Membrane Permeability

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Title Membrane Permeability

Aim To determine the effect of various chemicals and high temperature on the membrane permeability of beetroot

Hypothesis Organic solvent and high temperature will destroy the cell membrane and make it permeable to the red pigment. The higher the concentration of the alcohol, the greater will be this effect. Principle

Beetroot is the material used in this experiment to demonstrate the effects of high temperature and chemicals on the permeability of the cell membranes. Beetroot contains a red pigment called betalain, which is located in the large central vacuole of the beetroot cells. The vacuole is enclosed by a single membrane called tonoplast and the whole cell is enclosed by cell membrane made up of phospholipids. As long as the cells and their membranes are intact, the betalain will remain inside the vacuoles. However, if the membranes are damaged, betalain will leak out and produce a red colour in the water surrounding. More cells being damaged will cause a higher red colour intensity in the solution.

Cell membrane is made up of a bimolecular leaflet of phospholipids, which contains hydrocarbons and phosphate. Protein molecules can also be found embedded within and attached onto the surface of the membrane. The selective permeability of cell membrane can be easily destroyed by certain chemicals and high temperature because the function of a protein molecule depends on its structure, which is easily denatured.1. High temperature and alcohols denature membrane proteins, and increase fluidity of membrane lipids. 2. Alcohols at high concentrations can also dissolve phospholipids and as dehydrating agent to extract water form the cell. 3. Lipid (organic) solvents like chloroform and ether dissolve the lipid molecules of the membrane and thus increase permeability.

Independent variables: different types of organic solvent and water in different temperature the beetroot tissue immersed into for a fixed period of time. Dependent variables: the number of cells of which the cell membranes are damaged by the organic solvent as measured by its permeability to the red pigment.

Controlled variables: time of treatment by the different solvents, volume of organic solvent and water used, total number of beetroot discs used per treatment, thicknes of beetroot disc

1. Cell sap components in the beetroot cell are all colourless. 2. The concentration of the red pigment in different parts of the plant structure is the same. 3. The colour intensity of a red solution is proportional to the amount of red pigment diffused out which in turn is proportional to the number of cells with damaged cell membrane. 4. All the red pigments will diffuse out of the cell when the cell membranes become permeable. Apparatus 1,9,10-18

Materials 2-8 + 9
1. Cylinders of tissue from a beetroot were cut using a cork bore. 2. The cylinders of beetroot were cut into thin disc of 2 to3 mm thick using razor blade. 3. The beetroot discs were rinsed in running water to wash off pigment that leaked out as a result of cutting. 4. Equal volume, 10ml, of each solvent was pipetted to separate test tubes and all test tubes were labeled and stoppered. 5. The beetroot discs were blotted dry with paper towers and 5 discs were put into each tube 6. Test tubes were swirled occasionally.

7. After 20 minutes, all discs were taken out.
8. Colour intensity of the red solutions in all test tubes were compared and recorded.

1. Same volume of solutions should be used in each treatment so that the relative colour intensity of the solution will be valid indication of the permeability of the cell membrane. 2. Cut the beetroot tissue into thinner disc; say 2 mm thick to increase the total surface area to volume ratio. The effectiveness of the experiment can be increased because of greater contact surface area and shorter diffusion path. 3. Each beetroot disc should be washed thoroughly to wash out any...
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