In the history of cell biology, how did Zacharias Janssen most directly contribute to the development of ideas that later supported cell theory?

• A. He is often credited with helping invent the compound microscope, which enabled later scientists to observe cells and microorganisms.
• B. He discovered the cell nucleus and described it as a central component of the cell.
• C. He proposed that all living organisms are composed of cells and that cells arise from preexisting cells.
• D. He demonstrated that spontaneous generation does not occur by showing microbes come from other microbes.

Answer: (A)