Question

In blood, carbon dioxide is primarily carried in the form of _________.

• A. potassium bicarbonate
• B. sodium bicarbonate
• C. carbamino haemoglobin
• D. dissolved in plasma

Answer 1

The correct option is B sodium bicarbonate

Carbon dioxide is carried in blood in three forms- dissolved gas, sodium bicarbonate and carbamino haemoglobin. The transport of carbon dioxide is affected by several properties. Firstly, carbon dioxide is more soluble than oxygen in blood as carbon dioxide has higher affinity towards haemoglobin than oxygen. Only a small percentage of carbon dioxide is transported this way.
Secondly, carbon dioxide can easily bind to haemoglobin and form carbaminohemoglobin. This is a reversible process and about 20-25% of carbon dioxide is transported this way.
Thirdly, the majority of carbon dioxide molecules (more than 70-80%) are carried as bicarbonate ions. Carbonic anhydrase (CA) in the red blood cells quickly converts the carbon dioxide into carbonic acid. Carbonic acid being an unstable intermediate molecule immediately dissociates into bicarbonate ions.
Potassium bicarbonate is an inorganic salt which is generally used as an antacid (a substance that reduces stomach acidity). It is not found in the body naturally.