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An experiment to investigate the water potential of potato cells.

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Introduction

An Experiment to Investigate the Water Potential of Potato Cells Aim I aim to investigate osmosis through a selectively permeable membrane, which in this case will be potato cells. I will do this, by placing pieces of potato in different concentrations of sugar solution, measuring the changes in mass. Prediction I predict that the potato cells will have a higher water potential, so will gain water in the high sugar solution. It shall lose water in the more dilute solutions by osmosis. At some point, the potatoes will not lose or gain in mass, as the solution at this point will have the same water potential as the cells, so the mass will not change. Even if this doesn't happen in my experiment, I can estimate the point using my line of best fit in my results chart. I know that potatoes store starch which is insoluble in water. this will make the cells lose water in the higher sugar, low water potential solutions, and become plasmolysed. Theory Osmosis is the movement of water through a semi permeable membrane, also separating solutions of different concentrations. The water particles passes from where there is a high concentration or 'potential' to a region with low concentration. This occurs until both areas are equal in potential (concentration). Water molecule Sugar molecule Semi-permeable Membrane Flow of Water Many cell membranes behave as semi permeable membranes (ie. ...read more.

Middle

Main Investigation Method Key Variables: My variable will be the concentration of the solutions. I will use equal amounts of solution to make it a fair test, but will vary the concentration of sucrose in each solution. I will do a replicate of each solution, for more accurate results. Controlled Variables: * I will use as similar potato size as possible, but this is not essential as I am measuring the mass change and not the actual mass in this experiment. * I will use tweezers when taking the potatoes out of the solutions so as not to alter the mass. * I will use a different potato for each replicate to give more reliability of results. * I will measure the solution exactly with the use of accurate syringes. * I will leave no excess water when weighing. Safety For safety, I will ensure that I wear safety goggles, and make sure I cut downwards on a flat surface to protect my hands. I must also keep paper towels on the desk, so I can keep the area dry and avoid spillages. I must make sure that the apparatus is clean and in good working order. I must also wear a labcoat. Apparatus * Beakers (100ml) x 6 * Potato (fresh) * Cork Borer * Weighing scales * Sucrose Solution ( Different concentrations) ...read more.

Conclusion

Evaluation Even though it was lucky that I was able to fit in three repeats within the time restrictions, more repeats would always be useful. I would produce more replicates, using different potatoes, to prove that by coincidence, my conclusion doesn't apply to just the potato I used. A wider range of concentration samples and potato samples would also be useful in calculating the potato's water-potential more accurately. I found quite a few anomalous results, and this means that my results could have been more accurate and closer to my line of best fit. Also the potato chips could have partially dried in the time I had to place all the chips in the beakers with the solutions in. this would have altered the results. This could have been prevented if more assistance was used and or more time allowance was given for the experiment. The potato I used may have contained more starch towards the centre or different areas would contain more starch, so I could be using chips with different starch content that would change the rate of osmosis. For an extended investigation, I could test osmosis using various fruits instead of a potato. This is because I know that fruits have a lower water potential because they contain no starch, and also sugar molecules are soluble and therefore osmosis should occur faster, which will be interesting to see what extent osmosis differs in fruits then potatoes. ...read more.

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