1. Chapter 3: Cell Structure and Function Section 3.1 – History of Cytology

2. Objective: • Identify the scientists that helped discover the cell theory. • Discuss the importance of the invention of the microscope.

3. History of the Cytology • Many people feel that Anton van Leeuwenhoek invented the first microscope. • However this has been disputed in recent years - Zacharias Jansen is now thought to be the original inventor in 1595.

4. History of the Cytology • During the 1600’s, Leeuwenhoek used his microscopes to look at drops of pond water and other liquids. • He discovered that the water contained tiny living things. Animalcules

5. History of Cytology • At about the same time Robert Hooke, English physicist, used a microscope to observe plants. • He pointed out that the woody parts (cork) of plants contained tiny rectangular chambers, which he called cells.

6. History of Cytology • In 1839, German biologist Theodor Schwann, found that some animal tissues closely resembled the circular tissues of plants. • As he observed the tissues with better and better microscopes, he concluded that animals are composed of cells as well.

7. History of Cytology • Also during this time, Robert Brown discovered an object near the center of many cells – the nucleus. • German biologist Matthias Schleiden expanded on Brown’s work, suggesting that the cell’s nucleus plays a role in cell reproduction.

8. History of Cytology • In 1855, German physician Rudolf Virchow proposed that animal and plant cells are produced only by cell division.

9. The discoveries and observations of these scientists make up what is now known as the cell theory.

10. Cell Theory • All living things are composed of cells. • Cells are the smallest working units of living things. • All cells come from preexisting cells by cell division.