Chloride Shift Maintains Charge Balance in CO2 Transport

Steps:

• CO2 diffuses into RBC and reacts with water via carbonic anhydrase to form H2CO3, which dissociates into H+ and HCO3-.
• H+ is buffered by hemoglobin, allowing HCO3- to diffuse out of RBC into plasma.
• To preserve electrical neutrality, Cl- ions shift into RBC from plasma.
• This exchange enables efficient CO2 transport as HCO3- in plasma.

Why B is correct:

• It accurately describes the chloride shift, where HCO3- exits RBC and Cl- enters to balance ions, per the definition of anion exchange in erythrocytes.

Why the others are wrong:

• A: Reverses Cl- direction; Cl- enters RBC, not exits.
• C: Confuses chloride shift with Bohr effect, which involves H+ influencing O2 release, not Cl- directly.
• D: Inverts HCO3- flow; HCO3- exits RBC into plasma, not vice versa.

Final answer: B