1. All living organisms are made up of one or more cells. This means that cells are the fundamental building blocks of life. Everything from bacteria to humans is made up of cells.

2. The cell is the basic unit of structure and function in living organisms. This means that all the processes of life happen within cells, and the structure of a cell determines its function.

3. All cells arise from pre-existing cells. This means that cells don't spontaneously appear; they come from the division of other cells.

These three parts of cell theory form the foundation of our understanding of biology and how life works.