Permeability of Cell Membranes ( Topic 2)

Question 1

Why are beet roots used for this experiment?

Answer 1

The cells of the beetroot contain a pigment called betalain, which only moves out of the cells when the cell membrane is damaged.

Question 2

How can you make colour standards to make a calibration curve?

Answer 2

1. Mix known volumes of water and beetroot extract to create 6 tubes with 5 cm3 of solution with different percentage concentrations of extract.
2. Volume of water = 5, Volume of extract = 0, percentage = 0/5 x 100 = 0 %
3. Volume of water = 4, Volume of extract = 1, percentage = 1/5 x 100 = 20 %
4. Volume of water = 3, Volume of extract = 2, percentage = 2/5 x 100 = 40 %
5. Volume of water = 2, Volume of extract = 3, percentage = 3/5 x 100 = 60 %
6. Volume of water = 1, Volume of extract = 4, percentage = 4/5 x 100 = 80 %
7. Volume of water = 0, Volume of extract = 5, percentage = 5/5 x 100 = 100 %
8. Measure the absorbance of all the solutions and plot these results on a graph. X-axis: Percentage extract. Y-axis: absorbance.

Question 3

What variables should be controlled and how?

Answer 3

1. Temperature as it affects the permeability of the membranes: Place the test tubes containing the different alcohol concentrations in a water bath, set at 30 degrees.
2. The volume of alcohol solution.

Question 4

Why do you place a bung on top of the test tubes?

Answer 4

To prevent the water from evaporating and affecting the concentration of the alcohol solution.

Question 5

How can temperature affect the permeability of the membrane and the absorbance?

Answer 5

1. If the temperature is too high, the hydrogen bonds in the proteins of the cell membrane will break, causing the tertiary structure to change and the proteins to denature.
2. The damage to the cell membrane means more betalain will move out of the beetroot cells, and the concentration of betalain in the solution will decrease. This means absorbance will increase.

Question 6

How can the presence of alcohol affect the permeability of the membrane and the absorbance?

Answer 6

1. The alcohol will make the solution too alkaline, meaning the ionic bonds in the proteins of the cell membrane will break, causing the tertiary structure to change and the proteins to denature.
2. The damage to the cell membrane means more betalain will move out of the beetroot cells, and the concentration of betalain in the solution will decrease. This means absorbance will increase.

Question 7

How can the presence of acid affect the permeability of the membrane and the absorbance?

Answer 7

1. The alcohol will make the solution too acidic, meaning the ionic bonds in the proteins of the cell membrane will break, causing the tertiary structure to change and the proteins to denature.
2. The damage to the cell membrane means more betalain will move out of the beetroot cells, and the concentration of betalain in the solution will decrease. This means absorbance will increase.