# Explain why blood in the double circulatory system returns to the heart between the two circuits, and describe the advantages this provides for delivering oxygen to body tissues.

> Pearson Edexcel A-Level Biology A (9BI0) — Topic 4 Exchange and Transport · Explain · 5 marks

> Mammals have a double circulatory system. Blood travels from the heart to the lungs and back to the heart, then from the heart to the body and back to the heart again.

## Mark scheme (5 marks)

1. Blood returning to the heart after the pulmonary circuit is re-pressurised / pumped again by the heart
2. Blood can be delivered to body tissues at high pressure
3. This means blood / oxygen is delivered to tissues more quickly / at a faster rate
4. Oxygenated and deoxygenated blood are kept separate (in the double circulatory system)
5. This ensures fully oxygenated blood (at maximum oxygen concentration) is delivered to body tissues, supporting aerobic respiration

## 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 "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-blood-in-the-double-af8e3492) · Published by Druglandscape Ltd.