Through diffusion, oxygen enters the capillary blood from the walls of the alveoli. Then it reaches different cells of the body. Oxygen is transported in the blood in two ways. namely-
(i) Physical solution: 2% oxygen is transported in blood as physical solution. That is, in every 100 ml of blood, 2 ml of oxygen is transported as a physical solution.
(ii) As chemical compounds: 98% oxygen is transported as chemical compounds in the blood. Hemoglobin in red blood cells combines with oxygen to form oxyhemoglobin. Oxyhemoglobin reaches different cells of the body from the heart. When body cells lack oxygen, oxyhemoglobin breaks down and oxygen and hemoglobin are released. As a result, body cells get the necessary oxygen.
Hb4 + 4O2 → 4Hbo2