Bohr effect describes decreased hemoglobin affinity for O2 under conditions of higher CO2, lower pH, and higher temperature.

• A. Increased affinity with lower temperature
• B. No change in affinity with CO2
• C. Decreased affinity with higher CO2 and higher temperature
• D. Increased affinity with higher CO2

Answer: (C)

The Bohr effect shows that hemoglobin releases oxygen more readily when CO2 is high, the pH is lower, or the temperature is higher. This happens because higher CO2 increases hydrogen ion concentration, lowering pH, and promotes changes in hemoglobin that reduce its affinity for O2; higher temperature also shifts the oxygen dissociation curve to the right, making O2 release easier in tissues that are metabolically active. Therefore, the statement describing decreased affinity with higher CO2 and higher temperature best matches this effect, reflecting the rightward shift of the curve under these conditions. The other ideas—increased affinity with lower temperature, no change with CO2, or increased affinity with higher CO2—do not fit the Bohr mechanism, which favors oxygen unloading when CO2 is high and temperature is up.