Which is NOT part of the three parts of cell theory?

• A. All organisms are made of cells
• B. Cells are the basic unit of life
• C. Cells come from preexisting cells
• D. The nucleus controls cellular activities

Answer: (D)

Cell theory describes how life is organized and how cells arise. The three accepted ideas are that all living things are made of cells, the cell is the basic unit of life, and new cells come from preexisting cells. The statement that the nucleus controls cellular activities describes what happens inside a cell—how DNA in the nucleus guides gene expression and regulates processes—but it’s about intracellular regulation rather than a universal claim about what cells are or how they originate. Because of that, it isn’t one of the main postulates of cell theory, whereas the other ideas define the relationship between organisms and cells and how cells reproduce.