# A scientist investigates two samples of muscle tissue. Sample A is taken from a sprinter immediately after a 100 m race. Sample B is taken from a long-distance swimmer after a gentle 30-minute swim. Explain the differences in the products found in the two muscle tissue samples.

> WJEC GCSE Biology (Wales) — 1.2.1 Aerobic and anaerobic respiration · Explain · 4 marks

## Mark scheme (4 marks)

1. Sample A contains lactic acid (lactate) because the sprinter used anaerobic respiration
2. The sprinter's muscles worked at high intensity so oxygen supply was insufficient / muscles respired anaerobically
3. Sample B contains carbon dioxide and water because the swimmer used aerobic respiration
4. The swimmer's muscles had sufficient oxygen supply because the exercise was low intensity / aerobic respiration could meet the energy demand

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