1. All living organisms are composed of one or more cells. This means that cells are the fundamental building blocks of all life.

2. The cell is the basic unit of structure and function in living organisms. This means that cells carry out all the necessary life processes, such as metabolism, growth, and reproduction.

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