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Transport of CO₂ is much easier than O₂ because of the higher solubility of CO₂ than O₂. Almost 7% of CO₂ is transported in dissolved state in plasma. About 23% of the CO₂ is transported in the form of carbamino haemoglobin. 70% of CO₂ is transported in the form of bicarbonate ions. CO₂ reacts with water present in plasma.

1. Carbonic acid is unstable & gives H⁺ and HCO₃⁻. H⁺ bind with haemoglobin to maintain the pH of blood while HCO₃⁻ remain in the blood and carries the CO₂ to lungs.
2. The total volume of air that can be expelled from the lungs after maximum inspiration and then expiring to the maximum is known as the vital capacity. The volume of air that remains inside lungs at the end of maximum forceful expiration is the residual volume. Expiratory reserve volume is the maximum extra volume of air that can be expired by forceful expiration after a normal tidal expiration. Total lung capacity is the maximum volume of air that can be contained in the lungs after maximum inspiration.
3. The pathway of inhaled air is - Nostrils → pharynx (common passage for food & air) → larynx (voice box) → trachea (the wind pipe) → bronchi (2 for each side lungs) → bronchioles (give rise to alveolar ducts) → alveoli (the exchange site for gases in the form of small sacs or pouches).
4. Carbonic anhydrase is a zinc-containing enzyme present in RBCs. In presence of this enzyme, carbon dioxide reacts with water to form carbonic acid.

Correct answer: Carbonic acid is unstable & gives H⁺ and HCO₃⁻. H⁺ bind with haemoglobin to maintain the pH of blood while HCO₃⁻ remain in the blood and carries the CO₂ to lungs.

Solution

CO₂ is mainly transported after being converted to bicarbonate in blood. Carbonic acid dissociates into H⁺ and HCO₃⁻; hemoglobin buffers the H⁺, while bicarbonate carries most of the CO₂ to the lungs.

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