Permeability Of Membranes.

Question 1

Describe a method to investigate the effect of a named variable on the permeability of cell membranes.

Answer 1

1. Cut identical cubes of beetroot using a scalpel and a ruler.
2. Rinse to remove any pigment released during cutting.
3. Add the same number of cubes to 5 different tubes containing the same volume of water.
4. Place each tube in a different water bath, that is set to different temperatures.
5. Leave for the same length of time.
6. Remove the plant tissue and measure the amount of pigment released by measuring the intensity of colour or the concentration of the surrounding solution.

Question 2

What is a semi-quantitative method to find out how much pigment was released?

Answer 2

1. Use a known concentration of distilled water and the extract to produce a dilution series.
2. Compare the results with the colour standards.

Question 3

What is a quantitative method to find out the concentration of the surrounding solution?

Answer 3

1. Measure the absorbency of the dilution series using colourimetry.
2. Draw a calibration curve.
3. Measure the absorbency of the sample and read off the extract concentration that is associated with that absorbency.

Question 4

Why are the beetroot cubes washed before they are place in the solution?

Answer 4

1. To remove any excess pigment.
2. To show that it is the name variable that is causing the release of pigment.

Question 5

Explain why the volume of water needs to be controlled?

Answer 5

1. Too much water would dilute the pigment, so the solution will appear lighter/ more light will pass through in the colourimetry than expected.
2. So the results are comparable.

Question 6

How could you ensure that the temperature of the water baths remains constant?

Answer 6

1. Measure the temperature of the water in the water bath at regular intervals using a thermometer.
2. Add cold/hot water to bring the temperature back to normal.

Question 7

Describe the issue with comparing a colour standard?

Answer 7

1. Colour is subjective.
2. The colour obtained may not match any of the standard solutions.

Question 8

What does a high absorbency tell us about the membrane?

Answer 8

1. More permeable.
2. As more pigment has leaked out and increased the concentration of the surrounding solution.

Question 9

Explain how temperature affects the permeability of the membrane?

Answer 9

1. As temperature increases the permeability of the membrane increases.
2. This is because the phospholipids have more kinetic energy so the fluidity of the membrane increases.
3. The transport proteins denature at high temperatures. This is because the hydrogen bonds break and the tertiary structure changes.

Question 10

Explain how pH affects membrane permeability?

Answer 10

1. High or low pH increases permeability.
2. This is because the transport proteins denature. As the ionic binds break the tertiary structure changes.

Question 11

Explain how lipid-soluble solvents affect the permeability of the membranes?

Answer 11

1. As the concentration increases the permeability increases.
2. This is because they may dissolve the phospholipid bilateral.