# Explain why the mammalian circulatory system is described as a double circulatory system, and outline one advantage this arrangement provides over a single circulatory system.

> OCR A-Level Biology A (H420) — 3.2 Transport in animals · Explain · 4 marks

> Mammals, such as humans, have a heart divided into four chambers. Blood passes through the heart twice for each complete circuit of the body.

## Mark scheme (4 marks)

1. Blood passes through the heart twice per complete circuit of the body
2. One circuit carries blood to the lungs (pulmonary circulation) and the other carries blood to the rest of the body (systemic circulation)
3. Oxygenated and deoxygenated blood are kept separate / do not mix
4. Advantage: blood pressure can be raised/maintained in the systemic circuit after returning from the lungs, ensuring efficient delivery of oxygen to respiring tissues

## Key terms

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

## Related

- [Revision notes for OCR A-Level Biology A (H420)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-the-mammalian-circulatory-system-59fa6eec) · Published by Druglandscape Ltd.