How is oxygen and carbon dioxide transported in human beings?

Haemoglobin present in blood aids in the transportation of these gases.The blood serves as a transport system for both carbon dioxide and oxygen. Oxygen is carried to the cells whereas carbon dioxide is carried away from the cells.
(i) Transport of oxygen :

The oxygen molecule can bind to the haemoglobin molecules easily.One molecule of haemoglobin binds four molecules of oxygen.Haemoglobin present in the blood takes up the oxygen from the air in the lungs. It carries the oxygen to tissues which are deficient in oxygen before releasing it.

(ii) Transport of carbon dioxide :

Similarly, Carbon dioxide is more soluble in water. Therefore, it is mostly transported from body tissues in the dissolved form in our blood plasma to lungs in the form of carboxyhemoglobin. Here it diffuses from blood to air in the lungs.