# Explain why a person's breathing rate and heart rate remain elevated for several minutes after they finish a period of vigorous exercise.

> Cambridge International IGCSE Biology (0610) — 12.3 Anaerobic respiration · Explain · 4 marks

## Mark scheme (4 marks)

1. During vigorous exercise, anaerobic respiration occurs (because oxygen supply to muscles is insufficient), producing lactic acid.
2. Lactic acid accumulates in muscles, creating an oxygen debt that must be repaid after exercise.
3. Lactic acid must be transported to the liver where it is broken down / oxidised using oxygen.
4. Breathing rate remains high to take in extra oxygen to repay the oxygen debt, and heart rate remains high to transport this oxygen (and lactic acid) more quickly.

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