Answer: Contracting and moving down.
- A Relaxing and moving up
- B Contracting and moving down
- C Staying still
- D Moving sideways
Correct answer: B. Contracting and moving down
Explanation: During inhalation, the diaphragm contracts and flattens (moves down), increasing chest volume, decreasing pressure, and drawing air in.
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.