# Explain how the tracheal system of insects allows gas exchange to occur without the need for a circulatory system to transport respiratory gases.

> IB DP Biology Standard Level (2023 syllabus) — B3.1 Gas exchange · Explain · 4 marks

## Mark scheme (4 marks)

1. Tracheae branch into tracheoles that reach individual cells / tissues directly
2. Oxygen diffuses directly from tracheoles to respiring cells / along a short diffusion pathway
3. A concentration / diffusion gradient is maintained because respiring cells continuously consume oxygen and produce carbon dioxide
4. Air (containing oxygen) is brought close to cells by the tracheal system so the circulatory system does not need to transport respiratory gases / haemolymph transports nutrients and hormones but not O₂/CO₂

## Key terms

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

## Related

- [Revision notes for IB DP Biology Standard Level (2023 syllabus)](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-tracheal-system-of-28ccf117) · Published by Druglandscape Ltd.