A sprinter completes a 100 m race in under 12 seconds. Describe what happens in the sprinter's muscle cells to meet the high demand for energy during the race, and state one consequence of this process occurring in the muscles.

Eduqas GCSE Biology — 1.2.1 Aerobic and anaerobic respiration · Describe · 4 marks · View as Markdown

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

Model answer (4 marks)

During the 100 m sprint the muscles use anaerobic respiration because the oxygen supply cannot keep up with the demand. Glucose is broken down incompletely, releasing energy in the form of ATP. The end product of this anaerobic pathway is lactic acid, which accumulates in the muscle cells. A consequence of this is muscle fatigue (pain or cramp) caused by the build‑up of lactic acid and the resulting oxygen debt that must be repaid after the race.

Examiner tips

  • Use the term "anaerobic respiration" and mention "oxygen supply is insufficient". State that glucose is broken down incompletely and that lactic acid is produced. Give a specific consequence such as muscle fatigue or an oxygen debt. Keep the answer concise and to the point.

Common mistakes

  • Confusing aerobic with anaerobic respiration. Failing to mention lactic acid as the product. Giving a vague consequence like "muscle tiredness" without linking it to lactic acid or oxygen debt.

Mark scheme (4 marks)

  1. Muscles respire anaerobically (during the race / when oxygen supply is insufficient)
  2. Glucose is broken down (incompletely) to release energy
  3. Lactic acid is produced as a product of anaerobic respiration
  4. A named consequence — muscle fatigue / pain / cramp OR an oxygen debt is created (muscles need extra oxygen after the race to break down lactic acid)

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