarbonate will be taken out by its own H+ ions, which if they weren't there, the bicarbonate wouldn't be there either. So what's the big deal?

Also, why can't the H+ ions dissolve into the atmosphere?",when carbon dioxide dissolves in water it produces hydrogen ion. the water becomes acidic because of the hydrogen ions dissolved in it
The carbon cycle,what will happen if we did not had athmosphere?,"We probably wouldn't able to breathe - not just humans but other oxic and anoxic organisms.

Also, Earth would look like it looked way before atmosphere formed - full fo craters, volcanoes, extreme thunderstorms, extreme drought, UV light from the sun, etc...

Eroded lithosphere and unfriendly environment."
The carbon cycle,how many carbon dioxide are there in the atmosphere,"According to NASA§ the total mass of earth's atmosphere is 5.1 x 10¹⁸ kg.

As of 2018 the fraction of the atmosphere that is CO₂ is 622 parts per million by mass (409 ppm by volume).

So, since the mass of CO₂ is ~44 g/mol and using Avogadro's number:
5.1 x 10²¹ g ⋅ 6.22 x 10⁻⁴ / 44 g/mol ⋅ 6.022 x 10²³ molecule/mol ≈ 4.3 x 10⁴⁰ molecules of CO₂

§ https://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html"
The carbon cycle,Explain Carbon reservoirs,"There are four carbon reservoirs
1.  In rocks (this includes fossil fuels)
2. Dissolved in ocean water. 
3. As plants, sticks, animals, and soil (which can be lumped together and called the land biosphere)
4. As a climate-warming gas in the atmosphere."
The carbon cycle,What are the similarities and differences between carbon cycle and energy flow?,"Comparison of different scales. I'd understand comparisons of the Carbon cycle to the Nitrogen cycle, but the comparison to energy flow...

Energy flow is something that happens and inseparable from element cycles in the biosphere."
The carbon cycle,"Hi! I just had a quick question:

 Is calcium carbonate limestone?","Limestone is largely made of the mineral forms of Calcium Carbonate , but also has few other particles such as clay and quartz."
The carbon cycle,What is biogeochemical cycle?,A biogeochemical cycle is a pathway by which certain chemical (in this case Carbon) travels through Earth (abiotic and biotic).
The phosphorus cycle,phosphorous cycle is perfect or imperfect cycle ?,"It is an imperfect cycle. This is because not all phosphorous can be retained in the cycle no matter how hard you try. Even without human interference, some phosphorous is going to escape from the cycle."
The phosphorus cycle,"is there a way that we block the cycle?
example : after using phosphorous for fertilizer, we make irrigation canal for fertilizer residu to transport and we harfest the residu to make fertilizer again?
is that possible?",Do you mean to recycle? Sounds nice to me. Not sure what agriculture engineers can say about it. We should ask them :D
The phosphorus cycle,what happens if there is too much nitrogen or phosphorus in an environment?,"If too much nitrogen or phosphorus is present in an environment, plant growth is greatly increased. This is due to the fact that both nitrogen and phosphorus are limiting nutrients. While this abundance of nutrients may be fine in your backyard, it can potentially be very harmful. For example, when too much nitrogen and phosphorus are present in a marine biome, eutrophication takes place. This leads to dead zones."
The phosphorus cycle,how do you spell fofuros,Look at the title of the lesson you posted this on.
The phosphorus cycle,"If it takes such a long time for Phosphorous to go back to the land from the ocean, and it sounds like surface runoff carries phosphorous to the ocean much quicker, will we eventually run out of Phosphorus?","Well,  I do think it is possible,  mostly because most of the industrial phosphorous is obtained from rocks so of course it is necessary for millions of years to pass before new rocks are formed, it is a limited nutrient by all means.  But I don't think we are going  to be able to see such a thing happening in quite a long time.  I think it is by far easier that all our continental water reservoirs become euthrophicated before that."
The phosphorus cycle,How can phosphorus escape rocks?,"Phosphorus can escape rocks when natural processes like wind and weathering chip away phosphorus in a soluble form, where it is then ingested by animals"
The phosphorus cycle,what is the time frame of the phosphorus cycle?,"20,000 to 100,000 years"
The phosphorus cycle,What is the biological importance of the phosphorus cycle?,This seems to be covered in the introduction — did you have a more specific question?
The phosphorus cycle,does phosphate return to the soil and does phosphorus get decomposed by decomposers first?,Phosphate is not back in its chemical free form but via organism since it gets incorporated in living organisms therefore once they decay you have phosphorus in the soil.
The phosphorus cycle,What are the biotic and abiotic factors in this cycle?,"Biotic factors are the living things in an ecosystem so they do not recycle. Abiotic factors are the different physical and chemical components available like temperature, air, water, minerals, rocks,and PH"
Ecological succession,What are some of the stages that occur during primary succession ?,"This is an example of hydrarch primary succession (i.e. succession in a wet area):
*Stages*:
1. Phytoplankton stage
2. Submerged plant stage
3. Submerged free floating plant stage
4. Reed-swamp stage
5. Marsh-meadow stage
6. Scrub stage
7. (climax) Forest

Source: https://farm9.staticflickr.com/8109/8599159947_97e409f201_o.jpg"
Ecological succession,why does only one or two tree species dominate the environment of a forest?,"Maybe because it relies on the competition.
And predation.

It is really hard to have many dominating figures or leaders, right?

Imagine working in a workplace where out of 15 employees, 7 are bosses. Is that even possible?! :D"
Ecological succession,"When soil first forms over bare rock, what is it made of?",idk but its nutrients from lichens breaking down the rocks
Ecological succession,what is an ecosystem with diverse species,"Ecosystem which has as most possible diverse species with different niches - from water organisms (take bog) to the nearby meadow and eventually trees.
Ground species, birds, different types of vegetation etc."
Ecological succession,Why don't we see pioneer species dominating for long periods of time if there are not continued disturbances?,"As the pioneer species alters the environment, it makes it more suitable for other organisms to colonise. When they colonise the environment it is changed again which further makes the environment more suitable to a wider range of organisms, increasing biodiversity. It gets to the point that the environment is altered so much it is no longer able/suitable to support the pioneer species; as other more adapted species outcompete it for resources."
Ecological succession,what is primary succession ?,"Primary succession is the process by which a new environment begins to emerge without soil, after a disturbance (fires, earthquakes, etc..)"
Ecological succession,What does plagioclimax mean in primary succession?,"Human effect destroyed the community and prevented from further development.

It means that primary succession just started to develop but there is no possibility to persist and survive because of human influence."
Ecological succession,What is the difference between evolution and succession?,"Evolution involves changes in *allele* frequencies *within a species*.§

Succession involves changes in *species* frequencies *within an ecosystem*.

Does that help?


§Note: I'm simplifying a bit for clarity so these aren't perfectly correct definitions (e.g. I should say population rather than species and "ecological community" rather than ecosystem)."
Ecological succession,What are the processes of soil formation,"Soil formation takes place during primary succession - which is when plants colonise bare ground for the first time. The first species of plant that colonises the rock is usually lichen. They are able to survive extreme conditions.

While the lichen is present, they capture dust and other small particles present in the air. They then combine these together to form something soil like, however, it so thin that you are unlikely to see it. It is also completely devoid of any nutrients or minerals for any plants to make use of. 

This is taken care of by the weathering of rock - it gets broken down into smaller and smaller particles which allows the lichen to incorporate them into the 'soil'.

Once the lichen dies, it adds humus (organic matter) to the 'soil'. This allows the mineral and nutrient content to be much higher than the just the mixture of dust and other small particles. 

This process is repeated several thousand times before mosses and herbaceous plants are able to take root. Once these decompose, they too add humus and nutrients to the soil.

They make the soil deeper and thus allow more complex and larger plants to take root.

As you can see, it a very long and drawn out process!"
Community structure,"Is it possible for there to be more than one keystone species in an area, as well as foundation species?","Yes, there can be more than one keystones species and foundation species in an area. The densities will be similar for the species but one species can have reduced biomass than the other."
Community structure,Explain why we would expect low species diversity when disturbance/predation occur with a high frequency.,If a lot of the spices are being eaten by predators and disturbances are stopping the species from surviving and reproducing then the species will die off and it will lead to low diversity
Community structure,"Can you explain how, for example, an area with only 7 types of species and a total 27 individuals has greater biodiversity than an area with 10 different species and a total 48 individuals?","Because in the first case there is a smaller number of individuals.

7/27 = 0.25
10/48 = 0.20

Biodiversity is greater in the first case."
Community structure,How does climate shape a biological community?,"Climate is one of the abiotic factors that can introduce variation. According to the videos on niches and competition, no two species can coexist indefinitely if they use the same survival strategy. For example, both wolves and foxes may hunt rabbits, but wolves can run faster so they will eventually outcompete the foxes, driving them to extinction and reducing overall biodiversity. With temperature variation, the foxes' strategy might actually prove better in some years. For example, foxes might have better vision and find it easier to spot rabbits against snow, so they would do better in years with more snow, while wolves will do better in years with less snow. The constant change of climate allows both species to find a niche in otherwise identical conditions and therefore coexist. 

Another example would be tree populations - taller trees grow better because they get more sunlight, so if a single tree was to grow much taller than all the others and grow in an umbrella shape, blocking out sunlight and killing all the trees around it, giving other tress 0 chance of survival. If a tree would be much taller that all other trees, it would be more susceptible to breaking due to wind as it would have to take all the wind resistance by itself. A forest full of trees roughly the same height help each other break wind thus climate (wind intensity or lightning bolts) prevent one tree from pushing out all the others."
Community structure,what are the factors that affect species diversity in an ecosystem,"Several notable factors are listed in the article. I have copied/paraphrased them here.
- Climate of the community's location.
- Geography of the community's location. 
- Heterogeneity (patchiness) of the environment
- Frequency of disturbances, or disruptive events.
- Interactions between organisms
Hope this helps!"
Community structure,what are Dominant species?,"Generally, the predatory species, or species that have a greater amount of members end up being dominant. Hope that helps!"
Ecological interactions,Would overfishing affect other ecosystems than that of the fish themselves?,"Probably. Ecosystems are connected. While scientists do break the world down to study it in smaller pieces because we can't comprehend the ecosystem of the whole world at one time, the whole world is one big ecosystem. Some parts of it are more directly connected to others, and some parts are less directly connected. If something catastrophic happened in one ecosystem, it would affect other ecosystems. But also remember that the bigger the network, the less any one species affects it. Because there are so many species in the world, the world is a HUGE ecosystem. The affect would be somewhat absorbed by the vastness of the ecosystem. However, if the extinction of one species (such as fish) has a large impact on one ecosystem, it's impact on surrounding ecosystems might be noticed. When you look at the world as a whole, it's not the extinction of any one species that is very, very dangerous but the extinction of many species. If enough species (like the fish) died in "separate" ecosystems, eventually the ecosystem of the whole would be affected."
Ecological interactions,can someone give an example of parasitism in which the human being is not the definitive host?,"Of course yes. The protozoan of the genus plasmodium, which is the etiological agent that causes malaria in humans, has as its definitive host the anopheles mosquito within which it reproduces."
Ecological interactions,what does an ecosystem means,An *ecosystem* means *all the biotic factors* (organisms/living things) + *all abiotic factors* (nonliving factors) *interacting in a specific area*. I hope this explains it to you! :)
Ecological interactions,"By reading this article, I understand that there an ecosystem is made up of consumers, producers, etc. But what types of interactions happen or don't happen in an ecosystem when an organism is eliminated? What impact would this have on the interactions within an ecosystem?","When you say 'eliminated' it depends on what you mean by that.

If you artificially remove one individual o even species you create ruckus in an ecosystem and the system is crashing down.

While when an individual dies (this is not elimination until all matter is removed by detritivores) it acts as a source of food."
Ecological interactions,"If we took more than what we need from an ecosystem, would that upset the balance of nature? Or would everything stay the same?","It would upset it because since you are taking away, whatever needed that doesn't have enough now."
Ecological interactions,Would speciation reduce intraspecific competition?,"In one sense yes because then the two organisms would not even be the same species anymore! However, this would likely increase interspecies competition as even after speciation the organism may still compete for the same resources and occupy a particular niche."
Ecological interactions,"In an ecosystem, material is constantly doing what from one location to another","In an ecosystem, *matter and energy are constantly being transferred* from one location to another. For more info, watch this video: https://www.khanacademy.org/science/biology/ecology/intro-to-ecosystems/v/flow-of-energy-and-matter-through-ecosystems. I hope you find this useful! :)"
Invasive species,What damage can European starling do,"The article states, "The European starling, Sturnus vulgaris, may compete with native bird species for nest holes." This means they can take nesting holes away from the native birds, profoundly reducing the native bird's population."
Invasive species,Can releasing a pet into the wild like a turtle or an ant potentially turn it into an invasive species? Has this happened?,"Releasing a single pet into the wild is not likely to cause a problem but that is rarely the case where a single animal is released.  

For example the seemingly innocent goldfish is a species of carp that is not native to the US and is a fish that can grow to be 16 to 19 inches and weigh more than two pounds and has few natural predators and reproduces fairly quickly.  They out compete other species and even eat their eggs.  

Pet Burmese pythons being released have cause a drastic reduction in population of raccoons, foxes and bobcats in the ecosystems they have now become common in."
Climate,How May Pollution and Greenhouse gasses specifically destroy the Climate and atmosphere?(list the things that are harmed by pollution and greenhouse gasses as well as how they destroy that one thing),"Pollution causes greenhouse gases. These trap excess heat close to the earth, heating everything up. They affect everything."
Climate,"Why does dry air only travel to about 30 degrees north or south, why not any other location?","In other areas the conditions are not right for dry air. In most of these places you have allot of water which moistens the air. If the air is moistened it cannot be dry. This might not be true for all places but is true for most. As for the other places, all I know is that there is a reason, and that reason was carefully thought outt by God when he created the earth and there is a good reason for why this is the way it is. Hope this helps.😊"
Climate,So many animals that need to be in there natural habitat because they will die if they are not in there natural habitat,"Yes, because they are adapted to survive in that type of habitat."
Climate,what does it mean by tropic ?,"The tropics are the region of the Earth surrounding the Equator.
There is no special meaning behind it, it is the name."
Climate,Why is the Earth rotating on its axis?,"Angular momentum of all the mass that formed the Earth, plus all tidal forces that have altered it."
Climate,what causes wind?,The uneven heating of the Earth's surface by the sun.
N/A,why is the rain forest's soil not so rich,When the plants decompose the nutrients are quickly absorbed by the plants.The remaining nutrients in the decomposing plants are washed away with the plants to other areas.
N/A,did each animals of ecosystem depend on each other,"yes. in a ecosystem, each animal in the ecosystem is dependant on each other,"
N/A,Why temperature doesnt vary much over the year ?,"It is because the near the equatorwhich is the waist belt of the earth and it is in the middle the sun will still face it and that is why the temperature is normally hot all year round and the temperature doesn't vary but if you go farther away from it, you will discover the fluctuation in temperature.😉"
N/A,What are the most famous tropical rain forests?,"The Amazon rainforest is probably the most famous.  The Maya rainforest is also pretty big - it takes up parts of Mexico, Belize, and Guatemala.  The Congo rainforest is the largest in Africa.  The Daintree rainforest is in Queensland, Australia.  The island of Sumatra in Indonesia has three national parks that are considered rainforest:   Gunung Leuser National Park, Kerinci Seblat National Park and the Bukit Barisan Selatan National Park."
Life history strategies,Insects come under semelparity or iteroparity?,"I think it depends on the insect. Most insects, such as praying mantises and some moths would fall under semelparity, because they die right after reproduction. (some moths don't even have mouths!) But other insects, like the monarch butterfly, can come back year after year, so that would be iteroparity."
Life history strategies,How can you tell from a life table that the population of the organism is iteroparous or semelparous?,"You might not be able too,  but if you look at multiple tables over week periods, you will notice how a ton of elderly die and the base widens in *semelparity*. When it is *iteroparous*, the pyramid tends not to fluctuate as much."
Life history strategies,"Is there a connection between semelparity/iteroparity and fertilization? Could it be that when the female egg is fertilized frequently throughout an organism's lifetime, iteroparity will occur?",Exactly. The sexual behavior of an animal is intertwined with their parity.
Life history strategies,"Is it true that the more offsprings of one organism survive, the more fit one organism is?","Yes, that is the accepted definition for fitness in evolutionary biology.

To learn more:
https://en.wikipedia.org/wiki/Fitness_(biology)"
Life history strategies,How can you maximize the number of plant species (richness) in the smallest area you can?,To give area with many factors and different niches so plants are not in competitive relations to each other.
Population ecology review,"How isn't population growing when people are having babies and, what is a negative growth rate","Human populations are growing as long as the death rate doesn't surpass the birth rate. In case it does, we're speaking of a *negative growth rate*.

Hope this helps!"
Population ecology review,If people have babies shouldn't the population increase .?,it is increasing and the only way it would stop is if the death rate surpassed the birth rate
Population ecology review,How might a population capacity change in an environment; what's an example?,"If a population is at capacity due to predators, and then some of those predators die due to a virus. The population then doesn’t have as many predators holding it back and the population is able to increase."
Population ecology review,Did  ever find a solution to what happened in Australia?,I heard about a time when Napoleon was hunting and was swarmed by so many bunnies he had to retreat. Haha!
Community structure,"Is it possible for there to be more than one keystone species in an area, as well as foundation species?","Yes, there can be more than one keystones species and foundation species in an area. The densities will be similar for the species but one species can have reduced biomass than the other."
Community structure,Explain why we would expect low species diversity when disturbance/predation occur with a high frequency.,If a lot of the spices are being eaten by predators and disturbances are stopping the species from surviving and reproducing then the species will die off and it will lead to low diversity
Community structure,"Can you explain how, for example, an area with only 7 types of species and a total 27 individuals has greater biodiversity than an area with 10 different species and a total 48 individuals?","Because in the first case there is a smaller number of individuals.

7/27 = 0.25
10/48 = 0.20

Biodiversity is greater in the first case."
Community structure,How does climate shape a biological community?,"Climate is one of the abiotic factors that can introduce variation. According to the videos on niches and competition, no two species can coexist indefinitely if they use the same survival strategy. For example, both wolves and foxes may hunt rabbits, but wolves can run faster so they will eventually outcompete the foxes, driving them to extinction and reducing overall biodiversity. With temperature variation, the foxes' strategy might actually prove better in some years. For example, foxes might have better vision and find it easier to spot rabbits against snow, so they would do better in years with more snow, while wolves will do better in years with less snow. The constant change of climate allows both species to find a niche in otherwise identical conditions and therefore coexist. 

Another example would be tree populations - taller trees grow better because they get more sunlight, so if a single tree was to grow much taller than all the others and grow in an umbrella shape, blocking out sunlight and killing all the trees around it, giving other tress 0 chance of survival. If a tree would be much taller that all other trees, it would be more susceptible to breaking due to wind as it would have to take all the wind resistance by itself. A forest full of trees roughly the same height help each other break wind thus climate (wind intensity or lightning bolts) prevent one tree from pushing out all the others."
Community structure,what are the factors that affect species diversity in an ecosystem,"Several notable factors are listed in the article. I have copied/paraphrased them here.
- Climate of the community's location.
- Geography of the community's location. 
- Heterogeneity (patchiness) of the environment
- Frequency of disturbances, or disruptive events.
- Interactions between organisms
Hope this helps!"
Community structure,what are Dominant species?,"Generally, the predatory species, or species that have a greater amount of members end up being dominant. Hope that helps!"
Human impact on ecosystems review,Why doesn't the government do anything like reducing oil mines or cutting down trees.,"It's not really that simple. We need trees for coal and oil mines for well, oil. Without coal and oil, we can't create materials like, well, the device you wrote this comment on. We need to find a better alternative because we can't just stop. As long as people will be buying things, trees will be cut down."
Human impact on ecosystems review,What are the positive human impacts on ecosystems?,There are many positive things happening in ecosystems around the US.  There are many conservation agencies and organizations focused on improving water quality and biodiversity that have shown positive impacts on protecting watersheds and other key conservation targets.  Look at groups like your local Soil and Water Conservation District or The Nature Conservancy in your state to find a few positive examples.
Human impact on ecosystems review,How many new born animals die each day ?,30 million newborns will die within the first 28 days of life between 2017 and 2030. That's sad Dx
Human impact on ecosystems review,Is anything even being done about climate change and why is nothing be said.,"So much is being done!
The problem is that the focus is rarely on what is being done to fix climate change problems and is more on the negative. Many people, like you! have tried to put these issues in the spotlight through little things. So, it is incorrect to think that nothing is being said against these problems or is being done. Look into some of the many ways that are today!"
Invasive species,What damage can European starling do,"The article states, "The European starling, Sturnus vulgaris, may compete with native bird species for nest holes." This means they can take nesting holes away from the native birds, profoundly reducing the native bird's population."
Invasive species,Can releasing a pet into the wild like a turtle or an ant potentially turn it into an invasive species? Has this happened?,"Releasing a single pet into the wild is not likely to cause a problem but that is rarely the case where a single animal is released.  

For example the seemingly innocent goldfish is a species of carp that is not native to the US and is a fish that can grow to be 16 to 19 inches and weigh more than two pounds and has few natural predators and reproduces fairly quickly.  They out compete other species and even eat their eggs.  

Pet Burmese pythons being released have cause a drastic reduction in population of raccoons, foxes and bobcats in the ecosystems they have now become common in."
Intro to animal behavior,"Do humans exhibit any signs of hibernation, estivation, or migration in response to cues?","Humans don't really hibernate, estivate and migrate in response to cues actually. We don't really have a built-in system of doing these, so i hope this answers your question :D"
Intro to animal behavior,What are barnacles? Do they count as estivation?,"barnacles are a type of arthropod, relating closely to crabs, lobsters, and shrimps. they are often hermaphrodites, meaning they have both female and male sex organs within their bodies, allowing them to be both carriers and distributors in the reproduction process. barnacles don't survive by estivation, as they don't necessarily face the need to hibernate during the day, they just secrete a sticky "glue" and stick themselves to something or the other, and hitch rides until they die."
Intro to animal behavior,"Scientists have this theory that we evolved from apes. If it is true, have humans developed some innate behaviors that apes get? If we don't have them all, doesn't that mean we grew out of habits that were hardwired in our brains. In your opinion, do you think animals will grow out of those behaviors as we go into the future?","Keep in mind that the species that humans evolved from no longer exist, both modern apes and humans (humans are technically still under the classification of ape) evolved from a common ancestor.   

So there may well be innate traits shared between humans and other ape species but they would have been inherited from that common ancestor not each other."
Intro to animal behavior,If a Zebra Finch was raised in captivity but the person who raised it played music would the bird learn to sing a song that is related to the music that was played as it grew up?,"Hi There

That is an interesting question. I'm not sure if there really is a wrong or right answer for this question as the hypothesis would have to be thoroughly tested before one could undoubtedly give an answer. Since Zebra Finches' songs are partly innate and partly learned, I think it would have to depend on the music as well as many environmental factors. For example, if pop or rock music were to be played to it, I doubt any of music would be implemented into its song and it could have affect the birds mental health (and certainly not in a good way). On the other hand, many birds enjoy listening to classical music (which has positive effects on the brain), and parrots specifically, either imitate or show they enjoy it. Although the Zebra Finch would not imitate it exactly, there is the possibility that it would use patterns from the song. I'm honestly not 100% sure though as to whether or not it would use patterns found in the music. 
That said, picture a Zebra Finch which has been raised by humans who acquired it whilst it was still inside the egg. This little Zebra Finch never heard music and it was not was exposed to any other avians. The bird would not have learnt any specific songs, but without doubt, the bird would still sing, creating its own song/s and using different patterns. Likewise, there is a strong possibility that it would not relate its song to the music.

Hope this helps! :)"
Intro to animal behavior,"So, the mother cukcoo bird puts the her egg in some other birds nest, and the bird grows up with a totally different parent. Is it an innate behavior for all cukcoo birds to do that or, when they grow up do they see other birds that look like them doing it. This always confused me. :/ (I read an article on it and I thought it was best to ask the question here.)","I think it's innate. I do also know that the mother cukcoo comes back. If the egg is pushed out, the mother will destroy the other bird's nest and all her eggs/chicks."
Intro to animal behavior,When people started Natural Selection how did those traits and DNA come to mix and Them learn traits from eachother and pass it on from diffrent learned traits and how did they cope?,"DNA is where the information about how specific biological features or processes are encoded.  For example the trait of fur color is controlled by the pigment proteins that specific genes in the DNA code for.  The fur color can help the animal hide or attract a mate.  The better or worse the fur color is at allowing hiding or getting a mate will affect how well the animal is able to have offspring to carry its DNA into later generations.  

For things like learned learned actions it is not the learned actions that are encoded into DNA and passed on but the organisms ability to learn an adapt, this is indirectly the trait that natural selection acts on."
N/A,"Through training, can we improve the gorilla's IQ?",Yes probably we could. But gorillas have a lot of IQ of their own and we can't change that through boxes and bananas. In other words we can't train them out of their  Innate behaviors.  Its sort of like this: When you go to the doctors do they use a small hammer to bump your knee? They probably do. They are supposed to anyway. Do you flinch? If so this is one of the Innate responses and you can't be trained to stop doing it.
N/A,why are animals are alert when they are getting food?,Because that is a reward to the body - getting energy source: dopamine is produced in the brain. mother nature wired animals (including us humans) that way.
N/A,"if you raised a baby whooping crane in captivity, by humans, how would you teach it to fly?","Quite interesting question so I had to research a little.

It is possible if humans take the role of a bird and 'teach' baby bird with _reinforcement_. (since humans cannot fly and demonstrate flying to a bird).

'The main source of motivation for baby birds is food. The baby bird knows nothing more than that at regular intervals their mother will come and drop some food off in their mouth. Slowly the mother bird will stand farther and farther away from the nest, forcing the baby bird to come out of the nest in order to get food. The bird realizes it needs this food to survive and this is the motivation for them to venture out onto a branch'.

http://blogs.bu.edu/bioaerial2012/2012/10/09/nature-vs-nurture-how-do-baby-birds-learn-how-to-fly/


Meaning that humans may imitate parent birds. :D"
N/A,"why is habituation considered as a learned behavior ? I mean if the ducks recognize their "mother" the moment they hatch ( 0 experience), shouldn't it be an innate behavior?","First of all habituation is not the same as imprinting (just be careful not to confuse the terms).
Secondly: the interesting thing about imprinting is, that it actually combines innate parts with learned ones. It is innate for ducks to follow objects that move and make noises. But the ducks can't know how their mother locks exactly and have to learn a picture of her first (13-16 hours after they hatch).
So sure, it is inborn for ducks to learn the picture of their mother - but they have to learn it first (it is actually obligatory for them to learn as they have to be able to distinguish between their mother and other adult ducks)."
N/A,"So how does the mat maze work?
Do they let them see the maze from above or what?",No.They create a maze in their brain to the food or whatever. so they find a way to the thing they need so the have something like a maze creator i their brain
N/A,Can you give an example of a human expressing habituation because I can't think of anything.,"Where do you live? If you live in a city, do traffic noises bother you at night when you're sleeping? Or if you live near train tracks, do trains in the middle of the night disturb your sleep? Someone living in a rural area, or away from trains, may find those sounds disturbing."
N/A,"I was wondering, what is the term for when a new behavior is being taught, an old one breaks down? For example, if my dog knows how to sit and I am training him to lay down, he now is not sitting or presenting the sit behavior in a more broken and uncertain way.","Simple: the dog forgets trick 1 because the trick is not taught alongside trick 2. 
I make sure that my dog remembers all of her previously taught commands by praising her for old tricks and new ones, acknowledging both."
N/A,why do animals imprint at a early age?,It could be because of natural selection. I baby animal that knows who and where their mother is will more likely survive than a baby animal that wanders away from the mother.
N/A,How do animals know if other of their same kind is trying to threaten them??,"Some animals see thermal activity which allows them to see animals around them, if they see movement they are on alert and will either use a defense mechanism or try to run for it. If they relize it is not a threat then they will calm down."
N/A,How did communication between organisms evolve?,"From signaling one type of molecule and sensing it among unicellular Prokaryotes to nowadays using colors, shapes, touches, songs, etc among animals and of course using speech in humans."
N/A,Can one type of animal communicate with another type?,"Sure, my dogs communicate with me all the time. They tell me when they're hungry, thirsty, want to go outside for a walk, when strangers are at the front, etc..."
N/A,Can animals on land communicate to animals underwater?,"It depends on how loosely you define communication. A fish will understand if an osprey communicates its desire to eat the fish by, well, trying to grab the fish. Perhaps there's some poisonous fish that live near the surface and are brightly colored like poison dart frogs. But I'm not sure of any deeper communication than a predator-prey interaction that goes on between land and sea animals."
N/A,Whales come to surface for bathing oxygen but when they mistakely come on shore and can't get back why do they die they have all the oxygen they want,They don't suffocate when they're beached. They usually die of dehydration or other injuries due to being beached.
N/A,Why is communication important for animals?,"One of the key points at the beginning of the article: Communication behaviors can help animals find mates, establish dominance, defend territory, coordinate group behavior, and care for young.
Those are some reasons!"
Innate behaviors,When the two mouse interbreed do their burrows turn into something different? Or do they inherit on or the other?,They always inherit the beach mouse style of burrowing behavior
Innate behaviors,"It's hard to imagine reflexes begin; could these innate behaviors start as haphazard habits? For instance, sometimes I twitch uncontrollably when I'm bored. The way I'm seeing it, does that mean that if that habit helps me survive, it could become a reflex?","Excellent question!

They can! Even though I do not personally know of any example, but yours is great."
Innate behaviors,how would the offspring of the beach and the deer mouse act to survive in the wild?,"We need to crossbreed them and see. However, not sure whether they will give fertile offspring."
Innate behaviors,what's the difference between reflexes and fixed-action patterns?,"A *fixed-action pattern* is more complex in that it consists of a series of actions, whereas a *reflex* consists of a quick action (or reaction)."
Metabolic rate,Why do endothermic like humans need more oxygen?,"Endotherm's need to perform cellular respiration to maintain a constant internal body temperature. Oxygen and glucose are the reactants of cellular respiration, while the products are ATP, H20 and CO2. Although the main function of cellular respiration is to produce ATP, only 40% of the energy from glucose is stored in ATP--the rest of the energy is released as heat which is used to maintain body temp. by endotherms--Since endotherms rely on cellular respiration to maintain body temp., they consume more Oxygen than ectotherms. Ectotherms, on the other hand, release the heat from cellular respiration into the environment. Hope this helps!"
Metabolic rate,I don't understand what metabolic heat is itself?,Metabolic heat is generated as a side/waste product of cellular respiration
Metabolic rate,"hibernation and estivation are dictated by changes in temperature and day light in an animal's environment. How recent changes in world's temperature would affect those processes? For examples, will it affect an organism in any way needing to stay hibernated for longer period of time than normally?","Recent changes in the world's temperatures won't change it much. Do you allude to global warming and increased annual average temperature?


Luckily that increase does not disrupt circadian rhythm or annual cycles of hibernation/estivation. However, it does have greater impacts and implications (but that is a question of Ecology).

You ask about hibernation, so you mean if the temperature is lower than expected (for example on the Northern hemisphere, in May is still cold and under the snow).

Yes, I think it would affect the animal since animals also rely on the external temperature. The problem is once a bear is awake and hungry but cannot keep hunting in the spring since there is still snowball."
Metabolic rate,Is there any reason an organism would increase its metabolism in a temperature above its thermoneutral zone? I would think perhaps to evade a predator or to reproduce but I am not sure.,"In temperatures above the TNZ (thermoneutral zone), the organism has to find a way to lose the additional/excess heat, to prevent oveheating. The processes by which an animal might do that, such as Panting for example, requires some energy, which requires possibly increasing their metabolic rate."
Homeostasis,Can someone explain what is negative feedback?  I didn't understand the concept from the article....,"From what I understood, negative feedbacks is your body's response to keep things normal or stable, whereas positive feedbacks exacerbate certain effects on the body by repeating functions deliberately.  In essence, negative feedbacks preserve your body's original or 'set' condition and positive feedbacks do the opposite and change you body more by constantly pushing certain types of growth or development in the same direction until something has been accomplished. The example they used was a fetus's head constantly putting more and more pressure on the cervix until birth. Since this is very necessary and important, a positive feedback loops is run: the substance that  pushes the fetus' head towards the cervix, oxytocin, is released as a cause of contractions from the uterus, which are themselves a cause of pressure from the fetus' head on the cervix. So the pressure essentially causes contractions in the uterus which stimulate nerve impulses in the brain to release more oxytocin, which further increase the pressure of the fetus' head. Clearly the goal isn't to maintain the fetus' current state but rather push it to the point where it is primed for birth."
Homeostasis,"Is the system that regulates pH, homeostasis?","To be precise, homeostasis is a process/phenomenon not a system.

Homeostasis is actually the process of maintaining a stable internal environment despite changes in the external environment. 

There are mechanisms in organisms that regulate pH and this regulation is an example of homeostasis.  For example, if you have learned about buffers, then it may help to know that essentially all organisms use buffers (and other mechanisms) to maintain control over the pH — for example the different organelles within eukaryotic cells will consistently have different pHs:
http://book.bionumbers.org/what-is-the-ph-of-a-cell/

Does that help?"
Homeostasis,what is pH guys and how does it relate to homeostasis.,"pH is a measure of how acidic or basic a solution is. More specifically, pH=-log[H+], which essentially means that the more positively charged hydrogen ions you have in a volume of solution, the lower the pH is and the more acidic the solution is. You can also check out this video (if you haven’t already seen it): https://www.khanacademy.org/science/high-school-biology/hs-biology-foundations/hs-ph-acids-and-bases/v/introduction-to-ph

pH matters for homeostasis because it’s part of the chemical environment in which biochemical reactions have to take place. For example, enzymes (which help speed up chemical reactions in living things) have ranges of pH where they work best. Because these molecules’ proper functioning is necessary, pH is very important for maintaining homeostasis. 

Hope this helps!"
Homeostasis,what is the control center in temperature homeostasis hot?,The control center for temperature is the hypothalamus.
Homeostasis,How can very low temperatures be fatal?,"Low temperatures would mean that the enzymes would be inactive or they may not be able to catalyse as much. This slows down reactions in the body (lowers metabolism), meaning that you may be deprived of essential things such as energy etc, which can eventually lead to complications such as death."
Homeostasis,How does Blood clot relate to Homeostasis?,"Blood clotting is considered part of the Positive Feedback (PF) Loop. This is defined as an effector that will AMPLIFY the effect of the Negative Feedback (NF) Loop. For instance, when there is a hemorrhage (loss of blood), it will cause a sequential activation of clotting factors. Here, a single clotting factor results in the activation of many more clotting factors. This is also known as a PF cascade. This overall process will give the completion of the NF Loop because blood loss was prevented with the clotting factors, resulting in Homeostasis."
Homeostasis,How can blood vessels dilate result in heat loss？,"This is because the dilation of blood vessels increases their surface area making it easier for the blood to interact and transfer heat with cooler parts of the body, generally the more surface area, the more heat loss."
Homeostasis,can someone please tell me which organ in the body controls homeostasis?,"Homeostasis is mainly controlled by the organs in the central nervous system and the endocrine system (hormones). Organs in the two systems send commands to other organs in other systems to allow them to carry out certain functions. 

Example for the nervous system: You have stepped outside into some snowy weather. It is cold outside, and your body temperature is dropping. The nervous system sends signals to the muscles that tell them to shake. The shaking of the muscles generates heat, keeping you warm.

Example for the endocrine system: Unfortunately, your have not eaten anything for hours. This results in a low blood sugar level. To maintain homeostasis, cells from the pancreas release a hormone known as glucagon, which raises your blood sugar by decreasing the storage of sugar in body cells.

Does this help you?"
Homeostasis,What system controls homeostasis?,"There are *many* different systems that organisms use to maintain homeostasis.  

For example, the processes used for thermoregulation in mammals and birds are very different from the methods used to keep pH relatively constant."
Homeostasis,"I understand how homeostasis happens in our bodies, but why does it occur? Furthermore, why do we need it? Why do we try to control the internal functions of our bodies rather than the external stimuli that cause them? Why are there not more uses of positive feedback loops?","1. It occurs so our body can function.
2. (See number one)
3. It is much easier to control our bodily functions than the weather and climate.
4. What do you mean?"
Endotherms & ectotherms,What is the point of life?,To disappoint your parents.
Endotherms & ectotherms,"I have a question 
Are tuna endotherm or ectotherm? I have ever studied that tuna is Homeotherm in ectotherm. Now I feel confused.","I found this online.

"An *endotherm* is able to regulate its body
temperature via metabolic processes, these are commonly known warm blooded animals.
An *ectotherm's* body temperature is dictated by the environment surrounding it, the animals are commonly and incorrectly known as cold blooded. 
--
*Poikilotherms* are animals that do not require a fixed body temperature, their temperatures can fluctuate with little to no adverse effects to their overall health. Most terrestrial
ectotherm's are poikilotherms, such as snakes and many lizards, also the naked mole rat is considered to be the only mammal poikilotherm. *Homeotherms* are animals that maintain a constant body temperature. All endotherms are homeothermic, but some ectotherms, like desert lizards, are so good at maintaining their body temperature with behavioral means that they are
considered homeothermic."

source: https://faculty.mtsac.edu/trevell/bio2/bio2resources/thermo"
Endotherms & ectotherms,"I have two questions. 
First, is the thermoneutral zone for humans around 24 Celsius or 37? 
And second, why do we feel hot when the environment temperature is 37 Celsius, when 37 is the temperature we want our body to have?","Thermoneutral zone for humans is around 24, not 37.
The thermoneutral zone is defined as the range of ambient temperatures where the body can maintain its core temperature solely through regulating dry heat loss, i.e., skin blood flow. 

*This paper explains*
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4977175/

Why not 37? Because imagine even if we were nude at that temperature (anything above 30 is too much).
Also while it is plausible for our basal metabolic rate, not suitable for _any_ kind of work.

Have you noticed that slightest amount of work even at 27 makes you sweat?

We feel hot because we are _not static objects_ which just conduct temperature. We also _produce_ temperature in our core, plus have a skin which is _an insulator_.

So the reason why you feel hot at 37 is mainly that you have skin _whose surface temperature is lower than 37_ so your body surface is colder and starts absorbing environmental temperature."
Endotherms & ectotherms,Why would one expect the Q10 value of an ectotherm to be around 2?,"If Q10 is 2 it means an increase in the surrounding temperature with an increase in 10 ◦C, and usually resulted in a doubling of the reaction rate.

The Q10 values can be determined from the Arrhenius plots. (In chemical kinetics, an Arrhenius plot displays the logarithm of a reaction rate constant, (, ordinate axis) plotted against reciprocal of the temperature (, abscissa).)
https://www.google.com/imgres?imgurl=https%3A%2F%2Fupload.wikimedia.org%2Fwikipedia%2Fcommons%2Fthumb%2Ff%2Ff6%2FNO2_Arrhenius_k_against_T.svg%2F1200px-NO2_Arrhenius_k_against_T.svg.png&imgrefurl=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FArrhenius_plot&docid=knFyGYn7H893XM&tbnid=k3xTzrdU8e6HCM%3A&vet=10ahUKEwiC3IGzg8blAhUPKlAKHd82DDcQMwhNKAEwAQ..i&w=1200&h=912&bih=625&biw=1366&q=arrhenius%20plots%20for%20temperature&ved=0ahUKEwiC3IGzg8blAhUPKlAKHd82DDcQMwhNKAEwAQ&iact=mrc&uact=8

So I found the paper where Researchers have experimented on _Pseudomonas sp._ (ectotherm, relying upon external temperature) and phenol degradation was referent variable to detect metabolism of _Pseudomonas_.

https://www.researchgate.net/publication/322925209_Estimation_of_the_Q10_value_the_Temperature_Coefficient_for_the_Growth_of_Pseudomonas_sp_AQ5-04_on_Phenol


Again, your questions as *why is that so*?
And I cannot tell you for sure _why_ the rate usually is 2, it was experimentally obtained and concluded.

Probably it has to do something with Laws of Thermodynamics and logic.

Think about it, if it was 3, 4, or 7, what would it mean in BIological terms?! That metabolism would be super fast, and at 30*C, the organism may just burn out in half an hour. And it does not make sense."
Endotherms & ectotherms,"Which between a unicellular organism, ectotherm and endotherm has the highest BMR and which one is the lowest?","This is one of those questions that seem reasonable, but are so dependent on the specific organisms that they are probably impossible to get a useful answer for.

For example, unicellular organisms are incredibly diverse (contain organisms from all three domains of life and from multiple eukaryotic kingdoms) — they will not have similar metabolic rates.
Furthermore, unicellular organisms can't even all be grown at the same temperature — how would you meaningfully compare the metabolic rate of a marine bacterium that lives in arctic waters (prefers 4°C) vs. the rate for an archaebacterium that grows only on a "black smoker " (undersea thermal vent) and prefers 98°C (can grow at up to 122°C):
https://ocean.si.edu/ecosystems/deep-sea/microbes-keep-hydrothermal-vents-pumping

Another example, is what kind of endotherm — a blue whale? an elephant? a shrew? a hummingbird? an ostrich?

...

Well, hopefully you found some of that rant interesting or at least mildly entertaining ..."
Endotherms & ectotherms,Why does temperature affect the breathing and heart rates of ectothermic organisms?,"Because temperature per se affects any kind of work. At higher temperatures, the working machine (or int his case heart) has to work harder and easier gets overheated.

The same way temperature affects Ebdithersm, it also affects Ectitherms, especially because they _rely_ on the temperature. Because temperature directly correlates with metabolism rate.

The greater the temperature faster the metabolism and vice versa.

Here is one interesting paper depicting how also Ectotherms may have energy costs in their metabolisms because sudden increases and decreases impose some kind of stress on bodies. They are physiologically dependant on external temperature and their viability is reduced at extremes.

https://www.sciencedirect.com/science/article/pii/030645659400023C"
"Tissues, organs, & organ systems",Are glial cells part of nervous tissue?,"Yes. Glial cells are the neuron's "helper". They provide neurons with support, insulation, and protection."
"Tissues, organs, & organ systems",Which hormones are made in the brain,"One of the more well-known hormones that are made in the brain is the *Growth Hormone*, which is produced by the pituitary gland. It is a small gland that sits in the sella turcica (‘Turkish saddle’), a bony hollow in the base of the skull, underneath the brain and behind the bridge of the nose.

Apart from the growth hormone, other hormones produced in the brain included follicle stimulating hormone, also known as gonadotrophins. They act on the ovaries or testes to stimulate sex hormone production, and egg and sperm maturity. Apart from that, the brain also produces the prolactin, which stimulates milk production, and the thyroid stimulating hormone, which stimulates the thyroid gland to secrete thyroid hormones -- which are hormones that can affect energy levels, mood, even weight. They can also be factors in depression."
"Tissues, organs, & organ systems","Do you think that increasing the complexity of the organ systems and/or tissues, lead to a better survival of an organism/ species or do you think that would be a disadvantage?","I would say it depends on the organism and how it functions! For example, we are quite complex (organ-wise) and are obviously quite successful animals. But there are also sponges in the oceans (Porifera) that are some of the oldest animals, and they have continued to survive and thrive, with systems that aren't nearly as complex as ours! This was a very good question"
"Tissues, organs, & organ systems",what tissues are in the cardiovascular system?,Arteries have an outer tube of connective tissue for structural support. And smooth muscle tissue makes next layer.  Smooth muscle tissue layer allows to change the diameter of the arteries.
"Tissues, organs, & organ systems",how  does connective tissue repair injured parts of the body?,"Cells of connective tissue work in synergy. 
They provide matrix (as some form of a skeleton) which is 'invaded' with mobile or fixed cells of connective tissue. Also, it's mobility helps. By signaling from other cells they get 'orders' to come closer and work together until they seal wounds and form a *fibrous patch*. 

However, that *fibrous patch* may _reduce_ the lifespan and decrease the quality of the organ (for example after _cardiac arrest_ fibrous tissue starts to form on your heart. You know that the heart is myokard, heart muscle, which has the function of conducting an electrical signal and contracting. In the case of fibrous scar, fibrous tissue cannot conduct electricity or contract. It is _just a physical barrier to open wound but nothing else_.)"
"Tissues, organs, & organ systems",What primary tissue would be heavily involved in coordinating functions of different organs in an organ system?,"Every tissue has its role in an organ!
Epithelial gives protection, skeletal gives support, muscle helps locomotion and neural conducting signals!


If you say primary, it depends which organ system and which organ.

E.g. in the heart you can find cardiac muscle as the most abundant and primary tissue."
"Tissues, organs, & organ systems",Why don't you have anything about the arteries,"They do — arteries are a type of blood vessel (i.e. an element of the cardiovascular system), which is mentioned in this article.

In the future, for questions like this I encourage you to search on the Khan Academy website — for example, doing this for "arteries" would lead you to this material:
https://www.khanacademy.org/search?page_search_query=arteries

For example, you can start to learn more about arteries and the cardiovascular system on Khan Academy — here:
https://www.khanacademy.org/science/health-and-medicine/circulatory-system-diseases/blood-vessel-diseases/v/arteries-vs-veins-what-s-the-difference

Does that help?"
N/A,"If there is bacteria in our blood and there is only 1% of white blood cells, wouldn't that take a long time to dispose of the bacteria?","Most bacteria is good and makes our body function better. If we didn't have any bacteria in our body, we would die. A lot of the bacteria which gets into your body will actually help fight off bad bacteria, viruses, etc! A very small percentage of the bacteria in our body is bad, so when there is one, the white blood cells in addition to some of the good bacteria will help fight it off. 1% is actually plenty, because if the body can get to it before it multiplies constantly, then it can get rid of the bad thing quickly and we won't even know we were sick."
N/A,"Are erythrocytes (after maturation) still considered cells of the body? (No nucleus, etc)",Yes they are still considered cells if they stared of with a nucleus in which they did. so still have the functions of a cell. if it wasn't a cell how could it die?
N/A,"I thought red blood cells are already larger in diameter than the smallest capillaries, so that they have to squeeze through. but now white blood cells are even larger? Don't they also have to travel through the same capillaries?","Firstly, there are three types of capillaries in our body - continuous, fenestrated and sinusoid. The major difference n these three types are that continuous capillaries are less permeable than fenestrated, having sinusoid to be the most permeable and big-sized capillaries in our body. Apparently, the main functions of these types vary accordingly with the permeablity of the vessels and for sinusoid, as it is the largest capillary, allows larger molecules to flow through it, including white blood cells of any kind. 

Another idea unrelated to this also explains that the role of leukocytes are to fend off external breaches by activating immune system, phagocytosis, releasing substances, etc. Thus, leukocytes are able to escape through any vessel walls to arrive at the needed regions of the body ASAP. So they do not have to pass through the capillaries.

I've checked some biology sites and these are all informations I could gather, hope it helps :)."
N/A,What is the amount of time platelets use to clot where a person injured his or herself?,"The normal value of clotting time is 8 to 15 minutes

https://en.wikipedia.org/wiki/Clotting_time


I do not recommend testing it by cutting yourself on purpose."
N/A,how have we evolved if we have such a complicatid biology?,"Think of single-celled organisms.  They are among the first of all life-forms, and they are incredibly simplistic.  Evolution is the process of becoming better and adapting, therefore advanced beings have advanced biology.  It would definitely be hard for an amoeba to formulate the answer to a differential equation with simple flagellate motions.  However, our brains are capable of doing so thanks to the multiple support systems, which are complicated biology.

Hope this helped!"
N/A,"The text says: ''Red blood cells, white blood cells, and platelet-producing cells are all descended from a common precursor: a hematopoietic stem cell.''
My question is: Where are hematopoietic stem cells produced?
I'm referring to the section: Stem cells and blood cell production.",Hematopoietic stem cells reside in the bone marrow.
N/A,would the components of blood be effected by your blood type?,"Yes. Platelets and especially plasma have their own traits that are influenced by one's blood type. Plasma, for instance, can carry anti-A antibodies, anti-B antibodies, both antibodies, or none depending on blood type. This is why blood type still must be considered for plasma and platelet transfusions.

Does that help?"
N/A,Why is a stem cell an ethical issue?,"While everybody has stem cells, the cells used for research primarily come from human embryos. Here's the problem: when you harvest stem cells from an embryo, you destroy it. Killing a human being is typically viewed as murder; however, this being an unborn child raises several questions. Would it still be classified as murder if the child was never born? Can it even be classified as murder if the human being was very early in development, to the point where it was still only a mass of cells? Does it feel anything at that point? Is it part of the woman's body, or is it its own being?

Much of the questions asked about the matter tie closely to the issue of abortion. It is an ethical issue because when exactly something becomes its own being is unclear, and there is a clear and significant pro (forwarding science for the better) and a clear and significant con (the death of a potential child) to be seen. There is no definite answer to this question, and it is ultimately up to your morals and views to give you the answer.

Does this help?"
N/A,How many red blood cells are produced every day? And how come our bodies don't OVERproduce? Can you have too many red blood cells?,"I got this from the Internet, but I think it will help.
Approximately 2.4 million new erythrocytes are produced per second in human adults. In a normal adult  about half a liter are produced by the bone marrow every week. 
High red blood cell count - 
 high red cells count is caused by a disorder called Polycythemia Vera. This is a genetic condition that causes the bone marrow to produce too many blood cells.  People with polycythemia have an increase in hematocrit, hemoglobin, or red blood cell count above the normal limits.
for more information visit : -
http://www.medicinenet.com/polycythemia_high_red_blood_cell_count/article.htm
I know this page has a lot of ads and Spam, but it also has some valuable information"
N/A,what is nucleus,"The nucleus is a membrane bound structure that contains the cell's hereditary information and controls the cell's growth and reproduction. It is commonly the most prominent organelle in the cell.

The nucleus is surrounded by a structure called the nuclear envelope. This membrane separates the contents of the nucleus from the cytoplasm. The cell's chromosomes are also housed within the nucleus. Chromosomes contain DNA which provides the genetic information necessary for the production of other cell components and for the reproduction of life."
The membrane potential,do our physical  movements affect ion exchange?,"physical movement would cause afferent sensory neurons to fire and yourself to notice that you are moving. Also moving itself would cause afferent neurons to send action potentials to the muscles, which affects the ion exchange."
The membrane potential,"I understand the mechanisms, but what is the actual point in maintaining the concentration gradients? 
As the article states, if the sodium/potassium pump ceased to function, the concentration gradients would dissipate. If the whole purpose of the concentration gradients is to create an action potential, why can't the membrane be non polar and then instead of depolarising the membrane at threshold, it would merely, polarise it? this would still create an action potential would it not? I don't understand WHY there is a whole mechanism to maintain these gradients when an action potential could still be created if the membrane at rest was non polar. 

Is it because there wouldn't really be an resting membrane potential? I.e the membrane would never truly be at rest because of the different permeabilities and equilibrium potentials of the ions? Therefore an action potential would not be able to be created.. But if there was Na+ constantly moving in and K+ constantly moving out, why would this not keep a constant membrane potential?","I think it is because it is easier and faster to depolarize the membrane than to polarize it. The sodium/potassium pump needs energy and time to clear the intracellular space from sodium, and I guess it would be quite ineffective to take this mechanism for impulse transfer. 
And what one might forget is that _every_ cell has a concentration gradient! I even heard it as a definition of life, to have a specific concentration of ions which is not the same as the one surrounding the cell. This concentration gradient is important for metabolic processes, i.e. to build new molecules or to break them down, and for the osmosis - water always tries to equal concentration differences out by going towards the more salty regions. That is how we absorb water and why people can't drink sea water, for example. 
So the resting potential is very important."
The membrane potential,"Why Cl is not contributing much to the resting potential.  More importantly, why the Cl does not move into the cell during action potential when the electrochemical gradient (charge and concentration) is in favor for Cl to move in?","The membrane is relatively impermeable to Cl-, yes, but Cl- influence is also reduced because its equilibrium potential is already close to the resting membrane potential (I believe Cl- equilibrium potential is around ~71mV)! Keep in mind the equilibrium potential of ions that the membrane is more permeable to has a greater impact on resting potential than that of ions the membrane is less permeable to. So even if permeability to Cl- increased, I'm fairly certain the value of the resting potential still wouldn't be greatly affected. :)"
The membrane potential,at resting membrane potenital do Na go in and K out?  i cant understand resting membrane potential,"Resting membrane potential of a neuron is about -70mV which means that the inside of the neuron is 70mV less than the outside.  There are more k and less NA+ inside and more NA+ and less K+ outside. It is because the cell membrane is selectively permeable which means that is allows some substances to come in while restricting the others. The cell membrane is selectively more permeable to K than Na and hence there are more k inside than the outside, and hence outside is more positive then the inside."
The membrane potential,"what happens when the concentration of Na is increased in the extracellular fluid, is there a depolarization or hyperpolarization?
And the same goes for the increased concentration of K in the extracellular fluid, is there a depolarization or hyperpolarization?","When Na is increased in the ECF it will not have any major affect on the cell, a negligible depolarization if even measurable because the higher outside gradient will help push the Na into the cell (but remember that it isn't very permeable so it's minute).
K will have a bigger effect because the extra ECF will decrease the internal leakage of K from ICF to ECF because there would be a higher gradient outside now. The end result would be in depolarizing the cell, how much would depend on how much K was added to the ECF."
The membrane potential,"so during the neuron's resting state, large amounts of positive sodium ions are found in the extracellular fluid, whereas relatively more positive potassium ions are found inside the cell?",It would be accurate to say that there is a higher sodium concentration outside than inside the cell. And there is higher potassium concentration inside than outside the cells.
The membrane potential,Brief but detailed summary of how resting membrane potential is generated,"Resting membrane potential is generated by the combination of sodium and potassium pump and the leak channels of these ions. The function of the pump is to take out three sodium from the cell and two potassium into the cell with the use of ATP (changes the shape of pump to release these ions), already with the stoichiometry difference, we see a charge difference. Furthermore, because it is more postive outside of the cell, and negative inside the cell, plasma membrane becomes more permeable to Potassium on our leak channels. Therefore, even with leak channels of both ions, potassium is more permeable. Causing a standard measurement of -70mV resting potential"
"Q & A: Neuron depolarization, hyperpolarization, and action potentials",What is the significance of the undershoot that happens during the hyper polarization event?Does it serve a specific purpose?,"Yes, it prevents the action potential from going backwards."
"Q & A: Neuron depolarization, hyperpolarization, and action potentials","What happens if the sodium/potassium pump is nonfunctional and the membrane potential can't return to the resting membrane potential? Can another action potential be produced, or will the membrane potential never be able to reach the threshold again?","Hi, I'm a neurobio professor, and this is one of the biggest misconceptions in neuroscience.  The pump plays no *direct* role in returning to resting potential. The pump simply maintains the concentrations gradients over a long time period. 
But: When an action potential occurs, only a tiny, tiny amount of ions (<0.001%) need to move across the membrane to change the membrane potential. This is because membrane potential changes are not determined by concentration changes, but by *permeability* changes.  The membrane potential is a function of the relative permeability (through ion channels) of the membrane to each ion, and the equilibrium potential (E_ion) for that ion. The E_ion is determined by the concentration gradient set up by the pump. The membrane is hyperpolarized at the end of the AP because voltage-gated potassium channels have increased the permeability to K+. As they close, the membrane returns to the resting potential, which is set by permeability through the "leak" channels. Those are mostly K+ channels, so the membrane potential is still very close to E_K."
"Q & A: Neuron depolarization, hyperpolarization, and action potentials",Why does people with one sort of epilepsy suffer from seizures while others don't? Is it because some sort of abnormality in the membrane potential?,"Contrary to these other two answers, I think you're spot on with the mechanistic explanation. Of course, it gets much more complicated if you look into it. Fundamentally, the problem in epilepsy is that some resting membrane potentials in any of the clusters of cells in the brain can move closer to threshold. So, instead of needing to integrate enough excitatory signals to go from -70mv -> -55mV, someone with epilepsy might have a nucleus in the brain (a cluster of cell bodies) that only needs to depolarize from -60mV -> -55mV in order to fire action potentials. Genetic factors can cause this, but certain drugs can cause it as well, such as lamotrigine.  

Once this cluster of neurons recieves strong enough stimulus for the activation to spread (the stronger the stimulus, often the more neurons become involved), the entire cluster of neurons can easily depolarize at once, creating the characteristic waves of excitation seen in epilepsy. 

