CO2 uptake and chloride shift in red blood cells

Steps:

• CO2 diffuses from active tissues into red blood cells (RBCs), increasing its concentration.
• Inside RBCs, CO2 reacts with water via carbonic anhydrase to form H+ and HCO3-.
• Hemoglobin buffers the H+, preventing a significant rise in [H+].
• HCO3- concentration increases due to formation; HCO3- then exits RBCs in exchange for Cl- entering via the chloride shift, raising [Cl-].

Why D is correct:

• D matches no change in [H+] (buffered by hemoglobin), increase in [HCO3-] (from carbonic acid dissociation), and increase in [Cl-] (chloride shift for charge balance).

Why the others are wrong:

• A: [HCO3-] and [Cl-] increase, not remain unchanged.
• B: [H+] shows no change due to buffering, not an increase.
• C: [H+] shows no change, not a decrease.

Final answer: D