CBSE Class 10 Answered

This is so that the capillaries are able to profuse the tissues of the body and supply each cell with the required  oxygen and important nutrients supplied by blood. (Arteries and veins are larger and cannot reach each cell.)

Capillaries are tiny blood vessels that pass blood from the arteries into the veins. They are very thin and fragile. The capillary wall is actually only one epithelial cell thick. The exchange of oxygen and carbon dioxide takes place through the thin capillary wall.

Arteries and veins run parallel throughout the body with a web-like network of capillaries, embedded in tissue, connecting them.  The arteries pass their oxygen-rich blood to the capillaries which allow the exchange of gases within the tissue. The tissue releases its waste products, like carbon dioxide, which passes through the wall and into the red blood cells. The capillaries then pass their waste-rich blood to the veins for transport back to the heart.