Answer:
When four oxygen molecules are bound to hemoglobin's subunits and one subunit releases its oxygen, the other three subunits change shape again. This causes them to release their oxygen more readily.
Explanation:
Each hemoglobin molecule can bind up fou oxygen molecules, hemoglobin exhibits what it is call cooperative binding, as oxygen binding increases the affinity of hemoglobin for more oxygen. Incresed affinity is caused by a conformational change, or structural change in the hemoglobin molecule.
The cooperative binding of oxygen to hemoglobin is an important adaptation for gas exchange . Cooperativity allows hemoglobin to release much more oxygen to our body's tissues.