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  • Level: GCSE
  • Subject: Science
  • Essay length: 2686 words

An investigation to find out how temperature affects membrane permeability.

Extracts from this essay...


Philip Pearson AS Biology Practical Assessment An investigation to find out how temperature affects membrane permeability. Problem What we will hopefully try and find out in this investigation is if temperature affects the permeability of a beetroot membrane Hypothesis As the temperature in which the beetroot is put in increases there will be more red dye diffusing out of the beetroot due to the denaturing of the proteins in the cell membrane as a result of the high temperatures. Background Knowledge The cell membrane can be represented as the fluid mosaic model as shown below. It is selectively permeable and controls what enters and exits the cell. It does this by proteins, however small lipid molecules, non-polar molecules and small water molecules can enter and exit the cell straight across the membrane through the phospholipids, due to the properties of the molecules enabling them to do so. Extrinsic and intrinsic proteins in the cell membrane help other the molecules enter or leave the cell by either facilitated diffusion or active diffusion. Different proteins are specific to certain molecules hence the cell membrane being selectively permeable. Here is a diagram of the cell membrane: As you can see the cell membrane is made up of a phospholipid bilayer which the extrinsic and intrinsic proteins span through. Some of the extrinsic proteins act as antigens for cell recognition with a carbohydrate attaching to then forming a glycoprotein. Intrinsic proteins are usually associated with the movement of molecules in and out of the cell.


This has to be the same in every boiling tube otherwise if there was more distilled water in one boiling tube compared to another one then that red pigment in the boiling tube with more distilled water in would be more diluted. - Time in which the beetroot is placed in the water bath for. If the time that each beetroot piece is in the water bath for varied then more or less red pigment will be lost by the beetroot just because it has been in a certain temperature for longer not just because of the temperature itself, which is what we are measuring. Therefore we will keep each beetroot piece in the water bath for exactly 5 minutes. The way in which I will collect this data is by using a colorimeter. This is a digital piece of equipment, which measures the optical density of a substance, which has been placed in a cuvette. This means how much light the substance absorbs and is measured in arbitrary units. It comprises of a lamp, filament that will be blue, a photosensitive element and a digital display. The substance is added from one of the boiling tubes into a cuvette, holding the cuvette on the 'grooved' side so that no finger marks will affect the reading, the cuvette is then placed into the colourimeter with the notch facing forwards. The light should therefore shine through the clear sides on the cuvette. As the colorimeter is measuring how much light the substance in the cuvette is absorbing it obvious that the more red pigment that


A reason for the anomalous results could also be down to the fact that we used a bunson burner to gain the temperature for the water baths. A bunson burner cannot be very precise therefore the water baths may not have been to their specific temperatures as it is easy for the water bath to get warmer. If we had used electronic equipment to measure the temperature of the water then it would have made the results a lot more accurate and reliable as it would measure the temperature of the water bath a lot more accurately. Also another reason for the anomalies could be the fact that the beetroot pieces were cut out of different parts of the beetroot. This could mean that different parts of the beetroot could have more red pigment than others, resulting in those beetroot pieces with more red pigment diffusing out more red pigment when heated. Making sure each beetroot piece was cut out of the same place in the beetroot would cause all the beetroot pieces to hopefully contain the same amount of red pigment to start off with. All these things that may have caused the couple of anomalous results may cause my conclusion to change, but the significance of the anomalies is not very high therefore I still stand by my conclusion. Overall I think that the results have been fairly reliable, shown by the results from working out the standard deviation of each measurement, which show a small number therefore high reliability. Also the results do back up my prediction strongly; therefore the results must have been accurate and reliable.

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