High-Altitude Adaptation via Increased Hemoglobin-Oxygen Affinity

Steps:

• At high altitudes, atmospheric pO2 is lower, reducing oxygen availability.
• Animals adapt by evolving hemoglobin with higher oxygen affinity to load O2 effectively at low pO2.
• This shifts the dissociation curve leftward, lowering the partial pressure for 50% saturation (P50).
• The left shift ensures sufficient arterial oxygenation despite hypoxia.

Why A is correct:

• Higher affinity lowers P50 on the oxygen-hemoglobin dissociation curve, enabling saturation at reduced pO2 as defined by the curve's sigmoidal shape and cooperative binding.

Why the others are wrong:

• B: Readily releasing oxygen indicates lower affinity and a right-shifted curve, worsening loading at low pO2.
• C: Bohr effect involves pH/CO2-induced shifts, but the curve difference here is due to inherent hemoglobin structure, not acute gas changes.
• D: CO2 decrease via Bohr effect could shift left, but high-altitude adaptation is genetic, not environmental CO2 variation.

Final answer: A