Bohr Effect Lowers Hemoglobin's Oxygen Affinity

Steps:

• Actively respiring muscles produce CO2 from cellular respiration.
• CO2 reacts with water to form carbonic acid (H2CO3).
• Carbonic acid dissociates into hydrogen ions (H+) and hydrogencarbonate ions (HCO3-).
• Elevated H+ concentration triggers the Bohr effect, reducing hemoglobin's oxygen saturation.

Why D is correct:

• The Bohr effect defines how increased hydrogen ion concentration decreases hemoglobin's affinity for oxygen, shifting the oxygen dissociation curve rightward to facilitate O2 unloading in tissues.

Why the others are wrong:

• A. Hydrogencarbonate ions form during CO2 transport but do not directly influence hemoglobin's oxygen binding.
• B. Carbon dioxide contributes indirectly by generating H+ through carbonic acid formation.
• C. Carbonic acid acts as an intermediate that dissociates to produce H+, the direct effector.

Final answer: D