The determination of the water potential of potato tissue.
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EXPERIMENT REPORT --The determination of the water potential of potato tissue Introduction: This experiment involves the use of different sucrose solutions with different concentrations, in order to measure the water potential in a chosen potato. The theoretical background is the osmosis in plant cells: a plant cell loses water by osmosis if it is in a more concentrated solution (which has a lower water potential) than the cell's cytoplasm and vacuole. Reversely, a plant cell absorbs water by osmosis if it is placed in a solution of higher water potential. Hypothesis: The difference of water potential between the cell's cytoplasm and vacuole and the surrounding solution causes water to enter or leave the cell, resulting the change of the tissue's mass.
3. Put the samples into six test tubes containing the six different solutions and wait for 30 minutes. 4. After 30 minutes, take out the samples from the test tubes. Blot dry and weigh again, mark down their weight as ' Second weight'. Variables: Dependent variable: changes in mass of potato slides Independent variable: range of solutions Other variables needed to be controlled: size of slides (4 to 5 millimetres each), time in solution (30 minutes), source of samples (from the same potato), and personal accuracy. Prediction: Some samples will weigh heavier since water enters the cell by osmosis; while some will weigh lighter since water leaves the cell by osmosis.
Therefore, the potato has a concentration of 7.1%. Conclusion: One sample weighs lighter, which suggests the potato slides lose water by osmosis and the potato has a higher water potential (lower concentration) than the 10% sucrose solution. The rest of the samples all weigh heavier than before, which suggests that the slides absorbs water by osmosis and thus the potato has a lower water potential (higher concentration) than the 5% sucrose solution. Comment: According to the graph, we can see that as the concentration of the surrounding solution becomes lower, the change in weight increases. Placed in pure water, a plant cell becomes turgid because of the pressure generated by the cell wall which prevents more water from entering the cell. YIN WENYI 15/10/2002
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