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In this investigation I am going to find out the principles of osmosis and what factors can affect osmosis.

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PLAN In this investigation I am going to find out the principles of osmosis and what factors can affect osmosis. Osmosis is the movement of water from a dilute solution (high water potential) to a solution of greater concentration (low water potential) across a semi-permeable membrane. The water stops moving when the concentration of solution each side of the membrane are equal. This diagram shows what happens in osmosis. The water molecules move across the semi-permeable membrane from the low sugar concentration solution to the high sugar concentration solution. Water molecules are small and can travel through semi-permeable membranes this is the theory of free water particles, but sugar molecules are much bigger and cannot travel through a semi-permeable membrane. The water molecules move across the semi-permeable membrane by diffusion. Diffusion is the movement of particles of gas, solvent or solute, but water molecules in this case, from an area of high concentration to an area of low concentration. A high concentrated sugar solution will contain more sugar molecules and less water molecules than the same amount of low concentrated sugar solution. A lower concentrated solution is said to be a higher free-water solution than a higher concentrated solution. Potato cells always have a strong cell wall surrounding them because they are plant cells. When they take up water by osmosis they start to swell, but the cell wall prevents them from bursting. Plant cells become turgid when they are put in less concentrated solutions. ...read more.


to a high concentration by osmosis. METHOD I will use a cork borer to take 6 cores from a potato at roughly the same lengths. I will then use a paper towel to soak up as much of the surface moisture, on the potato core, as possible, then I will weigh them and cut them down with a knife so that all of them are exactly the same weight to 2d.p. in grams and the weight will be recorded. There will be six test tubes containing 10.0cm3 of solution they will be; H2O (0M), 0.1 moles, 0.2 moles, 0.3 moles, 0.4 moles & 0.5 moles. One core will be place in each of the test tubes and left over night. The test tubes will be covered up with paper towels to prevent any evaporation. After they have been left over night I will take the cores out and dry off the surface moisture using a paper towel. I will then reweigh the cores and calculate the percentage weight change. APPARATUS DIAGRAM > 6 test tubes > Test tube rack > 1 potato > 6 concentrations of solution; H2O (0M), 0.1M, 0.2M, 0.3M, 0.4M & 0.5M Solution > Measuring cylinder > Knife > Weighing balance Potato > Cork borer core > Paper towels I will make this experiment a fair test by using the same potato for the cores because different potatoes may have different concentrations. I will also make sure that the amount of solution I use each time is exactly 10.0cm3 and the weight of the cores are exactly the same to 2d.p. ...read more.


If I were to do this experiment again there are a number of changes that I would make. I would choose a wider range of concentrations at smaller intervals so that a graph can be more detailed and more accurate. If it were possible I would use a more accurate weighing balance to 4d.p. in grams. Drying off the surface of the potato cores reduced the weight somewhat but using a paper towel wasn't going to be the same on each core. If I were to do this again I would develop a more accurate and uniform way of drying the cores. I would also do one solution at a time so that when the cores are sitting on the paper towel waiting to be weighed they do not lose more weight. One of the most important improvements would be to do more repeat experiments and use averages. Also I would use different membranes other than potatoes and different solutions other than sucrose. There are errors in this experiment which influence the reliability of the data. Cores slough of the cells while they are in the solution which reduces the mass of the cores which will influence the weight at the end. Although there were no anomalous results I think the best-fit line could have been more accurate if the results had been more accurate. But there is sufficient information, by looking at the graph and analysis, to prove that osmosis did takes place and that my theories in my plan are correct. Overall I think this was a very successful investigation and the results I obtained show that osmosis did take place. Anit Patel - 1 - Biology Coursework ...read more.

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