A student touches a hot surface and quickly pulls their hand away before feeling pain. Explain how the nervous system coordinates this response, including the roles of the receptor, coordinator and effector.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
The nervous system allows the body to detect and respond to changes in the environment. Some responses happen very rapidly without conscious thought.
Model answer (5 marks)
1. A receptor in the skin detects the hot surface and generates a nerve impulse.
2. The impulse travels along a sensory neuron to the spinal cord.
3. The spinal cord acts as the coordinator, forming a reflex arc that bypasses the brain for a rapid response.
4. A motor neuron carries the impulse from the spinal cord to the effector.
5. The effector muscle contracts, pulling the hand away from the hot surface.
2. The impulse travels along a sensory neuron to the spinal cord.
3. The spinal cord acts as the coordinator, forming a reflex arc that bypasses the brain for a rapid response.
4. A motor neuron carries the impulse from the spinal cord to the effector.
5. The effector muscle contracts, pulling the hand away from the hot surface.
Examiner tips
- Use the exact terms: receptor, sensory neuron, spinal cord, motor neuron, effector. Show the sequence: receptor → sensory neuron → spinal cord → motor neuron → effector. Mention the reflex arc and bypassing the brain for speed.
Common mistakes
- Confusing the spinal cord with the brain as the coordinator. Omitting the role of the receptor or effector. Using vague language such as "body" instead of specific structures.
Mark scheme (5 marks)
- A receptor in the skin detects the stimulus (heat / high temperature)
- A nerve impulse / electrical signal is sent along a sensory neurone to the spinal cord (coordinator)
- This is a reflex arc, so the spinal cord acts as the coordinator and the response bypasses the brain (allowing a faster response)
- A nerve impulse travels along a motor neurone from the spinal cord to the effector (muscle)
- The effector (muscle in the arm) contracts, causing the hand to be pulled away from the hot surface
Key terms in this question
receptor · coordinator · effector
Related
- All OCR A-Level Biology B — Advancing Biology (H422) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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