2. Anton van Leeuwenhoek When: mid 1600’s Discovery: Credited with inventing the light microscope – tiny microscope with a glass bead Observations: observed “animalcules” in a drop of pond water.

3. Robert Hooke When: 1665 Discovery: Named the cell Observations: Looked at cork under a microscope (also spiders, insects, flowers, etc.) Observed that cork was made of empty little boxes he named cells.

4. Robert Brown When: 1800’s Discovery: Nucleus Observations: Observed objects in the center of cells.

5. Matthias Schleiden* When: 1830’s Observations: Used the microscope to study plant parts. Conclusion: All plants are made of cells. The nucleus plays a role in cell reproduction. (He expanded on Brown’s observations.)

6. Theodor Schwann* When: 1830’s Observations: Observed many animals under the microscope. Conclusion: All animals are made of cells. All living things are made of cells.

7. Rudolf Virchow* When: 1850’s Hypothesis: Cells divide to form new cells. Conclusion: Every cell comes from a cell that already exists.

8. *Contributed to the Cell Theory The Cell Theory: All living things are made of one or more cells. Cells are the basic units of structure and function in organisms. All cells come from preexisting cells by cell division.