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Investigating the Factors affecting the water relations of plant cells.

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INVESTIGATING THE FACTORS AFFECTING THE WATER RELATIONS OF PLANT CELLS By Emily Akena INVESTIGATING THE FACTORS AFFECTING THE WATER RELATIONS OF PLANT CELLS Introduction This investigation studies the affect of different variables on the rate of osmosis in plant cells. The variables that would affect this investigation are: * Surface Area * Temperature * Concentration of surrounding solution * Concentration of solutes inside plant * Plant tissue - age, species, time of year The plant tissue to be used in this investigation is potato tuber tissue, because handling it is simple. The variable that will be investigated is the effect of concentration on the water relations of the potato cells as the concentration can be varied and measured accurately. Visual results can also be obtained. Temperature will not be varied, as it is hard to control and would therefore lead to inaccurate results. Temperatures that are too high will cause the proteins in the cell walls to be denatured and the plant to cook. The concentration of solutes inside the potato cannot be determined using school laboratory equipment, is uncontrollable and also varies. For each concentration to be investigated, I will measure the mass of the potato chip before and after it has been submerged in the solution and then calculate the percentage gain or loss of mass. Prediction Osmosis is the diffusion of water molecules from a higher to a lower concentration of water molecules through a partially permeable membrane. If there is a higher concentration of water molecules outside the cells, osmosis takes place into the cells through the partially permeable cell membrane to the large central vacuole. This increases the turgor pressure inside the cell and causes the cell to become turgid. ...read more.


If the percentage mass change is found, the resulting figures can be compared and plotted on to a graph. I will calculate the percentage change in mass using this formula: Mass after - Mass before x 100 = Percentage Mass Change Mass before * Repeat the experiment three times to produce a more accurate average value to plot onto the graph. Preliminary Results Concentration (M) Mass before (g) Mass after (g) Change in Mass (g) Percentage Change in Mass 0.0 2.21 2.41 0.2 8.3 0.25 2.33 1.94 -0.39 -16.7 0.5 2.22 1.55 -0.67 -30.2 0.75 2.04 1.38 -0.66 -32.4 1.0 2.36 1.83 -0.53 -27.54 Improvements From my preliminary experiment, I have decided to make the following changes. 1) To prevent excess water loss from the potato pieces, I will prepare the solutions before extracting the potato core. If this is not done, the potato will begin to dry out, therefore experiment results will not be accurate. 2) The potato pieces should be prepared, i.e. measuring and weighing in consistent order so that each piece spends the same amount of time in similar conditions. 3) As a 30cm3 measuring cylinder was not available and the next size of 50cm3 was too large for accurate measuring of the volumes I require, if the volume exceeds volume cylinder of 25cm3, I will measure the difference using a measuring syringe. I will also use a measuring cylinder as well as a measuring syringe to measure the salt solution. This is because the measuring syringe only has a maximum value of 10cm3, so multiple measurings for the larger volumes will decrease accuracy. This will increase the accuracy of measuring the salt solution and water. ...read more.


For example, around the potato eyes where shoots will grow, the concentration of solutes may be higher. This would increase osmosis into the cells. This variation could be improved by using smaller lengths of potato so all the samples could be obtained from a single potato core. Further inaccuracies could be caused by errors in measuring the water and salt solution. This would cause more or less osmosis to take place than would occur. This could be improved by using a burette to measure the liquids. Also the way in which the potatoes were dried after being submerged differed. Some may have been dried more thoroughly than others this would have caused results to be higher or lower than they otherwise would be. Also the excess water was not removed as the potato was cut. This problem could be improved by rolling the potato under a tile of certain mass. This way, the same force would be applied to each piece. There are no anomalous results obtained in the investigation. This evidence is not sufficient to draw a firm conclusion as more than five points are needed to draw an accurate best fit curve. More data is needed to support the curve. To provide additional data to determine that the shape of the graph and increase reliability, the experiment could be repeated but using concentrations of smaller intervals, for example testing concentrations of 0.125M, 0.25M, 0.375M, 0.5M, 0.625M, 0.75M, 0.875M, 1.0M. This would provide more points on which to base the line of my graph. Also, to prove the graph is correct, the isotonic point could be tested. By using, according to the graph, the isotonic point of 0.15M there should be no change in the mass of a potato piece. However, the isotonic point would vary from potato to potato, so the piece used to test the isotonic point should be from the same potato tuber. 2 ...read more.

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