IB DP Biology- B3.1 Gas exchange- IB Style Questions For HL Paper 1A -FA 2025
▶️ Answer/Explanation
Type I pneumocytes are extremely thin, minimizing the diffusion distance for gases and allowing efficient oxygen and carbon dioxide exchange across the alveolar surface.
Type II pneumocytes contain numerous secretory vesicles (lamellar bodies) responsible for producing and releasing pulmonary surfactant, which lowers surface tension and prevents alveolar collapse during exhalation.
✅ Answer: (D)
Question
The diagram shows an alveolus from a healthy human lung with type I and II pneumocytes and phagocytes
What are the main functions of these cells?
▶️Answer/Explanation
Answer: D.
Explanation:
The alveolus is the microscopic air sac in the lungs where gas exchange occurs. It contains three main types of cells, each with a distinct function:
Type I Pneumocyte
- These are thin, flat epithelial cells that form the majority of the alveolar surface.
- Their primary function is gas exchange.
- Due to their thinness, they allow oxygen to diffuse from the alveolus into the blood, and carbon dioxide to diffuse from the blood into the alveolus efficiently.
Type II Pneumocyte
- These are cuboidal cells and are fewer in number compared to Type I cells.
- Their main role is the secretion of pulmonary surfactant.
- Surfactant is a lipid-protein substance that reduces surface tension within the alveoli, preventing their collapse during exhalation and helping maintain their shape for efficient gas exchange.
Phagocyte
- These are immune cells, typically macrophages, found within the alveolus.
- Their main function is the ingestion and destruction of pathogens, such as bacteria or dust particles that enter the lungs.
- They help in defending the lungs from infection and keeping the alveolar space clean.