Investigate the effect of surface area on osmosis in potato tissue.

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Biology Coursework Yr10                Tracy Kelly

To investigate the effect of surface area on osmosis in potato tissue

Hypothesis:

        The larger the surface area of the potato, the quicker osmosis will take place and the larger the mass will be at the end of the experiment, therefore the difference in mass of the potatoes from the start of the experiment to the end of the experiment will be larger. The potato pieces, which are left in the sucrose solution, will decrease in mass and the pieces of potato, which are left in water, will increase in mass.

Theory:

Osmosis: The diffusion of water through a partially permeable membrane, from a high concentration of water to a low concentration of water until the concentration is equal.

As cell membranes are permeable they allow certain molecules to pass through them, such as water (H2O), through tiny holes in the membrane. These molecules contribute to the contents of the plasma around the vacuole of the cell. Although the membrane is permeable to some molecules, others are too big to fit through the tiny holes in the membrane, therefore they cannot take part in osmosis.

The larger the surface area, the more cells are directly exposed to the liquid, therefore more water can transfer through the membranes of the cells at one time, therefore, because water has entered the cells, they will increase in mass. Osmosis takes place until the concentration of water on the outside of the cells is the same as the concentration of water on the inside of the cells, therefore, if the pieces of potato are left in 100% pure water then it will take a long time for the concentration of water in the cells to equal that of the water around them.

Osmosis between pure water and a plant cells is quicker then osmosis between 1molar sucrose solution and a plant cell. This is because it will take more water from the pure water solution to transfer into the cell to make both the concentrations equal then it would take for the water mixed in with the sucrose solution because the concentration isn’t as high, therefore it would take less transfer to make the concentrations equal. This proves that the mass of the potatoes at the end of the experiment in the water solution will be higher then the potatoes in the sucrose solution.

For example:-

With not as much water entering the cell when the concentration is 44% sucrose, therefore leaving 66% of the solution water, the cell will become dehydrated because the water will be transferring out of the cell, therefore it will become plasmolysed and the cell contents will shrink away from the cell membrane. When more water enters the cell then leaves the cell it will cause the cell to become turgid, and the cell will swell. Unlike animal cells, plant cells will resist the expansion and not burst because of the thick cell membrane.

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Expected Results:

        I expect that the blocks of potato with a bigger surface area will have a bigger mass at the end of the experiment then the blocks of potato with a smaller surface area. The blocks of potato in the sucrose solution will have a smaller mass then the blocks in the water because to balance the concentration of water in the two beakers between the potato cells and the liquid surrounding the potato there would have to be less water entering the cells when the potato is in the sucrose solution, but more water entering when ...

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****Overall a well planned and carried out experiment which needed a little more depth in the planning section. The inclusion of selected references to inform the plan would be helpful. To improve: Planning was well carried out with a trial experiment. The prediction could be made clearer. If the prediction could be made quantitative ( perhaps by doing some background research) this would be helpful. Obtaining results: The student carried out a trial experiment and a good range of the independent variable with a fair number of repeats. The student should try to ensure all units and concentrations are clearly recorded. Analysing Evidence and Evaluation: The graph was not available to view. The student needed to explain the extent to which the conclusion supported the prediction and look at ways of improving the reliability of the evidence. The student has tried to account for the anomalies mentioned but the suggestions for further work are a little limited.