For example, in photosensitive epilepsy, intense visual stimuli cause a critical mass of neurons in the visual cortex to fire synchronously, initiating a wave of excitation."
"Q & A: Neuron depolarization, hyperpolarization, and action potentials",How do synapses affect the speed with which a nerve impulse is transmitted?,"Electrical synapses are present, but rare- where the synaptic cleft is negligible in length (i.e. impulses can pass directly from the terminal to a dendrite.) They are much more common in invertebrates."
"Q & A: Neuron depolarization, hyperpolarization, and action potentials",are sodium and potassium gates ever open a the same time during the action potential?,"As I am informed so far, there is no such moment during the generation of an action potential. As soon as potassium channels open, before that sodium channels close (repolarization)."
"Q & A: Neuron depolarization, hyperpolarization, and action potentials",are there any other types of  neurons?  If so then how many,"Many different types, broadly categorized with respect to their shape or their function. Motor neurons, interneurons (AKA relay neurons) and sensory neurons are the traditional classifications with respect to function. Motor neurons transmit a signal to an 'effector' of some kind (a muscle or a gland perhaps),  interneurons transmit signals between surrounding neurons, and sensory neurons 'receive' stimuli (interpreting the stimulus and integrating it)."
N/A,is there any thing between the synaps any fluid or anyting else?,"Yes, the synaptic cleft is filled with extracellular fluid."
N/A,"I know this article talked about the flexibility of synapses, but I still don't understand how different kinds of signals can be transmitted. Does a certain neuron only send one kind of signal only (different signals would be sent by different neurons) or does a certain neuron send multiple kinds of signals by sending different kinds of neurotransmitters? If the former, how are specific cells targeted? If the latter, how are specific neurotransmitters released?","Each neuron may be connected to up to 10,000 other neurons, passing signals to each other via as many as 1,000 trillion synaptic connections.

Meaning that a *certain neuron* sends multiple kinds of signals by sending different kinds of neurotransmitters.

Functionally related neurons connect to form neural networks (also known as neural nets or assemblies). The connections between neurons are not static, though, they change over time. The more signals sent between two neurons, the stronger the connection grows.


When stimulated by an electrical pulse, neurotransmitters of various types are released, and they cross the cell membrane into the synaptic gap between neurons. These chemicals then bind to chemical receptors in the dendrites of the receiving (post-synaptic) neuron. In the process, they cause changes in the permeability of the cell membrane to specific ions, opening up special gates or channels which let in a flood of charged particles (ions of calcium, sodium, potassium, and chloride).

Meaning that upon stimulation, *many* neurotransmitters are being released into the synaptic cleft. 

https://human-memory.net/brain-neurons-synapses/

But there a  thing called membrane capacitance.  Another direct measure of exocytosis is the increase in membrane area due to the incorporation of the secretory granule or vesicle membrane into the plasma membrane. This can be measured by increases in membrane capacitance (Cm).

The specific capacitance is mainly determined by the thickness and dielectric constant of the phospholipid bilayer membrane and is similar for intracellular organelles and the plasma membrane.

https://www.ncbi.nlm.nih.gov/books/NBK27911/

There are only differences between fast secreting neurotransmitters (Acth, dopamine) and slow releasing neuropeptides from neuroendocrine cells."
N/A,"The 'Synaptic Cleft' has an approximately 20 nm separation, How do the axion/dendrite pre/post synaptic terminals maintain their correct separation, that is, how do they stop themselves from touching or stop themselves from separating too far?
 And if there is indeed- Failures in this gap separation, then what would be the diseases associated with both the touching condition and the over separation condition of the terminals?","In the Synaptic Cleft, there are neurotransmitters that are diffusing from one neuron to the next neuron, and then undergoing receptor-mediated endocytosis with the receptors in the "receiving" neuron (which should require space for receiving them). These neurotransmitters would diffuse away from the synaptic cleft or an enzyme would help clear the rest of the neurotransmitters. I believe that for these enzymes to be able to "sweep away" those neurotransmitters, some space is needed. Furthermore, as only milliseconds pass between some action potentials, the synaptic cleft maintains its distance."
N/A,"in "Overview of transmission at chemical synapses," it was stated that a depolarization of the membrane causes an influx of Ca2+ ions into the cell. However, doesn't this influx on positive charge cause depolarization of the cell? 

I don't understand why depolarizing the membrane would stimulate further depolarization. Wouldn't hyper-polarization of the membrane cause this?","You got confused because both carry a positive charge. I will tell you that speaking of the number of ions, this is almost minor.

Yes, we say an influx of Ca+ ions, but there are not many Ca+ ions. Sometimes, only one is enough to bind to SNARE complex of one vesicle to release neurotransmitters-"
N/A,"what makes an EPSP or IPSP, how are they determined to be excitatory or inhibitory?","EPSPs are graded potentials that can initiate an AP in the axon, whereas IPSPs produce a graded potential that lessens the chance of an AP in an axon.

I found one paper where it was investigated, but again - Cell-autonomous molecular mechanisms that control the balance of excitatory and inhibitory synapse function remain poorly understood; no proteins that regulate excitatory and inhibitory synapse strength in a coordinated reciprocal manner have been identified. 
The knockdown of cadherin-10 reduces excitatory but increases inhibitory synapse size and strength.


https://www.ncbi.nlm.nih.gov/pubmed/29030434"
N/A,"Where is the ACTH broken down into ethanoic acid and choline by the acetylcholinesterase, in the cleft, or postsynaptic neuron? It is definitely broken down after it enters the postsynaptic neuron, right? Why ACTH can not go back to the presynaptic neuron directly, but has to be broken down and brought back?","Acetylcholine interacts with postsynaptic receptors a few milliseconds before it is being degraded down by acetylcholinesterase. Then both taken up by presynaptic nerve terminal and recycled.

Meaning that degradation happens in the synaptic cleft, actually on the postsynaptic neurons, but right after it already finished its role.

https://www.us.elsevierhealth.com/vst-nurse-anesthesia-e-book-9780323444378.html?dmnum=12449"
N/A,How did cell membrane evolve in synaptic clefts?,"A primordial neurosecretory apparatus in choanoflagellates was identified and it was found that the mechanism, by which presynaptic proteins required for secretion of neurotransmitters interact, is conserved in choanoflagellates and metazoans. Moreover, studies on the postsynaptic protein homolog Homer revealed unexpected localization patterns in choanoflagellates and new binding partners, both of which are conserved in metazoans. 

I think this paper will satisfy you, everyzhing int he one place:
https://jeb.biologists.org/content/218/4/506"
N/A,Why are the neurotransmitter molecules cleaved so fast in the synaptic cleft ( 50molecules/ms)?,"Because it could cause potential disadvantages:
1. further delaying of response
2. overcrowding of neurotransmitters and too enhanced answer
3. what if new stimulation happens in a short time and neurotransmitters are not recycled? Who would respond to it then?"
N/A,how do synapses affect your reaction time?,"They little delay the reaction.

The overall synaptic delay and estimated number of synapses (ENOS) of simple tactile reaction neuronal circuits of normal subjects did not significantly vary with site of tactile stimulation or effector organ. 

The overall synaptic delay in the tactile reaction neuronal circuits between SOS and the left and right big toes were significantly lower in sniffers than in control subjects. This may be due to a decrease in either the average synaptic delay, the number of synapses, or both in the tactile reaction neuronal circuits between sites of stimulation and big toes (but not index fingers) in sniffers.


https://www.ncbi.nlm.nih.gov/pubmed/3393601"
Neurotransmitters and receptors,"If I understand correctly, the point in having different types of neurotransmitters is that they do different things. But if a neuron has only two states, firing and not firing, how can different neurotransmitters do different things?","The membrane potential has to reach a certain threshold for firing; this is known as summation (for which there are spatial and temporal components) and occurs at the axon hillock. Certain populations of neurons only express receptors for certain neurotransmitters. Excitatory and inhibitory NTs work with or against one another to bring the membrane potential closer to or farther from that firing threshold. Look on the wikipedia pages for summation, EPSPs, and IPSPs, for more information."
Neurotransmitters and receptors,What happens if receptor sites for the NT were blocked,"If the receptor sites for the neurotransmitter are blocked, the neurotransmitter is not able to act on that receptor. Most of the time, the neurotransmitter will then be taken back up by the neuron that released it, in a process known as "reuptake". However, in the case of Acetylcholine, there will be multiple copies of the enzyme known as acetylcholinesterase within the synapse that will break it down."
Neurotransmitters and receptors,What is the name of the receptor which take the neurotransmitters NE or Epinephrine?,"It's not just one, it's a group of receptors. They are called adrenergic receptors.

https://en.wikipedia.org/wiki/Adrenergic_receptor"
Neurotransmitters and receptors,Can someone just explain what a receptor does? Without very much science vocabulary? Thanks in advance.,"The receptor is the cellular structure (part of the cell) which binds certain molecule.


Its role - to catch the signalling molecule. Just like goalkeeper's role in football, is to catch a ball before it ends up in the mesh."
Overview of neuron structure and function,What exactly occurs during a reflex arc?,"A reflex "arC" is not a series of actions but the structure that allows a reflex "acT" to happen, and it comprises (in a sequential order) a stimulus, a receptor, an afferent pathway, a synapse, an efferent pathway, an effector and a response.
The reflex "acT" is an involuntary response to a stimulus, where the components I just mentioned interact. So what happens is the following:
1) A stimulus activates a receptor.
2) The receptor transmits the signal to an afferent pathway.
3) The afferent pathway carries the signal to a place (e.g. spinal cord) where this pathway synapses (or communicates with) the efferent pathway.
4) The efferent pathway carries a signal to an effector (e.g. muscle)
5) The effector executes a response (e.g. muscle contraction)"
Overview of neuron structure and function,Why do we need interneurons? Wouldn't a direct connection between motor and sensory neurons be faster?,"Interneurons also integrate signals, thus "determining" an appropriate response."
Overview of neuron structure and function,Is it possible that the dendrites on the cell body receives strong impulses of more than one type.In such a case how are all transmitted simultaneously?,"GOOD QUESTION

That is true and that is called *synapse*.


Dendrites convert these signals into small electric impulses and transmit them inward, in the direction of the cell body. Neuronal cell bodies can also form synapses and thus receive signals (Figure 21-3). Particularly in the central nervous system, neurons have extremely long dendrites with complex branches. This allows them to form synapses with and receive signals from a large number of other neurons (1000).



https://www.ncbi.nlm.nih.gov/books/NBK21535/"
Overview of neuron structure and function,What is the purpose of having different types of neuron structures?,"Different neuron structures change the way the signal is treated and conducted. Imagine a big tree. You are sitting in the area where all the branches come together and the trunk starts, this could be the same as the soma of a neuron since all dendrites come together. A friend of yours is sitting on the grass next to the trees roots (which is the terminals in the neuron analogy). Think of the signal as a ball that you want to give your friend; you let it fall.  If the trunk is long, then it will take longer for your friend to catch the ball, if the trunk is short, you might even be able to give it personally to your friend. So the axon is responsible for the temporal delay of the signal conductance, similarily to the dendrite. If the dendrites are long, it takes longer until they reach the soma. Therefore, weak signals will maybe not even arrive at the soma since they decay with time. Additionally, a huge dendritic tree means that it has a lot of potential for many many connections to other neurons. Therefore, for instance the Purkinje cell with its huge dendrical tree acts as an integrator of many different signals. 
So basically each anatomical structure has different functions to offer."
Overview of neuron structure and function,Human brain consist of cerebral cortex as its outermost layer below cranium . Does human beings have the capacity to use all areas of cerebral cortex or only few designated areas??,"interestingly enough, so-called idiot savants, do not have a greater capacity for computation, music, or art. Instead, the parts of their brains responsible for such tasks dominate the rest of their brain because the parts that would normally compete for attention are either damaged or unable to communicate effectively with the rest of the brain. Researchers have used something called TMS (trans-cranial magnetic stimulation) to induce small currents in parts of the brain, either shutting down or activating specific regions of the brain temporarily. Their research has shown that it is possible to temporarily induce a savant-like state in normally functioning brains. And, of course, some forms of brain damage can induce temporary or permanent savant-like states as well. I met a young man who had the ability to perform amazing feats of computation after a bad car accident."
Overview of neuron structure and function,How the neurons sense our taste and other stuff? sorry if the question is bad :P,"When eating, the taste receptor cells in our taste buds detect concentrations of different chemicals and fire electric signals to sensory neurons, which in turn fire a nerve impulse to the brain. That said, it is not the _neuron_ that senses the taste, but the _taste receptor cell_. The neuron is the one that transfers the message (nerve impulse) to the brain. In the same way, the cell that senses the stimuli in any part of the body is the receptor, not the neuron.

So about taste sensation, the stimuli is actually the chemicals in our mouth. When the pH is low, we feel that it's sour. When the pH is high, we feel that it's bitter. When there is sugar, we feel that it's sweet. When there is salt, we feel that it's salty. And certain proteins cause the taste of unami. When it comes to taste, it's actually the concentration of different substances that cause the senses. (pH is the concentration of H+ ions)

And no worries, your question isn't bad. If a question helps you learn, it's not bad. Even if we ask bad questions every now and then, there's nothing wrong with that either."
Overview of neuron structure and function,"In the axon of someone with Multiple sclerosis what happens to the myelin sheath and nodes of ranvier? I know that the myelin sheath is not there so it slows down the action potential, but I would like a bit more in depth explanation. thanks","Multiple sclerosis (MS) is the most common demyelinating and an autoimmune disease of the central nervous system characterized by immune-mediated myelin and axonal damage, and chronic axonal loss attributable to the absence of myelin sheaths.

with concomitant degradation of myelin, oligodendrocytes and axons, along with reactive astrogliosis and activated microglia - meaning that there is no only the problem of demzeliniyation but of hzperactive microglia. 


additional T-cell subsets play a prominent role in MS immunopathology: Th17 cells, CD8+ effector T cells and CD4+CD25+ regulatory T cells.


 There are different mechanisms for lipid antigen uptake depending upon the antigen source and its structure such that endogenous lipids are differentially distributed in subcellular compartments and internalized lipids are transported to different endocytotic vesicles.
 Lipids containing alkyl chains that have multiple unsaturation sites or shorter saturated tails are trafficked to early or recycling endosomes [62]; compartments surveyed by CD1c and CD1a that present these types of lipids.

Demyelinated plaques and associated astrocytic activation (gliosis) are the results of local inflammation and the major pathological characteristics of the disease.


https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4061877/"
Overview of neuron structure and function,"Article says  about relay neurones:Some of these interneurons would signal to the motor neurons controlling your finger muscles (causing you to let go), while others would transmit the signal up the spinal cord to neurons in the brain, where it would be perceived as pain. So what would happen first ? Would we first feel pain or we will drop the hot coal.is it possible that we drop the coal even before feeling pain? Where was the decision to drop the coal made?Spinal cord?","Yes, you would first drop the coal and only then have the conscious feeling of pain. There seem to be different kinds of reflexes, some complex ones maybe from the brain, some from the spinal cord and a wikipedia tells that some reflexes in the organs could be processed even in the axons."
Overview of neuron structure and function,Why don't some neurons have a myelin sheath?,"At some metabolic cost, neurons are not myelinated unless there is a significant advantage to they're being able to conduct faster."
Overview of neuron structure and function,Hi! I am doing a science paper on neurons and I was just wondering how big are there? Like can the size differ? What's the average size?,"This is tricky, as there are many different types of neurons and they all differ substantially in size and function. Neurons can range from 4 micrometers to 100 micrometers in diameter, depending on the type, but most are within the 10-25 micrometer range.

I should note that these measurements refer to the soma (the body) of the neurons. The axons and dendrites are not taken to account in these measurements. If you want some measurements for those, axons and dendrites are usually about one micrometer thick, and the longest axon in the human body can reach to roughly a meter long (from the base of the spine to the toes).

Does that help?"
Phototropism & photoperiodism,what could happen if I expose a plant to a large amount of light?,"*It would depend on the species*. Plants that grow on the tundra of the arctic circle and are exposed to 24 hours of daylight during the brief Summer are all species which evolved under those conditions.

Some plant species such a _Poinsettia_, demand a certain number of hours in total darkness or they will never bloom. Those adapted to life on the tundra will thrive. Some plants such as the vegetables you mentioned could grow much larger because of constant photosynthesis.

Plants do not _need nighttime to live_, only they use night for dark phases of photosynthesis, but it does not mean photosynthesis cannot proceed even during daylight.

However, there are _other growth-related mechanisms_ in plants that depend on photoperiod (large cycles of growth and rest, flowering, disease and pest resistance, and others). Some plants can be given hormonal supplements to counteract these negatives (often this is the case with commercially sold cut flowers). But with most plants, if you grew under lights 24/7, without any special treatment, they might start to decline."
Phototropism & photoperiodism,"Does phototropism and photoperioddism happen in every plant?Why did Darwin and his son choose coleoptile?Was it because the result of experiment is more obvious?And why choose a young plant?Was it because phototropism changes by time of the plant(age)?
How did Danish physiologist come up with the idea to cut off the tip of a coleoptile?","No, actually, it only happens in some plants. One plant that does phototropism is the sunflower. It will bend towards the sun as it moves around."
Phototropism & photoperiodism,Did you know a flower of a plant is the reproductive organ of the plant? I did not understand why it has a really great aroma and beauty? Is it for attraction for bees and other animals?,"Just to be clear, Pollination is not the same as fertilization. Just because the pollen is passed to the next plant doesn't mean it will fertilize the egg to make a seed. Fertilization is when the sperm in the microspores (pollen) reaches the megaspores (eggs) and then they combine into one. Pollination is just the movement of pollen from plant to plant."
Phototropism & photoperiodism,"I am curious, is negative phototropism a simple derivative of the positive phototropism as a mandatory part of the nomenclature, or is it actually a well-described phenomenon? And if so, which plants exhibit this behaviour and why?","I believe some forms of negative phototropism would involve things such as the roots of plants in order to ensure, along with other direction-of-growth determining factors, that the roots go into the ground and don't just grow out of the seed wherever."
Meet Erin Kane!,how did u you gain intrest in biology?,"She was inspired by the work of Jane Goodall ever since she was little, quote:
 _"When I was in 7th grade, my dad had me read Jane Goodall’s book In the Shadow of Man, which is about her experience studying chimpanzees in Tanzania in the 1960s and 1970s. I loved it, and told myself at age 12 that that was what I was going to be when I grew up! I have been focused on that goal since then."_"
Meet Chris Northard!,How did you get the idea to intern as a zookeeper? I thought it was pretty cool idea.,He probably just wanted to expand his horizon in the World of Biology!
N/A,"Where are the 10 electrons in the hydroxide? wouldn't it have 8, 6 in lone pairs and two in the covalent bond?","Do not think about the dot structure for this. 
Now, we know that oxygen has 8 protons & 8 electrons. And we also know that hydrogen has 1 electron.
The extra electron or the minus one sign at the top left of a hydroxide ion also contributes to the total number of electrons in the ion.
How we get this extra electron is,in the water molecule, H-O-H, one of the hydrogen's break their bond with the central oxygen atom, to become a proton, meaning they lose their only electron to oxygen & become a H+ ion. This happens due to ionisation of water molecules. 

Now what is left behind is a H+ ion with no electrons & only a single proton and an OH- ion with an extra electron that was donated by the hydrogen. 

Now, coming back to the question, the OH- ion will have: 1 hydrogen with 1 electron, 1 oxygen with 8 electrons and 1 extra electron. When you add these up, you get, 1 + 8 + 1 = 10 electrons in total in a hydroxide ion.

Hope this helps."
N/A,how are polyatomic ion formed?,"Polyatomic ions are formed through covalent bonds, most especially coordinate covalent bonds."
N/A,How many polyatomic ions are there in total (accurately)?,"Practically unlimited, even though there are some that are more and some that are less common. There is nothing preventing you from making more polyatomic ions"
N/A,Why is mercury (and oxygen) considered polayatomic? Does it bond to itself?,"Mercury and oxygen aren't considered polyatomic ions by themselves, but in the mercury (I) Hg2+2 and peroxide ions O2-2 you indeed have a bond between the same atoms."
N/A,"I am totally confused with the anions and cations and how to do them and all that basically I have no clue can some one explain it a little simpler please! Any help would be greatly appreciated 
thanks","*Cations* are positively charged, with less electrons than the number of protons (overall positive charge).
*Anions* are negatively charged, with more electrons than protons (overall negative charge).
Hope this helps! :)"
N/A,"In the paragraph about poly atomic ions, does all the atoms in the ion need to be negative or positive for the entire to be that charge?","No, the charge on the ion is the sum of all the + and - charges on all the atoms in the ion.
Usually, only one atom has the charge and the other atoms have no charge.
At this stage, all you have to know is the *overall charge* on the ion."
N/A,Very basic question.  If Cl gains 1 electron isn't it now fully satisfied having 8 electrons in its outer shell and hence no likely to interact with another atom but rather be content as a noble gas?,"But now it has a negative charge, so it's going to attract a positive charge, right?  That's a big difference versus noble gases, which are neutrally charged when they have their full valence shell.
And that's how you get salt:  a Cl- ion finds an Na+ ion and you have NaCl."
N/A,Is there an error in problem 1? Isn't it supposed to be Li_2(HPO_4) instead of Li_2HPO_4?,"You don’t have to put parentheses around a polyatomic ion if there is only one of them in the formula unit.
Thus, you write LiH₂PO₄ but Ca(H₂PO₄)₂."
N/A,"Why are these things called polyatomic ions?

At the top of the article, it says poly- means many, but atomic? These things are made mostly of ions, are they not?

Why aren't they called polyionic ions?","Polyatomic ions are groups of atoms *covalently* bonded together, but the group of atoms as a whole has a charge. They aren't made of multiple ions."
Naming monatomic ions and ionic compounds,Can you provide me an example of ionic compound where Hydrogen is the anion or the negatively charged section of the bond. Thanks,"In a chemical reaction with an alkali metal and hydrogen, the hydrogen atom will always form the anion as hydrogen can from both cations and anions, but alkali metals can only form cations. In this case, the alkali metal gets a 1+ charge, and the hydrogen gets a 1- charge. 
Lithium hydride (LiH)
Sodium hydride (NaH)
Potassium hydride (KH)
Rubidium hydride (RbH)
Caesium hydride (CsH)
Francium hydride (FrH)"
Naming monatomic ions and ionic compounds,"When we say "Transition metals", what does "transition" mean?","it's because they "have an incomplete inner electron shell and that serve as transitional links between the most and the least electropositive in a series of elements"

(http://www.thefreedictionary.com/Transition+metal)"
Naming monatomic ions and ionic compounds,"Hydrogen's preference to form ions will ultimately be related to the energy associated with the 1s shell. Although, I thought an atom's stability decreased upon forming ions, and so, an atom of hydrogen, with no external influences ( no transfer of energy between it and anything else ) could not form an ion. Energy would first have to be given too, or taken away from hydrogen before any electronic reactions could take place.

Returning swiftly back to why hydrogen can easily form ions, well, for the cation, I think it's because only a small amount of energy is needed to remove the electron. A little bit of research led to me ionization energies! 1,312 Joules of energy needed to remove hydrogen's electron. I'm not sure what I can relate that number too though, is it a lot?

For the anion, I think it's because the nucleus has a strong positive charge, which will attract any passing electrons. 

That's my answer, and it could all be complete nonsense.","For reference, it would take 1 liter of water that is at 0 degrees celsius and at 1 atm pressure 418100 joules to boil.

Also, there are 4184 joules in a kilocalorie.
Humans require anywhere from 1600-3000 calories to function."
Naming monatomic ions and ionic compounds,"In Example 3, PbCl4 is Lead (IV) Chloride, doesn’t Cl4 refer to tetrachloride?","Yes. For example, CCl₄ is carbon tetrachloride. But that's how you name *covalent compounds*.
The name of an *ionic compound* is: name of metal ion + name of anion ( with no multiplying prefix).
So, PbCl₄ is lead(IV) chloride."
Naming monatomic ions and ionic compounds,"When hydrogen loses an electron won't it just be a proton and no longer hydrogen?

Sorry if it's a stupid question",A single proton is still atomically hydrogen. It retains all the chemical properties.
Naming monatomic ions and ionic compounds,hydrogen exists as H2 or H in the atmosphere?,"In particular, there are 7 elements that are called "diatomic," meaning that on their own they will almost always form molecules consisting of two atoms of that element.  They are: bromine, iodine, nitrogen, chlorine, hydrogen, oxygen, and fluorine.  You can remember them by the acronym Br-I-N-Cl-H-O-F (pronounced "brinkle-hoff")."
Naming monatomic ions and ionic compounds,"So if you had a magnet attached to some compound, could you change the overall charge of the compound?if so, wouldn't it also be true that you could magnetically remove electrons and/or protons, thus changing the compound itself?","The magnet will not "steal" the electrons from other metallic items. The magnet will simply force all the electrons in the metal to one side (non-permanently) which is how they attract each other. Once you remove the magnet, all electrons go back to where they came from and the metal compound neutral again."
Naming monatomic ions and ionic compounds,"what does the roman numerals mean? like Cobalt(III) sulfide, or lead (IV)",The roman numerals show the amount of charge. Cobalt (III) has a charge of (+3) and Lead (IV) has a charge of (+4).
Naming monatomic ions and ionic compounds,"Why is PbCl4 named lead (IV) chloride? 

We said we specify the charge for transition metals, which Pb doesn't appear to be. Also, since Pb can only have 4+ or 4- ions, and it is named first, doesn't that automatically mean it will be the 4+ cation?","Lead forms Pb2+ or Pb4+ ions, post transition metals can form different ions too."
Naming monatomic ions and ionic compounds,"Hello there, 

in Example 2: Finding the name from the chemical formula
"Therefore, the name for the compound is magnesium phosphide."
Shouldnt it be magnesium ion phosphide or magnesium 2-plus phosphide?..  Im really new to this and it sounds weird but earlier in article its said that : "While we often refer to an ion such as Mg2+  as "magnesium 2-plus", we could also simply say "magnesium ion," "

or is "just" magnesium a good answer afteral ?l.","When we name an ionic compound, the charge is not included unless that element forms multiple ions.  For example, if I have Fe2O3, I have to call it iron(III) oxide because iron also forms an ion with a 2+ charge.
Magnesium only forms the ion with a 2+ charge, so you don't need to include it."
Preparing to study chemistry,This question has been bugging me for a while. are most of the man made elements on the periodic table a combination of other elements from the periodic tables? If so why aren't they classified as compunds?,They are individual atoms of a new element. Compounds are two or more atoms chemically bonded into a molecule.
Preparing to study chemistry,Does every element have an isotope(s),All atoms are isotopes. All atoms are elements. Therefore all elements have isotopes.
Preparing to study chemistry,"Hello 
I am 10th grade student and I do not have any basic knowledge of chemistry
I realised that there are no high school chemistry course in khan academy unlike physics
Will you recommand me to study with chemistry library or Organic chemistry?","If you’re beginning a study of chemistry with no prior exposure to it before, I would begin with the chemistry library on KA first. It begins with the fundamental concepts. The chemistry library is essentially equivalent to high school chemistry. The AP chemistry section would be the next step up in complexity. But there are some topics which are more fully explained in the AP chemistry section compared to the chemistry library so the best strategy would be to mainly rely on the chemistry library, but check out the AP chemistry section when needed. 

I would also recommend only beginning organic chemistry after you’ve completed the AP chemistry section. Organic chemistry is one step more complicated than AP chemistry.

Hope that helps."
Preparing to study chemistry,"Hi, can you please explain the last sentence?

Coulomb’s law is a mathematical relationship which describes the amount of force two charged objects exert on each other. Charged objects being objects with either a negative or positive electric charge. In a chemistry context we can understand this as atom having unequal amounts of protons and electrons, since those particles are responsible for the electric charge of atoms. And force just being the physics concept of either a pushing and pulling motion between objects.

The actual law is stated as an equation: F = (K(Q1)(Q2))/r^(2), where F is force, K is Coulomb’s constant equal to 8.988×10^(9), Q1 is the magnitude of one charged object, Q2 is the magnitude of the other charged object, and r is distance between the two charged objects. In a physics class we would be concerned with actually calculating numbers, but in a chemistry class we’re only concerned with it to show trends in the interactions between charged particles. *The main points of this law for a chemistry perspective is that there is greater force between particles which have greater magnitudes of charge, and less force between larger particles.b*","Electric force is directly proportional to charge magnitude, and inversely proportional to the square of the distance between the charged particles."
Preparing to study chemistry,What is an easy way to memorize the Periodic table of elements?,"Ummm. Hi. What helps me is repeating... Even if It's over and over again. Also write it down, writing is always a good way to help memorize certain material... :)"
Preparing to study chemistry,How do covalent bonds work?,"there are different kinds of bonds, but a covalent bond is one which involves the sharing of electrons. For example, when 2 hydrogen atoms covalently bond, they share their electrons, forming H2. Therfore, hydrogen (which is naturally found as H2 because the single electrons really want to bond with other electrons) has 2 protons, 2 electrons, and 0 neutrons. I hope this helped :)"
Preparing to study chemistry,What is the subatomic level?,"The level below the size of atoms. Usually used to refer to protons, neutrons and electrons."
Preparing to study chemistry,why is there not another table for different types of bonds and molecules and how different elements react with each other,It's better to understand the underlying concepts of bonding than to memorize each different molecule and interaction.  The number of molecules we can make is truly limitless.  Chemists synthesize molecules for the first time on a daily basis.
Preparing to study chemistry,can you please tell me what makes acids acid and bases base. what is special in them,"There are several definitions to acids and bases, all of which were created relatively at the same time. The Arrhenius theory states an acid donates a hydronium ion/proton(H+) and a base donates a hydroxide (OH-) subsequently increasing the concentration of each in a solution. The Bronstead-Lowry definition states an acid and base react to form their conjugate base and conjugate acid conterparts with the exchange of a proton (H+). Finally, the most emcompassing definition comes from Lewis theory. It states an acid is one that accepts electron pair (i.e. an electrophile) and a base is one that donates an electron pair (i.e. a nucleophile). This a very simiplified explanation for these definitions."
Molecules and compounds,"Here, electrons and protons are depicted using spheres. But in reality, protons and electrons aren't really spheres, are they? If not, what exactly do they look like?","It makes sense for protons and electrons to be spheres since the shape would allow the mass of the particles to be evenly distributed from all sides. If they were cubes, the corners would be sticking farther away from the center.

However, it is much more complicated than that. Sometimes the protons and electrons act like waves. They are not really spheres, but at the same time, they are.

Pretend you are holding a ball above a puddle of water. Now, drop the ball. When the ball hits the water, it disappears. The ripples travel outward from the point of impact. Then, a ripple hits a stick in the water. The ripples disappear, and the ball bounces back up from the stick.

Hopefully this answer is simple enough yet understandable at the time. If you are still interested in this topic, I suggest you look further into quantum physics.

Remember that I might be wrong. Anything that we think are facts may be later disproven. That is the beauty of science. :)

Anyone have any other thoughts on this?"
Molecules and compounds,"when NaCl crystal dissolves in water , what happens to it? what happens to electrostatic attraction between Na and Cl atoms?","The electrostatic attraction between the Na⁺ ions and the Cl⁻ ions is still there.
But the attractions between these ions and water molecules is greater than their attractions for each other.
The ions become surrounded by a shell of water molecules and move away from the crystal and into the water."
Molecules and compounds,How does bonding (covalent vs ionic) determine the properties of a substance?,"Do you know what properties from these bonds make that happen ? I remenber seeing in another video that intermolecular h-bonds typically make for high boiling points, like in water, because it takes alot of energy to break them apart. I would think covalent bonds would be even stronger and therefore harder to change phase. But maybe what matters for boiling is different than for melting, do you know how these bonds translate into the properties you cited ?"
Molecules and compounds,Is it possible for a molecule to lose all of it's electrons? Hydrogen for example?,"Absolutely, and hydrogen often makes a hydrogen ion (H+) which consists of only a proton"
Molecules and compounds,"Is there a limit to the number of electrons atoms can have, or is it specific to each element?","Each shell is limited to the number of electrons per subshell:
The first shell consists of an s-orbital, and so it will have max 2 electrons.
The second shell has an s and p orbital so it will have max 2+6=8 electrons.
The third shell has s p and d orbitals so it will have max 2+6+10=18 electrons."
Molecules and compounds,"Does the bond really exist and you can observe, or its a only an illustration of a kind of force within compound?","The bonds exist as electromagnectic atractions that tend to hold the molecule together. They can be measured through spectroscopy with infrared, ultraviolet, and other wavelengths of energy ."
Molecules and compounds,"In the "Ion and formation" part, can every elements form an ion?","Elements tend to try and reach more stable electronic distribuitions, therefore they can loose or win electrons, forming ions, not all elements form ions spontaneously, like noble gases, some form ions very very easily while others dont (they require high amounts of energy to do so)"
Molecules and compounds,"I still don't understand how there is no such thing as a molecule of an ionic compound. Earlier in the chemistry playlist, they said that a molecule consists of two or more atoms bonded together, so wouldn't that make ionically bonded sodium and chlorine a molecule cause it consists of two atoms? And how much of it do you need in order for it to be considered a formula unit?","Molecules are defined as two or more atoms connected by *covalent* bonds.

That might seem arbitrary (especially since covalent and ionic bonds are ends of a continuum rather than separate categories), but ionic bonding *is* fundamentally different.  

Ionic bonding is not directional — for example, each sodium cation in a crystal of table salt is equally attracted to all the neighboring chloride anions.  In contrast, covalent bonding is directional — a covalent bond is between two specific atoms.

This means that a salt crystal has a network of interactions, so there are no specific pairs of ions — this means you can't single out a "molecule" and therefore we talk about the more abstract "formula units" instead.  Formula units have no physical reality, they are just a way of talking about the stoichiometry (ratio of elements) within a compound.

Does that help?"
Molecules and compounds,"I have this question since the beginning and unfortunately nothing seems to clarify it. 
What is the difference between a molecule and a compound?",Molecules consist of two or more atoms bonded together. Compounds are molecules with two or more different elements.
Isotopes and mass spectrometry,"What is a neutrino? Also, what are quarks, gluons, mesons and bosons? A detailed explanation, please.","Neutrinos are fundamental particles similar to electrons but without a charge. Electrons and neutrinos are in a class of particles called leptons. 

Quarks are fundamental particles that are the constituent particles of matter. They combined to form a class of composite particles called hadrons. Hadrons include protons and neutrons, as well as mesons, which are quark-antiquark pairs.

Bosons are force carrying particles. They include: photons which mediate the electromagnetic force, gluons which mediate the strong force, W and Z bosons which mediate the weak force, the hypothetical graviton which mediates gravity, and the Higgs boson which mediates the Higgs field. Gluons are the bosons that quarks use to 'stick' together, but they also have the unusual property that they can stick to themselves too."
Isotopes and mass spectrometry,"At the end of this reading material, when determining the atomic weight of zirconium, why is the answer to the product of (0.0280 x 95.908u) equal 2.68u and not 2.69u?  I actually got 2.685424 and rounded up, but in the equation they figured, they did not round up as done normally in math.  I'm lost.  I actually got 91.24 to this equation.  So...can someone please explain the reasons behind not rounding up when appropriate??",I just want to mention here about significant figures. In science all numbers are rounded using significant figures. A nice video on khan academy teaches how to round in this way https://www.khanacademy.org/math/arithmetic/decimals/significant_figures_tutorial/v/significant-figures
Isotopes and mass spectrometry,"In the 5th paragraph it is said that "1 u is equal to exactly 1/12 of the mass of a single neutral atom of carbon-12". However if you add:
6 protons times |.007 u + 6 neutrons times 1.009 u= 12.096  (mass of carbon-12)
and then we divide by 12 we get something greater than 1 u.
Should n´t the mass of 1 u be  between the mass of the proton and the neutrón   1 p < 1 u <1 n?  So that the atomic mass for carbón-12 be exactly 12 u?","The total mass of 6 protons + 6 neutrons is indeed 12.096 u.
But these are *isolated* protons and neutrons.
Energy is released when you bring them together to form a carbon-12 nucleus.
Energy is equivalent to mass (E =mc²), and the energy released is equal to 0.096 u.
This difference is called the *mass defect*.
So the mass of a carbon-12 atom is 12.096 u – 0.096 u = 12.000 u"
Isotopes and mass spectrometry,"Historically, the units u and amu were defined slightly differently. Can someone please clarify?",Atomic mass units used to be defined on oxygen and it wasn't consistent in definition between chemistry and physics. It was redefined to Carbon-12 to unify all measurements in physical and chemical sciences and to be consistent. This was officially termed 'unified atomic mass unit' and the symbol set as _u._
Isotopes and mass spectrometry,Hey everyone...i just started learning chemistry (yep i'm a newbie) and i still can't understand the meaning of a charge...could i request a little help please? thankiew:),"Charge is just a fundamental property of an object or particle, just as mass is.  An object's mass tells you how hard a gravitational force will pull on the object.  An object's charge tells you how hard an electrical force will pull on the object. 

There's a lot more about it here
https://www.facebook.com/notes/ask-andrew-high-school-physics/electric-charge-and-field-ib-topic-51/675755755903814"
Isotopes and mass spectrometry,"why is it that 0.0280×95.908u = 2.68u
I used my calculator got this: 2.685424
if you round it to the hundredths place
you would get 2.69  [5 is a midway number, 
   so we should round it off to the higher hundredth]
Please explain what is going on.
thanks","Yeah, you’re right, they rounded that last number incorrectly, it should be 2.69 u if they wanted only three sig figs (or two decimal places). In this case whether it is 2.68 or 2.69, the final answer, with sig figs, remains the same. 

Really though, we shouldn’t be rounding for intermediate answers like the multiplication parts and only round at the very end to limit rounding errors affecting the final answer.  

Hope that helps."
Isotopes and mass spectrometry,Are there any disadvantages of mass spectrometry,"No "disadvantages" but limitations instead: mass spectrometry will not tell you anything about a structure directly. Also, some types of spectrometry will not allow every molecule to be fragmented in every possible way."
Isotopes and mass spectrometry,"In the section "Calculating the atomic weight of chlorine" you state:
atomic weight of chlorine=(0.7576×34.969 u)+(0.2424×36.966 u)
Where did the numbers 34.969 u and 36.966 u come from?  
Shouldn't they be:
for Cl 35 = 17 protons + 18 Neutrons = 17 x 1.007u + 18 x 1.009u = 35.281 u
and
for Cl 37 = 17 protons + 20 neutrons = 17 x 1.007u + 20 x 1.009u = 37.299u

FOLLOW UP TO QUESTION ABOVE:
okay, I found a table of atomic masses for all elements and their isotopes and the numbers you give are the same as what they give on the table. However, this confuses me even more.  You did say in the lesson above that "a proton has a mass of... 1.007 u.... A neutron is slightly heavier, with a mass of }1.009 u". Those are the numbers I used in my calculations above.  But to make the calculation work, the atomic masses have to be less than those I used (as per the table).  How can the weight of a proton and neutron change from element to element?","Adding up the individual masses of protons and neutrons doesn't work. You also need to account for the mass of electrons (yes, these make a small difference in getting to the exact mass) and binding energy when calculating the total atomic mass of an atom. Binding energy needs to be looked up for each individual isotope you are working with as it varies."
Isotopes and mass spectrometry,What is a subatomic particle?,""sub-atomic" literally means "below the atom." When we discuss subatomic particles, we talk about any particles smaller than the atom. These could be quarks (up/down quarks, which make up protons and neutrons), leptons (neutrinos but also electrons), as well as bosons. These are typically discussed in particle physics and less often in chemistry."
Isotopes and mass spectrometry,"Oh come on, I got 91.31u because I didn't round at each step, only at the end?","We really shouldn’t be rounding at intermediate steps, only at the final step. The issue is that when we round too soon it introduces rounding errors which trickle down to the final answer. It is important to keep in mind the amount of significant figures allowed after each operation to know how much you need to round off your final answer. 

If you do the full calculation without any premature rounding you should get 91.22377 if you do everything correct. Which would round off to 91.22 using proper significant figures. 

Hope that helps."
Balancing redox equations,"Why is the reduction half reaction is written like this:
2H​+​​(aq)+2e​−​​→H​2​​(g)
Isn't it:
H​+​​(aq)+2e​−​​→H​2​​(g)

Since the base equation contains:
H​+​​(aq) -> H​2​​(g)

I do not understand this...","H​+​​(aq)+2e​−​​→H​2​​(g) balances neither the charge nor the mass.
Left side: Charge of -1; one H
Right side: 0 charge; 2 H atoms (bonded as H2)
For balancing Redox reactions, it is necessary to first balance the main atoms (through adjusting stoichiometric coefficients), then the charges (through electron transfer and as per conditions - acidic/neutral/basic)."
Balancing redox equations,"In the example of combustion reaction, the oxidation number of C in C8H18 comes out to be -9/4. How is this possible? Electrons cannot be transferred in fractions right?","It may be better to consider that there are two different carbon oxidation numbers rather than the fractional one. 

The two on each end are bonded to 3 hydrogens so are -3, the six in the middle are bonded to 2 hydrogens so are -2"
Balancing redox equations,"It says above for Disproportionate Reaction: "If we analyze the oxidation numbers for chlorine, we see that the reactant ClO− ​is being oxidized to ClO​3​− (where the oxidation number increases from +1 to +5)."

I can't see what goes from +1 to + 5. Is it Cl? If so, how so?","Cl is +1 in ClO^- and goes to +5 in ClO3^-

As oxygen is more electronegative than chlorine (in the Pauling scale), we assign it its preferred oxidation number which is -2. 

In a molecule the oxidation numbers of all atoms sum to the charge. 

So in ClO^- the oxidation numbers need to sum to -1. If oxygen is -2 then chlorine needs to be +1

-1 = Cl + O
-1 = x + -2
x = +1

For ClO3^- it's the same idea, but now we have 3 oxygens. 

-1 = Cl + 3O
-1 = x + -6
x = +5"
Balancing redox equations,"In the Practice question above, it does not specify what type of redox reaction it is. How do I know what type it is and what to put in as my answer? P.S. I got it wrong.","Compare the reaction to the types explained in the article -- 
1) Is there molecular oxygen (O2) involved? *NOPE* not oxidation
2) Has a single reactant undergone both oxidation and reduction? *NOPE* not disproportionation
3) Are two elements trading places within a compound? 
Doesn't look like it, but what if we look at the complete equation (rather than the net ionic equation we are given).
• there must be a counter ion that came with the "H+" ... let's pretend that we added HCl ...
This gives us the reaction:
`Al(s) + HCl(aq) → AlCl3(aq) + H2(g)` 
Now we can see that it fits the definition for a single replacement reaction!


To answer the question you don't need to know what type of reaction it is, you just need to make sure that you've balanced electrons (charges) as well as atoms.

The method shown above is to separate the oxidation and reduction reactions into half reactions ... did you try that?"
Balancing redox equations,What do you mean by saying "we can check to see if any reactants and products appear on both side"? Do you have an example?,"In this context, I think what he means is that if any ion is in an identical form on the left and right side of the equation then they cancel out and can be crossed out. In other words, identify any spectator ions."
Balancing redox equations,Why is MnO4 reduced and not oxidised ? It was an anion (permanganate) and became neutral MnO2 so it must have LOST electrons?,"We compare the oxidation states of atoms to determine if they’ve been oxidized or reduced. For the half-reaction of permanganate going to manganese dioxide, we’re comparing the oxidation states of the manganese and oxygen atoms individually, not the entire ions. Oxygen almost always has a -2 oxidation state so it stays constant here and is neither reduced or oxidized. Manganese begins with a +7 oxidation state in permanganate and is reduced to +4 in manganese dioxide. Since the oxidation state decreased, it was reduced. 

Hope that helps."
Balancing redox equations,Where does the water from the combustion example go? (car engine example) Steam?,"Yes, you are correct in the form of vapour it comes out of the engine and enters the air."
Balancing redox equations,"For Fe2O3, I know that the oxidation mu,her for oxygen is always -2 but then it says that the oxidation state of iron is +3. How does that make the compound neutral? Wouldn't the charge be +1 and not neutral?","You aren't taking in to account that there are 2 iron atoms and 3 oxygen atoms in one Fe2O3 molecule. 

3 oxygens with oxidation numbers of -2 each, -2 * 3 = -6
Fe2O3 is a neutral molecule so we know the oxidation numbers all must sum to 0
So the two irons must have oxidation numbers that equal +6, +6 / 2 = +3"
Balancing redox equations,"1.)Im not sure how to recognize if the oxidation number is -2 or +2.....
2.)For example, in CO2, is 2 the oxidation number or the number of atoms or the valency??
Pls answer in detail...Im really confused.","The oxidation number is the number of valence electrons an atom is assumed to have when the electrons are counted according to certain arbitrary rules.
Two important rules are;
1. The oxidation number of O in its compounds is almost always -2.
2. The charge on a molecule or ion is equal to the sum of the oxidation numbers of its atoms.
Thus the oxidation number of an O atom in CO₂ is -2.
The two O atoms have a total oxidation number of -4.
Since CO₂ is neutral, the oxidation number of C is +4."
Gravimetric analysis and precipitation gravimetry,I am very confused about this just for fun question - how do we go from knowing the mass of mixture to figuring out n and m?,"We have 1.032 grams of AgCl. We can use some stoichiometry to calculate this includes 7.201*10^-3 moles of chlorine atoms. Since all chlorine atoms come from the MgCl_2 and NaCl, we get our first equation:
7.201*10^-3 = n + 2m

Next up we can look at the mass of the original mixture (0.4015 g) together with the molar masses of MaCl_2 (58.44) and NaCl (95.20). This gives us our second equation:
0.4015 = 58.44n + 95.2m

Now it's required to do some algebra. One way is to first multiply the first equation by 58.44: 0.42082644 = 58.44n + 116.88m
Next we subtract the second equation from that equation:
0.42082644 - 0.4015 = 58.44n + 116.88m - 58.44n - 95.2m
0.01932644 = 21.68m
By dividing both sides by 21.68 we get:
*m = 8.914 * 10^-4*

Plugging that into the first equation we get:
7.201*10^-3 = n + 2 * 8.914 * 10*-4
7.201*10^-3 = n + 1.7828*10^-3
*n = 5.418*10^-3*

This answer is 6 years late, but better late than never I suppose."
Gravimetric analysis and precipitation gravimetry,What is the chemical equation for "just for fun" problem? Don't we have to work out stoichiometry (to make sure the equation is balanced) before doing other calcuations?,"If there was only one chemical reaction occurring here, yes! That would be the right way to approach a problem like the example above (Determining the purity of a mixture containing MgCl2 and NaNO3), because the precipitating agent, AGNO3, only reacts with MgCl2 (it does NOT react with NaNO3). However, because our precipitating agent in the "just for fun" problem reacts with both MgCl2 and NaCl, a different approach must be taken. Even if we did write out the chemical equations for both reactions, it wouldn't do us much good, because AgCl, the precipitate, is produced in two separate ways. That's why this new, clever approach that uses two mathematical equations needs to be applied here. This question is a bit unfair at this stage - you would need to look at the types of chemical reactions section (I would think the info would be there) to know that both MgCl2 and NaCl react with AgNO3."
Gravimetric analysis and precipitation gravimetry,"I am kinda lost, can someone explain to me where I went wrong and why ?
step 1 - set up the equation
MgCl2 + NaCl + AgNO3 = AgCl + Na + NO3 + Mg
step 2 - balance the equation
MgCl2 + NaCl + 3AgNO3 = 3AgCl + Na + 3NO3 + Mg
step 3 - cross out the spectators
MgCl2 + NaCl + 3AgNO3 = 3AgCl
step 4 - map the solution
g(AgCl) > mol(AgCl) > mol(MgCl2)
step 5 - plug in numbers
1.032g(AgCl) x ( 1mol(AgCl)/143.32g ) x ( 1mol(MgCl2)/3mol(AgCl)
results =  2.400 x 10^-3 mol(MgCl2)","You have two *separate* equations.
*Step 1*. Set up the equations.
MgCl₂ + AgNO₃ → Mg(NO₃)₂ + AgCl
NaCl + AgNO₃ → NaNO₃ + AgCl
You don't get Na and Mg as products.
*Step 2*. Balance the equations
MgCl₂ + 2AgNO₃ → Mg(NO₃)₂ + 2AgCl
NaCl + AgNO₃ → NaNO₃ + AgCl
*Step 3*. Cross out spectators.
Cl⁻ + Ag⁺ → AgCl
*Step 4*. Map the solution.
g AgCl → moles AgCl
We can't go further without more information, like mass of MgCl₂ and AgCl."
Gravimetric analysis and precipitation gravimetry,"In the example, why  is NaNO3 mentioned in the question but not used in the equation?",why does sodium nitrate not take part in the reaction? Doesn't chemical (all) react once it is mixed?
Gravimetric analysis and precipitation gravimetry,"Hi - it may be that my maths is so poor but - how did he find the value of m and n from: 0.4015=58.44n+95.20m ?? 

The other equation is 7.201×10​−3 mol=n+2m?","The first equation has two unknowns, n and m, so this equation cannot be solved without using the second equation, which also has the same two unknowns, n and m.

By rearranging the second equation, you can get that n = 7.201×10​−3 - 2m (this is done by subtracting 2m from both sides). 

This equation for n can then be substituted into the first equation in place of n that is in that equation:

0.4015 = 58.44 (7.201×10​−3 - 2m) +95.20m

After multiplying out and collecting together like terms you can solve for m. Once you have m, then you substitute that into either of the equations to get n."
Gravimetric analysis and precipitation gravimetry,What does (aq) stAnd for?,"(aq) stands for aqueous. This means that the compound has been dissolved in water and is now in solution. 
For example, if you dissolve (solid) table salt in water you have: NaCl(s) --> NaCl(aq)"
Gravimetric analysis and precipitation gravimetry,What is le chatelier's principle ?,"You can watch this video to learn more about le Chatelier's principle:
https://www.khanacademy.org/science/chemistry/chemical-equilibrium/factors-that-affect-chemical-equilibrium/v/le-chatelier-s-principle"
Stoichiometry,"1 mole of Fe2O3" Can i say  1 molecule ? Because im new at this amu/mole thing,"No, because a mole isn't a direct measurement. Mole is a term like dozen - a dozen eggs, a dozen cows, no matter what you use dozen with, it always means twelve of whatever the dozen is of. So a mole is like that, except with particles. There are always 6.022*10^23 atoms in a mole, no matter if that mole is of iron, or hydrogen, or helium."
Stoichiometry,"How did you manage to get [2]molNaOH/1molH2SO4. 
How will you know if you're suppose to place 3 there? Or 4?","Go back to the balanced equation.
2 NaOH + H2SO4 -> 2 H2O + Na2SO4
Look at the left side (the reactants). You have 2 NaOH's, and 1 H2SO4's. The ratio of NaOH to H2SO4 is 2:1. So you get 2 moles of NaOH for every 1 mole of H2SO4. I hope that answered your question!"
Stoichiometry,Where did you get the value of  the molecular weight of 98.09 g/mol for H2SO4?? Are we suppose to know that?,"To get the molecular weight of H2SO4 you have to add the atomic mass of the constituent elements with the appropriate coefficients.
Here the molecular weight of H2SO4 = (2 * atomic mass of H) + (atomic mass of S) + (4 * atomic mass of O)
Hope that helped!"
Stoichiometry,Is mol a version of mole? I just see this a lot on the board when my chem teacher is talking about moles.,"Mole is the SI unit for "amount of substance", just like kilogram is, for "mass". And like kilograms are represented by the symbol 'kg', moles are represented by the symbol 'mol'. That's it! :)"
Stoichiometry,I not able to get it,What do you need help with?
Stoichiometry,"hi!
i am new to this stoichiometry,i am a bit confused about the the problem solving tip you gave in the article.","What it means is make sure that the number of atoms of each element on the left side of the equation is exactly equal to the numbers on the right side. The equation is then balanced. 

If the numbers aren't the same, left and right, then the stoichiometric coefficients need to be adjusted until the equation is balanced - earlier videos showed how this was done.

When counting up numbers of atoms, you need to take account of both the atom subscripts and the stoichiometric coefficients. For example, Fe2O3 contains two iron atoms and three oxygen atoms. However, if it was 2Fe2O3, then this would be four iron atoms and six oxygen atoms, because the stoichiometric coefficient of 2 multiplies everything."
Stoichiometry,Can someone tell me what did we do in step 1? why did we multiply the given mass of HeSO4 by 1mol H2SO4/ 98.09 g HeSO4?,"That is converting the grams of H2SO4 given to moles of H2SO4. When we do these calculations we always need to work in moles.
Why moles? Because 1 gram of hydrogen has more atoms than 1 gram of sulfur, for example. But 1 mole of hydrogen has exactly the same number of atoms as 1 mole of sulfur."
Stoichiometry,What is the purpose of crossing out some of the units in these stoichiometry calculations?,It's to figure out what the units are for your answer. for example. Let's say you have 3 moles of carbon. And you want to find the mass of your sample. The molar mass of carbon is about 12 g/mol. so 3 mol*12 g/mol. You cross out the moles on both sides of the fraction to give you grams for your units. So 36 Grams of carbon.
Stoichiometry,What is the relative molecular mass for Na?,58.5g is the molecular mass of na
Stoichiometry,Is there a simpler way to to this?,This is the simple way.
Limiting reactant and reaction yields,"It said that if you get a percent yield over 100 it'sometimes because you made a mistake in the lab, which makes sense to me, but I've heard that there can be other, more scientific reasons.... how does that work?","Nice question! The theoretical yield is maximum 100% by definition. You can run an experiment correctly and still get >100% although It's not quite a "mistake" as you say: your final product will often include impurities (things other than your pure desired compound) so it will seem like you made more than you could have gotten because you also weigh the impurities. The other, simillar, reason is that your final product is not completely dry, in which the "impurity" would be water."
Limiting reactant and reaction yields,"In Step 3, Calculation of Percent Yield  the equation shows 1.82/2.15 as equaling 83.9%. I believe it should say 84.7%, If I'm incorrect in this I blame Texas Instruments the producer of my calculator. ","You are correct. The answer is not 83.9, but 84.6.
It's 84.6 instead of 84.7 because of minor rounding issues.

Kudos to Texas Instruments."
Limiting reactant and reaction yields,Where do you get the actual yield from? Thanks:),"If speaking in terms of doing a lab or experiment, the actual yield comes from the actual result of the lab (hence the name)."
Limiting reactant and reaction yields,"For the percent yield equation, must the equation be in grams or can it be done in moles as well?","You can use whatever units you wish, provided the actual yield and the theoretical yield are expressed in the same units."
Limiting reactant and reaction yields,"On a standardized test, how would you distinguish differences between a solely stoichiometric problem and a limiting reagent problem?",The amount of the reactants would be given to you.
Limiting reactant and reaction yields,So there isn't a way to find the actual yield without doing an experiment?,"Theoretical yield is what you think should happen:,
and is a calculated amount derived through stoichiometry. 
        Actual yield is what you observed to happen or you have been told happened:
and is derived by measurement in an experiment or manufacturing  process.
Expected yield is the amount that has been consistently reported, when control measures are used.
       So there is another way to figure yield as expected yield,  which would include the parameters and control methods used to increase yield in a real life manufacture of a chemical process.
We can use theoretical yield or expected yield to calculate percent yield."
Limiting reactant and reaction yields,why are there no videos for the hard stochiometry for unit 6?,```They want to challenge us.```
Limiting reactant and reaction yields,How would you express the actual yield if a side reaction occurs?,"In general, the theoretical yield is calculated assuming no side reactions will occur (this is almost never actually the case! But still that is the assumption that is usually made). In the case that there is a side reaction, you would calculate the actual yield based on how much pure product you were able to make. This means you need to be able to either separate your product from the side products (or leftover reactants), or you have some analytical method to analyze the purity of your product."
Limiting reactant and reaction yields,Could anyone give more detail about why the actual yield is almost always lower than theoretical? What exactly is meant by side reactions and purification steps?,"The theoretical yield assumes that all of your reactants (100% of them) react together in the desired reaction to produce your products. But real life is more messy than idealized math solutions and mistakes happen. Your actual yield is almost always going to be less than your theoretical yield because you do not obtain the entirety of your product.

One reason is that you can simply have unreacted reactants which do not produce products. This can be remedied by increasing the contact reactants have with each other such as by better (or constant) stirring. 

Another reason if that often you are transferring solutions to and from glassware for entire reactions and products can simply be spilled by accident. Or they can be left in the glassware attached to tiny scratches on the inside of the glassware where you are unable to collect it. This is mendable by having good quality glassware and being careful as a chemist when transferring solutions.    

Another common frustration is the occurrence of side reactions, or undesired reactions which creates a product that you did not wish to have. This can actually create a scenario where your percent yield is actually higher than your theoretical yield because it is contaminated with impurities. These can possibly be fixed by being extra cautious to not expose your reaction to air since chemicals like water vapor in the air can react with your reaction to create impurities. 

That being said if you performed your reaction well and produced a pure sample your percent yield will be less than 100%. An excellent percent yield would be somewhere in the 90% range. 80% is considered good. Around 50% is considered adequate. 

Hope that helps."
Single replacement reactions,"In problem 1, why is the correct answer NaCl(aq)+Br​2​​?

what happened to the second Cl? did it just disappear? and where did we get the second Br?",Bromine forms a diatomic molecule when it is by itself. Hence the Br2 and not 2Br.
Single replacement reactions,"In Problem 2, why Zinc as opposed to Silver?","Silver is below copper in the activity series, so it will not displace copper.
Zinc is above copper, so it will displace copper."
Single replacement reactions,How do we know Mg has +3 charge and PO4 has - 3 charge? Explain it to me.,"mg is +2
the electronic configuration is 2,8,2. To achieve octet state it gives 2 electrons . Now it has 2 more protons so the overall charge is +2.
p needs 5 more electrons. each oxygen gives 2 electrons , so 4 will give 8
5-8 is 3 . it has 3 more electrons so the overall charge is -3"
Single replacement reactions,What is the difference between a single replacement and a double replacement reaction?,"A *single-replacement reaction* is a chemical reaction in which one element replaces another in a compound. 
The general equation is
A + BC → AC + B
Examples are
Zn + 2HCl → ZnCl₂ + H₂, where Zn replaces H in HCl, and
F₂ + 2NaCl → 2NaF + Cl₂, where F replaces Cl in NaCl.

