# Explain why the human circulatory system is described as a 'double circulatory system' and explain the advantage this arrangement gives over a single circulatory system.

> Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 1.3 Mass transport in animals · Explain · 5 marks

> The human heart pumps blood around the body continuously. Blood passes through the heart twice on each complete circuit of the body.

## Mark scheme (5 marks)

1. The circulatory system is called 'double' because blood passes through the heart twice per complete circuit of the body
2. One circuit carries blood from the heart to the lungs and back (pulmonary circulation)
3. The other circuit carries blood from the heart to the rest of the body and back (systemic circulation)
4. The advantage is that blood is repressurised/pumped again by the heart after the lungs before being sent to the body
5. This means oxygenated blood reaches the body tissues at higher pressure, so oxygen and nutrients are delivered more efficiently/quickly to cells

## Key terms

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

## Related

- [Revision notes for Edexcel A-Level Biology A: Salters-Nuffield (9BN0)](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-the-human-circulatory-system-e0ac762b) · Published by Druglandscape Ltd.