# Explain why the human circulatory system is described as a 'double circulatory system' and give two reasons why this type of system is an advantage to mammals.

> Eduqas A-Level Biology — 2.3 Adaptations for transport in plants and animals · Explain · 5 marks

> Mammals such as humans have a double circulatory system, whereas some other animals have a single circulatory system in which blood passes through the heart only once per circuit.

## Mark scheme (5 marks)

1. Blood passes through the heart twice in one full circuit of the body
2. One circuit goes from the heart to the lungs (pulmonary circulation) and a separate circuit goes from the heart to the rest of the body (systemic circulation)
3. Advantage 1: The system can maintain a high blood pressure, so oxygen and nutrients are delivered to tissues more quickly / efficiently
4. Advantage 2: Oxygenated and deoxygenated blood are kept separate (by the septum), so fully oxygenated blood reaches the body's cells
5. Mammals are large organisms with a greater need for oxygen (for respiration), so a double circulatory system meets this higher oxygen demand

## Key terms

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

## Related

- [Revision notes for Eduqas A-Level Biology](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-human-circulatory-system-2ce5af49) · Published by Druglandscape Ltd.