Vacuole fills with
water, therefore
pushing against
the cell wall.
Normal Plant cell
Water moves into cell by osmosis, making the cell turgid.
Diagram 2
Cell membrane will pull away from the cell wall
Normal Plant cell
Water moves out of cell by osmosis cells become flaccid. Cytoplasm may also shrink from cell wall, this is called plasmolysis.
Factors and Variables
In this experiment the control will be the test with pure water, we are going to vary how much sugar is in the solution, which the potato chip is to be added. The amount of water will be the same in each test tube so that it is a fair test. If the water is different the osmosis that takes place may be different and affect the results. The first one will have 5% sugar, then 10%, 15% and 20%. Going up by 5% is a good even way to increase so the results will be clearer. The weight of the potato chips will obviously be slightly different because it is almost impossible to get them all at the same weight however they will still lose or gain weight. I will measure the size of the potato chip so they are close as possible to two grams. The experiment will be repeated three times for each solution and the control and then an average worked out from those results.
Fair Test
For this experiment the main factor to make it a fair test was keeping the amount of solution the same for each test tube and making sure each potato chip was exactly the same. For a fair test there has to be a control of variables. The things that may affect the result of this experiment are: temperature, blotting and volumes. The temperature will just be room temperature and there will be no heating. It may be affected by the weather, how much sunlight there is. When drying the potato chips I will try and keep it fair but blotting each one just for a few seconds with the tissue paper. The volume of solution will be the same and the potato chips will all be as near to 2g as possible so other factors such as the surface do not change the outcome of the results.
Apparatus
5 test tubes
Potato
Test tube rack
Sucrose solution
Knife
Tissue paper
Measuring scales
Water
Diagram
Preliminary Work
Osmosis is the movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of low water concentration. In a previous experiment two cubes of potato were cut roughly the same size. Cube A was placed in a beaker of distilled water. Cube B was placed in a beaker with concentrated sugar solution. They were left for one hour.
Cube A – the water concentration in this beaker was higher than the concentration of water in the potato cube so water moved into the potato cube by osmosis. The potato cube became harder and seemed heavier
Cube B - the water concentration in the potato cube was greater then the concentration of the water in the beaker. Water moved out of the potato by osmosis. The potato cube became soft and appeared lighter.
From this experiment one can see how osmosis works and the same rules should apply for the following experiment if the prediction is correct.
Method
First of all I took the potato and using the knife (which was only sharp enough to cut through the potato for safety) I sliced it into 15 pieces, then placing them individually on the tissue paper on the measuring scales and cutting them down until they each weigh 2 grams. After this I got the test tube rack and the test tubes and marked on them 0%, 5%, 10%, 15% and 20% and then filled them with the according solutions. In each test tube I added 100ml of solution and then added 3 potato chips into each one. Once this was done they were left on the rack by the window overnight, the next day I emptied the test tubes and put the potato chips on tissue paper to dry them so the excess water would not affect the results. Once dry I weighed them and recorded the weight in a table.
Results to show the change in weight of the potato chips
Conclusion
The results show that the higher the concentration of sugar in the solution the less it weighed. The graph shows that the potato chips in the less concentrated solutions gained weight or didn’t have much affect. As shown in the following diagram the water has moved from an area of high concentration to an area of low concentration and passed through the partially permeable membrane of the potato cell.
Cell wall resists stretching.
Vacuole fills with
water, therefore
pushing against
the cell wall.
The potato chips in higher concentrated solutions lost weight. This happens due to osmosis. As shown in the following diagram the water has moved out of the higher concentration in the potato cell to the lower concentration of the sugar solution.
Cell membrane will pull away from the cell wall
This happened because osmosis needs a permeable membrane if it is to take place. The permeable membrane in this case is the cell membrane of the potato chips. The tendency for water to move through a partially permeable membrane is described as its water potential and is at a maximum in pure water. This water potential can be lowered on how much sugar is added to the water. This means that more concentrated solutions will have lower water potentials than ones with less concentration. Also when there is a strong sugar solution water will start to leave the potato cell by osmosis and it will become flaccid and may begin to break down causing the potato chip to lose weight. When there is a weaker solution the water will enter the potato cell by osmosis and cause the cell to become only just turgid giving the overall potato chip more weight. When there is an even weaker solution the water will enter easily until no more can enter and the cell becomes fully turgid giving it maximum support and probably the most weight it will be able to gain
Evaluation
The experiment suited the investigation well and it showed a good set of results. The results are reasonably reliable because the test was fair and there was a familiar trend shown in the results. There did not seem to be any anomalies but due to the fact that the potato chips were stacked upon one another in the test tubes it may have caused the results to be altered. I think to improve this, one potato chip should be placed in the test tube and the experiment repeated three times instead of all three at once. Further studies could be carried out with the same experiment, it could be tried under different situations such as heat or different solutions to a see if this affects the results or shows up with a new pattern to see how accurate the results were.
Peter Larkin 4B 27th April 27, 2003
