Final answer:
Oxygen binds to hemoglobin in the lungs and is released from it as blood travels through systemic capillaries.
Step-by-step explanation:
In the lungs, oxygen diffuses out of the alveoli and into the capillaries surrounding the alveoli. Oxygen (about 98 percent) binds reversibly to the respiratory pigment hemoglobin found in red blood cells (RBCs). RBCs carry oxygen to the tissues where oxygen dissociates from the hemoglobin and diffuses into the cells of the tissues.