# Explain why, as an organism increases in size, it requires specialised exchange surfaces and a transport system to survive.

> AQA A-Level Biology (7402) — 3.3.1 Surface Area to Volume Ratio · Explain · 5 marks

## Mark scheme (5 marks)

1. As an organism gets larger, its volume increases faster than its surface area
2. The smaller surface area to volume ratio means the outer surface is not large enough to supply all the cells with oxygen/nutrients/remove waste quickly enough
3. Diffusion distances from the outer surface to cells deep inside the organism become too large/long
4. Specialised exchange surfaces provide a large surface area relative to the organism's volume, increasing the rate of exchange
5. A transport system is needed to carry substances quickly from the exchange surfaces to the body cells (and remove waste)

## Key terms

- [exchange surface](https://www.gradenine.co.uk/glossary/exchange-surface)
- [transport system](https://www.gradenine.co.uk/glossary/transport-system)

## Related

- [Revision notes for AQA A-Level Biology (7402)](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-why-as-an-organism-increases-c7c758ae) · Published by Druglandscape Ltd.