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Osmosis. The results show that when a high concentration of sucrose is used, the potato loses water and when a low concentration of sucrose is used the potato takes in water

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Introduction

Planning Osmosis is the movement of water molecules across a partially permeable membrane form a region of high water concentration to a region of low water concentration. Osmosis will occur if a partially permeable membrane separates a vessel. If a solute is added to one side then water molecules will move to the solution side. Osmosis can be stopped or reversed by exerting pressure on the solution side, this technique is used to purify water. If no osmosis occurs then the two solutions are said to be isotonic, if it does occur, the transfer of solvent is from the hypotonic side to the hyper tonic side. The pressure needed to stop osmosis is called osmotic pressure. Osmosis is very important for living things. Living cells of both plants and animals are surrounded buy a semi permeable membrane that regulates the flow of liquids, dissolved solids and gases. ...read more.

Middle

* The same amount of solution will be in each test tube so that pressure is not an issue. * The potato pieces will all be the same size and shape so that surface area is not a variable. * All the experiments will be done on the same day so that temperature does not affect the rate of diffusion. Equipment List * 5 Test tubes * Test tube holder * Electronic scales * Hard board mat * FILL THIS BIT IN * Knife I have done a preliminary experiment. % Sucrose Mass before Mass after Change in mass 20% 2.45 2 -0.4g 2.5 2.1 -0.4g 10% 2.2 1.8 -0.4g 2.2 2.0 -0.2g 5% 1.8 1.8 0 1.8 1.6 +0.2g 2% 2.0 1.9 +0.2g 2.0 1.9 +0.15g Distilled water 2.3 2.3 0 (anomalous) 1.8 1.9 +0.1 I predict that the 20% sucrose solution will make the potato lose mass and the pure water will make it gain mass. ...read more.

Conclusion

When the solution is 0% - 7.6% sucrose it is hypo tonic and the potato cells are hyper tonic, when the solution is above 7.6% it is hyper tonic and the potato cells are hypo tonic. When both sides are 7.6% no net movement of water molecules occurs because the movement of water molecules from the solution to the potato is the same speed as the movement of water molecules from the potato to the solution. Evaluating I think that the results are definitely strong enough to carry the conclusion because there were no anomalous results are the negative correlation on the graph was very strong. This is probably because the process of osmosis is too slow for the results to be affected by things like somebody stopping the stopwatch to early or too late. If I were to do any further work I would investigate osmotic pressure. I could have improved the experiment by using a water bath, so that osmosis would happen quicker (because the molecules are moving around faster) and all the test tubes would be exactly the same temperature. ...read more.

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