Bohr Effect: Rightward Shift in Oxygen Dissociation Curve

Steps:

• Identify the Bohr effect as the phenomenon where hemoglobin's oxygen affinity decreases under physiological conditions.
• Recognize that a rightward shift (X to Y) indicates lower oxygen affinity, promoting oxygen release to tissues.
• Link the shift to factors that stabilize deoxyhemoglobin: elevated CO2 forms carbonic acid, lowering pH.
• Conclude the shift occurs with increased CO2 and low pH, as these enhance H+ binding to hemoglobin.

Why D is correct:

• The Bohr effect is defined as reduced hemoglobin-oxygen affinity due to increased CO2 (raising H+ via carbonic acid) and low pH, shifting the curve rightward.

Why the others are wrong:

• A: Decreased CO2 and high pH increase affinity, causing a leftward shift.
• B: Decreased CO2 opposes the effect, while low pH alone is insufficient without CO2 increase.
• C: Increased CO2 lowers pH, but high pH contradicts and reverses the shift.

Final answer: D