Question

Chloride shift is essential for transport of

• A. CO${}_2$ and O${}_2$
• B. N${}_2$
• C. CO${}_2$
• D. O${}_2$

Answer 1

Answer: (C)

Chloride shift is essential for the transport of CO${}_2$. CO${}_2$ diffuses into the red blood cell and combines with H${}_2$O to form carbonic acid (H${}_2$CO${}_3$). This reaction is catalysed by the enzyme carbonic anhydrase inside the red blood cells. Carbonic acid (H${}_2$CO${}_3$) then readily dissociates into hydrogen ions (H+) and hydrogen carbonate ions (HCO${}_3$-). HCO${}_3$- ions diffuse out of the red blood cell into the plasma where they combine with Na+ ions from the dissociation of sodium chloride to form sodium hydrogen carbonate (NaHCO${}_3$). To balance the outward movement of negatively charged HCO${}_3$- ions, chloride (Cl-) ions diffuse in. This is known as the chloride shift and it is by this means that the electrochemical neutrality of the red blood cell is maintained.

Thus, option C is the correct answer.