Answer: Chemoreceptors signalling the medullary centre to raise ventilation.
- A Inhibition of the pneumotaxic centre located in the pons
- B Reduced oxygen-carrying capacity of plasma proteins
- C Chemoreceptors signalling the medullary centre to raise ventilation
- D Direct contraction of the diaphragm with little nervous input
Correct answer: C. Chemoreceptors signalling the medullary centre to raise ventilation
Explanation: Central and peripheral chemoreceptors detect a fall in blood pH (rise in H+/CO<sub>2</sub>) and signal the medullary respiratory centre, which increases the rate and depth of breathing to expel more CO<sub>2</sub>.
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.