required practical 4 - membrane permeability

Question 1

explain why the beetroot is washed before placing it in the water.

Answer 1

to wash off any pigment on the surface so that any release is due to temperature only.

Question 2

explain why each test tube containing cubes of plant tissue is regularly shaken.

Answer 2

to ensure all surfaces of cubes remain in contact with liquid to maintain a concentration gradient for diffusion.

Question 3

explain why the volume of water needs to be controlled.

Answer 3

too much water would dilute the pigment so the solution will appear lighter and more light passes through in colorimeter than expected.

Question 4

describe the issues with comparing to a colour standard.

Answer 4

its subjective and the colour obtained may not match any of the colour standards.

Question 5

what does a high absorbance suggest about the cell membrane?

Answer 5

its more permeable as more pigment leaks out making the surrounding solution more concentrated.

Question 6

explain how temperature affects permeability of cell mmembrane.

Answer 6

as temp increases the permeability increases - phospholipids gain kinetic energy so fluidity increases
- transport proteins denature at high temps as hydrogen bonds break, changing the tertiary structure.

Question 7

explain how pH affects permeability of cell membrane.

Answer 7

high or low pH increases permeability because transport proteins denature as hydrogen bonds break, changing the tertiary structure.

Question 8

explain how lipid-soluble solvents e.g alcohol affects permeability of cell membrane.

Answer 8

as concentration increases, permeability increases - as these solvents may dissolve the phospholipid bilayer, creating gaps.