Answer: Remains in the lungs even after the most forceful expiration.
- A Can be forcibly exhaled after a normal tidal expiration
- B Is inhaled or exhaled during normal quiet breathing
- C Remains in the lungs even after the most forceful expiration
- D Can be additionally inhaled after a normal tidal inspiration
Correct answer: C. Remains in the lungs even after the most forceful expiration
Explanation: Residual volume is the air that remains in the lungs after the most forceful possible exhalation, preventing the alveoli from collapsing completely.
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.