Question

Most of the carbon dioxide transported in our blood is

• A. dissolved in the plasma
• B. as carbaminohaemoglobin
• C. as bicarbonate
• D. bound to the heme of haemoglobin

Answer 1

The correct option is C

as bicarbonate

Carbon dioxide is transported by our blood in three different ways:
(i) Physically dissolved in the blood plasma - Although carbon dioxide is more soluble than oxygen in the blood plasma, only about 10 % of the blood's carbon dioxide is transported in this manner.
(ii) Bound to haemoglobin - Around 30 % of the blood's carbon dioxide combines with haemoglobin to form carbaminohaemoglobin. Carbon dioxide binds to the globin part of the haemoglobin and not to haeme, unlike oxygen.
(iii) As bicarbonate (HCO₃⁻) - About 60 % of the carbon dioxide is transported this way. Carbon dioxide diffuses into the red blood cells. Carbonic anhydrase (CA) within the red blood cells quickly converts the carbon dioxide into carbonic acid (H ₂CO₃). Carbonic acid is an unstable, intermediate molecule that immediately dissociates into bicarbonate ions (HCO₃⁻) and hydrogen (H ⁺) ions.