Remember what you learned about diffusion in pbs or another science class. use the principles of diffusion to explain why oxygen molecules in the tissues of the lung go into the blood, and then in other tissues the oxygen molecules leave the blood.

Difussion occurs from a high concentrated region to a low concentrated region. The velocity of diffussion is proportional to the differential of concentrations. In the lung arrives blood with low levels of oxygen while the long is rich with fresh oxygen so the oxygen flows from the lung tissues to the blood.

The other tissues consume oxygen continually them they get poor in oxygen and so the oxygen that is in the blood diffuses to the tissue that is poor in oxygen.