Multiple choice

CO is transported mainly as ______.

  1. bicarbonates dissolved in plasma

  2. bicarbonates carried by white blood cells

  3. carbonic acid in plasma

  4. carbonic acid in RBC

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A Correct answer
Explanation

About 70% of carbon dioxide is transported as bicarbonate ions (HCO3-) dissolved in plasma. CO2 enters red blood cells, is converted to carbonic acid by carbonic anhydrase, which dissociates into H+ and HCO3-, with HCO3- moving into plasma.