Paper 3

Question 1

Describe how the stimulation of a Pacinian corpuscle produces a generator potential.
[3 marks]

Answer 1

1. Stretch mediated sodium ion channels in the membrane
2. Increased pressure deforms sodium ion channels in the membrane
3. Sodium ions channels open
4. Sodium ions diffuse in
5. Depolarisation occurs

Question 2

What is meant by the all-or-nothing principle?
[2 marks]

Answer 2

1. An action potential is only generated if threshold is exceeded
2. High pressure can generate an action potential

Question 3

What is the time period called where no new generator potential can be produced?
[1 mark]

Answer 3

1. Refractory period

Question 4

A student investigated the effect of different sugars on the ratio of respiration in yeast.
Yeast normally respires glucose.

For her first experiment:
• She completely filled a small test tube with yeast in glucose solution. She pushed the small test tube up inside a larger test tube.
• She inverted the larger test tube and placed it in a water bath at 30°C for 25 minutes.
• After 25 minutes she measured the length of the bubble of carbon dioxide produced in the small test tube.

Other than those stated, suggest TWO variables the student needed to keep constant in her investigation.
[1 mark]

Answer 4

1. Concentration/mass of yeast
2. Concentration/mass of glucose
3. Concentration of oxygen
4. Volume of yeast
5. Volume of glucose
6. pH

Question 5

The student repeated the experiment using yeast in maltose solution. She found the rate of carbon dioxide production was slower than with yeast in glucose solution.
Suggest why.
[2 marks]

Answer 5

1. Maltose is a disaccharide
2. Takes time to be hydrolysed into glucose