<prompt> Bohr effect is described as: September 2009Decrease in CO2 affinity of hemoglobin when the pH of blood risesDecrease in CO2 affinity of hemoglobin when the pH of blood fallsDecrease in O2 affinity of hemoglobin when the pH of blood risesDecrease in O2 affinity of hemoglobin when the pH of blood falls  <response>: Ans. D: Decrease in O2 affinity of hemoglobin when the pH of blood fallsThe decrease in O2 affinity of hemoglobin when the pH of blood falls is called the Bohr effect and is closely related to the fact that deoxygenated hemoglobin deoxyhemoglobin binds H more actively than does oxyhemoglobin. The pH of blood falls as its CO, content increases, so that when the PCO2 rises, the curve shifts to the right and the P5,, rises. 