The primary function of the respiratory system<span> is the exchange of oxygen, which is needed by the body's cells, for carbon dioxide, which is produced as a waste product of cellular metabolism.</span>
The smallest particle of an element is an atom.
Answer - Viruses are not made out of cells, they can't keep themselves in a stable state, they don't grow, and they can't make their own energy. Even though they definitely replicate and adapt to their environment, viruses are more like androids than real living organisms.
