What Is the Cell Theory?

The cell theory of biology is that all living things are made up of individual elements called "cells." There are several exceptions to the theory. First, viruses meet most, if not all, criteria to be considered life, but are not cells. Second, mitochondria and chloroplasts contain their own DNA and are capable of self-replication but are not found outside cells, Finally, the first thing that could be called a "cell" must necessarily have come from something that wasn't quite a cell. (http://en.wikipedia.org/wiki/Cell_Theory)