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An investigation to determine the water potential of potato tissue.

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An investigation to determine the water potential of potato tissue Aim The aim of this experiment is to find the water potential (?) of potato tissue by finding at what concentration of sucrose solution, the ? of the potato is the same as the ? of the sucrose solution it is in. Preliminary work The Simple Osmometer A capillary tube with semi-permeable 'visking' tubing over the end was filled with a sugar solution and placed in a beaker of distilled water. The original height of sugar solution in the capillary tube was marked on the tube. The height of sugar solution in the capillary tube was then measured once every two minutes until there was no change. The height of the solution in the capillary tube went up. This was because the distilled water had a greater ? than the sugar solution and there was a net gain in the volume of the solution in the capillary tube. As a result of the water moving in though the partially permeable membrane, the concentration of sucrose in the solution within the capillary tube drops which in turn means that the ? of the solution in the tube goes up. A Simple Preliminary Osmosis Experiment Aim The aim of this preliminary experiment is to approximately find the water potential ? of potato tissue so that the range for the main experiment can be narrowed down. ...read more.


As the H2O molecules still have kinetic energy, they can still move but if one H2) molecule moves from the right hand side of the partially-permeable membrane, another molecule moves across from the left hand side to maintain the balance. N.B. In osmosis, only the H2O molecules are small enough to pass through the partially permeable membrane. Sucrose is too big to pass through. Osmosis in plant cells Water moves into the cell by osmosis because the ? inside the potato cell is less than the ? of the 0.0M solution. . The volume of liquid inside the cell increases and thus the pressure exerted by the cell membrane exerted on the cell wall is increased as well. When this happens, the cell is TURGID. If a plant cell is placed in a concentrated sucrose solution, it will lose water by osmosis. This is because the ? of the sucrose is lower than the ? of the cell cytoplasm, so water moves out of the cell. This will cause the volume of the cytoplasm to decrease. The membrane is pulled away from the cell wall as its contents shrink. The cell is then said to plasmolysed. At the point between turgidity and plasmolysis, a cell is said to be flaccid. The plant cell's wall is not involved in osmosis because it is freely permeable. A cell becomes flaccid when it is placed in a solution which has the same ? as the cytoplasm/vacuole. ...read more.


Fair Test and Safety To ensure a fair test: * Do not mix up the cylinders of potato. * Put lids on the specimen tubes to prevent contamination. * Cut the skin off the end of the potato cylinders as they have a 'waterproof' layer which prevents osmosis from occurring properly. * Make sure there is the same volume of solution in each specimen tube. * Ensure that the potato cylinders are kept in the solutions for approximately the same amount of time. * Ensure that the potato cylinders are of the same size and have the same surface area. To perform the experiment safely: * Wear goggles and take care when handling the sucrose as it is an irritant. * Take care when using the scalpel as it is sharp. Results Sucrose Concentration (M) Initial mass of potato cylinders (g) Final mass of potato (g) Change in mass of potato (g) % Change in mass Average % change in mass of potato 0.1 A 1.16 1.2 0.04 3.4 5.2 B 1.26 1.35 0.09 7.1 C 1.37 1.44 0.07 5.1 0.2 A 1.12 1.16 0.04 3.6 2.3 B 1.2 1.17 0.03 2.5 C 1.26 1.25 0.01 0.8 0.3 A 1.37 1.32 -0.05 -3.6 -3.8 B 1.11 1.08 -0.03 -2.7 C 1.17 1.11 -0.06 -5.1 0.4 A 1.22 1.1 -0.12 -9.8 -12.3 B 1.14 0.97 -0.17 -14.9 C 1.33 1.17 -0.16 -12.0 0.5 A 1.21 1.05 -0.16 -13.2 -16.9 B 1.15 0.93 -0.22 -19.1 C 1.19 0.97 -0.22 -18.5 SC1 Osmosis Alastair Yap SC1 Autumn 2002 ...read more.

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