Answer: Flatten, increasing the volume of the thoracic cavity.
- A Pull the lungs downward without changing thoracic volume
- B Dome upward, decreasing the volume of the thoracic cavity
- C Remain stationary while the rib cage does all the work
- D Flatten, increasing the volume of the thoracic cavity
Correct answer: D. Flatten, increasing the volume of the thoracic cavity
Explanation: During inspiration, the diaphragm contracts and flattens, increasing the volume of the thoracic cavity and lowering intrapulmonary pressure, drawing air into the lungs.
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.