Cell theory — incorrect statement

All cells have cell walls.

Explanation

"All cells have cell walls" is incorrect. Cell walls are found in plant cells, fungi, and bacteria — but animal cells do not have cell walls. The correct tenets of cell theory are: (1) cells are the fundamental units of life, (2) cells are the smallest entities that can be called living, (3) all organisms are made up of one or more cells, and (4) cells arise only from the division of other cells.