Explain why simple reflex actions are important for survival, and describe the role of effectors in producing a response.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A cat steps on a sharp thorn and immediately withdraws its paw. This response happens without the cat deciding to move its paw.
Model answer (5 marks)
Simple reflex actions are automatic and do not require conscious thought, so they can occur immediately after a stimulus. They are rapid, often faster than voluntary responses, because the signal travels a short pathway through the spinal cord. This speed protects the organism from damage or harm, giving a survival advantage. Effectors are the muscles or glands that carry out the response. When a motor neurone sends a signal to an effector, the muscle contracts (or the gland secretes) to produce the withdrawal of the paw.
Examiner tips
- Use the word ‘automatic’ and ‘rapid’ to show understanding of reflex characteristics.
- Explain the survival benefit – protection from harm – to earn the full marks.
- Mention that effectors are muscles or glands and describe the motor neurone signal leading to contraction.
- Keep the answer concise and use correct terminology.
Mark scheme (5 marks)
- Simple reflexes are automatic / do not require conscious thought
- Reflexes are rapid / faster than voluntary responses
- This protects the organism from damage / harm (survival advantage)
- Effectors are muscles or glands that carry out the response
- The effector receives a motor neurone signal and produces the response (e.g. muscle contracts to withdraw the paw)
Key terms in this question
simple reflex · effector · response
Related
- All AQA A-Level Biology (7402) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →