Bohr shift: pH and CO2 effects on hemoglobin oxygen affinity

Steps:

• Recall Bohr shift as rightward oxyhemoglobin dissociation curve shift, reducing O2 affinity in tissues.
• Identify key processes: increased CO2 forms carbaminohemoglobin; decreased pH (increased H+) protonates hemoglobin.
• Assume choices: 1 = temperature change; 2 = CO2 binding; 3 = H+ binding (standard factors).
• Match to options: 2 and 3 drive Bohr shift, excluding 1.

Why C is correct:

• Bohr effect defined as O2 affinity decrease from CO2 and H+ binding to deoxyhemoglobin, per Haldane's law on acid-base and CO2 influence.

Why the others are wrong:

• A includes 1 (temperature), which causes separate thermal shift, not Bohr.
• B only 1 (temperature), irrelevant to Bohr's acid/CO2 mechanism.
• D only 3 (H+), misses CO2's direct carbamino role.

Final answer: C