AQA A-Level Biology: Nervous Coordination and Muscle
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.
Describe and explain how an action potential is generated at, and propagated along, a myelinated motor neurone.
In your answer you should refer to:
- the resting potential
- depolarisation
- repolarisation and the refractory period
- saltatory conduction
A physiologist measured how long a nerve impulse took to travel a fixed distance along two axons of the same diameter: one myelinated and one non-myelinated. The results are shown below.
| Axon | Distance travelled / m | Time taken / ms |
|---|---|---|
| Myelinated | 0.60 | 5.0 |
| Non-myelinated | 0.60 | 30.0 |
(a) Calculate the conduction velocity of each axon in m s⁻¹. Show your working. (4 marks)
(b) Explain why the myelinated axon conducts the impulse faster. (2 marks)
A student investigated reaction time using a falling-ruler test. A partner dropped a ruler without warning and the student caught it; the catch distance was converted to a reaction time. The student repeated the test five times and recorded the results.
| Trial | 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|---|
| Reaction time / s | 0.21 | 0.19 | 0.20 | 0.42 | 0.18 |
(a) Calculate the mean reaction time. Identify any anomalous result and justify whether you included it. (3 marks)
(b) Evaluate the reliability or validity of this method and suggest one improvement. (2 marks)
An experimental drug, compound NX-7, binds to and inhibits acetylcholinesterase in the synaptic cleft of a cholinergic synapse. Acetylcholinesterase is the enzyme that normally breaks down the neurotransmitter acetylcholine after it has acted.
Suggest and explain the effect of compound NX-7 on transmission across this synapse and on the postsynaptic neurone.
After an action potential passes a point on an axon, that region enters a refractory period during which it cannot generate another action potential.
Explain the importance of the refractory period for the functioning of a neurone.
Describe the roles of calcium ions (Ca²⁺) and ATP in the contraction of a myofibril.