ICSE Class 9 Answered
The capillaries of the cardiovascular system deliver oxygen-rich blood to the tissues of the body. Oxygen then diffuses across the thin capillary walls from the high concentrations in the blood to the low concentrations in the tissues. At the same time, carbon dioxide that has been produced as a waste product by the tissues diffuses through the thin capillary walls into the blood where it is transported back to the alveoli.
During External Respiration
Oxygen from the inhaled air is diffused into the alveoli in the lungs and the waste product carbon dioxide from the body diffuses out through the alveoli to be exhaled back into the air. With the help of the cardiovascular system, the freshly inhaled oxygen-rich blood is transported to the tissues of the body.