There are three major types of blood vessels: the arteries, which carry the blood away from the heart; thecapillaries, which enable the actual exchange of water and chemicals between the blood and the tissues; and the veins, which carry blood from the capillaries back toward the heart.
<span>It is identical or nearly identical to the first DNA molecule.</span>
Cellular respiration is the process by which organisms use oxygen to break down food molecules to get *chemical energy *for cell functions.