A *double-replacement reaction* is a reaction in which the metals in two ionic compounds exchange partners.
The general equation is
AB + CD →AD + CB
An example is
CuCl₂ + 2AgNO₃ → Cu(NO₃)₂ + 2AgCl, where Cu and Ag exchange partners."
Single replacement reactions,Are the  products of single replacement reactions related to the electronegativities of the elements in the reactants?,"I was also wondering the same question, and I googled out this aritle. http://www.madsci.org/posts/archives/1999-09/936330555.Ch.r.html"
Single replacement reactions,"2AgNO3(aq)+Cu(s)→Cu(NO3)2(aq)+2Ag(s)
In this formula, how do we know that copper has a +2 charge ?",You can't really know it other than memorising. Cu2+ is generally more stable than Cu+.
Single replacement reactions,"what will happen if the element reacting with a compound is less reactive then the element present in the compound . will the reaction not occur ?
 eg 
 mg3( po4)2 + 2al = ??","reaction would not occur. in example, compound with magnesium is more stable than compound with aluminum so phosphate tends to keep bonding with magnesium"
Single replacement reactions,"So I have to ignore Zn + 2 H2O = Zn(OH)2 + H2 in the aqueous solution here? I don't understand why I'm supposed to be ignoring this reaction in question 2. 

If I ignored the fact I am asked to find a single replacement reaction (which in fact isn't specified but implied from context), then my reasoning tells me that the Ag in AgNO3 will give up its place to form CuNO3  because we can see in the reactivity that Cu is more reactive than Ag. Ag can form AgSO4 and then balance the equation. Why is this incorrect?","The reaction CuSO4 + AgNO3 would not be a single replacement reaction since the reactants are both compounds, i.e. there are no pure elements. Also the reaction of CuSO4 + AgNO3 would cause a double displacement reaction where you will not be able to obtain copper on its own as a precipitate.

The correct answer is Zn, zinc, since it is more reactive than copper and is a pure element. Check a reactivity table or list to find which elements will want to react with compounds in a single displacement reaction."
Single replacement reactions,"Why is it Cu 2+, but Ag +? They are in the same column and nowhere does it say that","Transition metals have variable valencies. So, transition metals in the same column might have different valencies."
N/A,What's the dot in BaCl​2​​⋅2H​2​​O supposed to mean? I've never seen an equation like this before...,"The dot shows that a crystal of BaCl₂ contains 2 molecules of water for every formula unit of BaCl₂. 
The BaCl₂·2H₂O is called a *hydrate*, and the H₂O is called the *water of hydration*."
N/A,what does taring a piece of glassware mean? Is it related to balancing the weight of a container?,"Imagine trying to weigh some jellybeans in a glass jar. If you placed them on a scale you would get the weight of the Jellybeans + the weight of the Jar. If you wanted to just find out the weight of the Jellybeans, you would weigh the Jar when empty, then weigh the Jellybeans and the Jar together, calculate the difference between the two measurements and you'd get the weight of just the Jellybeans. e.g
weight of Jar without Jellybeans = 100g
weight of Jar + Jellybeans = 400g
weight of Jellybeans = 400g - 100g = 300g
Measuring the weight of the empty container (in this case the Jar) is what Taring is... Taring isn't limited to jellybeans in glass jars though, it's really common in lots of chemistry stuff..."
N/A,I'm having a really hard time learning from these write-ups. I can read the same paragraph over and over but it just doesn't make sense to me. Videos I can typically watch on 1.5X speed and fully grasp the concept. Is there anything I can do to improve my ability for learning from write-ups?,"I think that if you rush, it can easily get really confusing... I think you should try to take it slow, read more slowly and carefully. Comprehend the meaning of each sentence before moving on to the next. You know?"
N/A,You stated that KCl wasn't included in the equation because it is not going through physical or chemical reaction. How do we know that?,"It didn't said that KCl is not going through chemical reaction, instead we analyzed that KCl didn't reacted in the reaction and it was like spectator reactant. So rather that including this in our reaction and confusing ourselfs further we just cancelled it from both sides of the reaction since it didn't change at all ( didn't go through reaction)."
N/A,"In Step 4, molecular weight for BaCl2.2H2O is 244.47g, that is when, the H2O is multiplied by the two in front. But in Step 2, to calculate the mass of water, the molecular weight used was 18.02, but, in the products side of the equation, the coefficient 2 is there infront of H2O. So why do we have to take into account the 2 in BaCl2.2H2O but not the one in 2H2O?","The equation for the reaction is
BaCl₂⋅2H2O → BaCl₂+2H₂O
It tells you that 1 mol of BaCl₂⋅2H₂O forms 2 mol of H₂O.
In step 4, you are finding the mass of 1 mol of BaCl₂⋅2H₂O.
1 mol of BaCl₂⋅2H₂O contains 1 formula unit of BaCl₂ and 2 mol of H₂O
∴ MM of BaCl₂⋅2H₂O = MM of BaCl₂ + 2 × MM of H₂O = 208.23 g + 2 × 18.016 g = 208.23 g + 36.03 g = 244.26 g

In step 3 and the step 5 shortcut, you *are* accounting for the 2 in front of H₂O.
It is in the mole ratio (1 mol hydrate/2 mol H₂O)."
N/A,what is the purpose of gravimetric analysis,A simple example would be to weigh a tree limb before and after baking it to determine the water content of it.
N/A,"In the beginning of the example problem, BaCl2 and 2H2O are separated by a dot rather than a plus sign. Why is that, and what is the different? 

I'm also confused about how we got those stoichiometric coefficients. The explanations says we expect to make 2 moles of H2O (g) for every one mole of BaCl2 [dot] 2H2O. But shouldn't it be 2 moles of H2O (g) for everyone one mole of BaCl2 and 2 moles of H2O (g) for every 2 moles of H2O from the reactant? I'm not sure if that makes a difference, and I apologize if my question in unclear, but hopefully someone will understand what I'm asking and be able to provide me an explanation.",The dot means that the BaCl2 is chemically combined with two molecules of water.  The compound is called barium chloride dihydrate.
N/A,"Under the *Lab tip*, you said "having a high surface area will increase the rate of evaporation." Shouldn't it be "having a low (flat/plane) surface area will increase the rate of evaporation ?","Since molecules can only leave a liquid by escaping its surface, more molecules have the opportunity to escape from a larger surface area than from a smaller surface area. 

To look at it another way, imagine you have a liquid under conditions in which 
one in 1000 molecules on the surface will escape each second. Imagine you have two samples with equal numbers of molecules, but in differently shaped bottles. One bottle gives the liquid a surface of 1000 molecules, while the second bottle gives the liquid a surface of 1,000,000 molecules. 
Which sample will evaporate more quickly?"
N/A,How do you know whether or not there will be no reaction?,"You can use a solubility chart, or solubility rules. The solubility chart is used based on the products - if the combination of ions that are produced results in a down arrow on the solubility chart, it means it precipitates, and there is a reaction. If it says AQ, it means it's aqueous. If both products are aqueous, there is no reaction. If a product isn't on the chart, assume that it is aqueous."
N/A,Where did that third OH come from in the first practice example? Are we assuming the charges would balance because it's in water with an abundance of oxygen and hydrogen atoms?,"It is because we know that the iron ion, Fe(III) has a charge of 3+, so it has to combine with 3 OH- ions to make a neutral compound. 

We know the iron has a charge of  3+ from looking at the starting material, FeCl3. Since FeCl3 is a neutral compound and chloride has a charge of -1 (and there are three chlorides), then Fe must have a 3+ charge in the starting material and product."
N/A,"How do you know when or IF the many reactions will occur and when/if they will then decompose?

What is a salt? (just any ionic compound?)

How do you know if something is an acid or base just from the formula? (or do you need to memorize these)

Is everything that is soluble considered to be in aq state?

How do you know what medium the reaction takes place in or what medium it needs? (water, non-polar solvent, in air, in space, etc etc)","A salt is generally any ionic compound, though I have also seen it defined as an ionic compound that is formed when you react an acid and a base. The cation (or positively charged ion) of the salt comes from the base, and the anion (or negatively charged ion) comes from the acid. 

It is helpful to have the strong acids and bases memorized, since they have special reactivity. Luckily, there aren't that many strong acids and bases, and you can learn morem about this from this video: https://www.khanacademy.org/science/chemistry/acids-and-bases-topic/acids-and-bases/v/strong-acids-and-strong-bases

Anything that is soluble in water and dissolved (separated into individual cations and anions) is in the aqueous state. Double replacement reactions always occur in water, with the reactants in the aqueous state. Water is a really great solvent whenever you want to have ions around. 

In general, it's tricky to predict for any random reaction what medium it might need. The more you know about how the reaction occurs, and the more you know about the properties of different solvents (like their polarity), the more educated of a guess you can make! For example, in double replacement reactions, we know that the solubility of the reactants is important because we need free ions around. So we might predict that a non-polar solvent that doesn't dissolve salts would be a bad solvent for a double replacement reaction. 

I know that's a lot of information, I hope you find some of it helpful!"
N/A,"This may be an obvious question but, what classifies a chemical as a salt? For example, when an acid-base neutralization reaction occurs and water and a salt is formed, what are the characteristics of the salt formed that makes it a salt?",A salt includes an anion from acid and cation from base
N/A,What are the solubility rules?,"This link may help:
https://chem.libretexts.org/Textbook_Maps/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Equilibria/Solubilty/Solubility_Rules"
N/A,"What is the name of the equations which produce salt water and carbon dioxide?
I cant seem to find this topic on here.
Please help.","They are double replacement reactions followed by decomposition.

Double replacement: 2HCl(aq) + Na₂CO₃(aq) → 2NaCl(aq) + H₂CO₃(aq)
Decomposition:  H₂CO₃(aq) → H₂O(l) + CO₂(g)"
N/A,what would have to be the situation in which there would be no possible reaction in a double displacement ?,Can double displacement reactions be reveresed?
N/A,"How do you know that Fe has a 3+ charge? It's not in groups 1,2,13,14,15,16,17,or 18 so how can we predict the charge without knowing it's roman numeral?","You have to apply the rules to whatever else it is bonded to and go from there. 
In this case it is Cl which is in group 17 and so forms Cl- anions, so if the formula is FeCl3 then the Fe must be 3+ to have no charge overall."
N/A,"When you're predicting the products of the reactions, like in the example, how can you recognize that as double replacement and not synthesis or something else?","If its two ionic compounds, it is usually a double replacement. If it is an element and a compound it is single, if it has O2 in the reactants and produces H2O and CO2 then its combustion. When there is a single product it is a synthesis."
N/A,"In the first example, how was it determined that Barium and Sodium are the cations? Are cations always written before anions in a neutral compound? Is there a list or set of rules that chemists memorize?","Barium and Sodium are both metals, so they have few numbers of valence electrons. Barium has two and Sodium has only one. So, to achieve their perfect 8 electrons in their outer shell (octet rule), they will lose electrons to make their full previous shells their new valence electrons. When an atom loses electrons, it becomes a positive ion, or a cation. I hope that helped!"
Oxidation–reduction (redox) reactions,Shouldn’t equation H2 + O2 -> 2 H2O be balanced to 2 H2 + O2 -> 2 H2O?,"I'm not seeing that original equation you wrote. Did they change the document above?

EDIT: I guess, they did."
Oxidation–reduction (redox) reactions,"In the last paragraph, it states  that there is a transfer of electrons. Is there not always a transfer of electrons?","There is not always a transfer of electrons (not all reactions are redox reactions). An example of a reaction that is not a redox reaction might be a neutralization reaction:
H3O+ + OH- ---> 2 H2O
The oxidation number of H is +1 and the oxidation number of O is -2 for for both the reactants and products, so it is not a redox reaction."
Oxidation–reduction (redox) reactions,"Is it possible to have reaction where only oxidation or reduction happens, or does the occurrence of one result in the other? Thank you.","They must both occur. The sum of all the oxidation states cannot change unless there is a change in the overall charge of the ion/molecule. Even with a change in the charge, there must be somewhere else that the change in charge (and thus oxidation states) is exactly offset. That is because of conservation of electrical charge."
Oxidation–reduction (redox) reactions,What is the difference between a monatomic ion and an atom in its elemental state?,"An ion is an atom that has gained or lost electrons. Atoms in their elemental state are not ionised. 

Also, atoms in their elemental state can be joined to other atoms. For example, H2 is the elemental state for hydrogen."
Oxidation–reduction (redox) reactions,"Above it says, "oxygen is usually assigned a −2 oxidation number (except in peroxide compounds where it is −1, and in binary compounds with fluorine where it is positive);"

The part where it says "...with fluorine where it is positive", did they mean +1 or +2? Or did they mean, it varies depending on the binary compound with fluorine but it'll always be positive?",With Florine it forms OF2 where it shows +2 oxidation state otherwise it shows a -1 or -2 oxidation state
Oxidation–reduction (redox) reactions,do we have to memorize these rules?,"I mean, if you want to solve redox problems, yeah."
Oxidation–reduction (redox) reactions,What is the use of knowing about oxidation numbers ?,"Knowing oxidation numbers allows you to predict what compounds or reactions will form when different elements mix together. This is really important, as you will need to be able to write compounds and reactions to do everything else you will learn in chemistry.
I hope this helps!"
Oxidation–reduction (redox) reactions,Does anyone know what the OH radical is? It is in one of my compounds for my experiment,The OH radical (hydroxyl radical) is the neutral form of the hydroxide ion. Hope this helps.
Bohr's model of hydrogen,what is quantum,"A quantum is the minimum amount of any physical entity involved in an interaction, so the smallest unit that cannot be a fraction."
Bohr's model of hydrogen,"I don't get why the electron that is at an infinite distance away from the nucleus has the energy 0 eV; because, an electron has the lowest energy when its in the first orbital, and for an electron to move up an orbital it has to absorb energy, which would mean the higher up an electron is the more energy it has. So if an electron is infinitely far away(I am assuming infinity in this context would mean a large distance relative to the size of an atom) it must have a lot of energy. Right?

Thanks very much!","you are right!

but what you need to remember now, is that the energy at infinity is DEFINED as being zero. Your next queston might be 'why?' :)

but, knowing that, does it now make sense that nearer to the nucleus, the energy is minus??"
Bohr's model of hydrogen,What does ΔE stand for?,"*The triangle stands for Delta, which also means a change in, in your case, this means a change in energy.*"
Bohr's model of hydrogen,what is the relationship between energy of light emitted and the periodic table ?,"Its a really good question. Here is my answer, but I would encourage you to explore this and similar questions further..

OK: I would say that the periodic table tells us about the number of protons in an element; and, therefore the number of electrons too. 

Now, the energy of the photon emitted from any element does not depend on the number of electrons in the atom. The value of the energies of  photons does depend on the available energy levels in the atom. Hydrogen, for example, although the simplest atom, has a whole range of photon energies that it emits.  This is because the electron can exist in many energy levels... as it switches from one energy level to another, then it emits / absorbs photons. 

We can, however, say that the more electrons there are in an atom, the greater the variety of photon energies there will be so this may be a link worth exploring

I hope that makes sense ok.

As I say, you are asking a great question.... looking for relationships in a meaningful way. I would encourage you to explore further.... maybe compare the number of different energies emitted by an element with its position in the periodic table, or the maximum / minimum energies emitted by the element vs position

Well done and keep up the good work."
Bohr's model of hydrogen,"Actually, i have heard that neutrons and protons are made up of quarks (6 kinds? up down ......)
Is it true? and how does the scientists found that out?","yes,       protons are made of 2 up and 1 down quarks whereas neutrons are made of 2 down and 1 up quarks . hope this helps."
Bohr's model of hydrogen,"Hi, great article. I was wondering, in the image representing the emission spectrum of sodium and the emission spectrum of the sun, how does this show that there is sodium in the sun's atmosphere? If both pictures are of emission spectra, and there is in fact sodium in the sun's atmosphere, wouldn't it be the case that those two dark lines are filled in on the sun's spectrum. The text below the image states that the bottom image is the sun's emission spectrum. Wouldn't that comparison only make sense if the top image was of sodium's emission spectrum, and the bottom was of the sun's absorbance spectrum? 

Thanks!","Sodium in the atmosphere of the Sun does emit radiation indeed. However, after photon from the Sun has been absorbed by sodium it loses all information related to from where it came and where it goes. So re emittion occurs in the random direction, resulting in much lower brightness compared to the intensity of the all other photos that move straight to us."
Bohr's model of hydrogen,Bohr said that electron does not radiate or absorb energy as long as it is in the same circular orbit. But according to the classical laws of electrodynamics it radiates energy. What is the reason for not radiating or absorbing energy?,Bohr did not answer to it.But Schrodinger's explanation regarding dual nature and then equating hV=mvr explains why the atomic orbitals are quantised
Bohr's model of hydrogen,why does'nt the bohr's atomic model work for those atoms that have more than one electron ?,"As far as i know, the answer is that its just too complicated.

With one electron and one proton you can figure out (with some difficulty) how they interact with one another because you have one centripetal force acting in the same 'direction' and analyse-able using classical circular motion etc. 

But with two electrons, now you have three forces; not just centripetal but also electron to electron. You can imagine in the classical view, how complex the change on force would be between the electrons and also the nucleus. It may be tht some one has figured a way of doing it or approximating to it, but, as far as I know this is the reason bohr model is only used for hydrogen."
Bohr's model of hydrogen,"so do we still not know that why do electrons not fall into the nucleus of the atom,i mean they are continuously emitting energy and of course at a point in time they should fall into the nucleus,what is the explantaion for that?","This is one of the main reasons we know that the Bohr model of the atom is wrong.  

In the quantum model of the atom electrons in their lowest possible orbital are in their ground state and can't be in any lower energy state and they do not radiate energy."
Bohr's model of hydrogen,Is Bohr's Model the most accurate model of atomic structure?,"No, it is not.  The quantum description of the electron orbitals is the best description we have."
Discovery of the electron and nucleus,How can we calculate e/m value of elactron?,"The angle of deflection in the thomson experiment depends on the e/m value.
This is because F = ma
So a = F/m
F is proportional to e
So a is proportional to e/m
And therefore the acceleration in the  direction of deflection is proportional to e/m"
Discovery of the electron and nucleus,comparing thomsons exp. and rutherford's exp. why does the rays deflect in rutherford's model due to presence of nucleus but travel straight in thomson's exp.,"@Afeefdk Because they very different experiments...Look at both the experiments. In the Thomson's experiment, J.J Thompson didn't strike the cathode rays to any metal like in case of Gold foil experiment."
Discovery of the electron and nucleus,"In th Rutherford experiment, why did he use alpha particles ( He2+) ? wouldn't it have been better if he had used ( H+) particles ( which we now know are protons ) because these are smaller ?","Rutherford was interested in radio-chemistry (radioactivity) and what it might reveal about the atom. is focus was on alpha particles (from alpha rays, type of radioactivity), which he then discovered consisted of two protons and two neutrons: the equivalent of a helium nucleus (He2+)"
Discovery of the electron and nucleus,How Rutherford told that atom is like a solar system?on which base ?,"Because he used classical physics (although he quantized the angular momentum) to conceive his model....and classical physics is based on intuitive thinking and empirical observations....thinking of subatomic particles as if they were planets is therefore, in line with the way we perceive reality....(a wrong way according to quantum mechanics)....."
Discovery of the electron and nucleus,"why did we have to name positive ions cations and not anions, since most of the naming in science seems to be such that the names are easy and a lot telling, why didnt we call positively charged ions anions since a positively charged electrode is called an anode, which leads to a whole bunch of confusion for me atleast.","The negatively charged electrode is the anode, this is where the electrons in a current originate. The positively charged electrode is the cathode and is where the electrons finish their journey at. Electrons are negatively charged and are pushed away from the negative charge of the anode towards the positive charge of the cathode which they find an attraction to. 

As for the anions and cations part, the names originate from William Whewell who worked with famous scientist Michael Faraday and his work in electricity. Whewell actually coined a lot of famous words including anode, cathode, ion, and probably most famously; scientist. Whewell suggested using anions for the ions that were attracted to the negatively charged anode and cations for the ions that were attracted to the positively charged cathode.

Hope that helps."
Discovery of the electron and nucleus,How did Rutherford make the alpha particles of helium and how did he concentrate those particles so as to make them travel out of a pinhole of the lead box to bombard the gold foil?,He put the radium in a container with only one 'hole' for the alpha particles to get out. Any alpha particles going in other directions simply don't escape.
Discovery of the electron and nucleus,is anode rays consist of proton ?,"You are right, both kinds of rays are emitted simultaneously. the cathode rays consist of electrons, while the anode/canal rays are the positively charged gaseous ions. 
The experiment for canal rays was carried out in modified cathode ray tube, by E. Goldstein.
  
:: some properties of anode rays:
1. The positively charged particles depend upon the nature of gas present in the cathode ray tube. Those are simply the positively charged gaseous ions.
2. The charge to mass ratio of particles depends on the gas from which it originates.
3. Some positively charged particles carry a multiple of a fundamental unit of electric charge.
4. The behavior of these particles in a magnetic or electric field is opposite to that of electrons or cathode rays. 

THE SMALLEST AND LIGHTEST POSITIVE ION WAS OBTAINED FROM HYDROGEN AND WAS CALLED PROTON.

Image of a canal ray experiment:-

https://www.google.co.in/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwi41_ra0tTVAhXCOY8KHZJNC7kQjRwIBw&url=http%3A%2F%2Fchem-guide.blogspot.com%2F2010%2F04%2Fdiscovery-of-proton.html&psig=AFQjCNEUcp3n61_aLrSJ5u4dzti4Ozepvg&ust=1502728671172162

Hope it's helpful."
Photoelectron spectroscopy,Is there a substantive reason for the distinction in terminology between the work function and the binding energy? Does the difference simply exist to dinstinguish between contexts?,"The distinction between work function and binding energy exists primarily to distinguish between different contexts and conceptual frameworks.

The work function refers specifically to the minimum energy required to emit an electron from the surface of a material into vacuum. It is considered in the context of electrons interacting with a material surface.

Binding energy, on the other hand, refers more generally to the energy required to separate constituents that are bound together. It is used in a variety of contexts beyond just electrons and material surfaces.

So the work function deals specifically with the energy required to remove an electron from the surface of a material, while binding energy is a more general term that can refer to the energy required to separate any kind of bound particles or entities.

Though numerically these values may be similar for a given system, the work function and binding energy terminology serve to clarify the conceptual framework being considered:

• Work function - focusing on electrons interacting with a material surface

• Binding energy - considering a more general interaction between any type of bound particles

So in summary, while the numerical values may coincide in some cases, the work function and binding energy concepts originate from different frameworks and serve different purposes. The distinction in terminology helps clarify whether we are focusing specifically on electron emission from a material surface or considering a more general separation of bound particles. The difference is primarily one of context and emphasis rather than substantive numerical difference."
Photoelectron spectroscopy,"In the third paragraph, how the energy analyzer "count" number of electrons correspond with one determined ionization energy ? Are there any proportion of energy to that number !","I don't think there can be a simple proportion of ionization energies from element to element. Remember, the Bohr model [E=(1/n^2)*13.6eV] fails beyond H and He+ so the ionization tables that this article refers to are empirical."
Photoelectron spectroscopy,"When analyzing the binding energy of an element, does it matter what type of ionizing energy is first used to eject the electron(s) from a sample? 

For example if you first bombarded a sample with XPS (according to the description under the subtitle "The basics of photoelectron spectroscopy" this would in theory eject the core electrons) would this alter the binding energy data? If the core electrons were ejected prior to the valence electrons, wouldn't shielding effects be attenuated and consequently, the binding energy of the outer-shell electrons would be increased?","Yes, your thinking is correct. However, we can quite safely assume that you would not hit the same atom twice during the experiment. Hence, you should not see this effect in the spectra."
Photoelectron spectroscopy,"The PES spectra show all electrons in a given shell to have the same binding energy. But that leads me to two questions on the same topic. If it were because other electrons were blocking it, than wouldn't further ionizing an already ionized sample make it easier? Or, if it had to do with the fact that protons are positive and electrons are negative, and therefore it takes more energy to remove more electrons to counteract the unequal charge, wouldn't the positive charge increase even more the moment one electron in a shell is removed, therefore increasing the binding energy for every electron rather than for every shell?","You are correct that after the first ionization event, the energy of the orbitals changes. However, in PES we can safely assume that you will not ionize the same atom twice. Hence, all peaks correspond to the ionization of the neutral atom."
Photoelectron spectroscopy,"I thought an electron has a huge amount of kinetic energy in the atom, I heard that it is moving at a third of the speed of light. Why is this not taken into account?","Electrons do have a significant amount of kinetic energy in atoms due to their high velocity. However, this kinetic energy is generally not taken into account when calculating work functions and binding energies for a few reasons:

The kinetic energy of electrons in atoms is not well-defined. Due to the Heisenberg uncertainty principle, we cannot precisely know both the position and momentum of an electron at the same time. So while we know electrons move fast, we can't pinpoint their exact location and velocity.

The important energy for work function and binding energy calculations is the potential energy, not the kinetic energy. The potential energy determines how strongly the electron is bound to the atom and how much energy is required to remove it. The kinetic energy, while large, does not reflect the strength of this binding.

When an electron is removed from an atom, its initial kinetic energy is lost and it gains new kinetic energy based on the work function or binding energy. So its final kinetic energy depends on the difference in potential energies, not its initial kinetic energy within the atom.

Work functions and binding energies are measured experimentally by seeing how much energy is required to remove an electron. This measures the change in potential energy, not any initial kinetic energy the electron may have had.

So in summary, while electrons do have significant kinetic energy due to their fast motion within atoms, this kinetic energy is generally ignored when calculating work functions and binding energies. The important factor is the change in potential energy, which determines how strongly the electron is bound and how much energy is required to remove it from the atom. The initial kinetic energy is lost during this process."
Photoelectron spectroscopy,"can you have the PES graph of an ion like Li+? If so, how would you be bale to tell the difference from the graph of an element that looks the same like He in this case?","I don't know the answer but from what I have read so for in this article once you eject an electron from one of its shell the binding energy changes. Lets say you would eject an the valence electron in this case the 2s electron from Li. Since the nucleus of Li has three protons and Helium has two 1s^2 electrons the binding energy for the remaining 1s^2 for Li+ would be different compared to the binding energy of the 1s^2 from He. I would belive this to be the case since the effective charge of the nucleus is not the same as for He. So I would believe if one could have a PES graph for ion like Li+ it would be different from the graph of He. 
Could it be so that the the binding energy would by shifted by som factor for the two peaks compared with the peaks of He? Lets say He has it 1s^2 peak at 100 MJ/mol would it be the case then that Li+ (assuming that the 2s electron was ejected) would have it lets say a PES graph of peak of 130 MJ/mol. The 130 is just arbitrary I'm thinkin of som factor a>1 => 100*a is the new peak."
Photoelectron spectroscopy,"I'm curious - is there a way that a travelling electron can further increase its kinetic energy? For instance, if it was hit by another photon or traveled next to a negative charge. Or will it maintain the energy once got knocked off, until affected by other charges..","You can increase the kinetic energy of charged subatomic particles by accelerating them through an electric field. This is the basis of particle accelerators.

I don't think a travelling electron can absorb energy from a photon - at least, I've never heard of that happening but it might be a question better answered by a physicist."
Photoelectron spectroscopy,"It states that, "However, the binding energy of the 
1s peak is not equal to the second ionization energy of lithium. Once the first electron is removed from lithium, the 1s,  electrons will be held even more tightly by the nucleus, increasing the binding energy of these electrons." 

So it's saying that the second ionization energy is not equal to the second binding energy, in the sense that when you ionize it initially it changes the electron configuration making the electrons closer to the nucleus less shielded by the outer electrons. However, I don't see the difference between sequentially removing an electron from an atom and measuring the electron ionization energy to photoelectron spectroscopy's binding energy. 

Both of those methods remove electrons sequentially and measure their energies, so why can't you determine the second ionization energy from a photoelectron spectroscopy chart?","at first glance, it may seem like photoelectron spectroscopy binding energies should correspond directly to ionization energies. However, there are a few key differences:

Ionization energies measure the energy required to remove an electron from a neutral atom, leaving an ion. Binding energies, on the other hand, measure the energy of electrons within an already ionized atom.

As you noted, removing the first electron changes the electron configuration, pulling the remaining electrons closer to the nucleus and increasing their binding energy. This effect is not accounted for in ionization energy measurements, which consider the removal of each electron independently from the neutral atom.

Ionization energies refer specifically to the process of electron removal - ejecting an electron into vacuum. Binding energies, however, reflect the energy of the remaining electrons within the ionized atom, not just the energy required to remove them.

Experimental measurements of ionization energies and binding energies involve different processes. Ionization energies are measured by exposing atoms to radiation or electric fields and detecting the ejected electrons. Binding energies are determined from the kinetic energies of photoelectrons ejected from ionized atoms."
Photoelectron spectroscopy,what is first ionization energy and second ionization energy ?,"Ionization energy is energy required to remove the outer most electron from an atom. The first ionization energy would be the energy required to remove the first electron, the second ionization energy would be the energy to remove the second electron, and so on. The reason it's called ionization is that when you remove an electron from a neutral atom, it becomes a positively charged ion, or cation, having lost a negatively charged electron. Hope that helps."
N/A,how can a flame test be used to excite electrons when it is stated that IR cant excite electrons but it can only vibrate its chemical bonds?,"The flame is not an IF, It´s a heat energy  that can exite  the electrons my friend. Greetings from Colombia."
N/A,"In the Beer-Lambert Law section, what is path length?",The path length is the distance that the light travels through the sample.
N/A,"Let's assume that the electron of some atom requires x J of energy to move to the next energy level, then can it absorb 2 photons carrying x/2 J of energy to do so? If not, then why and if this can occur, then why don't electrons just absorb energy from more photons of lesser frequency to move to the next energy level?","Firstly, it is possible. But it is highly not probable. I mean, the probability of two photons of x/2 J of energy striking the electron at the same time is very very low. And as we already know, electron can't absorb x/2 J first, and wait for another photon of the remaining amount. It either takes all of the energy ( exactly equal to the energy difference of the shells, here as you have taken x) at the same time, or doesn't take at all.
Hope that helps!
Cheers!!"
N/A,"Above, it says that for a transition to occur the energy of absorbed photon must be equal or greater than the difference in energy between the two levels. But, after a transition the electron quickly falls down to the ground state and in doing so it emits a photon with an energy equal to the difference in energy levels. So if the absorbed photon has a greater energy than the difference between the two energy levels then where does the rest of the energy go after the electron falls back to it's ground state?",I'd imagine that the remaining photon energy not absorbed to excite an electron becomes heat/vibration in the material which absorbed the photon.
N/A,"How can an electron in the hydrogen atom move up to the 6th energy level when excited? The hydrogen atom has only the first energy level right? 
Also, it looks like there are four different electrons that are moving back down to the 2nd energy level, one by emitting a violet photon, the second one by emitting a blue photon, the third by green and the fourth by red; but the hydrogen atom has only one electron, no?
And, why is the ground state level 2? The only electron of the hydrogen atom resides on the first energy level, Right?

Thanks very much!","For a hydrogen atom, the lowest energy state has an electron in only the n=1 level, but every atom has access to every energy level.         When an atom absorbs a certain amount of energy an electron can be promoted to a higher energy level."
N/A,"when we heat the metals, does it takes different amount of heat to excite atoms of different element ?","When we heat metals, we are usually increasing the kinetic energies of vibration of the atoms in the metal structure.
Usually, we have to supply the energy as electrical energy, and then it does take different amounts of energy to excite the electrons in different elements."
N/A,"When we stand under the sun, is the heat we feel the result of UV light causing molecular vibrations in our cells, since more kinetic energy through vibrating molecules translates to an increase in temperature? And can the same be said about all heat sources that are also sources of visible/near-visible light, such as ovens and lightbulbs?","You are thinking along the right lines, but it is infrared (IR) radiation from the sun, and other sources, that you feel as heat. Although UV light comes from the sun, this is not felt as heat. The UV light, however, can break chemical bonds and this can lead to skin damage or even cancer."
N/A,"Does the spectra of a element have differences if compared between their different isotopes, like between deutrium and tritium? Do they also have differences in spectra if an atom of a given element is positively or negatively charged?","hmm, I have NO expertise in this but from what I understand, isotopes shouldn't change the spectrum. Isotopes are the same atom but with different neutrons. The spectrum has to do with electrons and them changing levels. so I think that it would NOT change. Again, I am. NO professional in this subject."
N/A,"The emission spectrum for each element is different, but why exactly is that? There could be different elements with the same number of electrons.","It's not the electrons that determine the emission spectrum. It is the protons, which also define the element."
Photoelectric effect,what is the difference between ionization energy and the work function of a metal?,"work function refers to the energy required to remove the electron from the sea of electrons in a metal body whereas ionization energy refers to the energy required to eject the electron when it is present in the valence shell of the atom.
hope it explains the difference."
Photoelectric effect,Do non-metal elements emit photoelectrons?,"Yes, but they have higher binding energies.
You have to use UV light or X-rays to dislodge the electrons.
This is the basis of the technique called *photoelectron spectroscopy*."
Photoelectric effect,"We know that the photon is mass-less, so what is it's structure, how does it carry energy, where does it store it?
Or is the mass of the photon negligible not zero??",well I technically we cant treat light the same way we treat matter because daily things travel very slowly but when you are travelling at speeds beyond 10^6 ms^-1 the science is different matter and energy are interconvertible (e=mc^2) so it doesn't really store energy it is energy itself.
Photoelectric effect,"Is intensity the same as brightness? Does it just refer to how much light there is?  Also, I get that if there is more light shining on a metal, the current will increase. However, why does the current not increase when the kinetic energy increases? If the particles are moving faster, wouldn't that speed up the current?

Finally, I don't really understand amplitude. Amplitude is the height of a wave's peak compared to its resting position. So wouldn't high amplitude mean there is a lower frequency and therefore lower energy?","Yes, intensity is the same as brightness.
The only way to increase the kinetic energy of the electrons is to increase the frequency.  If the frequency remains constant. the kinetic energy is also constant.
The amplitude of a wave does not affect its frequency. Two waves of different amplitude can have the same frequency."
Photoelectric effect,"During the photoelectric effect, light knocks electrons out of metals. So why don't the metals in our home lose their electrons when we turn on the lights? 
Thanks in advance.",The metals in the home have too high a work function for the light to be able to knock out the electrons.
Photoelectric effect,"I'm having a bit of trouble understanding the wave/particle duality. Is a photon a wave-like particle? When I think of the equation E=hv, I think about frequency in terms of a wave, but I think of the E in terms of a particle-like atom, so it is a bit hard for me to reconcile the two and understand why high frequency of the wave would mean that the photon has a higher kinetic energy.","A photon is a particle of light.   All very small particles sometimes act more like what we think of as waves.  By experiment, we know that the energy of the photon is given by E = hf."
Photoelectric effect,What will happen if the energy of the photon is just equal to the work function of the metal? will the electron be pulled back in the orbit of the atom?,The electron will be "free" from the atom but will feel a pull because of the positive charge of the atom and likely will get pulled back into the atom.
Photoelectric effect,How is amplitude proportional to the number of photons with the same frequency?,"The intensity of the light is a result of the number of photons. 
If the light were a wave, the intensity would be represented by the amplitude of the wave."
Photoelectric effect,Is the quantum realm a real place or is it just a myth in ant man?,"I mean, the quantum realm is a fictional place in the MCU. It’s little more than magic portals made to sound more serious and scientific by adding quantum. 

In the real world quantum usually refers to quantum mechanics, or simply the workings of matter and energy at the very small, atomic level."
Photoelectric effect,how can light have momentum if it has no mass,Light also has a wave nature which allows it to have momentum
"Light: Electromagnetic waves, the electromagnetic spectrum and photons","Does light have different speeds depending on the medium (e.g. air, water, etc) it is in? If it does, does it change wavelength, frequency, or both? When the speed decreases, does the light has less energy? Does light traveling through air, then water, then air again, has the same speed as it does in the beginning and in the end?","The speed of light can change.
The highest ever recorded is 299 792 458 m / s.
In 1998, Danish physicist Lene Vestergaard Hau led a combined team from Harvard University and the Rowland Institute for Science which succeeded in slowing a beam of light to about 17 meters per second, and researchers at UC Berkeley slowed the speed of light traveling through a semiconductor to 9.7 kilometers per second in 2004.
 Hau later succeeded in stopping light completely, and developed methods by which it can be stopped and later restarted."
"Light: Electromagnetic waves, the electromagnetic spectrum and photons",So do different kinds of lightbulbs give off different spectrums?,yeah! for example some lightbulbs are more "warm" and orangy and some are more white
"Light: Electromagnetic waves, the electromagnetic spectrum and photons",Where do we find a photon in an atom?,"Any kind of Electro-Magnetic wave travels in small energy packets called photons. In the visible range of light these are called photons and in the invisible range, i.e Infrared, UV and others the energy are called quanta. When a electron gains a certain amount of energy then it jumps to a higher energy orbit unless it has absorbed so much energy that its ejected, it again comes back to its original orbit after losing the energy i.e emitting it in form of Electro-magnetic Radiation. That is called emission spectrum."
"Light: Electromagnetic waves, the electromagnetic spectrum and photons","Why do things travel in waves and not in a straight line ?
simply if I throw  a ball , it doesnt make a wave. So why do electrons make waves ?","actually, you thrown ball does make a wave. its just that the wavelength is so small, you could not observe or measure it

DeBroglie said:
Wavelength = h/p h/mv  = (approx) 6 x 10>-34  /  (0.01 kg  x  20m/s)  = (roughly)  3 x 10>-33 m

a nucleus of an atom is about 10>-15 so, the wavelength of your thrwon ball is verrrrry small 

:)

ok??"
"Light: Electromagnetic waves, the electromagnetic spectrum and photons",from where photon is emmited or absorbed?,"Photons can be absorbed by electrons. These will increase in energy and jump energy levels. Afterward, the same electron can emit the photon to jump down energy levels."
"Light: Electromagnetic waves, the electromagnetic spectrum and photons",I am confused: is wave the energy itself or the disturbance in electromagnetic field caused by energy (like throwing a stone into a pond and wave forms),a wave can be described as the transmission of disturbance from one point to another OR the transmission of energy from on point to another
"Light: Electromagnetic waves, the electromagnetic spectrum and photons","Planck's equation for energy of an electromagnetic waves depends on only one factor - frequency or wavelength. Shouldn't amplitude, in some way, be directly related to energy? (I'm saying this after a comparison to sound .. sound is 'louder' when it has a large amplitude or a comparison the energy lost in a resistor in an AC circuit which equal to ((Vrms^2)*t)/R here Vrms is directly related to Vpeak which is the amplitude of the voltage signal. The energy is a directly related to the voltage's amplitude (square relationship) in an AC circuit , same as energy stored in a capacitor ..). All of this could be so wrong.. please correct me.","it might be too late but ill try to answer.
as per my understanding, a photon's energy is dependent only on its wavelength, that's what quantum mechanics tells us. photons do not have a "real" discernable amplitude. However, classical mechanics associates energy with amplitude. here's the problem though, you cannot use classical mechanics to deal with photons. we can approximate that the "amplitude" of a light wave is proportional to the number of photons hitting a particular surface per unit time. in other words, it is proportional to the intensity of the wave. this does not hold true when we consider one photon, only a system of many photons.

I am not an expert so PLEASE correct anything wrong I said :)"
"Light: Electromagnetic waves, the electromagnetic spectrum and photons","So the only thing I'm having trouble with is the relationship between a photon's frequency and a light wave's frequency. Is this correct?:

If you take the "frequency of a light wave" and multiply it by "6.626*10tothe-34" you get the frequency of a photon of that light wave?","First you cannot treat the energy of a classical light wave the same way as the energy of a photon.
The energy of a photon is E = hf.
The energy of a light wave is proportional to the square of the amplitude of oscillation of the electromagnetic wave.
These are two completely different models of light, classical vs quantum mechanical."
"Light: Electromagnetic waves, the electromagnetic spectrum and photons",How do you sole for wavelength?,"c/v gives [m/s] / [Hz]. And knowing that Hz (Hertz) is equal to 1/s, then we have [m/s] / [1/s] which gives us after removing the seconds unit to get meters as the wavelength's unit. Hope this helps!"
"Light: Electromagnetic waves, the electromagnetic spectrum and photons",What are some of the different effects that various frequencies of electromagnetic radiation have when absorbed by matter?,"The different effects light has on atoms can best be understood when considering the energies of types of light. And since energy and frequency are directly proportional, the trend we describe using energy will be the same for frequency. 

Higher energy light such as gamma rays, X-rays, and high energy UV light cause ionizations. They transfer enough energy to electrons so they can escape from the pull of the atom’s nucleus and turn the atom into an ion. 

Low energy UV and visible light cause electron transitions. The electrons are able to move between the energy levels within the atom, but do not have enough energy to escape. 

Infrared light causes molecular vibrations. The bonding atoms of a molecule vibrate back and forth like an oscillating spring. 

Microwaves cause rotational motion where a molecule rotates.

Radio waves cause nuclear spin transitions which is when a proton changes its spin state.

The lower the energy the light, the less work can be done with it by the atom when it absorbs that light. 

Hope that helps."
Dalton's atomic theory,Why is Daltons theory still taught if it is not 100% accurate?,"It is also helpful to think about how science is always evolving-we are always learning new things and modifying existing theories to take into account new discoveries. That happened to Dalton's atomic theory, and that will likely to happen to many more theories to come!"
Dalton's atomic theory,Why is not possible to further separate atoms??,"Actually, it is.  Atoms are made up of protons, neutrons, and electrons.  However, if you remove any of these particles the atom will have different properties.  An atom is the smallest particle of an element that has all the properties of the element.  For example, sodium in its pure form reacts violently with water.  When you take away one of its electrons, it becomes part of table salt and no longer reacts with water."
Dalton's atomic theory,"In part 3 of the article,(Compounds are combinations of 2 or more different atoms) how is it possible that we don't get affected by the different properties of the elements and get sick if chlorine is a TOXIC gas and sodium is a highly REACTIVE metal?","Sodium and chlorine are toxic/explosive because they are unstable and therefore very reactive. If you look at the electrons in the shells, they want to react to fill their outer shell of electrons. Once they react, they exist as ions and then lose their property of being super-reactive because they then become stable."
Dalton's atomic theory,Why can't there be half an atom? And why are chemists so sure?,"We say that an atom can't be cut in half, not because it can't actually be split (aka nuclear fission - reactor, bomb) but rather because the resulting parts would no longer be atoms the elements the you started with.  Ex: you can't split a Helium atom because to do so would result in 1 or 2 Hydrogen atoms and some leftover bits - but it would no longer BE Helium."
Dalton's atomic theory,cant we put protons (h+) into a nucleus of  he (he+) to get  nucleus of an new element,"To do this would require nuclear fusion (combining smaller atomic nuclei to form a larger one), a process which is not yet quite possible in the lab.  It would produce more energy than an atomic bomb would.
It is not nonexistent, however.  This process occurs constantly in the core of the sun - basically, what you asked about is what gives Earth the energy necessary to support human life!"
Dalton's atomic theory,Did Dalton make up another theory that we can use instead of the one that was originally created?,"Well there are several parts to Dalton's theory. His only theory is the atomic theory and today we know that atoms can be destroyed by nuclear reactions but not by chemical reactions. Also, there are different kinds of atoms (differing by their masses) within an element that are known as "isotopes", but isotopes of an element have the same chemical properties. Hope that helped. But his theory was not 100% correct.

-http://www.iun.edu/~cpanhd/C101webnotes/composition/dalton.html"
Dalton's atomic theory,Didn't Antoine Lavoisier propose the law of conservation of mass?,"A peer reviewed journal, ERIC, published "A Historical Note on the Conservation of Mass." This states in their abstract that this is not entirely true:

"Although most historians of science attribute the formulation of the law of conservation of matter in chemical reactions to Antoine Lavoisier at the end of the eighteenth century, several earlier researchers had already assumed this law in their work. These researchers include Joseph Black, Henry Cavendish, M. V. Lomonosov, and Jean Rey.""
Dalton's atomic theory,"well as far as I understand this concept,atoms cannot bee further divided but we know that atoms are further divided into fundamental particles as protons,electrons and neutrons.So why does this conclusion given by dalton sir still hold true??","Many of Dalton's original postulates of an atomic theory have had to be modified in the light of later discoveries.
As far as chemical reactions go, the essential concept that chemical reactions involve atoms and molecules still remains.
In many other cases, chemists have to use the concept of electrons, protons, etc.
Dalton's atomic formed the basis of chemistry, but modern chemists have long since adapted their understanding to include later discoveries."
Dalton's atomic theory,What is the difference between an element and molecule?,"in summary:
element - a basic substance that can't be simplified (hydrogen, oxygen, gold, etc...)
atom - the smallest amount of an element
molecule - two or more atoms that are chemically joined together (H2, O2, H2O, etc...)
compound - a molecule that contains more than one element (H2O, C6H12O6, etc...)"
Dalton's atomic theory,Why can you not add protons/neutrons/electrons to an atom?,"You cannot add protons and neutrons because they are in the center of an atom and held tighly by the strong nuclear force. However, you can add electrons to atoms and this happens all the time: the gaining and losing of electrons is precisely what chemical reactions are!"
Bohr's model of hydrogen,what is quantum,"A quantum is the minimum amount of any physical entity involved in an interaction, so the smallest unit that cannot be a fraction."
Bohr's model of hydrogen,"I don't get why the electron that is at an infinite distance away from the nucleus has the energy 0 eV; because, an electron has the lowest energy when its in the first orbital, and for an electron to move up an orbital it has to absorb energy, which would mean the higher up an electron is the more energy it has. So if an electron is infinitely far away(I am assuming infinity in this context would mean a large distance relative to the size of an atom) it must have a lot of energy. Right?

Thanks very much!","you are right!

but what you need to remember now, is that the energy at infinity is DEFINED as being zero. Your next queston might be 'why?' :)

but, knowing that, does it now make sense that nearer to the nucleus, the energy is minus??"
Bohr's model of hydrogen,What does ΔE stand for?,"*The triangle stands for Delta, which also means a change in, in your case, this means a change in energy.*"
Bohr's model of hydrogen,what is the relationship between energy of light emitted and the periodic table ?,"Its a really good question. Here is my answer, but I would encourage you to explore this and similar questions further..

OK: I would say that the periodic table tells us about the number of protons in an element; and, therefore the number of electrons too. 

Now, the energy of the photon emitted from any element does not depend on the number of electrons in the atom. The value of the energies of  photons does depend on the available energy levels in the atom. Hydrogen, for example, although the simplest atom, has a whole range of photon energies that it emits.  This is because the electron can exist in many energy levels... as it switches from one energy level to another, then it emits / absorbs photons. 

We can, however, say that the more electrons there are in an atom, the greater the variety of photon energies there will be so this may be a link worth exploring

I hope that makes sense ok.

As I say, you are asking a great question.... looking for relationships in a meaningful way. I would encourage you to explore further.... maybe compare the number of different energies emitted by an element with its position in the periodic table, or the maximum / minimum energies emitted by the element vs position

Well done and keep up the good work."
Bohr's model of hydrogen,"Actually, i have heard that neutrons and protons are made up of quarks (6 kinds? up down ......)
Is it true? and how does the scientists found that out?","yes,       protons are made of 2 up and 1 down quarks whereas neutrons are made of 2 down and 1 up quarks . hope this helps."
Bohr's model of hydrogen,"Hi, great article. I was wondering, in the image representing the emission spectrum of sodium and the emission spectrum of the sun, how does this show that there is sodium in the sun's atmosphere? If both pictures are of emission spectra, and there is in fact sodium in the sun's atmosphere, wouldn't it be the case that those two dark lines are filled in on the sun's spectrum. The text below the image states that the bottom image is the sun's emission spectrum. Wouldn't that comparison only make sense if the top image was of sodium's emission spectrum, and the bottom was of the sun's absorbance spectrum? 

Thanks!","Sodium in the atmosphere of the Sun does emit radiation indeed. However, after photon from the Sun has been absorbed by sodium it loses all information related to from where it came and where it goes. So re emittion occurs in the random direction, resulting in much lower brightness compared to the intensity of the all other photos that move straight to us."
Bohr's model of hydrogen,Bohr said that electron does not radiate or absorb energy as long as it is in the same circular orbit. But according to the classical laws of electrodynamics it radiates energy. What is the reason for not radiating or absorbing energy?,Bohr did not answer to it.But Schrodinger's explanation regarding dual nature and then equating hV=mvr explains why the atomic orbitals are quantised
Bohr's model of hydrogen,why does'nt the bohr's atomic model work for those atoms that have more than one electron ?,"As far as i know, the answer is that its just too complicated.

With one electron and one proton you can figure out (with some difficulty) how they interact with one another because you have one centripetal force acting in the same 'direction' and analyse-able using classical circular motion etc. 

But with two electrons, now you have three forces; not just centripetal but also electron to electron. You can imagine in the classical view, how complex the change on force would be between the electrons and also the nucleus. It may be tht some one has figured a way of doing it or approximating to it, but, as far as I know this is the reason bohr model is only used for hydrogen."
Bohr's model of hydrogen,"so do we still not know that why do electrons not fall into the nucleus of the atom,i mean they are continuously emitting energy and of course at a point in time they should fall into the nucleus,what is the explantaion for that?","This is one of the main reasons we know that the Bohr model of the atom is wrong.  

In the quantum model of the atom electrons in their lowest possible orbital are in their ground state and can't be in any lower energy state and they do not radiate energy."
Bohr's model of hydrogen,Is Bohr's Model the most accurate model of atomic structure?,"No, it is not.  The quantum description of the electron orbitals is the best description we have."
The quantum mechanical model of the atom,"Why is the spin number expressed as +1/2 or -1/2, rather than just +1 or -1  ?","In the spin quantum number the electrons are represented either by +1/2 or -1/2, and as shown in the quantum numbers video it is said that the electrons in this type, i.e the spin number can move in two directions ,one towards the left and one towards the right, so as electrons possess like charges(-ve) and because they might be travelling in the opposite directions and finally when they come close to each other they repel, so the electron almost covers 1/2 the circular orbit so probably that is why it is assigned the value +1/2 and -1/2."
The quantum mechanical model of the atom,"I've some questions on this statement:
The square of the wave function​​ represents the probability of finding an electron in a given region within the atom.
Why function square related to probability?","It's mostly a function in mathematics. It would be like asking "what is the average distance of a cosine wave from the center?" - and this might seem easy at first until you realize that the gradient of the wave function keeps changing. Mathematically, the average distance, or in this case the energy or probability of finding the electron, is just the square root of the wave property."
The quantum mechanical model of the atom,"referring to the image on orbital shapes,
why do the p,d,f orbitals have such "out of the blue" shapes? how were these shapes found out or calculated?","The shapes have been calculated from Schrodinger's equation.

Moreover , the shapes represent the region where the probability of finding the electrons is maximum. The orbitals have NO physical BOUNDARY."
The quantum mechanical model of the atom,"So the formula for de Broglie equation says that
 
lambda= h/mv
and..the v of a stationary object will be 0,
so by mathematical solving it means that the wavelength of a stationary object is infinite?
is this the correct thinking or is there some other theory for a stationary object's wavelength?","Isn't to do with the fact that the velocity is not quite 0? if you know it is exactly 0 then the uncertainty in the position is infinite as well (momentum is a function of velocity, so delta P = 0 -> delta V = 0 -> delta X = inf) therefore it has an equal probability of being anywhere. If you take the infinite wavelength interpretation, then it would be nearly 0 (1/inf) but constant everywhere. The square (probability function) shows that it has an equal chance of being anywhere.

So, if you know with 0 uncertainty what the velocity is, then you have no idea where it is, and all future involvement of the particle is pretty much irrelevant (how is the electron going to diffract around an atom if the electron is in a different galaxy?). As we can't physically measure to perfect accuracy, there is an uncertainty in both measurements of the degree that we know it's probably stationary and it's probably 'over there'. With this uncertainty, the velocity is almost definitely not 0. (1 value in a range of reals is like trying to throw a dart at a dartboard with an infinitely thin wire and hitting the wire). For another layer, you can take the fact that you can never cool anything down to exactly 0K (-273.15C) (although you can get close) and so nothing will ever have 0 velocity."
The quantum mechanical model of the atom,"On Schrödinger's equation, what exactly is the Hamiltonian operator? 
How do we work with it mathematically and what would be its physical interpretation?","This has to do with Laplacian operator (partial derivative) of a wave function.
Here's the formula http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/sch3d.html (I can't type out the partial derivative operator -__-")

The h-bar in the equation is defined by h/(2pi)"
The quantum mechanical model of the atom,"In reference to Shrodinger's Equation, what's the difference between the V (wave function symbol) on the left side of the equation and the right? There must be some difference, or else they would cancel.","You can't cancel out the ψ's like that because Hψ is not H times ψ but rather H operating on ψ (that's what the ^ over the H indicates).
The Hamiltonian operator H is actually
H = -ℏ²/2m * d²/dx² + U(x)
so the time independent Schrodinger equation is actually
-ℏ²/2m * d²ψ/dx² + U(x)ψ = Eψ
solving for E gives the allowable energy states of the system."
The quantum mechanical model of the atom,I have a really blurry picture of what it means for small particles to behave as both particles and waves. What does it exactly mean when we say that small particle have characteristics of both waves and particle ?,"I think I can safely say that nobody understands quantum mechanics.
- Feynman
So you are right on track! :)
But to be more pedagogical, you can view them as different behaviors in different situations. When behaving as particles, they show all what we "expect" them to based on our experiences. But under different conditions, they behave as waves, where in these "waves" are equations that determine, in a simple sense, the probability of the particle to be at a particular place at a particular time. Since these equations are not the classic Newtonian equations, their predictions often create the strange outcomes we usually see. (See the double slit experiment to understand the differing behaviors.)"
The quantum mechanical model of the atom,Can we specify type of the wave in schrodinger wave? like transversal or longitudinal,"I never thought about it before. Its interesting question.

My guess is that it is transverse. though, to honest, there is so much dispute about the wave function and what it actually is, maybe we need to answer that quesiton before we can say tranverse, longitudinal or.... something else?"
The quantum mechanical model of the atom,"Does anyone know exactly what "spin" is? If a particle has "spin", it doesn't actually physically spin/turn/rotate, right?
In the article, it said that the opposite "spins" of electrons are determined by how the react in a magnetic field. But does this explain what it means for other particles - other leptons, quarks, hadrons - to have spin? What is spin? Please help!","Spin is just a property that electrons (and other particles)  have.  It got named spin back when people were working with the Bohr model and trying to extend it to atoms beyond hydrogen.  Just as Bohr imagined that the atoms were little planets revolving around the nucleus as though it were a sun, other scientists tried to extend that idea by imagining that the little planets, just like real planets, had spin.  Using this concept actually helped a bit, just like Bohr's imagination of little orbits helped a bit, but again, the electrons are not like little planets: they don't revolve around the nucleus, and they don't rotate on their axes.   Still, they have a property that works sort of like an orbit (orbitals) and they have a property that works sort of like rotation about an axis (spin).   But there is no point in trying to answer "what is electron spin" by referring to some familiar object like a ball or a planet, because electrons are not balls or planets, they are their own thing, and you just have to accept that they have a property whose effects we understand very well, and we happen to have named it spin.  "What is spin" doesn't have any deeper answer than does the question "what is charge".  It's just a characteristic that particles have or don't have, and we know what the effect is of having or not having that property.

We have other properties like this for other particles.  A quark can be an up quark or a down quark.  "Up" and "down" don't have any meaning other than to identify the type of quark.  THere's nothing "up-ish" about an up quark.  THere's a top quark and a bottom quark.  There's a charmed quark and a strange quark.  There's nothing unusually strange about the strange quark.  It's just the name that we've given a quark that has certain properties.  

IN the field of quantum chromodynamics, we say that particles have a color.  They don't really have a color, we just use that idea because it's sort of helpful, just like using the idea of positive and negative for charges is helpful."
The quantum mechanical model of the atom,"Do nodes of the 1s, 2s, 3s... subshells overlap?
(wrt to the graph shown above, it seems they do)
If yes, do the nodes of another subshell also overlap,


[in fact, if the probability of finding an electron is 0, shouldn't the nodes always overlap(even if multiple subshells /orbitals pass through)?]",Atomic orbitals are defined by energy levels not positions. The electron clouds that are depicted are usually where there is a 90% chance of finding the electron at that energy level.  The electron clouds for different energy levels do have overlaps.
"The periodic table, electron shells, and orbitals","If the Bohr model is an inaccurate representation of electron's movement, why is it so universally accepted?","Because in Bohr’s model for hydrogen atom we consider only Coulombic interactions between one proton and one electron.

