investigating membrane permeability

Question 1

why do you use beetroot cells ?

Answer 1

Beetroot cells contain a coloured pigment that leaks out.
The higher the permeability of the membrane, the more pigment leaks out of the cell.

Question 2

what is the 1st step ?

Answer 2

1. Use a scalpel to carefully cut five equal sized pieces of beetroot. (Make sure you do your cutting on a cutting board.) Rinse the pieces to remove any pigment released during cutting.

Question 3

2nd step?

Answer 3

2. Add the five pieces to five different test tubes, each containing 5cm3 of water. Use a measuring cylinder or pipette to measure the water.

Question 4

3rd step ?

Answer 4

3. Place each test tube in a water bath at a different temperature, e.g. 10 °C, 20 °C, 30 °C, 40 °C, 50 °C, for the same length of time (measured using a stopwatch).

Question 5

4th step?

Answer 5

4. Remove the pieces of beetroot from the tubes, leaving just the coloured liquid.

Question 6

5th step?

Answer 6

5.Now you need to use a colorimeter — a machine that passes light of a specific wavelength through a liquid and measures how much of that light is absorbed. Many colorimeters use filters to make sure the light passing through the liquid is at the desired wavelength.

Question 7

6th step ?

Answer 7

6. Firstly, switch the colorimeter on and allow five minutes for it to stabilise. Then set up the colorimeter so you’re using a blue filter (or a wavelength of about 470 nm).

Question 8

7th step?

Answer 8

7. Add distilled water to a cuvette so it is three quarters full (a cuvette is a small container that fits inside a colorimeter — see Figure 7). Put the cuvette into the colorimeter. Two of the cuvette’s sides may be ridged or frosted — you need to make sure you put the cuvette into the colorimeter the correct way, so that the light will be passing through the clear sides. Calibrate the machine to zero.

Question 9

8th step?

Answer 9

8. Next, use a pipette to transfer a sample of the liquid from the first test tube to a clean cuvette — again it should be about three quarters full.

Question 10

9th step?

Answer 10

9. Put the cuvette in the colorimeter and read and record the absorbance of the solution.

Question 11

10th step ?

Answer 11

10. Repeat steps 8-9 for the liquids in the remaining four test tubes (using a clean pipette and cuvette each time)

Question 12

11th step ?

Answer 12

11. You’re now ready to analyse your results — bear in mind, the higher the absorbance reading, the more pigment released, so the higher the permeability of the membrane.

Question 13

how would you investigate the effect of solvents?

Answer 13

by placing the beetroot cubes in different concentrations of a particular solvent (such as alcohol or acetone). Surrounding cells in an increasing concentration of a solvent increases membrane permeability because the solvent dissolves the lipids in the cell membrane, causing it to lose its structure.