Science Assessment

Which of the following statements is TRUE about the movement of oxygen molecules between the lungs and cells of the body?

1. Most oxygen molecules move from the lungs to cells of the body by entering microscopically small blood vessels (capillaries) and then moving to cells through the circulatory system.
2. Most oxygen molecules move from cells of the body to the lungs by moving through the circulatory system and then leaving the circulatory system by way of capillaries at the lungs.
3. Most oxygen molecules move from the lungs to the heart by way of special respiratory tubes where the oxygen molecules mix with the blood.  Blood then moves to cells of the body by way of the circulatory system.
4. Oxygen molecules enter and leave the body by way of lungs, but they do not move between the lungs and the blood.