In the lungs, oxygen diffuses into the blood and is loaded onto hemoglobin for transport. In the tissues, oxygen is unloaded from hemoglobin and diffuses from the blood into nearby cells. What drives the diffusion of oxygen?

(A) body temperature

(B) partial pressure of oxygen

(C) concentration of nitric oxide

(D) partial pressure of carbon dioxide

(E) blood pH

B) partial pressure of oxygen

Explanation: All tissues and cells in the body require oxygen to carry our respiration for the provision of energy in the form of ATP. Oxygen is exchanged in the lungs and is loaded into hemoglobin, a pigment in the red blood cells that carries oxygen in the tissues. This occurs through simple diffusion that is facilitated by a concentration gradient. In the tissues, internal respiration takes place where oxygen is unloaded from hemoglobin and diffuses into nearby cells. Diffusion occurs as a result of the difference in the partial pressure of oxygen in the blood vessels and that in the blood tissues. The partial pressure of oxygen in the blood vessels is higher compared to partial pressure in the cells, thus, the oxygen gas will diffuse into the cells.