Required Practical 4

Question 1

How do you calculate percentage uncertainties?

Answer 1

percentage uncertainty = uncertainty/mean value x 100%

Question 2

Which part of the phospholipid is affected if temperature changes?

Answer 2

The fatty acid tails

Question 3

What happens if the temperature is very high?

Answer 3

• The fatty acid tails gain kinetic energy
• They become less rigid and more fluid
• They gain enough energy to break the hydrogen bonds holding the bilayer together
• Permeability and fluidity of the membrane is increased
• More substances can exit and enter the cell

Question 3

What happens if the temperature is much too high?

Answer 3

• The integral and peripheral proteins can denature completely
• Membrane becomes so fluid that dangerous substances can exit and enter the cell

Question 4

What happens if the temperature is very low?

Answer 4

• The fatty acid tails lose kinetic energy
• More rigid and close together
• Less gaps in the bilayer, preventing more substances than usual to enter the cell
• Includes essential substances like oxygen and glucose

Question 5

What happens if the temperature is much too low?

Answer 5

• The liquid inside the cells can freeze
• Creates crystals that can pierce the membrane and kill the cell

Question 6

What is the optimum temperature for most cells?

Answer 6

37.5°C

Question 7

What is a colorimeter?

Answer 7

A light-sensing device that is used to measure the absorbance of light as it moves through a sample of liquid.

Question 8

Why is red cabbage used in the required practical?

Answer 8

Red cabbage has a red dye inside its cells which will leak out if the cell membrane becomes permeable