Required Practical 4

Question 1

How is beetroot used to measure the permeability of cell membrane

Answer 1

The higher the permeability the more red pigment that leaks out into to the surrounding solution within a given time. A calorimeter can be used to determine the absorbance

Question 2

Outlines the procedure to investigate the effect of temperature on permeability of cell membrane

Answer 2

Cut beetroot into 6 identical cubes with scalpel
Place each cube in a different test tube with equal volumes of distilled water
Place each cube in a different test tube with equal volumes of distilled water
Place test tubes into water bath ranging from 30-80 degrees
Check temp using thermometer at equal intervals
Leave for 20 mins
Filter solution out using a cuvette
Use calorimeter to measure absorbance

Question 3

What do you need to do before using a colorimeter

Answer 3

Set it to give an absorbance reading of zero

Question 4

How can you use colour standards

Answer 4

Prepare a series of different concentrations at equals intervals
Eg 20% 40% 60% 80%
Compare colour of the solution from each temperature with range of colour standards

Question 5

Why should you wash the beetroot discs in distilled water after cutting them

Answer 5

So that any pigment in the the distilled water has been released from the cells due to the effect of temperature on membrane permeability

Question 6

Why were the test tubes left in the water baths for 5 minutes before adding beetroot

Answer 6

This allows the water to equilibrate

Question 7

Why did the student shake the tube every 5 minutes

Answer 7

To maintain the diffusion gradient for the pigment to pass out of the cells and into the distilled water

Question 8

Why is fresh beetroot used and not cooked

Answer 8

Cooking would involve heating the beetroot to high temperatures that would denature the proteins in the plasma membranes and allow the pigment to leak

Question 9

Describe the effect of increasing temperature on the permeability of the beetroot cell membranes

Answer 9

Increase in membrane permeability
Proteins in membrane denature
Bonds break in tertiary structure

Question 10

Describe the effect of low temperature on permeability

Answer 10

Phospholipids have little energy and are packed Closely so make the membrane ridgid
Decrease in permeability
Ice crystals at very low temp can pierce membrane and increase permeability

Question 11

Effect of ethanol concentration on permeability

Answer 11

Causes cell surface membrane to rupture