Bisphosphoglyceric acid (BPG) is a byproduct of glycolysis released into the bloodstream when an animal's supply of oxygen is low. Like protons, it decreases hemoglobin's affinity for O2. The effect of high BPG levels would be that:
a. hemoglobin now binds more oxygen at low partial pressures than at high partial pressures.
b. hemoglobin picks up more O2 in the lungs than it would without BPG.
c. hemoglobin loses its cooperative binding of oxygen.
d. hemoglobin releases more of its bound O2 than it would without BPG.
e. hemoglobin holds on to more of its O2 than it would without BPG.