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To investigate the effect of varying concentration of glucose solutions on the osmotic activity between the solution and potato slices.

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Introduction

INVESTIGATING OSMOSIS IN PLANT CELLS AIM: To investigate the effect of varying concentration of glucose solutions on the osmotic activity between the solution and potato slices. SCIENTIFIC THEORY: Osmosis is defined as the net movement of water molecules from a region of high concentration to a region of low concentration of water, through a partially permeable membrane, which only lets smaller molecules through. This can also be described as movement down the concentration gradient. The molecules continue to diffuse through the membrane until both sides reach a state of equilibrium. This is also known as the isotonic point when the molecules are equally distributed on both sides of the membrane so that no one area has a higher or lower concentration than the other. Plant cells have a strong cell wall and a partially permeable cell membrane around them. When cells are surrounded by a solution more dilute than their own, (hypotonic solution-with more water than solute molecules), the cell swells up and becomes "turgid". This is because the water molecules diffuse from the solution to the plant to equal out the concentration levels. The strong cell wall prevents them from bursting. Figure 1- A turgid plant cells in more dilute surroundings (from "Biological Sciences Review") When they are surrounded by a solution more concentrated than their own, (hypertonic- less water molecules), they shrink and become "plasmolysed". This is because the water molecules are highly concentrated in the plant, so they diffuse out into the solution to create a state of equilibrium. ...read more.

Middle

Website: " www.ukonline.co.uk/website/spinneret/life/osmdia.htm" 6) Preliminary Results from classmate Yasmine Li ANALYSING EVIDENCE AND DRAWING CONCLUSIONS From Tables 2 and 3 and Figure 1, it can be seen that as predicted the potato slices that were put in a low glucose concentrated solution gained mass and the potato slices that were put in a high glucose concentrated solution lost mass. Table 4 shows the visual observations made at the time. They correspond with the quantative data as the loss and gain of mass is visible as the potato slices placed in a low glucose concentration visibly swelled and the slices placed in a higher concentration of glucose solution could be seen to shrink and became extremely thin and wrinkly. The graph in Figure 1 shows the straight line of best fit for the percentage change in mass of the potato chips over the course of 24 hours. It can be seen that all of the readings and mean results are very close to the straight line of best fit, clearly showing that my results are fairly accurate and reliable. It can also be observed from Figure 1 and Table 3 that the potato slices placed in a o.4M concentrated solution and below have a percentage increase in their mass. This means that the 0M, 0.2M and the 0.4M solutions were hypotonic as they were more dilute (contained more water molecules) than the plant cells that they surrounded and so as a result there was a net movement of H20 molecules from the solution to the plant cells to equal out the concentration levels. ...read more.

Conclusion

All of these factors contributed to a fairly reliable set of results. However there was limited time and I needed to test a wide range of concentrations to improve the validity of the data being collected. As a result two groups set up the experiment together. One group measured 0M, 0.4M, 0.8M and 1.2M solutions and the other measured the 0.2, 0.6M and 1M solutions. However all the final measurements were taken by the first group. As a result the results could have been inaccurate as both groups had different cutting and measuring methods for the potato slices and the solutions. Also different equipment was used e.g mass balance and potato tuber although they were to the same accuracy. However as the first group took all the final results only one drying method was used. To further investigate osmosis in plant cells: > I could measure the mass change every 1 hour for 4-6 hours to work out when all the percentage change took place and not leave the slices in the solution any longer than they should be. However this is rather difficult in a school situation. > I could possibly use more concentrations so that my results would be more varied. I.e. 0.10M, 0.30M, 0.50M, 0.70M e.t.c. Many concentrations around 0.37M, the estimated isotonic point, should be tested on to find out a more accurate level at which there is no net movement of water or glucose to equal out the unbalance. > I could cut all the potato slices from one potato so that the variation between individual potatoes does not interfere in the experiment and undermine the experiment's accuracy ...read more.

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