It cannot be extended for other atomic species containing more than one electron. Because in this case in addition to the interaction between nucleus and electron there arises the interactions between electron and electron of the same species. Bohr couldn't solve this problem and this problems are successfully explained on the basis of later developed quantum mechanics.o

But Bohr's model can be applied successfully for hydro genic species like He+, Li2+ etc……."
"The periodic table, electron shells, and orbitals","I'm kinda also confused on what an electron shell is and what an electron subshell is. Is the elctron subshell the s, p, d and f orbitals? And is it a probability function describing where an electron is likely to be? What's the difference between an electron shell and subshell?
Thanks c:","All atoms are made up of energy levels (called shells) that hold 1 or more subshells.
Each subshell holds a certain type of orbit.

Each individual subshell has slightly varying energies from its "shell" energy level, depending on the distance from the nucleus.

Every subshell has a # of orbits s/p/d/f that can each hold 2 electrons each (one has the opposite spin of the other).

The first shell (of all atoms) has 1 subshell of s-orbitals containing 1 s orbital. This means that the first shell can hold 2 electrons.
The second shell has 2 subshells: 1 s-orbital and 3 p-orbitals. This means that the second shell can hold 8 total electrons.

Every orbital is a shape (that can be determined by a trigonometric function I believe). This shape tells us where it is likely to spend most of its time, so in a sense it is a probability function.

Hope this helps someone. :-)"
"The periodic table, electron shells, and orbitals",How can you determine the number of outer shell electrons based on the full electron configuration?,"I'll try to explain with the help of an example. Consider Sodium (Na)
Its electronic configuration is 1s2, 2s2, 2p6, 3s1
The largest value of the Principle Quantum Number (n) is 3, so that is the outermost orbital.
Counting the number of electrons, we find that only the s orbital is present and it has only one electron. So Na has one electron in its outermost orbital.

Another example that I'll use is Fluorine (F).
Its electronic configuration is 1s2, 2s2, 2p5.
Since the largest value of n is 2, we count all the electrons in the s and p orbitals that have n = 2. So we get 2 + 5 = 7. So fluorine has 7 electrons in the outermost shell.

Basically, count the number of electrons in the orbitals with the highest principle quantum number, and that'll give the number of electrons in the outermost shell."
"The periodic table, electron shells, and orbitals","I'm confused about all the 1s2 2s2 and 2p6.  It's hard for me to understand, I was wondering if you could help out with that?","The 1s is the first orbital electron shell and it is closest to the nucleus. The 2n is the second shell. It consists of the 2s and 2p shells. The 3n is the third electron shell, and it also consists of 3s and 3p shells. The number after it stands for the amount of electrons in each orbital."
"The periodic table, electron shells, and orbitals","In the second last paragraph, I don't really get why because of the d subshell having more energy, argon is stable with 8 valence electrons? Thanks",I am not sure where the confusion is. Argon has a full outer shell of electrons already. It will not have a d-subshell
"The periodic table, electron shells, and orbitals",How do scientists figure this out? Do we have microscopes powerful enough to view atoms and observe this behavior or is there some other method?,"No, it can't be figured out using microscopes. Most of it is based on theory worked out using a lot of maths. Experimental observations, such as the energy released or absorbed when electrons move from one state to another, corroborate the theory.

Experimental observations, using techniques such as X-ray crystallography, provide information on the shape of molecules which, in turn, corroborates the theoretical shapes of the orbitals."
"The periodic table, electron shells, and orbitals",How much space does electrons take up,"Overall, the electrons are much smaller than the protons and neutrons. But, they take up more space when you think about how they move. They are constantly moving, and at different wavelengths and frequencies. And, they also move fast and they act like gas particles, in a way."
"The periodic table, electron shells, and orbitals",Can Hydrogen lose its only valence electron? Can an element exist without electrons?,"Hydrogen can lose its one electron and became an ion, or the hydrogen cation H^(+). However, it is so reactive that it does not exist for long before reacting with other atoms.  

Hope that helps."
Non-ideal behavior of gases,Why do gas molecules behave ideally in high temperature & low pressure,"Real gases behave ideally in *high temperatures* because at high temperature intermolecular forces are nearly negligible. [At very _low_  temperatures, intermolecular forces become significant and molecules travel with low average speed and hence, can be captured by one other due to their attractive forces more easily than when at high temperatures]"
Non-ideal behavior of gases,"In the van der waals equation, we add something to P. However, in a real gas, we account for intermolecular forces of attraction where particles attract each other- should this not 'reduce' the pressure since now the particles are attracted to other particles so they might not hit the wall with the same force or speed?","The VdW equation above is a derived form. If you divide both sides by [V-nb] and then subtract [an^2/V^2] from both sides, you can see that the pressure P = nRT/(V-nb) - (an^2/V^2) <--- this is the inter-molecular force correction which you can now see becomes significantly subtractive when T is small."
Non-ideal behavior of gases,I dont understand the "can we be more precise" part (just before the Summary). Can someone explain the math part? How the equations simplify? If this is explained I'll likely grasp Z. Thanks in advance.,"Lets see, you re-derive the Z equation using Van der Waals version of the gas law. 
`Z = [P + ​an²/V²] * [V - nb] / nRT`

Then you say what happens if *P* is really big (and *n* stays small) then `P + an²/V²` will become very close to *P* (i.e. the other term will become insignificant). This gives us:
`Z = P * [V - nb] / nRT
  = (PV - nbP) / nRT`

If we replaced PV by nRT (I'm not sure that makes sense ...) and simplify, we get:

`Z = 1 - bP/RT`

Hmmm ... I guess I don't understand what they are doing here either ..."
Non-ideal behavior of gases,What makes a gas non-ideal.,"The higher the temperature and the lower the pressure, the less the deviation from ideal gas behaviour. Under these conditions, the volume of the gas particles compared to the volume of the container which contains the gas can be considered negligible, and so are the intermolecular forces of attraction and repulsion between the gas particles."
Non-ideal behavior of gases,"i  dont understand why in the VDW equation something was added to P. Since for real gases, the forces of attraction slow down the particles and they hit the wall with 'less pressure'. So in this case, something should be subtracted from P right?","We are trying to get an equation that matches the Ideal Gas Law (=nRT)
Since the real pressure is less than the ideal pressure P, we must add something to the real pressure to bring it up to the "ideal" value."
Non-ideal behavior of gases,"What exactly is the "real molar volume" and" Ideal molar volume"? What are the equations to calculate the real and ideal molar volumes to even be able to compare the ratio? I've only ever heard of molar volume being 22.41(at stp), how are we getting two different molar volumes at the same temperature and pressure?","The "ideal molar volume" is the volume that one mole of a gas would occupy if its molecules had zero volume and no intermolecular forces of attraction.
No real gas is ideal. All molecules have a volume and intermolecular forces of attraction.
So a "real molar volume" is different from an ideal molar volume.
At STP ( 0 °C and 1 bar of pressure), the ideal molar volume is 22.71 L."
Non-ideal behavior of gases,"in terms of calculations, if we calculated the substances using ideal and non ideal gas eq, which one is more accurate?",There is no "non ideal gas equation" so I assume you are referring to the Van der Waal's equation and in regards to accuracy for real gases the Van der Waal's equation would be more so because we are assuming there will be some inter molecular attractions and the real gas will take up some volume in the container.
Dalton's law of partial pressure,"For example 1 above when we calculated for H2's Pressure, why did we use 300L as Volume?  Isn't that the volume of "both" gases? Why didn't we use the volume that is due to H2 alone?","One of the assumptions of ideal gases is that they don't take up any space. In addition, (at equilibrium) all gases (real or ideal) are spread out and mixed together throughout the entire volume. 

Even in real gasses under normal conditions (anything similar to STP) most of the volume is empty space so this is a reasonable approximation."
Dalton's law of partial pressure,"Under the heading "Ideal gases and partial pressure," it says the temperature should be close to 0 K at STP. Shouldn't it really be 273 K?",""This assumption is generally reasonable as long as the temperature of the gas is not super low (close to 0 K), and the pressure is around 1 atm."
The sentence means *not* super low that is *not* close to 0 K."
Dalton's law of partial pressure,Oxygen and helium are taken in equal weights  in a vessel . The pressure exerted by helium in the mixture is,"Since oxygen is diatomic, one molecule of oxygen would weigh 32 amu, or eight times the mass of an atom of helium.  If you have equal amounts, by mass, of these two elements, then you would have eight times as many helium particles as oxygen particles.  Therefore, the pressure exerted by the helium would be eight times that exerted by the oxygen."
Dalton's law of partial pressure,"In the first question, I tried solving for each of the gases' partial pressure using Boyle's law
P_1*V_1 = P_2*V_2

For Nitrogen :
P2 = P_N2 = P1*V1/V2 = 2*24/10 = 4.80atm
For Oxygen:
P2 = P_O2 = P1*V1/V2 = 2*12/10 = 2.40atm

P_total = 4.80+2.40 = 7.20atm which is pretty close to the 7.19atm calculated here.

Can anyone explain what is happening lol
EDIT: Is it because the temperature is not constant but changes a bit with volume, thus causing the error in my calculation?",The minor difference is just a rounding error in the article (probably a result of the multiple steps used) - nothing to worry about. The temperature is constant at 273 K.
Dalton's law of partial pressure,In question 2 why didn't the addition of helium gas not affect the partial pressure of radon? please explain further.,"The pressures are independent of each other. In other words, if the pressure from radon is X then after adding helium the pressure from radon will still be X even though the _total_ pressure is now higher than X. The total pressure is the sum of the individual partial pressures."
Dalton's law of partial pressure,"In step 1, we were asked to find the total pressure. The pressure of nitrogen is 2atm and that of oxygen is 2atm. Why could we not say that total pressure is equal to pressure of the individual gases(nitrogen and oxygen). Ptotal= Pn + Po. Ptotal= 2+2 which is equivalent to 4atm. I understand the fact that we`ve the pressure of nitrogen as P1, P1 is equivalent to n1RT/V and P total is equivalent to P1 + P2. P2= n2RT/V. So we find P1 and P2 and add them together using n1RT/V + n2RT/V will give the total pressure.","Using Dalton’s law as you’re suggesting only works if all the gases are already mixed together in the same container where the volume and temperature are the same. For the nitrogen and oxygen gas example, they begin in two separate containers with different volumes. And finally we mix them together in a third container with a different volume from the previous two containers. 

The 2atm pressures represent the pressures of the gases in their original containers before mixing. Their sum, 4atm, isn’t automatically the pressure in the third container when they are mixed because of the different volumes. 

Using the idea gas to create new equations to substitute for the partial pressures in Dalton’s law like you’ve done is how they solved the problem in method 1."
Dalton's law of partial pressure,idk if this is a partial pressure question but a sample of oxygen of mass 30.0 g is confined in a vessel at 8°C and 3000. torr. Then 2.00 g of hydrogen is pumped into the vessel at constant temperature. What will be the final pressure in the vessel? (no reaction just mixing) how would you approach this question?,"I initially solved the problem this way:
You know the final total pressure is going to be the partial pressure from the O2 plus the partial pressure from the H2. And you know the partial pressure oxygen will still be 3000 torr when you pump in the hydrogen, but you still need to find the partial pressure of the H2. 
You can find the volume of the container using PV=nRT, just use the numbers for oxygen gas alone (convert 30.0g to moles of O2 first). Once you know the volume, you can solve to find the pressure that hydrogen gas would have in the container (again, finding n by converting from 2g to moles of H2 using the molar mass). Then the total pressure is just the sum of the two partial pressures.

But then I realized a quicker solution-you actually don't need to use partial pressure at all
 First, calculate the number of moles you have of each gas, and then add them to find the total number of particles in moles. Then, since volume and temperature are constant, just use the fact that number of moles is proportional to pressure. Set up a proportion with (original pressure)/(original moles of O2) = (final pressure) / (total number of moles)"
Dalton's law of partial pressure,Is there a way to calculate the partial pressures of different reactants and products in a reaction when you only have the total pressure of the all gases and the number of moles of each gas but no volume?,"Yes. As has been mentioned in the lesson, partial pressure can be calculated as follows:
P(gas 1) = x(gas 1) * P(Total); where x(gas 1) = no of moles(gas 1)/ no of moles(total).
As you can see the above formulae does not require the individual volumes of the gases or the total volume. Of course, such calculations can be done for ideal gases only."
Molarity,"Hi there,  
I was just wondering shouldnt the answer in example 1 be 0.48 mol/Litre
and NOT 4.8 M? I get the same answer to the last step before the answer, but when i do the calculation i get 0.48 mol/litre.
thank you so much.",I believe you're correct.  There was likely a typographic error in the example.  We see in the previous step the conversion was done correctly (50 mL = .050 L) so we have 0.02401 mol / .050 L.  A quick check with the calculator shows that this is in fact 0.48 mol/L or 0.48 M.
Molarity,"I was told in school that molarity should be moles/dm^3, but is this different from moles/litres?","A liter is equal to a cubic decimeter, so it is the same."
Molarity,"So this isn't quite the right place for my question, but I can't find the right place for the life of me... If someone could maybe point me to a video/article on converting between concentration units, especially molarity to ppt or ppm, that'd be great.

In the mean time, I've been asked to take a known molarity of a solution and convert it into parts per thousand. I tried Google and I /think/ I got the right formula but I'm not positive, so can someone check it for me please?

So what I did was start with my given molarity as mol/L. I assumed there wouldn't be enough solute to drastically affect density and so I changed 1 L to 1000g, so I now have mol/1000g. Then I multiply by the molar mass of the solute (NaOH - 39.998) so I'm now g NaOH/1000g solution. Then I multiply the whole thing by 1000 to get ppt, right? Sort of like calculating a percent?","You did it almost perfectly.
A concentration of 1 g NaOH/1000 g solution is 1 g per 1000 g or one part per thousand (1 ppt) — no need to multiply by 1000.
In the same way, a concentration of 1 g per 100 g is one part per hundred (1 %)."
Molarity,in hint one how do you know there is .1L of solute?,There must have been a typo. I think in the description they meant 0.100L instead of 0.100mL.
Molarity,How would you find the molarity of SO2 if you have it dissolved in 100 grams of water at 85 degrees Celcius?,"Assuming that you do not know the amount of SO2 that was dissolved to prepare the solution, you may try to invoke Henry's Law and determine the concentration of SO2 in the headspace (just above) of the solution. 

For a primer on Henry's Law, you can check out this article:
https://www.thoughtco.com/henrys-law-example-problem-609500

You can also check these links below for sample procedures on determining the amount of SO2 vapor (<- what causes acid rain!):
https://www.law.cornell.edu/cfr/text/40/appendix-A-2_to_part_50
https://www.astm.org/Standards/D2914.htm

Finally, you can check this link, so you can convert your determined SO2 vapor concentration to SO2 molarity in water:
https://www.ems.psu.edu/~brune/m532/m532_ch5_aqueous_phase.htm

Yeah, this is some detective work (and a lot of hard work!)."
Molarity,"Question:  Is this just coincidence, or does this make sense...
In the equation, we have 1 Pb(NO3)2 + 2 KI...we have twice as many KI as Pb(NO3)2.  Since we have 0.1L of 1Pb(NO3)2, can I just multiply the 0.1 L x 2, since we use twice as much KI as we do Pb(NO3)2?  (Or if the equation happened to have 4KI, could we simply multiply 0.1L x 4)?  Thanks for the help!","What you suggest is fine just as long as the concentrations of the two solutions are the same. But if, say, the Pb(NO3)2 solution was twice the strength of the KI solution then you would only need 0.1 L of each to get the same number of moles."
Molarity,"I understood what molarity is quite well......but what is normality, formality and molarity? If we have molarity why are they even needed then?","With any luck, like most people, you will be able to safely ignore normality and formality.

Molality is moles / mass of solvent (SI unit: mol/kg) -- for use see: https://en.wikipedia.org/wiki/Molality#Usage_considerations

Normality is explained here: https://en.wikipedia.org/w/index.php?title=Equivalent_concentration&redirect=no

Formality is more or less totally ignored and often when we say molarity we actually mean formality see: http://www.chemiasoft.com/chemd/node/25

A good discussion of most of these is here: https://socratic.org/questions/what-is-molarity-molality-and-normality"
Molarity,What is the difference between molarity and molality?,"Molarity is (mol of solute)/(L of solution).
Molality is (mol of solute)/(kg of solvent).
More on the difference here: https://www.khanacademy.org/science/health-and-medicine/lab-values/v/molarity-vs-molality"
Calculating equilibrium constant Kp using partial pressures,Why do we not include liquids and solids in equilibrium expressions? What do you mean by "their concentration is equal to 1"?,"The concentration of the solids never changes, as its density remains the same. Regarding liquids, adding or removing liquids has an insignificant effect on the concentration of the system, as the system is in an aqueous solution. Yes, the liquids do change the concentration, but not by a measurable amount. It's like adding another fish to the sea, making pretty much no difference to the concentration of fish in the ocean"
Calculating equilibrium constant Kp using partial pressures,"In example 2, how do you know that you are finding the constant in terms of bar and not atm?","It is because the Universal Gas Constant R=8.314 is substituted and pressure calculated by using this will give you the answer in terms of barr
If you want to calculate in terms of atm then use R=0.0820"
Calculating equilibrium constant Kp using partial pressures,"For the ICE Table, how do we know that the Change has +2x and +x?  I mean, why did we choose plus instead of minus?","With the ICE table, you initially assume that the reaction is entirely on the left, with water but no hydrogen or oxygen gases. Then, as the reaction proceeds, hydrogen and oxygen are formed, which are written as +2x and +x atm in the "change" line.   

If you used minus signs, that would indicate that the gas concentrations were decreasing as the reaction moved towards equilibrium, which is not the case."
Calculating equilibrium constant Kp using partial pressures,Can anyone explain why Pressure does not change the equilibrium constant for a reaction but temperature does?,"The equilibrium constant is a *constant*.
If you change a pressure, *all* the pressures change so that their new values will give the same value for the equilibrium constant."
Calculating equilibrium constant Kp using partial pressures,"in the formula Kc = Kp * (RT)^n
if we use double the reactants then the difference b/w the number of moles will also get double Kc will change","but you cant arbitrarily double the moles of reactants or products in a particular BALANCED reaction.
all values for the moles should be calculated using a balanced equation simplified to its lowest form.
increasing quantity of reactants will not change the value of kc either, kc always is a constant for a given temperature.
but it has no effect on difference in moles for a balanced reaction.
(correct me if i'm wrong)"
Calculating equilibrium constant Kp using partial pressures,"As in example 3, why are we taking the partial pressure of water in liquid form as 1,  why not any other value (say less than 1)?","adding or removing liquid makes a very negligible difference in the pressure of the system.
you can assume it as 1 without changing the answer.
at least for calculation purposes
besides taking any value apart from 1 will unnecessarily increase the difficulty of your calculations."
Calculating equilibrium constant Kp using partial pressures,"In example 3, what does N/A in the ICE table indicate?",N/A is a common abbreviation for "Not applicable".
Calculating equilibrium constant Kp using partial pressures,"When the do the PV=nRT, shouldn't the final equation be P=nRT/V, not P=(n/V)RT?","The two expressions P=nRT/V and P=(n/V)RT are the same. The second one is written specifically to separate out the expression n/V, which is equal to the concentration. This helps emphasize the relationship between concentration and the ideal gas equation."
The reaction quotient Q,I'm confused with the difference between K and Q. I'm sorry if this is a stupid question but I just can't see the difference. How can you have a K value of 1 and then get a Q value of anything else than 1?,"K is the equilibrium constant. Therefore K is revealing the amount of products to reactants that there should be when the reaction is at equilibrium. Q is used to determine whether or not the reaction is at an equilibrium. At any given point, the reaction may or may not be at equilibrium. By calculating Q (products/reactants), you can compare it to the K value (products/reactants AT EQUILIBRIUM) to see if the reaction is at equilibrium or not. If Q=K, the reaction is at equilibrium."
The reaction quotient Q,Can i get help on how to do the table method when finding the equilibrium constant,"http://www.chem.purdue.edu/gchelp/howtosolveit/Equilibrium/ICEchart.htm

Try this website if you need help with ICE tables and calculating the equilibrium constant K. I don't think Khan Academy has any videos on ICE tables but I am not sure; if they do not, then I will try to get some ICE table videos in. It is a fundamental topic of chemistry and, in my opinion, just as important as stoichiometry."
The reaction quotient Q,when setting up an ICE chart where and how do you decide which will be -x and which will be x?,"if the reaction will shift to the right, then the reactants are -x and the products are +x.
If the reaction will shift left, do the opposite."
The reaction quotient Q,"in the above example how do we calculate the value of K or Q ? As in how is it 
1.0M or 15M?","15M is given
Co2=H2=15M"
The reaction quotient Q,"in the example shown, I'm a little confused as to how the 15M from the products was calculated.","We didn't calculate that, it was just given in the problem."
The reaction quotient Q,"This is a little off-topic, but how do you know when you use the 5% rule? Cause I'm not sure when I can actually use it.","You use the 5% rule when using an ice table. When you plug in your x's and stuff like that in your K equation, you might notice a concentration with (2.0-x) or whatever value instead of 2.0. If the K value given is extremely small (something time ten to the negative exponent), you can elimintate the minus x in that concentration, because that change is so small it does not matter. After finding x, you multiply 0.05 to the 2.0 from 2.0-x and compare that value with what you found for x. If x is smaller than 0.05(2.0), then you're good to go!"
The reaction quotient Q,why shouldn't K or Q contain pure liquids or pure solids? and isn't hydrofluoric acid a pure liquid coz i remember Sal using it in the video of Heterogenous equilibrium so why did he use it?,"The equilibrium constant is a ratio of the concentration of the products to the concentration of the reactants. Keyword- concentration. While gas changes concentration after the reaction, solids and liquids do not (the way they are consumed only affects amount of molecules in the substance). Concentration of the molecule in the substance is always constant. For hydrofluoric acid, it is an aqueous solution, not a liquid, therefore it is dissolved in water (concentration can change - moles per unit volume of water)."
The equilibrium constant K,"This article mentions that if Kc is very large, i.e. 1000 or more, then the equilibrium will favour the products. 

I thought that if Kc is larger than one (1), then that's when the equilibrium will favour the products. Conversely, if Kc is less than one (1), the equilibrium will favour the reactants.","If Kc is larger than 1 it would mean that the equilibrium is starting to favour the products however it doesnt necessarily mean that that the molar concentration of reactants is negligible.
for example - is the value of Kc is 2, it would mean that the molar concentration of reactants is 1/2 the concentration of products. In this case though the value of Kc is greater than 1, the reactants are still present in considerable amount.
 Khan academy was trying to show us all the extreme cases, so the case in which Kc is 1000 the molar concentration of reactants is so less that practically the equilibrium has shifted almost completely to the product side and vice versa in case of Kc being 0.001.
And if you read carefully, they dont say that when Kc is very large products are favoured but they are saying that when Kc if very large mostly products are present and vice versa.
Hope this helps :-)"
The equilibrium constant K,why aren't pure liquids and pure solids included in the equilibrium expression?,"Equilibrium constant are actually defined using activities, not concentrations.  The activity of pure liquids and solids is 1 and the activity of a solution can be estimated using its concentration.  So, pure liquids and solids actually are involved, but since their activities are equal to 1, they don't change the equilibrium constant and so are often left out."
The equilibrium constant K,""Kc is often written without units, depending on the textbook."

When Kc is given units, what is the unit?","Depends on the question.
For example, in Haber's process: N2 +3H2<---->2NH3
Kc=[NH3]^2/[N2][H2]^3
Using molarity(M) as unit for concentration:
Kc=M^2/M*M^3=M^-2
i.e Kc will have the unit M^-2 or Molarity raised to the power -2.
Hope you can understand my vague explanation!!"
The equilibrium constant K,"​​I get that the equilibrium constant changes with temperature. I don't get how it changes with temperature. The formula for calculating Kc or K or Keq doesn't seem to incorporate the temperature of the environment anywhere in it, nor does this article seem to specify exactly how it changes the equilibrium constant, or whether it's a predicable change. With this in mind, can anyone help me in understanding the relationship between the equilibrium constant and temperature?","You forgot *main* thing. Kc depends on Molarity and Molarity depends on _volume_ of the soln, which in turn depends on 'temperature'. Hope you get it!"
The equilibrium constant K,Any suggestions for where I can do equilibrium practice problems?,Try googling "equilibrium practise problems" and I'm sure there's a bunch. Some will be PDF formats that you can download and print out to do more. Sorry for the British/Australian spelling of practise.
The equilibrium constant K,"If the equilibrium favors the products, does this mean that equation moves in a forward motion? Or would it be backward in order to balance the equation back to an equilibrium state?","If it favors the products then it will favourite the forward direction to create for products (and fewer reactants). As the reaction proceeds, the reaction will approach the equilibrium, and this will cause the forward reaction to decrease and the backward reaction to increase until they are equal to each other."
The equilibrium constant K,Any videos or areas using this information with the ICE theory?,"Check out 'Buffers, Titrations, and Solubility Equilibria'."
The equilibrium constant K,Say if I had H2O (g) as either the product or reactant. Would I still include water vapor (H2O (g)) in writing the Kc formula?,"YES! Very important to know that with equilibrium calculations we leave out any solids or liquids and keep gases. So with saying that if your reaction had had H2O (l) instead, you would leave it out!"
The equilibrium constant K,"Excuse my very basic vocabulary. 
So basically we are saying that N2O4 (Dinitrogen tetroxide) is put in a vial or a container, it reacts to become 2NO2 overtime until they are constant (forward and reverse). What I keep wondering about is: Why isn't it already at a constant? I mean, so while we are taking the dinitrogen tetroxide why isn't it turning? so that it disappears? I don't know if my vague terms get the idea explained but why aren't things if they have the same conditions change so that they always are in equilibrium.
Why we can observe it only when put in a container? Why until the time we put it, it starts changing why not since it formulated, it changes, and if it does, then how come hasn't the reactants finish (becomes all used)?","That's a good question! However, the position of the equilibrium is temperature dependent and lower temperatures favour dinitrogen tetroxide. In fact, dinitrogen tetroxide is stable as a solid (melting point -11.2 °C) and even in the liquid state is almost entirely dinitrogen tetroxide. Only in the gaseous state (boiling point 21.7 °C) does the position of equilibrium move towards nitrogen dioxide, with the reaction moving further right as the temperature increases.

There are really no experimental details given in the text above. Therefore, the experiment could be done by adding liquid dinitrogen tetroxide and allowing it to warm up and become a gas whereupon an equilibrium will be established. (At 100 °C, only 10% of the mixture is dinitrogen tetroxide.)"
The equilibrium constant K,What happens if Q isn't equal to Kc?,"If Q is not equal to Kc, then the reaction is not occurring at the Standard Conditions of the reaction
but the reaction will take place.There can be two cases :
1) If Q>Kc - The reaction will proceed in the direction of reactants.
2) If Q<Kc - The reaction will proceed in the direction of products."
Water autoionization and Kw,"in Example 2 , i didn't  understand why [H] = 6.3x10...+ x ,why was x added to the concentration of H what does it have to do with that ?","The HCl is so dilute that we must consider both the concentration of H⁺ from the HCl *and* the concentration of H⁺ from the ionization of the water.
[H⁺] from HCl = 6.3 × 10⁻⁸ mol/L
[H⁺] from H₂O = x mol/L
∴ Total [H⁺] = (6.3 × 10⁻⁸ + x) mol/L"
Water autoionization and Kw,"In this article, the value of Kw has been given as 10^-14. But should it not be 10^-14(mol/L)^2? Why have the units been dropped?",That's a really great question! My not so great answer is that it is pretty common in textbooks to drop the units for concentrations when calculating equilibrium constants. This online source has some more detailed explanations (and sources) for why that is the case: http://chemistry.stackexchange.com/questions/1137/why-are-equilibrium-constants-unitless
Water autoionization and Kw,"In exercise 2, the question states that the solution has a hydronium ion conc. of 6.3*10^-8 M. It doesn't specifically say that this measure excludes the number of H+ ions that come from water. Do we always have to assume that?",The article also left me wondering this. If someone states that "a HCl solution with a hydronium ion concentration of 6.3 * 10^-8 M" I would assume that the aqueous solution has the mentioned hydronium ion concentration and use that to calculate the pH. Shouldn't the creator of the article have seperately mentioned that the concentration excludes the H+ coming from autoionization of water. Or maybe I'm missing something? Idk.
Water autoionization and Kw,How come we multiply the pH value by 2 when the temperature is 0C°?,"In pure water, at any temperature, [H3O+] equals [OH-]. 

At 0 C, pKw = 14.9. 

pKw = pH + pOH. As [H3O+] equals [OH-], then pH must equal pOH because these are just the negative logs of the respective concentrations, which are equal. 

Therefore, the equation becomes pKw = pH + pH = 2 x pH.  Therefore, pH = pKw/2.

So the division by two has nothing to do with temperature. It is just because [H3O+] equals [OH-], which is the case at any temperature for _pure_ water."
Water autoionization and Kw,"I understand how adding an acid such as HCl to water increases the number of H30 ions as the released H+ attaches to H20, but I dont get it why should it decrease the number of OH in a way that keep the product of both constant. Say for the sake of easy math there was 1000 of each ion, the product of both would be 1 million. However, since  there is aproximatly 560 million H20 for every 1 OH in neutral water, if I dump over 1 billion HCl molecules there should be about 1 billion more H30 ions and only about 2 fewer OH ions. and 1 billion and a thousand X 998 dosent make a million.","you can use reaction equilibrium to explain this:
at 25 degree Celsius, K(w)= 10^(-14)
Let [H+] and [OH-] be the initial concentration of H+ and OH- in water
Before adding acid: K(w) = [H+]*[OH-] = 10^(-14)
After adding acid with x mol/l concentration of [H+]: Q(c) = {[H+] + x}*[OH-]
Since {[H+] + x} > [H+]   =>  {[H+] + x}*[OH-] > [H+]*[OH-]   =>  Q(c) > K(w)
According to Lechatelier's equilibrium law, the reaction must reach equilibrium by decreasing the new [H+] in the solution. To do this, it must use OH- to react with this newly added H+.
As a result, after the reaction reaches equilibrium, both [H+] and [OH-] decreases."
Water autoionization and Kw,"We see that the pKa of water is 14 at 25 degrees Celsius, since the -log of 10^-14 is 14. However, my organic chemistry textbook says the pKa of water is 15.7 at 25 degrees Celsius. Can you please shed some light on this?","There is an article about this via the following link: http://chemwiki.ucdavis.edu/Core/Organic_Chemistry/Fundamentals/What_is_the_pKa_of_water%3F
Apparently the organic textbooks are wrong, and the pKa at 25 degrees Celcius is 14. I hope this helps ;)"
Water autoionization and Kw,do the ph and the poh change with the change of the temperature,"Yes. If the water changes temperature then so does the Kw value, and pH and pOH depend on the kW value. 

Hope that helps."
Water autoionization and Kw,"When an acid is added to pure water, the resultant solution will have more hydronium ions and fewer hydroxide ions. So, the new equilibrium could be something like [H3O+] = 10^-9 and [OH-] = 10^-5. Is this correct?","If it has more hydronium ions and fewer hydroxide ions, then H3O+ might have a concentration of 10^-5 and OH- could have 10^-9. You have them in the reverse order. But yes, that is possible."
Water autoionization and Kw,""Since the concentration of OH- can't be negative, we can eliminate the second solution.
Doesn't it sound too loose and unlogical? We can just casually remove a certain value from calculation?","If you're solving a quadratic equation, you can receive a maximum of two real solutions. In this case we get that with one being positive and one being negative. So it makes mathematical sense that we get two answers, but physically only the positive answer makes sense.

A negative concentration means you have less than 0 moles of hydroxide, or less than nothing. We can have no hydroxide possible, 0 moles of hydroxide in the solution, but not less than that.

It's similar to problems in geometry where we can only have positive areas or volumes since we're considering real physical objects even if the algebra sometimes allows a negative answer. 

Hope that helps."
Relationship between Ka and Kb,"How can we theoritically understand the relation , Kw=Ka.Kb. I mean why does it hold true?What exactly is going on in the solution?","I'm not sure if I need any credentials to answer this... but here I go.

When writing an equilibrium expression, you MULTIPLY the products and DIVIDE The reactants. In that same sense, Ka * Kb can be conceived as multiplying the products of both Ka and Kb and dividing by the reactants of both Ka and Kb. Reverse the process you use for writing equilibrium expressions: multiplication = add to the products, division = add to the reactants. 

When you follow this process, adding HA + H2O <-> H3O+ + A- (acid) with A- + H2O <-> HA + OH- (base), HA and A- turn out to be "spectators" (not sure if that's the 100% correct term), so you can remove them, resulting in the net equation of H2O <-> H+ + OH-, the equation for the autoionization of water, which is represented by Kw.

To summarize: Ka * Kb is equivalent to adding the acid and base reactions together, which results in a net equation of the autoionization of water. 

It's not a neutralization/acid-base reaction, but I think the Kw = Ka * Kb is a mathematical relation made to expedite calculations. Which works by the nature of how equilibrium expressions and chemical equations are related."
Relationship between Ka and Kb,What's the difference between Kb and pKb?,"pKb is the *negative logarithm* of  Kb.
If  you're  not introduced to logs, go to this link: https://www.khanacademy.org/math/algebra2/exponential-and-logarithmic-functions/introduction-to-logarithms/v/logarithms"
Relationship between Ka and Kb,At what state/situation when [H30+] is equal to [A-]?,"That could never really happen... for [H30+] to be a conjugate base, it would have to start as [H40]2+, which I have never seen. While it probably does exist, I doubt that it would ever come up."
Relationship between Ka and Kb,What does Ka1 and Ka2 mean?,"Ka means the acid dissociation constant, it’s a measure of how much an acid splits up into H+ In solution. 

Acids that have multiple ionisable protons (eg. phosphoric acid H3PO4) have a Ka for each H+ that can be removed. 

Ka1: H3PO4 -> H+ + H2PO4^-
Ka2: H2PO4^- -> H+ + HPO4^2-
Ka3: HPO4^2- -> H+ + PO4^3-

See how it works? Each successive Ka will be smaller in value as it gets harder to remove more H+"
Relationship between Ka and Kb,"are there not "medium" acids, and is there not variation in what equilibrium constant value would separate strong from weak acids?","No there’s no such classification as medium acids. 
Strong acids have a Ka > 1, weak acids have a Ka < 1."
Relationship between Ka and Kb,Why can you not find the Ka of NH3? Couldn't you just divide the Kb from 10^-14?,"NH3 is a base. Ka is the ACID dissociation constant, which would be calculated from the concentration of NH4. Kb is the BASE ionization constant, which would be calculated from the concentration of NH3."
Relationship between Ka and Kb,"In step 3, where did the 10 come from? Can some one explain the process of rearranging this equation in step 3?","you use 10 to the negative pKb because that is the inverse of the negative log/how you undo the negative log, which leads you to get Kb instead of pKb"
Relationship between Ka and Kb,"When Ka = 1.0*10^-14, does Kb = 1? This would be under the equilibrium of water.

#MCATprep",yeah it does
Brønsted-Lowry acids and bases,"How is a reaction such as LiOH(aq)+HBr(aq)→H​2
​​ O(l)+LiBr(aq) considered an acid-base reactions by this new definition. LiOH does not accept a proton and become LiH2O.","I see what you are saying, but it is the OH- of the LiOH that is accepting the proton to give H2O, so the OH- is acting as a Brønsted-Lowry base. LiOH will completely dissociate in water to give Li+ and OH-. So LiOH is the source of the OH- ions that accept the protons. LiOH is regarded as being a base despite the Li+ ions not being involved in proton transfer."
Brønsted-Lowry acids and bases,Can someone explain why LiOH + HBr --> H20 + LiBr is an acid base reaction (practice problem 1)?,"The HBr is an acid, because it donates a proton to the OH⁻ of the LiOH.
The OH⁻ of the LiOH is a base because it accepts the proton from the HBr."
Brønsted-Lowry acids and bases,I have a very basic question. Why did chemists select the concentration of H+ ions to calculate acidity?,Acidity is just the name we give to the presence of extra H+ ions.
Brønsted-Lowry acids and bases,"At what point would you balance the equation you write to show the reaction of acids or bases in water?
Also, when do you use equilibrium arrows, for an acid-base reaction or for an acid or a base reacting with water?","You must balance an equation before you do any calculations that will need the coefficients in the balanced equation (i.e. stoichiometry or equilibrium calculations).
You use a reaction arrow (→) for any acid-base neutralization in which you have at last one strong acid or strong base.
NaOH + HCl → NaCl + H₂O
NaOH + CH₃COOH → CH₃COONa + H₂O
HCl + NH₃ → NH₄Cl
You use equilibrium arrows (⇌) if none of the reactants is a strong electrolyte:
CH₃COOH + NH₃ ⇌ CH₃ COONH₄
CH₃COOH + H₂O ⇌ CH₃COO⁻ + H₃O⁺
NH₃ + H₂O ⇌ NH₄⁺ + OH⁻"
Brønsted-Lowry acids and bases,How do we know which reactions are one way and which are reversible? Is there some fundamental concept that I should study?,"Where the _activation energy_ is low, the reaction is reversible. This typically occurs in reaction where the equilibrium (equilibrium constant) is affected by factors so that it can change from >1 (forward direction) to <1 (backward direction). This is mostly the case where concentration of solutions or pressure in gases has an effect."
Brønsted-Lowry acids and bases,Does ammonia act both as an acid and a base in aqueous solution? because it is given that it repeatedly accepts and donates protons,Ammonia is a weak base in water. It behaves as a Bronsted-Lowry base because its lobe pair accepts a H+ ion. Its conjugate acid NH4+ behaves as an acid a Bronsted-Lowry acid.....
Brønsted-Lowry acids and bases,Why aren't strong acid and base reactions also reversible?,"Because they fully dissociate, or fully react. Their Equilibrium constant is so high, and the equilibrium is shifted so far right that all of a strong acid dissociates and does't want to be put back together."
Brønsted-Lowry acids and bases,"In the "Example 3: Ionization of a weak base", why NH3 acts like a base and not like an acid?","I was wondering as well, but possibly that ammonia likes to form ammonium ion by accepting a proton, and that's why it acts like a base."
Brønsted-Lowry acids and bases,"The word "species" in this article means "compound", right?","Chemical species are atoms, molecules, molecular fragments, ions, etc., being subjected to a chemical process or to a measurement. Generally, a chemical species can be defined as an ensemble of chemically identical molecular entities that can explore the same set of molecular energy levels on a defined time scale."
"pH, pOH, and the pH scale",How does the temperature affect the pH and pOH?,"At 100C the pH of water is 6.14, so higher temperature decreases the pH. The opposite is true for pOH: higher temperatures increases the pOH."
"pH, pOH, and the pH scale",What does M stand for in the unit labels?,M stands for the unit of Molarity of the solution.
"pH, pOH, and the pH scale",Can someone please explain what are monoprotic and diprotic acids? Thanks.,"H2SO4 is a typical diprotic acid (2 protons can be released in aqueous solution, however one at that time)
H2SO4 +H20 gives HSO4- + H+/H3O+
then,
HSO4- +H2O gives SO42- + H+/H3O+"
"pH, pOH, and the pH scale","Could someone explain the difference between acid strength and concentration? According to me, a strong acid will fully ionise in water compared to a weak acid which will partially ionise. Therefore a strong acid will contribute more H+ ions than a weak acid. Therefore, the pH of a strong acid solution will be higher than a weak acid solution.

Is this correct?","Nice question!! It is important that you don't confuse the words strong and weak with the terms concentrated and dilute. At the same concentration, a weak acid will be less acidic than a strong acid. However, if you have highly concentrated weak acid (almost pure) and compare this to a very diluted strong acid (like 1 drop of HCl in a swimming pool) then the pH of the weak acid will be much more acidic than that of the strong acid."
"pH, pOH, and the pH scale","how can we solve pH,pOH numericals without using scientific calculator during our examination?","Unless you are using perfect numbers of base ten (e.g. 10^-7, 10^-2, etc.) there is no way to do it because you cannot easily do logarithms. If you are asked to do these calculations without a calculator, there is a good chance minimal if any extensive calculations are required.

Example: log(10^-6) = -6"
"pH, pOH, and the pH scale",How can NaOH have a pH scale? How can a base add H+ ions to the solution? It adds OH- ions right?,"NaOH does not have a pH, but an aqueous solution of NaOH does.
Water contains both H⁺ and OH⁻ ions.
Adding NaOH increases the concentration of OH⁻ ions and decreases the concentration of H⁺ ions.
But there are *always* some H⁺ ions present, so aqueous NaOH solutions have a pH, usually between 7 and 14."
"pH, pOH, and the pH scale",How does pH+pOH= 14? Where does the random number come in?,"There is no random number.
The formula comes from the ion product for water.
[H⁺][OH⁻] = 1.00 × 10⁻¹⁴
∴ pH + pOH = 14.00"
"pH, pOH, and the pH scale","Hi
I feel like there's a step missing.I'm not sure why the pH as an exponent is negative & where the minus sign comes from.I understand that the logarithm (of base 10) was changed to an exponent.What is this law of logarithms called?
pH= -log (H+)
10^-pH = (H+)

Also I was trying to figure it out with numbers pH=-(log 10^-4)
and I got 10^-pH =10^-4 and I'm not sure where to go from there to obtain the pH.Do I just cancel out the 10s & minuses that are on both sides to get a pH of 4,to cross off these I have to divide/multiply both sides by some number(s) would these numbers be 10 and multiplying the exponents by -1 to get rid of the minuses because the pH scale is usually positive numbers?
Thanks!","This is the _power rule_ of logs. When you have a number in front of a log term, this is the same as raising the log term to that number. For example, 4log(3) is the same as log(3^4).

With pH, the number in front of the log is -1 (because pH = -log [H+]). Therefore, using the power rule, we can re-express this as pH = log ([H+]^-1).

Using another log rule, we can express each side of this equation as an exponent of 10 and  we get:

10^pH = 10^log ([H+]^-1). 

Using a definition of logs, the right hand side of this equation now just becomes [H+]^-1. So we have:

10^pH = [H+]^-1    

The right hand side can be expressed as 1/[H+] giving us:

10^pH = 1/[H+]

Multiplying each side by [H+] and dividing each side by 10^pH gives:

[H+] = 1/10^pH which is the same as saying [H+] = 10^-pH.

As an example, if the pH is 7, then [H+] = 10^-7."
"pH, pOH, and the pH scale",what is -log? is it a number?,"Log is a maths function, it stands for logarithm. 

We use a log scale so we can visualise the concentration of H+ ions easier as we don't without have to deal with lots of decimal places etc."
Arrhenius acids and bases,what is the difference between Aqueous and liquid,"Aqueous means it's in a solution, liquid is just a state."
Arrhenius acids and bases,are hydrogen atoms the cause of the acidic taste,"Yes, though to be more specific, it is the H+ *ions* that indirectly cause an acidic food to taste sour. 

To put it simply, when acids found in the food combine with saliva in your mouth, H+ ions are produced. These H+ ions react with the protein molecules on your tongue and cause them to change shape. The change in shape causes the protein molecules to send an electrical signal to your brain that you experience as a sour taste.

Source: Introductory Chemistry(Third Edition) by Nivaldo J. Tro"
Arrhenius acids and bases,"Are certain compounds acid only when in aqueous solutions? For example, I found something saying, "The compound, H2S, is called hydrogen sulfide when it is in pure form but it is called hydrosulfuric acid when its acidic properties in an aqueous solution is being discussed." I am a little confused","The thing is an acid is any substance that increases the hydronium ion concentration of the solution or yields hydronium ions on dissociation. Thus, in aqueous solution only can a substance dissociate and form hydronium ions and be classified as an acid. Not in any other form can it yield a H+ ion. I hope it helps..."
Arrhenius acids and bases,What is meant by "dissociation?","It means "to fall apart" or the opposite of parts coming together (opposite of association). Basically, when A-B are together then they can dissociate by forming A separated from B."
Arrhenius acids and bases,Are Arrhenius and Bronsted-Lowry just different ways to define an acid or a base or are they a different class of acids and bases all together??,"It's a different way to define acids and bases. It's simply an extension to the theory of Arrhenius. Arrhenius defines acids and bases by the dissociation products that are formed when the acid or base is added to water, while Bronsted and Lowry define acids and bases by the reactions that occur when both are added together. Basically, acids in the Bronsted-Lowry theory donate protons (H+) to other substances while bases accept them to produce water (OH- + H+ = H2O)."
Arrhenius acids and bases,i have read somewhere that water is a bit acidic but H is neutral  in nature?so what can we say about it?,"Water contains H⁺ ions, which are acidic, and an equal number of OH⁻ ions, which are basic.
The two effects cancel each other, so water is neutral."
Arrhenius acids and bases,"if we are able to separate cl- ion from hcl solution what do we get ? if we get hydromium ions , is it is acidic ?","HCl + H₂O → H₃O⁺ + Cl⁻
Yes, we get hydronium ions, and the solution is acidic because the HCl increases the concentration of hydronium ions in the water."
Arrhenius acids and bases,"I don't understand that when hydronium exists instead of hydrogen ions in water, why doesn't hydronium react with water instantly to form something else since it's an ion.","Not all ions are reactive (think of dissolving salt in water to give Na+ and Cl- ions) - it depends on the circumstances. 

H+ ions are more reactive than H3O+ ions, so when an acid dissociates in the water, the protons immediately latch on to water molecules to give H3O+ ions which are more stable than H+ ions."
Arrhenius acids and bases,What other definitions are there?,"Bronsted Lowry acids see basically the same thing as Arrhenius acids, but it also introduces the idea of conjugate bases and acids.

Lewis acids accept a pair of electrons and Lewis bases donate a pair of electrons. Lots of metal chemistry is based on them being Lewis acids."
Weak acid-base equilibria,"for the example 1: calculating the % dissociation, the part where the ICE table is used and you can use the quadratic formula to find concentration "x", the two answers I got for x was x= -0.01285M and x=0.01245M. You guys said the concentration I should have found is 0.0126M. I was trying to figure out which of the "x" is the correct one ( I assume since a negative concentration can not exist, the concentration has to be 0.01245M) and I have gone through my calculations a few times, and I don't know where I went wrong. Is it a rounding error?","What you've calculated using the quadratic formula is correct. As you rightly say, you can't have a negative concentration, so the viable answer is 0.01245 M. 

If you use the small x assumption, then it comes out as 0.012649 M. You would expect a small difference in the result depending on which method is used. So it's strange that the article says that either method will give x=0.0126 M. 

My guess is that the author of the article probably used the small x method and perhaps didn't check the quadratic formula result. 

However, the difference is so small that it's negligible,"
Weak acid-base equilibria,"In example 1, why is the formula for % dissociation [A-]/[HA]*100% and not [H3O+]/[HA]*100% or [H3O+][A-]/[HA]*100%? Is this a stupid question? Sorry, if it is.","It's not a stupid question.
You can use either [A⁻]/[HA]₀× 100 % or [H₃O⁺]/[HA]₀× 100 % to calculate % dissociation of a weak acid.
Your last formula is just Kₐ×100 %, so that one is wrong."
Weak acid-base equilibria,So all of these are happening in water. What if these reactions aren't happening in water? Is there a situation like that? Like in gas? or something? Not something necessary to think about?,"This is an interesting area, but I don't know much about this – I certainly don't remember learning about this in 1st or 2nd year undergraduate chemistry.  However, acid-base reactions definitely take place in solvents other than water and even in the gas phase.  

For non-aqueous solvents, the pKa values for an acid may be higher or lower than they are in water depending on the acid and the solvent.  The wikipedia article on this is somewhat readable: 
https://en.wikipedia.org/wiki/Acid_dissociation_constant#Acidity_in_nonaqueous_solutions  

An example I found for a gas phase acid-base reaction:
https://www.youtube.com/watch?v=60vtFe42sGs
(NB: the demonstrator shows a deplorable lack of concern for modeling safe laboratory practices!)"
Weak acid-base equilibria,"Is it possible to find the percent dissociation of a weak base, or is it only applicable to weak acids?","You can find the percent ionization of a weak base. This is analogous to finding the percent dissociation of an acid, except you are interested in what percentage of the base became ionized by bonding to an H+ ion."
Weak acid-base equilibria,why are we making ICE tables here?,"ICE tables are just a way of organizing data. You don't have to use them, but it often is one of the best ways to keep track of lots of different numbers."
Weak acid-base equilibria,Well i'm a 3rd grader and I want to learn this and isn't OH weak?,"OH- is actually considered to be a strong base, as its conjugate acid, water (H2O), is a weak acid."
Weak acid-base equilibria,"In the percent dissocation example above, and in the last step (step 4), why did we use the [HNO3] as 0.400 M rather than (0.400-x) which should be the more accurate concentration (after we found x=0.0126)?",Because that’s how percent ionisation is defined. It’s dissociated / initial.
Pressure-volume work,"Work = Pext * V ..but why Pext ,why not Pinternal ??, it doesnt sense to me ,please explain.","Another way to think about it:  if you are strong enough to lift 100 lbs, but only lift 20 lbs, is the work based on what you COULD move or ACTUALLY move?  It's similar for a gas.  Just because its internal pressure is 100 atm, if it only has to push against 20 atm, then that defines the amount of work.  Would it take any work to push against a vacuum (Pext = 0)?  No.  Just like it wouldn't take any work to lift 0 lbs (or 20 lbs if there was no gravity).  It's all about the resistance."
Pressure-volume work,"I'm a bit confused with the sign of work in physics and chemistry. 
In physics it is given that work is negative when the gas compresses and is positive when expands but in latter it is given that work is positive when it compresses.  Also i just saw equation for internal energy,  in chemisrty it's  dU=q+w and in physics it's dQ=dU+dW.  Why are they different?","In chemistry, the convention is that anything going out of the system is negative and anything coming into the system is positive.
If your system is a gas in a piston, work is being done on the system when it is being compressed, so the work done *on* the system is positive, and the work done *by* the system is negative."
Pressure-volume work,"Can we state:
During a process, (work done by system) + (work done on system) = '0'
?",but as i understand there are no such perfect system an there is always some amount of  conversion loss as friction or heat.
Pressure-volume work,In the work done equation w=−Pexternal×ΔV why is the external P negative? what does it have a negative sign before it?,"Yeah, think of it as -(PdV) rather than (-P)dV, although those are mathematically identical.  If anything, think of it as P(-dV) since a decrease in volume is positive work and an increase in volume is negative work."
Pressure-volume work,"Hello,
Could someone please simplify this text in the article (below)?
Thank you!
This schematic also shows how the movement of the piston can be translated into other motions within the engine. In a gasoline engine, the pressure inside the piston changes when the fuel is combusted inside the piston, releasing thermal energy and causing the volume inside the piston to increase. The volume inside the piston decreases when the gas is allowed to escape from the piston. As that process is repeated, your wheels can move!","It's basically saying that the gasoline combusts inside the piston and this releases heat. The heat causes the gases in the piston to expand and this forces the piston out. This movement of the piston is mechanical work that can be used to move the wheels. 

The combustion gases are then released through a valve and the piston moves back, ready to start the cycle again."
Pressure-volume work,Why is the conversion between Liter-atmospheres and Joules the same as atmospheres to kiloPascals?,101.325J = 101.325N*m ; 1L*atm*(1m^3/1000L)*(101.325kPa/atm) = (1m^3*101.325kPa)/1000 = 1m^3*101.325Pa = 1m^3*101.325N/m^2 = 101.325N*m = 101.325J    tried to break that down as much as possible hope it helps. Essentially the 1000 factor from converting L to meters cubed cancels out the kilo in the the kilopascal. Then the only other factor left is the 101.325.
Pressure-volume work,why is it -P in the equation of pressure-volume work?,"It's meant to show if energy is flowing into or out of the system when work is involved. 

For example if you have a sample of gas in a flexible container and it expands the container to a greater volume than its initial volume, then that results in a positive ΔV. So without the negative sign in the front of the PΔV, the work would be positive. And a positive work means energy went into the system and resulted in a higher amount of energy than when it began. Which doesn't make sense since the gas has to exert force to expand the container and hence had to use up energy to do so. So if it used energy to expand the container, why then would it have gained energy? That's why the negative sign is include to show that the gas was performing work and losing energy to the surroundings. 

Hope that helps."
Pressure-volume work,What is the s you are squaring in the first  formula above for the energy of work? (5th paragraph of Pressure-Volume Work: Work Done by a Gas),If you are referring to the 1 J= 1 kg*m^2/s^s. They are just saying that 1 Joule = 1 kilogram meter-squared per second-squared
N/A,Well I got what the formula for gibbs free energy is. but what's the nature of this energy and why is it called 'free'? It does free work is what textbooks say but didn't get the intuitive feel.,"The word "free" is not a very good one! In fact, IUPAC recommend calling it Gibbs energy or the Gibbs function, although most chemists still refer to it as Gibbs free energy.

Gibbs originally called it _available energy_ and that is a good term because it is the energy associated with a chemical reaction that is available (or you could say _free_) to do work, assuming constant T and P."
N/A,"Is there a difference between the notation ΔG and the notation  ΔG˚, and if so, what is it?",STP is not standard conditions. Standard conditions are 1.0 M solutions and gases at 1.0 atm. Standard conditions does not actually specify a temperature but almost all thermodynamic data is given at 25C (298K) so many people assume this temperature.
N/A,"In the subject heading, 'When is ΔG is negative?', is it a typo that it says 
'When the process is endothermic, ΔHsystem > 0, and the entropy of the system decreases, ΔSsystem>0, the sign of ΔG is positive at all temperatures. Thus, the process is never spontaneous' shouldn't the entropy be < 0? if there is a decrease in entropy?","I think you are correct. Change in entropy must be smaller than zero, for the entropy to decrease. It is a typo. You can cross-check from the figure."
N/A,The Entropy change is given by Enthalpy change divided by the Temperature. Then how can the entropy change for a reaction be positive if the enthalpy change is negative?,"Great question!  Figuring out the answer has helped me learn this material.

One way to define entropy is `Q/T` (where `Q` is the heat associated with a *reversible* process {also note that `∆H` is only equal to `Q` when `P` is constant}).

For spontaneous and thus *irreversible* reactions, the `∆S` is the same as for a *reversible* reaction (because `S` is a state variable it doesn't depend on how we got from one condition to another). In contrast, `∆H` is not equal to `Q` (because this is not a *reversible* reaction). 

A later video helps explain this:
https://www.khanacademy.org/science/chemistry/thermodynamics-chemistry/gibbs-free-energy/v/more-rigorous-gibbs-free-energy-spontaneity-relationship"
N/A,"Hey I´m stuck: The ∆G in a reaction is negative but the ∆H was positive and it is assumed that a change temperature doesn´ t significantly affect entropy and entalpy. What does this do to 1) spontanity 2) spontanity at high temp 3) value or sign of ∆S 

i read it 3 times now but i´m still insecure - :(","This looks like a homework question, so I'll give you some hints to get you on the riht path rather than answering directly.

3) We know that ∆G = ∆H - T∆S.  Solving for ∆S, we have:

∆S=(∆H-∆G)/T.

We know (from the question) that ∆G is negative and that ∆H is positive.  Temperature is always positive (in Kelvin).  From these values, we can know for certain whether ∆S is positive or negative (hint: remember that we are subtracting ∆G!).

1) Knowing the sign of ∆G is enough to say whether the reaction is spontaneous or not under these conditions.  If ∆G is negative (from the question), is the reaction spontaneous or non-spontaneous?

2) Let's use ∆G = ∆H - T∆S again.  Since ∆H and ∆S don't change significantly with temperature (given in the question), we can assume that they keep the same signs and values: i.e. ∆H is still positive and ∆S is still whatever sign you figured out above.  As T increases, the T∆S component gets bigger.  T is always positive, so if ∆S is positive then a bigger T∆S will make ∆G more negative (since we subtract T∆S).  If ∆S is negative, then the negative signs (from the subtraction and the sign of ∆S) will cancel out, and so as T∆S gets bigger, ∆G will get more positive."
N/A,"Hi all,  Sal sir said we would  prefer the reaction to proceed in a particular direction (the direction that makes our product!), but it's hard to argue with a positive ΔG! ( located before summary at other applications of del G) .can anybody please explain?","If ΔG is positive, then the only possible option is to vary the temperature but whether that would work depends on whether the reaction is exo- or endothermic and what the entropy change is."
N/A,how do i see the sign of entropy when both reactant and product have the same phase,"We have to look up the ΔS for the whole reaction in a table (or test the reaction ourselves... I'd rather look it up!). The value will be either positive or negative. If the reaction can result in a phase change then we might be lucky enough to find a list that has the reaction with reactant and products in the phases we need.

