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Potato Chips

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Skill Area P: Planning Aim: To investigate the influence of the concentration of the surrounding solution on potato tissue Background Information: Osmosis is a special type of diffusion. It is the diffusion of water molecules through a selectively permeable membrane, it goes from a place of a high water concentration to a place of low water concentration to try and make the two concentrations equal - this is called a concentration gradient but in the case of water it is known as water potential. Cells placed in distilled water, absorb water by osmosis. This happens because the cells contain dissolved chemicals and therefore they have a lower water potential than the surrounding liquid. Eventually the cells stop absorbing the distilled water even though the concentrations inside and outside the cell are not equal. This is because the cell wall of the cells become stretched and prevents any more water entering. The cell is said to be turgid. In a turgid cell (left diagram) the vacuole and cytoplasm swell causing the content of the cell to push against the cell wall. The cell wall resists this pressure and pushes back. The cell cannot take in any more water so consequently osmosis stops. In a concentrated sugar solution the cells lose water by osmosis, as there is a higher concentration of water in the cell, water moves out of the cell by osmosis into the sugar solutions. This causes the cell to become limp; this is called a plasmolyzed or flaccid cell. In a plasmolyzed cell (right diagram) placed in a concentrated sugar solution, the cytoplasm and sap vacuole shrink causing the cell content to pull away from the cell wall. Prediction: I predict that as the concentration of the sugar solution around the potato chip decreases, the size of the potato chip will increase. I have come to this conclusion due to previous work I have done on osmosis in class. ...read more.


Therefore backing up my prediction and reasoning behind it. Skill Area O: Obtaining Evidence Preliminary Work For my preliminary work I used a 30mm potato chip. Preliminary work is important to do so that you can foresee if any complications could arise whilst doing your experiment. Complications that may occur are; the potato chip getting wedged in the test-tube, if the solution would overflow when the potato chip was added, that osmosis might not occur in the allowed time etc. My original plan was that the potato chips would be left in their solutions for thirty minutes and then removed. This however proved to be too short a time for osmosis to occur in any huge amount. This can be seen in the table below. Concentration Before Length (mm) After Length (mm) Average Change in Length (mm) Difference in Length against 30mm 0% Test 1 30 30 30.0 0.0 Test 2 30 31 30.5 + 0.5 5% Test 1 30 28 29.0 -1.0 Test 2 30 35 32.5 +2.5 10% Test 1 30 32 31.0 +1.0 Test 2 30 34 32.0 +2.0 20% Test 1 30 27 28.5 -1.5 Test 2 30 27 28.5 -1.5 30% Test 1 30 29 29.5 -0.5 Test 2 30 28 29.0 -1.0 This table shows me that in thirty minutes the results produced are too minute to conclude my prediction. Modifications As a direct result of the preliminary experiment I have learnt to increase the time needed for osmosis. This is because the results I obtained from my preliminary work did not show a clear trend, this could be because osmosis was still occurring. Therefore I felt it appropriate to increase the time limit that the chips are in their solutions in my plan. Other than this I did not need to change any other part of my plan. Modified Method: 1. Core five potatoes chips using the potato corer. ...read more.


The experiments produced results that were all convincingly similar with one or two anomalies. I have accounted for these anomalies in my analysis. My results show that I was consistently accurate with my experiments as there is little chance that I could have completed every experiment incorrectly. My experiment was suitable because it provided me with the information I needed to confirm my initial predication (which can be found on pages 2-3). There are however places and ways that errors could have occurred. First starting with the concentration. It is possible that when I made-up my sucrose solutions they were not accurate. They might not have been accurate because I could have used the wrong amount of distilled water - which should have been equal to 100cm� or I might have measured the amount of sugar incorrectly. Also a major factor was the cutting of the potato chips. I could have easily left a larger surface area on one and not on the others. Therefore one potato chip would be at an advantage as a larger surface area induces more osmosis to occur. One way to avoid this would be to use complicated machinery to weigh and cut the potato; although this would have been beneficial, this wasn't practical. So by just taking extra time and care with the cutting would make the experiment more accurate. Logically I could have done more work. I could have repeated the experiment more times to gain a more accurate average. Also, if I had tested a wider range of concentrations it may have made my results more accurate. Also I could experiment with exposing the same weight pieces, but with different surface areas. This would be helpful to do, as it would show if surface area greatly affects osmosis. If I were to repeat the experiment again I would go to a higher range of concentrations as explained in my conclusion on page 22. I would also use concentrations with smaller differences so I could plot a more accurate graph. Biology Coursework Francesca Tate 1 Mrs Dolan 10D ...read more.

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