# Describe the double circulatory system in humans, explaining why having two separate circuits is important for efficient transport of substances to body tissues.

> Pearson Edexcel A-Level Biology A (9BI0) — 1.2 Heart, blood and blood vessels · Describe · 5 marks

> The human heart pumps blood around two separate circuits simultaneously. One circuit supplies the lungs and the other supplies the rest of the body.

## Mark scheme (5 marks)

1. One circuit carries blood from the heart to the lungs (pulmonary circulation) and back to the heart
2. The second circuit carries blood from the heart to the rest of the body (systemic circulation) and back to the heart
3. Blood is oxygenated in the lungs / oxygen is picked up at the lungs before being pumped to the body
4. Because blood returns to the heart between circuits, it is repressurised / pumped at high pressure to body tissues
5. This means fully oxygenated blood reaches body tissues, making transport of oxygen (and other substances) more efficient

## Key terms

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

## Related

- [Revision notes for Pearson Edexcel A-Level Biology A (9BI0)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" 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/describe-the-double-circulatory-system-in-a7c583a8) · Published by Druglandscape Ltd.