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Effect of temperature on membrane permeability

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Effect of temperature on membrane permeability Aim This investigation aims to determine what effect an increase in the surrounding temperature has on the plasma membrane of a typical plant cell structure. Hypothesis An increase in temperature will damage and denature the plasma membrane, which would cause the substances contained within the cytoplasm to leak out of the membrane. The investigation carried out was to see the "effect of temperature on membrane permeability". Different temperatures were used, ranging from room temperature to 87°C. Three test tubes were used to give a range of results. They were placed in a colorimeter, from which a percentage was recorded showing how much light had passed through. Figure 1 shows the results obtained from the investigation. A mean has also been calculated and included in the results. Temperature (°C) Test tube 1 (%) Test tube 2 (%) Test tube 3 (%) Mean (%) 23 98 96 96 96.67 45 95 93 91 93.00 53 74 73 73 73.33 65 54 45 34 44.33 87 1 1 1 1 Figure 1: A table showing the results obtained. From the above results it can be seen that as the temperature increases, the permeability of beetroot membrane increases. This shows that the plasma membrane must be denatured.


The permeability of the beetroot membrane does depend on the temperature that it is placed in. Choosing a random temperature shows that the higher the temperature the more permeable the membrane, thus the more dye bleeds out of the membrane. The following will now outline an explanation of the above theory by referring to the cell membrane structure, diagrams and references will be used from the books listed on the cover of the coursework page. After collecting and correlating the results, I have come to the conclusion that the experimental hypothesis is correct, in that an increase in temperature will damage and denature the plasma membrane and cause the cytoplasm and other substances contained within the membrane to leak out. This has been shown by the steady increase in anthocyanin leaked out of plant cells as the temperature increases. A description of the plant cell's membrane structure will be given to show how temperature affects its structure. Figure 5 is a diagram of a typical cell membrane. Figure 5: A diagram showing the plasma membrane of a cell. The cell membrane (or plasma membrane) surrounds all living cells. It controls how substances can move in and out of the cell and is also responsible for many other properties of the cell.


From 23°C to 45°C, the light % transmission does not decrease rapidly; the figures do not differ greatly. This could be due to the number of proteins being less denatured in 45°C as I would expect it to be, as this temperature would be considered above the optimum temperature that the plant cell could survive within. The betacyanin pigment of beet roots is normally sequestered in the vacuole and, by means of the properties of the tonoplast and cell membrane, does not leak into the cytosol or the extra-cellular sap of the beet root. Of course if the beet root is cut, cells are sliced open and the pigment spills out, but if the membrane is altered (phospholipid bilayer + proteins) more subtly leakage (diffusion) of betacyanin is induced. Although, the results help explain the hypothesis they may not be entirely reliable. Three readings were taken to increase accuracy; however this does not mean that the three results were accurate. Limitations in the apparatus could have encouraged this to occur, for example the standard deviation calculation for 65 C shows that the results are not reliable. There is also an anomalous result for 45 C. This is circled on the graph. The reason for the anomalous result could be due to a number of factors which will be discussed further in the evaluation. Manpreet Virdee Page 1

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