1. The Cell Theory

2. The Cell Theory
The CELL THEORY, or cell doctrine, states that all organisms are composed of similar units of organization, called cells.

3. History Leading up to Cell Theory
First compound microscope developed
Zacharias Jansen, of Middleburg, Holland, around the year 1595.

4. History Leading up to Cell Theory
Robert Hooke
English Scientist
Observed cells in cork
Approx. 1663

5. History Leading up to Cell Theory
Antony van Leeuwenhoek
First to observe bacteria and protozoa
Called “animacules”
Approx. 1673

6. Development of Cell Theory
Robert Brown
British botanist
Discovered the nucleus of a cell
1833

7. Development of Cell Theory
Theodor Schwann
German zoologist
Described animal cells with nucleus
1838

8. Development of Cell Theory
Matthias Schleiden
German botanist
Described plant cells with a nucleus
1838

9. Development of Cell Theory
Rudolf Virchow
German doctor
Stated “every cell originates from another cell”.
About 1855

10. Tenants of Modern Cell Theory
All known living things are made up of cells.
The cell is structural & functional unit of all living things.
All cells come from pre-existing cells by division.

11. Tenants of Modern Cell Theory
Cells contains hereditary information which is passed from cell to cell during cell division.
All cells are basically the same in chemical composition.
All energy flow (metabolism & biochemistry) of life occurs within cells.  

12. Historical Problem with the Cell Theory
Flew in the face of current belief
Then, current belief was life originated from non-living
Known as Spontaneous Generation
Disproved by Louis Pasteur

13. Pasteur’s Work
Nutrient broths were heated and sterilized in a flask with a straight neck and a curved neck.

14. Pasteur’s Work Step 1 of his procedure
As his control, straight-neck flask
Allowed bacteria to grow

15. Pasteur’s Work Step 2 of his procedure S-shaped necks.
With such necks bacteria could not enter
Therefore no bacteria grew.

17. Pasteur’s Work Straight-neck, bacteria S-shaped neck, no bacteria
So, based on his observations, what can you conclude?

18. General Observations 1. All cells posess: Cell membrane Cytoplasm
Ribosomes
Hereditary Information (DNA)

19. General Observations 2. Prokaryotes 3. Eukaryotes Single celled
Genetic material is a single, circular strand
No nucleus
No membrane bound organelles
3. Eukaryotes
Began as single-celled
Genetic material – many, strings
Has a nucleus
Membrane bound organelles
Became multi-celled

20. General Observations 4. Why are cells so small?
Exchange sufficient amount of material
Surface area to volume ratio