How is oxygen transported in the blood?
Air enters the lung. In the alveoli, oxygen diffuses across its concentration gradient (partial pressure gradient) into the blood, where it binds to molecules in red blood cells. Oxygenated blood flows to the heart, where it is circulated throughout the body. When the oxygenated blood passes through tissues with low partial pressure of oxygen, some of the oxygen is released from hemoglobin and diffuses into the tissue.
