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Water potential is a measure of the free kinetic energy of water in a system or the tendency of water to leave a system, it is measured in units of pressure (KPa) and is given the symbol .

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Introduction

BIOLOGY COURSEWORK Introduction Water potential is a measure of the free kinetic energy of water in a system or the tendency of water to leave a system, it is measured in units of pressure (KPa) and is given the symbol . Where is the solute potential which is a measure of the reduction in water potential due to the presence of solute molecules <always -ve> Where is the pressure potential which is the pressure exerted on the cell contents by the cell wall and the cell membrane <always +ve> When a plant cell is placed in a solution of higher (hypotonic) e.g. pure water than the cell , water will enter by osmosis causing the vacuole to expand and push the cytoplasm outward against the cell wall .As more water enters the cell ,the pressure potential rises until it is equal (and opposite) to the solute potential .The water potential now is zero .No more water can enter the cell . A cell in this state is said to be turgid. When a plant cell is placed in a solution of lower (hypertonic) e.g. sucrose solution than the cell , water will leave the cell by osmosis. As water leaves the cell, the protoplast starts to shrink until it is exerting no pressure at all on the cell wall .At this point, the pressure potential is now zero, so the water potential of the cell is equal to its solute potential. ...read more.

Middle

Switch to medium or high power as appropriate and, moving the slide about if necessary, record the state (plasmolysed or unplasmolysed ) of the first 50 cells viewed. Cells in which there is only a slight sign of the cell membrane pulling away from the cell wall should be counted as plasmolysed. 8. Repeat this procedure for the other 5 squares of epidermis, mounting them in their respective solution. Conclusion: From 0.0M to 0.45M, all cells are found turgid, but starting from 0.5M, there are about half of the cells observed are plasmolysed and when it is 0.6M, about 96% of the cells observed are plasmolysed. This suggests that the water potential of red onion cells is between 0.45M and 0.5M. Reason for next test: To see if different plants have different water potentials. Secondary sources: Biology 1, Cambridge University Press, endorsed by OCR. Test for potato and parsnip Materials required: Potato 5ml plastic syringe Parsnip 10ml plastic syringe 12 petri dishes 1M-sucrose solution 12 test tubes (boiling tubes) distilled water test tube rack fine forceps wax pencil graph paper white tile *sharp knife *Should be extremely careful when using it Method: 1. Label 6 petri dishes and 6 test tubes appropriately for each of the following distilled water and sucrose solutions for potato with a wax pencil :0.0M, 0.3M, 0.45, 0.5M, 0.6M, 1.0M .Label again 6 petri dishes and 6 test tubes appropriately for each of the following sucrose solutions for parsnip :0.0M, 0.3M, 0.45M, 0.5M, 0.6M, 1.0M.Put all test tubes in a test tube rack. ...read more.

Conclusion

~Cut the chips with machine to make measurements more precise. ~Use readily prepared concentration of solutions instead of mixing the solutions yourself. Reasons for anomalous result: Al though I have no anomalous results, I got several ideas about why anomalous results may arise. 1. The time provided is not long enough for full changes. 2. Different parts of plants may have different water potentials. 3. The slight difference in size of the chips may affect the results pretty much as the bigger it is, the more cells it has. 4. The chips may float on the water surface during experiment, therefore affects the changes in water potential of the cells. Reliability of results: I think my results are quite reliable despite the fact that many errors might have affected my experiment. The reason I am confident with my results is because it does not have anomalous result, it looks reasonable. Moreover the repeated measurements are more or less the same, difference between figures I got are just a few tenths after 4 hours and the results I got after 24 hours. By the way, I have rounded off my results to the nearest whole number which may have a chance that I have affected the figures slightly. As a result I think my conclusion is also relatively safe and it is still valid as I made my conclusion based on my results and with reference to my research, knowledge and data, despite the inevitable errors that would arise in every experiment. ?? ?? ?? ?? 1 ...read more.

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