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I aim to find out whether osmosis happens in potatoes, and how different water concentrations affect the rate at which it happens.

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Introduction

Biology Coursework - Osmosis in Potatoes Planning Aim I aim to find out whether osmosis happens in potatoes, and how different water concentrations affect the rate at which it happens. Prediction I predict that the weight of potato will steadily decrease as the salt water concentration increases, because less water will pass through the semi-permeable membrane. I think this because osmosis will happen more quickly as the level of concentration is at a greater difference. Plan In a high concentration of water the amount of solute (e.g. Salt) is low. This could be called a weak or dilute solution. In a low concentration of water the amount of solute is high. This could be called a strong or concentrated solution. When two such solutions are divided by a semi-permeable membrane, the water will move from the area of high concentration to the area of low concentration, until both sides are equal (have reached equilibrium). Or in the words of The "Biology CGP Revision Guide" Osmosis is the movement of water molecules across a partially permeable membrane from a region of high water concentration to a region of low water concentration. The first thing I needed was a partially "permeable membrane". I knew that I could use potato or visking tubing. I wanted to opt for visking tubing as this would be more accurate, because visking tubing isn't affected as strongly by age, and as I would be spanning my experiment over a couple of days, this could be a problem. ...read more.

Middle

I will need 75ml of each solution, 25ml for the 3 tests per solution) - These will be used to see at what rate osmosis occurs. I have chosen these concentrations, as they were readily available and will give me a good spread of results. * A stop clock - I will use this to time the how long each potato rob has been in the solution. * A scale correct to 2DP of a gram - This will be used to weigh the potato before and after each test. Method I will set up the apparatus like this. The arrows show the process the potato goes through, start and ending at. I will first record the potatos weight and put it in a solution a 4g salt to 200ml of water. I will leave it then for 15 minutes. After 15 minutes I will record the weight again. I will repeat the experiment 3 times for each solution, the solutions being 4/200ml, 12/200ml, 20/200ml, 28/200ml and 36/200ml. To make this a fair test I will * Make sure the size of the potato stays the same * Make sure there is no skin on the potato * Make sure I have no exess water on the potato, but I will not dry it with a paper towel as different concentrastions of salt water could absorb at different rates and/or leave salt behind. ...read more.

Conclusion

I expected the blue line to be the same as the line of best fit. I think that the weight loss is only slight at the beginning because the difference in concentration was small, end therefore the transfer will not have happened as quickly. However, this theory doesn't work for the end result. I suspect this was because the potato had reached a concentration where the transfer could not happen more quickly. To prove this theory I would have to repeat the experiment with higher concentrations, and see whether the results changed at all, or just more slowly. I don't think that these result are anomalous because of the pattern they make 7 6 1 6 7 I could've made the experiment more accurate by * Bringing the scale closer to the experiment, as I had to walk across to the other side of the room to take the reading. * Repeat the experiment more times * Find some method of drying the potato without taking some of the salt away. I did not dry the potato as I thought it would be more unfair to dry them with cloth because it would take salt the too. The amount of salt on the outside of the potato would change for each experiment, but the amount of water wouldn't change greatly. If I were to do this experiment again I would take the potato out and weight it again at regular intervals to see the rate at which osmosis happens. Daniel Hill 10S Biology Osmosis.doc Page 1 of 5 ...read more.

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