Explain the transport of CO2

Plasma and red blood cells transport carbon dioxide. This is because they are readily soluble in water.

1. Through plasma:
   About 7% of CO₂ is carried in a dissolved state through plasma. Carbon dioxide combines with water and forms carbonic acid.
   {tex}CO_2\;+H_2O\rightarrow\underset{Carbonic\;acid)}{H_2CO_3}{/tex}
   Since the process of forming carbonic acid is slow, only a small amount of carbon dioxide is carried this way.
2. Through RBCs:
   About 20 – 25% of CO₂ is transported by the red blood cells as carbaminohaemoglobin. Carbon dioxide binds to the amino groups on the polypeptide chains of haemoglobin and forms a compound known as carbaminohaemoglobin.
3. Through sodium bicarbonate:
   About 70% of carbon dioxide is transported as sodium bicarbonate. As CO₂ diffuses into the blood plasma, a large part of it combines with water to form carbonic acid in the presence of the enzyme carbonic anhydrase. Carbonic anhydrase is a zinc enzyme that speeds up the formation of carbonic acid. This carbonic acid dissociates into bicarbonate (HCO₃^–) and hydrogen ions (H⁺).
   {tex}\mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O} \stackrel{\text { Carbonicanhydrase }}{\longrightarrow} \mathrm{H}_{2} \mathrm{CO}_{3}{/tex}
   {tex}\mathrm{H}_{2} \mathrm{CO}_{3} \frac{\text { Carbonic }}{\text { anhydrase }} \mathrm{HCO}_{3}^{-}+\mathrm{H}^{+}{/tex}