1. All living organisms are composed of one or more cells. This means that all living things, from the smallest bacteria to the largest trees, are made up of cells.

2. The cell is the basic unit of structure and function in living organisms. This means that cells are the smallest unit that can perform all the functions necessary for life, such as obtaining nutrients, producing energy, and replicating.

3. All cells arise from pre-existing cells. This means that new cells are not spontaneously generated, but rather are produced by the division of existing cells.

These three principles are foundational to our understanding of biology and form the basis for further research into the workings of living organisms.