Answer: Diffuse from the alveoli into the blood.
- A Diffuse from the blood into the alveoli
- B Remain in the alveoli without net movement
- C Diffuse from the alveoli into the blood
- D Bind irreversibly to carbon dioxide in the alveolar air
Correct answer: C. Diffuse from the alveoli into the blood
Explanation: Because alveolar oxygen partial pressure is higher than in deoxygenated capillary blood, oxygen diffuses down its concentration gradient from the alveoli into the blood.
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.