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Investigating the water potential inside a potato chip.

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AS Biology coursework Investigating the water potential inside a potato chip Introduction In the experiment I will be trying to find the water potential inside a potato cell. Plants absorb water for photosynthesis by the process of osmosis. Water moves in and out of the cell by the process of osmosis through a partially permeable membrane. Osmosis by definition is the "diffusion of water only, It is the net movement of water molecules from a region of their higher concentration to a region of their lower concentration through a partially permeable membrane". "We call the overall tendancy of a cell or system to gain or lose water as water potential"- (taken from Collins AS Biology- Mike Boyle and Katharyn Senior). In terms of Water potential (?), water will always osmose "from a region of higher water potential to a region of lower water potential through a partially permeable membran"-Cambridge Biology 1 AS- Mary Jones and Dennis Taylor. In this experiment I will be trying to find out the point where the water potential outside the cell is equal to the water potential inside the cell, so there is no movement of water in or out of cell and therefore the potato chip neither gains or looses mass. At that point the water potential of the solution the potato chip is, equal to the water potential inside the potato cell. ...read more.


The results I got for the repeated experiment appear to lie near the line of best fit. I calculated the % mass change for each sucrose concentration: Concentration of sucrose solution (M) Average Mass before (g) Average Mass After (g) % Mass Increase 0.00 3.37 4.09 21.365 0.1 3.27 3.63 11.009 0.2 3.01 3.33 10.790 0.3 3.41 3.60 5.570 0.3 3.20 3.30 3.125 0.4 3.28 3.16 -0.043 0.5 3.14 2.65 -14.494 0.6 3.29 2.74 -16.176 Look at Graph 3 shows the % Average mass change at different sucrose concentrations. I drew this graph to show % mass change as this is a better indicator of showing the gaining or loosing of mass of the potato chip. I drew a line of best fit to show the general trend. The results I repeated for 0.5 and 0.6 (M) concentrations appear to fit the trend of the graph so I will keep theses results. The line of best fit shows the general negative trend that as the sucrose concentration increases the increase in potato mass became less and less. At 0.00M sucrose concentration (pure water) you can see the chip has gained most mass, this is because there is a much greater sucrose concentration inside the cell compared to its surroundings, lowering the ? inside the cell. As the ? outside the cell is much greater than ? ...read more.


Also when drying off the potato it was difficult to remove al the excess solution off the potatoes without pressing to hard and removing the fluid from inside the potatoes. This would have resulted in an inaccurate decrease in mass therefore the percentage change in mass would also be inaccurate. This could be changed by using a rolling technique of the tissue paper to remove the excess fluid instead of just pressing on the potato tubes. I think I took enough results for the amount of molarities that I was given, and the time restrictions that I had to follow, The range was big enough, but to fill in the gaps in my graph, I could have taken results of more molarities, so instead of taking results from 8 different molarity levels I should take 10 molarity levels. This would make the lines of best fit on the graphs more reliable, therefore the end results would be more reliable. Furthermore repeating the whole experiment and taking more averages will increase the accuracy and reliability of the results. I could extend my enquiry by testing the percentage change in mass with molarity using a different substance. By this I mean using a different vegetable, perhaps celery or cucumber. Then I could find out whether the water potential of different vegetable cells differ I could also investigate other external factors which effect the process of osmosis in plant cells. 2 ...read more.

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