To ensure that the offspring has only one complete diploid set of chromosomes, only one sperm can fuse with one egg. These and the other steps of fertilization are described here:. Fertilization is the process in which sperm and egg fuse to form a zygote. The acrosomal reaction help the sperm degrade the glycoprotein matrix protecting the egg and allow the sperm to transfer its nucl eus.
The video below provides a nice overview of sex cells and fertilization, including the acrosome and cortical reactions:. And this video shows what happens in sea urchin eggs immediately following fertilization, including the calcium wave that initiates the cortical reaction:. After fertilization successfully activates the egg, the egg begins a series of rapid cell divisions called cleavage , illustrated below.
Normal cell division occurs every hours, but cleavage cell divisions can occur as frequently as every 10 minutes. During cleavage, the cells divide without an increase in size; that is, one large single-celled zygote divides into multiple smaller cells called blastomeres. After the cleavage has produced over blastomeres, the embryo is called a blastula. The blastula is usually a spherical layer of blastomeres that are considered to be the first embryonic tissue, the blastoderm.
The very early stages of mammalian development are extremely similar to other animals. Later stages of cleavage are a little different though, resulting in a structure called the blastocyst , which has an inner cell mass and an outer cell layer called the trophoblast. The inner cell mass will go on to form the embryo, and the trophoblast will contribute to the embryonic portion of placenta and nourish the embryo.
Pre-embryonic cleavages make use of the abundant cytoplasm of the fertilized egg as the cells rapidly divide without changing the total volume. The rearrangement of the cells in the mammalian blastula to two layers, the inner cell mass and the trophoblast, results in the formation of the blastocyst. You can visit the Virtual Human Embryo project at the Endowment for Human Development site to step through an interactive that shows the stages of embryo development, including micrographs and rotating 3-D images.
Intrinsic lineage information is inherited from the mother cell, via cell division. Intrinsic information is fate-specifying information found within a cell. For instance, a cell might get chemical signals from a neighbor, instructing it to become a particular kind of photoreceptor light-detecting neuron. Extrinsic information is fate-specifying information received from outside of the cell.
Biological classification is a form of scientific taxonomy. Modern taxonomy is rooted in the work of Carl Linnaeus , who grouped species according to shared physical characteristics. These groupings have since been revised to align better with the Darwinian principle of common descent — grouping organisms by ancestry rather than superficial characteristics. While scientists do not always agree on how to classify organisms, molecular phylogenetics , which uses DNA sequences as data, has driven many recent revisions along evolutionary lines and is likely to continue to do so.
The dominant classification system is called Linnaean taxonomy. It includes ranks and binomial nomenclature. The nomenclature of botanical organisms is codified in the International Code of Nomenclature for algae, fungi, and plants ICN and administered by the International Botanical Congress. Kingdom Plantae belongs to Domain Eukarya and is broken down recursively until each species is separately classified. The scientific name of a plant represents its genus and its species within the genus, resulting in a single worldwide name for each organism.
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Lilium is the genus, and columbianum the specific epithet. The combination is the name of the species. When writing the scientific name of an organism, it is proper to capitalise the first letter in the genus and put all of the specific epithet in lowercase. Additionally, the entire term is ordinarily italicised or underlined when italics are not available. The evolutionary relationships and heredity of a group of organisms is called its phylogeny. Phylogenetic studies attempt to discover phylogenies. The basic approach is to use similarities based on shared inheritance to determine relationships.
They do not obviously resemble a typical leafless cactus such as an Echinocactus. However, both Pereskia and Echinocactus have spines produced from areoles highly specialised pad-like structures suggesting that the two genera are indeed related. Judging relationships based on shared characters requires care, since plants may resemble one another through convergent evolution in which characters have arisen independently.
Some euphorbias have leafless, rounded bodies adapted to water conservation similar to those of globular cacti, but characters such as the structure of their flowers make it clear that the two groups are not closely related. The cladistic method takes a systematic approach to characters, distinguishing between those that carry no information about shared evolutionary history — such as those evolved separately in different groups homoplasies or those left over from ancestors plesiomorphies — and derived characters, which have been passed down from innovations in a shared ancestor apomorphies.
Only derived characters, such as the spine-producing areoles of cacti, provide evidence for descent from a common ancestor. The results of cladistic analyses are expressed as cladograms : tree-like diagrams showing the pattern of evolutionary branching and descent. From the s onwards, the predominant approach to constructing phylogenies for living plants has been molecular phylogenetics , which uses molecular characters, particularly DNA sequences, rather than morphological characters like the presence or absence of spines and areoles.
The difference is that the genetic code itself is used to decide evolutionary relationships, instead of being used indirectly via the characters it gives rise to. Clive Stace describes this as having "direct access to the genetic basis of evolution. Genetic evidence suggests that the true evolutionary relationship of multicelled organisms is as shown in the cladogram below — fungi are more closely related to animals than to plants. In , the Angiosperm Phylogeny Group published a phylogeny for flowering plants based on an analysis of DNA sequences from most families of flowering plants.
As a result of this work, many questions, such as which families represent the earliest branches of angiosperms , have now been answered. From Wikipedia, the free encyclopedia. For other uses, see Botany disambiguation and Botanic disambiguation. For the journals, see Plant Science journal and Plant Biology journal.
Main article: History of botany. Further information: Human nutrition. Plants make various photosynthetic pigments , some of which can be seen here through paper chromatography. Chlorophyll a. Chlorophyll b. The Calvin cycle Interactive diagram The Calvin cycle incorporates carbon dioxide into sugar molecules. Carbon fixation. Carbon dioxide. Glyceraldehydephosphate G3P. Inorganic phosphate. Ribulose 5-phosphate.
Main article: Plant ecology. Main article: Plant genetics. A Punnett square depicting a cross between two pea plants heterozygous for purple B and white b blossoms. Further information: Molecular genetics. Main article: Epigenetics. Main article: Evolutionary history of plants. Further information: Plant physiology. Further information: Plant hormone and Phytochrome. Play media. A diagram of a "typical" eudicot , the most common type of plant three-fifths of all plant species. Further information: Taxonomy biology. Two cacti of very different appearance. Although Pereskia is a tree with leaves, it has spines and areoles like a more typical cactus, such as Echinocactus.
Branches of botany Evolution of plants Glossary of botanical terms Glossary of plant morphology List of botany journals List of botanists List of botanical gardens List of botanists by author abbreviation List of domesticated plants List of flowers List of systems of plant taxonomy Outline of botany Timeline of British botany. A bunch of other chlorophylls exist in cyanobacteria and certain algal groups, but none of them are found in land plants.
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[Plant Hormones and Tropisms] | AP Biology | irufijim.ga
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In summary, one or the other plant growth regulator influences every phase of growth or development in plants. These roles could be individualistic or synergistic; promoting or inhibiting. Additionally, more than one regulator can act on any given life event in a plant. Along with genes and extrinsic factors, plant growth regulators play critical roles in plant growth and development. Factors like temperature and light affect plant growth events vernalisation via plant growth regulators. Read more about Vernalisation here in detail.
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