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To demonstrate the Water Potential of Potato Cells.

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Patrick McCreanor BIOLOGY 4/12/02 Aim: To demonstrate the Water Potential of Potato Cells. Objectives: * To show the water potential of potato cells using various measured concentrations of a sucrose solution and pieces of potato. * To record and analyse data to verify observed results. The method and procedure was carried out as per instruction sheet. Observations: The experiment shows that the lower the concentration of the sugar solution, in the Petri dish, the mass of the potato increased. This is because the water molecules passed from a high concentration in the water, to a low concentration, in the piece of potato. Therefore, the potato in higher water concentrations will have a larger mass than in higher sucrose concentrations. i.e. The potato pieces are shown to have water potential. The attached graph shows the concentration of the sucrose solution plotted against the average mean change in mass. At point A the graph shows that no change in mass, of the potato, would have have occurred had we used a 0.2 (m) ...read more.


The graph shows that the potato cells increase in mass in solutions with a high water/low sucrose concentration and decrease in mass in solutions with a low water/high sucrose concentration. The graph shows that water transfer has occurred across the potato cell membranes in a process known as osmosis. From the graph an estimate to the concentration of the potato can be made as 0.2 M, as this is the theoretical point where the potato would not increase or decrease in mass. This is the point where no osmosis is taking place; both the potato and the solution have an identical molar concentration. At 0.25 M the potato pieces loose a mean average of -0.8 g in mass. This shows that the water potential of the sucrose solution in the Petri dish is weaker than that of the potato. At 0.50 M, the potato looses -0.23 g in mass. Indicating that the sucrose solution has an even weaker water potential than 0.25 M and that osmosis took place. ...read more.


This may have shown a relationship between the potato mass loss and the concentration of sucrose, such as an inverse proportional relationship. 6. Distilled water could have been used instead of tap water. Tap water may contain chemicals, such as chlorine and salts that could interfere with the water potential. 7. Using a percentage of mass loss rather than the actual mass loss may have given more accurate results on the graph, due to the differing masses of the potato pieces. (One for the Maths boffins!) 8. The potatoes could have been completely submerged in the solutions so that all the surface area was exposed to the liquid e.g. placed in covered test tubes. 9. The potatoes could be handled by mechanical devices e.g. tweezers so that different body heats and contamination by people's hands was eliminated. 10. The potato could have been sliced into smaller pieces. A pin could be pushed through the pieces, maintaining the spaces, and the whole submerged in the solution. This would increase the surface area and speed up the osmosis. ...read more.

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