CBSE Class 10 Answered

Red blood cells are able to carry oxygen so efficiently because of a special protein called haemoglobin inside them. Haemoglobin contains a haem prosthetic group that has an iron atom at its centre.  Haemoglobin has an affinity for the oxygen present. As blood passes through the lungs, the haemoglobin picks up oxygen because of the increased oxygen pressure in the capillaries of the lungs, and can then release this oxygen to body cells where the oxygen pressure in the tissues is lower.  

The remaining gases or air molecules are inert with respect to the blood's constituents and hence, red blood corpuscles only capture oxygen molecules and not other air molecules.