What is an example of a cell theory?

In biology, cell theory is a scientific theory which describes the properties of cells. These cells are the basic unit of structure in all organisms and also the basic unit of reproduction. The cell theory states that: All living organisms are composed of cells. Multicellular organisms (example: humans) are composed of many cells while unicellular organisms (example: bacteria) are composed of only one cell. Cells are the basic unit of structure in all organisms.