Gas Exchange Structure

IGCSE Edexcel Biology
2.46-2.48 Gas Exchange
Key Concept: The thorax and alveoli are adapted for efficient ventilation and diffusion.

Section A: Thorax Structure

1. Label the thorax with: ribs, intercostal muscles, diaphragm, trachea, bronchi, bronchioles, alveoli, pleural membranes. [8]
[Thorax diagram]

Section B: Ventilation

2. Describe what happens during inhalation. [4]

Section C: Alveoli

3. Explain three adaptations of alveoli for gas exchange. [3]
Total marks: 15

Mark Scheme

1. All eight labels correct [8]
2. External intercostals contract and ribs move up/out; diaphragm contracts and flattens; volume increases; pressure decreases; air moves in [4]
3. Large surface area, thin walls, moist surface, rich capillary supply (any three) [3]