Otherwise we could calculate the change in energy and the use the specific heat equations to see if the phase would change. The example above with melting ice looks a little different because the reaction was a phase change (ice to water) instead of the usual combining or splitting of molecules."
N/A,can an exothermic reaction be a not spontaneous reaction ?,"Sure.  Paper doesn't light itself on fire, right?"
N/A,"Is the reaction H2O(l) to H20(s) spontaneous or non spontaneous? The entropy, S, is positive when something goes from a solid to liquid, or liquid to gas, which is increasing in disorder. However, in this equation, water is going from a liquid to solid, so S is negative, and in the Gibbs free reaction equation, S must be positive for a reaction to be spontaneous. How do we determine, without any calculations,  the spontaneity of the equation?","Using that grid from above, if it's an exothermic reaction (water is releasing heat into its surroundings in order to turn into ice), we know it's on the left column. The entropy of liquid water is higher than ice (water as a solid state)so therefore it is not always going to be spontaneous. Putting into the equation, ΔH<0 because it's exothermic, and ΔS<0 because entropy is decreased. Therefore, the reaction is only spontaneous at low temperatures (TΔS). If you think about its real-world application, it makes sense. Liquid water will turn into ice at low enough temperatures."
Bond enthalpies,"In Step 4, why is it required to add the C-C bond enthalpy? That bond was formed prior to the double bond, it doesn't disappear during the reaction. Or does the double-bond enthalpy account for both bonds instead of just the pi bond that is destroyed?","The double bond enthalpy counts for both bonds. Also remember that single, double, and triple bonds are not additive!  E.g. the bond enthalpy of a single bond + single bond =/= double bond."
Bond enthalpies,"Why do fuels with more Carbon bonds, when combusted have a larger delta H value?","My answer is pretty long and based on my observation of calculating what happens when you burn Methane, Ethane and Propane. There is a  tl;dr at the end of the answer.

In Alkane series (saturated) hydrocarbons (CnH2n+2), every time you add a carbon to the chain you essentially add another C-C bond and 2 C-H bonds but you will also have to create another CO2 and H2O molecule (C02 comes from the C added and 02 used for combustion, and H2O comes from the 2 H added and 02 used for combustion).
Now minding that the bond strength of C-H is 337kj/mol and C-C is 607 kj/mol you will have to add an additional 944kj/mol every time you add a Carbon to your chain to break the "fuel" compound. 
Now don't forget that everytime we add a Carbon we will need more oxygen for the combustion reaction, from what I saw trying to balance some combustions of Alkane fuels we will need an extra 1.5 O2  for every 1 Carbon we add to the chain.
So every time we add a Carbon we need to break an extra 1.5 0=0 bond which is 1.5x498kj/mol=747kj.
Now we know that for every C we add we need to add 944+747kj (1691kj) to break the bonds on the reactants side.
Now remember that ever additional C yields us additional 1 CO2 and 1 H2O.
Thats 2 C=0 bonds and 2 H-O bonds we need to create.
The required energy to break a C=0 bond is 749kj/mol and the energy to break an H-O bond is 428kj/mol, so in order to form those bonds we have to add a - for each of those values.
That means we will have to release 749x2 + 428x2 (2354kj/mol) of energy for every C we add to the chain.

tl;dr: So for every carbon we add we get 1691kj to break bonds and then 2354kj is released to form bonds, so net Enthalpy change is -663kj every time you add an additional Carbon (and 2 Hydrogens).

Hope this helps :)"
Bond enthalpies,The definition for bond enthalpy is the energy required to break 1 mole of bonds in gaseous covalent molecules under standard conditions? What are the standard conditions? High temperatures and low pressure?,"standard temperature and pressure (STP) as a temperature of 273.15 K (0 °C, 32 °F) and an absolute pressure of exactly 100 000 Pa (1 bar, 14.504 psi, 0.98692 atm)."
Bond enthalpies,"change in enthalpy during a reaction is mainly due to change in internal  energy of the system which includes potential,rotational,translational KE as well. But in this case we are considering only the potential energy.So does that mean rotational,translational KE are not affected?","We are explicitly calculating *bond* enthalpy - to me this suggests that we are focusing on the potential energy. 

However, when we calculate an enthalpy of a reaction, we are often§ talking about how much 'heat' has been released (or absorbed) and this must be due to changes in the motion of the individual molecules. 

So, I think we could veiw these calculations as describing the interconversion between potential and kinetic energies of the molecules.  

§note: Clearly there are many exceptions such as:  Chemiluminescence, where the energy is given off as light; and ATP powering molecular motors such as kinesins.  However, in these cases we just replacing heat with other forms of light and (non-heat) kinetic energy, respectively (or more likely a mix of heat and these other forms of energy)."
Bond enthalpies,"In Step 1 of the example, why would the Carbon = Carbon bond need to be broken if the resultant has a Carbon - Carbon bond? Wouldn't just one of those bonds need to break? Is there a chemical reason they both need to break & then later one re-forms? It just seems inefficient.","It is done this way as an accounting exercise. Three C-C bonds are broken and one C-C bond is formed - in others words, to do the calculation you assume that all relevant bonds are completely broken and then reformed. But this is _not_ to suggest that this is the mechanism by which the chemical reaction occurs - it certainly wouldn't go by this route. Neither, for that matter, would the H-H bond split to give two hydrogen radicals.

Think of this as just a way of doing the calculation."
Bond enthalpies,Is it mandatory to learn the bond enthalpy values for all chemical bonds?,"It will depend on your school/teacher but usually, they won't expect you to memorize all of the bond enthalpy values. My teacher when I did AP Chemistry gave us a bond enthalpy value table whenever we had a test or quiz."
Bond enthalpies,"I had a few questions:
- Can there be a reaction, which has ∆H = 0, so that the energy of reactants (e.g 500Kj) and products (e.g 500Kj) is equal, so that the enthalpy of reaction is zero (∆E = 500 - 500 = 0)?
- I read that the enthalpy also depends on the state of the reactants, e.g when oxygen and hydrogen gases react to produce water vapor, the enthalpy change is -483.7 kJ. But, when the same reactants react to produce liquid water, the enthalpy change is -571.5 kJ. Why the difference?","Yes it is possible to have a reaction with an enthalpy change of 0. Which I suppose would make it neither exothermic or endothermic technically. 

Matter has different amounts of energy at different physical states. Think back to energy calculations for phase changes using Q = MCΔT. In general the gaseous version or a chemical has more energy than the liquid version of it. So producing liquid water versus gaseous water will release more energy because the liquid is at a lower energy level than the gas. Essentially that 87.8 kJ difference is how much more energy gaseous water has compared to liquid water.

Hope that helps."
Bond enthalpies,how to identify which carbon bond will break on reactant side and which carbon will form bond .Is it just the carbon with more bonds will break but how could we identify with which carbon bond will form on product?,This will become more obvious as you study organic chemistry. But a triple C-C bond is far more reactive than a single C-C bond and it loves to combine with hydrogen.
N/A,"For I know that Kelvin is always positive, but why in the example, why Kevin degree is negative?","Couple things:
1.  Be careful not to call it "Kelvin degree" or "degrees Kelvin."  They are called "kelvins" (lowercase K).
2.  The temperature in kelvins is still positive, but the CHANGE was negative."
N/A,"Why is it in my book it is indicated that q = C x change in T, where C is heat capacity (J/C). C is then equal to (m x s x change in T)hot + (m x s x change in T)cold/-change in T, where s is the specific heat capacity (J/gC). Can you please explain to me? I'm quite confused.","q = CΔT and q = msΔT, so C = ms.
C is the *total* heat capacity of the object.
s is the *specific* heat capacity, i.e. the heat capacity per gram.
If you multiply the heat capacity per gram (s) by the number of grams, you get the total heat capacity (C).
Usually you know the specific heat capacity for water, but you don't know the specific heat capacity of the calorimeter.
But it is quite easy to do a separate experiment to determine the total heat capacity of the calorimeter.

You often set up your calculations like this:
heat for water + heat for object + heat for calorimeter = 0
q₁ + q₂ + q₃ = 0.
q₁ = m₁s₁ΔT₁ for the water
q₂ = m₂s₂ΔT₂ for the object
q₃ = CΔT for the calorimeter.
If you then know everything but one of the variables, you can calculate it from the above equations ."
N/A,i did not understand how chemists use the melting point to identify  the purity of a substance,"Chemists can heat up substances to the point when they start to melt. At this temperature, the chemists can compare this value to a table of standard results from a data table/source/reference. The standard results are the true results for that particular substance. However, when a substance has an experimental melting point significantly higher than the standard data book value, then we know there must be impurities present. Impurities may have a higher melting point than the substance we're interested in, so the overall melting point for the impure substance is higher than expected."
N/A,"Why the Zeroth Law of thermodynamics is called so,is it the most basic law?","zeroth law was discovered after the first law and other thermodynamic laws 
and because it was the most basic law they named it zeroth law."
N/A,"Underneath the picture of the ice cubes, the caption reads, "As ice melts, heat is transferred from the water to the surroundings." Shouldn't it read, "As ice melts, heat is transferred from the surroundings to the ice" or something similar?","yeah, i would say you're right. heat is always spontaneously transferred from (object of) higher to lower temperature."
N/A,Why do kelvins don't have degree?,"In general, 'degrees' are found in units which are mainly arbitrary. Fahrenheit and Celsius are meant to be convenient instead of absolute. The same goes for angle degrees, since that also divides the circle into 360 degrees arbitrarily. Like, there is no 'degrees' in radians, which is the 'natural' way of measuring angles.

The kelvin is the SI base unit of temperature. it is the absolute temperature scale. *By absolute we mean that the zero on the Kelvin scale, denoted by 0 K, is the lowest temperature that can be attained theoretically*. On the other hand, 0 F and 0 C are based on the behavior of an arbitrarily chosen substance.

For Kelvin. Temperature is defined in terms of the average energy of particles in a system, and Kelvin is directly proportional to that -- the zero in the Kelvin scale corresponds to absolute zero, and not any arbitrary temperature, and Kelvin is the 'natural' unit to measure temperature."
N/A,Can somebody give me an example that shows the difference between heat and temperature?,"A thermometer shows the temperature because it measures (compare) the degree of agitation of its molecules in relation to the degree of agitation of the molecules of the environment, but this is only possible because you transfer heat to the thermometer. This is because 2 bodys at different temperatures tend to get in the thermal balance between them with the one that is hot by giving energy to the coldest in the form of heat, so on a cold day you wear a jacket not to heat yourself but to reduce the loss of thermal energy to the environment in the form of heat."
N/A,Difference between work and heat?,"Work is a measure of amount of energy transferred to the system by applying force on it along the displacement , heat is the process of transferring of energy between two systems due to difference in the temperature"
N/A,Why is the heat of an iceberg greater than that of a pot of boiling water?,"Heat isn’t something that objects possess. Thermal energy, the energy associated with an object’s temperature, is what people usually mean when they say heat. Heat itself is the transfer of thermal energy from one object to another. Thermal energy is the thing that object possess, but heat is a process that occurs between objects.

If we compare an iceberg to a pot of boiling water, each of the molecules of both objects have their own amount of thermal energy. All pieces of matter, even very cold ones, have at least some thermal energy because they are in motion at the atomic scale and this is motion is thermal energy. Probably the part that confuses people with a question like this is that a pot of boiling water is hotter than an iceberg and we associated high temperature with thermal energy. Which that is partially true, but temperature is a measure of the average thermal energy of all molecules in a system. The pot’s molecules are on average more energetic than the iceberg’s molecules, but the iceberg has substantially more molecules than the pot. And the total amount of all these iceberg molecule’s thermal energies is greater than the pot’s molecule’s total thermal energy. 

Hope that helps."
Balancing redox equations,"Why is the reduction half reaction is written like this:
2H​+​​(aq)+2e​−​​→H​2​​(g)
Isn't it:
H​+​​(aq)+2e​−​​→H​2​​(g)

Since the base equation contains:
H​+​​(aq) -> H​2​​(g)

I do not understand this...","H​+​​(aq)+2e​−​​→H​2​​(g) balances neither the charge nor the mass.
Left side: Charge of -1; one H
Right side: 0 charge; 2 H atoms (bonded as H2)
For balancing Redox reactions, it is necessary to first balance the main atoms (through adjusting stoichiometric coefficients), then the charges (through electron transfer and as per conditions - acidic/neutral/basic)."
Balancing redox equations,"In the example of combustion reaction, the oxidation number of C in C8H18 comes out to be -9/4. How is this possible? Electrons cannot be transferred in fractions right?","It may be better to consider that there are two different carbon oxidation numbers rather than the fractional one. 

The two on each end are bonded to 3 hydrogens so are -3, the six in the middle are bonded to 2 hydrogens so are -2"
Balancing redox equations,"It says above for Disproportionate Reaction: "If we analyze the oxidation numbers for chlorine, we see that the reactant ClO− ​is being oxidized to ClO​3​− (where the oxidation number increases from +1 to +5)."

I can't see what goes from +1 to + 5. Is it Cl? If so, how so?","Cl is +1 in ClO^- and goes to +5 in ClO3^-

As oxygen is more electronegative than chlorine (in the Pauling scale), we assign it its preferred oxidation number which is -2. 

In a molecule the oxidation numbers of all atoms sum to the charge. 

So in ClO^- the oxidation numbers need to sum to -1. If oxygen is -2 then chlorine needs to be +1

-1 = Cl + O
-1 = x + -2
x = +1

For ClO3^- it's the same idea, but now we have 3 oxygens. 

-1 = Cl + 3O
-1 = x + -6
x = +5"
Balancing redox equations,"In the Practice question above, it does not specify what type of redox reaction it is. How do I know what type it is and what to put in as my answer? P.S. I got it wrong.","Compare the reaction to the types explained in the article -- 
1) Is there molecular oxygen (O2) involved? *NOPE* not oxidation
2) Has a single reactant undergone both oxidation and reduction? *NOPE* not disproportionation
3) Are two elements trading places within a compound? 
Doesn't look like it, but what if we look at the complete equation (rather than the net ionic equation we are given).
• there must be a counter ion that came with the "H+" ... let's pretend that we added HCl ...
This gives us the reaction:
`Al(s) + HCl(aq) → AlCl3(aq) + H2(g)` 
Now we can see that it fits the definition for a single replacement reaction!


To answer the question you don't need to know what type of reaction it is, you just need to make sure that you've balanced electrons (charges) as well as atoms.

The method shown above is to separate the oxidation and reduction reactions into half reactions ... did you try that?"
Balancing redox equations,What do you mean by saying "we can check to see if any reactants and products appear on both side"? Do you have an example?,"In this context, I think what he means is that if any ion is in an identical form on the left and right side of the equation then they cancel out and can be crossed out. In other words, identify any spectator ions."
Balancing redox equations,Why is MnO4 reduced and not oxidised ? It was an anion (permanganate) and became neutral MnO2 so it must have LOST electrons?,"We compare the oxidation states of atoms to determine if they’ve been oxidized or reduced. For the half-reaction of permanganate going to manganese dioxide, we’re comparing the oxidation states of the manganese and oxygen atoms individually, not the entire ions. Oxygen almost always has a -2 oxidation state so it stays constant here and is neither reduced or oxidized. Manganese begins with a +7 oxidation state in permanganate and is reduced to +4 in manganese dioxide. Since the oxidation state decreased, it was reduced. 

Hope that helps."
Balancing redox equations,Where does the water from the combustion example go? (car engine example) Steam?,"Yes, you are correct in the form of vapour it comes out of the engine and enters the air."
Balancing redox equations,"For Fe2O3, I know that the oxidation mu,her for oxygen is always -2 but then it says that the oxidation state of iron is +3. How does that make the compound neutral? Wouldn't the charge be +1 and not neutral?","You aren't taking in to account that there are 2 iron atoms and 3 oxygen atoms in one Fe2O3 molecule. 

3 oxygens with oxidation numbers of -2 each, -2 * 3 = -6
Fe2O3 is a neutral molecule so we know the oxidation numbers all must sum to 0
So the two irons must have oxidation numbers that equal +6, +6 / 2 = +3"
Balancing redox equations,"1.)Im not sure how to recognize if the oxidation number is -2 or +2.....
2.)For example, in CO2, is 2 the oxidation number or the number of atoms or the valency??
Pls answer in detail...Im really confused.","The oxidation number is the number of valence electrons an atom is assumed to have when the electrons are counted according to certain arbitrary rules.
Two important rules are;
1. The oxidation number of O in its compounds is almost always -2.
2. The charge on a molecule or ion is equal to the sum of the oxidation numbers of its atoms.
Thus the oxidation number of an O atom in CO₂ is -2.
The two O atoms have a total oxidation number of -4.
Since CO₂ is neutral, the oxidation number of C is +4."
Reaction mechanism and rate law,How do we determine the slow or fast step?,"There are multiple ways to find which step is the slow/fast step without it being given to you.

1) Look at k. The smaller k is probably the slower step.

2) Look at the activation energy for each step. The step with larger activation energy is the slower step (as the fraction of collisions w/ enough energy to react will be smaller - activation energy requirement is higher) This derives from the Arrhenius equation:

k = A * e^(-Ea/RT)

where A and R are constants, T = temp, and Ea = activation energy.  As you can see, as Ea increases, k decreases. Thus, the higher the Ea, the slower the reaction rate."
Reaction mechanism and rate law,"The article says, "Intermediates are produced in one step and consumed in later step, so they do not appear in the overall reaction equation or overall rate law." What if the rate determining step involves a reaction intermediate? Then shouldn't the overall rate law contain the intermediate as well? Please tell what am I missing.","They don't go over this, but from what I've learned from my textbook, it is possible to have a rate-limiting step containing an intermediate. However, algebraic maneuvering is required to substitute an expression for the concentration of the intermediate so that it's removed from the overall rate law. These reactions will often have a fast equilibrium reaction as their first step."
Reaction mechanism and rate law,"How can you determine which step is fast or slow if you are told reaction order. For example, if you are told the reaction is a first order, how do you know which step is fast or which is slow?","If you are provided the complete mechanisms and the rate law of the overall reaction, it may be possible to infer the bottleneck reaction. If a curve that illustrates the change in energy throughout the reaction is provided, then the RDS is the step with the highest summit."
Reaction mechanism and rate law,Are we always going to be given whether or not the elementary steps are slow or fast,"In most formal tests, I think you would be given that, or they'd tell you how fast they are and you would be able to figure out which one is the slowest yourself."
Reaction mechanism and rate law,How do we decide whether a reaction is slow or fast?,By doing the experiment I believe. Or it was given in the question.
Reaction mechanism and rate law,If A + 2B  > C is a third order reaction does it have to be Rate = k {A} [B] squared? If B is mor influential on rate than A?,"No. You have to determine the rate law experimentally. The rate law may be rate = k[A]²[B].
The exponents in the rate law do not have to correspond to the coefficients in the balanced equation."
Reaction mechanism and rate law,"Hi,
I have some questions:
1- How we can determine the intermediate (elementary reactions) for our overall reaction? Assume that we are doing a leaching experiments and we have derived a reaction about our process. Now, how we can derive intermediate reactions? Should we assume them and use the trial and error method?
2- Is there any way, for example fixing some parameters and varying the other one to derive the leaching mechanism? 
Thanks for veryyyyyyy helpful courses :)","In all problems of equilibrium systems and reaction rates, we mainly deal with the gaseous substances. Liquids or solids( in small amount) don't affect the reaction. The leaching experiment doesn't conclude any gaseous substance. So, we can't derive intermediate reaction for a leaching experiment.
For your second question, the same logic can be applied. Leaching experiments are not associated with any gaseous substance. So, if you will change the phases, by varying parameters, it'll not be a leaching experiment any more."
Reaction mechanism and rate law,"Hello friends,
Just to be sure, mechanisms are given, correct? Or you have to perform the experiment. You don't have to just make one up?","Mechanisms don't necessarily have to be given. For example, in a test you may be asked to suggest a possible reaction mechanism considering a certain rate expression. This could mean that there could be multiple possible "correct" answers for the reaction mechanism. So yeah, you may "have to just make one up." I hope this answers your question."
Reaction mechanism and rate law,isn't rate order only determinable through experimentation? How come it says that it's always the coefficient next to the molecule here?,"We can create rate laws based on the coefficients of elementary reactions. And these elementary reactions can be combined to form a single, overall chemical equation. The rate law from the slowest elementary reaction will be the same as the rate law for the overall reaction. 

The issue is that we can potentially create several combinations of different valid elementary reactions which will combine to create the same overall chemical equation. This is what is referred to as a reaction’s mechanism, or how exactly it progresses from the original reactants to the final products. The question becomes, how do we determine which of these mechanisms is the actual one the reaction is progressing with? And now this is why we need to experimentally determine the rate law and the orders of the reactants. 

The rate law we determine experimentally will tell us which mechanism is correct because the rate laws (for the slowest elementary reaction) will be identical. So we can create any number of possible rate laws, but to know the true one we use experimental kinetic data.

Hope that helps."
Types of catalysts,"What are some common catalysts to reactions in a school lab, for example?","Acid and base catalysts are extremely common! If you have ever used super glue, the reaction that makes the glue become tough is actually catalyzed by trace amounts of acid on the surfaces of things (like your finger, if you are unlucky)."
Types of catalysts,"Can a catalyst change the product of a reaction,? I meant ,if we get any product without using catalyst could be different from that ,we get from the reaction using catalyst?","Yes, that can happen. When two reactants are mixed in the absence of a catalyst, there may be a major route to Product A and a minor route to Product B, each route involving different reaction mechanisms. Hence Product A will predominate in this situation.

However, in the presence of a catalyst, it is possible that the minor route could be speeded up but not the major route. This would then lead to a predominance of Product B."
Types of catalysts,Can you further explain what a heterogeneous catalyst is? What does "a different phase mean"? An how would you test for a heterogeneous catalyst?,"Phase refers to solid, liquid, gas, or aqueous. A catalyst is heterogeneous when it is a different phase from the reactants whose reaction it is catalyzing. So if you have a platinum metal catalyst (solid) catalyzing the reaction of H2 and ethene (gases) then you would consider the platinum to be a heterogeneous catalyst."
Types of catalysts,"If the catalyst will not be consumed, will it work until all reactants are turned into products? Also how to determine how much of a catalyst is needed? is it by stoichiometry (as if it's a reactant)?","Since a catalyst is not used up in a reaction, you only need a small amount (a lot less than stoichiometric ammounts).

Catalysts speed up the rate of reaction, but they do not alter the position of equilibrium of a reaction. If without the catalyst your reaction would go to completion(all to products), even if very slowly, then yes, in the presence of catalysts, the reactants will all be turned into products. But if the reaction you are catalysing doesn't go to completion anyway, then the catalyst won't change that. This is because a catalyst increases both the rate of the forward and back reaction.

Whilst catalysts don't get used up in the reactions they catalyse, they may stop working for other reasons. For example catalytic converters in cars can be 'poisoned' when certain chemicals cover their surfaces."
Types of catalysts,How to know which catalysts to use in a chemical reaction or when the mechanism of such is given?,"There is really no way of predicting what will catalyse any particular reaction. This has to be determined experimentally.

If you are given an overall equation for a chemical reaction, if a catalyst is involved, its chemical formula should be given above the arrow in the equation (such as shown above in the sucrose example). If it's not, and you are just given a sequence of elementary steps for the overall reaction, then you need to identify a component that gets involved in the reaction but is then regenerated (ie, something that is not consumed so is there at the start and at the end).   

Be careful to distinguish between catalysts and intermediates. Catalysts are present at the start and at the end, while intermediates get formed part way through and then get consumed."
Types of catalysts,how do catalyst work on a particle level?,"If we go by collision theory, 
positive catalysts may either:
(1) *Reduce the activation energy* required for the reactant particles to become an activated complex.
(2) Force the particles to attain *multiple or altered 'transition states' in* such a way that the reaction takes place faster or with less energy.

BTW, positive catalyst is a term for a catalyst that speeds up a reaction. Negative catalysts slow down, or make it harder for a reaction to occur.

*Please note:  This* is a very simple explanation for an extremely complex topic and I cannot do it full justice. I suggest researching enzymes in the body to get a better idea of how intricate this subject is."
Types of catalysts,How do catalysts use adsorption process?,"For gas phase reactions, one or more of the gases are adsorbed onto the surface of the catalyst. Exactly what happens will depend on the reaction in question, but adsorption may, for example, weaken the bonds in the reactant molecules which facilitates the chemical reaction. 

This diagram shows the sort of thing that might happen - http://www.docbrown.info/page07/SSquestions/heterocatalysistrans1.gif. The intermolecular forces shown as dotted red lines are responsible for weakening the H-H and C=C bonds, which promotes the reaction."
Meet Syud Momtaz Ahmed,What is organic chemistry,"Organic chemistry focuses on carbon and carbon compounds.
Because each carbon atom can form up to 4 bonds, and can bond to other carbon atoms to make chains and rings, there are many, many, many kinds of organic molecules. 
Organic chemistry is also central to the chemical reactions of life, making organic chemistry important in understanding biology, too."
Meet Karen Wheeler,"I don't understand how you went from Chemistry research to OB/GYN.   Did you go to medical school after your BS in Chemistry?  If so, how long did it take?","Most Universities and Colleges accept Biology or Chemistry degrees as a Premed course, as they both are in Premed..."
Meet Mary O'Reilly,"ma'am, could you please explain to me exothermic and endothermic reactions?also could you please give a few examples","An exothermic reaction is one where heat is released.  An example is a hot pack that you might use to warm your hands when you're camping.

An endothermic reaction is one where heat is absorbed.  An example is a cold pack that you might have in your first aid kit."
Meet George Zaidan,"In the atmosphere, water is solute. How?","In the atmosphere, water droplets and water vapors are suspended in minute quantities, relative to the constituents like Oxygen and Nitrogen. Atmosphere or air is basically an aerosol, where the gases form the bulk dispersion medium and moisture (and actually some other unwanted SPM) form the dispersed phase."
What is velocity?,Can an object have a northbound velocity and southbound acceleration,"You can imagine throwing a ball into the air, the ball would have an upward (positive) speed immediately after throwing, but would be slowing down with an acceleration of -9.81m/s^2 (The acceleration due to gravity on Earth). So it'd have a positive velocity and negative acceleration, then when it peaked and started going down, it'd have a negative velocity and negative acceleration."
What is velocity?,"What if the line of the graph is curved? I know how to find the instantaneous speed given the function, but how do you find it given only the graph?","choose a time (t) at which  you want to find the instantaneous speed. 
Draw a tangent to the curve at that point (t)
Find the gradient of the tangent.

Its the same as differentiating and plugging in the value of t

OK??"
What is velocity?,Speed and Velocity are almost the same with the exception that speed is a scalar quantity and velocity is a vector quantity. Is this true?,"Not entirely actually. Speed takes into account the entire distance travelled over a time period, while velocity is the displacement over a time period. This usually doesn't matter unless the direction the particle is travelling switches"
What is velocity?,"example 2: Hungry Dolphin.
I thought that to find instantaneous velocity I would just look at where the line intersects 1 second. This gave me the answer of 4 instead of -4. Could anyone explain to me why it is -4? 
thanks, Jack.",The answer is -4 because the slope is negative.
What is velocity?,"How would you calculate velocity if the displacement is zero? For instance, a car traveling on a circular track that begins and ends at the same position.","size circumference of circular track is displacement. Starting position and ending at same position count as lap. Wherefore let *`C = pi*d`* where `C` is circumference, `pi = 3.1415` and `d` is diameter of circle. So now you can calculate velocity  like this:
`v = C / t`   or   `v = (pi * d) / t`"
What is velocity?,"An average in algebra is where you add numbers, say, 80, 40 and 30, and you divide that number by three, one for each quantity. So, if you can lay out where someone is running or driving a car, and they stay at a constant rate except for three speed changes, can you just add up the three speeds and divide by three?       So,  
     52mph        70mph        40mph
 |________|________|_________|
             52+70+40=162
               162/3
                 54mph average?","There is more that one type of average though. You're using the mean average. If you were to use the median, mode or range depending on the numbers you've been given you'd get a different answer with each of them. I would say it's best to stick with speed and velocity when dealing with physics questions. If you really want to find out if you can do it that way, try work some speed/velocity questions out both ways and see if you get the same answers."
What is velocity?,"for the example 1 where we used the disoriented iguana, how is the time interval 28 seconds?
I thought the formula for change in time was final time - intial time.
shouldn't it be 8-20=-12s?","You don't need a formula here, they tell you he went one way for 20 seconds and the the other way for 8 seconds.  That's 28 seconds. 
If you were using a stop watch, the initial time would be 0, the time when he turns around would be 20, and the final time would be 28.  28-0 = 28."
What is velocity?,what is terminal velocity?,"Terminal velocity is reached when gravity and air resistance balance, keeping an object in free fall from accelerating."
What is velocity?,Im not understanding how to find Instantaneous velocity is there any videos on this explaining how its done Thanks,The video before this doesn't really explain it very well. The next video here 'Position vs. time graphs explains it much better.
N/A,"I don't get why the slope is shown to be negative in the two examples, while both objects are gaining speed. Seems like the slope should be positive... What's the reasoning behind this?","These are acceleration vs time graphs. Any line ABOVE the time axis (a=0) indicates positive acceleration. and a line below the time axis indicates negative acceleration (Slowing down)
BUT The slope of the lines says NOTHING about the amount of  acceleration.
 The slope is only a measure of 'jerkiness' (or rate of change) of acceleration."
N/A,"Are there quantities like acceleration of jerk, jerk of jerk and so on?","Change in jerk is called jounce or snap. Change in jounce is called crackle. Change in crackle is called pop. (Yes, the names are hilarious!)
More information can be found here:
https://en.wikipedia.org/wiki/Jounce
https://en.wikipedia.org/wiki/Crackle_(physics)
https://en.wikipedia.org/wiki/Pop_(physics)"
N/A,"They keep referring to straight lines as curves. (i.e. "But multiplying the acceleration by the time interval is equivalent to finding the area under the *curve*. The area under the *curve* is a rectangle, as seen in the diagram below.") Why is this? _Is_ there a reason?","Area under a curve generally talks about the area under a specific geometric shape, be it a line or a curvature(sometimes known as concavity). Some teachers also teach it as 'area under the graph', so as long as you know what you're calculating, you should be fine."
N/A,"ok, but how do you go about making a acceleration time graph?",Or you could measure acceleration at each point in time with an accelerometer.
N/A,"The area under the acceleration-time graph is velocity.
That under the velocity-time graph is displacement (or may be distance).

What about that under the displacement-time graph, what would it be?","I believe it represents a negative derivative of displacement. This is called Absement and is essentially the "total" displacement. Essentially, the derivative of this is displacement, the "change" in Absement, and velocity would the derivative of displacement, the "change" in displacement, the acceleration being the second-order derivative, and so on.

The area under the curve is the anti-derivative, and in lay terms moving upwards. For instance, the area under acceleration-time graph is the velocity, moving upwards.

For reference, I located a list of the derivatives of displacement.

-1. Absement
0. Displacement
1. Velocity
2. Acceleration
3. Jerk
4. Jounce (snap)
5. Crackle
6. Pop
7. Lock
8. Drop
9. Shot
10. Put"
N/A,"in Example 1: Race car acceleration it is said that the driver had a constant velocity of 20 m/s and again she had it at 0s. but in the graph it is shown that at 0s she had a acceleration of 6 m/s2. so my question is if the graph is mistaken or it is right. since its clear that constant velocity means 0 acceleration and she had a constant velocity of 20 m/s at 0s, so it means the acceleration at 0s would also be 0m/s2 . am i right?","It states that the constant velocity was until the driver began accelerating at the end. At time = 0, velocity was no longer constant."
N/A,How can we calculate the jerk using only the information given by a velocity-time graph ?,"Take the second derivative of the v(t) graph to get J(t).
J(t) = da(t)/dt = d²v(t)/dt²"
N/A,last graph how did you find Vi = 10 m/s ?,It is written in the text of Example 2:"A sailboat is sailing in a straight line with a velocity of 10 m/s." Otherwise you can not know exact velocity from acceleration vs. time graph. You only know change of velocity (Δv).
N/A,"In the example 1 , retardation is taking place instead of acceleration (according to the graph because the line is pointing downwards). So how can the velocity of the car after 8 seconds be more than 20m/s, similar confusion in example 2 .  I don't understand at all!!",I think the slope should be rising because acceleration at time t=0 is 0 since velocity is constant............ but yes velocity can be more than 20m/s even if acceleration is decreasing ..... see the top question's answer......... but still it should be a rising slope..
What is acceleration?,Can't something change direction and not be accelerating??,"an alternative way of thinking about it would be if velocity equals rate x direction, if you change any variable in that it would change the velocity, which is the definition of acceleration."
What is acceleration?,Can someone please give the correct answers for the car exercise? I don't understand the explanation. and what is exactly meant by flooring in?,"Quite late, but "flooring it" does refer to suddenly speeding up, and applies especially to cars- It stems from the fact that (at least in older cars) the lower you press the gas pedal the faster the vehicles goes. Ergo, flooring the gas pedal would cause the car to take off at full speed."
What is acceleration?,"Could someone re-explain the picture with the four cars? I'm not quite sure about why the car slows down if the signs of velocity and acceleration are oppposite and why it speeds up when they have the same signs. 
Actually, the first two pictures where the velocity is positive is quite simple to get, but the cases that confuse me the most are the ones in which the velocity is negative.

Someone please help?","Good, clear question.

Maybe this helps...

F=ma right? so if they are equal, they are in the same direction. Kinda makes sense I guess:  if you push something, it will accelerate in that same direction.
So, if you are ok with that idea, think about the acceleration arrow (vector) in your diagrams as being replaced or equal to the force vector.

Does that help or no??"
What is acceleration?,"So when we accelerate, we feel as if a force was dragging us backwards and let us feel the inertia. Can we use this principle to make some thing which measures acceleration?","Probably no. 

And the force that drag us backward IS inertia. (Sorry if I'm mistaken. You seemed to treat inertia and 'the force that drag us backwards' as a separate thing.)

Inertia is the tendency of an object to remain in its state. For example, a rolling ball will continue rolling in a straight line due to its inertia unless compelled by an external force. (friction, gravity, somebody kicking it etc) Same thing, inertia keeps a ball stationary unless someone apply force on it.
And to correspond to your given example, I think the bus and passenger situation will be a better explanation:
Passengers tend to move backwards when a bus accelerates. This is because the inertia in their body keep them at rest. So, passengers will lean backwards when the bus moves forward.

Well, inertia is a measure of mass though.

Hopes this helps."
What is acceleration?,"If i'm traveling east at 20 mph in my toyota camry and got bored with the traffic and changed lanes at 25 mph to my right of the car in front of me, is'nt that changing velocity on a positive?","It all depends on what directions you assign to positive direction of your axis, if it is in the positive direction then is it positive."
What is acceleration?,What is the main or basic difference between speed and velocity? Acceleration is used only for change in velocity or even for a change in speed?,"Speed is the magnitude of velocity.  Velocity is a vector, which means it has two parts: first, your velocity has a magnitude, which just answers the question "how fast?", but does not say anything about the direction the object is moving.  The second part of velocity is its direction, which answers the question "which way?".  So a velocity might be "20 m/s, downward".  The speed is 20 m/s, and the direction is "downward".  Acceleration is the rate of change of velocity.  Usually, acceleration means the speed is changing, but not always.  When an object moves in a circular path at a constant speed, it is still accelerating, because the _direction_ of its velocity is changing."
What is acceleration?,I don't understand: How does -34m/s+8m/s^2(3s)= -10m/s?,"Your current velocity is 34 m/s in the opposite direction of what is considered the "positive" direction, so it is -34 m/s. Acceleration, 8 m/s^2, is the change in velocity, and in this case it is in the positive direction. So, the velocity will become 8 m/s more positive for every second that this acceleration is present. (8 m/s^2)*(3s)=24 m/s, This is a positive change in velocity, so -34 m/s + 24 m/s=-10 m/s. You are still moving in the opposite direction but at a slower magnitude."
What is acceleration?,how do we know which is positive or negative direction when the origin point is not given ?,"Generally, the right side is indicated as the positive direction whilst the left side as the negative direction."
What is acceleration?,how do u determine if the acceleration is positive or negative?,"Just look at the direction of the CHANGE in velocity.  If the change is toward the positive direction, it's positive."
What are the kinematic formulas?,"I understand that these equations are only for acceleration being constant. I looked ahead and I noticed that acceleration being constant is a lot of the content ahead. Will there be any equations where we can find the other variables (time, distance, etc) where the acceleration is not constant? And if so, what are those equations and how can we get them?",You will work with variable acceleration in calculus. You will learn how to do this when you do differential calculus. You will learn this when you apply derivatives.
What are the kinematic formulas?,How to derive equations of motion by using calculus ?,"We usually start with acceleration to derive the kinematic equations. 

We know that acceleration is approximately -9.8 m/s^2 (we're just going to use -9.8 so the math is easier) and we know that acceleration is the derivative of velocity, which is the derivative of position. We can use this knowledge (and our knowledge of integrals) to derive the kinematics equations.

First, we need to establish that acceleration is represented by the equation a(t) = -9.8.

Because velocity is the antiderivative of acceleration, that means that v'(t) = a(t) and v(t) = int[a(t)]. Simplifying the integral results in the equation v(t) = -9.8t + C_1, where C_1 is the initial velocity (in physics, this the initial velocity is v_0). This means that for every second, the velocity decreases by -9.8 m/s.

To find the position equation, simply repeat this step with velocity. Position is the antiderivative of velocity, so that means that x'(t) = v(t) and x(t) = int[v(t)]. Simplifying the integral results in the position equation x(t) = -4.9t^2 + (C_1)t + C_2, where C_1 is the initial velocity and C_2 is the initial position (in physics, C_2 is usually represented by x_0).

In order to make this equation more universal, the position equation can be generalized as x(t) = 1/2(at^2) + v_0 + x_0"
What are the kinematic formulas?,the gravity magnitude for the free fall is always -9.81 ?,"Near the surface of the Earth, yes.  Not other places.  Pretty much all high school physics problems will assume the Earth's gravity will be constant near the surface of the Earth.  In reality, the acceleration will get weaker the further from the surface you get, but accounting for this change makes the problems considerably more difficult.  But the approximation of g as a constant 9.81 m/s² is a very good one as long as your distance from the Earth's surface is very small compared to the radius of the Earth."
What are the kinematic formulas?,"In example 3, where the pencil is being thrown upward, should g = +9.8 m/s^2 or -9.8 m/s^2  ? I thought it should be positive (upward), but here it is negative. Could someone explain this to me.","For this situation (any most situations), any vector that point UP or to the RIGHT is taken as positive.

Whilst the initial vertical VELOCITY vector is upwards and therefore positive, the force of graviy is always downwards, and therefore (F=ma) the acceleration is always downward and negative.


(Note: when the velocity vector and acceleration vectors are in opposite direct this means that the object is slowing down. When the pencil starts to fall, the velocity and acceleration are in the same direction and so it is speeding up)

ok??"
What are the kinematic formulas?,How can two objects with different masses experience the same acceleration (-9.8m/s^2)? I thought heavier things fall to the ground quicker.,"You're close, but not quite there. While it's true that there is more gravitational force acting on a heavier object, this doesn't correspond to an increase in acceleration. In fact, the opposite is true. A heavier object has more inertia, which is a resistance to a change in motion.
If you look at Newton's law of universal gravitation, you see that the force of attraction between two objects is proportional to the product of their masses and inversely proportional to the square of the distance between them. If we take this equation and frame it in terms of somebody standing on the earth, we get a force due to gravitational attraction that is the product of their masses divided by the square of the earth's radius. 
From here, we can take Newton's second law of motion, f = ma. Here, we are looking for the force on the person from the earth. So, the mass on the left side of the following equation would refer to the person, which we can arbitrarily call m2. We can plug this in for the attraction force, giving us this:
m2 * a = G (m1 * m2) / (r^2)
Canceling out m2, we get a definition for gravitational acceleration:
a = G (M1) / R^2
From here, we have to use measurements to help us. Using measurements of the earth's mass and radius, as well as Newton's constant of gravitation, we can determine that the average value of a on the Earth's surface is about 9.81 m/s^2

Hope this helped!"
What are the kinematic formulas?,"Could someone please explain in a step by step fashion; how to solve for Vf in the first kinematic equation: 
a=vf-v0/delta t. 
I cannot seem to be able to wrap my mind around the manipulation. 

Thank you.","We want to get Vf = something, so we start by multiplying both sides of the equation:
A(delta t) = vf - v0.
The add v0 to both sides, and voila!
A(delta t) + v0 = vf"
What are the kinematic formulas?,why did they assume a positive value of vx=15.0m/s and not vx=-15.0m/s when taking the root in the final example?,"In the note in that example it says: In taking a square root, you get two possible answers: positive or negative. Since our motorcyclist will still be going in the direction of motion it started with and we assumed that direction was positive, we'll choose the positive answer"
What are the kinematic formulas?,I've seen a different list of five kinetic variables with position as one of them. Is there one standard list of "the" five kinetic variables that I should know? Or is it more subjective and situational?,"I don't think you should look for such a list, try and understand the most important concepts like position, velocity (how position changes over time) and acceleration (how velocity changes over time). We can visually understand these three simply, you probably already have an accurate intuition of how each should look like. Position is merely an object's location in space; its also easy to notice when something has some sort of velocity; About acceleration, its noticeable whenever the object's velocity is changing somehow (becoming faster or changing direction)."
Preparing to study physics,"What is Quantum Physics, and what is its difference to Quantum Mechanics?","Quantum Physics can be used synonimically to Quantum Mechanics and even Quantum Theory.

Quantum Physics is theory which try to explain why Classical Mechanics doesn't work in cases for example very small particles or also explains some "more visible" phenomenon like superconducting. There is the series of videos in Khan Academy, so if you are interested you can learn from them a lot :)"
Preparing to study physics,"I don't know if it even makes sense but consider this, if I hit my head against let's say a table with some force and then hit my head against a wall with the same force, it hurts more in the second case. If the reaction force is same for both cases, why dont i get hurt in both cases the same way?",Is it possible that the table moved after hitting it which slightly reduced the impact while the wall did not move at all so the unlucky person got the full brunt of the blow?
Preparing to study physics,"It all sounds very interesting, though I have a question, Since even light can't escape from a black hole, so until it (as in black hole) explodes the light just sits there?","There could be something behind a black hole like an infinite randomness.
Because according to Stephen Hawking universe originates in white holes and ends in black holes.
So the laws of universe may not apply there."
Preparing to study physics,I'm 13 years old i have not studied trigonometry or algebra yet but I have a very open mind and I am very eager to learn about physics.What should I do?,"Study trigonometry and algebra.  The more math you know, the better at physics you will be.  Physics is essentially applied math."
Preparing to study physics,what is physics,"Physics is the study of the different laws of the universe, and how they affect our lives. This facet of science provides the foundation for other sciences, such as chemistry and biology."
Preparing to study physics,"Hi, whats the difference between HS Physics and HS Physics NGSS?","NGSS is a program of newer education. They have more concise lessons, and they have cut out certain information that might not be needed as much. The best way to know if you should use it is (1) what state you are in and (2) what you're using the course for. NGSS has only been implemented in the following states' education: Arkansas, California, Connecticut, Delaware, Hawaii, Illinois, Iowa, Kansas, Kentucky, Maine, Maryland, Michigan, Nevada, New Hampshire, New Jersey, New Mexico, Oregon, Rhode Island, Vermont, and Washington, which is 20 out of the fifty states in the US. If you live in a state not listed (like mine, I live in Texas), then your state does not use it in their curriculum. If you are taking the course on your own and not taking a credit by exam or taking it for your school or university, then you can choose whichever you prefer. If you are taking it for school, then I would recommend using whichever one is used according to your state/country. (I'm not sure if Khan Academy teaches for out of the US or not)"
Preparing to study physics,What is  Pythagorean theorem,"If we have a right triangle whose hypotenuse has a length of C and the other two sides have lengths of A and B, then A^2 + B^2 = C^2."
What are velocity vs. time graphs?,How would you calculate the average speed on a velocity/time graph?,"On a position vs time graph, the average velocity is found by dividing the total displacement by the total time. In other words, (position at final point - position at initial point) / (time at final point - time at initial point)."
What are velocity vs. time graphs?,"In the last graph, to find the area of the area under the graph couldn't we use the formula of a trapezoid?","Yeah, you can use the formula of a trapezoid 
Area of a trapezoid = 1/2 * sum of the parallel sides * the distance between them 
Area of the trapezoid = displacement
= 1/2 * (7 + 3) * 6
=30
thus, the displacement = 30m"
What are velocity vs. time graphs?,"If a curve represents the motion(velocity) of a body, then when the curve slopes downwards, is it just slowing down compared to the previous velocity or is it the fact that it immediately decelerates or else is it the case as if it moves too another direction as indicated by the y-axis?","When (on a Position time-graph), the line (which represents velocity) is sloping downwards, it means that the object is moving in the opposite direction and has nothing to do with acceleration or deceleration.

Acceleration and deceleration can be determined by the slope, if the velocity is decreasing, the it is decelerating and and if the speed is increasing, there is acceleration."
What are velocity vs. time graphs?,Is acceleration both for speed and velocity? Cuz' now I'm getting confused,"When a position vs time graph is concave up, the acceleration is increasing. When a position vs time graph is concave down, the acceleration is decreasing."
What are velocity vs. time graphs?,"Can speed decrease over time, but acceleration increase over time? If yes, how is it possible?",If you had a ball traveling to the right at a speed and then you applied a force impeding that movement that becomes bigger in magnitude. the speed of the object would decrease because of the force acting opposite its direction of motion however the acceleration of the ball would increase because of the increasing force acting upon it. This is how you can achieve the situation you described.
What are velocity vs. time graphs?,So you can only use average velocity to find displacement when the acceleration is constant? Which you could still do on this breaking it up where the acceleration is zero and where its 3/2 per second,"You can always use average velocity to find displacement.
Calculating the average becomes more difficult if acceleration is not constant."
What are velocity vs. time graphs?,"If the triangle is stated to be between t=3s and t=7s, why was t=4 used in the Triangle Formula?","Bcuz you're trying to find the base, the base being 4 (the distance between 3 and 7)."
What are velocity vs. time graphs?,if I have a problem like justin drives west at 20M per S then slows down to stop at a red light  and there is a graph that shows his velocity over time where westword is negative and asks for the acceleration what doesthe diretions have to do with this i mean what ireally want is the slope and if it is constant or not and the velocity on the y axis so there is really no use from knowing thedirections ofhis motion,The direction tells you if his change in velocity is negative or positive.
What are velocity vs. time graphs?,"When distance (r) between two objects is zero i.e they are touching each other, the the G force between them must be
F = g X m1Xm2/r2
   =gXm1Xm2/0 square
    = infinite
That means the force by which they both attract each other is infinite, so they cannot be separated at all. How is this possible?","It's very important to understand that the distance r "between objects" is not the distance between their surfaces, but the *distance between their centers*.  So when a person is standing on the earth, and we want to use that formula to find the force between them, we don't say "r = 0 because they are touching", we say "r = 6400 km, the distance between the the center of the earth and the center of the person"."
What are velocity vs. time graphs?,Is negative acceleration still considered "high acceleration" if the graph is curving downwards steeply?,High acceleration usually refers to a large magnitude of acceleration so it doesn't matter if it is positive or negative.
What are position vs. time graphs?,are there ways to calculate the slope of a curved graph without using calculus,"It turns out to be possible for the conic sections: circles, parabolas, hyperbolas, and ellipses, but I think that's about it for the functions used by most people today.  You could invent or define some curves by what you want their slopes to do, and before Newton came along, people played with these a lot -- osculating curves and evolutes and such.  But Newton basically INVENTED CALCULUS _precisely because_ he needed to calculate the slopes of curved graphs of given functions, and there was no way to do it."
What are position vs. time graphs?,"What is the meaning of negative acceleration? Since an object cannot slow down/decelerate beyond zero.  
The velocity is negative when object moves in the opposite direction(the negative direction) so is negative acceleration the acceleration when the object is moving in the opposite direction(the negative direction)?","Yes, negative acceleration would be acceleration in the negative direction. Acceleration is a vector quantity."
What are position vs. time graphs?,"I have a few questions:

1.  Since velocity is "Speed with given direction", and the acceleration is negative when the slope is going down, why is the velocity constant when the slope is constant? (Refer to graph 4) 

2. In example 2, "The motion of an extraordinarily jubilant bird flying straight up and down is given by the graph..." states that the bird flies STRAIGHT UP AND DOWN. But why is the slope of the graph down and then up? Is the sentence just an intro?

3. If the slope is going up, the acceleration remains at a constant rate and will not increase anymore unless the slope goes even higher, the same goes for the velocity, am I right?","1. Velocity is the slope of position vs. time.   If that slope is not changing, the velocity is constant.  If the slope is negative and not changing, the velocity is a negative constant.
Acceleration is slope of velocity vs time.  

2.  Yes, it's an introduction. 

3. Can't tell what slope you are referring to, so can't answer."
What are position vs. time graphs?,"In the average velocity, why don't we simply calculate the instantaneous velocity when t=0 and when t=10, add them and divide them over 2 to get their average? It gave me a different result! what's wrong then?","it's because  "average velocity" in physics is different from the "average of the initial and final velocity". This is admittedly confusing, but the definition of average velocity is displacement over time. The definition of the average of the velocities is the sum of the velocities divided by two. Like Andrew said, if the acceleration was constant then it turns out these two quantities will be equal. But if acceleration was not constant you can't assume they will give the same answer."
What are position vs. time graphs?,"For the Hungry Walrus question, what does -1 m/s velocity mean? At first I thought that it meant the walrus was going slower, but actually the walrus went faster, right? What does the -1 imply? He was going back in the direction he came from?","Yes, the (-) tells us that he is going back in the direction he came from. And yes, he is actually going faster. 
At 2 s -> slope = 0.5 m/s. 
At 5 s -> slope = 0 m/s. 
At 8 s -> slope = -1 m/s. 
At 8 s the MAGNITUDE or SIZE (aka number) for the velocity is the greatest from the three (since 1  > 0.5 > 1). Thus, he goes faster at the end. 
As for the signs, we only have them to indicate direction, since VELOCITY is speed with direction. For example, if we were just calculating SPEED, which has no direction, we would not put the (-). However, since we were calculating VELOCITY, which has direction, we put the (-) because he went back in the direction he came.

Hope that helps. :)"
What are position vs. time graphs?,"In example two, wouldn't the variable x in the formula change to y since it is measuring vertical position?",How am i supposed to know the slope of a curvy graph
What are position vs. time graphs?,How do you calculate the Instantaneous Velocity of a Position - Time graph when the acceleration is constant? Is there a way to do it with the graph alone (no calculus)?,"draw a line that is tangent to the curve at that point, and find the slope of that line"
What is displacement?,"I didn't understand why they picked the values c = 8m + 2m +2m= 12m, at least not by reading the diagram. What are these numbers?","Its because the object first travels 8 m straight and take a 180 degree turn. After taking the turn it travels 2 m and then again it takes a 180 degree turn and travels more 2 m.
Thus making the distance 8 m+2 m+2 m=12 m."
What is displacement?,"Regarding the person who is walking to the back of the plane, does it matter that the plane is actually moving forward when we are considering his displacement?","Im just learning this but it is explained here
https://www.khanacademy.org/science/physics/one-dimensional-motion/displacement-velocity-time/v/introduction-to-reference-frames"
What is displacement?,what is the difference between displacement and magnitude of displacement? Thank you!,"Bare minimum: Displacement gives where it was and where it is, but magnitude of displacement gives where it was and infinitely many places where it could be.

Slightly more detail: Displacement will give you both the current and previous locations of the object in question, but magnitude of displacement will give you the previous location of the object, and a radius from the original location. This radius can be used to describe a circle to represent all of the possible current locations of the object in question."
What is displacement?,What is the difference between "distance traveled" and "Displacement"??,"Displacement has to be the shortest path between the two points. 
If you go around in a circle back to where you started, distance is the circumference of the circle.  Displacement is zero."
What is displacement?,What is the difference in saying "distance" and "distance travelled"? Isn't "distance" a scalar quantity?,"Distance can refer to the magnitude of displacement, or it can refer to the length of the path taken from one point to another.  To clarify, people sometimes use the term distance traveled when they mean path length."
What is displacement?,"if the variable is y, does that change anything","Physics is all about conventions and symbols. The symbol for displacement is `x` or `s` by convention and so physicists and students normally use that. 

But for the question of "does that change anything" - it of course does not change anything if you evidently describe using a statement "Let y be displacement", and continue using `y` as the symbol.

P.S.: However you might need to know `y` refers to vertical displacement (along y-axis) and `x` refers to horizonal displacement (along x-axis) in 2-dimensional motion."
What is displacement?,What is the difference between circular motion and projectile motion?,In most cases with projectile motion you have a constant acceleration in the negative Y direction where as in circular motion the acceleration is a constant magnitude but is constantly changing direction.  If you deal with a more generic case of projectile motion where the distance traveled along the earth's surface is far enough so that you have to start to factor in the curvature of the earth the projectile motion get closer and closer to being circular motion.
What is displacement?,"When object C changes its direction and goes upwards, shouldn't the distance that was covered in the upward direction also be counted?","The small upward direction of the arrow is for illustrative purposes only, so as not to draw the arrow on top of itself."
What is displacement?,what does the whole paragraph means,read it and find out
What is displacement?,I still don't get the difference between distance and distance traveled. Can someone simplify this for me please?,The usually way I look at it is if you have a circular track that you are running around.  If you go all the way around the circle you are at a distance of 0 from where you started but you have traveled the distance of the circumference of the track.
What is physics?,What is G-Force,"A G force is when you feel your same weight against you. for example a roller coaster is 2 Gs,which means you will feel 2x your weight which ever direction the roller coaster is going."
What is physics?,Does the study of physics alter what we discover in mathematics?,For sure.  Newton invented calculus to solve the specific problem of calculating planetary motion.  Bessel functions were invented to solve the spherical harmonics of electron orbital wavefunctions.
What is physics?,anyone on here just to try to get ahead before school starts up again .,Yes. Lol.
What is physics?,"This wasn't mentioned in the text, but what is dark matter? Why is there so much of it, but it is unobtainable?",dark matter is matter that doesn't emit or absorb light. We can't directly measure it.
What is physics?,What is electric force?,"An electric force would be a specific type of force (a push or pull, such as gravity or friction) that is caused by the electrical interaction of objects. 

An example of this would be the electrons moving in a circuit. The electrons from the negative battery terminal are attracted to the positive terminal due to the electrical force. The electric force is a small component of a larger force called the electromagnetic force."
What is physics?,Can Newton’s 1st and 2nd law of motion both be active at the same time?,"Sure. Newton's first law states that an object at rest or moving with a constant velocity will stay at rest or stay moving with a constant velocity as long as no force acts upon it. Newton's second law states that the net force on an object is equal to the mass of the object times the acceleration of the object. So if an object is moving with constant velocity and no force is acted upon it (1st law), you can calculate with Newton's second law that its acceleration is zero. In this sense both laws are active in the same time."
What is physics?,so if i finish a physics course on khan academy it wouldn't be enough to score  700 ON SAT physics? is it just the surface of physics?,"Just completing a course doesn't directly mean that you'll do good on a test. You still have to do applied practice for the test.
The AP Physics 1 course on Khan Academy doesn't cover much of the subject material of the SAT Subject test on Physics, including thermodynamics, magnetism, and optics. You'll have to get that information, and some more, from another course or source."
What is physics?,why is there no gravity in space? and why do we have gravity?,"There actually is gravity in space: the whole reason the Earth orbits around the sun is because the sun is a 'heavy' object that makes an impression on the fabric of spacetime, like   your body would on a trampoline. The sun's sheer mass makes the earth and all of the other planets orbit around it because the gravity is so strong on this cosmic scale that the Earth will never actually stop spinning and be incinerated by the sun: what will likely happen first is the sun will become a red giant near the end of its life and swallow up Mercury, Venus, and Earth. 
The reason we have gravity is because gravity is a property of matter, anything that has mass and takes up space. Fundamentally, all matter attracts other matter, and the bigger the object, the stronger gravitational pull it has."
What are velocity components?,What is the meaning of terminal velocity?,How do we calculate the air resistance and in turn terminal velocity?
What are velocity components?,"Although the same question has been asked, i didn't quite get your conclusion. When finding the angle of the vector, you didn't keep the y-component negative. i did and my angle was negative. Does it matter? My answer's still correct?","In that part of the Angry Seagull question he isn't taking the exact velocities, he is taking the magnitudes of the velocities (just the number, not the sign). Magnitudes are always positive. The angle he gets is positive, because it's the magnitude of that angle.  If you were to look at it on a polar graph, you could indeed list that as a negative angle, and it would indicate that the bird is flying right (positive) and down (negative). 

To sum it all up, if you want to succinctly tell what direction the bird is heading, the negative angle is the correct answer [on a polar graph this would read (17.0 , -30.6 degrees)], but if all you care about is the size of the angle, the answer in the article is correct."
What are velocity components?,"I notice in the presentations, you use double lines on each side of the components. What do the double lines mean?","Hello Bob,

When we work with vectors double lines such as this ||X|| or single lines such as |X| are referring to the length of vector X.

I hope this is the answer to your question as I did not see this nomenclature in this link. Please leave a comment below.

