Help with this instruction booklet

It says you can pick any organ system. Organ systems are Respiratory system, Muscular, Nervous that looks like a brain, and skeleton. Just pick one of these. Say what it does and why its needed for the human?

It is a mixture. simply put, a compound must be pure, that is, of only one chemical structure and composition. a mixture is made of different chemical substances (i.e. elements, molecules, compounds) that are not chemically bonded to each other, but instead physically grouped together, as in the case of gasoline (a homogeneous solution).