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How does temperature affect the permeability of a cell membrane in a beetroot.

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How does temperature affect the permeability of a cell membrane in a beetroot. Introduction: The purpose of the cell membrane is to control the transport of substances moving into and out of the cell. It is made of a phospholipid bilayer that has proteins floating in it. The proteins span the membrane and touch both the inside and outside of the cell. The cell membrane is between 6-8 nanometers (nm) thick and made up of many different molecules. These are shown in the diagram below. The phospholipid bilayer is the basic structure of the membrane. The fatty acid tails are non-polar; this means it is difficult for polar molecules or ions to pass through them as they act as a barrier to most water-soluble substances. The molecules move in and out of the cell through diffusion, osmosis and active transport. Diffusion is the net movement of molecules from a high concentration to a low concentration. In the cells of a beetroot plant a substance called anthocyanin is contained in the plasma membrane. The anthocyanin gives the beetroot its purple appearance. If the cell membrane becomes damaged then the anthocyanin "bleeds" from the cell like a dye. This characteristic of beetroot will be used in this experiment. The experiment is to test the effects of temperature on the cell membrane. The molecules in the membrane move using kinetic energy. As the temperature increases the molecules gain more kinetic energy and diffuse faster. Temperature also causes the lipids of the membrane to be more fluid. ...read more.


This is because an increase in temperature will damage and denature the proteins in the plasma membrane this will cause the substances inside the membrane to be released and leak into the surrounding liquid. The proteins in the cell membrane are at a tertiary level, which means that there are globular in shape as, in the picture below. When the proteins are heated the hydrogen bonds (in red) are broken. This allows the anthocyanin and other substances from inside the membrane to escape. The higher the temperature the quicker the proteins will denature so the more anthocyanin will be able to escape. Method: 1. Collect equipment 2. Set up the bunsen burner, tripod, gauze and beaker with 150ml of water. 3. Place 3 test tubes filled with 10ml of water in the water baths to heat, using the thermometer to measure the heat of the water. I am using 3 test tubes at once so the experiment will be quicker as I can do three results at once. 4. Using cork borer remove a cylinder out of the beetroot. 5. Place on white tile and cut into 1cm long cylinders. 6. Rinse the beetroot and roll dry on paper towel. 7. Place the cylinders in the test tubes, one per test tube. 8. Leave for 10 minutes 9. After 10 minutes, remove the beetroot from the test tube. And shake the mixture. This will distribute the colour equally. 10. Remove 3ml of the liquid using a pipette and place in cuvette. 11. ...read more.


By using the same beetroot throughout the experiment it keeps the concentration of pigment more constant, and means that the cells have been exposed to the same things so they will react in the same way. 5 Area of beetroot segment taken from The area that the segment of beetroot is taken from will determine the concentration of the pigment. As there is a higher concentration of pigment in the centre of the beetroot than on the outer layers. This means that if you remove the segment from the inner of the beetroot when the proteins denature there will be more pigment to be released. To improve this I would remove segments of beetroot from the same area. By removing segments from the same area of the beetroot, I will be removing cells with similar concentrations of anthocyanin. 3 Time Inaccuracies in time that the beetroot was in water were caused by not being able to remove them all after exactly 10 minutes or place all in at the exact same second and start the stop clock. This slight increase in time for some of the beetroot sections will have meant that were exposed to the heat for longer than the 10 minutes this means that the beetroot has had more time to diffuse the pigment, this would have caused a decrease in the transmission of light. To improve this experiment I would use only one test tube at a time heating one test tube for 10 minutes then removing it and doing the next. By using only one test tube at a time this will allow me to concentrate on it and remove it after exactly 10 minutes. 2 ...read more.

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Here's what a teacher thought of this essay

4 star(s)

This report of an investigation into the effect of temperature on membrane permeability in beetroot tissue is well-structured and clearly written. Some sections, notably the variables and evaluation, are especially well written, both in table form which make it easy for the reader to follow.

There are, however, a number of ways in which the report could be improved:

[1] The hypothesis (referred to as a prediction) needs to be stated at the end of the introduction. It needs to be clear and testable, linking the IV and DV.

[2] The purpose of the technician's results needs to be more clearly explained. They are presented as something of a bolt-on to the writer's own results.

[3] Identification of anomalies needs more care. In view of there only being 3 replicates, it is very difficult to identify any anomalies.

However, these are relatively minor criticisms and overall, this is a good piece of GCSE coursework which would gain the higher grades.

4 stars

Marked by teacher Ross Robertson 24/06/2013

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