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.

States that all life is composed of cells, that cells arise only from other cells, and that the cell is the fundamental unit of structure and function in living organisms. © 2005 by W. H. Free [..]

n. in biology, refers to the scientific study which proposes that cells are the basic unit of structure making up all living organisms. First proposed for plants by German botanist Matthias Schleiden [..]

Principle that all organisms are composed of one or more cells. Proposed in 1839 by Theodor Schwann for animals and by Matthias Jakob Schleiden for plants.

one of the five basic principles of biology. It states that the cell is the basic unit of life. Centrioles

major theory based on observations and conclusions by many scientists that states that the cell is the basic unit of life, organisms are composed of one or more cells, and all cells come from other ce [..]

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.

(biology) the theory that all living organisms are made of cells as the smallest functional unit