Why does hemoglobin accept oxygen molecules in the lungs but give up oxygen molecules in tissue?
In the lungs where the oxygen concentration is high the binding of oxygen to hemoglobin is high. In respiring tissue where the oxygen levels are low and the CO2 levels are high the affinity of hemoglobin for oxygen is reduced and so the oxygen comes off the hemoglobin and is used by the cells. The driving force for this is the Bohr Effect whereby CO2 produced by the respiring cells dissolves in the blood as follows CO2 + CO2 –> H2CO3 –> H+ + HCO3-.
