# Explain how the structure of a vein makes it well suited to returning blood to the heart.

> Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 1.3 Mass transport in animals · Explain · 5 marks

> Blood is transported around the body in three types of blood vessel: arteries, capillaries and veins. Veins carry blood from the organs back towards the heart, often against the force of gravity.

## Mark scheme (5 marks)

1. Veins have a wide lumen
2. Wide lumen reduces resistance / allows blood to flow easily / allows blood to flow at low pressure
3. Veins have valves
4. Valves prevent the backflow of blood / ensure blood flows in one direction (towards the heart)
5. Veins have thin walls / less muscle and elastic tissue than arteries, which is sufficient because blood is at low pressure

## Key terms

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

## Related

- [Revision notes for Edexcel A-Level Biology A: Salters-Nuffield (9BN0)](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-c8925d0c) · Published by Druglandscape Ltd.