Nerve cells are adapted to carry electrical impulses quickly and efficiently. Describe four structural adaptations of a neurone and explain how each adaptation helps the neurone to carry out its function.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
1. The axon is wrapped in a myelin sheath produced by Schwann cells, which electrically insulates the axon and increases the speed of the action potential by saltatory conduction.
2. The axon is long, allowing the impulse to travel over large distances without the need to cross a synapse, thereby reducing transmission time.
3. Dendrites extend from the cell body to receive electrical impulses from other neurones, providing the initial input that initiates the action potential.
4. Neurotransmitter‑containing vesicles are released at the synaptic terminal, enabling the impulse to be transmitted chemically to the next neurone.
5. The cell body contains a nucleus and mitochondria, supplying the ATP required for ion‑pump activity and neurotransmitter synthesis, which sustains the neurone’s function.
2. The axon is long, allowing the impulse to travel over large distances without the need to cross a synapse, thereby reducing transmission time.
3. Dendrites extend from the cell body to receive electrical impulses from other neurones, providing the initial input that initiates the action potential.
4. Neurotransmitter‑containing vesicles are released at the synaptic terminal, enabling the impulse to be transmitted chemically to the next neurone.
5. The cell body contains a nucleus and mitochondria, supplying the ATP required for ion‑pump activity and neurotransmitter synthesis, which sustains the neurone’s function.
Examiner tips
- Use the exact terminology (axon, myelin sheath, Schwann cells, dendrites, neurotransmitters).
- Show the link between structure and function for each point.
- Include the optional point about the cell body to reach 5 marks.
Common mistakes
- Confusing Schwann cells with oligodendrocytes (not relevant to WJEC).
- Omitting the role of mitochondria in ATP production.
Mark scheme (5 marks)
- The axon is surrounded by a myelin sheath (made of Schwann cells) which provides electrical insulation, speeding up the nerve impulse along the axon.
- The axon is long, allowing the impulse to be carried over large distances quickly without crossing a synapse (which would slow it down).
- The neurone has dendrites which pick up electrical impulses from other neurones, allowing the impulse to be received and passed on.
- The neurone contains neurotransmitter substances which are released at synapses, allowing the impulse to continue into the next neurone.
- Any one further valid point clearly linking a structural feature to its function — e.g. the cell body contains a nucleus and mitochondria to provide the energy (ATP) needed to maintain the impulse / produce neurotransmitters. (Accept any creditworthy point not already awarded.)
Key terms in this question
Related
- All WJEC A-Level Biology (Wales) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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