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The Cell Theory
The Cell Theory
All organisms are composed of
similar units of organization,
called cells.
History Leading up to Cell
Theory
1. First compound microscope developed
Zacharias Jansen, around the year
1595 in Holland.
History Leading up to Cell
Theory
2. Robert Hooke
English
Scientist
Observed
cells in cork
Approx.
1663
History Leading up to Cell
Theory
3. Antony van
Leeuwenhoek
First to observe
bacteria and
protozoa
Called
“animacules”
Approx. 1673
Development of Cell Theory
1. Robert Brown
British botanist
Discovered the
nucleus of a
cell
1833
Development of Cell Theory
2. Theodor
Schwann
German doctor
Described
animal cells
with nucleus
1838
Development of Cell Theory
3. Matthias Schleiden
German botanist
Described plant
cells with a
nucleus
1838
Development of Cell Theory
4. Rudolf Virchow
German doctor
Stated “every cell
originates from
another cell”.
About 1855
Tenants of Modern Cell
Theory
1. Everything alive is made up of cells.
2. The cell is the smallest unit of life.
3. All cells come from pre-existing cells.
Historical Problem with the
Cell Theory
Disagreed with current belief of the
time
Which was known as
Spontaneous Generation
- life originated from non-life
Disproved by Louis Pasteur
Pasteur’s Work
Nutrient broths were heated and
sterilized in a flask with a straight
neck and a curved neck.
Louis Pasteur
1822-1895
Father of the Germ
Theory
QuickTime™ and a
decompressor
are needed to see this picture.
Pasteur’s Work
1.
Step 1 of his procedure
As his control, he used a straight-neck flask
This allowed bacteria to grow
Pasteur’s Work
2. Step 2 of his procedure
S-shaped necks.
These necks did not allow
bacteria to enter
Therefore no bacteria grew.
Pasteur’s Work
Straight-neck, bacteria
S-shaped neck, no bacteria
So, based on his observations,
what can you conclude?
General Observations
All cells posess:
1. Cell membrane
2. Cytoplasm
3. Ribosomes
Prokaryotes
1. Smallest and
simplest of all cells
2. Single celled
3. Genetic material is a
single, circular strand
4. No nucleus
5. No membrane bound
organelles
6. Have a cell wall
7.Lived over 3.5 billion
years ago
8. For 1 billion years were
the only organisms on
earth
9. Include
a.Archabacteria
b.Eubacteria
10. Known as Bacteria
Eukaryotes
1. Began as singlecelled
2. Genetic material
– many, strings
3. Has a nucleus
4. Membrane bound
organelles
5. Became multicelled
6. Evolved about 2.5
billion years ago
7. Protists
8. Fungi
9. Plants
10. Animals