Cell theory has three basic tenets 1. All organisms are composed of one or more cells 2. The cell is basic unit of structure and function for all organIsms. 3. All cells arise only 区19. Schleiden(1804~1834) M 20.Schwann(1510-18s from preexisting cells by divisionCell theory has three basic tenets: 1. All organisms are composed of one or more cells. 2.The cell is basic unit of structure and function for all organisms. 3.All cells arise only from preexisting cells by division