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Investigate the effect of different concentrations of salt solution on potato cells.

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Introduction

Plan Problem To investigate the effect of different concentrations of salt solution on potato cells Hypothesis Osmosis is the diffusion of water from a dilute to a more concentrated solution through a selectivley permiable membrane. A selectivley permiable membrane is a thin layer which is found underneath the cellulose wall in plant cells, or on the outer edge of animal cells. This membrane contains tiny holes whih allow passage of smaller molecules but not larger ones, in this case, the small water molecules can pass through whearas the larger salt molecules cannot. When potato cells are immersed in salt solution, there will be less water per cubic centimetre outside the cells than inside. This difference in the concentration of water will result in a net diffusion of water out of the potato cells into the salt solution. This net movemet of water out of the potato cells will cause them to lose weight and become flacid. Severe loss of water will cause the potato cells to pull away from the cell walls and become plasmolysed, once this has happened, no more diffusion can occur and so the weight and rigidity will remain constant. The lower the concentration of salt solution, the slower the rate of osmosis will occur. This is because the concentration gradient is not as steep. When the salt solution reaches concentration which is equal to the natural concentration of the solution in the potato cells, there will be no net movement of water. ...read more.

Middle

A seperate syringe will be used for the salt solution and the water in order to prevent contamination. Then cut 6 fries from the potato slice of equal length and width using the scalpel. Weigh the fries and record the details. Place the first piece of potato into the first test tube and start the stop watch. Place the other pieces of potato into the corresponding test tubes at 10 second intervals, noting the order and recording which potato piece goes into which salt solution. Once 25 minutes has passed, remove the first potato piece and carefully remove excess water with a paper towel. Remove the other potato pieces in the order in which they were put into the test tubes at 10 second intervals. Weigh each potato piece individualy using the electronic balance and record its mass in a table. Conclusion The results confirm my hypothesis. The negative corelation between the change in mass and the salt concentration shows that as the concentration rises, the mass falls. the graph also shows that the expected point at which no osmosis would occur is just over 0.1M. The curve of the graph leads me to believe that the rate of increase in osmosis would decrease and above a certain concetration of salt solution, there would be no difference in the decrease in mass due to plasmolysis. ...read more.

Conclusion

One of the problems with this experiment is that the potato pieces were put onto a paper towel before being weighed. The difference in time taken from removal from the solution to weighig may have had an effect on the results. A solution to this would be to stagger the start and finnish times even more in order to be able to remove and weigh each potato piece before removing the following piece. Another way to vary the rate of osmosis would be to alter the temperature at which the solutions were kept. This could be done usig water baths and a thermostat. Though I have no previous experience in altering this variable in an osmosis experiment, I believe that the extra heat energy present in the water molecules would speed up the rate of osmosis. The surface area of the potato could be changed while maintaining its mass by covering the sides of a piece or merely leaving the skin on which would act as a barrier and prevent osmosis on that surface. As all of these factors contribute to osmosis it woul be necesarry to take them into consideration when doing further experimental work. Taking into account the aparatus that was available to me I believe I carried out my experiment fairly and produced reliable results from which to draw conclusions. I am pleased with the overall results as any anomolous results were close enough to the expected result that they do not discredit the experiment. ...read more.

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