# After a period of vigorous exercise, a person continues to breathe rapidly even though they have stopped moving. Explain why the breathing rate remains high after vigorous exercise has ended.

> Cambridge International IGCSE Biology (0610) — 12.1 Respiration · Explain · 4 marks

## Mark scheme (4 marks)

1. During vigorous exercise, anaerobic respiration occurs (because oxygen supply to muscles is insufficient)
2. Lactic acid builds up / accumulates in the muscles
3. An oxygen debt is created / extra oxygen is needed to remove the lactic acid
4. Lactic acid is transported to the liver where it is broken down / oxidised using oxygen, so breathing rate stays high to supply this extra oxygen

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