# A patient is diagnosed with a faulty valve in their heart. Explain how the double circulatory system normally works and why a faulty valve would affect the delivery of oxygen to the body's cells.

> OCR A-Level Biology B — Advancing Biology (H422) — 2.5 Cardiovascular system · Explain · 5 marks

> The human heart pumps blood continuously around the body. It contains valves at each end of both ventricles, and blood travels through two separate circuits before completing a full body circuit.

## Mark scheme (5 marks)

1. The double circulatory system means blood passes through the heart twice in a full body circuit
2. The pulmonary circuit carries deoxygenated blood from the heart to the lungs (via the pulmonary artery) and returns oxygenated blood to the heart (via the pulmonary vein)
3. The systemic circuit carries oxygenated blood from the heart to the body via the aorta
4. Valves prevent the backflow of blood, ensuring blood flows in the correct direction through the heart
5. A faulty valve allows blood to flow backwards / reduces the efficiency of pumping, so less oxygenated blood reaches the body's cells

## Key terms

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

## Related

- [Revision notes for OCR A-Level Biology B — Advancing Biology (H422)](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/a-patient-is-diagnosed-with-a-4bb63f94) · Published by Druglandscape Ltd.