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An experiment to test the effect of different temperatures on the permeability of cell membrane.

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Introduction

An experiment to test the effect of different temperatures on the permeability of cell membrane. Aim In this experiment, I am trying to find out how, why, and by how much does the difference in temperature affects the permeability of cell membrane of plant cells. Prediction Having done a pilot experiment and by using the scientific knowledge gathered, some predictions can be made. The permeability of cell membrane should increase as the temperature increases, and this is shown by the decrease in the percentage transmission of light on the colorimeter. As guidance, the results of the pilot experiment could be used: Readings taken from the pilot experiment Time taken(min) Temperature(�C) % Transmission of light Volume of water(ml) 20 20 96 5 20 30 81 5 20 45 70 5 20 60 48 5 Graph to show the relationship of temperature and the % transmission of light. Results similar to the pilot experiment are expected, and so at 20�C, the cell membrane is not very permeable, shown by the high % transmission of light, expected to be about 90-100%. The membrane would start getting more permeable at around 30-40�C, shown by the decreased % transmission of light, expected to be about 85-65%. The cell membrane would get much more permeable when temperature rises above 45�C, shown by the low % transmission of light, expected to be below 50% at around 60�C. We can see the permeability of the membrane by the amount of anthocyanin, the polar red dye in the vacuole of the beetroot cell, leaking out. The more dye coming out the more permeable the membrane is, and this means that the lower the % transmission of light, the more permeable the membrane. Graph of the relationship of permeability of cell membrane and temperature Theory of prediction There are five possible ways that the dye could leak out of the cell in normal condition without the aiding of heat, and these are simple diffusion through the lipid bi-layer, facilitated diffusion by protein carriers, and facilitated diffusion via ion channels, active transport, and exocytosis. ...read more.

Middle

-5ml of distilled water is added to each test tube, using the syringe. -7 water baths of different temperatures are now being set up using the electrical water baths, having temperatures of 20�C, 30�C, 40�C, 50�C, 60�C, 70�C, and 80�C. -When the water baths are at the correct temperature, checked by using the thermometer, each of the 4 test tubes could be placed into a different water baths for 20 minutes, counted using the timer. -At the end of the 20 minutes, the test tubes are taken out of the water baths immediately, and the dyed water in each would now be poured into a different curvette, prepared to be placed into the colorimeter. -One by one the 4 cuvettes with the dyed water can be placed into the colorimeter and the % transmission of light passing through the dyed water can then be recorded. Risk assessment Normal lab safety precautions must always be taken, but apart from those, there are few other precautions that are needed for this experiment. The water bath can get up to 80�C, and might burn the skin, and so caution is needed when putting the test tubes in. When cutting the beetroot with the scalpel, safety spectacles are needed to be worn as the blade could break off and damage the eye. Sources -A pilot experiment -The Microsoft Encarta Encyclopaedia 2002 search 'Cell Membrane'. -OCR Cambridge Advance Science Biology 1, written by Mary Jones, Richard Fosbery, and Dennis Taylor. Pages 58-60, 30-36. -Collins Advanced Science Biology, written by Marcus Barbor, Mike Boyle, Mike Cassidy, Kathryn Senior. Pages 10, 80-83, 86, 88-95. -Europress A-Level Biology CD-ROM. -DK Interactive Learning A-Level Biology CD-ROM. -www.studentcentral.co.uk/coursework/essay/688.html at 20.02.2002 -www.ocr.org.uk at 20.02.2002 Analysing evidence and drawing conclusions When the temperature range was between 20�C and 60�C, the drop in light transmission, from 95% at 20�C to about 80% at 60�C, was in proportion to the increase in temperature, creating a steady group of results, lying on a straight line on the graph. ...read more.

Conclusion

and the length of time the test tubes are in the water bath would both have an error of less than 1%. Although the colorimeter is only accurate to the nearest one % of light transmission, it should have a minimal amount of error as it is digital. Improvements To improve on the experimental procedures, several things could be done. The reliability of the experiment could be improved by trying to use the beetroot pieces cut out from the same beetroot, or at least from the same type of beetroot, instead of using beetroot of different sizes. For most experiments, doing more repeats would increase the reliability, but this would not apply to this experiment as over 90 readings were taken and there were at least 10 repeats done for each set of conditions. However doing the same experiment at more temperature conditions would increase the reliability as a smoother trend could be seen. To minimise sources of error, the first way to improve the experiment will be to cut the beetroot personally, instead of having them pre-cut, and also that a more accurate template could be used, which would keep a consistent surface area for different pieces of beetroot. Another way is to use proper electronic water baths to maintain the exact temperature for each of the different temperatures; although this is not practical as it would take time, however errors would be reduced greatly if this could be done. How safe is the conclusion Although there are noticeable amount of errors in the experiment, shown by the size of the error bars on the graph, the conclusion is still very valid and reliable. This is because although the possible amount of error is great, the line on the graph being not erratic shows that these possible errors did not occur in this experiment. Even if we try to plot the worst line on the graph within the range of the error bars, a line leading to the same conclusion would still appear. ...read more.

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