# Explain how the structure of the human trachea and bronchial tree facilitates the movement of air to and from the alveoli whilst maintaining airway patency.

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

## Mark scheme (4 marks)

1. C-shaped / incomplete rings of cartilage in the trachea prevent collapse of the airway by providing rigid structural support, maintaining an open lumen.
2. The gap / opening in the C-shaped rings faces the oesophagus, allowing the oesophagus to expand during swallowing without obstruction.
3. Progressive branching / repeated bifurcation of bronchi into bronchioles greatly increases total cross-sectional area, reducing airflow resistance and allowing air to reach all regions of the lungs.
4. Smooth muscle in the walls of bronchioles can contract or relax to adjust airway diameter / resistance, regulating airflow to different parts of the lung.

## Key terms

- [airway patency](https://www.gradenine.co.uk/glossary/airway-patency)
- [bronchial tree](https://www.gradenine.co.uk/glossary/bronchial-tree)

## Related

- [Revision notes for IB DP Biology Higher 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-d790ba44) · Published by Druglandscape Ltd.