Which condition will cause a rightward shift of the oxygen dissociation curve, decreasing hemoglobin's affinity for oxygen?

Which condition will cause a rightward shift of the oxygen dissociation curve, decreasing hemoglobin's affinity for oxygen?

• A. Low plasma pH level
• B. Low PCO2 level
• C. Low concentration of 2,3-bisphosphoglycerate
• D. Low temperature

Answer: (A)

A rightward shift in the oxygen-hemoglobin dissociation curve means hemoglobin releases oxygen more readily to tissues. This happens when conditions push Hb to hold onto O2 less tightly, such as when hydrogen ion concentration is high. Low plasma pH increases H+ levels, and the Bohr effect shows that these protons bind to hemoglobin and decrease its affinity for oxygen. As a result, the curve shifts to the right, promoting O2 release where it’s needed most, like active tissues producing CO2 and acid. The other described conditions would do the opposite or have no such effect: lowering PCO2 reduces the acidifying effect and tends to shift the curve left, increasing affinity. Lowering 2,3-bisphosphoglycerate reduces factors that promote unloading, so the curve shifts left. Lowering temperature also tends to stabilize Hb’s oxygen-binding, shifting left.

A rightward shift in the oxygen-hemoglobin dissociation curve means hemoglobin releases oxygen more readily to tissues. This happens when conditions push Hb to hold onto O2 less tightly, such as when hydrogen ion concentration is high. Low plasma pH increases H+ levels, and the Bohr effect shows that these protons bind to hemoglobin and decrease its affinity for oxygen. As a result, the curve shifts to the right, promoting O2 release where it’s needed most, like active tissues producing CO2 and acid.

The other described conditions would do the opposite or have no such effect: lowering PCO2 reduces the acidifying effect and tends to shift the curve left, increasing affinity. Lowering 2,3-bisphosphoglycerate reduces factors that promote unloading, so the curve shifts left. Lowering temperature also tends to stabilize Hb’s oxygen-binding, shifting left.