The carbon dioxide released in oxidation of food diffuse out of the cells into the capillaries from where it transported to lungs by three ways : [a] In form of bicarbonate: About 70% of CO2 transported by this way. The CO2 in blood reacts with water to form carbonic acid. This reaction is accelerated 5000 times by carbonic anhydrase in RBCs. As rapidly all carbonic acid of RBCs dissociates info hydrogen and bicarbonate ions. Most of the bicarbonate ions formed within RBCs diffuse into the blood plasma and combine with haemoglobin to form haemoglobinic acid (H. Hb.). [b] In dissolved state: About 7% carbon dioxide gets dissolved in the blood plasma and is carried in solution to lungs. [c] As carbaminohaemoglobin: About 23% of CO2 is transported in combination with haemoglobin and plasma proteins.