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Investigating WaterPotential of Plant Cells

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Investigating Water Potential of Plant Cells Aim: To devise an experiment which will determine the water potential of a sample of root potato cells. Background Information Osmosis is the movement of water molecules through (partially permeable) membranes of cells. The overall movement of the molecules will be from a region with high water potential to a region of low water potential. A solution can be given a value which gives a measure of the tendency of the water molecules to move from one region to another. The water potential value of a solution is given based on two variables; the concentration of water molecules within the solution, and the pressure applied to the solution. If the water potential of two regions, with a (partially permeable) membrane between them, is the same; then the overall movement of water molecules between them will be at equilibrium. The molecules will not move between the regions with the same rate going in as going out. I can use this principle to find (approximately) the water potential of a sample of potato cells. Potato cells are surrounded by a partially permeable membrane; this will allow water molecules to pass freely between the cells and its surroundings. I could place the potato cells in solutions with different water potentials. ...read more.


The inside of the sample had the same 'toughness' as the outside. I will use samples of potato with 5mm radiuses. A length of 2.5cm should be sufficient; it is enough to be covered by all 15ml of solution. The samples will be kept overnight. The samples from the first set of results showed little sign of change when left for 30 minutes; 24 hours is a better option. It gives the water molecules enough time to diffuse through the whole of the sample. My second set of tests was to help me narrow down the range of solution I would use in the final experiment. The first potato samples' water potential was the same as (approx.) 0.3M sucrose solution. If the second potato samples' ideal solution is close to this, I can use concentrations closer to this figure. The results from the second set showed equilibrium of osmosis at 0.45 (approx.). Because the ideal concentrations are quite far apart, I will have to experiment using a wide range of solutions. Because of this I can narrow down my prediction and say that the sucrose solution with the same water potential as the potato sample is between 0.2 M and 0.6 M. This would be a water potential between -540 ? ...read more.


The samples were left for 24 hours and may have decayed slightly in that time. There were some other minor factors. The balance used had a 0.01g degree of accuracy. This would have affected the calculated percentile mass change. This change would however be so small is can be disregarded. Some parts of the potato cut would have had a different makeup to other parts of the potato. There could be impurities or air pockets within samples. This would affect the mass of the sample; this in turn would result in a random error. The cork borer would have cut into the potato at different angles. Since the potato cells are arranged in a particular way, cutting through at different angles would have altered the number of cells exposed and would have killed a different number of cells. This would have produced a slight random error. The potato samples were trimmed to lengths of 2.5cm, the cutting was done by hand. This would have also created a small random error. Excess water was removed from the potato samples before weighing them a second time. This was done by rolling them down a paper towel. This would have resulted in a small random error. If I was to repeat the experiment, I would use distilled water instead of regular tap water and would make sure that the temperature of the solutions was constant. ...read more.

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