Generated by claude-sonnet-4-6 · 2026-06-15 06:51 · grounding rag
Model Answer
(i) Names of labelled parts:
- A – Sensory nerve fibre (afferent neuron)
- B – Relay/Association neuron (within spinal cord)
- C – Motor nerve fibre (efferent neuron) / effector region
(ii) Functions:
- A (Sensory nerve): Carries impulse from the receptor (sense organ/skin) to the spinal cord.
- C (Motor nerve): Carries impulse from the spinal cord to the effector (muscle), causing response.
(iii) Reflex arcs have evolved because they allow animals to respond immediately to dangerous stimuli (like heat or pain) without waiting for the brain to process information. This quick, involuntary response protects the body from harm and increases survival chances.
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Explanation
- Part (i) is pure labelling — one mark for all three names.
- Part (ii) asks for functions of A and C only (not B) — state direction of impulse transmission clearly.
- Part (iii): Emphasise speed/survival advantage — examiners expect the idea that brain involvement takes time, so spinal reflex arcs evolved for faster protective responses. Avoid vague answers.