Required practical 4 - Investigating cell membrane permeability

Two factors that affect permeability of cell membranes:

• Temperature

  • At high temperature there is more kinetic energy so phospholipids have more kinetic energy vibrating on the spot and increasing the permeability of the cell

  • At very very high temperatures the transport proteins will denature, and the phospholipids begin to break down.

• Concentration of solvents (ethanol)

  • The solvents such as ethanol with dissolve the non-polar fatty acid tails making the membrane more permeable

How is beetroot used to measure the permeability of cell membranes?

The higher the permeability the more red pigment that leaks out into the surrounding solution within a given time.

A colorimeter can be used to determine the absorbance, so the concentration of pigment.

Higher absorbance means higher the permeability the more pigment moves out of the cell

Outline the procedure to investigate the effect of temperature on permeability:

1. Cut the beetroot into 6 identical cubed with a scalpel

2. Place each cube in different test tube with equal volume of distilled water

3. Place each test tube into water baths between 30-80 degrees

4. Leave for 20 minutes

5. Filter the solution, and place in cuvette and measure the absorbance using a colorimeter

Outline the procedure to investigate the effect of organic solvents on permeability

Repeat the same experiment keeping the temperature constant, but (if you are testing on the effect of organic solvents use that an independent variable)