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Potato Cores in Salt Solution.

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Potato Cores in Salt Solution Aim The aim of this experiment is to investigate the movement of water into and out of plant cells by osmosis. The cells chosen for study will be taken from potato tubers as they provide a ready supply of uniform material. Background Information Any substance dissolved in water is called a solute; a solvent is a liquid that is able to dissolve another substance, called a solute, to form a solution. The water content of plants varies depending on environmental conditions. In land plants it plays a vital role in structural support and mineral transport and thus a lack of water may lead to wilting or possibly death. Water is mainly absorbed through the roots, which are covered in specially adapted root hair cells, with large surface areas and thin cell walls to aid absorption by osmosis. The evaporation of water through stomata on plant leaves causes a transpiration stream, causing the water to be drawn up through xylem vessels. Osmosis is the flow of water molecules by diffusion through a partially permeable membrane from areas of high water potential (low solute concentrations) to regions of low water potential (high solute concentrations). All plant cell membranes are partially permeable, which means they allow some some substances to penetrate them but not others. Whether water enters the cell by osmosis will depend on the balance between external and internal solute and water potentials. ...read more.


� Place all boiling tubes into boiling tube rack. � Place 20cm3 of each solution into each of three separate boiling tubes. This will result in eight sets of three test tubes, with each of the eight sets containing different molar concentrations of sodium chloride ranging from 0.05molar to 0.40 molar. � Place 20cm3 of pure distilled water into each of three separate boiling tubes. � Cut 27 potato cores from the same large potato and place them onto a ceramic tile. � Using a scalpel and ruler (calibrated in millimetres) cut the cores into 50mm lengths, with care taken to ensure no potato peel being left on them. The cutting will be to an accuracy of 1 millimetre. � The cores will then be individually weighed on a top pan balance to an accuracy of 0.01 grams. � Each of the cores will then be placed, into one of the 27 boiling tubes for a duration of 2 hours. � The timing will be done using a stopwatch. � After 2 hours the cores will be removed and weighed directly on the top pan again to measure changes in mass. � Directly after weighing the cores, they will be measured again on a ceramic tile using a ruler in order to note any changes in length. � After the experiment has been completed all the apparatus will be properly placed away and all the potato cores will be disposed of. ...read more.


If the cells have become fully plasmolysed then the plant cells are unable to cope with the low external water potential. If the cells have not become fully plasmolysed then recovery could be possible and the effects of osmosis have not been life-threatening for the plant in the short term. Improvements It would have been beneficial to have repeated the experiment more times to make certain that the results were not gained through chance or by an external factor. A greater range of molarities over smaller increments would have shown more accurately any changes in length and masses of potato cores. Ideally all samples should have come from the same part of the potato, as this would have decreased the chances of variations in texture. The size of the potato cores were more than likely to be inconsistent in shape as they were cut by hand using a ruler for measurement. It may have been more appropriate to use a template of some sort. A variety of other similar plant roots could have also been placed through the same procedure in order for comparison. The experiment was also limited by the accuracy of the top pan balance, which was to one decimal place, and the calibration of the ruler. It was also unlikely that room temperature and pressure remained consistent throughout the experiment conduction, and changes in temperature may have altered the rate of diffusion. The potato cores should have had any excess water on their outer surfaces removed by blotting with blotting paper before being re-measured, as this is likely to have altered the masses of the cores. ...read more.

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