Which statement is NOT part of the cell theory?

• A. All organisms are made of cells.
• B. Cells are the basic units of structure and function.
• C. New cells arise from existing cells.
• D. Mitochondria are the site of energy production.

Answer: (D)

Cell theory describes the basic properties of cells and how they come to be. The ideas that all organisms are made of cells and that cells are the basic units of structure and function are central tenets, and the notion that new cells arise from existing cells is another core principle. The statement about mitochondria being the site of energy production is about what a specific organelle does inside cells, not a principle defining cell theory. It’s true biology, but it doesn’t express the fundamental claims about cells’ origin or organization, which is why it’s not part of the cell theory.