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Investigate the water potential of potato.

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Aim: to investigate the water potential of potato. Research: Osmosis in plant cells Osmosis is the net movement of water molecules from a region of their higher concentration to a region of their lower concentration through a partially permeable membrane. If the concentration of water molecules is the same in the plant cell and the surrounding liquid, there will be no net movement of water into or out of the cell; and if the concentration of water molecules is greater in the cell than the surrounding liquid, there will be a net movement of water from the plant cell to the surrounding solution. Osmosis will occur whenever a partially permeable membrane separates two solutions containing different concentrations of water molecules. If the cell is surrounded by pure water, or by a solution whose solute concentration is lower, and water potential higher, than that of the cell's contents, water flows into the cell by osmosis and swells up. The external solution is said to be hypotonic to the solution in the cell. This means the solute concentration is lower than that of the cell. If the cell is surrounded by a solution whose solute concentration is higher and water potential lower than that of the cell, then water will flow out of the cell causing the cell to shrink. ...read more.


This part of the preparation must be done very accurately as a change in the surface area may allow more or less osmosis to occur. I will then use an electric balance to weigh the potato tubers, once a tuber has been weighed the mass will be recorded as well as the test tube it has been placed into. The potato is going to be left in solution for 24 hours to allow the processes to occur and to allow the water movement to settle. After 24 hours I will return to the experiment and take each piece of potato out of the test tube with tweezers, dry them off by dabbing them with tissue on by one and weighing them on the electric balance and record their final mass. Apparatus: * 18 test tubes and bungs * Test tube rack * White tile * Scalpel * Potato corer * Thermometer * Tissue paper * Electronic balance * Sucrose solutions * Distilled water * Ruler * Measuring cylinder * Tweezers Variables: To create a fair test certain aspects of the experiment will have to be kept the same whilst one key variable will change. I have chosen to vary the concentration of the sucrose solution. ...read more.


This anomalous result could be explained by numerous errors, for example the balance may not have been very precise; water from previous potatoes may still have been on the balance. Also it may have been measured in accurately from the other cuttings of potato. The precision of measuring the concentration of the solution may also have changed for this result. However there were a few areas where there could be improvement. Firstly, when I dried off the excess water on the potato cylinders after the experiment and before I weighed them, I used a paper towel. This might have either taken some water out of the potato or it might of left some excess water on the potato. This part of the experiment is difficult to come up with an accurate and fair method, as other ways would also lead to some slight mistakes. Also the potato itself was not from the same potato and was not exactly the same size, although I did try to cut them to 1.5cm each, this could have effected the amount of water gained or lost. Finally, I could extend the experiment to a more exact level by looking at the potato cylinders under a microscope, then I would be able to see the cells in greater detail and draw some more observational results. ?? ?? ?? ?? Isabel Murtough Biology coursework MR ...read more.

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