Cooperative Oxygen Binding in Hemoglobin

Steps:

• Identify the process: Oxygen uptake in lungs involves hemoglobin binding up to four O2 molecules efficiently.
• Recall hemoglobin's structure: It has four subunits; binding is cooperative, not independent.
• Analyze choices: Look for the mechanism enabling rapid, maximum saturation in high-oxygen lung environment.
• Select best fit: Option describing increased affinity after initial binding matches cooperative effect.

Why B is correct:

• Cooperative binding (positive allostery) in hemoglobin: Binding the first O2 induces conformational change (T to R state), raising affinity for subsequent O2 molecules, per the sigmoidal oxygen-hemoglobin dissociation curve.

Why the others are wrong:

• A: Hemoglobin formation doesn't alter red blood cell capacity; each cell has fixed hemoglobin amount.
• C: Opposite of reality—first O2 binding increases, not decreases, affinity for more O2.
• D: Carboxyhemoglobin involves carbon monoxide, not CO2; CO2 transport is mainly as bicarbonate, not via dissociation for O2.

Final answer: B