Answer: Decreases hemoglobin affinity for O 2 (more O 2 released to active tissues).
- A Raises hemoglobin's affinity for O<sub>2</sub> by stabilizing the relaxed conformation
- B Decreases hemoglobin affinity for O<sub>2</sub> (more O<sub>2</sub> released to active tissues)
- C Leaves the oxygen-hemoglobin binding curve completely unshifted
- D Denatures hemoglobin's quaternary structure within red blood cells
Correct answer: B. Decreases hemoglobin affinity for O<sub>2</sub> (more O<sub>2</sub> released to active tissues)
Explanation: Bohr effect: increased CO<sub>2</sub> (and H+) decreases Hb affinity for O<sub>2</sub>, promoting O<sub>2</sub> release to metabolically active tissues.
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.