Energy is required for the normal functioning of the organs in the body<span>. Many tissues can also use fat or protein as an energy source but others, such as the brain and red blood cells, can only use </span>glucose<span>. </span>Glucose<span> is stored in the </span>body<span> as glycogen. The liver is an important storage site for glycogen.</span>
The homology of animals is based on scientists current understanding on the evolutionary history of living species.
