8. The partial pressure of oxygen is lower in the blood capillaries alveoli than that in the alveoli. This is because the blood that reaches the alveoli comes from body tissues. Most of the oxygen has been taken up by the tissues for cellular respiration. Thus, oxygen diffuses from the alveoli in to the blood capillaries.
9. Blood capillaries has a relatively higher partial pressure of carbon dioxide compared to that in alveoli. This is because carbon dioxide is