Question

The major form of CO2 in the blood is

a) bicarbonate

b) carbonic acid

c) dissolved CO2 gas

d) carbamino hemoglobin

e) carbon monoxide

Answer 1

Answer-(bicarbonate)

This is the major mechanism of CO2 transport. About 70% CO2​​​​​​ is transported in bicarbonate form.

During this process CO2 diffuses into RBCs and carbonic anhydrase present in red blood cells converts carbon dioxide into carbonic acid (H2CO3). Carbonic acid is unstable compound and quickly dissociates into bicarbonate and H+ ions. The newly formed bicarbonate ion leave to liquid component of blood in exchange of Cl- (chloride ions) from blood plasma to RBCs and called as "chloride shift".

When blood reaches to the lungs bicarbonate ions return back into the RBCs from the blood and H+ dissociates from hemoglobin & binds with bicarbonate ions to form carbonic acid again and converted back to carbon dioxide (CO2) with the activity of carbonic anhydrase enzyme. Now free CO2 exhaled out from the lungs.