In the history of cell biology, how did Antonie van Leeuwenhoek contribute to the development of cell theory?

• A. He discovered the cell nucleus and argued it controls cell division and heredity.
• B. He used handcrafted single-lens microscopes to observe and describe living microorganisms (“animalcules”), providing early evidence that microscopic life exists.
• C. He developed the first cell-staining dyes and used them to identify chromosomes during mitosis.
• D. He proposed that all living organisms are composed of cells and that cells arise only from preexisting cells.

Answer: (B)