1. Cell Theory The idea of cell started with Robert Hooke. He first observed cork cells and named the compartments he saw “cells”, named after the rooms that monks lived in. Leeuwenhoek was one of the first to look at living cells. He called the living things he saw “animalcules”.

2. Cell Theory The cell theory grew out of the work of many scientists and improvements in the microscope. Many scientists contributed to the cell theory. More was learned about cells as microscopes improved. The cell theory is a unifying concept of biology.

3. Cell Theory The cell theory has three principles. All organisms are made of cells.

4. Cell Theory The cell theory has three principles. All organisms are made of cells. All existing cells are produced by other living cells.

5. Cell Theory The cell theory has three principles. All organisms are made of cells. All existing cells are produced by other living cells. The cell is the most basic unit of life.

6. Cell Theory Prokaryotic cells lack a nucleus and most internal structures of eukaryotic cells. All cells share certain characteristics.

7. Cell Theory Prokaryotic cells lack a nucleus and most internal structures of eukaryotic cells. All cells share certain characteristics. Cells tend to be microscopic. Bacterium (colored SEM; magnification 8800x)

8. Cell Theory Prokaryotic cells lack a nucleus and most internal structures of eukaryotic cells. All cells share certain characteristics. Cells tend to be microscopic. All cells are enclosed by a membrane. Bacterium (colored SEM; magnification 8800x) cell membrane

9. Cell Theory Prokaryotic cells lack a nucleus and most internal structures of eukaryotic cells. All cells share certain characteristics. Cells tend to be microscopic. All cells are enclosed by a membrane. All cells are filled with cytoplasm. Bacterium (colored SEM; magnification 8800x) cell membrane cytoplasm

10. Cell Theory There are two cell types: eukaryotic cells and prokaryotic cells.

11. Cell Theory There are two cell types: eukaryotic cells and prokaryotic cells. Eukaryotic cells have a nucleus. nucleus cell membrane

12. Cell Theory There are two cell types: eukaryotic cells and prokaryotic cells. Eukaryotic cells have a nucleus. Eukaryotic cells have membrane- bound organelles. nucleus cell membrane organelles

13. Cell Theory There are two cell types: eukaryotic cells and prokaryotic cells. Prokaryotic cells do not have a nucleus. nucleus cell membrane organelles

14. Cell Theory There are two cell types: eukaryotic cells and prokaryotic cells. Prokaryotic cells do not have a nucleus. Prokaryotic cells do not have membrane-bound organelles. nucleus cell membrane organelles cytoplasm

15. Cell Theory Some prokaryotic and some eukaryotic cells have flagella. Flagella allow the organism to move the organism through it’s environment.

16. Cell Theory Some eukaryotic cells have cilia. Cilia allow the organism to move the organism through it’s environment. Cilia also can be used to move things along the cell’s surface. For example, cilia on the cells of the human respiratory system sweep mucus and other debris out of the lungs.