1. All living organisms are composed of one or more cells. This means that cells are the basic building blocks of all life, from the simplest bacteria to the most complex plants and animals.

2. The cell is the basic unit of structure and function in all living organisms. This means that cells are not only the building blocks of life, but they are also the smallest units that can carry out all the essential life processes, such as metabolism, growth, and reproduction.

3. All cells arise from pre-existing cells. This means that cells do not spontaneously generate from non-living matter. New cells are always produced by the division of existing cells.

These three principles form the foundation of our understanding of biology and have revolutionized our understanding of life.