Why is it possible to deliver more O2 to vigorously working cells without increasing respiration rate or cardiac output?
A. It isn't; a small decrease in PO2 has little effect on hemoglobin unloading.
B. Once one molecule of O2 is bound to hemoglobin, the other molecules bind much more rapidly.
C. At a PO2 between 0 and 40, hemoglobin saturation changes rapidly and a greater degree of unloading occurs with even small changes in PO2.
D. CO2 released from the vigorously working cells enhances O2 binding to hemoglobin.
Answer: C
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