Physiology & Biochemistry · single question
How is most carbon dioxide transported in the blood back to the lungs for elimination?
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Correct answer: C. As bicarbonate ion (HCO3-), formed via the carbonic anhydrase reaction inside red blood cells
About 70% of CO2 is carried as bicarbonate (CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3-, catalyzed by carbonic anhydrase in RBCs), about 20-23% is bound to hemoglobin as carbaminohemoglobin, and only about 7% is dissolved as free CO2 in plasma. ('Carbonic anhydride' is not a real transport form — the enzyme is carbonic anhydrase.)
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