NEET 2021 Zoology Question 179 Solution

Binding of oxygen to haemoglobin is a reversible, cooperative oxygenation process governed by the oxygen-haemoglobin dissociation curve. At the pulmonary alveoli: - High $pO_2$ (~104 mm Hg): Provides the steep diffusion gradient driving conformational transition of deoxyhaemoglobin (T-state) into relaxed oxyhaemoglobin (R-state). - Low $pCO_2$ (~40 mm Hg): Minimizes carbamino-haemoglobin formation and prevents carbamylation of N-terminal amino groups. - Lesser $H^+$ concentration (Higher pH ~7.4): Prevents protonation of histidine residues that otherwise stabilize deoxyhaemoglobin (Haldane effect). - Lower Temperature: Exothermic binding of $O_2$ to haem is thermodynamically favoured at lower temperatures.

In metabolically active systemic tissues, the reverse occurs: low $pO_2$, high $pCO_2$, high $H^+$ (acidic lactic/carbonic acid), and elevated temperature facilitate the uncoupling and unloading of oxygen (Bohr effect, rightward shift).