Question

Most of $C{O}_2$ is removed from the body in the form of?

• A. Carbamino compound of haemoglobin
• B. $HC{O}_3^{-}$
• C. Carboxy haemoglobin
• D. Amino acids

Answer 1

Answer: (B)

$HC{O}_3^{-}$

B. HCO3-

Reason: A large amount of carbon dioxide molecules are carried in the form of a bicarbonate ion which is part of the bicarbonate buffer system. In this system, carbon dioxide diffuses into the red blood cells. Carbonic anhydrase (CA) within the red blood cells quickly converts the carbon dioxide into carbonic acid ($H_{2}C{O}_3$), an unstable intermediate molecule that immediately dissociates into bicarbonate ions and hydrogen (H+) ions. When the blood reaches the lungs, the bicarbonate ion is transported back into the red blood cell in exchange for the chloride ion. The H+ ion dissociates from the hemoglobin and binds to the bicarbonate ion. This produces the carbonic acid intermediate, which is converted back into carbon dioxide through the enzymatic action of CA. The carbon dioxide produced is expelled through the lungs during exhalation. So the correct option is B.