Regards,

APD"
What are velocity components?,But how would we know if our triangle is right angled? would we have to make a scale diagram first or?? im so confused,"Assuming you draw a horizontal and a vertical vector, as they showed, you will always end up with a right triangle.  This is because the horizontal and vertical lines are perpendicular to each other, creating a right angle.  Of course, you can instead draw the vectors as non-horizontal and vertical lines (as they also showed), but I think it would make the triangle much harder to use.  Just remember that as long as your triangle has two lines perpendicular to each other, it is a right triangle with a right angle.
Hope this helps!  Let me know if you still don't understand =)"
What are velocity components?,"so this is kind of like finding the degrees of a point on the unit circle using:
sin( )
cos( )
tan( )
csc( )
sec( )
cot( )
arcsin( )
arccos( )
arctan( )
arccsc( )
arcsec( )
arccot( )

Right?
Or no?",Sorta? But you will not need to know the list after tangent from what I have read up on the MCAT.
What are velocity components?,Can I have more than two vectors that affects my velocity?,Yes. There is a 3rd axis of movement known as z used in 3-D diagrams. Movement on this axis implies going in or out of the page.  Also you can have an infinite quantity of vectors affecting velocity as long as you account for each individual vector's velocity.
What are velocity components?,Can any one give me the all formulas of Projectile motion chapter,http://formulas.tutorvista.com/physics/projectile-motion-formula.html
What are velocity components?,How do we solve for the components if we are only given the length in which the 2 directions are traveled rather than the velocity?,"You need time if you want to solve for velocity components.
Maybe you want to solve for displacement components?"
What are velocity components?,How to  use inverse trig functions without a calculator?,"You should know the trig values for these common angles (0, 30, 45, 60, 90, 120, etc...) which can be expressed with algebraic numbers (ie. roots of integers).  If you know the trig values, you also know the inverse trig values as well."
What are velocity components?,Is arcsin the same as sin^-1 ? And for the rest too?,sin^-1(x) is sometimes used instead of arcsin(x) but if you ask me it is a terrible notation because it can be easily confused with 1/sin(x) which is definitely not arcsin(x).  So my suggestion is never use sin^-1(x).
What is 2D projectile motion?,Can all of these answers be abstracted by doing all the algebraic manipulations beforehand and just plugging in the variables into one gigantic formula?,"Yeah, and it's actually a great way to gain insight into the nature of the thing. When you solve a thing numerically, you just get some number (or a vector, etc.) at the end (and maybe some units). But when you solve the thing symbolically, you can interpret the equation, see clearly what's proportional to what, any algebraic symmetry (functional symmetry, being able to swap variables, so on), you can see patterns or that some other quantity might be hidden in the thing. For example, Maybe the expression for the area of a circle shows up somewhere in the final expression, which can suggest a different derivation or interpretation. 

There are other benefits, too. In general, whenever you can – that is, whenever it's not prohibitively difficult – you should try to solve the thing symbolically to gain the greatest insight. Also, once you have a general expression for a thing, you've essentially solved that _class_ of problem. Imagine if you had to rederive the Pythagorean theorem every time you wanted to use it instead of just being able to plug the numbers into the formula."
What is 2D projectile motion?,"For two-dimensional projectile motion, is there ever an instance where the initial horizontal velocity is not constant?","Not if it's a projectile.  But if it's some other type of object, like something with an engine, then sure.   We don't call airplanes projectiles, though, right?"
What is 2D projectile motion?,"I tried to do the pumpkin launch problem on my own, using the tactic that Sal used in the last video where he used time to construct the final velocity, but I couldn't get the answer to match up. I realize it takes much more time to do it that way, but is it even possible?","Yes, it's possible. I did the same thing and then used the initial vertical velocity and time to solve for the final vertical velocity. My time calculation was 3.04 seconds. So 9+3.04(-9.81) = -20.8, the same final vertical velocity they came up with."
What is 2D projectile motion?,""Besides, when the pumpkin hits the ground the acceleration will no longer be ay = –9.8 m/s2 since the collision will cause a huge unknown acceleration. "

What exactly is this huge acceleration?",It is when the ground stops the movement of the pumpkin.
What is 2D projectile motion?,"in the second question, if it was projected upwards with some angle should'nt the vertical displacement be more than 18 m?","Yes. If the projectile is launched at an angle, there's a non-zero vertical component of initial velocity, as compared to the zero vertical initial velocity the object would experience if launched at a 0 degree angle. This non-zero initial velocity would cause an increase in the max vertical displacement, because it takes some time for the object to start traveling downwards, and in that time, it's going up."
What is 2D projectile motion?,"Hi everyone! Just wondering if anyone knows a good place to learn about air resistance? I know it said here it's to do with calculus and differential equations, both of which I am still a beginner in, but is there anyway to learn it a bit more simply to get a better understanding of it?","The only thing you need to know about air resistance is that ideally, it is directly proportional to the velocity of the object experiencing the resistance.
Therefore f-sub-a = kv where k is a constant. In your differential equations, remember that velocity is the first time derivative of displacement.
Note: I'm using the word 'ideally' a bit loosely here."
What is 2D projectile motion?,Why is the acceleration of projectiles always -g and not g? Why is g negative for projectiles?,"I agree with Andrew M's answer, but it also depends on what you make in your equation and drawing (if you do a drawing) positive and negative. If you want down and to the right positive then anything going in those directions are positive and opposite negative, if you make left and up positive then right and down negative. You do whatever you want with equations as long as you know how to do it. To answer you question mainly its because projectiles fall so they go down and that's down like acceleration due to gravity....negative and negative make positive. The projectile might even be negative when it is first launched until it reaches max height."
What is 2D projectile motion?,If sin(theta)=y and cos(theta)=x what is z?,There isn't this is 2D motion. Z has to include 3D.
What is Newton's first law?,"while watching the astronauts eating in the ISS, it got me thinking... does gravity affect blood circulation? ?   i guess food has no problem in digesting because we have peristalitic movements in the esophagus to aid the movement of food. On the other hand the  blood travelling through the veins and arteries are powered or made to move with the help of the heart, so does 0 - gravity affect the circulatory system? and therefore strain the heart??","Though I'm 6 years late, this article from NASA may help: https://www.nasa.gov/vision/earth/livingthings/arterial_remodel.html."
What is Newton's first law?,"3rd Example : I get why the probe follows the straight movement but why it went diagonal is still not clear to me. Can someone elaborate that?

Thanks for the help.","Because of the thrust to the right, the probe would move to the right, but also forward because it was moving forward. The forces combine, and the probe goes diagonal. Hope this helps.😉"
What is Newton's first law?,how to the astronauts eat in mid air there is no gravitational force pulling them down doesn't that hurt their bodies when they come down ?,"great question. When they swallow the food, the body pulls it down into the stomach. Its a special movement called 'peristalsis' (looks like a Caterpillar walking :-) and it pushes the food along the digestive system in a wave-like motion.
I dont know if it hurts them when they land, but I guess they will feel various pains as they come back down to Earth, depending on how long they were up there. It would be an interesting quesiton to ask them."
What is Newton's first law?,is dark matter considered as an external force??,"I honestly don't know the answer to that. I would assume the answer is "yes", however, if you look at the universe as a singular body, dark matter and white holes could both be considered internal forces. This shows how suggestive internal and external forces can be."
What is Newton's first law?,"In free fall, when an object reaches terminal velocity, why does the force of drag (air resistance) become equal to the weight ? Why doesn't it become greater ? practically, this would be a silly question, but i want to know the theory behind it. Thanks a lot, I love your work and would love to one day contribute to this website as one if its own.","Drag, like friction, is a reaction force.  It can't be greater than the force that it is a reaction to.  If it could, objects would reach terminal velocity and then start slowing down.  But if they slow down, the drag force would decrease, so then they would speed up, and then slow down, and then speed up...."
What is Newton's first law?,"Sir,What will happen if we are in a lift and the cable of the lift breaks down.",You will fall.
What is Newton's first law?,"Example 2: how the answer is b, not a. The elevator is moving upward at a constant velocity, and the magnitude of the upward force(Fc) is greater than the downward force(Fg).",If an object is moving at a constant velocity it is not accelerating so there is no net force.
What is Newton's first law?,i didnt understand what is inertia ?,Inertia is property of mass. That property is maintaining momentum unless a force acts on it.
What is Newton's first law?,Can anyone give me a better visualization of inertia? I am having a hard time imagining that.,"I like Charles' answer but I think something else that can be said is that the concept of inertia is how we define the idea of mass. The idea that having "more of something" makes it harder to modify its motion with a given force as compared to trying to modify the motion of "less of that something" with the same force - is essentially how we get the concept of mass, and this is the very definition of inertia."
What is Newton's first law?,Is there any time interval between when the force is applied and when an opposite force is given?,"No, there is no lag between a force being applied and the reaction force.  

Let's consider what is happening when you push on an object.  As your hand get close to the object the electrons in the outer shells of the atoms and molecules of your hand and the object start to interact.  This interaction is the force on the object and your hand, you can't separate the force from the reaction force, they are all part of the same interaction."
What is Newton's third law?,how did newton figure out his third law?,"By noticing that an apple pushes downwards against his hand(because of gravity), as his hand pushes up on the apple(by holding it)."
What is Newton's third law?,"For example, if a baseball ball is applying force on a ball of 1000N and ball moves away. If the ball is applying the same force on the bat why doesn't the bat moves away?","Great question.  There are two factors to consider. 
First, the masses are different.  The mass of a baseball is .145kg, while a bat has a mass of about 1.0 kg.  So, from F = ma, this tells us that a = F/m, and so the acceleration of the ball will be about 7 times the acceleration of the bat.  We know that the average acceleration is given by a = Δv/Δt, which tells us that Δv = a * Δt.  Thus, since the Δt is the same for both, and the acceleration of the ball is 7 times bigger, the Δv of the ball will be 7 times bigger.
The Second factor is that the bat is already moving with a fairly high speed, and so its momentum  is much greater than the momentum of the ball, at least *in the frame of reference of the spectators*.  Thus, the bat is only slowed down, while the ball is turned completely around.  Here is an example:
mass of bat = 1kg
mass of ball = (1/7)kg
initial velocity of bat = +35 m/s
initial velocity of ball = -35 m/s
final velocity of bat = +20 m/s
final velocity of ball = +70 m/s
You can see that the Δv for the bat = 20 - 35 = -15m/s, while Δv for the ball = 70 - -35 = +105m/s, which is 7 times as big as the Δv for the bat.  

If you were to watch the collision from a car moving at v = +35m/s, you would see the bat initially at rest and finally moving at -15 m/s, so you would see it "moving away" from the collision.

One final factor is that the player keeps pushing on the bat during the hit, so although the ball pushes on the bat equal and opposite to the bat pushing on the ball, there is additional force on the bat that tends to counteract the ball pushing on the bat."
What is Newton's third law?,Assume that I drop a ball from the 2nd floor to the ground. Why is it that the ball could not bounce all the way back to my position if Newton's third law state that the ground will exert an equal amount of force to the ball?,"Energy is lost every time the ball bounces because of the air friction. In a (hypothetical) perfect vacuum where nothing acts on the ball except for gravity, the ball would bounce all the way back to the 2nd floor every time, forever (or until stopped by an external force)."
What is Newton's third law?,How does one differentiate between an action force and a reaction force if they are both "reacting" to each other?,Actually there is no difference between the two since they both occur at the same time. Action and reaction are just terms given for better understanding.
What is Newton's third law?,"Newton’s law states that if we apply force to an object, it will push back with the same amount of force in the opposite direction. So if I push a pen with 10 Newton it is supposed to push me back with 10 Newton too. And as the forces cancel out, the net displacement should be zero. Then how does the pen move?","Forces can only cancel out on a single object. In this scenario *you* experience a force of 10 N in one direction and the *pen* experiences a separate force of 10 N in the opposite direction. The net force on the pen is 10 N. There is no reason to add the 10 N on you to the pen because those 10 N are being exerted on you, not the pen."
What is Newton's third law?,Why is lying in bed not an example of Newton's 3rd law? My text book says its because the forces acting on you come from a different interaction pair but doesn't explain further.,"When you lie on your bed, you push on the bed and the bed pushes on you.  That's Newton's third law. 
At the same time, earth's gravitational force is pulling on you, and your gravitational force is pulling on earth.  That's another example of 3rd law. 
Note that 3rd law pairs have to be of the same type.  contact force and contact force, in the bed/you situation.  Gravity and gravity in the earth/you situation.
Now we can ask a different question: why are you stationary when you lie on your bed.  That's because the contact force from the bed on you is equal to your weight.  Here we have two different types of forces - the contact force and the gravitational force.  The sum of those forces is zero, so you don't accelerate.  That's Newton's 2nd law, F = ma."
What is Newton's third law?,""This law represents a certain symmetry in nature: Forces always occur in pairs, and one body cannot exert a force on another without experiencing a force itself. We sometimes refer to this law loosely as “action-reaction,” where the force exerted is the action and the force experienced as a consequence is the reaction." [ was seen in paragraph 3 ] 
QUESTION ; how do we know that forces always occur in pairs ? is it just due to Newton's third law ?","We can't know for sure, but we can be quite confident about it since but no one was able to disprove this theory up until now, with centuries of tries.
Also you can prove that this law holds for the types of forces we already know: gravitational, electromagnetic, weak and strong. The only way it could be wrong would be finding out new types of forces."
What is Newton's third law?,"If a push a table, that means it will apply a reaction force on my my hand.If the table moves forward, shouldn't my hand move backwards due to the force applied by the table?","No, because your hand is attached to your body, and your hand, like everything else, responds to the sum of all the forces on it, not just one particular force."
What is Newton's third law?,what if two boxes equal is mass and force collided in space head on,"The answer to this depends on how elastic the collision is, see Coefficient of restitution (https://en.wikipedia.org/wiki/Coefficient_of_restitution). If kinetic energy is conserved, they bounce back with equal speed. If the collision has loss (i.e. they make a noise, their surfaces heat, they plastically deform etc), they bounce back with lower speed.

Think of 2 cars in a head on collision. They crumple and don't bounce much at all - an inelastic collision.

Note that momentum is maintained in all collisions: 2 objects the same mass travelling equal speed along the same line in opposite directions have a sum of 0 momentum. For momentum to be conserved they must have equal speeds in opposing directions after the collision."
What are inclines?,"Wouldn't the driveway be a case where we can't round up?  At 37 degrees, the car would slip down the driveway, since the maximum was 36.86... degrees.",If I were to build my drive way based on this math I would choose to round down though ;-)
What are inclines?,I don't understand the angle part. Is the angle of incline the same as the angle pictured between the mg and mgcos?,"Yes , the angle of incline and the angle between mg  and  mgcos are the same. Lets take a simple example. Say , let the angle of incline be 30 , then draw the mg force downwards so as it forms a right angled triangle including angle of incline 30 . In that triangle the other two angles will be 90 ( the right angled part ) and 60. Now draw the mgcos force from the same point as mg. We see the mgcos is perpendicular to the surface of incline , where one angle we already found out was 60 , therefore the angle between mg and mgcos has to be 90-60 = 30 , which is equal to the angle of incline.  
  draw the forces on the body on the incline , take this example and solve , your doubt will be dispelled. Thank you !"
What are inclines?,"In example 1, wouldn't all the snow piling up in front of the sled change things?","It would but there is no indication in the question about *snow piling up* . So, you don't need to think about that when solving this problem."
What are inclines?,Why do you cancel both the masses in the numerator for 1 mass in the denominator?,When you have something of the form (a*x + a*y)/(a*z) this is equivelent to ((a*x)/(a*z)) + ((a*y)/(a*z)) and you can see that the a's in the numerator and denominator to the left of the + sign cancel as do the numerator and denominator to the right of the + sign giving you (x/z) + (y/z)) which is also equivalent to (x + y)/z
What are inclines?,Which way does the force of friction act on an inclined plane if the force acting on the mass is in a horizontal direction and the mass is moving?,friction always opposes motion.
What are inclines?,can somebody explain why there should be max. steepness for max. static friction!,"Because when you go past that point, the object starts to slide, and that's not static friction anymore"
What are inclines?,I am literally so lost on the last example. Like how did sine theta get on the other side without being negative? Wouldn't you have had to subtract it from the side it was on with the cosine theta and the friction coefficient? Also why did we do tan negative one all of a sudden? I don't feel like there was a good explanation for that.,"For the first question you asked, let's take a look.
0=sin(theta)-coefficient (cos theta)    (hopefully this makes sense to you :/ )
-sin(theta)=-coefficient (cos theta)
sin(theta)=coefficient (cos theta) Is this makes sense to you? It should! :)
The next question was that why did (sin theta) / (cos theta) became tan(theta). right?
Sine theta is equal to opposite/hypotenuse. Cosine theta is equal to adjacent/hypotenuse. If you do (sin theta) / (cos theta), the hypotenuse thing will cancel out and it is left with opposite/adjacent, which is same as tangent(theta)! Yay!
Hopefully, this makes sense to you. It took a long time to type all these."
What are inclines?,Ok I am lost on question 1...so we draw the force diagram...then we have the equation a= F/M ..then you start subsiting cos and sin and im lost at that point...please help,"You should probably watch the videos on vectors and splitting up a vector into component parts.  If you don't understand that, you won't understand this video."
What is Newton's second law?,I don't understand how an object with an acceleration of 0 could have a Force. If F=ma and a=0 [so F=m(0)] then why doesn't the Force end up as 0?,"Yes, the force would be zero, but that is the *Net Force*. So the forces acting on the object can cancel each other out and the object would have 0 acceleration. Using the example of hanging cheese, the vertical forces cancel each other out, as sin60 times 23 is approximately equal to 20, so the net force would end up zero, but there are still these forces acting on it."
What is Newton's second law?,When do i know when to use cos and sin?,"There is a common saying in math called Soh Cah Toa. For Sine, Cosine, and Tangent. If the problem gives you the opposite and hypotenuse sides then you will you Sine, because sine is Soh which contains o and h for opposite and hypotenuse. You will use cosine is you are given adjacent and hypotenuse."
What is Newton's second law?,"Hey guys! My question is in reference to the second example and has to do with direction. We typically assign the left/down as negative and up/right as positive. Is it because the question is asking for the magnitude that the direction of the force not important? Clearly, F1 is pointing up and to the right, so I can see why that vector is positive, but F2 is pointing left, yet the magnitude was still positive. Why?","The problem only asks for magnitude. Magnitude refers to a size or quantity ( disregards direction),  it is always positive."
What is Newton's second law?,"In example 1, the  tan = -9/3.3=2.7 why is positive not negative . is tan always(+), also the theta was positive it should be negative ! please explain this ?","Well, you missed something. The numbers were both between *modulus* sign, which means that we are only going to work with the *positive* value."
What is Newton's second law?,In example 1 (newton the turtle) why is there  tanθ = absolute values of acceleration vector a_y / a_x. In physics can't you have negative angles?,"I'm not sure why they did that but maybe for simplicity, although they added a line *The total acceleration vector points right and down* it's says everything about the direction, there is no need to show that by using a negative sign too. This would've been counted as a repetitive error.
You can have negative angles in physics though saying the direction of something is downward is the same as putting a negative sign followed by the *magnitude or absolute value* ."
What is Newton's second law?,i need to know about newton's second law on variable mass systems.. in which playlist on khan academy i can find this?,All of the videos on Newton's second law is in Forces and Newton's laws of motion
What is friction?,"what happens to co-efficient of friction ,when a body weight is doubled?",the coefficient of friction does not depend upon weight.... as far as I know it is a function only of the materials?
What is friction?,"So,  coefficient of kinetic / static friction cannot be a negative number?",Correct. No friction is when the coefficient is 0 (zero). 100% friction (no movement) is when the coefficient is 1.
What is friction?,Friction helps us to walk but in water why we cannot walk,"We can walk on Land because the number of irregularities present on the surface are very plentiful, and differ from area to area, whereas in water, there are no irregularities and it is actually often used only as a lubricant, which is why the wet floor is extremely difficult to walk on. So, technically the only reason we can walk on land and not on water is actually because the number of irregularities is present in solids and is absent in liquids"
What is friction?,"I don't understand why when force applied is less than the maximum value of static friction then its value is the same as the value of frictional force. Can someone explain?, thanks.","A good question


Imagine you are pushing against a table trying to slide it across the floor.

The maximum value of static friciton is 100N. If you reach this force or exceed it, the table will slide. 

OK??

So you start pushing with a small force; say, 15N. The table does not slide.

Why? because the force of friction is opposing your force.

how much force is the table pushing back on you with? 

This force you feel pushing back on you is the force of friciton.

Now increase your force to 60N. The table still does not slide.

How much force will you feel from the table? again, this the force of friciton. now increased.

as you increase your force, the force opposing you (friciton) will also increase according to Newtons third law. Until you exceed the force that friction can push back with.... when you reach or exceed 100N then the table will slide. 

OK??"
What is friction?,how can cars accelerate if its static friction that acts on them. cause the net force would always equal 0 ? plz explain thanks.,why would the net force equal zero?  Cars have engines.
What is friction?,"In Example 1 : iii) before the fridge starts moving the person must exert a force of 647 N to overcome the static friction, So, the force just after begining of motion would be 800-647=153 N ! 
Am I right!","It would seem so but no. The coefficient of friction changes from static to kinetic once the fridge starts moving, and as long as it stays moving it won't change no matter how much you accelerate/decelerate (as long as you don't go back to cero velocity). As you can see in the formula of kinetic friction there is no mention of the force you're aplying, it's only proportional to the kinetic friction coeficient and to the normal force. If you calculate that you get that the force of the kinetic friction is (110kg*9.8m*s^-2)*(0.4)=431.2N. You can then calculate the real magnitude of the force your'e applying using that value: 800N-431.2N=368.8N.  At least I believe this is correct :d 
Be carefull though since the normal force is not allways the same as the weight, in this case it is since there are no other vertical forces."
What is friction?,can someone please explain how the formulas for static and kinetic frictional forces were derived? is there a way to understand the formula w/o just memorizing it? thanks :),"They're not derived, they're based on observation and on the definition of the coefficient of friction.

The harder surfaces press against each other, the bigger the frictional force is.  That's all the formula says.  The coefficient says that the amount of the force depends on the specific combination of materials that are being pressed together."
What is friction?,"so does a small coefficient of friction correspond to a smoother surface? Like 0.2, for example, would represent a smoother surface than 0.9. Also, i saw something saying that 0.6 is the least value for the coefficient of friction possible. is that true?","You can generally use the intuition that low friction corresponds to a smooth surface, but strictly speaking that's not always true, because there can be some very smooth surfaces that are very sticky.  You generally won't encounter them in an early physics course, though. 

you need to understand that friction is actually a very complex phenomenon that is still a very active area of investigation by physicists who specialize in that sort of thing.  We use a very simplified version of it to get the basic idea of how it works and how to incorporate it into our understanding of F = ma."
What is weight?,"Why do we say "I am 70 kilograms" then if weight has units of Newton and mass has units of kg? If i am 70 kg, is my mass 7,14?","The kilogram is not actually a unit of weight, although people use it as such. It is actually a measure of mass, measurable only because we rarely need to have a force of gravity other than Earth's. The Newton is the real measure of weight, although it is used almost never. So 70 kg is your mass, not your weight.
I hope this helps."
What is weight?,"this article says that astronauts in the int'l space station experience weightlessness because they are in a free fall orbit around earth. if it's free fall, then why are they remaining in orbit and not falling to the ground where gravity is pulling it? thanks! :)","It's not contadictory. The object is still falling. Just because it never reaches ground doesn't mean it isn't falling toward that ground.
Essentially, an object in orbit means that object is constantly falling toward another object (an object in orbit around Earth constantly falls toward Earth), but because it is also moving sideways (and not just straight down, imagine throwing a ball how it moves 2 directions: down and in the direction you threw it) then it never actually hits the ground. If you could throw a baseball fast enough, it would circle the earth because the farther the ball goes forward the further down "ground" is since the earth is curved, if you would move in a straight line the ground would eventually recede beneath you. (If you are having trouble seeing this just imagine the horizon and how ships can go 'over' it. It's because the earth curves that the ships will drop below a point where they can be seen.)
That's what makes science and math so great is that it explains why things like this, that initially sound counterintuitive, are actually correct."
What is weight?,"How do we define how much is a kilogram, or a pound, etc?","An excellent question.
This video provides an excellent answer.
https://www.youtube.com/watch?v=ZMByI4s-D-Y"
What is weight?,Whats the point of the 6700 N force of the thrusters and 4300 N of the air resistance have to do with problem 1? Are they just there to confuse us? Thanks for your help!,They're given as additional information to test whether the student understands the concept of weight which remains a constant or gets befuddled by the presence of extra forces.
What is weight?,"In example 1, the thruster force of the airplane as well as the air resistance is given. But why we are not taking them into consideration while solving the problem??","You can calculate the vertical and horizontal components of forces separately. 
The extra numbers are "red herrings" meant to trip up students who have some idea of what to do but not a solid foundation. This sort of tactic is used on tests a lot."
What is weight?,"Normally, even when filling up medical records, how much you weigh is called weight, not mass. But when you step down on a weighing scale, the downward pull of gravity gives you the weight you're seeing in the scale as lbs or kgs which are units of mass, not weight. Are you saying that we've been perceiving weight and mass incorrectly all this time? I mean you explain all these stuff about weight vs. mass to other people and they'd just give you a big "huh?" and might even laugh at you and think you're being ridiculous.","Since the conversion between mass and weight is fairly constant for every day activities they have been used fairly interchangeably. When you are dealing with science you usually have to be more precise about the terms you use because you can be dealing with conditions that are not as simple as you standing on a stationary scale in a doctors office where.  

For pounds it is considered a unit of mass and can be used as force, also referred to as the pound-force, but that causes confusion with formula like F = m * a for example if you have a 1 pound (mass) object accelerated by gravity at 32 ft/s^2 you have a force of 32 pounds (force) but a 1 pound mass produces a 1 pound-force force under standard gravity.  Because of this there is a unit called a slug that is used for mass where a 1 slug mass will accelerate at 1 ft/s^2 when a 1 pound force is applied and using this a 1 slug mass will produce 32 pound-force under standard gravity.  If you don't use slug & pounds you need to modify F = m * a to be something like F = k * m * a where k is a unitless scaling constant equal to 1/32 to adjust the result so that 1 pound mass under standard gravity produces 1 pound-force."
What is weight?,The text says that the Earth still exercises a gravitational force at the height at which the ISS orbits. Would an astronaut who jumps out of the ISS fall down to earth? And do the pods that bring astronauts back from ISS missions need an engine for acceleration?,"yes they wuld fall eventually, but they are travelling in a circular path, very quickly. In fact they need some way to slow them down so they can fall towards the Earth..."
What is weight?,what is the difference bw gravity and gravitational force,"The terms *Gravity* and *Gravitational Force* are mostly used interchangeably, and it is more or less permissible to do so. However, the difference between these two terms is considered prominent in some studies. 

Gravitational Force *describes the attraction force between any two masses*. Gravity specifically *describes the resultant force with which a mass is attracted towards the Earth*.

Gravitational Force means the force of attraction between *any two masses*. Weight is the Gravitational force with which the Earth attracts the masses towards its center.

Gravity is related to the resultant force with which a mass is attracted to Earth. So, this happens *only between Earth and a mass*, unlike gravitational force which occurs between any two masses.

Hope this helps."
What is weight?,"'The astronauts in the International Space Station experience weightlessness not because there is no force of gravity, but since they are in a free fall orbit around the Earth.' What do you mean by ' a free fall orbit' ?","Yes, they are falling all the time toward the earth. Hard to understand till you see an example. Put a dot on a piece of paper and draw a Circle around the dot with a 10 cm radius. Now, put another dote 15 cm directly above from the center dot (it should be 5cm above the surface of the circle). Have your dot go 15 cm to the right and 15 cm down the paper. You should still be 5cm from the circle (same as before) even though your dot fell for 15 cm; that's because it's moving forward in a way that keeps it getting any closer to the surface. If you repeat (15 cm down, plus 15 cm back to to the left now) you should still be 5cm from the middle circle; even though your dot 'fell' toward the circle another 15cm. Once you see it, it makes sense."
What is weight?,What is the difference between Weight and Gravitational Force? My textbook doesn't clarify this.,Weight is the gravitational force from large celestial objects like the earth.  The gravitational force between you and your computer is not considered to be weight.
What is normal force?,"it is said that even rigid object would be deformed during contact, does that mean all objects are naturally elastic?",What happens to a rigid object depends on the atomic and molecular forces.  If these forces allow the object to undergo elastic deformation then they will deform and then go back to their original shape once the force is removed.  If the forces between the atoms and molecules shift without breaking then the object undergoes plastic deformation and stays in the new shape.  If the forces do not stretch or shift then the object cracks.  Most objects that we conciser rigid will react to a force on them with a combination of all three responses.
What is normal force?,"Does the normal force exist due to the deformation of the object exerting the normal force, or the repulsion between the electrons in the two objects?","i'm not sure but i think repulsion between electrons is the root cause of both

when we concern the shape of contacting objects, we tag them deformed by that very repulsion
when it comes to forces (and thus acceleration), we see them exerting normal forces each other by the same cause of repulsion

in other words, the two (deformation, normal force) might be 2 symptoms from 1 cause (electron repulsion)"
What is normal force?,"Hi, when I solved for example one, I used a as -9.8 m/s2, because isn't acceleration from gravity always downward and in this case to the opposite of upward (considered positive) direction, thus should be negative ? I got my answer wrong because of this and don't understand why the plug a as a positive value. Please clarify. Thank you.","There is NO acceleration because the table is pushing up on the object with as much as the object is pushing on the table.  The object is not accelerating at all, so a is equal to zero."
What is normal force?,In the first example why is 13.5N not negative since it was subtracted to be placed on the other side of the equation.,"It is algebra.
Ok, since you are confused, I will explain step by step.
It says 13.5N=Fn-mg-5N
We will solve for Fn
-Fn=-mg-5N-13.5N Multiply by -1
Fn=mg+5N+13.5N
Guess what? it is positive 13.5N!"
What is normal force?,Another question I had was if the normal force was greater than that of the force of gravity then wouldn't the object be floating in the air?,"If it is floating in the air, there can't be a normal force on it."
What is normal force?,"So I've asked this question in the normal force video about the shoe on the floor, but the same type of problem came up in this article. In the first question, the box of bubble gum is inside an elevator that is accelerating upward. If we assumed the elevator wasn't moving, then the normal force exerted by the elevator floor onto the box would equal in magnitude the downward forces acting on the box of bubble gum. What I don't understand is, why would the normal force of the floor change at all if the elevator was accelerating? It's not like the elevator floor is exerting more force to move upwards; it's the cables attached to the elevator that are exerting more force to accelerate isn't it?","The normal force must change because now the floor must not only oppose gravity but also provide enough extra force to accelerate the object upward. 
To understand the motion of the gum we don't need to know anything about the cables, we just need to know that the gum is getting pushed on by the floor.  How the floor is managing to do that is irrelevant (could be cables, could be hydraulic, could be giant magic hand reaching down from sky...)"
What is normal force?,"After going over the problem again, is it because we can ignore the horizontal force because the normal force in this question only applies to vertical forces, therefore making F sub A of x irrelevant?","Normal force is perpendicular to the surface of contact, so yes."
What is normal force?,Could it be considered that when an object is in free fall it could be perpendicular to the air?  I was wondering if that could be what causes air resistance at higher altitudes.,You could think of it that way but it's not going to help you figure out the force.
What is tension?,How come in these questions you always use cosine and sine functions? In an example(example 2 i think) you had to find the opposite. Tangent also deals with the opposite side(opp/adj) but we always use the sine/cosine. Why?,"But if you don't know the hypotenuse the you must use tangent, otherwise you can't calculate your answer. For example:
angle=60 deg, hypotenuse=?, adj=10, opp=?
tan 60=opp/10 --> 10*tan 60deg=opp=17.320508075688772935274463415059"
What is tension?,"If two masses are connected by the same rope, in what circumstances would the force tension differ between the two masses?","The rope is acting as a transferring agent of a force, so there should never be a scenario in which two objects connected by one rope experience tension forces of different magnitudes."
What is tension?,"In example 1, there's an expandable explanation for what would happen if you tried to solve for the vertical force. It says "Well, since there are two unknown vertical forces (tension and the normal force), we just wouldn't be able to solve in that direction since there would be two unknowns."

Why is the normal force unknown? Isn't it the same as the downward force which is mass * gravity or approximately 20 newtons in this case?","Normal force exists only when the object is in contact with the surface.. when upward force acting on the body, it will be going to decrease."
What is tension?,"In example 1, it says solve for the tension of the rope. But we only solved for the tension (Tx) in the horizontal direction. How would I find the total tension of the rope with consideration to fg=mg, normal force Nf, and Tsin(60)? Thanks.","No, it is solved for the total tension. Tx is 6N (from ax = sum(Fx)/m 3m/s^2 = Tx/2kg    -> Tx = 6N) and Tx / cos 60 is T, so T is 12N."
What is tension?,"I don't understand the -T1 and -Fg? Why is it there and if so, how do we know if it is + or -  ?","you are free to choose sine conventions, its up to you nature don't understand positive or negative sign. The thing you must understand is tension act in the opposite direction of the gravitational force. If your object is hanging it must balanced by tension, otherwise it will accelerate down due to gravity."
What is tension?,"in simple pulley problem, like 2 mass on the rope. I've found out sometime in the tension of ther rope you have same tension and some time not. It"s sam when the mass of pulley ignored, and different when using rotaional dynamic. Can someone explain to why, and  tell me how to know the tension is the same or not ?","you said it yourself:  if the pulley and rope a massless, tension is the same throughout the rope.    If not, it's not."
What is tension?,"Do you have to account for the mass of the rope, too?",Yes but until you get to the point where you able to use calculus on these problems the wire/rope is considered to be massless.
What is tension?,"Σ" what is the meaning of this symbol?,Sum. It is a greek letter called sigma when is showed means a sum of the numbers.
What is tension?,How does this principle work vertically? Is it solved the same way? How is gravity included?,"If the string is vertical, the tension is equal in magnitude to the weight force (F = mg)"
What is a centripetal force?,How do you know when to use angular velocity (w) as opposed to finding a velocity using the circumference ( that would be in m/s) ?,"One can use either. 
You can convert angular velocity to velocity if you know the radius,  There isn't a rule as such.  One chooses based on the data given and the ease of solving the problem. 
For example, if the data specifies velocity in radian/sec or revolutions/sec, using the angular velocity formula is probably the better choice as you avoid the hassle of all the mathematics involved in conversion of velocities.  Similarly, if the data specifies velocity as meters/sec, go for the usual velocity formula."
What is a centripetal force?,why does the m1rw^2 = m2g? i don't understand how both equal?,"With physics problems, they do this 'massless string approximation' where you ignore the mass of the string (since in most cases it is much smaller than the masses attached) and so you can treat the two objects connected to the string as directly interacting with each other. It follows that the tension in the string must therefore be the same at all points, and so the tension (you can find from mass 2, which is m2*g) is equal to the centripetal force causing mass 1 to spin around. If there is anything you need me to clarify feel free to ask!"
What is a centripetal force?,"I do understand the solution of exercise 1, but something else about it confuses me. the force of gravitation should be acting on m1 as well, right? so why is m1 not accelerating downwards? which force balances the force of gravitation out?","I think you are supposed to imagine that the ball is on a table with a hole drilled in the table.  Otherwise the rope going from m1 to the tube would be at an angle and there would be two components of force applying tension to the rope, and m2 would have to be large enough not only to provide the centripetal force but also to provide the upward force to offset m1's  weight."
What is a centripetal force?,why does the centripetal force equal to the tension force in some cases?,"Centripetal force, for an object in circular motion, is just the force maintaining the circular motion, the force that prevents the object from flying away tangentially. Unless this force is present, no object can execute a pure circular motion, because in absence of a force, a body moves uninterrupted along a straight line (Newton's first law).

In most scenarios you see in physics' problems, a string is the provider of the centripetal force; it acts as the tether to the object making it go in a circle rather than flying off straight. In such a scenario, the force acting on the object (centripetal force) is the tension in the string. They are the same things."
What is a centripetal force?,"In Exercise 1, if the ball was made to rotate faster, would the system (of the ball and mass m2) start accelerating upwards?","Sure, why not?
To see this, imagine what happens if the ball rotates slower, or comes to a stop.  m2 will fall, right?  So it must rise if the opposite happens."
What is a centripetal force?,"In the last question, why is 35 divided by 2? Thanks!","Since each blade is length 35 meters, to find the radius we divide by two. The center of mass for the radius of rotation is located in the middle of the blade, thus you divide 35 by 2 in order to find the distance from the center to the edge of the blade."
What is centripetal acceleration?,why is the triangle ABC and triangle PQR similar?,the vector v1 (PR) form a right angle to AC and v2 (PQ) form a right angle to AB. Given this and a given angle between AC and AB you can draw up the lines and prove that the angle between PR and PQ must have the same angle. Thus the triangles are similar :)
What is centripetal acceleration?,how can deltaS equal deltaR?,"That's a good question. Notice how the article says: when Δθ is _very small_, Δs = Δr. That's calculus at work - by _very small_ it means infinitesimally small. On a bigger scale, it's obvious that an arc and a chord are not equal, but the bigger scale is just an illustration of the ideas, an approximation. As θ gets smaller and smaller, Δs and Δr (the arc length and chord length) get closer and closer to being the same length. By using limits, you can actually prove that as Δθ approaches 0, Δs = Δr. It seems to defy "common sense", but it's true and it works. To get a little more intuitive picture of what's going on, start with a circle of radius 1 and a 90° arc, figure out the arc length and the chord length. Then figure out arc and chord for a 9° angle, then 0.9°, etc. See how close arc and chord get in just a few steps? Imagine you did that infinitely many times."
What is centripetal acceleration?,what  is  the real forces that provide centripetal  acceleration,"centripetal actually means - towards the center .So centripetal force is not a new type of force .Any force which is acting towards center can be called as centripetal force. To understand it better think of gravitational force , it acts in downwards direction so we call it  downwards force because of its direction .There are only four real forces in nature i.e. Gravitational , Electromagnetic ,weak nuclear and strong nuclear .
whenever any of these four forces acts towards center that force is called centripetal(towards center) . In case of earth and sun system ,real force acting is Gravitational but as it is always pointing towards center we call it centripetal . In case  of an electron revolving around nucleus ,the real force between electron and positive nucleus is electromagnetic but because of its direction always pointing towards center ,it is centripetal force. Friction too is electromagnetic force."
What is centripetal acceleration?,"If an object has a centripetal acceleration towards the center, why does it not go towards the center?","Technically they are. They are "falling", but also moving sideways at a large velocity, so they maintain a circular path."
What is centripetal acceleration?,Why does centripetal force does not work?,because the force is always perpendicular to the displacement.
What is centripetal acceleration?,what is meant by utlracentrifuge?,An ultracentrifuge is just a centrifuge that operates at very high angular velocity.
What is centripetal acceleration?,"Can centrifugal force be thought of as the "equal and opposite force" to centripetal force? When turning in a car, it seems as if one tends away from the turn (away from the center). Maybe centrifugal force is just a vernacular term for Newton's first law when moving in a circle. The object is "trying" to maintain its fixed velocity, and when centripetal force acts on the object, it tends to stay in motion at its fixed velocity.","No these are not action reaction pairs, if they were then they would have acted on two different bodies but centripetal and centrifugal force act on same body."
What is centripetal acceleration?,why is centripetal acceleration equal to negative of v^2/r,"As to why the sign of centripetal acceleration is negative, this is because we denote it to be in the radial direction. The radial direction is the direction that starts at the center of a circle and goes directly outwards. Since the centripetal acceleration points inwards, we give it a negative sign.

As to why the magnitude is v^2/r, there are many derivations, but a simple one that uses a more geometric picture is this one: https://www.youtube.com/watch?v=TNX-Z6XR3gA

or using calculus: https://www.youtube.com/watch?v=YRBRarbMCyE"
What is centripetal acceleration?,How do you know that the 7.5×10^4 is in cm? it will be equal to 7500cm? in 1 meter has 100cm which you divide the 7500/100= 75meters and no 0.0750cm. I'm confused,"The radius is 7.5 cm, which equals .075 m (that is, 7.5 / 100).

The *angular velocity*, ω, is 7.5×10^4 *revolutions per minute*.  The two numbers are totally separate.  They use ω to calculate v (tangential velocity) by saying that 1 revolution is 2π*r = 2π*(.075) meters, and 1 minute = 60 seconds."
N/A,I don't understand how random motions of molecules can cause thermal energy. Is it because the molecules rub against eachother and cause friction?,The random motion of molecules IS thermal energy.
N/A,"If the object were to stop moving there would still be some residual motion of the fluid.
i don't  understand why or how it happened if there are a photo to help me for more explanation","When the paddle stopped turning, the water still spins around a little; it does not immediately stop moving.  The residual motion is caused be the fact that water is a chain reaction.  Once some of the water is pushed, that water pushed the water in front of it and so on.  It takes a while for the reaction to lose all its energy to the environment and for the chain reaction to stop."
N/A,Is thermal energy due to friction considered internal energy?,Sure. thermal energy is usually the most important component of internal energy in problems that we will do at this level of physics.
N/A,Can you state a difference between thermodynamics and conservation of energy in brief? Thank you.,"Thermodynamics is the study of thermal energy and its movement from one place or form to another. 
Conservation of energy is a principle that informs the field of thermodynamics, along with all other fields of physics."
N/A,"For question 1a and  2a, why do they convert the units from Joules to kilojoules in the final answer? Is it wrong if we use Joules instead?","Its not wrong to write in Joules. Its just that when you have very high values, its more elegant to write in kJ."
N/A,What is specific heat?,"Source from Google:

The specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius. The relationship between heat and temperature change is usually expressed in the form shown below where c is the specific heat."
N/A,if the box is moving at with constant velocity; then how can force of friction and the applied force are equal in magnitude. But for an object to move force of friction must be lesser than applied force.,"Therefore if you started the box off and kept it at a certain speed, at that certain speed, the forces of friction/drag are equal to the pushing force? I think that's right"
What is kinetic energy?,I don't understand what net work means. It says in the article that kinetic energy can be equal to the net work done on a system. What does net work mean?,Net-work just means the _total work_ done by the system. And the value of *net work* = change in kinetic energy.
What is kinetic energy?,"in the exercise 2 , how is the total chemical potential energy stored in the propellant is (Energy density) x (mass of hydrazine)??","By definition, "energy density" tells you energy per mass for the propellant. In other words, energy density is equal to the amount of energy contained in each kilogram of propellant. Multiplying by the number of kilograms of propellant will thus give you the total energy."
What is kinetic energy?,"Why is kinetic energy related to the square of the velocity, as opposed to momentum which varies linearly with velocity? How do I know when I'm dealing with a momentum problem or a kinetic energy problem?","The simplest derivation is this..... Work W=Fx sort of definition.
Then putting F=ma and x=(1/2)at^2 in above gives 
W=(1/2)m(a^2)(t^2) 
    =(1/2)m v^2 
This is called the kinetic energy, KE.
If you realise it doesn't matter how one arrives at the given speed v then this result must be quite general."
What is kinetic energy?,"For exercise 2, I want to know the units of factors used in the last step to calculate the V value. When I calculated the velocity with Ed = 1.6MJ/kg, Mp = 1000kg, and Mr = 100kg, I got 5.657. It looks like 1000 was multiplied to the value, but why? Is it because of the MJ to J? But isn't 1megajoule = 1000000J?","Yes, you should convert MJ to J. The reason that your answer must me multiplied by 1000 since sqrt(10^6)=10^3=1000"
What is kinetic energy?,"if the propellant is contained by rocket then the K.E of rocket shouldn't be => K.E= 0.5(mr+mp)(v)^2
i know it's incorrect but can't figure out .... please clarify , its confusing me
plus , how can the K.E of rocket equal to the CHEM P.E of hydrazine?","The propellant is used up as the rocket gains speed, right? When the propellant is all gone, the rocket's KE has to be equal to whatever energy was produced by the propellant as it burned (actually the propellant leaves as gas and that gas has KE, too, so it' really the sum of that KE plus the KE of the rocket that has to add up)"
What is kinetic energy?,Can you say that kinetic energy is the source of sound energy? Can you say that kinetic energy and sound energy exist together?,Sound energy is a type of kinetic energy.
What is kinetic energy?,prove that K.E = 1/2 mv2?,"You are asking a question, which is answered very well in the current topic :( However, here is somewhat a different proof based on the same idea, although I tried to increase the understanding. Hope this helps.
```
To prove that Kinetic Energy is ½ mv^2
```
We already know that _Energy w = f x s_ that is *force x displacement*.
So, ```
ΔK = W = FΔs = maΔs
```
From the *third equation of motion* that is _v^2 - u^2 = 2aΔs_ (-1) 
where ```
v = final velocity, u = initial velocity, a = acceleration, and Δs denotes change in displacement
```
ΔK = maΔs, so from equation (1)
```
 ΔK = m(v^2 - u^2) / 2
=> ½ mv^2 - ½ mu^2
```
 _but If kinetic energy is the energy of motion then, naturally, the kinetic energy of an object at rest should be zero. Therefore, we don't need the second term and an object's kinetic energy is just_
```
½ mv^2
```"
What is kinetic energy?,"If you see in first paragraph,how will object move with a constant speed if I apply 
energy only once?     It will stop after a certain interval of time","If it stops, that means someone or something else was "applying energy".  In physics we call that "doing work".  Friction does work to stop the object after you did work to get it moving.  If you did it in outer space the object wouldn't stop"
What are energy and work?,"in the numerical for how long do i have to push a heavy box......, further down it is given that work done = 200 * 30 but the distance travelled at that point is 0 if we refer to the X coordinate, so why is it given 200*30??","To calculate the work done one has to estimate the area under the force vs. position graph. To do so for the initial displacement of 30 m, one has to split up the area into a rectangle and a triangle. So the rectangle is equal to 200N*30m and the rest (0.5((500 N−200 N)⋅30 m)) is equal to the triangle."
What are energy and work?,what is chemical potential energy?,"Chemical potential energy is the amount of potential energy tied up in a substance.  The term is a little ambiguous because it can refer to the amount of energy you can get from breaking atomic bonds, as in the energy you get out of propane when you burn it, or the amount of energy stored as an ionic potential between molecules, such as in a neuron.  Chemical energy can define the amount of work you can do with the proteins in your muscles, or how much energy you can store in a battery."
What are energy and work?,""However, remember that our bodies are about 25% efficient at transferring stored energy from food into work."
Why is it that it is 4x more efficient, rather than 1/4 times? Doesn't it say 25%? I'm confused.","If you use up 100% of your energy, you are getting only 25% of the work done. That means you have only 25% efficiency. 100 is 4x25. That is why,  the percentage of work done is being multiplied by 4 to get the actual amount of energy you have spent doing the work."
What are energy and work?,"Doesn't it make more sense to say that because of our body's 25% efficiency the available energy for work is 4 times smaller, instead of saying the work done is 4 times larger?","same

and you can even say like human body is wasting 75% of its energy while working

which one is fit to your taste is surely up to you!"
What are energy and work?,"`One frequent source of confusion people have with the concept of work comes about when thinking about holding a heavy weight stationary above our heads, against the force of gravity. We are not moving the weight through any distance, so no work is being done to the weight.` But what if we just let go of that weight? It does have some gravitational potential energy (U=mgh), meaning we had done some work on it.","The key point here is the difference between lifting the weight and holding the weight. While you are lifting the weight from the ground to over your head, it is changing distance, and thus you are performing work. If you hold it over your head, it is not changing distance, and thus you are not performing work. Just because something has potential energy, doesn't mean that work is being done on it - you have gravitational potential energy right now, but no work is being done unless you move through space. In other words, you did work on the weight to get it above your head, but you aren't doing work on the weight right now if you are currently holding it over your head."
What are energy and work?,""W=(50kg)(9.81m/s2)(0.5m)=245.25J" in this equation, should't the acceleration due to gravity be negative since it's accelerating in the opposite direction?!",kinetic energy
What are energy and work?,"If we take friction into account, is the force we use in the work equation with or without the friction?  (Do we use net force or the total force exerted?)","Friction is just another force on the object.  There's the work done by the moving force, and then there's work done by friction, and you have to net them out to find out how the energy of the object changes."
What is gravitational potential energy?,In the Exercise 1b (extension): I think that instead of saying $0.10 kW/hr there should be $0.10 kW.hr because units of Power - kW already have over time value in them. And we are paying for energy not for power - therefore energy equals power.time not power/time,You are correct.  Good catch.  I have reported it to the person in charge of the physics section at KA.
What is gravitational potential energy?,"I'm confused by the exercise with the gravity wells of Charon and Pluto. It states that for the descent onto Pluto, work needs to be done equal to the GPE in order to land with zero speed. 

But I read earlier that if I'm holding a dumbell and lower my arm, I'm performing negative work on the dumbell. The solution says that the spacecraft is performing positive work in this procedure (if I'm reading it right). Shouldn't it be negative?

Edit: To clarify, what's still confusing me is that if the spacecraft is lifting out of one gravity well and then descending into another, I would think that the work of lifting off Charon (the less massive body) would be a positive value, because the spacecraft is thrusting itself up out of the gravity well, and then when it descends to Pluto (more massive), it would being doing negative work since it's now losing the GPE it gained before, and then some, since Pluto's surface would be a deeper gravity well. So the work would be opposite to the first part, and greater in magnitude. Then the net work done would essentially be the difference between the GPE on the surfaces of the two bodies. Am I on the right track?

The solution takes the energy requirement of getting to the point where the two gravitational wells meet, and *adds* it to the energy in descending, though, where I would expect it to be subtracted. Can you point out where I'm going wrong?

I appreciate the help. This work/energy thing has eluded my understanding for many years.","algebraically
GPE_final - GPE_initial
= work (or energy) "needed" to move an object from initial to final



1. from Charon_surface to Charon_out
= GPE_Charon_out - GPE_Charon_surface
= -0.07 - (-0.17)
= -0.07 + 0.17
= 0.10 GJ
meaning you "need" 0.10GJ to escape Charon

2. from Charon_out to Pluto_surface
= GPE_Pluto_surface - GPE_Charon_out
= -0.74 - (-0.07)
= -0.74 + 0.07
= -0.67 GJ
meaning you "need" -0.67GJ on the way to Pluto
= you "gain" 0.67GJ on the way to Pluto
= you dash toward Pluto surface with 0.67GJ
= you "need" 0.67GJ to offset (-) the gained 0.67GJ to make you land on (rather than crash into) the surface
# if you "add or do work" -0.67GJ to this spacecraft, you actually push it down to crash on the surface 2x harder
## same for the case of a dumbbell, if you do negative work, you're not landing it gently. you're crashing it to the ground on top of -mg

3-1. from Charon_surface to Pluto_surface
= (GPE_Charon_out - GPE_Charon_surface) + -(GPE_Pluto_surface - GPE_Charon_out)
= 0.10 + -(-0.67)
= 0.10 + 0.67
= 0.77 GJ

3-2. or you can do the math at once tweaking 3-1 a bit
= (GPE_Charon_out - GPE_Charon_surface) + -(GPE_Pluto_surface - GPE_Charon_out)
= GPE_Charon_out - GPE_Charon_surface - GPE_Pluto_surface + GPE_Charon_out
= 2GPE_Charon_out - GPE_Charon_surface - GPE_Pluto_surface
= 2(-0.07) - (-0.17) - (-0.74)
= -0.14 + 0.17 + 0.74
= 0.03 + 0.74
= 0.77 GJ

3-3 don't apply the uppermost euqation directly to Charon and Pluto though
from Charon_surface to Pluto_surface
= GPE_Pluto_surface - GPE_Charon_surface
= -0.74 - (-0.17)
= -0.74 + 0.17
= -0.57 #it's ignoring 1) work for escaping Charon and 2) work for offsetting what's gained on the way to Pluto



in short
a. to escape Charon, you need + work
b. to land on Pluto, you need + work to offset - work gained on the way to Pluto (if you do - work, you actually crash it to the surface harder)
c. in sum you need two + works to escape and then land on Pluto without crashing"
What is gravitational potential energy?,Why gravitational  potential energy is defined as the negative of the work done by conservative forces?,"Because it's acting down. Think about when you are jumping. Why do you come down after you jump? Because, the GPE acts downside which is negative.

Hope this helps! If you have any further questions or need help, please ask! :)"
What is power?,how is P=m.a.v instantaneous velocity?,"V= instantaneous velocity; Since acceleration and velocity are in the same equation, then the velocity is changing (accelerating) over time, so it would only make sense to pluck in the velocity of a specific time. However, Pavg= m . a . 1/2 (Vf+Vi) because you are using the AVERAGE velocity. So when using P = m . a . v , this is using the instantaneous velocity at a specific time and actually results in Pi (instantaneous power) not just P; you will need to use the average velocity in order to get the average power. In other words, to find Pavg you must specify that you are also using Vavg, and when using V (velocity at a specific time) you get Pi."
What is power?,How can we measure power,"If you know how much energy is being converted per unit time, that is all you need to calculate power.  Ex. measure the current from the battery in a circuit and multiply by voltage to get power."
What is power?,"In "Can the concept of power help us describe how objects move?", in the last few steps, why is Pavg = m a (1/2 vfinal). Isn't it 1/2 ( vfinal + vinitial) ? Thanks.","Vinitial is 0, therefore it is 1/2Vfinal"
What is power?,"Power can be expressed as P = Work/Change in Time, instead of P = Change in Energy/Change in Time, because the change in energy is basically the work done. Is this correct?","Hello Alex,

In general I would agree. In both cases you end up with joules / time. Watch out for context. It seems each field of study has it's own vocabulary.

Regards,

APD"
What is power?,"how does finding the area under, of a power vs time graph gives me an average power? shouldn't that be finding the slope?","Area under a power vs. time graph is the equivalent of integrating power with respect to time, which gives work or change in energy. To find average power, you could divide the integral by the time interval."
What is power?,"About the last exercise, the first thing I thought about was 4.17/8 = 0.52, therefore 48% of the time is being spent on something else (fighting air drag)
Then i applied the same ratios to the engine power
Is this a wrong way to think about it?  

(if I sound somewhat weird, well,English is not my first language,sorry)","This is actually a very good way to think about it. Its good to know equations sometimes, but you just solved a rather tricky problem in a very elegant way. Also, there were no English errors in your question in case you were wondering :)"
N/A,"In the rubber band example, is the heat dissipated as work is done stretching the rubber band, or as the rubber band is being unloaded?","I'm fairly new to this topic, but from past experience of doing this in 3rd grade, we used to stretch a rubber band really quickly, then put it to our upper lip (while it was still stretched.). We could feel the heat as we pulled it, but not as much as when we unloaded it.

So mathematically, I can't tell you the answer, but from experimentation, it does produce heat when loaded."
N/A,"Exercise 2 is worded very strangely. It sounds like 0.6m is just the distance the string gets pulled back when 300N is applied, which would imply a specific spring constant, so why does the question make it sound like the spring constant could be anything? Is 0.6m just the maximum limit to how far the bow can be pulled back? That should be stated more clearly. Also, wouldn't any spring constant greater than 500N/m also allow the archer to use his full strength?","The way I understood it, 300N is his maximum strength. If he useed 250N and produced an extension of 0.6m, the spring constant would be different (in which case the bow would probably be made in a different shape or size or with a different material)."
N/A,"In question 2C, 2 x U should be 180, (2 x 90N) as figured out in the previous question. So how does 2 x U = 2.9? Someone please explain, thanks.",Dude it not 2.9. Its 2*90. The dot there is for multiplication
N/A,Why in Exercise1 250J/spring = 1000J? ( solution),"There are four springs on the truck in exercise 1 (one per wheel.) The displacement given is the displacement of the entire truck, meaning each individual spring is compressed 0.1 m. The calculation done (PE=(0.5)(5*10^4)(0.1)^2) gives you the amount of energy stored in each individual spring. Therefor the total energy stored in all four springs is 250 J * 4 springs = 1000 J total."
N/A,"Why do we multiply the volume of the rubber by the heat in the last exercise?
Thanks","Just above exercise 3 it states that 
"Where a three-dimensional elastic material obeys Hooke's law,
Energy/volume=(Stress*Strain)/2"
The rubber band we are using for this exercise is a 3-dimensional object and figure 3 is a stress vs strain plot. Notice that the first part of the equation is Energy/volume. When you find the area of the yellow part that corresponds to heat you get an expression of (Energy that is spent on heat)/(Volume of the object). So in order to find the energy spent on heat we have to multiply by the volume."
N/A,"In the extension vs force graph, what if the force was always constant? (e.g. the weight of a ball pulling down a vertical spring). In the graph, it isn't and just keeps growing as the displacement grows.","If the force was constant, you wouldn't have a spring.  That's not what springs do."
What is conservation of energy?,"In the golfer problem why is Em (Mechanical Energy) = 0 in the equation Em = Ep + Ek?  In general What does Em = 0 mean in relation to PE and KE?  I understand how the algebra works but I don't understand the general relationship of Em to the other terms in the equation.  Does Em = 0 generally mean that Em is constant?  And, when Em is constant, does that always mean Ek = 0 and Ep will be at its maximum positive value?","The mechanical energy does not equal zero. Think of it this way. The conservation of energy formula goes Ki+Ui=Kf+Uf. U is potential energy and K is kinetic energy. In this case the golf ball at the start has zero potential energy. We are considering the surface of the moon to be the height h. The height is zero therefore, we have no initial potential energy(mgh). We are left with Ki=Kf+Uf=>1/2m(vi)^2=1/2m(vf)^2+mgh. 

