Explain why the body continues to breathe faster and deeper for several minutes after a period of vigorous exercise has stopped.

AQA GCSE Biology (8461) — 4.4.2 Respiration · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

During vigorous exercise the muscles use anaerobic respiration because the oxygen supply cannot keep up with demand.
Anaerobic respiration produces lactic acid, which accumulates in the muscles and bloodstream.
After exercise the body must remove this lactic acid, which requires extra oxygen to react with and break it down.
The extra oxygen needed is the oxygen debt, so the breathing rate remains high to take in that oxygen.

Examiner tips

  • Use the word ‘anaerobic’ and ‘lactic acid’ – these are key terms. Explain the link between lactic acid and the need for extra oxygen. Show the cause–effect chain: exercise → anaerobic respiration → lactic acid → oxygen debt → increased breathing.
  • common_mistakes
  • :
  • Confusing aerobic with anaerobic respiration. Failing to mention lactic acid or the oxygen debt. Using vague phrases like ‘more oxygen’ without explaining why it is needed.

Mark scheme (4 marks)

  1. During vigorous exercise, anaerobic respiration occurs (in the muscles) because not enough oxygen is supplied
  2. Anaerobic respiration produces lactic acid which accumulates in the muscles/blood
  3. After exercise, extra oxygen is needed to react with / break down the accumulated lactic acid
  4. This extra oxygen required is the oxygen debt, so breathing rate remains elevated to take in that extra oxygen

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