An investigation to find out how temperature affects membrane permeability.

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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.

   Proteins are enzymes and are made up of specific amino acids and only work in certain conditions, for example the pH has to stay constant and the temperature also has to stay constant. If these two factors are not controlled e.g. the temperature around the cell becomes higher or lower than the optimum temperature for that cell, then the hydrogen bonds that keep the proteins tertiary structure (overall 3D shape) will be broken (denaturing the protein). Consequently the proteins in the cell membrane are unable to function correctly. Therefore a higher temperature will denature the proteins and diffusion will be able to take place easily due to the proteins being unable to manage what enters or leaves the cell.

     The optimum temperature of the beetroots normal working conditions should be around 40 °C as the optimum temperature for animal cells is 40 °C, therefore I assume that the beetroot should be around that temperature due to similar living conditions of both organisms. Therefore if the temperature goes above this optimum temperature then the proteins in cell membrane of the beetroot will become denatured and anything can enter or leave the cell. A good indication of this easy diffusion, due to denatured proteins, would be the amount of red dye that diffuses out of beetroot. This is what the experiment is investigating.

Equipment list and why using it:

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Plan

The variable that will be changed in this experiment will be the temperature of each water bath. The steps of each measurement will be around 30, 40, 50, 60, 70, and 80 degrees centigrade. I have chosen these steps because I have predicted that 40 °C will be the optimum temperature for the beetroot and will indicate little red pigment diffusing out of the beetroot therefore showing if the cell membrane has kept its integrity. Referring to my prediction 30 C should show the temperature being to low for the proteins to work properly, and ...

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