During sudden intense exercise, a person experiences muscle cramps. Using your knowledge of respiration, explain the biochemical cause of these cramps.
Generated by claude-sonnet-4-6 · 2026-06-15 06:44 · grounding rag
Model Answer
During sudden intense exercise, the body cannot supply oxygen fast enough to muscles. As a result, muscle cells switch to anaerobic respiration, breaking down glucose without oxygen:
Glucose → Lactic acid + Energy
Lactic acid accumulates in the muscle tissue, causing a drop in pH. This build-up of lactic acid is the biochemical cause of muscle cramps and fatigue experienced during intense exercise.
Source: Life Processes, Chapter 5 — Respiration (Anaerobic pathway)
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Explanation
- The key concept being tested is anaerobic respiration in humans and its product — lactic acid.
- Examiners expect you to: (1) state that oxygen supply is insufficient, (2) name the pathway (anaerobic respiration), (3) write the word equation, and (4) link lactic acid accumulation to cramps.
- Do not confuse this with yeast/anaerobic respiration which produces ethanol + CO₂ — that is for organisms like yeast, not human muscles.
- Writing the word equation earns a dedicated mark, so never skip it.