(biology) the theory that cells form the fundamental structural and functional units of all living organisms; proposed in 1838 by Matthias Schleiden and by Theodor Schwann WordNet 3.0 & Open English WordNet

In biology, cell theory is a scientific theory first formulated in the mid-nineteenth century, that organisms are made up of cells, that they are the basic structural/organizational unit of all organisms, and that all cells come from pre-existing cells. Wikipedia

Scientific theory that living organisms are made up of cells, that they are the basic structural/organizational unit of all organisms, and that all cells come from pre-existing cells Wikidata

The scientific theory that all living organisms are made of cells as the smallest functional unit. Wiktionary

Scientific theory. Wiktionary (translation)