Chloride Shift Maintains Electrical Neutrality

Steps:

• CO2 diffuses into red blood cells and converts to HCO3- via carbonic anhydrase.
• HCO3- diffuses out of the cell into plasma.
• Cl- ions enter the cell in exchange for HCO3- to balance charges.
• This anion exchange prevents charge imbalance across the membrane.

Why B is correct:

• It upholds Donnan equilibrium by exchanging anions (HCO3- out, Cl- in), maintaining equal positive and negative charges between cell interior and plasma.

Why the others are wrong:

• A: pH buffering occurs via hemoglobin binding H+, not the chloride shift.
• C: The shift does not affect the oxygen dissociation curve; left shift prevention relates to Bohr effect from pH changes.
• D: No direct causation of left shift; oxygen release ties to CO2/pH, not anion exchange.

Final answer: B