The ideas that all living matter consists of cells, cells are the structural and functional units of life, and all cells come from preexisting cells. 61
One of the four (or five) unifying concepts in biology. The cell theory states that all living things are composed of at least one cell and that the cell is the fundamental unit of function in all organisms. Corollaries: the chemical composition of all cells is fundamentally alike; all cells arise from preexisting cells through cell division.
All living things are composed of cells; cells arise only from other cells. No exception has been found to these two principles since they were first proposed well over a century ago.
The cell theory is a scientific theory that is one of the foundations of biology.