Also Em is a measure of energy at a certain time. We can rewrite the conservation of energy formula as Em(i)=Em(f).  If Em equals zero that means U+K=0 . I hope this helps."
What is conservation of energy?,If an object hits another but if friction force doesn't allow the second object to move then where is the energy of the first object gone ? Heat ? How ?,"The collision's kinetic energy vibrates both body and nearby air's molecules, increasing their quadratic average speed, which is directly related to temperature. Small but quick compression/expansion processes from the impact also dissipate energy as sound waves. The latter is usually a neglectible amount, though. Like Andrew said, missing energy usually turns out to be heat."
What is conservation of energy?,How did you get 28.16m/s as your answer for Problem 1? I am very confused and I need help,"I can help you with this.
For get 28.16m/s you have to do the next equation:
*Vf = sqrt[(28.28^2) - (2·2·1.625)]*

Take care about:
- "g" is 1.625 (*one coma six hundred and tweenty-five*) & not 1625 (one thousand six hundred and tweenty-five)
- "Vi" is 28.28 squared.
- Remeber to do the square root to the result.

I hope I help you & sorry if my english isn't the best."
What is conservation of energy?,isnt mass also conserved? howcome it isnt a fundamental ?,"mass can be destroyed when an antimatter and matter collide with each other and also annihilate energy in the form light energy.Antimatter posses the properties  just opposite to matter , like antimatter have positively charged electrons called positron . Though mass can be destroyed energy remains constant. This process involves the conversion of mass into energy. The law of conservation of mass-energy states the same"
What is conservation of energy?,"In Ex. 1 above, I used the conservation of energy equation in the vertical direction.  I got a final velocity of 19.84 m/s then divided by sin 45 and got close to the same answer (28.05 m/s instead of 28.16 m/s).  Why is the direction not considered?","Because the calculation is for energy, which is not a vector quantity. 
I also tried to calculate in the vertical direction after reading this post. I was curious as to why the difference between the two answers. It's because the angle also shifts slightly from 45 degrees as the vertical velocity drops slightly. Using the pythagorean theorem on the vertical and horizontal directions gives the correct diagonal velocity, and taking the inverse tan of the horizontal and vertical velocities gives the new angle of 44.77 degrees. :)"
What is conservation of energy?,So is conservation of energy the same as conservatives forces?,"No, but when you have conservative forces then mechanical energy will be conserved."
What is conservation of energy?,"In the golfer question, why is Mechanical Energy = m*vi^2/2?","The Mechanical energy is actually zero.
0 = (1/2*m*vf^2) - (1/2*m*vi^2)+(mgh)
You take the negative term to the other side, so it becomes positive.
(1/2*m*vi^2) =  (1/2*m*vf^2) +(mgh)

Note ; KE = (1/2*m*vf^2) - (1/2*m*vi^2)"
What is conservation of energy?,"Hi!
I had doubt 
that energy can't be created nor destroyed so how someone could tell this is  correct or not 

I am Rashi Manvar 
From India",This is what hundreds of years of experiments and observation have led us to conclude. No one has ever found an example of energy being created or destroyed.  Hence we  believe this law to be true.
N/A,What is nominal length?,nominal length = original/initial length
N/A,I didn't understood what that minus in formula was for?,It just tells us that the exerted by the spring will be in the opposite direction to the force applied.
N/A,The spring constant is the same for all springs or different? explain.,"It varies between spring to spring, depending on what it is made of, the shape of the spring, and the width of the wire."
N/A,is spring constant is same on another planet?,"gravity won't change the rigidity of the spring, so I think it is the same on other planets"
N/A,"I have a question on example 2a. If the nominal length is 50mm, and the compression is of 50mm then shouldn't the length under compression(L = Li- x = 50mm - 50mm = 0) become zero?","The nominal length is 50m. But the spring is being extended not compressed and therefore, the formula is L = Li + x= 50 mm +50 mm = 100 mm"
N/A,"I don't understand what the length notations of springs refers to. For example, strain is defined as change in length over initial length. I understand what change in length is, but what is the initial length referring to ?  Is it the entire length of the spring ? 
I'm referring to the so called nominal length or "initial length".","The spring has some length when it is relaxed, right?  That's the initial length."
N/A,"Why is k=E.A/L? if we put K = -F.x and E=stress/strain = (F/A)/(x/L) = F.L/(A.x)
then we get -F.x = F/x
Please help me",I think we are only interested in the absolute value. You need not include the negative sign.
N/A,"In exercise 1, how come the F (force) is equal to mg, not mgh? When the person steps on, there is still some height (from the spring's nominal height of 0.25 m). I plugged this in and got 0.21325. I am so confused.","I think you're confused as to the difference between gravitational force and potential energy.  Close enough to the Earth's surface, we always feel the force of gravity (equal to mg).  

Potential energy on the other hand is mgh.  This energy can be converted into kinetic energy to make the object move, but energy and force are two different physical quantities."
N/A,"in exercise 1, when we divided F over K, why the K isn't negative as hooke's law said?","Hooke's law doesn't say that the constant k is negative. The negative sign is only saying that the force is in the opposite direction of the displacement. Springs pull back on you, they don't push you more in the direction you are already pulling them."
What is center of mass?,Why is it that we define centre of mass as the sum of masses times their perpendicular distances from a reference point divided by the total mass of the body?.. How exactly does this give us the location of the centre of mass..?,"It's defined that way because the point you get from this calculation has a lot of interesting properties, like:
1) If you hang the body somehowand let it in equilibrium, a line parallel to gravity will connect the suspension point and the center of mass.
2) If you apply a force on the center of mass, the body will feel no tendency to spin, just translate.
If you don't apply a force on the center of mass, the rotation axis in the body will cross the center of mass.
3) If a body is both translating and spinning due to previous action of a single force, you can find the speed of each of its points by adding vectorialy the center of mass' velocity and the body's rotation relative to the center of mass.
4)It can greatly simplify calculations of elastic collisions
These are characteristics satisfied by the point defined as you said. Since they are very special indeed, the point was given a name and is often studied."
What is center of mass?,i'm not understanding The COM reference frame and the Toppling Stability.  Can someone help me?,"For toppling stability (let's take the Truck example):
First, it'd be important to take note of its coordinate reference.
There are two important values here: The x-coordinate of the center of mass, and the x-coordinate of the part of the object that touches the ground; it has to be the most extreme point at the direction of 'toppling'.

For example, check this image: https://ka-perseus-images.s3.amazonaws.com/fd327f9a43e55a7a26319969805b9cce7fb51d89.svg

Notice that for (b), Fg directly intersects with the second important point I was referring to (the extreme point), Because at that angle (and at angles less that it), the wheel is still able to support the Truck.

Notice what happens when you increase the angle just a little bit.. Gf and that part won't intersect anymore and Fg will go beyond the wheel.
What that means is that there will be nothing to support the load of the truck and will eventually topple over."
What is center of mass?,"If we apply a certain force on the COM then the object moves in the direction of the applied force . But , what if the COM is not located on the object ?
Does it mean that we can never make the object move in the direction of the applied force ?","If you apply a force off-center from the COM, then some of that force will create a torque on the object causing the object to have both rotational and translational motion.  To determine how much force goes into rotational vs translational motion, you need to break up the applied force vector into a component that goes straight through the COM and a component perpendicular to the COM.  The force component going through the COM will cause the translational motion and the component perpendicular to the COM will cause the rotational motion."
What is center of mass?,IN GENERAL OTHER THAN EQUATIONS  can any one give a simple example when center of mass is same as center of gravity and when not ... and i might be a wrong thinking but to sure??  what i was think  that for regular bodies like ruler etc it have both centre of mass and  center of gravity  SAME and for  irregular body there might be Different points for both is this right or wrong,"One way to look at this is that the center of mass is a point where the amount mass of an object is equal in all directions where the center of gravity is a point where the amount weight of an object is equal in all directions.  

So if the gravitational field that the object is in can be considered uniform across the volume of the object then the center of mass and center of gravity are the same point, the shape of the object doesn't matter."
What is center of mass?,Is it impossible to balance a donut from one point? (Its center of mass is at the emptied part of it.),"If the circle of the donut is vertical rather than horizontal, it can be balanced from any point on the circumference. If the donut is oriented horizontally,  no, it cannot be balanced from a single point."
What is center of mass?,"For the Figure 8 problem, why is it tan inverse of (0.7/7.6)? According to SOHCAHTOA, is it not supposed to be OPPOSITE over ADJACENT? Therefore, the side opposite of alpha is 7.6 and the side adjacent to alpha is 0.7?","You are correct about alpha, but note that they are finding theta, not alpha.  So while it's true that alpha = tan⁻¹(7.6/0.7) = 84.74° (the big angle), they want theta = tan⁻¹(0.7/7.6) = 5.26° (the small angle).  To be honest, I'm not sure why they labeled that angle alpha, when they didn't ever want to solve for it."
What is center of mass?,can center of mass depend on gravity,"No, center of mass is independent of gravity. Center of gravity can be different from center of mass if an object is not in a uniform gravitational field."
What is center of mass?,Is the entire mass of a system located at its center of mass ?,"no

but it is sometimes AS IF it is at the centre.

for example our world has mass in the seas and mountains and all around you. but it pulls you towards the centre of its mass

ok??"
What is conservation of momentum?,"In the exercise 2b when we calculate the force, why is it the mass of the ball in the equation? Shouldn't it be the mass of the golf club?","This is rather confusing... If they are imputing the acceleration and mass of the ball, you find its force. Right. But, if instead of using the mass of the ball, we take the mass of the golf club, the resulting force will be a lot biger (!) Which is not compatible with Newton's third law because the force exerted on the ball by the club will be larger than the force exerted on the club by the ball. Can someone comment on this?"
What is conservation of momentum?,"Hello. I believe in 2b acceleration is negative because the final velocity of the club minus the initial velocity is 32-40=-8, which would make the force negative, thus the answer to 2b should be -4kN.  Which make sense since the ball applies an impulse force opposite to the swing of the club (Newton's 3rd).","Also, the club is losing force since some of it transferred to the ball.  So, in the question the force obtained should be negative."
What is conservation of momentum?,what's smaller than miliseconds?,"Microsecond, nanosecond, picosecond and etc."
What is conservation of momentum?,Why did we not subtract 20m/s from 25m/s in exercise 3?,"In the problem the ball is thrown from person A to person B at 25 m/s then the ball is thrown from person B to person A at 20 m/s.  

The direction from A to B is the opposite direction than B to A so if you consider the velocity of the ball from A to B to be positive then the velocity from B to A is negative giving you Vi = 25 m/s and Vf = -20 m/s.  

When you  put them into the Vi - Vf part of the equation you have (25 m/s) - (-20 m/s) = 25 m/s + 20 m/s = 45 m/s."
What is conservation of momentum?,Is conservation of momentum only applied for two objects that are in motion and are colliding? Is there a conservation of momentum for a ball hitting a wall? How is conservation of momentum differ from Newton's third law of motion?,"Conservation of momentum is separate from Newton's third law and it is applicable in any isolated system.  So a ball hitting a wall is subject to conservation of momentum.  

Even when you have a system that seems to violate conservation of momentum you can almost always increase the system to include enough to have momentum conserved."
What is conservation of momentum?,"In the facts about conservation of momentum in third point you said KE is likely not conserved, can you please explain that in detail and state some examples where KE  cannot be conserved","Here is a video of an experiment where KE is not conserved but momentum is: https://www.youtube.com/watch?v=N8HrMZB6_dU

The KE and momentum of the two bullets should equivalent to each other.  The two blocks travel to the same height because of the conservation of liner momentum but the KE of the bullet gets split between heat, sound, block and bullet deformation as well as rotation in one of the blocks..  

Since both blocks attain the same height  so the KE from vertical motion but the block that was shot off center also has KE from rotation so it has retained more the the bullets KE as KE.  In the block that is shot in the center there is more of the KE transferred to heat, sound, block and bullet deformation than in the one shot off center."
What are two dimensional collisions?,"What does it mean to write 0.72angle180degrees? How do we solve them?

Also, can someone please explain exercise 2b?","No idea if this is relevant anymore but why not. The answer I got was slightly off by 10N but the process should be similar. Starting off, we need to know what Δpx is and what Δpy is, because to find the force on the ball we can use the impulse-momentum theorem and say that FΔt=mΔv. This means that Δp/Δt is equal to force. The only way we can find the Δp is if we fine Δpx and Δpy and add them together (or subtract correct me if I'm wrong, but in this problem the way doesn't really matter, you'll see why). To find Δpx, we have to use the mΔv formula, but to find Δv, we need to carry out trig function. Vf is 9.23 m/s, which we found in 2a. So we take 9.23 m/s and now have to find the x component in the triangle. And with the triangle being a right triangle, we can simply do 9.23cos40. To find the initial, we would just change the numbers accordingly. 9.23 would become 10 and 40 would be 45. And since the ball is moving right on the plane, the question says that that is positive. So then we would subtract Vf-Vi and then multiply by the mass (mΔv remember) meaning that we should get -6.93x10^-5 or -6.93E-5. For the y component, we would carry out the same task, but instead, we would switch the cos out for a sin. Another change is that since the ball bouncing off is considered in the -y direction, we would make 9.23sin40 to -9.23sin40. And once we subtract ((-9.23sin40)-(10sin45)) and multiply that also by 0.145 kg (mΔv), we get -1.8855. So now (correct me if I'm wrong), but I just subtracted the two and got -1.8855 (see the other number was so small the difference barely changed). Then I divided that by 0.0005s (0.5ms converted to seconds), it became -3780N. Hope this helped!"
What are two dimensional collisions?,In exercise 1a the total initial momentum is .72. If the final momentum is equal to the initial momentum and the yellow ball gains a velocity of 2.857 and a momentum of .428 then the white ball's velocity could be .72-.428 divided by .18 which is 1.619m/s instead of 2.2m/s?,"I did the exact same thing as +david rominee and +ham1988 . I don't know the answer. I'll try implementing angles into it and see if I get a different answer. If I do, I will notify everyone."
What are two dimensional collisions?,"In exercise 1C, why is even there any energy loss? We didn´t consider frictional forces nor sound nor gravity. All of the calculations were based in considering no change in momentum. there shouldn´t be any losses. Can someone please provide with an explanation?",The ending velocities imply that there must have been some energy loss..  The collision was not 100% elastic.  The energy loss would be via heat.  Conservation of momentum does not at all imply conservation of kinetic energy.
What are two dimensional collisions?,Can you give an explanation for exercise 2a? I assumed the horizontal speed remained the same and only verticle speed reduced so that the ball bounces off 40 degrees instead of 45 degrees. I don't understand where 1.025 tan (40) and 1.025/cos (40) come from.,"You are correct, the initial x momentum is 0.145 * 10m/s * cos(45) = 1.025. Then divide that x momentum by cos(40) to get the total momentum (x and y) after the collision. This value, 1.025/cos(40), represents the hypotenuse of the right triangle. Thus the leg representing the y momentum (for part 2b) after the collision is that value times sin(40). sin(40)/cos(40) = tan(40), So it reduces to 1.025 * tan(40)."
What are two dimensional collisions?,"In the bouncing ball example, why was 1.45 used in the calculations instead of the given 0.145 kg in the problem?","Hi! Because 0.145 is the mass of the ball, and we are calculating the momentum. So, 0.145 kg * 10 m/s (initial velocity) gives us 1.45 =)"
What are momentum and impulse?,I as well am not really understanding what impulse is exactly.,"so....
if you want to change the momentum of an object, you have to apply a force. OK??


But if you apply that force for a long time then the momentum will change more.

and the effect of the force AND the time the force is applied, is the impulse of the force.

so the change in momentum = size of force   x   time for which the force was applied

ok??"
What are momentum and impulse?,"the problem in the paragraph momentum in space , i dont think the acceleration should be 9.8 ms^-2 cuz gravitational acceleration decreases with increasing altitude ! 9.8 ms^-2 is only applicable for objects on the earth under 100m altitude ! am i right ?",The first part of the question requires us to find out how much impulse the astronaut is *capable* of applying which depends on how strong she is. This is found based on her ability to lift weights *on earth* as given in the problem.. Knowing this we can find the effect of the same impulse on the spacecraft.
What are momentum and impulse?,"So from what I understand, Impulse is change in momentum but it is a bit different. For instance Acceleration is rate of change of velocity v/t ,velocity is rate of change of position x/t but impulse is not F/t it's F*t , furthermore p= f*t ==> f=p/t This indicates that force is rate of change of momentum. Can someone help me here? (P.S. I haven't done Calculus yet but I think that integral is a function for area under the curve and derivative would be for slope {rate of change} So what's the derivative of momentum, since its integral is impulse )","Yes! That's entirely correct.
Impulse is a certain amount of force you apply for a certain amount of time to cause a change in momentum.  That is why it is F*t.  For example, when you hit a ball with a cricket bat, you apply a force for a time(a very short period in this case) to  cause a change (or transfer) of momentum in the ball.
Also, you saying that F=p/t is correct.  When we focus on the mathematics a little bit, it is quiet obvious.  F=p/t => F=m*v/t => F=m*a (here the change in the quantities is considered)."
What are momentum and impulse?,what is the difference between force and thrust?,They are different things thrust is a type of force but they do share the same units this is because force is a general term whil thrust is a subset that is measured in the same way.
What are momentum and impulse?,"Hi, what are some of the most important everyday uses of momentum? I mean how can I benefit from my simple physics knowledge about momentum in my daily life?","I think airbag is one of of it . Force and time is inversely proportional in momentum calculation so if time is increased, force is decreased. The airbag is designed so that it can increase the time required to stop our body momentum in a collision, reducing force impact, minimise injury to our body."
What are momentum and impulse?,"Hello. In the "Impulse of an aircraft", it says that the aircraft "can produce a thrust force of up to 250 kN" and that it "takes around 30 s for the aircraft to get up to take-off speed". I understand how to take the area under the curve, but we know the force and we know the time. Why can't I just multiply the thrust force of 250 kN and 30 s to get impulse? What is the difference between the impulse from the multiplication I just described and the area under the curve? Thank you.",If the force is constant at 250 for 30 s then taking the area under the curve IS multiplying 250 * 30.  But if the force is not constant then you cannot do that.
N/A,"In Exercice 2b, solution: I do not understand how " we should recognize that the kinetic energy which must be dissipated in the block is now four times higher". Can someone explain this further?","I believe he meant two times higher. The kinetic energy carried by the bullet in the previous problem was mv²/2, while now is (m/2).(2v)²/2 = mv². Since all the kinetic energy is transferred to the block, it dissipates twice as much energy"
N/A,">Object A collides with an equal mass object B. Objects have equal but oppositely directed velocity.

Does that mean If I use a 2-ball Newton's Cradle (sealed in vacuum, not friction of any kind, no energy loss).

If I release the two balls at the same height and at the same time, they'll bounce of each other forever?",If there is no energy loss then yes they will bounce for ever.
N/A,""A light object collides with a much heavier target which is at rest.
The light object bounces off the target, maintaining the same speed but with opposite direction. The heavy target remains at rest." How can the heaver target remain at rest after having a force applied from the collision?","Maybe the question is a little confusing?? Not sure since I dont see the whole thing.

How about if the quesiton was rephrased:

"A ball moving with velocity v strikes a wall and bounces off with velocity -v"

(This means that the collision was perfectly elastic)

Any thoughts?.."
N/A,"In second case of elastic collision that is:
Object A collides with an equal mass object B. Objects have equal but oppositely directed velocity.
It state that both mass of objects are equal and velocity of both object should be in opposite direction.
so if we take initial velocity of object A is positive and initial velocity of object B is negative.
so after putting those value in formula of final velocity. We get
Vaf = - Vbi and Vbf = Vai instead of Vaf = Vbi and Vbf = Vai
Please check and reply Thanks. 
David Sir you done a great job as usual..","Vaf = Vbi and Vbf = Vai are the correct expressions.
In the formula shown in the article, instead of using minus sign to denote a velocity along the negative axis, simply Vi and Vf are used to get a general relation (one that will give the correct answer according to the initial velocity directions.)
 
For ex: According to your assumption of B having an initial velocity along the negative axis, you will find that Vaf = - Vbi. Had I assumed B to be initially moving in a positive direction, ie., initial velocity of object B = +Vbi and A in a negative direction, - Vai, i would have found the final result to: Vaf = +Vbf. 
The given expression for final velocities work for both cases."
N/A,""Some kinetic energy gets transformed into heat, sound, and used to deform the block. However, momentum must still be conserved." Does this mean that the loss in kinetic energy is small or that the loss in kinetic energy has a small affect on the momentum? With the momentum and kinetic energy coming from the projectile and some of the kinetic energy being transferred to the surroundings after impact then 1/2mv^2 decreases?","Its a difficult concept to work on. But you need to keep the following in mind...

Somehow: Momentum is always conserved AS momentum. (Does not convert to energy)

Kinetic energy is rarely conserved. Only in perfectly elastic collisions. BUT total energy is always conserved in whatever form.

Here is a useful thing to remember about inelastic collisions

In a perfectly inelastic collision (ie when the objects 'stick together' or coalesce, the MAXIMUM amount of KE is lost. Not necessarily ALL of it. 
I like this phrase because it reminds us that the priority here is conservation of momentum. Once that has been honoured and  calculated, then we can determine the resulting kinetic energy.

Hope that helps"
N/A,"Alright, I dont get it. In excersise 1b... 
vfr = velocity, final, racket
vir = velocity, initial, racket
mr = mass, racket
ms = mass, shuttle
..

In my way:
(mr×vir²)/2+(ms×vis²)/2 = (mr×vfr²)/2+(ms×vfs²)/2
(5×0)/2+(100×20²)/2 = (5×vfr²)/2+(100×0²)/2
(100×20²)/2 = (5×vfr²)/2
100*20²=5×vfr
(100*20²)/5=*vfr²
8000=vfr²
63,24=vfr

Where is this wrong, I dont get...","I we can't use only kinetic formula to find Vfs, because we DON'T know final velocity of racket after collision, So vfr is NOT equal to 0"
Rotational inertia,"I do not understand how rotational inertia increases with increasing distance of mass?
isn't it easier to push open a door from a farther point than a point close to its hinges?","Good question.

OK; so there are two concepts here and we much keep them seperate.

The pushing of the door is correct; ie the further away from the hinge, the easier it is to turn. This is the concept of moments. (or torque) and the moment of the force = distance x force. bigger distance = easier to turn.

Moment of inertia is a different concept. This is about how easy it is to turn a body based on its mass and the distribution of the mass. 

so, if you have a mass of 20kg attached to your door near the hinge and you push the door handle, it will be easy to 'get it moving' or, indeed, to stop it moving. If, however, you now replace the 20kg mass nearer to the edge of the door (far away from the hinge) then it becomes more difficult to get it moving (or stop it moving).

two concepts: moment of a force
Moment of inertia.



make sense??"
Rotational inertia,"how do you derive the moment of inertia, using calculus?","You do the surface integral of the object described by its boundaries. It becomes the double integral of d^2.y.dS, where d is the distance of the particles that make the object to the axis, y is the density function, which is usually known and not linear and dS is the area element, which is defined as being the square root of your external product sqrt(Dg1 x Dg2), where g is the parametrization of your surface, Dg1 is the first column of your derivative matrix and Dg2 is the second column of your derivative matrix."
Rotational inertia,how did you find  d in exercise 3?,Although it is not exactly stated it is implied by Figure 5 that the center of each disk is right in the middle between the outer radius (ro=1 meter) and the inner radius (ri=0.75 meters) of the main steel ring. So by  d=1/2(1+0.75) he finds the mean of the outer and inner radius.
Rotational inertia,"In the previous video, I think David said that for objects rotating around a point external to them (like the three disks in exercise 3), we should consider them as if all the mass was in the center of mass. However, in the solution of exercise 3, it's calculated the moment of inertia for each object, considering its shape, and then it's used the parallel axis theorem, which gives a different result. How shall I solve this exercises?","Imagine what would happen as the ring gets bigger, and the radius of the disk gets relatively smaller. Inertia is increased more per unit of radius than per unit of mass. In exercise 3, much of the three disks mass was distributed throughout the ring. But as you increase the radius of the ring, the mass of the disks stays close to the ring, and treating those masses as 'point masses' on the ring, and also treating the thickness of the ring as negligible becomes more feasible.

Just like when we use 'g' for acceleration due to gravity on earth, and for acceleration due to gravity 100m above earth. It's true that there is a difference, but not usually a significant difference. However if Earths radius where only 200m, then that difference would be very significant."
Rotational inertia,If the cylinder has the center of mass in a different position (not in the object center) how do I calculate the rotational inertia about this reference? For example if I have a cylinder of  length 120 cm and the center of mass is at 80 cm from the top how do I calculate the rotational inertia Ix=Iy? Thank you,"A cylinder whose centre of mass doesn't coincide with it's geometrical centre has a non-uniform density - the density is variable throughout the object. Without a function for its density  it's going to be impossible to know it's rotational inertia, but if you do know the function, you can use calculus to calculate the rotational inertia, specifically by solving the integral I = ∫ r² dm (which is just the calculus counterpart of I = ∑ mr² ). Using a function for density you can relate dm to r and then integrate with respect to r."
Rotational inertia,"What's the idea behind moment of inertia? In my physic book it says that moment of inertia of something comes from the kinetic energy of it (E=1/2(m(v)^2)).

This is how it is explained:

-Explain Begin-
E=1/2(m(v)^2)..............................................a
"But because v=rw the equation become this:"
Ekrotation=1/2(m(rw)^2)...........................b
Ekrotation=1/2(mr^2)(w)^2.......................c
Linear speed v analog with angular speed w and physicists think that to make the equation c analog with equation a, the mr(r)^2 must be analog with m on equation a. This formula is now called moment of Inertia (noted as I)
-Explain End-
I photographed my book (It's in Bahasa Indonesia) if you're curious: https://s30.postimg.org/sm6dwqcm9/20170206_161635.jpg
Now what he heck is analog with? What is analog? Why should it be analog-ed?",Watch next the next video on rotational kinetic energy.....You may find it illuminating.....
Rotational inertia,who discovered inertia,Galileo discovered inertia. He created the Law of Inertia.
Torque,"In the middle of the article, it says P = (F * 2pi* r)/t. 
F*r is torque. So P = ((torque)*2pi)/t. Then I am stuck. 

Why is P = 2pi*(torque)*(angular velocity)?  
The unit of angular velocity is rad/sec. I don't know why the angular velocity pops up.","My first reply was just wrong, and here is the correction:

You are correct that F*r = torque, and that angular velocity is rad/sec. To see why P = 2pi(torque)*(angular velocity) plug in the units rad/revolution next to 2pi, and like the article says plug in rev/sec next to angular velocity. The revolutions cancel and rad/sec is leftover. Since P = torque * angular velocity for the final equation the article shows in that part of the article, angular velocity is just 2pi rad/sec. I hope this is far more helpful than my first reply. This link https://en.wikipedia.org/wiki/Torque, in the "Conversion to other units" section may also be helpful."
Torque,Isnt a Newton-meter a joule?,"The units for torque (Newton-meter) and energy (Joules) are dimensionally the same, but torque and energy are not equivalent.  The difference is that in the unit for torque there is also radians which we treat as dimensionless (ie. radians have no units) but that unit is still in the expression for torque which is not in the expression for energy.

So really energy unit is [N*m] or [J] and torque unit is [N*m*rads], but again radians are unitless since they are defined as the ratio of circumference/radius which is [m/m]."
Torque,"I didn't understand how we solved exercise 2b, can someone please explain it in a better way?","The formula for finding the (tangential) velocity is v=rω
This comes from taking the derivative of both sides of s=rθ (where s is arc length) with respect to time.

We also know that the engine has an angular velocity of 300 but then is reduced by a factor of 50.

300 rad/sec * 1/50 = 6 rad/sec
   Engine        Reduction      Winch
    speed               ratio            speed

Plugging this back into our equation gives us:
v = r ω
= (0.25 m) (6 rad/sec)
= 1.5 m/sec

(Does this help?)"
Torque,"In 2a, can anyone explain how tau(w)=tau(m)/r? R is only the factor by which speed reduces right? How is that going to affect our torque?","Power= τ*ω
P of winch drum= τ(of winch drum)*ω(of winch drum); or in other words:
P_w=τ_w *ω_w where that w stands for winch drum
The power remains the same, therefore, P of winch drum= P of machine; I will replace P of machine with P_m
P_w= P_m; therefore, τ_w *ω_w=τ_m *ω_m
The exercise says "is driven from the engine via a 1:50 speed reduction gear"; therefore,  ω_w=ω_m*R (R stands for ratio).
P_w=τ_w *ω_m *R  P_w has to equal P_m; τ_w *ω_m *R= τ_m *ω_m;
 τ_w *R= τ_m; or τ_w=τ_m/R"
Torque,Can we solve this problem using law of conservation of momentum?,"No, I suppose momentum will not remain conserved because a constant force is acting on the system.  which will lead to acceleration and thus velocity will not remain constant. which will in turn vary momentum"
Torque,so how to tackle a question with the wheel size of a car and torque ? what happens when increased and decreased the radius of tire ? can u explain in detail ?,"Let us take the force at the edge of tyre that is applied on the road (and then road applies equal frictional force to push the vehicle forward) as F .  The radius of tyre as r and then calculate the relation between the torque available at the wheel shaft and the force applied on the road.
F*r=T   (T=torque at wheel) (angle is 90 degrees so we eliminate that)
F=T/r
Therefore, when we increase the radius of the wheel, the force available at the road decreases and it will be difficult accelerating the vehicle.

There are also  other practical effects of increasing wheel size such as increased friction, raised centre of gravity among others."
Torque,"I don't get the answer on 2b. 
Shouldn't the angular speed of the winch drum be 2π*6/s? (delta theta over delta time)
I get 3π for answer (12π*0.25)
What am I missing?","We aren't solving for angular speed, rather tangential (or linear) velocity.

The formula for finding the tangential velocity is v=rω
This comes from taking the derivative of both sides of s=rθ (where s is arc length) with respect to time.

We also know that the engine has an angular velocity of 300 but then is reduced by a factor of 50.

300 rad/sec * 1/50 = 6 rad/sec
   Engine        Reduction      Winch
    speed               ratio            speed

Plugging this back into our equation gives us:
v = r ω
= (0.25 m) (6 rad/sec)
= 1.5 m/sec

(remember that radians are a dimensionless unit)"
Torque,"What is the relationship between torque and velocity? In Example 2 B, I wasn't sure where the formula came from to find the velocity...","The formula for finding the (tangential) velocity is v=rω
This comes from taking the derivative of both sides of s=rθ (where s is arc length) with respect to time.

We also know that the engine has an angular velocity of 300 but then is reduced by a factor of 50.

300 rad/sec  *  1/50  =  6 rad/sec
   Engine        Reduction      Winch
    speed               ratio            speed

Plugging this back into our equation gives us:
v  =  r  ω
    =  (0.25 m) (6 rad/sec)
    = 1.5 m/sec

(remember that radians are a dimensionless unit)"
Torque,what is the relationship between torque and radius?,Torque = force  x radius (perpendicular distance from turning point to the force)
What is buoyant force?,"if upward force is more than downward force then in zero gravity, will a object in water will go upward?","You're correct if there was gravity acting on the water but not the object. However, in zero gravity there would be no water pressure at all and therefore the water wouldn't push you upwards. Buoyancy is a result of gravity acting on a liquid."
What is buoyant force?,if we put a cone inside a fluid such that it is in the lowest most point and there is no water beneath it but there is water around it. then the buoyant force should  act downward . but if the density of the fluid is greater than the cone then who will provide the force to float??,"If there is no chance for the fluid to get beneath  the cone, the cone might stay in place. But I've seen a video on which a screwdriver floats in mid air just because the air pressure is decreased at the right spot above the screwdriver. Of course things are a bit different with gasses and fluids. 

Keep looking and asking around and I'm sure you'll find out soon enough how things really are!"
What is buoyant force?,Does the laws stated above also apply to an object moving to the surface of the water??,"Yes they do. It doesn't matter whether it is stationary or moving, the follow the same laws."
What is buoyant force?,"Can we calculate the pressure acting on a submerged object in a liquid, on it's side?","Yes you can! It's more complicated though, because you need to break it down with some of your calculus and geometry tools, see why? The classic types of problem are "calculate the pressure on the sides of a pool, dam, tank.... etc." You should find problems like these in the section of integral calculus applications of many calculus books :) 
If you'd want me to recommend a book and a page with the answers to the problems, i'll be gald to do so. 

Cheers,"
What is buoyant force?,"If I place an object in water. It will exert a force equal to its weight on the water below. Now, the water below will exert a reaction force upwards on the object. Isn't that buoyant force?","sorry but it's not. buoyant force is different from reaction force

1. condition of reaction force
reaction force (normal force in the case of gravity) only works when two objects meet on a surface

2. analogy of reaction force
in the case of a ball in water, we don't treat water or whatever fluid around it as another object. it is environment. as much as we don't consider a freefalling ball in air as having any reaction force from any surfaces, even though it keeps contacting with air pressure (this is a buoyant force too)

3. definition & example of buoyant force
1) definition
then what pushes the object upward (and any-wards)? the whole water itself and its weight by gravity. 
2) example
let's say a ball is inside a sea. then the sea itself has a mass thus weight by gravity. so all the water molecules in the sea are pushed down. and there's something less dense than them. what will happen? they want to occupy that very volume of that less densy invader! in all possible directions. that's what happens inside the mercury barometer we checked previous chapters here. no matter how small the density differene is (vacuum to a tiny tiny mismatch), water molecules don't miss that chance to exploit it and then steal that volume. and the left is what we've learned. h of a lower part of the ball is a bit larger than that of upper part, thus the net force pushes upward it. that's buoyant force. and that very force is not from the ball itself. or its reaction force from water "surface". but from water molecules around it (insdie the entire sea, to be exact)



plus, it's after the ball lands on the bottom of the sea when the reaction force works. the bottom ground functions as a surface. it keeps the ball from drilling down underground by forcing the same magnitude but opposite direction of reaction force to the ball's weight. thus the ball stays still (happily ever after, i hope)"
What is buoyant force?,"why do some objects float when partially submerged, but sink when fully submerged?","Nice answer Charles. (I was thinking bucket :) 

There is also the situation in which 'surface tension' can play a part.

So, for a small object such a a needle, it might float on the surface but this is not due to displacement. When you push it under water, then surface tension can no longer keep it up so it sinks.

ok??"
What is buoyant force?,"As stated above the buoyant force can be calculated by subtracting the downward force  from the upward force exerted by the water on the object.But the upward force itself is buoyant force by water ,then how do we arrive at the above equation?please make it a little clear I'm too confused.",F (upwards) stands for the force applied by water in an upward direction while F(downwards) stands for the force applied by the water on the can in the downward direction. Buoyant force is the net upward force on the can by the water.
What is buoyant force?,"Suppose that we are discussing an ice cube in a beaker containing water. When the cube melts, it takes the volume of the water that was initially displaced by its weight.

My doubt is that at some point of time, there will be saturation of some kind. The water will eventually start coming out of the beaker if we keep on putting ice cubes one after the other and allowing them to melt. When will such a thing happen?",Liquid water is denser than frozen water so as the ice melts.  The volume of water displaced is equal to the volume of water equivalent to the weight of the ice so the level of the waster will not rise or fall while the ice melts.  If you put ice into the beaker and it can overflow when it is put in but if it is not overflowing when you put it in it will not overflow as it melts.
N/A,Why is not possible to have negative absolute pressure?,If you have no pressure then there are no atoms that can be there.
N/A,why boiling point of water decreases as the pressure goes down? Is here a video that explain this phenomena?,"What applies pressure to the surface of a boiling liquid? You may answer, the air molecules. That is absolutely correct. But what about the molecules of the liquid which are above the surface of the liquid, that have been converted into gaseous phase? It is this pressure that prevents additional molecules of the liquid from escaping from the surface of the liquid. So, greater amount of energy(heat) has to be provided to the liquid to make it boil. So, if the pressure is reduced, you are essentially reducing the amount of molecules above the surface of the liquid(like vacuuming them out of the container). Ah yes, this happens only in a closed container. Now, there is no opposition to the liquid molecules to prevent them from escaping from the liquid phase. Therefore the liquid vaporizes quickly, lowering the boiling point of water.
By the way, the pressure exerted by the gaseous molecules on the surface of the liquid in a closed container is called vapour pressure. So, boiling point is not the temperature at which the liquid boils as the temperature is dependent on the pressure. Therefore, a more precise definition of boiling point would be, 'The temperature at which the vapour pressure of the liquid is equal to the atmospheric pressure.'

Hope this helps"
N/A,"It is said in the article that the weight of air is actually not negligible. My question is: if you're on an open field you would have more air above you than if you were in, say, your house. How come we don't feel that difference at all?","Pressure acts in all directions. When you are in your house, the air is pushed through windows, through doors, through every little crack until the pressure inside is equal to the pressure outside. This is because air is a fluid which conforms to its environment. Solids, on the other hand, behave as you are suggesting."
N/A,""unlike the water example, the density of the air in the atmosphere is not the same at all altitudes."
It seems to me that the density of water should increase, if only slightly, with the massive increases in pressure as one declines to the base of the ocean. (The text implies that there is one atmosphere of pressure increase with every 30 meters below water surface.)
Is it really the case that water's density does not change even under these massive pressures, and if so can you please explain that?","You are right.

Water is often considered "incompressible" to simplify physics calculations, because it is so hard to compress. This is the same kind of simplification as saying that the surface of the Earth is "flat" or that a ball rolling down a hill experiences no friction.

In fact the density of water does increase with pressure. For water initially at normal pressures, you need about 217 atmospheres of pressure per one percent increase in density."
N/A,How can we differentiate Pressure from stress?,"When we are dealing with fluids (liquid and gases) ,, we use the term pressure 
And when we are dealing with metals or any solid object we use the term stress 
That's why most mechanical books use the term stess because they're dealing with solids 

However stress and pressure are basically the same"
N/A,"I have a question, if im in space am i exerting pressure on something?","if there is zero gravity then no .as weight = mg, if g is zero then weight is zero.as there is no force(weight)there is no pressure"
N/A,so can we also say that the pressure of the air above us is counteracted by our blood pressure that is why we feel a bursting sensation from inside of our body when our blood pressure is high ? and feel a squeezing sensation from the atmosphere when our blood pressure is low ?,Generally the pressure inside our blood vessels is 80-120 mm-Hg (gauge pressure). So why we do not burst out: Because of the mechanical strength of our blood vessels. Like a plane flying high in the sky. Note that hypertension occurs if blood pressure rises above 140 mm.
N/A,i understood that the fluid is pushing downwards on the top of the immersed object due to gravity but why does the fluid want to push onto the sides and the botttom of  immersed object and create pressure?,"when you go underwater, where do you feel the pressure? top of your head? or ears?

any deeper, you would feel it on your chest too.


its because you have 'displaced' some water and you could think of it like the water is trying to get back into the space that you are taking...

in fact, the upthrust is equal to the weight of that water that you are displacing


okay??"
What is volume flow rate?,"In the paragraph titled, "What is the equation of continuity?" it says that the volume in must equal the volume out. I am a physics novice/dunce so I really need this spelled out for me. It has a "for instance" that I am struggling with. I am hoping it is a mistake, but honestly with my physics knowledge I can't be sure. 

 "For instance, if in one hour you pump 2 meters cubed of water into a pipe that is already full of water, 3 meters cubed has to flow out of that pipe during that same hour. "

Is this correct? I am trying to understand why the two numbers wouldn't be the same...Please let me know if I am missing something! Thanks!","Hi J

You are correct in thinking this is a typo. The volume flowing in and out of the pipe are the same so the statement should read, "if in one hour you pump 2 meters cubed of water into a pipe that is already full of water, *2* meters cubed has to flow out of that pipe during that same hour.""
What is volume flow rate?,""People often mix up the ideas of volume V and speed v since they look so similar." Wait a second, I thought v stood for velocity, not speed! Am I mistaken, or is the text wrong?","You're correct, but in this case, velocity and speed are the same thing. Speed is a magnitude (in other words, a number representing distance over time) while velocity is a vector - a speed that has a direction. Since liquid through a pipe is flowing in one direction, the direction part doesn't matter. Sal probably used the word speed to make it easier to understand."
What is volume flow rate?,"In the Mountain Dew problem,  the soda is carried from downstairs to upstairs. Should we consider the pressure that is needed to pump the soda up?","If you only want to relate the speeds and areas of the pipe, you don't need to consider the pressure. The continuity equation Av=Av has to be true for any incompressible fluid (since the volume flow must be constant) )even if the pressure and height changes. If you wanted to determine the pressure necessary to pump the Mountain Dew, you would need to use Bernoulli's equation as well as the equation of continuity."
What is volume flow rate?,"as per the continuity equation A1vi = A2v2  it says that the value of Avhas a constant value throughout the pipe. So, if the area, A of a section of pipe decreases, the speed, v of the liquid there must increase so that the product, Av remains the same.
 So, if the area, AAA, of a section of pipe decreases, the speed, vvv, of the liquid there must increase so that the product, AvAvA, v, remains the same. This means that fluids speed up when they reach a narrow section of a pipe and slow down when they reach a wider section of a pipe. This matches everyday experience—think about what happens if you block a portion of the water hose with your thumb, effectively reducing its area, AAA. The water must come out with higher speed, v, to ensure the volume flow rate, Av remains the same. This is why narrow nozzles, which reduce the area (A), attached to water hoses cause a significant increase in the speed, v of the fluid at that point.
but  i noticed that in my home tap , when i fully open the tap it  fills the bucket quickly as compared to when i open it half,(reducing the opening area of tap).  but as per law of continuity ,bucket  should be filled within same time in both cases.","I hope someone answer this question. 

Nicholas:
Can you elaborate more, I don't get how the tap can regulate the (volume flow rate) by reducing the area. This is clearly doesn't explain the equation of the continuity.

Sharma
"Doesn't the Equation of Continuity have nothing to do with time. Because as per A1v1=A2v2, there is no time"
Equation of continuity has everything to do with time, v is speed, speed is meter per second. 

Furthermore, A1v1=A2V2 ---> volume flow rate at 1 = volume flow rate at 2
This means, the amount of water passing in 1 sec is the same at both ends."
What is Bernoulli's equation?,"It's a lot more difficult than the videos, and if I hadn't watched the videos before, I probably couldn't understand this. 
But I have a question about "steady flow", Do you mean that all molecules have the same velocity at any chosen point? Then, if all the water moves along the pipe, every molecule has its velocity directed along the pipe. Then there's NO molecule moving towards the walls and applying pressure on them, how is that not contradicting with the rest?","Hmm, sorry it was confusing. If other people feel the same way I'll rewrite it. 
As for the steady flow question, the water molecules have randomly directed velocities that can be quite high and cause pressure on the walls of the container, but since these are randomly directed they add nothing to the bulk motion of the fluid along the pipe. The velocity I'm referring to is the overall bulk motion of the fluid causing it to move along the pipe. This is similar to the difference between air pressure caused by the random motion of air molecules, and the bulk motion of air across large distances which we would call wind."
What is Bernoulli's equation?,"Under the explanation of the question "Wait, does that really follow?", I have a question on why when the fluid flows from right to left (From the narrow to wide region), the pressure P1 still acts to the right and P2 still acts to the left? Or why does P2 do negative work?

Im confused here, would anyone clarify?","Fluids exert pressure in all directions. So the parts of the fluid on the left (P1) of the highlighted region are exerting a pressure on the highlighted region _from  the left_. They still exert a pressure in all directions, but the only part of this pressure that is relevant is the part that is pushing the highlighted region. So when the fluid flows from right to left, the parts of the fluid on the left (P1) still exert a pressure on the highlighted region from the left. Similarly, P2 always exerts a pressure from the right because it is on the right side of the highlighted region (the section we are interested in).

Whether work done is negative or positive depends on which direction the fluid is flowing and whether the work done is helping the movement or hindering it.
When the fluid is moving from left to right, work done to the right is positive (as it is in the same direction as the flow) and work done to the left is negative (as it hinders the flow).
When the fluid is moving from right to left, work done to the left is positive and work done to the right is negative.

At least, that's how I understood it. Hope that helps."
What is Bernoulli's equation?,"Hang on, Isn't the pressure always supposed to be constant? I mean, I know from the previous videos that P1 = P2. (Pascal's law). Are we talking about different pressures here?","Pascal's Principle applies to fluids that are initially static. In this case, we have a dynamic fluid whose motion is being analyzed...hope that makes sense!"
What is Bernoulli's equation?,how is pressure on static fluid different from that of a moving fluid?,"Since Bernoullis theorem proved that for a horizontally flowing fluid without the height, the P+1/2*ρv^2 is constant, if the velocity is possessed by the fluid(Which means its in motion) it should have less pressure, to satisfy the constant.
​"
What is Bernoulli's equation?,"Why would we use +9.8 as our gravity, when it acts in the negative direction?","Gravity is not negative or positive, it's just downward.  If you define down as the positive direction, g is 9.8 m/s^2.  If you define up as positive, g is -9.8 m/s^2.  Nature doesn't know or care which way you want to draw your axes."
What is Bernoulli's equation?,"The numbers of the last question don't add. I get a pressure of about 613,890 Pa. Anyone else got that problem?",The numbers in the last question do add up: P1=601229.01 Pa
What is Bernoulli's equation?,"I still don't understand "Incompressible fluids have to speed up when they reach a narrow constricted section in order to maintain a constant volume flow rate. This is why a narrow nozzle on a hose causes water to speed up. But something might be bothering you about this phenomenon. If the water is speeding up at a constriction, it's also gaining kinetic energy. Where is this extra kinetic energy coming from? The nozzle? The pipe?" ?","this is due to the pressure energy...at the constriction, pressure energy decreases so kinetic energy increases"
What are PV diagrams?,If work done by a system is equal to change in pressure-volume. Why does an upward and rightward shift in the pressure-volume diagram cause an increase in internal energy? Work done by the system should reduce the systems internal energy shouldn't it?,"The work done in expanding does in fact take energy out of the system, so the only way the state can shift to a higher PV value while the gas does work is to have even more heat Q added to the gas during the process so that overall the gas gains energy."
What are PV diagrams?,"maybe this is not a good doubt .. but if the gas has been compressed why is the work done on the gas positive?  is nt work  done = PdeltaV
so the work done by the gas should be negative if im not wrong
...
correct me if im wrong","I would say is more a matter of semantics
- The work done on the gas is positive
- The work done by the gas is negative
The conservation of energy (first law of thermodynamics) states:
Internal Energy Change  =  Heat added into the System  +  Work done on the System
or
Internal Energy Change  =  Heat added into the System  -  Work done by the System"
What are PV diagrams?,What if there is a closed path for a cyclic process?- This is confusing me.,"This is now explained in a little pop-up box in the middle of the article, but you may have missed it or it may have been added after your question.

While the cycle is moving L to R (increasing volume) the work done BY the gas (area under the curve) is considered positive.  While the cycle is moving R to L (decreasing volume) the work done BY the gas is considered negative.  The total work of the cycle is the sum of these two works (areas under the curves), but since one is negative, it's essentially the difference.   The difference between the two areas is, by definition, the area *within* the cycle and that is the work done BY the gas during the cycle.

As for the sign, if the cycle is clockwise, that means the higher line (higher work area) was L to R (positive work), so the total W is positive.  if the cycle is counterclockwise, that means the higher line (higher W area) was R to L (negative work), so the total W is negative (work was done ON the gas).  But in the either case, the *magnitude* of the work is still the area inside the PV cycle."
What are PV diagrams?,"The slope of the PV diagram has the units N/m^5, does that mean anything?
Thanks","The slope tells you how fast the pressure is changing with respect to volume. Slope m, is equal to Pressure/Volume, or dimensionally: m=(F/A)/V in SI units, it will be kg/(m^5) or kg*(m^-4)*s^(-2). This tells you how fast the pressure is changing with volume for every kg of gas/atoms in the system per volume. If you think about classical mechanics, for example, a ball heading towards the earth, (neglecting air resistance and approximating the distance near the surface of the earth), the force is F=N=kg*(m/s^2). Intuitively, you can think of it as I need to apply this force to move this object with this mass. And to see how long it takes, you divide by the time interval (1/s). The extra s is to account for the extra time needed to move the object that is already traveling with some velocity.

Sorry if I ended up confusing you more... The slope essentially tells you how fast the dependent variable (y-axis) is changing when you let the independent (x-axis) vary.

- (senior) physics/mechanical engineering"
What are PV diagrams?,"When a gas is doing work yet increasing its pressure, can we say that the pressure increase is definitely due to heat being added?","Unless gas is added, it is. If gas is doing work, its volume is increasing. As pressure and volume increases, T=PV/nR is increasing too. Thus, Delta U = Q - W is positive. As W is positive, Q should be positive."
What are PV diagrams?,"why does the volume change determines work sign in the first place? to me, pressure change would be much more intuitive since thats what causing the imbalance - increasing alerady higher pressure in containter, while decreasing already low pressure in surrounding","Work is force*distance.  The volume change occurs because a wall of the container is being displaced.  If you just increase the pressure and there is no volume change (think about how you would do that), no work is being done."
What is the Maxwell-Boltzmann distribution?,Why isn't V(rms) equal to V(avg) ? Here V(avg) is avg speed of the molecules.,"Hey Nitin, I think I can answer your question. Let's say there are 6 molecules in a sample of gas. These 6 molecules have the following velocities, respectively: -1 m/s, -2 m/s, -3 m/s, +1 m/s, +2 m/s, and +3 m/s. If we want to find the average speed of a molecule in this sample of gas, we need to convert these 6 vector quantities (i.e. velocities) into 6 scalar quantities (i.e. speeds) by removing the signs. After performing this conversion, we have the following speeds: 1 m/s, 2 m/s, 3 m/s, 1 m/s, 2 m/s, and 3 m/s. To find the average speed, v(avg), we need to add these 6 speeds together and then divide the sum by the total number of speeds:

1 + 2 + 3 + 1 + 2 + 3 = 12
12 / 6 = 2

So the average speed is 2 m/s. On the other hand, if we want to find the root-mean-square speed of a molecule in this sample of gas, we don't need to convert those 6 velocities into 6 speeds. Instead, we need to find the square root of the average of the squares of the velocities:

(-1)^2 + (-2)^2 + (-3)^2 + 1^2 + 2^2 + 3^2 = 28
28 / 6 = 4.67
The square root of 4.67 is 2.16.

So the root-mean-square speed is 2.16 m/s, which is greater than the average speed (2 m/s). This is why the root-mean-square speed does not equal the average speed. I hope this helps. If my reasoning is incorrect, please let me know."
What is the Maxwell-Boltzmann distribution?,"Just above the section "What does the area under a Maxwell-Boltzmann distribution represent?", should the 605 m/s quantity be v(rms) instead of v(p)?",Area under Maxwell distribution curve represents the number of molecules in the system
What is the Maxwell-Boltzmann distribution?,"Hello!
 Why is it that the average kinetic energy is proportional to the rms speed instead of the average speed .I understood about squares and roots, but still if i have the average speed of particles it would be normal for me to take the average speed for the average kin,energy?
Thank you.","This is a very good question that gets to the root (pun not intended) of something that is apparently so subtle that it was never explicitly stated to me all the way through second year college physics.  Massive bodies in motion have two parameters that diverge the greater their velocity becomes.  Momentum is simply mass times velocity, while kinetic energy is one half of the product of the mass and the square of the velocity.  So when we look at the simple mode and mean of the Maxwell-Boltzmann distribution (which assumes a uniform mass) we are looking at momentum, but when we consider the rms value we are now looking at a description of kinetic energy.
I'm pretty sure you've already understood that, but are still as unsure as I am about why that matters.  First off, in the context of this lesson, all we need is to be aware that there is a difference, and that at some point in the future it will become significant.
Looking beyond the scope of this lesson, I expect the implications of this follow from the two facts that a) both momentum and kinetic energy must be conserved, in any non-relativistic event at least, and b) they begin to scale at radically different rates as the velocity increases.
At the human scale, if my car hits another car at 1 mph the momentum is conserved as we both continue at 1/2 mph until various frictions bring us to a stop, and pretty much all of the excess kinetic energy is distributed without too much trauma.  However, if I hit the same stationary car at 100 mph and momentum is conserved as we both continue down the road at 50 mph, there is now 10,000 times as much energy to dissipate.  My car retains one half times m times 50 squared in its residual velocity, the second car absorbs the same amount as it accelerates, leaving one half m times 10,000 - 2500 - 2500,  that is fully half the original kinetic energy to be dissipated as a bunch of highway ugliness.
Just how that translates into behaviours at the molecular scale, I am not sure.  Hopefully, I'll get a better handle on this as these lessons progress."
What is the Maxwell-Boltzmann distribution?,"If we're plotting speed on the x axis, is there then a maximum (the speed of light) the individual particles can't go beyond? So the graph doesn't tail off to infinity?","Technically yes, but it is a bit more complex. As particles approach the speed of light they are called relativistic particles. At that point, special relativity must be taken into account. Look up the Maxwell–Jüttner distribution. It describes the distribution of speeds for relativistic particles.
If any of this is incorrect please let me know and I will correct it."
What is the Maxwell-Boltzmann distribution?,"Hi, I don't quite understand the idea of "number of molecules per unit speed" on the y-axis. What is this idea of "unit speed"? Which "unit speed" are we dividing the number of molecules by? Could you explain? Thanks!","The wording is a little confusing.  In order to get a distribution, you are dividing up the molecules into bins according to their speed (like a histogram).  In this case, the bins are so thin that instead of a lot of bars, you get a smooth curve that represents the top of each thin bar.  So when they say "number of molecules per unit speed" they aren't mathematically dividing, it's more like "number of molecules in each bin of speed" with the bins on the x-axis.   But remember that the bins are so thin that we actually refer to them just by the x-value (speed).  So there is a number of molecules at 600.000 m/s, and a number at 600.001 m/s, and a number at 600.002 m/s, and thus you get a continuous curve of number of molecules vs speed."
What is the Maxwell-Boltzmann distribution?,Can V(rms) be equal to V(avg)?,"yes when all the velocity data values are same. 
eg. -3,-3,-3,3,3,3 then V aver.: 3 and V rms : 3 ."
What is the Maxwell-Boltzmann distribution?,"So, why are there three kinds of mean speeds/velocities? i mean why not just one kind but three. Any reason?","It's kind of like how you'd have a mode, mean and median in statistics. They're all averages, but represent different things. For example, here, the most probable speed is equivalent to the mode, and the average speed is equivalent to the mean. Root mean square is a type of generalised mean, I believe."
What is thermal conductivity?,i want a very specific and a very to the point definition of thermal energy. help me .,Thermal energy is the energy that comes from the heat . This heat is generated by the movements of tiny particles within an object.
What is thermal conductivity?,"Can you say that liquid water is a bad thermal conductor? I'm thinking that it often just eats the heat for itself (for example use it to to evaporate) instead of passing it down.

