Gas exchange and pH regulation in active tissues

Steps:

• Active tissues consume O2 and produce CO2 and H+ ions, lowering local pH.
• Blood releases O2 from hemoglobin via the Bohr effect due to increased CO2 and H+.
• CO2 diffuses into blood, forming H2CO3 catalyzed by carbonic anhydrase, then dissociating to HCO3- and H+.
• H+ is buffered by hemoglobin, and HCO3- is transported; chloride shift maintains electroneutrality.
• Identify reactions: 1 (O2 unloading), 3 (CO2 to HCO3-), 4 (buffering or shift) occur, but not 2 (likely irrelevant like urea formation).

Why B is correct:

• In active tissues, the Haldane effect enhances CO2 loading as O2 unloads, involving O2 dissociation (1), CO2 hydration to bicarbonate (3), and ion exchanges (4) per respiratory physiology.

Why the others are wrong:

• A includes 2, which is not a tissue-specific blood reaction (e.g., no protein synthesis here).
• C omits 3, ignoring CO2 conversion to bicarbonate for transport.
• D excludes 1 and 4, missing O2 release and buffering essential for tissue oxygenation.

Final answer: B