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Describe how the effect of temperature and alcohol concentration on membrane structure can be investigated practically.

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Describe how the effect of temperature and alcohol concentration on membrane structure can be investigated practically. Method and apparatus: Apparatus: * Test tube rack * Test tubes x20 * Marker * Graduated syringe (10cm ) * Beaker x2 * Thermometer * Clock/ watch * Forceps * Colorimeter * Cylinders of beetroot x20 Method: Temperature 1. Wash the beetroot cylinders overnight with running tap water. 2. Transfer them over to a large beaker with distilled water in, filled about 1/2 full. 3. Heat some water in a water bath up to a temperature of 95.C. 4. Use the syringe to measure 10cm of distilled water into each of the 10 test tubes. 5. Label the test tubes; 80, 75, 70, 65, 63, 60, 55, 50 and 45 respectively. 6. Place a beetroot cylinder into a beaker containing water at 80.C and note the time, leave the cylinder in the water for 1 minute then, using forceps, place it into the test tube marked 80. Note the time again. 7. Repeat step 6 for the remaining temperatures; 75, 70, 65, 63, 60, 55, 50 and 45. note the time each time you put the cylinder into the test tube. 8. After a cylinder has been in the distilled water for 30 minutes, remove it and discard appropriately. 9. When that has been done there should be 10 test tubes containing a differing amount of pigment. 10. Using a colorimeter, compare the amounts of pigment which has diffused out of the beetroot. Note these results. Alcohol: 1. ...read more.


A colorimeter is used to measure the colour of liquids, by passing a white light through the liquid, to a sensor. It should be calibrated so that distilled water is 100%, so that any colouration of the water can easily be identified by an alteration of the value. Controlled variables: In order to make this experiment reliable and accurate, there are some variables which must be controlled to the best of our ability. * The volume of water in the test tubes needed to be equal as the more water in the test tube, the more dilute the pigment will be. If there were different volumes of water in each test tube, there would be a greater variation of concentrations of pigment. This would produce false results as we are measuring the colour of the water and varying concentrations produce varying colours. * The calibration settings on the colorimeter must also be maintained to ensure that all of the results are in comparison to 100%. Alterations of the calibration settings will result in unreliable readings for some of the samples. If the settings are kept the same, all results will be in comparison to the same value and minor initial deviations from 100% can be accounted for. * The amount of time the cylinders are left in the hot water/ alcohol, and in the distilled water in the test tubes. This is an important factor as the water/ ethanol needs to permeate into the cylinders equal distances. ...read more.


Around the 63-65.C level, the amount of pigment in the water drastically changes. There is a further change between 63-60.C. this must be where the cell membranes start being denatured completely and quickly. For the alcohol however, there is a definite trend, but there is no point where the amount of pigment changes drastically, showing no critical changing point. The water experiments show that temperature can affect the cells proteins and lipids. The proteins will become damaged at higher temperatures, which prevents then from containing all of the substances within the cell. This results in pigment and other substances being allowed out of the cell. The phospholipids that make up the cell membrane become more fluid at higher temperatures and the cell membrane begins to lose its integrity. This causes it to become "more leaky" and therefore it is more likely to begin leaking pigment. The proteins will also denature at the higher temperatures which will allow pigment to escape through the area where the protein was. Increasing alcohol concentration will make the solution less polar, which will gradually disrupt the integrity of the cell membrane of the beet root. The structure of the bi-layer of the beetroot cell membranes depends upon the surrounding water molecules. If the solution becomes less polar (as the alcohol concentration increases) the cell membrane will become more fluid and lose its integrity. This will cause the membrane to become more permeable and allow pigment and other chemicals to pass through the membrane. ?? ?? ?? ?? Biology Luke Harlow - 1 - 06/11/06 ...read more.

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