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# Investigating Osmosis.

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Introduction

Kate's Biology Coursework. Investigating Osmosis. Aim I am going to investigate how different concentrations of water affect osmosis in slices of potato. Prediction I think that as the water concentration in a salt and water solution rises, then the weight of the potato will rise too. This is due to osmosis. I believe that because there will be a higher water concentration in the solution than in the potato then water will enter the potato to make the concentrations both inside and outside the potato equal. This corresponds with the scientific theory of osmosis: Osmosis: water moves from an area of high concentration to an area of low concentration across a semi-permeable membrane In this scenario the high concentration is the high water concentration in the solution of salt and water. The low concentration is in the potato slice. The semi-permeable membranes are the potato cell membranes. I used some preliminary experiments to help me along with this one. For example, this 'thistle funnel' experiment. We put sugar solution in the thistle funnel and filled it to point A. After two hours the level of solution in the funnel had risen to point B. ...read more.

Middle

water 15cm3 of salt 75% salt solution 0cm3 of water 20cm3 of salt 100% salt solution I will make 3 of each concentration combination and pour them into the 15 test tubes. I will then measure the mass of each potato cylinder on a balance. Then I will drop a cylinder into each test tube. Using a stopwatch I will leave the test tubes alone for 15 minutes. After this time I will carefully blot the potato cylinders to remove excess water and weigh them again, recording my results. Safety measures: * to prevent salt getting in eyes -----> always wear goggles * to prevent cutting your hands -----> cut the potatoes on a tile Fair testing procedures: * use the same technique for blotting the potatoes each time * use the same species of potato all the time * repeat the whole experiment again to get more reliable results if the first set of results are wrong * use the same width cork borer each time * keep the temperature of the water consistent * same volume of solution (20ml) * same time left for Results My first set of results did not seem accurate as when I drew them as a graph, the line of best fit was a zigzag (I was looking for a curve). ...read more.

Conclusion

2. the potatoes may have been blotted differently. inadequate blotting may not have removed all the excess water, making the weights increase. Too much pressure may have forced all the water out of the potato. 3. the solutions may have been measured incorrectly 4. different balances may not be as reliable or accurate. the same balance should be used throughout the experiment. I think my second set of results are very accurate. If I was to redo the experiment I would use more accurate equipment such as measuring cylinders that measure to 0.01cm3 or burettes for measuring the solutions. These would improve the accuracy of my results. I would find a better way of cutting the potato so that the slices are not damaged in the process and are all uniform length and surface area. Once again this would give more accurate results. I would give one person the job of doing all the blotting, and he/she could perhaps just roll the potato cylinder once along a paper towel each time. This would make the experiment more consistent and fair. I believe with these new arrangements, my experiment would be a much fairer test. To get more information on osmosis, I could try using another vegetable, perhaps a courgette. I could check whether courgettes take in as much water as potatoes. xxx ...read more.

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