# Explain how the double circulatory system in mammals is suited to their needs, and describe two features of this system that make it more efficient than a single circulatory system.

> WJEC A-Level Biology (Wales) — 2.1 Classification and biodiversity · Explain · 5 marks

> Mammals such as humans have a double circulatory system, meaning blood passes through the heart twice in each full circuit of the body.

## Mark scheme (5 marks)

1. In a double circulatory system, blood passes through the heart twice per full circuit (once through pulmonary circulation and once through systemic circulation).
2. Oxygenated and deoxygenated blood are kept separate, so cells receive fully oxygenated blood.
3. A double circulatory system can maintain a higher blood pressure, allowing oxygen and nutrients to be delivered to cells more quickly / efficiently.
4. Mammals are larger organisms with a greater demand / need for oxygen for respiration, so a double circulatory system is needed to meet this demand.
5. Blood returning from the lungs is re-pressurised by the left ventricle before being sent to the body, preventing a drop in pressure that would reduce the rate of delivery of substances.

## Key terms

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

## Related

- [Revision notes for WJEC A-Level Biology (Wales)](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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-double-circulatory-system-ed0ad25c) · Published by Druglandscape Ltd.