# A marathon runner's heart adapts over years of training, becoming larger and able to pump more blood per beat. Explain how the structure of the cardiovascular system allows oxygenated blood to be delivered to the muscles during a race.

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

> During a marathon, muscles require a greatly increased supply of oxygen. The cardiovascular system must work efficiently to meet this demand. Blood travels through two circuits in a full body cycle before returning to deliver more oxygen.

## Mark scheme (5 marks)

1. The heart pumps blood around the body / heart is the organ that pumps blood
2. The double circulatory system means blood passes through the heart twice in a full body circuit
3. The pulmonary circuit carries deoxygenated blood to the lungs via the pulmonary artery, where it picks up oxygen
4. Oxygenated blood returns to the heart via the pulmonary vein and is then pumped to the body through the aorta
5. Arteries carry blood away from the heart under high pressure, ensuring rapid delivery of oxygenated blood to the muscles

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- [Revision notes for OCR A-Level Biology B — Advancing Biology (H422)](https://www.gradenine.co.uk/learn)
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