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Investigating the effect of temperature on the permeability of cell surface membranes

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Investigating the effect of temperature on the permeability of cell surface membranes Background knowledge of membranes- Membranes are made up of a phospholipid bilayer; a phospholipid is simply a phosphate group (AKA the head) connected to a lipid (AKA the tail). The polar heads are hydrophilic and point outwards to the external environment or inwards to the cytoplasm. The non-polar tails on the other hand are hydrophobic, this means they do not like water; this is why they point inwards. The diagram below shows how a phospholipid bilayer behaves in water (notice the lipid tails are pointing inwards, away from the water). The membrane is not quite as simple as this though, it also has other components to it. There are also proteins in the bilayer which can allow certain molecules in and out of the cell. Small molecules such as the respiratory gases (Oxygen and Carbon dioxide) pass through the membrane by diffusion, in between the phospholipids. Larger molecules however, do not fit in between these gaps. Instead, they pass through channels created by the proteins in the bilayer. This process can be active, which means it requires ATP (active transport) or it can be passive, which means no energy is required (facilitated diffusion). Even though water molecules are very polar, they too can diffuse rapidly through the phospholipids because they are small enough. ...read more.


To get a good set of results, I will be testing at 6 temperatures. The 6 temperatures are 0�C, 20�C, 40�C, 60�C, 80�C and 100�C. I have explained why these temperatures are significant in my predictions. I will repeat the test 5 times for each temperature; I feel this would be enough to get accurate results. If there were any anomalies I could simply disregard them and still have a fairly accurate average. The sample I will cut my samples all from the same beetroot. When I am cutting the beetroot I will cut a 1cm3 sample. These samples will be large enough to produce enough dye but still small enough to easily fit into the test tube. How I would carry out the experiment Once I have all of my samples of beetroot placed into the test tubes of water, I will place them in water baths that will be set at the 5 temperatures I am testing. The samples will be left in the water baths for 30 minutes; this will be enough time for the sample to get to the temperature of water. I must make sure that all of the samples are in the water for a fair result. After the 30 minutes, I will place the samples in a colorimeter. Colorimeters transmit light at the sample and calculate the percentage of the light absorbed. ...read more.


if I did not do this it would have been unfair because different plants may have a higher concentration of Betalain in their vacuoles. The water I put the samples in was distilled water, this was to make sure that the water concentration was 100% at the beginning of the experiment and make sure there were no other chemicals in it. For the first test at 65�C the % transmission read 0%, I consider this result as an anomaly. I believe this because the other 2 results were 22% and 25%, the solution was clearly letting some light pass through as I could see this. This may have been down to human error or an error in the colorimeter which I believe is more probable. As a result of this, I disregarded the anomaly and just done the average of the 2nd and 3rd tests. Doing 3 repetitions of each test may not have given me the most accurate result, I may have got a more accurate result if I done more repetitions (e.g. five). If I had repeated the test more, the anomaly would not have affected the result as much, and my results would have been more accurate. Even with the anomalous result, I still feel my results are accurate enough. The predictions I made before the experiment were correct according to the results, and the scientific background knowledge fits in with the results too. ...read more.

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