OCR A-Level Biology: Neuronal and Hormonal Communication
6 exam-style questions with full mark schemes and model answers. Write your own answer and the AI examiner marks it against the mark scheme.
In a healthy person the concentration of glucose in the blood is held close to a set point of about 5 mmol dm⁻³, even though glucose enters and leaves the blood at very different rates throughout the day.
Describe and explain how the hormones insulin and glucagon return blood glucose concentration to its set point after it has risen following a meal and after it has fallen during prolonged exercise. In your answer you must refer to the cells that secrete each hormone, the effects of each hormone on the liver, and the principle of negative feedback.
(6 marks)
A physiologist measured the time taken for a nerve impulse to travel a fixed distance of 0.30 m along four different axons, W, X, Y and Z. The diameter and myelination of each axon were recorded. The results are shown below.
| Axon | Diameter / µm | Myelinated? | Time for impulse to travel 0.30 m / ms |
|---|---|---|---|
| W | 2 | No | 200 |
| X | 4 | No | 100 |
| Y | 4 | Yes | 6.0 |
| Z | 12 | Yes | 2.5 |
(a) Calculate the conduction velocity of axon Y in m s⁻¹. Show your working. (2 marks)
(b) Using the data, explain how myelination and axon diameter each affect conduction velocity, and explain the mechanism by which myelination produces this effect. (4 marks)
The table shows the membrane potential recorded at one point on an axon during a single action potential. Four points are labelled P, Q, R and S.
| Point | Time / ms | Membrane potential / mV |
|---|---|---|
| P | 0.0 | −70 |
| Q | 1.0 | +35 |
| R | 2.5 | −75 |
| S | 4.0 | −70 |
(a) State the value of the resting potential and name the process occurring between P and Q. (2 marks)
(b) Using the data, explain the movements of sodium and potassium ions that produce the change in membrane potential from Q to R. (3 marks)
In a glucose tolerance test, a person drinks a fixed dose of glucose after an overnight fast and their blood glucose concentration is measured over the next two hours. The table shows the results for three people, A, B and C. One has no diabetes, one has type 1 diabetes and one has type 2 diabetes.
| Time / minutes | Blood glucose of A / mmol dm⁻³ | Blood glucose of B / mmol dm⁻³ | Blood glucose of C / mmol dm⁻³ |
|---|---|---|---|
| 0 | 4.8 | 7.6 | 8.9 |
| 30 | 7.5 | 12.4 | 15.2 |
| 60 | 6.2 | 13.0 | 17.1 |
| 120 | 4.9 | 9.8 | 16.8 |
(a) Identify which person, A, B or C, does not have diabetes, and justify your choice using the data. (2 marks)
(b) Person B still produces some insulin, but person C produces almost none. Using this information and the data, explain which of B and C has type 1 diabetes. (3 marks)
A marine snail produces a toxin called conotoxin-M in its venom. Researchers found that conotoxin-M binds to and blocks the voltage-gated calcium ion channels in the pre-synaptic membrane of cholinergic synapses. It does not affect any other part of the synapse.
A small dose of conotoxin-M was applied to a nerve–muscle preparation. Action potentials still travelled normally along the motor neurone axon, but the muscle failed to contract.
Explain why blocking the voltage-gated calcium ion channels stops the muscle from contracting, even though action potentials still reach the pre-synaptic knob. (4 marks)
A cereal seedling is grown in a box with light shining on it from one side only. After two days the shoot has grown so that it is curved towards the light (positive phototropism).
Explain how the plant hormone IAA (auxin) causes the shoot to curve towards the light. (3 marks)