# Explain how the structure of a vein is related to its function in returning blood to the heart.

> Pearson Edexcel A-Level Biology A (9BI0) — 1.3 Mass transport in animals · Explain · 5 marks

> Veins carry blood from the body's organs back towards the heart. The blood in veins is at a lower pressure than the blood in arteries.

## Mark scheme (5 marks)

1. Veins have a wide lumen / large internal diameter
2. Wide lumen reduces resistance to flow / allows blood to flow easily back to the heart at low pressure
3. Veins have thin walls / less muscle / less elastic tissue than arteries
4. Thin walls are sufficient because the blood is at low pressure / there is no need to withstand high pressure
5. Veins contain valves to prevent the backflow of blood / to ensure blood travels in one direction towards the heart

## Key terms

- [vein](https://www.gradenine.co.uk/glossary/vein)

## 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-how-the-structure-of-a-202e73c7) · Published by Druglandscape Ltd.