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Investigation Into the Osmotic Potential of Potato Cells.

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Introduction

INVESTIGATION INTO THE OSMOTIC POTENTIAL OF POTATO CELLS. Aim: To find the exact concentration at which there is no net osmosis in potato cells. Relevant Information: Osmosis - the diffusion of water molecules through a partially permeable cell membrane down a water potential gradient. Osmosis is the main biological idea that will be looked at in this investigation, both how it travels in and out of cells, and the effect this has on the cells. Osmosis occurs mainly when there are two areas containing water molecules at different concentration, it moves from areas of high water molecule concentration to areas of low concentration. It has to occur through a partially permeable membrane, such as a cell membrane, as it allows small molecules through, like water molecules, but not larger ones such a glucose molecules. In the diagram above the direction in which there is most water flow is from left to right. This means that the net diffusion is in this direction. The reason that it is in this direction is that there are a larger amount of free water molecules on the left-hand side than there are on the right, as the water molecules on the right are taken up by sugar molecules. This is also the theory behind the varying amounts of osmosis in different strength solute solutions. ...read more.

Middle

It is also possible to measure the droopiness of a cylinder of potato. This can be done by measuring the angle of droop before the potato is put in a solution and then after and comparing the change in angle. Variables: There are many factors that have to be controlled during this experiment. These are: * Amount of Potato, * Quantity of Concentration, * Time in Solution, * Type of Potato, * Surface Area of Potato, The independent variable, the factor that will be changed, will be the concentration of the solution that the potato will be placed in. The dependent variable, the factor that will change in response to the independent variable, will be the change in weight of the potato discs. Preliminary Work: A small-scale experiment was carried out so that it was possible for us to see the methods that could be used so that it could be decided which method we wanted to use. Both length and weight were tested to see which gave most accurate answers. In this experiment only three solutions were used so that a vague idea of the results in the actual experiment could be gained. This was so that the range of solutions that is to be used in the actual experiment could also be chosen. Preliminary Test Results: Measurement Solution Starting Final Percentage Method Strength Weight/Length Weight/Length Change Weighing 1m 2.12g 1.7g -20% 0.5m 2.09g 1.78g -14.09% Dist. ...read more.

Conclusion

I believe that the point at which there is no net osmosis will be just above 0.2 molar. Method: The apparatus will be set as shown in the diagram below. Using a cork borer, six 4cm cylinders will be cut out of the potato. Twenty 2mm discs will be cut from each of the 4cm cylinders. The discs will be dabbed dry and weighed, these will be recorded and marked on the test tube. The eight sets of discs will be placed into 10ml of 6 varying solutions of concentration. These will be distilled water, 0.1m, 0.2m, 0.3m, 0,4m and 0.5m. This will be done three times. 3 x 6 = 18 The next lesson the discs will be removed using a tea strainer, dabbed dry and the re-weighed. These weights will then be recorded on the results table. The apparatus will be cleaned and cleared away. The percentage change will be worked out. This is done with the following formula: Percentage change = Change in mass x 100 Original Mass Apparatus Diagram: Risk Assessment: Although this seems like a very safe experiment there are a few precautions that have to be taken. Knives will be used to cut the potato into the correct shaped pieces. Then a cork borer will be used, which has a sharp end used to cut into the potato. Finally small, but very sharp blades will be used to slice the potato into the required discs. ...read more.

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