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Plan an experiment to compare the water potentials (Ø) of beetroot, potato and turnip.

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Biology - Planning Exercise Task Plan an experiment to compare the water potentials (?) of beetroot, potato and turnip. Preliminary experiments Two preliminary experiments were carried out. One into the water potential of beetroot and one into the water potential of potato. Beetroot and potato tissue both store food substances for the plants from which they grow. The cells therefore have large vacuoles, filled with cell sap, which is a solution of ions, sugars and enzymes capable of digesting proteins. The composition of cell sap is different in potato and beetroot cells and this will affect their water potentials. Although there are differences between the two tissues, their structures are sufficiently similar that they will respond in the same way to being immersed in hypertonic and hypotonic solutions. Preliminary experiment 1 (20th November 2003) 6 specimen tubes were labelled and equal volumes of various concentrations (molarities) of sucrose solution were added to the tubes. The first tube contained 10ml of distilled water, the second contained 10ml of 0.1 molar solution, the third had 10ml of 0.2 molar solution, the fourth had 10ml of 0.3 molar solution, the fifth had 10ml of 0.4 molar solution and the sixth had 10ml of 0.5 molar solution. Then 6 pieces of potato were borne, and each was cut down to 12mm in length. ...read more.


This increases turgor pressure inside the cell and the cell is referred to as being turgid. I would expect that the greatest change in all tissues would be in the samples present in the 1.0 mol.dm-3 solution. I believe that the masses of these tissues will decrease because water will pass down the water potential gradient and out of the cell, into the greater molarity of the surrounding solution. If the results of the preliminary experiments and the secondary source are reliable, beetroot will have the lowest water potential, potato will have the next lowest and turnip will have the highest water potential. Method A similar method to the one in the preliminary experiments will be used to find the point of equilibrium, hence, the water potential of beetroot, potato and turnip. * Wash all apparatus with deionised water * Label 11 specimen tubes 'P' (potato), and the molarity between 0.0 - 1.0 mol.dm-3, which will be placed in the tube. E.g. 'P 0.0 mol.dm-3', 'P 0.1 mol.dm-3', and so on. Do the same with 11 specimen tubes labelled 'T' (turnip) and 'B' (beetroot). * Fill each tube with 10cm3 of the corresponding molarity sucrose solution. * Use a cork borer and cutting tile to take a cylinder from the potato and using the scalpel, cut 11 discs of approximately equal size. ...read more.


Also, when using the borer and scalpel, make use of the ceramic tile and do not hold the vegetables. Variables and Fair testing In all experiments certain variables must be kept the same in order to make the experiment fair. In this experiment, the independent variable will be the molarity of the solution in which the sample tissues are kept. In order to ensure that the experiment is fair these variables must be kept the same: * The same beetroot, potato and turnip should be used to take all samples of the corresponding tissue. This ensures that all samples of a vegetable have the same water potential. * The same cork borer should be used to ensure that all samples have an equal diameter. * The length of time that each tissue sample is kept in the solution should be the same. This is to allow and equal amount of time for osmosis to take place. In this experiment, there are a number of factors that must be considered, in order to obtain accurate and valid results: * An accurate top pan balance should be used to give an accurate mass of the sample tissues. * A wide range of results should be taken so that anomalous results can be easily spotted. This also shows the reliability of the results collected. E.g. 0.1 - 1.0 mol.dm-3. * The experiment should be carried out a minimum of 3 times and mean results calculated. This will increase the overall reliability of the results. Dean Armstrong ...read more.

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