Which of the following factors contributes to a rightward shift of the Hemoglobin dissociation curve?

• A. Increased hydrogen ion (decrease pH)
• B. Decreased hydrogen ion (increase pH)
• C. Decreased temperature
• D. Decreased CO2

Answer: (A)

The key idea is how hydrogen ion concentration affects hemoglobin’s affinity for oxygen. A rise in H+ (lower pH) lowers hemoglobin’s oxygen affinity by promoting the deoxygenated (T) state. This Bohr effect means oxygen is more readily released to tissues at the same partial pressure of oxygen, so the curve shifts to the right. In practice, acidosis or increased metabolic activity raises H+ and CO2, causing more oxygen delivery where it’s needed.

Decreasing hydrogen ions (raising pH) would make hemoglobin hold onto oxygen more tightly, shifting the curve to the left. Lowering temperature also strengthens oxygen binding, another leftward shift. Decreasing CO2 reduces H+ via carbonic acid formation, again tending toward a leftward shift.