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Investigating Water Potential Of Potatoes.

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Investigating Water Potential Of Potatoes. AIM To investigate the effect of various sugar solutions (which have different concentrations of sugar solutions. on a potato. We will be investigating the length of the potato after a certain amount of time. Thus, enabling us to investigate the water potential of a potato. INTRODUCTION The fact that organisms rely on diffusion for the fulfilment of many of their needs has had a profound effect on their structure. Consider, for example, the way gas exchange relates to the size of an organism. The organism's oxygen requirements (its needs) are proportional to its volume, i.e. the bulk of respiring tissue, which it contains. Its exchanges however, are proportional to the surface area over which diffusion of oxygen can take place. In an organism, the effective surface area must be sufficient to fulfil the needs of the respiring tissue (pg. 48 Biology a Functional Approach MBV Roberts). This simple fact also occurs in Osmosis (movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane). Although the plasma membrane of a cell is fully permeable to respiratory gases, it is by no means permeable to all substances. The porous nature of the membrane means that only those molecules that are small enough will diffuse through it swiftly. The plasma membrane is thus selectively permeable (or semi- permeable), permitting the passage of some substances but not of others. (Pg. 49, Biology a Functional Approach, MBV Roberts). To appreciate the significance of this we must examine the properties of selectively permeable membranes. Consider the situation, where the mouth of a thistle funnel is covered with a selectively permeable membrane such as a cellophane or pig's bladder. The funnel is then filled with a strong sugar solution and immersed in a beaker of pure water. What happens? Quite quickly, the level of solution in the tube starts to rise. ...read more.


Firstly, the only thing that should be changed throughout this experiment should be the concentration of the solution and nothing else. The potato cylinders should be approximately the same in length, which should make them roughly the same in weight. The temperature is being kept the same in our test for all our beakers by placing them all in the same place. So if there is an increase or decrease in temperature it will be the same for all the beakers and so affect them all. The skin will be removed of all the potato pieces and the shape will be kept the same by using a borer. This is so to keep the surface area of the cylinders the same. The volume of the liquid can also affect the outcome so it must also be kept the same. Having repetitions of all the solutions will also make this test more reliable. If all of these features are looked at the experiment conducted will be a fair test. RESULTS My results that I received during my experiment are shown below. Concentration of solution (molar) Initial mass(g) Final mass(g) Change in mass(g) % change in mass Average % change in mass 1 molar 0.66 0.33 -0.33 -50.0 -45.00 (2nd) 1 molar 0.65 0.39 -0.26 -40.0 0.5 molar 0.61 0.46 -0.15 -24.6 -23.15 (2nd) 0.5 molar 0.60 0.47 -0.13 -21.7 0.2 molar 0.69 0.73 0.04 5.79 05.28 (2nd) 0.2 molar 0.63 0.66 0.03 4.76 0.1 molar 0.60 0.68 0.08 13.3 18.60 (2nd) 0.1 molar 0.67 0.83 0.16 23.9 Distilled water 0.63 0.83 0.20 31.7 26.15 (2nd) Distilled water 0.63 0.76 0.13 20.6 ON THE NEXT PAGE IS A GRAPH SHOWING MY RESULTS. CONCLUSION The results on the last page have formed a line for which I have drawn a line of best fit. This line of best-fit states that there must be a reason for what has occurred in my experiment. ...read more.


The fact that we did not repeat our experiments more than just twice makes our results less reliable. In our experiment, controlling the variables was very limited. For example temperature was not perfectly controlled, using a water bath would have been more accurate. Controlling the weight of the potato before was all very well however, afterwards measuring it's increase or decrease in weight was limited as not drying the potato cylinders properly could affect the result. If not dryed properly water would remain on the potato and so the reading would be greater than it's actual mass. All of this could have concluded to giving us anomalous results. Besides this, I think the method was performed accurately and on the whole we did not make any errors in our experiment however, there is still room for improvement. Firstly, I could have measured the individual cells in the potato using a microscope. This could have included the length and the area or volume of the cells this would have made the experiment very accurately as to how much water enters the cells. Not only this but it would also have made it very accurate in finding the difference before leaving the potato in the solution and after. To make an investigation of this, we could have done some further work, this could have included investigating what effect this had on different cells, such as animal cells or even to see what effect this would have on the cells of a tree's bark. We could have even used different vegetables and even roots of different flowers to see what happened. Another way to investigate further would be to use a different range of sugar solutions such as * Distilled water * 0.1molar * 0.2molar * 0.3molar * 0.4molar * 0.5molar * 0.6molar * 0.7molar * 0.8molar * 0.9molar * 1 molar A wider range of sugar solutions will achieve a wider range of results and in turn will induce a more reliable conclusion. ...read more.

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