Transport of Carbon dioxide — Prelims Strategy

Prelims Strategy

To excel in NEET questions on carbon dioxide transport, a multi-pronged strategy is recommended. Firstly, memorize the approximate percentages of $CO_2$ transported by each mechanism: 7% dissolved in plasma, 20-25% as carbaminohemoglobin, and 70% as bicarbonate ions.

Secondly, thoroughly understand the chemical reactions involved, especially the role of carbonic anhydrase in converting $CO_2$ to carbonic acid and its subsequent dissociation. Pay close attention to the chloride shift (Hamburger phenomenon) – know its purpose (maintaining electrical neutrality) and direction (Cl- into RBCs in tissues, out in lungs).

Thirdly, differentiate clearly between the Bohr effect (how $CO_2$/$H^+$ affects $O_2$ binding) and the Haldane effect (how $O_2$ affects $CO_2$/$H^+$ binding). These are frequently confused. For numerical problems (though rare), ensure you understand partial pressure gradients.

Practice identifying the correct sequence of events in both tissues and lungs. Trap options often involve mixing up percentages, misidentifying enzymes, or reversing the direction of ion movements. Always read the question carefully to determine if it refers to tissue-level or lung-level gas exchange.