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Investigating to find the concentration of potato cells using osmosis

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Introduction

Biology GCSE Coursework Investigating to find the concentration of potato cells using osmosis Introduction Osmosis is the net movement of water molecules from a low concentration (high concentration of water) to a high concentration, (low concentration of water) through a semi permeable membrane. For example2, potato cells in a sugar solution. Aim To find out the concentration of potato cells using osmosis, by putting potato cells in different amounts of sugar solution and seeing by a graph when there is no change as the concentration of the solution is the same as the potato. Factors that effect osmosis Temperature and light - The molecules will get more kinetic energy and so more osmosis will take place, and also a higher temperature would make the water evaporate, increasing the concentration of the solution Amount of solution - The larger the surface area, the more osmosis will happen Size of potato - More solution might also increase the rate of osmosis by increasing the surface area Type of potato - Different potato cells might change the rate of osmosis Things that will change with experiment: Length of potato Weight of potato I have decided to look at the difference in mass to find the concentration of potato cells, by seeing when the mass stays the same. Preliminary Experiment Apparatus * 50ml measuring cylinder in 0.5ml steps - to measure accurately * One large potato - so it is fair and only one potato is used * Three medium sized test tubes - to put the solution in * Rack - to hold three test tubes * Balance that can measure to 0.01 of a gram - to be accurate * Medium sized corker borer - to cut pieces out of potato which are all the same size * Scalpel - ...read more.

Middle

* The plastic cups were left for four and a half hours. * The potatoes were blotted with kitchen paper and weighed again, using the same balance, to the nearest 0.01g. Results were taken and the results are in the table below. Results Results Tables A table to show the results of set 1 of potatoes, which were put in different amounts of sugar solution Sugar concentration % Mass of potato before (g) Mass of potato after (g) Change in mass (g) Change in mass in percent (%) 0.00 1.81 2.34 +0.53 +29.3 0.05 0.82 0.93 +0.11 +13.4 0.10 0.95 1.03 +0.08 +8.4 0.15 1.34 1.43 +0.09 +6.7 0.20 1.32 1.41 +0.09 +6.8 0.25 1.23 1.31 +0.16 +6.5 0.30 1.04 1.06 +0.02 +1.9 A table to show the results of set 2 of potatoes, which were put in the same test tubes as set 1 Sugar concentration % Mass of potato before (g) Mass of potato after (g) Change in mass (g) Change in mass in percent (%) 0.00 1.84 2.22 +0.38 +20.7 0.05 2.13 2.46 +0.33 +15.5 0.10 2.22 2.45 +0.23 +10.4 0.15 1.76 1.32 -0.44 -23.2 0.20 1.63 1.78 +0.33 +9.2 0.25 1.49 1.62 +0.13 +8.7 0.30 1.62 1.73 +0.11 +6.8 Average of the two sets of results Change in mass (g) Change in mass in percent (%) +0.45 +25.0 +0.22 +14.5 +0.15 +9.4 -0.17 -8.3 +0.21 +8.0 +0.14 +7.6 +0.06 +4.4 Analysis What was found, trends or patterns I have found that the more concentration of sucrose, the less the percentage change is. There is a general trend in the lines, and they slope downwards. The slope is a curve, that starts of with a steep gradient, then it gets shallower, and at the end steeper again. ...read more.

Conclusion

Measuring the correct amount of sugar solution was also quite hard, and I may have made a few errors while making them. Reliability I think my results were quite reliable as I did the test twice and both curves were similar, proving they are reliable. The results for my preliminary and actual method -were very different and did not both follow the same pattern. The results are quite strong to support my conclusion, albeit they didn't go negative, as they show a downward curve. They would have gone negative with a few more sugar concentrations. Changes to improve the reliability To improve, I would use the same sort of potatoes as used in my preliminary experiment. The potatoes were easier to cut, and a cork borer could be used. This would make all my potatoes the same size. I would also put a thermometer in each plastic cup/test tube to check the temperature stays constant. I would also place each potato in a separate plastic cup/test tube, and not put two together. I would make sure that they were placed roughly in the same place inside the cup to increase fairness. I might even repeat the test again to get three sets of results. I would also increase the range of concentrations by two or three concentrations e.g. 3.5, 4.0 and 4.5 so the results would go negative. Further work For further work I could investigate what would happen if I carried out my experiment further, and do a few more concentrations, e.g. 0.35, 0.40 and 0.45. I could see if my prediction on where the potato is at equilibrium was correct. I could also investigate whether surface area does affect osmosis, and use different sizes of potato at the same concentration. I could also see if temperature increases the rate of osmosis. ?? ?? ?? ?? Sarah Lowman 10W ...read more.

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