# Explain how the structure of the human trachea and bronchioles enables efficient delivery of air to the alveoli.

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

## Mark scheme (4 marks)

1. The trachea is reinforced by C-shaped cartilage rings that prevent the airway from collapsing during inhalation when internal pressure drops.
2. The gap in each C-shaped ring (at the posterior/oesophageal side) allows the oesophagus to expand when food is swallowed.
3. The ciliated epithelium lining the trachea/bronchi, together with goblet cells that secrete mucus, traps pathogens and particles, which are then moved towards the pharynx by ciliary action, keeping the lower airways clear.
4. The bronchioles lack cartilage but have smooth muscle in their walls, allowing them to dilate or constrict to regulate airflow to different regions of the lung.

## Key terms

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

## 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-structure-of-the-e7de0c15) · Published by Druglandscape Ltd.