Chloride shift is due to -

Ans. is 'a' i.e., Generation of HCO-3 in RBCs o Carbon dioxide is transported in blood as plasma bicarbonate.o Red blood cells (RBCs) play a major role in the mechanism because RBCs contain the enzyme carbonic anhvdrase that catalyzes the reaction CO2 + H2O = HCO3- + H+o Hence when CO2 diffuses into the RBC, it reacts chemically with water to generate HCO3-o The H+ ions are mopped up by hemoglobin, which is an excellent buffer,o This enables the reaction to proceed in the forward direction.o The HCO3- ions generated diffuse out into the plasma in exchange for Cl- ions that diffuse into RBCs simultaneously,o The movement of chloride ions into RBC is called Chloride shift.o The above events results in an increase in total number ions inside the RBC, which increases its osmolarity.o As a result, water enters the RBC through osmosis.o The RBCs carrying CO2 in bicarbonate form will therefore be somewhat larger than normal,o Hence the hematocrit of venous blood is normally 3% greater than that of arterial blood.o In the lungs, Cl- moves out of the RBCs and they shrink.