Thanks!","interesting question...

the thing is, water is hungry for heat.... ie it has a large heat capacity. but that is different to conductivity. i guess it depends on the context...ie if you talk about heat passing through, or heat being absorbed

make sense??"
What is thermal conductivity?,"Let's say there are 2 pieces of metal (copper and iron) which have different constants, k and they are put together. To calculate the rate of heat flow, is it still possible to use the formula as stated in the article?","I think that the formula can still calculate the "rate flow" at "a moment of time" because when the time pass the difference of temperature in two material will decrease and also the rate flow. BUT in the example2, they assumed that the temperature inside and outside the window remain constant even the heat was transferred. Sorry for bad English!"
What is thermal conductivity?,Does this equation only work if the temperature on both sides remains constant?,"Nope. If temperature on both sides remain constant, there will be no thermal conductivity. [Don't mistake me. The formula does hold good for this case too!] The formula is meant to be used to find thermal conductivity and that generally happens when there are different temperatures. :)"
What is the ideal gas law?,"Where do _R, Na(Avogadro's Number) and k(Boltzmann's constant)_ come from and why? Is there an explanation for how they have been calculated? Thanks in advance. I wouldn't mind if the answer involved calculus.","No calculus needed :-) Like most any constants, they are simply needed if there is always that same factor missing in an equation. 
For example, in statistical mechanics you have a formula that is: S=k*ln(W). If you know S and W for at least two cases, then you might realize that, _for both cases,_ S = ln(W) only if you multiply the right side by k constant"
What is the ideal gas law?,"In the section "What is the molar form of the ideal gas law?" and the first example, shouldn't the atm version of the ideal gas constant be 0.082 L*atm/mol*K instead of 0.082 L*atm/K? Or is there some reason the number of moles isn't included?","You are right, the R actually does have the "mol" units, and it should read, as you correctly mentioned, L*atm/mol*K.
Nevertheless, the reason why this was probably excluded here is because the units of n are mol, and then if you combine n and R, the mol units will cancel."
What is the ideal gas law?,How do I know when a gas behaves like an ideal gas?,most real gases do as long as the temperature is not too low and the pressure is not too high
What is the ideal gas law?,"When converting, why should we use Kelvin?","One of the most important formulas in thermodynamics is P1 * V1 / T1= P2 * V2 / T2. However, if we used Celsius or Fahrenheit, what if, for example, the temperature was 0 degrees Celsius? Since you can't divide by 0, the formula would not work. 
The Kelvin scale is made with 0 being equal to absolute zero, the coldest possible temperature, where the molecules stop moving completely. Therefore, you will never get a zero or negative temperature in your formula if you use Kelvin. 
 Kelvin is also the widely accepted temperature scale. If, for example, some people used Celsius and some people used Kelvin, we would all get different answers, so everyone uses Kelvin."
What is the ideal gas law?,"In the "Units to use for PV=nRT" section, It says 1 liter=0.001 m​^3​​=1000 cm​^3.
This doesn't make sense to me. Isn't 1000 cm^3 = ​​10m^3 since c is a SI prefix for 10^-2?
10m^3 isn't equal to 0.001m^3. What am I missing? I'm sorry if this is a silly question.","Your math is a little bit wrong. Check it:
1 cm = (10^-2) m
(1 cm)^3 = (10^-2 m )^3
1 cm^3 = (10^-6) m^3
(1 cm^3)*1000 = (10^-6) m^3 *1000
1000 cm^3 = (10^-6)*(10^3) m^3
1000 cm^3 = 10^-3 m^3 = 0.001 m^3"
What is the ideal gas law?,What factor is found in the ideal gas law which is not in the previous laws?,"Nothing extra. The ideal gas law is the integration of Boyle's, Charles' and Avogadro's laws into a single equation."
What is the ideal gas law?,"Where do we get the gas constant ,R, from?
Thanks","Choose any gas, assuming its ideal. For example, 1 mole of Ar = 39.948 = 22.4 L at standard pressure ( 1 atm) 

Just solve for R using the same formula, PV=nRT or in this case, R = PV/nT

Subsitue values into the equations :- R = (1atm)  (22.4) / (1mole) (273K)

        Solve:  R  =  0.0821 atm L / mol K

There are also alternate values for different units.
If R is needed in units of pressure (kPa)  =  8.314 kPa L / mol K

If R is needed in units of pressure (mm Hg)  =  62.396 mm Hg L / mol K

 I would suggest always using the value of 0.0821 atm L / mol K for R unless stated otherwise.

Hope this helped!"
What is the first law of thermodynamics?,"I understand that Q isn't the same thing as T, Q is heat that enters/exits the gas. ΔT might increase as Q enters, but ΔT also might stay constant or even decrease as Q enters the system, and so the opposite.
 
But it's still confusing me that from this expression Q = m.c.ΔT it shows that Q is the function of ΔT (delta T) which is the change in temperature, and from this ΔT is proportional to Q.

 I would be grateful if anyone can help me with this confusion.","You say "ΔT also might stay constant or even decrease as Q enters the system, and so the opposite" - that is to do with the effect of W (work done on or by the gas in question), where ΔT is proportional to ΔU. In the expression Q = m.c.ΔT, W is not taken into account as it assumes a constant volume. You're just looking at raising the temperature of the substance with regard to the mass and specific heat capacity of the material, but not really considering the expansion of the gas pushing a piston or the piston pushing down on the gas (W). The Q = m.c.ΔT expression is only really appropriate for a constant volume.

See: https://chemistry.stackexchange.com/questions/4722/when-is-it-okay-to-use-q-mc-delta-t-is-this-equation-only-for-calorimetry-que"
What is the first law of thermodynamics?,why do we need second law of thermodynamics?Is energy really lost in second law of thermodynamics?,"Hello Muhammad,

This law concerns energy conversion. Suppose we had a machine that could convert electrical energy to mechanical energy (motor). In an ideal world it could do so without any loss. In reality the efficiency is not 100% and so we loose some energy to waste heat. The 2nd law of thermodynamics states that  you can NEVER make a machine that converts 100% of the energy. 

Likewise with a battery. When you charge the battery (electrical to chemical energy) there will be losses. When you discharge the battery (chemical to electrical) there will be losses.

Don't let anyone tell you otherwise - there is no such thing as perpetual motion machines!

Regards,

APD"
What is the first law of thermodynamics?,How does doing work on the system increase the kinetic energy of the gas molecules,"If the piston is pushed down (form of work done), its base would collide against the gas molecules, causing them to move faster and hence their kinetic energy is increased.
Hope this makes sense :)"
What is the first law of thermodynamics?,"If the piston moves up when the gas expands (due to heat) and if the volume of the gas does not decrease, what allows the piston to move down again?
Thanks","not sure of your exact question

but if the piston moves back down, it is usually because it is being pushed by a mechanical force to squash (compress) the gas (or to push the gas out of the cylinder as waste)

The mechanical force comes from another part of the engine such as fly-wheel or other picston.


OK?"
What is the first law of thermodynamics?,"In the article it says " temperature and internal energy are proportional", but I still don't understand. Internal energy is every kind of energy that exists in a system, including KE, PE and others. I understand that temperature is proportional to Kinetic energy, but KE is just part of what comprise total energy (Internal energy is every kind of energy that exists in a system, including KE, PE and others). So is temperature directly proportional to internal energy? And by saying A is proportional to B, is it necessarily equal to saying that A=kB, where k is a constant?","I think the case that Internal energy is proportional to kinetic energy is mostly based on monoatomic ideal gas, which means in the system there are no other forms of energy except kinetic energy."
What is the first law of thermodynamics?,"In example 2,Sample 1 I cannot understand how does Heat Exits the system even when the work was done by the gas?
Similary in Sample 4 the heat enters the system even when work is done on the gas.
Explanations please anyone.","the most easy way to clarify this doubt is that consider yourself to be a candle. when it lights there is noble work done by the candle [ giving light to others (thermodynamically, work done by the gas ) ] but sadly the candle itself gets shorter and shorter( i.e thermodynamically heat loss) but when we add a little wax to it ( thermodynamically work done on the gas ) , the height increases ( heat enters the system)"
What is the first law of thermodynamics?,If you measure a liquid's heat (coffee for example) with a thermometer. Do you also lose heat to the thermometer?,"A hot liquid will lose heat to a cooler thermometer.  The thermometer has to absorb thermal energy in order to measure it.  Also a cold liquid might gain heat from a hot thermometer, right?
But note that you don't measure "heat" when you use a thermometer.  You measure temperature.  They're not the same thing."
What is the first law of thermodynamics?,while preparing for the SAT subject tests physics from Barron's I read that they have taken the work done on the gas as positive.But we are told that W=P(change in volume). But if we apply force on the gas then its volume must decrease hence the work done must be negative please explain(its given on page 375),"Its a good question... You will see that W changing sign and meaning throughout your reading unfortunately.

My answer to students is this: use your intelligence to define it within the context (or question) you are lookking at

for example, if a gas is expanding, it is doing work ON the atmosphere. Work is being done BY the gas.

If a piston squashes a gas, then it is doing work ON the gas. Work is being done BY the piston. 

When you know what is doing the work and what its being done ON, then you can fix the signage in your equaitons appropriately. 

Sorry to say, I have seen the negative sign in books given in different ways and not always clear; hence I am reluctant to give signage in equations on this topic : rather give clear understanding of the equaitons mean.


Hope that helps"
What is the first law of thermodynamics?,"If I move a bottle of gas from a low place to a high place (it seems I am doing work, so "W" is positive), according to "ΔU=Q+W", is there an increase in internal energy?","The gravitational potential energy of a system like the bottle is not part of the internal energy since it is not internal to the system, the bottle.  Similarly the kinetic energy of the system from the motion of the entire system is not part of the internal energy.  If you have two bottles of the same size, same amount of material in it at the same pressure and temperature but one is sitting on a table and the other is zipping by in a plane at 1000 meters above the table they have different kinetic energies but the internal energies are the same."
Kirchhoff's laws,When I see the words "voltage on each resistor" - what does that mean? that voltage is getting eaten up or used by the resistor? Is it wasting energy?,"The phrases "Voltage on" and "Voltage across" mean the same thing. One end of the resistor is at a higher potential than the other end. The difference in potential is called the "voltage across" the resistor. It is the nature of resistors that when they have a voltage across them, a current flows. When current flows, there is energy being dissipated. If the circuit is doing something useful, then we say "Nice job using the energy! I like this song." If the circuit is not useful, then we might say "What a waste of energy, how sad"."
Kirchhoff's laws,"How is this affected if there are multiple batteries, and therefore multiple currents? What if the resistors are in parallel?","Kirchhoff's Laws work for every circuit, no matter the number of batteries or resistor configuration.  KCL tells you about the sum of currents at each specific node in the circuit. KVL tells you about the sum of voltage rises/drops around every loop of a circuit. KVL and KCL aren't fooled by multiple voltage or current sources, or parallel resistors. They always work."
Kirchhoff's laws,"Where does the current flow when it enters the node.? What if all the current (arrows) are pointing inward, how is the sum of current zero in that case?","good question.

If all the arrows are drawn as going into the node, then one of the currents going 'in' will have a negative value in your calculations.

Of course, there must be just as much going in as out"
Kirchhoff's laws,what is voltage?,"It is the electric potential between two points. You probably know potential energy, like when a bowling ball is sitting on a skyscraper it has the potential energy stored from gravity because it could fall. Voltage is the same thing but with electrons (negatively charged) that have potential because they will try and move to a postive (or "less" negative) area."
Kirchhoff's laws,is kirchhoff's law applicable for ac circuits?,"Hello Drakshaspodia,

Yes, both KVL and KCL apply to AC circuits. 

You will find AC circuit are more interesting than DC circuits as capacitors and inductors change impedance as frequency changes. Think of impedance as the resistance to an AC signal.

Regards,

APD"
Kirchhoff's laws,"In circuit diagrams for example the circuit diagram before KVL(having Vab,VR1,VR2...) how we can give + and - signs to a voltage I mean how we can give polarity signs to a component","When you apply voltage to a circuit and let currents start to flow, each component will have some current and there will also be a voltage appearing between/across the terminals of the component (by virtue of Ohm's Law). When we put voltage labels on components we are just giving names to those voltages so we can talk about them between ourselves and in equations.

You name a voltage by calling it something and putting + and - signs on it. You might be worried that the signs could be "wrong". Don't worry. We just give them names and signs so we have something to talk about. It's like saying that the top of a map is North. Just a reference direction. If (after we do the analysis) the voltage ends up being the other way around, it just gets a negative value. Just like if I'm walking South, I could say I'm walking -North."
Kirchhoff's laws,what is the algebraic sum?,"It's a fancy way of saying "total summation".
_Example: the algebraic sum of 8, -1, -2 is 5._"
Kirchhoff's laws,"what do we understand from the arrows in the voltage diagrams
what is voltage polarity","Hello 

Here is how you make the arrows. 

1) Assume a direction of current flow.

2) Walk around the loop in the chosen direction of current flow. For sake of argument lets start at the 200 Ω resistor. 

2)  As you walk along the circuit you will encounter a component. Ask yourself if the voltage as you enter this component is greater than or less than the exit terminal. 

3) If the voltage on the terminal you entered is greater than the exit terminal then the entrance terminal gets a “+”. And the other terminal gets a “-.”

For a resister you don’t need to think very hard. If you are traveling in the direction of the current then the voltage on the terminal you enter will be higher than the exit.

The battery is  more interesting. As we travel we will enter the battery on the negative terminal. When we look across we see the positive terminal. Consequently the entrance terminal gets a ‘-’ and the exit terminal gets a “+” symbol.

One last point - if you were tr travel all the way around this loop the sum of the voltages is equal to zero. This property is essential to you study of electronics. We give it the special name KCL (Kirchhoff's Voltage Law).

Regards,

APD

P.S. You could have assumed the opposite direction for the current and everything would have mathematically worked out..."
Kirchhoff's laws,Isn't the answer to the second question for i5 "-6 mA"? The answer key suggests "+6 mA" but this would give you a summation of +12 mA. I believe the description below the problem states the same.,"Hi cptlaurion,
the answer key says "-6mA" going into the node OR "+6mA" going out of the node, they have the same meaning. the "+ve" sign means that your arbitrary direction you suggested is true and the "-ve" sign means that your arbitrary direction you suggested is false and the true current direction is in the opposite one.
I hope you got what you need from my answer."
"Basic electrical quantities: current, voltage, power","I still don't get Amperes, can someone please help with a simple analogy so I can understand better?","Think of a tank of water with a hole in it. The amount of water in the tank is the voltage, aka the potential/volts. The size of the hole is the resistance, aka the ohms. The amount of water that flows would be the amps in this example. If you wanted to add watts into this system, say you put a water wheel in that stream of water. The power produced would be watts."
"Basic electrical quantities: current, voltage, power",what is quantum mechanics ? please explain in brief,a body of principles that explains the behaviour of matter and it's interactions with energy on the scale of atoms and subatomic particles
"Basic electrical quantities: current, voltage, power",Can someone elaborate the formula dU/dt,I posted in tips if you are not familiar with derivatives.
"Basic electrical quantities: current, voltage, power","If water is a poor conductor of electricity, why do we get electrocuted if we stand in water and electricity is introduced?","Pure water is poor conductor of electricity but the water in your tap contains many minerals that  provide the ions for conduction of electricity. Similarly if you take pure water and dissolve a teaspoon of table salt (NaCl), it would become a good conductor because now it would have sodium and chlorine ions to help conduct electricity.

Do note that at very high voltages, even pure water starts to conduct electricity because water molecules become ionized and separate into H+ and OH- ions which results in increased conductivity."
"Basic electrical quantities: current, voltage, power","In the analogy for voltage, where you compare it to a ball rolling down a hill, does voltage increase as it rolls down the hill, i.e. does it build momentum with gravity?","nice question:

OK, so think about potential. : it means stored energy or energy capable of doing work...

So think about the ball, at which point does it have most potential energy? top of hill or bottom??

OK?"
"Basic electrical quantities: current, voltage, power",Why is I the symbol for current?,"intensité de courant, (current intensity) in French. It was used by André-Marie Ampère. You can guess who that guy was.

That is why we use I as symbol for current"
"Basic electrical quantities: current, voltage, power","what's the difference between charges and electron/proton? since in my mind, current is caused by the moving of electron, but the text says that charges cause it.","Current is the movement of charge.  Since electrons are particles with negative charge, their movement creates current."
"Basic electrical quantities: current, voltage, power","The electric power consumed by a device may be calculated by using either of the two expressions P=I^2 R or P=V^2 /R. The first expression indicates that it is directly proportional to R whereas the second expression indicates inverse proportionality


I Know, if you have a constant voltage, increasing the resistance decreases the current flowing in the system by Ohm's law and hence decreases the power consumption

However, if you have a constant current source, increasing the resistance increases the voltage dropped across the resistor and hence increases the power consumption. 


But more intuitively I wanna know about this, with some example....can anyone please explain me? Thanks is advance","Hello Leo,

CAUTION - this is an answer from an electrical engineer...

In my opinion the voltage source is relatively straightforward. Examples include a battery or wall outlet. As you stated as the resistance is decreased more current flows. With more current and a fixed voltage there will be more power.

The current source is a different animal. I'll give you a few examples to consider:

1) The current source is a mathematical construct that maintains a constant current. It will take on whatever voltage is necessary to do so including both positive and negative voltages. It has an infinite impedance. To my knowledge there are no perfect constant current sources. To make one you would need a device that could produce an infinite voltage (not possible).

2) Please search "Thevenin Norton Equivalent." Here you will find that a voltage source with series resistance can be modeled as a current source with parallel resistor. Note that there is no such thing as a perfect constant voltage source. Such a device would demand infinite current (again, not possible in this universe).

3) Please search "inductor kickback." Here you will find than an inductor acts as a constant current source for a limited amount of time. As the inductor is "turned off" it will act as a constant current source and do whatever is necessary to maintain the same current before and after the transition. 

4) Please search "transistor characteristic curves." Here you will find that a transistor appears to operate as an acceptable constant current source. 

I hope you like these examples. Know that it will take some time for the material to sink in. May I recommend you print this note and check things off as you have master the topics. 

Please leave a comment below if you have any questions.

Regards,

APD"
"Basic electrical quantities: current, voltage, power","This is more of a "dumb curiosity" question and is purely hypothetical, but if salt water is as good as copper and silver could it be used to help power most things we use today?","Good day dream question. Salt water happens to be NOT as conductive as copper and silver. Those two metals are _very_ good conductors compared to sea water.

Sea water has a conductivity of 5 x 10^6 S/m
Copper has a conductivity of 6 x 10^7 S/m, or 10 times higher.

But suppose these numbers were closer. Water is a lot cheaper than copper, so that's an advantage for water. Now all you have to do is figure out how to use the water to build the electronic gizmos we all love. That's where water becomes distinctly useless as an electrical interconnect. Can you imagine if all the phone lines and power lines you see going from pole to pole were garden hoses?"
"Basic electrical quantities: current, voltage, power",Is there a reason why proton's charge is called positive and electron's charge is called negative?,"A long time ago, Ben Franklin (the American statesman) proposed a theory of electricity where he thought electricity was a fluid. This was back when the only thing anyone knew about electricity were those static electricity experiments you can do with a comb through your hair or rubbing a balloon on your sweater. Nobody knew about atoms or electrons or protons. Anyway, Franklin proposed an object could have extra electric fluid or lack fluid, depending on what you rubbed it with, and that's what caused the static attraction, the different levels of electric fluid in two materials.  He called the "lacking" material negative, and the extra material "positive". About 150 years later the electron was discovered, and it turned out that the "lacking" materials actually had an excess of electrons. And that's how the electron got its negative sign."
What is Faraday's law?,There is a direction of the current indicated with an arrow on Figure 1 ("Charge in a moving wire."). Shouldn't the arrow point in the opposite direction? I used the formula *V* = L *v* × *B* and the right-hand rule. Thank you.,"I think the figure is very misleading, or maybe just plain wrong, depending on where we are supposed to understand the magnetic field is located.  They have TWO black arrows on the wires, indicating the current going in a loop.  The current is shown going "southwest" in the wire near us, and "northeast" in the wire far from us.  For any wire moving in the direction indicated, the induced current will be SOUTHWEST only.  So if ONLY the near wire is "in" the B field, then the diagram is actually OK.  But if the entire loop (both parallel wires) is in the B field, then there would be no induced current.  The current would be trying to flow southwest in both wires.

Because they only draw B field arrows along a single line which looks like it is BETWEEN the wires, it is a very ambiguous figure."
What is Faraday's law?,"Question on inducing current  in the coil
I  cannot understand why the emf produced in the coil be opposite after the magnet has moved halfway through the coil. Thank you","Because the direction of the flux change is reversing.  At first it's increasing ,then as the magnet leaves, it's decreasing.  The induced EMF depends on the rate of change of the flux.  If the flux goes from increasing to decreasing, that's a reversal in the rate of change, ergo a reversal in the EJMF."
What is Faraday's law?,"If the rate of change plays a role in the amount of induced voltage then why different frequencies of AC voltage still get transformed by the same amount by a transformer? Wouldn't 120hz AC came out higher than 60hz AC on the other end of the transformer? (like lets say we connect 10V 60hz AC and 10V 120hz AC to a 1:2 transformer, why both of these voltages end up 20V at the secondary?)","The rate of change cancels out because induction happens twice in the transformer.  First the primary coils induce a magnetic field, then the magnetic field induces voltage in the secondary coils."
What is Faraday's law?,"If the rate of change plays a role in the amount of induced voltage then why different frequencies of AC voltage still get transformed by the same amount by a transformer? Wouldn't 120hz AC came out higher than 60hz AC on the other end of the transformer? (like lets say we connect 10V 60hz AC and 10V 120hz AC to a 1:2 transformer, why both of these voltages end up 20V at the secondary?)",Keep in mind that going from 0 V to 10 V at 60 Hz it is happening in 1/240 s (a quarter of a cycle) where as at 120 Hz it is happening in 1/480 s.  So the higher rate of change does create a greater change in induced voltage but it acts over a shorter period of time and these offset each other.
What is Faraday's law?,what is the difference between moving the magnet through the coil from the right side versus the left side?,"When you move the magnet from left side ( towards the coil), the coil induces current in a direction to repel the North/South pole ( whichever way you place the magnet).
When you move through the right side , the current direction just reverses from the previous one.

Hope it helps!
:>"
What is Faraday's law?,I don't understand Faraday's experiment : Induction from a magnet moving through a coil . Can some one explain it better for me please,"I'll try to explain it
   Consider that the magnet's north pole moves towards the coil. Upper end of the coil acquires north polarity, hence work is done against the force of repulsion to move the magnet.
   If the magnet is withdrawn from the coil upper end acquires south polarity, so work is done against the force of attraction.
  
    Now we know that as the magnet moves through the coil magnetic flux linked with the coil changes inducing a current. The  direction of the induced current is found from Lenz' law as follows.

   The work done in moving the magnet towards the coil is converted into electrical energy, which gets dissipated into heat energy.The current flows in a direction to oppose the motion of the magnet. If in case the induced current promotes the motion of the magnet, it stars moving at a faster rate and the electric energy(induced) and kinetic energy(of the magnet) starts increasing, without any work done. This is not possible (law of conservation of energy) .
So induced current always flows in a direction that oppose the motion of the magnet.This is Lenz's law.

pheww....Hope it helped!"
What is Faraday's law?,I am not able to understand the difference between potential difference and electro motive force.,"Hello Aryan,

Here is an answer from an electrical engineer's perspective - it may not line up with a physicists answer.

If you have a voltmeter in had you could measure voltage as the difference between any two point in a circuit. The red probe goes to one part of the circuit and the black probe goes to another. It does not matter what is being measured. It could be a battery, solar cell, or coil of wire as shown in this video. We would say the the meter is measuring the potential difference between the two points. This is often called voltage.

Forgive me as I add an analogy that would appear not to belong. Suppose you are riding a bicycle on a level road. You would have a "no-load" speed. As you started to climb a hill you will experience an increased load and start to slow down.

The same thing happens to sources of electrical energy. It will have a certain "no-load" voltage that usually drops when a load is applied. For example, a battery may have a no-load voltage of 13 VDC that drops to 12 VDC when a load is applied.

EMF is the no-load voltage.

Regards,

APD"
What is magnetic flux?,Why we use cos( theta ) instead of sin (theta) in magnetic flux density's equation? I mean what is the reason behind using cos ( theta ),"Hello Faria,

Consider COS(θ) as shown in Figure 1. If θ = 0° as shown in part B then the maximum number of flux lines pass through the blue coil. When the coil has physically rotated 90 degrees we find θ = 90° and there are no flux lines passing through the coil.

We could have used SIN(θ) but we would need to rotate our plane of reference (green) to be vertical instead of horizontal.

Regards,

APD"
What is magnetic flux?,"Solution to How do we measure magnetic flux? Exercise 2
I agree with the calculations up until they say
Magnetic Flux Φ = (0.05 m ⋅ 0.06 m) ⋅ (4.1 mT) = 0.451 mWb
As far as I can tell Magnetic Flux Φ should = 0.0123 mWb? I could be wrong, if so please explain what I'm doing wrong. Thanks so much for taking the time to address this!","Yes, it looks like they added .05 and .06 rather than multiplying.  
I have notified the physics specialist at KA.
Good catch.  Thanks."
What is magnetic flux?,"I'm confused as to how the solution for the last exercise was derived. Firstly, how that graph was plotted seems out of context to me, but since it's one of the ways this question can be solved I would think of a different approach. Secondly, the SI unit for magnetic fields are supposed to be in Tesla, but the solution above says Tm (Tesla meters). Why is that? And what other approach can be used to solve this problem?","The graph was plotted by taking the equation for the magnitude of the magnetic field B = (μ0I)/(2πr) and treating it as a function of distance r from the wire:
B = f(r) = (μ0I)/(2πr) [assume I is constant].

To get the flux we need to multiply B times A, but the value of B is changing over the length of the side of area A which is perpendicular to the wire.

This is why we use the area under the curve of the function (the integral) to get a precise sum of the varying magnitudes of B over the length of the side of A moving away from the wire, rather than just multiplying by the value of B at some arbitrary point."
What is magnetic flux?,"Third Paragraph.
Where do we get the Magnetic Field Vector? Is it the Magnetic Flux Density?
I feel like Magnetic Flux is defined as Magnetic Flux Density times the area, and that Magnetic Flux Density is defined as Magnetic Flux divided by the area.","The magnetic field vector B is defined by the force it would apply to a charge moving in it.  
B = F/qv, so the units are (N *s) / (C *m), which we call a Tesla, or T.  This is also called flux density.  Flux is then given by B*A, so it is in T*m^2, which we also call a Weber."
What is magnetic flux?,"I don't get why closed surfaces have zero magnetic flux. Also, how is it different from magnetic flux in a non closed area?","A closed surface is something like a ball or balloon (even if its a weird shaped one). If a magnetic flux line cuts the surface going in, then it must cut the surface on its way out. So the net 'in' = zero

non-closed is like one side of a window or a sheet of paper.  

flux lines usually all go into your side of the paper or come out of it. (Sometimes, if its a loop of flux it goes in then comes back out. )
ok??"
What is magnetic force?,what is electromagnetic induction,"Hello Yashwin,

Electromagnetic induction is what keeps the lights on! 

Our generators operate on this principle. All you need is a wire and a moving magnetic field. Or you could have a stationary magnetic field and a moving wire. Either way, the magnetic field appears to be changing from the wire's perspective. When this occurs a current will be induced in the wire. Sal has done a few videos on this topic. See:

https://www.khanacademy.org/science/physics/magnetic-forces-and-magnetic-fields/magnetic-flux-faradays-law/v/flux-and-magnetic-flux

Regards,

APD"
What is magnetic force?,what is left hand slap rule,">Find out if the charge is negative or positive
>If positive use right hand, if negative use left hand
>hold left/right hand out in front of you
>point thumb in direction charge is going
>the way your palm is facing tells you which way the field is going
> ?
> profit."
What is magnetic force?,"Is exercise 2b correct? The answer when I calculate it is 1.422 x 10^-4 T. Unless I'm entering the information in the calculator wrong, there maybe an arithmetic error here...

Here is what I punched in (even within google, you can copy and paste):
((9.1 * 10^-31) * (2 * 10^7)) / ((1.6 * 10^-19) * .8)",Good spot. Perhaps they rounded it off to 3 significant figures.
What is magnetic force?,""From the left-hand slap rule, we know that the magnetic force is perpendicular to the velocity. This is also the condition that gives rise to circular motion." 

I don't understand how magnetic force when perpendicular to the velocity gives rise to circular motion?","That's how you move in a circle, by constantly accelerating in a direction that is perpendicular to your velocity at that moment.  Review circular motion."
What is magnetic force?,what does 'in/out of the page' mean?,In the page means the vector is pointing straight perpendicular into the page/screen.  Similar for out.
What is magnetic force?,How was the formula F=qvB derived ?  Can somebody explain?,"It's not derived, it's an empirical observation."
What is magnetic force?,I could not understand the exercise 2b solution. I have problem with the cathode ray tube experiment.,I need more understanding.
What are magnetic fields?,why is the direction of magnetic field is from north to south why not south to north?,"It is not a fact but is an agreement that was once made and is now the standpoint. They are just labels, the north seeking point of an magnet (northpole) turns to the North (magnetic southpole of the earth). The agreement is that all northseeking magnet sides are called northpoles and vice versa."
What are magnetic fields?,"In exercise 1a what would the compass point to when distracted by the magnetic field generated by the current flowing through the wire? And also why does the direction of the current matter, I understand it determines the direction of the field with respect to the wire but how does that affect, the effect the field has on the compass? it still generates a magnetic field regardless of the direction the current flows in and would essentially 'confuse' the compass anyway. Right?... HELP. SOMEONE. ANYONE??","Hello Alex,

Let's consider the compass without the added complexity of the wire. Here the magnetic field of the compass needle is influenced by the magnetic field of the earth.

When current flows in the wire the compass needle moves. It does so because the magnetic field of the wire is considerably stronger than the magnetic field of the earth.

To better understand please research "right hand rule." Also, you may be interested in the Tangent galvanometer.

Ref: 
https://en.wikipedia.org/wiki/Right-hand_rule

http://physics.kenyon.edu/EarlyApparatus/Electrical_Measurements/Tangent_Galvanometer/Tangent_Galvanometer.html

Please leave a comment if you still have questions.

Regards,

APD"
What are magnetic fields?,"Ok, so we say 1 pole is north other is south. But if like charges repel and unlike charges attract, how in the world we know if one is north or south. How can you even tell the difference. Is there any way? Two north repels. Two south repels. South and North attract and North and south attract. There's no way to tell!! :(",The way they are defined is geographic. The north pole points towards the north and vice versa.
What are magnetic fields?,is there something like magnetic compass and geographic compass? or all compasses are the same? and what's the difference between earth's magnetic and geographic poles?,The geographic pole is where the imaginary line representing the earth's axis of spin exits the earth.  The magnetic pole is where a compass points.
What are magnetic fields?,What would happen to a steel ball kept at the neutral point between two magnets?,If it is perfectly balanced between the magnets then it will stay there but it is in what is called an unstable equilibrium and any little change because of vibration or tap would cause it to fall out of equilibrium and the ball would move towards one of the magnets.
What are magnetic fields?,"If all magnetic fields are caused due to moving charges, how do magnets work?",go to youtube and search for "veritasium how do magnets work" and watch both videos
"Light: Electromagnetic waves, the electromagnetic spectrum and photons","Does light have different speeds depending on the medium (e.g. air, water, etc) it is in? If it does, does it change wavelength, frequency, or both? When the speed decreases, does the light has less energy? Does light traveling through air, then water, then air again, has the same speed as it does in the beginning and in the end?","The speed of light can change.
The highest ever recorded is 299 792 458 m / s.
In 1998, Danish physicist Lene Vestergaard Hau led a combined team from Harvard University and the Rowland Institute for Science which succeeded in slowing a beam of light to about 17 meters per second, and researchers at UC Berkeley slowed the speed of light traveling through a semiconductor to 9.7 kilometers per second in 2004.
 Hau later succeeded in stopping light completely, and developed methods by which it can be stopped and later restarted."
"Light: Electromagnetic waves, the electromagnetic spectrum and photons",So do different kinds of lightbulbs give off different spectrums?,yeah! for example some lightbulbs are more "warm" and orangy and some are more white
"Light: Electromagnetic waves, the electromagnetic spectrum and photons",Where do we find a photon in an atom?,"Any kind of Electro-Magnetic wave travels in small energy packets called photons. In the visible range of light these are called photons and in the invisible range, i.e Infrared, UV and others the energy are called quanta. When a electron gains a certain amount of energy then it jumps to a higher energy orbit unless it has absorbed so much energy that its ejected, it again comes back to its original orbit after losing the energy i.e emitting it in form of Electro-magnetic Radiation. That is called emission spectrum."
"Light: Electromagnetic waves, the electromagnetic spectrum and photons","Why do things travel in waves and not in a straight line ?
simply if I throw  a ball , it doesnt make a wave. So why do electrons make waves ?","actually, you thrown ball does make a wave. its just that the wavelength is so small, you could not observe or measure it

DeBroglie said:
Wavelength = h/p h/mv  = (approx) 6 x 10>-34  /  (0.01 kg  x  20m/s)  = (roughly)  3 x 10>-33 m

a nucleus of an atom is about 10>-15 so, the wavelength of your thrwon ball is verrrrry small 

:)

ok??"
"Light: Electromagnetic waves, the electromagnetic spectrum and photons",from where photon is emmited or absorbed?,"Photons can be absorbed by electrons. These will increase in energy and jump energy levels. Afterward, the same electron can emit the photon to jump down energy levels."
"Light: Electromagnetic waves, the electromagnetic spectrum and photons",I am confused: is wave the energy itself or the disturbance in electromagnetic field caused by energy (like throwing a stone into a pond and wave forms),a wave can be described as the transmission of disturbance from one point to another OR the transmission of energy from on point to another
"Light: Electromagnetic waves, the electromagnetic spectrum and photons","Planck's equation for energy of an electromagnetic waves depends on only one factor - frequency or wavelength. Shouldn't amplitude, in some way, be directly related to energy? (I'm saying this after a comparison to sound .. sound is 'louder' when it has a large amplitude or a comparison the energy lost in a resistor in an AC circuit which equal to ((Vrms^2)*t)/R here Vrms is directly related to Vpeak which is the amplitude of the voltage signal. The energy is a directly related to the voltage's amplitude (square relationship) in an AC circuit , same as energy stored in a capacitor ..). All of this could be so wrong.. please correct me.","it might be too late but ill try to answer.
as per my understanding, a photon's energy is dependent only on its wavelength, that's what quantum mechanics tells us. photons do not have a "real" discernable amplitude. However, classical mechanics associates energy with amplitude. here's the problem though, you cannot use classical mechanics to deal with photons. we can approximate that the "amplitude" of a light wave is proportional to the number of photons hitting a particular surface per unit time. in other words, it is proportional to the intensity of the wave. this does not hold true when we consider one photon, only a system of many photons.

I am not an expert so PLEASE correct anything wrong I said :)"
"Light: Electromagnetic waves, the electromagnetic spectrum and photons","So the only thing I'm having trouble with is the relationship between a photon's frequency and a light wave's frequency. Is this correct?:

If you take the "frequency of a light wave" and multiply it by "6.626*10tothe-34" you get the frequency of a photon of that light wave?","First you cannot treat the energy of a classical light wave the same way as the energy of a photon.
The energy of a photon is E = hf.
The energy of a light wave is proportional to the square of the amplitude of oscillation of the electromagnetic wave.
These are two completely different models of light, classical vs quantum mechanical."
"Light: Electromagnetic waves, the electromagnetic spectrum and photons",How do you sole for wavelength?,"c/v gives [m/s] / [Hz]. And knowing that Hz (Hertz) is equal to 1/s, then we have [m/s] / [1/s] which gives us after removing the seconds unit to get meters as the wavelength's unit. Hope this helps!"
"Light: Electromagnetic waves, the electromagnetic spectrum and photons",What are some of the different effects that various frequencies of electromagnetic radiation have when absorbed by matter?,"The different effects light has on atoms can best be understood when considering the energies of types of light. And since energy and frequency are directly proportional, the trend we describe using energy will be the same for frequency. 

Higher energy light such as gamma rays, X-rays, and high energy UV light cause ionizations. They transfer enough energy to electrons so they can escape from the pull of the atom’s nucleus and turn the atom into an ion. 

Low energy UV and visible light cause electron transitions. The electrons are able to move between the energy levels within the atom, but do not have enough energy to escape. 

Infrared light causes molecular vibrations. The bonding atoms of a molecule vibrate back and forth like an oscillating spring. 

Microwaves cause rotational motion where a molecule rotates.

Radio waves cause nuclear spin transitions which is when a proton changes its spin state.

The lower the energy the light, the less work can be done with it by the atom when it absorbs that light. 

Hope that helps."
Photoelectric effect,what is the difference between ionization energy and the work function of a metal?,"work function refers to the energy required to remove the electron from the sea of electrons in a metal body whereas ionization energy refers to the energy required to eject the electron when it is present in the valence shell of the atom.
hope it explains the difference."
Photoelectric effect,Do non-metal elements emit photoelectrons?,"Yes, but they have higher binding energies.
You have to use UV light or X-rays to dislodge the electrons.
This is the basis of the technique called *photoelectron spectroscopy*."
Photoelectric effect,"We know that the photon is mass-less, so what is it's structure, how does it carry energy, where does it store it?
Or is the mass of the photon negligible not zero??",well I technically we cant treat light the same way we treat matter because daily things travel very slowly but when you are travelling at speeds beyond 10^6 ms^-1 the science is different matter and energy are interconvertible (e=mc^2) so it doesn't really store energy it is energy itself.
Photoelectric effect,"Is intensity the same as brightness? Does it just refer to how much light there is?  Also, I get that if there is more light shining on a metal, the current will increase. However, why does the current not increase when the kinetic energy increases? If the particles are moving faster, wouldn't that speed up the current?

Finally, I don't really understand amplitude. Amplitude is the height of a wave's peak compared to its resting position. So wouldn't high amplitude mean there is a lower frequency and therefore lower energy?","Yes, intensity is the same as brightness.
The only way to increase the kinetic energy of the electrons is to increase the frequency.  If the frequency remains constant. the kinetic energy is also constant.
The amplitude of a wave does not affect its frequency. Two waves of different amplitude can have the same frequency."
Photoelectric effect,"During the photoelectric effect, light knocks electrons out of metals. So why don't the metals in our home lose their electrons when we turn on the lights? 
Thanks in advance.",The metals in the home have too high a work function for the light to be able to knock out the electrons.
Photoelectric effect,"I'm having a bit of trouble understanding the wave/particle duality. Is a photon a wave-like particle? When I think of the equation E=hv, I think about frequency in terms of a wave, but I think of the E in terms of a particle-like atom, so it is a bit hard for me to reconcile the two and understand why high frequency of the wave would mean that the photon has a higher kinetic energy.","A photon is a particle of light.   All very small particles sometimes act more like what we think of as waves.  By experiment, we know that the energy of the photon is given by E = hf."
Photoelectric effect,What will happen if the energy of the photon is just equal to the work function of the metal? will the electron be pulled back in the orbit of the atom?,The electron will be "free" from the atom but will feel a pull because of the positive charge of the atom and likely will get pulled back into the atom.
Photoelectric effect,How is amplitude proportional to the number of photons with the same frequency?,"The intensity of the light is a result of the number of photons. 
If the light were a wave, the intensity would be represented by the amplitude of the wave."
Photoelectric effect,Is the quantum realm a real place or is it just a myth in ant man?,"I mean, the quantum realm is a fictional place in the MCU. It’s little more than magic portals made to sound more serious and scientific by adding quantum. 

In the real world quantum usually refers to quantum mechanics, or simply the workings of matter and energy at the very small, atomic level."
Photoelectric effect,how can light have momentum if it has no mass,Light also has a wave nature which allows it to have momentum
The quantum mechanical model of the atom,"Why is the spin number expressed as +1/2 or -1/2, rather than just +1 or -1  ?","In the spin quantum number the electrons are represented either by +1/2 or -1/2, and as shown in the quantum numbers video it is said that the electrons in this type, i.e the spin number can move in two directions ,one towards the left and one towards the right, so as electrons possess like charges(-ve) and because they might be travelling in the opposite directions and finally when they come close to each other they repel, so the electron almost covers 1/2 the circular orbit so probably that is why it is assigned the value +1/2 and -1/2."
The quantum mechanical model of the atom,"I've some questions on this statement:
The square of the wave function​​ represents the probability of finding an electron in a given region within the atom.
Why function square related to probability?","It's mostly a function in mathematics. It would be like asking "what is the average distance of a cosine wave from the center?" - and this might seem easy at first until you realize that the gradient of the wave function keeps changing. Mathematically, the average distance, or in this case the energy or probability of finding the electron, is just the square root of the wave property."
The quantum mechanical model of the atom,"referring to the image on orbital shapes,
why do the p,d,f orbitals have such "out of the blue" shapes? how were these shapes found out or calculated?","The shapes have been calculated from Schrodinger's equation.

Moreover , the shapes represent the region where the probability of finding the electrons is maximum. The orbitals have NO physical BOUNDARY."
The quantum mechanical model of the atom,"So the formula for de Broglie equation says that
 
lambda= h/mv
and..the v of a stationary object will be 0,
so by mathematical solving it means that the wavelength of a stationary object is infinite?
is this the correct thinking or is there some other theory for a stationary object's wavelength?","Isn't to do with the fact that the velocity is not quite 0? if you know it is exactly 0 then the uncertainty in the position is infinite as well (momentum is a function of velocity, so delta P = 0 -> delta V = 0 -> delta X = inf) therefore it has an equal probability of being anywhere. If you take the infinite wavelength interpretation, then it would be nearly 0 (1/inf) but constant everywhere. The square (probability function) shows that it has an equal chance of being anywhere.

So, if you know with 0 uncertainty what the velocity is, then you have no idea where it is, and all future involvement of the particle is pretty much irrelevant (how is the electron going to diffract around an atom if the electron is in a different galaxy?). As we can't physically measure to perfect accuracy, there is an uncertainty in both measurements of the degree that we know it's probably stationary and it's probably 'over there'. With this uncertainty, the velocity is almost definitely not 0. (1 value in a range of reals is like trying to throw a dart at a dartboard with an infinitely thin wire and hitting the wire). For another layer, you can take the fact that you can never cool anything down to exactly 0K (-273.15C) (although you can get close) and so nothing will ever have 0 velocity."
The quantum mechanical model of the atom,"On Schrödinger's equation, what exactly is the Hamiltonian operator? 
How do we work with it mathematically and what would be its physical interpretation?","This has to do with Laplacian operator (partial derivative) of a wave function.
Here's the formula http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/sch3d.html (I can't type out the partial derivative operator -__-")

The h-bar in the equation is defined by h/(2pi)"
The quantum mechanical model of the atom,"In reference to Shrodinger's Equation, what's the difference between the V (wave function symbol) on the left side of the equation and the right? There must be some difference, or else they would cancel.","You can't cancel out the ψ's like that because Hψ is not H times ψ but rather H operating on ψ (that's what the ^ over the H indicates).
The Hamiltonian operator H is actually
H = -ℏ²/2m * d²/dx² + U(x)
so the time independent Schrodinger equation is actually
-ℏ²/2m * d²ψ/dx² + U(x)ψ = Eψ
solving for E gives the allowable energy states of the system."
The quantum mechanical model of the atom,I have a really blurry picture of what it means for small particles to behave as both particles and waves. What does it exactly mean when we say that small particle have characteristics of both waves and particle ?,"I think I can safely say that nobody understands quantum mechanics.
- Feynman
So you are right on track! :)
But to be more pedagogical, you can view them as different behaviors in different situations. When behaving as particles, they show all what we "expect" them to based on our experiences. But under different conditions, they behave as waves, where in these "waves" are equations that determine, in a simple sense, the probability of the particle to be at a particular place at a particular time. Since these equations are not the classic Newtonian equations, their predictions often create the strange outcomes we usually see. (See the double slit experiment to understand the differing behaviors.)"
The quantum mechanical model of the atom,Can we specify type of the wave in schrodinger wave? like transversal or longitudinal,"I never thought about it before. Its interesting question.

My guess is that it is transverse. though, to honest, there is so much dispute about the wave function and what it actually is, maybe we need to answer that quesiton before we can say tranverse, longitudinal or.... something else?"
The quantum mechanical model of the atom,"Does anyone know exactly what "spin" is? If a particle has "spin", it doesn't actually physically spin/turn/rotate, right?
In the article, it said that the opposite "spins" of electrons are determined by how the react in a magnetic field. But does this explain what it means for other particles - other leptons, quarks, hadrons - to have spin? What is spin? Please help!","Spin is just a property that electrons (and other particles)  have.  It got named spin back when people were working with the Bohr model and trying to extend it to atoms beyond hydrogen.  Just as Bohr imagined that the atoms were little planets revolving around the nucleus as though it were a sun, other scientists tried to extend that idea by imagining that the little planets, just like real planets, had spin.  Using this concept actually helped a bit, just like Bohr's imagination of little orbits helped a bit, but again, the electrons are not like little planets: they don't revolve around the nucleus, and they don't rotate on their axes.   Still, they have a property that works sort of like an orbit (orbitals) and they have a property that works sort of like rotation about an axis (spin).   But there is no point in trying to answer "what is electron spin" by referring to some familiar object like a ball or a planet, because electrons are not balls or planets, they are their own thing, and you just have to accept that they have a property whose effects we understand very well, and we happen to have named it spin.  "What is spin" doesn't have any deeper answer than does the question "what is charge".  It's just a characteristic that particles have or don't have, and we know what the effect is of having or not having that property.

We have other properties like this for other particles.  A quark can be an up quark or a down quark.  "Up" and "down" don't have any meaning other than to identify the type of quark.  THere's nothing "up-ish" about an up quark.  THere's a top quark and a bottom quark.  There's a charmed quark and a strange quark.  There's nothing unusually strange about the strange quark.  It's just the name that we've given a quark that has certain properties.  

IN the field of quantum chromodynamics, we say that particles have a color.  They don't really have a color, we just use that idea because it's sort of helpful, just like using the idea of positive and negative for charges is helpful."
The quantum mechanical model of the atom,"Do nodes of the 1s, 2s, 3s... subshells overlap?
(wrt to the graph shown above, it seems they do)
If yes, do the nodes of another subshell also overlap,


[in fact, if the probability of finding an electron is 0, shouldn't the nodes always overlap(even if multiple subshells /orbitals pass through)?]",Atomic orbitals are defined by energy levels not positions. The electron clouds that are depicted are usually where there is a 90% chance of finding the electron at that energy level.  The electron clouds for different energy levels do have overlaps.
Bohr's model of hydrogen,what is quantum,"A quantum is the minimum amount of any physical entity involved in an interaction, so the smallest unit that cannot be a fraction."
Bohr's model of hydrogen,"I don't get why the electron that is at an infinite distance away from the nucleus has the energy 0 eV; because, an electron has the lowest energy when its in the first orbital, and for an electron to move up an orbital it has to absorb energy, which would mean the higher up an electron is the more energy it has. So if an electron is infinitely far away(I am assuming infinity in this context would mean a large distance relative to the size of an atom) it must have a lot of energy. Right?

Thanks very much!","you are right!

but what you need to remember now, is that the energy at infinity is DEFINED as being zero. Your next queston might be 'why?' :)

but, knowing that, does it now make sense that nearer to the nucleus, the energy is minus??"
Bohr's model of hydrogen,What does ΔE stand for?,"*The triangle stands for Delta, which also means a change in, in your case, this means a change in energy.*"
Bohr's model of hydrogen,what is the relationship between energy of light emitted and the periodic table ?,"Its a really good question. Here is my answer, but I would encourage you to explore this and similar questions further..

OK: I would say that the periodic table tells us about the number of protons in an element; and, therefore the number of electrons too. 

Now, the energy of the photon emitted from any element does not depend on the number of electrons in the atom. The value of the energies of  photons does depend on the available energy levels in the atom. Hydrogen, for example, although the simplest atom, has a whole range of photon energies that it emits.  This is because the electron can exist in many energy levels... as it switches from one energy level to another, then it emits / absorbs photons. 

We can, however, say that the more electrons there are in an atom, the greater the variety of photon energies there will be so this may be a link worth exploring

I hope that makes sense ok.

As I say, you are asking a great question.... looking for relationships in a meaningful way. I would encourage you to explore further.... maybe compare the number of different energies emitted by an element with its position in the periodic table, or the maximum / minimum energies emitted by the element vs position

Well done and keep up the good work."
Bohr's model of hydrogen,"Actually, i have heard that neutrons and protons are made up of quarks (6 kinds? up down ......)
Is it true? and how does the scientists found that out?","yes,       protons are made of 2 up and 1 down quarks whereas neutrons are made of 2 down and 1 up quarks . hope this helps."
Bohr's model of hydrogen,"Hi, great article. I was wondering, in the image representing the emission spectrum of sodium and the emission spectrum of the sun, how does this show that there is sodium in the sun's atmosphere? If both pictures are of emission spectra, and there is in fact sodium in the sun's atmosphere, wouldn't it be the case that those two dark lines are filled in on the sun's spectrum. The text below the image states that the bottom image is the sun's emission spectrum. Wouldn't that comparison only make sense if the top image was of sodium's emission spectrum, and the bottom was of the sun's absorbance spectrum? 

Thanks!","Sodium in the atmosphere of the Sun does emit radiation indeed. However, after photon from the Sun has been absorbed by sodium it loses all information related to from where it came and where it goes. So re emittion occurs in the random direction, resulting in much lower brightness compared to the intensity of the all other photos that move straight to us."
Bohr's model of hydrogen,Bohr said that electron does not radiate or absorb energy as long as it is in the same circular orbit. But according to the classical laws of electrodynamics it radiates energy. What is the reason for not radiating or absorbing energy?,Bohr did not answer to it.But Schrodinger's explanation regarding dual nature and then equating hV=mvr explains why the atomic orbitals are quantised
Bohr's model of hydrogen,why does'nt the bohr's atomic model work for those atoms that have more than one electron ?,"As far as i know, the answer is that its just too complicated.

With one electron and one proton you can figure out (with some difficulty) how they interact with one another because you have one centripetal force acting in the same 'direction' and analyse-able using classical circular motion etc. 

But with two electrons, now you have three forces; not just centripetal but also electron to electron. You can imagine in the classical view, how complex the change on force would be between the electrons and also the nucleus. It may be tht some one has figured a way of doing it or approximating to it, but, as far as I know this is the reason bohr model is only used for hydrogen."
Bohr's model of hydrogen,"so do we still not know that why do electrons not fall into the nucleus of the atom,i mean they are continuously emitting energy and of course at a point in time they should fall into the nucleus,what is the explantaion for that?","This is one of the main reasons we know that the Bohr model of the atom is wrong.  

In the quantum model of the atom electrons in their lowest possible orbital are in their ground state and can't be in any lower energy state and they do not radiate energy."
Bohr's model of hydrogen,Is Bohr's Model the most accurate model of atomic structure?,"No, it is not.  The quantum description of the electron orbitals is the best description we have."
Right-hand rule,"*How could we measure the force through the loop*?
Use a compass. In practise, wrap the wire around the compass and observe how strongly the needle aligns with the direction of the field.",That is how you make electromagnetisism.
Force over distance,"Force of magnet m= Strength of magnet M/Distance from the affected object
Is my equation correct?",In 3 dimensional space the strength of fields like magnetism and gravity decrease with the square of the distance so if you double the distance you decrease the strength by 4 times.
Force over distance,Does anyone know why earths magnetic field went berserk at the exact same time the each WTC tower fell to the ground?,Do you have a citation for that?  Sounds like BS to me.
Force over distance,"if there is a giant strong magnet bigger than the earth, will the earth move?","good question... I guess it would feel a force. But the magnetic field of the Earth is relatively weak. It is strong enough to change the direction of charged particle coming from the Sun and outer space but i think the force due to another big magnet would be fairly small. 

Also, consider that the Sun also has magnet fields which are fairly strong.

Any thoughts??"
What's next,Can you do an experiment that shows some of the topics from the physics videos about magnetism?,Yes I'm currently planning the next bath of videos. Is there something specific you are hoping to see?
What's next,"What does it mean when its says, "Multiple windings?"","A winding is several loops of wire, grouped together. In the video he made one winding comprised of seven loops. Most motors have several windings comprised of 10s to 100s of loops each, depending on the design of the motor.

When electric current passes through the wires of a winding, the winding produces a magnetic field which is attracted to one of the fixed magnets and repelled by the other. This is what causes the winding to rotate. By having more windings, a motor can be made more powerful."
Lever,How is simple machine useful in lifting thing,"Simple machines increase force, increase distance, and change direction"
Lever,Is there a relationship between the distance the load force moves and the distance the effort force moves?,"Absolutely! He explains this in the mechanical advantage videos but more easily you can think of it like a wrench turning a stuck bolt. Just using the wrench doesn't work but if you put a pipe on the handle of the wrench to extend the handle, the bolt easily breaks loose. Why? Because the force you apply times the distance of the handle creates what we call a "moment" (a turning force) on the bolt. Mathematically expressed" F * d = P (where P is the moment)"
Lever,What materials do you use for this demonstration so that we can try a hands-on as well? Thanks!,"Hi! You could use a ruler and a slim pencil rubber. The advantage of using a ruler is that you can literally measure the distances as you change the mechanism! And the rubber won't let the ruler slide apart, but remeber that it has to be slim, otherwise it won't represent a fulcrum. As for the weight, some coins will do the job. Hope you can do it yourself! Thank you!"
Lever,in the middle of the video how did he know to put on the coins,it was probably part of an experiment he had to demonstrate.
Lever,"in a lever just like the fulcrum was moved to different positions to equalise the position of load and effort... does situation comes where the load has to be moved towards the fulcrum to balance the lever arrangement,, if so can load be moved by keeping fulcrum intact?",yes in the 2nd class lever the load is near the fulcrum eg luggage bag
Pulleys,what's the point of a fixed pulley if there's no mechanical advantage?,They can change the direction of a force not the actual speed.
Pulleys,"Whoo, first question ok! So looking at the figure in 2:28 in the Simple Machines video specifically, I'm intuitively confused about how we "lost" 50N of force/ only have to exert 50N to pull a 100N block? What happened to the other 50N? Who's pulling that part? Also, if we assume that both pulleys are massless, what is the force on the "bar" holding the fixed pulley, and the force (tension) and direction of force on string 1 and 2?","The 50N of force are not lost. When you pull with a 50N force to move a 100N block, it moves 1/2 the distance. The energy is conserved."
Pulleys,"This is really col but i don't know if I have all the stuff to make this,isn't there an easier way to make it.",why not take a tube like object (a desk lamps adjustable neck) that is suspended in mid air. take a string and tie it round a eraser and then put the string over the top. that way when you pull the non eraser end the eraser will rise up. just like a pulley! YAY!
Pulleys,"Please review, and correct my thoughts:

Video 1:
Q1. no mechanical advantage.
Q2. Can use this, so that instead of lifting something above your head (against gravity), you can push something else down and work with gravity.

Video 2:
Q1. No idea, but I can see the effects i.e. A heavy gondola on the right can easily be raised. A force downward on the left, causes a much larger upward force on the right.
Q2. The right gondola moves approximately half the distance of the one on the left.
Q3. Since the right gondola moves half the distance, it implies that it also requires double the force. Therefore, a force on the left applies about double that force to the right, indicating a mechanical advantage to the right gondola.

Video 3:
Q1. So that the left can apply a large force over a small distance causing the right to travel a large distance with a minimal force applied.
Q2. The gondola on the left travels much less distance, approximately 1/4 the distance travelled by the right gondola.
Q3. The gondola on the left requires more force, therefore, it has the mechanical advantage.

Motorized Pulley Video:
Q1. Didn't quite understand what was done to even it out.. I had my own idea, but it wasn't the technique used. My idea: Add an identical second motor and wheels on the right side, which would cause the weight to tilt to the right. Thus, the same force is applied on either side. 
Q2. I need to understand question 1 first! - But thoughts: The pulley wheel on the right requires the most amount of force, therefore, it has the mechanical advantage?","Motorized Pulley Video:
The video's way was to connect the end of the string on the right side to the original motor so it reeled in the load from both ends, making it level.
The second question wasn't asking which pulley has mechanical advantage, but rather what the mechanical advantage was in terms of numbers. The "Simple Machines" video shows you how to calculate that."
Pulleys,what is better for lifting heavy objects a pulley or a lever,"Pulley pros:
1. Easy to transport (if you attatch a pulley system to a crane, for example)
2. Able to lift the object much higher

Cons:
1. Non-efficient for small tasks
2. Time-consuming to make 

Lever pros:
1. Easy to make.
2. Object easily slides off the lever to destination

Cons:
1. It's almost impossible to push a lever and an object at the same time so it's not really great for transport.
2. Cannot lift objects straight (it will tilt to one side) so if you were carrying, say, a big basket of some sort with items inside, the items inside the basket could fall out due to the tilting.
3. Not great for lifting things off into the sky.

So to answer your question, it depends on what the situation is. Hope this helps!"
Pulleys,How is the mechanical advantage equal to the number of strings?,The tension in the string is the same throughout the pulley system.  If you look at the the tension on the strings  that are doing the lifting you will see that if there is 1 string there is 1 times the tension lifting but if you have 2 string you have twice the tension lifting so the lifting force it is directly proportional string tension times the number of strings.
Experiment: What's the shape of a magnetic field?,"If you turn on the switch to operate a lamp, and the lamp has no light bulb, does it consume any electricity?","No electricity is consumed, because there is no complete circuit enabling electricity to pass."
Simple machines and how to use this tutorial,"Technically there are only three simple machines, right?","No, there are 6 distinct simple machines. Pulley Screw, Wheel, Lever, Wedge, and Inclined plane.  I really liked the explanations given at http://iqa.evergreenps.org/science/phy_science/ma.html
Mathematically a Wedge and  Inclined plane are similar, but as far as application they are very different tools for different purposes.  I'm also not sure which of the other 3 you think are the same but I can assure you there are 5 types of simple machines."
Wheel,how can a jack wheel lift a car,"Physically, the center of gravity for a car is right in the middle, but the jack has strong suspenders/ leverage that is can lift a car off the ground, moving the center of gravity not too much, but still sustainable to not break down, so you can lift the car! (Well, maybe only 1 side, but ok)."
Measure the Earth's field!,Is there a way to measure magnetivity? How would you measure something like that?,"Yes, you can do it with Teslameter. It´s relatively expensive apparatus or cheep (free) application on mobile. :-)"
Measure the Earth's field!,What are the materials that i can use to make a compass & one household magnet.,magnet that attract is northpole and sorthpole and the one that replling are northpole and northpole and sorthpole  and sorthpole
Measure the Earth's field!,i liked to play with magnets alot when i was little,so do i its because of the gravity on the earth!