An investigation into the effect of glucose concentration on osmosis.

The aim of my experiment is to investigate the effect of glucose solution on osmosis in potato chips. I shall be observing how the mass of the potato chip changes in different concentrations of glucose solutions. Simply, will the effect of the action of osmosis be affected by the concentration of the solution?

Firstly, I measure the mass of the potato chips, each one was to be 10 grams in weight. The chip will be placed into a glucose solution of a certain concentration. After leaving the chip for an hour I shall take it out, blot the excess liquid and measure the mass. I shall record the differences in masses and then calculate the percentage weight changes of the recorded masses when a potato chip has been in different concentrates.

To ensure that my results are as fair and accurate as possible shall use a number of controls. These will hopefully eliminate any extreme variables in my results. Firstly, I shall choose the same variety of potato for each chip because the permeable membrane will have a similar genetic makeup. This will exclude this possible difference from affecting my results. Secondly, I shall attempt to prepare the chips so that they are cut uniformly. This will keep the surface area of the chips as constant as possible. Thirdly, I shall leave each potato chip in the solution for exactly 3 hours. In my preliminary work , in preparation for this experiment , I found that this length of time obtained a sufficient amount of results. If I had left them for thirty minutes the results may not have been noticeable and so more difficult to measure. Fourthly, I shall take care when removing the chip from the solution, particularly when removing any excess fluid, by blotting. Any excess fluid will affect the recorded mass when weighing.

Because I want the experiment to reflect the average results and not one based on any extreme results, I shall weigh each potato chip twice. One shall be the average and so it shall act as a guide or marker point at which extremes can be identified. This constancy of conditions shall also be sustained by regulating the room temperature. This will minimise the effects of changes in temperature on the solutions used, for instance, risk of water loss due to evaporation, and the possible effects of temperature change on the action of osmosis.

I did come up against a ...

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I did come up against a problem in that some potato chips floated to the surface of the higher concentrated solution, so excluding some of the cross sectional area from the solution. I did not find a remedy for this problem. Any possible remedy would be one that did not interfere with the solution or potato chip. If the chip does float to the surface during the experiment, I shall abandon that particular sample and repeat the process until a chip remained submersed.

The glucose concentrations shall range from 0.0 mol/l, which is pure de-ionised water, to 0.2 mol/l, 0.4 mol/l, 0.6 mol/l 0.8 mol/l and finally the highest concentration which is 1.0 mol/l. These solutions were pre-prepared apart from the 0.0 mol/l.

I predict that the mass of the chips will increase as the concentration of the glucose solution increases. I predict that as the solution then becomes more concentrated, the increase in mass will begin to decline and eventually the chips mass will decrease fro its original 10g. Therefore, more concentrated the solution is, the lower the mass gain should be. The reasons for my predictions are that when the solutions concentration is low the water in the solution (outside the potato and its cells) is greater than that inside the potato cells. Therefore osmosis occurs and the potato cells take in the water in the solution. If the solution is a stronger concentration of glucose osmosis will work in reverse in that water will be drawn out of the potato cells into the solution. The cells will become plasmotised as it loses mass. When the water osmoses into the potato chip cell they become turgid. The potato chip will become rigid when turgid.

The method of the experiment will be:

Using a scalpel I shall cut 12 cylindrical chips of identical diameter and weighing 10 grams.

0.0 0.2 0.4 0.6 0.8 1.0

I shall place two chips into each of the concentrations of glucose solution (above), after weighing and recording their mass. After leaving them for 3 hours I shall remove them, blot the excess solution from them, and then weigh them again. I will then calculate the mass and express this as a percentage, using the formula below.

Change in mass (g)

----------------------- X 100

Original mass (g)

(g = grams)

Apparatus

. Thermometer - to check temperature of room

. 6 small beakers

. set of scales ( accurate to 1/100 of a gram)

. scalpel

. tweezers

.whiteboard

I intend to take 12 results, 2 from each level of concentration. I shall then calculate an average resulting in 6 results that will be used to plot on a graph.

If I successfully implement the controls over the experiment (as outlined above) my results should be fairly accurate. Inaccuracies may occur if the conditions of the experimental environment are not adequately regulated. Any irregularities will be noted and taken into consideration when evaluating the final results.