Final answer:
The ratio of O2 bound to Hgb compared to the total amount of Hgb that can bind oxygen is determined by the oxygen-hemoglobin saturation/dissociation curve. When all of the heme units in the blood are bound to oxygen, hemoglobin is considered to be fully saturated.
Step-by-step explanation:
The ratio of O₂ bound to Hgb compared to the total amount of Hgb that can bind oxygen is determined by the oxygen-hemoglobin saturation/dissociation curve. As the partial pressure of oxygen increases, the hemoglobin becomes increasingly saturated with oxygen. Each hemoglobin molecule can bind up to four molecules of oxygen. When all of the heme units in the blood are bound to oxygen, hemoglobin is considered to be fully saturated.