# Explain why mammals have a double circulatory system rather than a single circulatory system.

> Cambridge International IGCSE Biology (0610) — 9.2 Heart · Explain · 4 marks

## Mark scheme (4 marks)

1. In a double circulatory system, blood passes through the heart twice per circuit, allowing pressure to be restored after passing through the lungs.
2. Oxygenated and deoxygenated blood are kept separate, so tissues receive fully oxygenated blood.
3. Mammals are larger / more active and have a greater demand for oxygen for respiration.
4. A double circulatory system is more efficient at delivering oxygen / nutrients to tissues, allowing a higher metabolic rate to be sustained.

## Key terms

- [double circulatory system](https://www.gradenine.co.uk/glossary/double-circulatory-system)
- [single circulatory system](https://www.gradenine.co.uk/glossary/single-circulatory-system)

## Related

- [Revision notes for Cambridge International IGCSE Biology (0610)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-mammals-have-a-double-1104f85b) · Published by Druglandscape Ltd.