Answer: CO binds hemoglobin far more strongly than oxygen, blocking O 2 sites.
- A CO reacts with plasma proteins to form toxic precipitates in typical laboratory settings
- B CO destroys red blood cells within minutes of exposure as generally observed
- C CO drives an excessive rise in red blood cell production under usual circumstances
- D CO binds hemoglobin far more strongly than oxygen, blocking O<sub>2</sub> sites
Correct answer: D. CO binds hemoglobin far more strongly than oxygen, blocking O<sub>2</sub> sites
Explanation: Carbon monoxide binds hemoglobin with about 200 times greater affinity than oxygen, forming stable carboxyhemoglobin and effectively blocking the sites needed for oxygen transport.
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.