# Explain how the ultrastructure of a type II pneumocyte (alveolar cell) is adapted for the production and secretion of pulmonary surfactant.

> IB DP Biology Higher Level (2023 syllabus) — B2.3 Cell specialisation · Explain · 4 marks

## Mark scheme (4 marks)

1. Numerous mitochondria provide ATP for the energy-demanding synthesis and secretion of surfactant components (phospholipids and proteins).
2. An extensive rough endoplasmic reticulum (RER) allows large-scale synthesis of surfactant-associated proteins on membrane-bound ribosomes.
3. A prominent Golgi apparatus processes and packages surfactant components (proteins and phospholipids) into secretory vesicles called lamellar bodies.
4. Lamellar bodies (specialised lysosomes / secretory organelles) fuse with the plasma membrane by exocytosis, releasing surfactant into the alveolar fluid to reduce surface tension.

## Key terms

- [type II pneumocyte](https://www.gradenine.co.uk/glossary/type-ii-pneumocyte)
- [pulmonary surfactant](https://www.gradenine.co.uk/glossary/pulmonary-surfactant)

## 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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-ultrastructure-of-a-f3105f03) · Published by Druglandscape Ltd.