1. All living organisms are composed of one or more cells. This means that cells are the basic building blocks of life, and everything that is considered alive 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 that occur in a living organism happen within cells, and the structure of a cell determines its function.

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

These three ideas form the foundation of our understanding of biology and are fundamental to many scientific disciplines.