Practical: Factors Affecting Membrane Structure & Permeability

Question 1

How does this practical work?

Answer 1

Investigating permeability of membranes by using beetroot. It contains a dark purple-red pigment. The higher the membrane permeability, the more pigment leaks out of the cell.

Question 2

Investigating effect of temperature on membrane permeability METHOD

Answer 2

1. Using a scalpel, cut 5 equal sized cubes of beetroot (equal SA and V, these factors affect the rate which pigments leak out)
2. Rinse beetroot pieces (removes pigment released during cutting)
3. Add beetroot pieces to 5 different test tubes with the same volume of water
4. Put each test tube in a water bath of different temperature for THE SAME LENGTH OF TIME (long enough to allow pigment to diffuse into water)
5. Remove beetroot pieces
6. Use colorimeter to measure how much light is absorbed as it passes through each of the 5 samples of coloured liquid

Question 3

Limitations of Practical

Answer 3

Cuvettes may differ in thickness, thicker cuvettes may absorb more light than thinner ones. Cuvettes may be scratched too.

Beetroot pieces may not be identical in size and shape.

Some parts of beetroot have more pigment in cells than others.

Solutions :
- Use a scalpel and ruler to cut beetroot
- Repeat experiment for different parts of beetroot, find mean, eliminate anomalies