Factors Affecting the Movement of Water Through Osmosis
Factors affecting the movement of water through osmosis Introduction In this I will be investigating what effects the movement of water through osmosis. Osmosis is the diffusion of water. It is the process in which fluids pass through a partially-permeable membrane. It is the movement of water from high water concentration to low water concentration. Plant cells react to osmosis by hypertonic, isotonic and hypotonic. Keywords Hypertonic – is when the water outside of the cell is lower than that inside. Isotonic – is when the net movement is the same in both directions.
Hypotonic – is when the water potential outside the cell is higher. Therefore the water has moved into the cell and the cytoplasm is pushing against the cell wall and the cell has become turgid. (Pictures from http://www. bbc. co. uk/schools/gcsebitesize/science/add_ocr_21c/life_processes/plantfoodrev3. shtml) Water Potential is when the water molecules in a system have a tendency to move from one place to another, it is usually represented by the Greek letter ? (Psi). Water potential is caused by osmosis. Water potential (? ) is calculated by using the following equation: Pressure potential (? ) + Solute potential (? s) Factors that affect the movement of water * Concentration – As the water molecules will move from a high concentration of water to a low concentration of water. * Temperature – The hotter the temperature is the faster osmosis will take place as the particles will move more. Chosen Factor – Sugar Concentration In this investigation, I will be monitoring the effect sugar concentration has on the movement of water. My hypothesis is: By changing the concentration of sugar, I think that the water will move from a high water concentration to a low concentration via osmosis.
I predict that the more sugar concentration there is, the rate of osmosis will increase and therefore will have an effect on the results of the experiment. Strategy I found three different methods I could use to measure the rate of osmosis: * Observing osmosis using a model cell  – With this one I will be using an artificial membrane to act as a cell membrane. For this I will use visking tubes. * Observing osmosis using potato cylinders and measuring the gain or loss of mass  – For this one you use bits of potato in different sucrose solutions. Observing osmosis using aubergine chips and measuring the gain or loss of length – This one is similar to the potato one but with aubergine instead. Model Cell Pros| Cons| Easy to do| The visking tubes are fiddly| Don’t need to keep an eye on it| The visking tubes are easy to break| Quick process| Might have leaks in the visking tubes| Easy to get hold of the equipment| |
Aubergine Chips Pros| Cons| Don’t have to keep an eye on the experiment| Hard to cut the aubergine to exactly 1cm? ubes| You can tell by the colour of them what has happened to them in the solutions| The aubergine goes brown really quickly as bacteria is getting to it. | Equipment is easy to use and to get hold of| Aubergine is easy to break| Safe to use the equipment, other than the scalpel | Long to do | Potato Cylinders Pros| Cons| All the potato cylinders are the same width and length | Long process to do| Easy to do | The potato cylinders are easy to break| Easy to cut them to sensible length| Hard to get out of the corer| Easy to use the equipment, apart from the corer. Difficult to get a certain number of potato cylinders from one potato| I’ve decided to use the potato cylinder method to observe the rate of osmosis. Observing osmosis using a model cell does not give very reliable results as the visking tubes might have leaks in them. It is also a very fiddly job to open the visking tubes, to pour the solution in. Observing osmosis by using aubergine chips is tough one to do, as you have to cut the aubergine chips to exactly 1cm? and put them all into the same amount of solution at the same time to make it fair, but if you leave it too long the aubergine starts to go brown because of bacteria.
I think that using potato cylinders to observe osmosis is the best method to use as it doesn’t take too long to do, it is simple to do and can give reliable results as the potato cylinders would be the same length and width, and most likely the same weight as well, meaning it would be easier to tell which solution had the greatest effect on the potato cylinders, by weighing the potato cylinders to see what the difference in mass is. Chosen Method 1) I will be taking several samples from the same potato by using a potato corer to give me eighteen potato cylinders in equal size, a second potato is allowed if it is needed. Pictures from: http://eve. kean. edu/~breid/plantlab2/plant_2. html) 2) Then you measure all eighteen cylinders to see what their starting mass is, I will use a set of scales to do this. 3) Once you have the starting mass you will need to add each potato cylinder to different solutions, sucrose 0. 1m/dm? , sucrose 0. 2m/dm? , sucrose 0. 4m/dm? , sucrose 0. 5m/dm? and sucrose 1m/dm? , you will need to make sure there is enough solution to cover the potato cylinder. 4) Then you need to leave the potato cylinders in the solution for a long enough period of time, i. e. an hour. )
Once an hour is up you need to take the cylinders out of the solution and dry them off with some paper towel. 6) After that weigh the potato cylinders again and calculate the change in mass (g). Also work out the average difference in mass using a calculator. Potato cylinder Weighing scales 7) Finally plot a line graph of the change in mass against the morality (how strong the solution is). Equipment * Potato – To test osmosis. * Corer – To get equal sized potato cylinders. * 6 different solutions (I will use 10ml of each solution) – To see which solution effects the potato cylinder more. 18 boiling tubes (to test it 3 times) – To test the different solutions. * Scalpel – To cut the potato to equal lengths.