Answer: Inspiratory reserve volume.
- A Expiratory reserve volume
- B Residual volume
- C Inspiratory reserve volume
- D Vital capacity
Correct answer: C. Inspiratory reserve volume
Explanation: Inspiratory reserve volume (IRV) is the extra air, about 2500-3000 mL, that can be inhaled by forcible inspiration beyond a normal breath.
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.