And that is precisely what allows the hemoglobin to unload so much oxygen to the tissues, to the tissues and cells of that exercising area. So once again, in red blood cells, hemoglobin is able to unload 66% of the oxygen when going from the lungs to the exercising tissue. While if we compare the pure hemoglobin, we see that pure hemoglobin only unloads 8% of that oxygen. The question is, why is there this difference? What accounts for this difference in the first place inside the red blood cells? Why is it that inside the red blood cells, the affinity of hemoglobin for oxygen is so much lower than in the pure hemoglobin case?