The Cell Theory

1. The Cell Theory Biology 11 S. Dosman

2. What are cells? • Cells are defined as the smallest unit of life. • All living things are either unicellular (composed of only one cell) or multicellular (composed of more than one cell).

3. Robert Hooke • In 1665, English scientist Robert Hooke discovered cells while looking at cork under his primitive microscope . • Hooke first viewed cells in a thin slice of cork. He named them “cells” as they reminded him of the shape of the cells (rooms) in a monastery.

4. Cork cells • Hooke did not realize that what he was seeing was the cell walls and the empty space inside the dead cork cells. • So although he was the first to see cells he did not fully understand what he was seeing.

5. Anton van Leeuenhoek • Anton von Leeuenhoek was one of the major contributors to the invention of the microscope. • In 1674, Leeuenhoek first described living cells – blood, bacteria & unicellular pond organisms.

6. Robert Brown • Robert Brown was a Scottish botanist who is credited with naming the nucleus of the cell around 1820. • The nucleus had been observed before however he was the first to name it.

7. Felix Dujardin • In 1835, Felix Dujardin recognized the existence of one-celled organisms and that protoplasm seemed to be associated with all forms of life.

8. Matthias Schleiden • In 1838, the German botanist Schleiden stated that all plants are composed of cells.

9. Theodor Schwann • One year later in 1839, another German physiologist named Theodor Schwann stated that all animals are composed of cells.

10. Rudolph Virchow • In 1858, the Polish scientist Rudolph Virchow made a very important generalization that all cells come from other cells. • In other words, all cells come from pre-existing cells.

11. And after many, many years we have what many refer to as the cornerstone of modern Biology….

12. The Cell Theory • All living things are composed of cells. • The cell is the basic living unit of organization • All cells arise from pre-existing cells.