The Effect of Temperature on the Permeability of Beetroot Membrane

The Effect of Temperature on the Permeability of Beetroot Membrane
Analysis The graph shows the colorimeter readings increase as the temperature increases, they increase by the most at higher temperatures. This is shown by a smooth curve. This means that the beetroot samples release more dye at higher temperatures. This is because higher temperatures cause the membrane structure to break down. The membrane structure: Membranes have two layers of molecules called phospolipids to make up their structure. Phospholipis consist of a glycerol molecule plus two molecules of fatty and a phosphate group, this looks like a head with two legs, their head is attracted to water, this means theyÂ?re hydrophilic. The rest of the lipid (the fatty acid legs) is hydrophobic, which means they repel water. In aqueous solutions the phospolipids automatically arrange themselves into a double layer so that the hydrophobic legs are packed inside the membrane (away from the water) and the hydrophilic heads face outwards into the aqueous solutions. The molecules are represented in the Â?fluid mosaic modelÂ? shown below (the red bits are the legs of the phospolipids): [draw diagram here] If it was only made from phospolipids the membrane would be a barrier to water, this is why there are other components scattered throughout the phosphlipid by-layer. Glycolipids are lipids which have combined with polysaccharides.
These may be involved with cell recognition but their exact role is not yet known. They are found in the outer layer of cell membranes. Glycoprotiens (seen in green on the diagram) are proteins with polysaccharides attached. They are chains of monosaccharides, which branch off to form different shapes. The shape depends on what cell they are attached to, allowing the cell to be recognised correctly. Intrinsic proteins occur across the whole width if the protein allowing the intake of substances into the cell. Extrinsic proteins occur only in the outer or inner phospholipid bi-layer, but not through both. These proteins are usually receptors. Intrinsic channel proteins allow water soluble molecules to pass through it by forming a tiny gap in itself, this is large enough for the substances. Intrinsic carrier proteins carry water-soluble molecules through the membrane, this method is called Â?Active TransportÂ? Extrinsic proteins recognise and bind on specific molecules, eg. hormones. Membranes can also be embedded in the inner membrane The reason why the membrane structure breaks down at higher temperatures is because the proteins are not very stable and break down with heat, called denaturing. An enzyme denatures because the heat changes the shape of the active site o the substrate can not fit into it. Enzymes are always denaturing, but at higher temperatures this occurs more rapidly. But at higher temperatures there are more collisions between the substrate and the active site so this would increase the reactivity, so a good balance must be found. The optimum temperature is about 43ËšC, this is called the optimum temperature. As the proteins start to break down, there is no longer a barrier to the cell The lipids in the bi-layer are slightly more stable than the proteins but Â?meltÂ? and breakdown at higher temperatures too. This in effect creates Â?holesÂ? in the membrane. Also the membrane is in part held together by the interaction of proteins and lipids with the cellÂ?s cytosceleton. These also fall apart as the temperature is raised making the membrane more permeable. This means that diffusion can take place easier. Diffusion Diffusion is the passing of molecules through a membrane, from a high concentration to a low concentration. In the experiment the beetroot dye (betalain pigments) can diffuse out of the cell through the permeable membrane into the water. Higher temperatures break down more of the membrane allowing more dye to diffuse out, therefor the water becomes a darker red (and lets less light through) as the temperature is raised. Evaluation Reliability Anomalies There were no anomalies. I can tell this because all my results fitted with the pattern. None of the class had anomalies either, as everyoneÂ?s readings were within a similar range and they all fitted the pattern. One personÂ?s results were far higher than the rest of the classÂ?s, but their results were still in the same pattern with the rest of his/her results. Limitations - The temperature range we used only went up to 70ËšC, therefore we can only guess what happened if it went higher. - There was not enough time to repeat the results and get an average. - Colorimeter readings varied a very large amount, on all the machines. and even gave wrong readings, as was the case with one person even though we could clearly see the concentration got higher as the temperature increased - Each person used a different beetroot - The discs were cut from different parts of the beetroot - No instructions were given on how long to wash the beetroot before analysing - The water baths were not at the suggested temperatures. - Everyone used a different beetroot, there could have been variation between them. Sources of error - No instructions were given on how much to shake the test tubes and when. - People washed the retreat samples for different amounts of time - People may not have cut the beetroot cylinders in to exactly 1mm thick disks I do not believe these errors effected my results as my results fitted the pattern exactly and were roughly in the middle of the variance bars. Error Reduction/Relative Influence The Instructions should be improved by adding these points - Have everyone shake the tubes moderately for 10 seconds only at given times. - Make everyone wash the beetroot until the excess dye is completely washed off (at least for three minutes) - Everyone should vary the place in the beetroot they extract the cylinders from to be cut - The classes cylinders should all be cut by the teacher (or any other person) to ensure there is minimal variation between the thickness of the discs. Conclusion The experiment was successful as it clearly showed the effect of temperature on the beetroot membrane. It showed that the membrane becomes more permeable at higher temperatures, as was expected. This was explained by the fact that proteins denature with high temperatures and the phospholipids structure changes and becomes less stable, having devastating results on the membrane structure. Despite the limitations and errors, the results of the experiment were conclusive.

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