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The determination of the Water Potential of Potato Tuber Cells

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Introduction

Joe Riley AS assessed practical investigation The determination of the Water Potential of Potato Tuber Cells Hypothesis I predict that the potatoes in the solutions with the highest sucrose content will shrink and lose weight and that the potatoes in the weakest solutions will gain weight and increase in size. The ones in the solution where the sucrose and water content is the same as the potatoes sucrose and water content, will not increase or decrease in size and will not increase or decrease in weight. I think this is because of a process that takes in the potato place called osmosis. This is when water molecules diffuse from a dilute solution into a concentrate solution through a semi permeable membrane. Method * Collect all needed apparatus. * Label 6 test tubes, relating to the strength of solution being placed in them, 1 being distilled water, 6 being 0.5 molarity sucrose solution. Fill the test tube one third full with the appropriate solution. * Using a cork borer and a razor blade prepare 6 cylinders of potato 10mm in diameter and 12mm in length. Slice up each cylinder of potato into 6 equally sized pieces and place onto filter paper, making sure that the groups of 6 are kept together and not mixed with any other group of six from another cylinder. ...read more.

Middle

This is where water molecules pass through a semi permeable membrane until the two solutions become equal in concentration. Both osmosis and water potential differences explain the results of my experiment. The water potential of the potato tuber cells can be easily worked out using my graph. Take the point on the x-axis where the percentage change in mass is equal to zero. Using my line of best fit, the solution molarity where no mass is gained or lost is 0.18. Using a conversion table, I can see that the water potential of the potato cells is around -500 kPa. At this water potential the potato's don't gain or lose mass, this is because the potentials are equal so the water into the cells equals the water out of the cells. In my experiment I incurred anomalous results. This could be due to inaccuracies in the experiment. Some of the inaccuracies that could have happened are, inaccurate cutting of the potato discs, as changing the shape, and surface area of the potato chips could make it easier for osmosis to take place and for molecules to diffuse along the down-gradient. Also another inaccuracy that could have occurred is that the excess water may still have been present on the potatoes when they were weighed. ...read more.

Conclusion

The ones in the solution where the sucrose and water content is the same as the potatoes sucrose and water content will not increase or decrease in size and will not increase or decrease in weight. As you can see for my results and graph where 0 is distilled water to 0.5 which is the solution with the highest sucrose molarity, my prediction was proved right. I predicted this because I knew that the different water potentials would lead to the movement of water from the cells into the solution or vice versa meaning weight would be either lost or gained. Also I knew that osmosis would take place, osmosis is when water molecules diffuse from a dilute solution into a concentrate solution through a semi permeable membrane. So with solution O the water from outside the potato, diffused through the PPM to dilute the high concentration of sucrose in the cells of the potato. This gave the appearance that the potato chip had grown and increased in weight, this is because of the excess water in the cells. Where as in solution 0.5 the potato lost weight and decreased in size. This is because the water from inside the cells diffused out through the PPM into the high concentrate sucrose solution to try and dilute it and make it equal to the cells sugar concentration. ...read more.

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