Carbonic Anhydrase in CO2 Transport

Steps:

• CO2 diffuses from tissues into blood plasma and red blood cells.
• Inside RBCs, CO2 reacts with water to form carbonic acid, accelerated by carbonic anhydrase.
• Carbonic acid dissociates into bicarbonate and hydrogen ions.
• Bicarbonate exits RBCs via chloride shift for transport.

Why C is correct:

• Carbonic anhydrase catalyzes CO2 + H2O ⇌ H2CO3, the hydration of CO2 to carbonic acid.

Why the others are wrong:

• A involves passive diffusion of CO2 into blood, no enzyme required.
• B is binding of CO2 to hemoglobin as carbaminohemoglobin, uncatalyzed.
• D is dissociation of H2CO3 to H+ + HCO3-, spontaneous after catalysis.

Final answer: C