CO2 to bicarbonate conversion in red blood cells

Steps:

• CO2 diffuses into red blood cells from tissues.
• Carbonic anhydrase enzyme catalyzes CO2 + H2O to form carbonic acid.
• Carbonic acid dissociates into hydrogen ions (H+) and hydrogen carbonate ions (HCO3-).
• HCO3- exits the cell via chloride shift for blood transport.

Why B is correct:

• Matches the reaction: CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3-, catalyzed by carbonic anhydrase, the primary CO2 transport pathway.

Why the others are wrong:

• A: Describes carbaminohemoglobin formation, a minor CO2 binding to hemoglobin, not the main enzymatic pathway.
• C: Carboxyhemoglobin involves CO poisoning, not CO2 transport; includes irrelevant carbon dioxide reversal.
• D: Starts with hemoglobin and "acid," misrepresenting the enzyme-driven process without carbonic anhydrase.

Final answer: B