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Comparing The Water Potential Of Plants

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Introduction

Comparing The Water Potential Of Plants Aim The aim of this experiment is to compare the water potential of two different plant tissues, potato and sweet potato tubers, by measuring the gain or loss of water when samples of the tissue are placed in a range of concentrations of sucrose solutions. Background information Osmosis is the movement of water molecules from a region of their higher concentration to a region of their lower concentration through a semi permeably membrane. If the cell is surrounded by pure water (which has a water potential of zero), or by a solution that has a lower concentration and therefore a higher water potential, than that of the cell's contents water flows into the cell by osmosis and the cell would swell up (become turgid). The external solution is said to be hypotonic to the solution in the cell (hypo meaning lower than and applies to the solute concentration). If the reverse was to occur and the cell was surrounded by a solution whose concentration is higher and whose water potential is lower then that of the cell, the water would flow out of the cell into the solution. In this case the external solution would be known as hypertonic to the solution in the cell. ...read more.

Middle

To do this I placed a tile under the potato so that the surface was protected, and also took care while handling the knife so to protect myself and others. Once the potato samples were cut, I weighed them and then placed them into test tube with 20cm3 of different strength solutions. The potato was then left in the solution for approximately 2 hours 30 minutes. On taking the potato out of the solution I blotted it and reweighed it, to find out the new mass. Results On the next page can see two tables of results, these are from the experiment that I done and also a copy of the results supplied by Imogen Freeman. The reason that I also used Imogen's results was because I did not have time to conduct another experiment, so by using these results it is going to allow me to draw better conclusions, and also allow me to compare my results, and to look for consistencies or differences that might stand out. Please see attached graphs for experiment one and two, where I have compared the percentage change in mass against the different solution strengths. Sweet Potato Table of Results 1 Start mass (g) end mass (g) ...read more.

Conclusion

This is because when the cell is turgid, the vacuole has reached its maximum volume and no more water can enter the cell. When the cell is in a state of total plasmolysis then the vacuole has almost disappeared from the lack of water within the cell. If I was to do this experiment again, there are several improves and changes that I would make. The first thing I would do is to use smaller increases in solution strengths, at the point where the line on the graph appears to cross 0, this would allow me to find the exact point that water potential is equal to solute potential plus pressure potential. I would also repeat the experiment more times to enable me to find an average result and also spot a spurious result. Something else I could do, would be to leave both potato samples in the distilled water for longer to see how long it takes for them to become fully turgid. When doing this experiment you are never going to be able to all the samples of potato weighing and measuring exactly the same, and because of this the experiment is not going to be totally reliable. Nor are you going to be able to blot the potato sample's the same why every time you remove them from the solutions. Again this is going to cause inconsistencies in the results. ...read more.

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