Answer: Alveoli collapse by reducing surface tension.
- A Gas exchange across the alveolar membrane surface
- B Alveoli collapse by reducing surface tension
- C Infection from inhaled bacteria and airborne pathogens
- D Blood clotting occurring within the lung capillary network
Correct answer: B. Alveoli collapse by reducing surface tension
Explanation: Pulmonary surfactant (from type II pneumocytes) reduces surface tension inside alveoli, preventing collapse during exhalation.
The S-shaped (sigmoid) curve reflects cooperative binding between Hb's four O₂ sites; the Bohr effect shifts the whole curve to the right under conditions found in actively respiring tissue (more CO₂, more acid, more heat), making haemoglobin release oxygen more readily exactly where it's needed.
Concept context
The mechanics of breathing, lung volumes, gas transport in blood, the Bohr effect, and respiratory regulation.