Identify the correct statement with reference to transport of respiratory gases by blood?
a)	Haemoglobin is necessary for transport of carbon dioxide and carbonic anhydrase for transport of oxygen
b)	Haemoglobin is necessary for transport of oxygen and carbonic anhydrase for transport of carbon dioxide
c)	Only oxygen is transported by blood
d)	Only carbon dioxide is transported by blood

(b)

Transportation of oxygen from lungs to body tissues and of  from tissues to the lungs is vital role of blood.

Transport of carbon dioxide : Most of the  that dissolves in blood plasma reacts with water to form carbonic acid :

An enzyme carbonic anhydrase present in RBCs, which accelerates the carbonic acid formation about 5000 times. About 70% of the  received by blood from the tissue immediately enter into RBCs and hydrated to carbonic acid. All carbonic acid of RBCs dissociates into hydrogen and bicarbonate ions  The  mostly combine with haemoglobin for keeping the pH of blood (7.4) in steady state, whereas the bicarbonate ion diffuse from RBCs into the plasma. To maintain electrostatic neutrality of plasma many chloride ions in turn diffuse from plasma into RBCs. This is termed chloride or Hamburger shift.