# Describe how the structure of arteries, veins and capillaries is adapted to their functions in the human circulatory system.

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

## Mark scheme (5 marks)

1. Arteries have a thick muscle and elastic layer / thick wall to withstand or maintain high blood pressure (preventing bursting).
2. Veins have a thin muscle and elastic layer / thin wall because blood is at low pressure.
3. Veins contain valves to prevent backflow of blood.
4. Capillaries have a thin wall / narrow diameter to decrease diffusion distance, allowing exchange of substances between the blood and tissues.
5. Capillaries have a large surface area and slow blood flow to allow time for exchange to take place.

## Key terms

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

## Related

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Source: [GradeNine](https://www.gradenine.co.uk/q/describe-how-the-structure-of-arteries-6cecdc3d) · Published by Druglandscape Ltd.