Transcript The Cell Theory

The
Cell
Theory
WHAT ARE CELLS AND WHERE DID THEY COME FROM?
What is a Cell?

Use the pictures below and follow the procedure on pg. 168
Plant Cells
Nerve Cell
Paramecium
Bacteria cells
Think About It
1.
Use your observations to write your own definition of a
“cell” (may use background knowledge)
Example: A cell is a structure within a living thing that has a
definite boundary enclosing the material inside
2.
Classify the cells that you observed into two or more
groups. Explain what characteristics you used to put
each cell in a particular group.
Possible answers: Plant cells vs. other cells, cells with a
nucleus vs. cells without a nucleus
The Cell Theory
Erythrocytes: Red Blood Cells (RBC) carry O2 and CO2
Some Random Cell Facts

The average human being is composed of
around 100 Trillion individual cells

There are about 200 different cell types in the
human body

There are more bacterial cells in a human body
than human cells (19:1)

Cells will “self destruct” if damaged or infected
(called apoptosis)
Visualizing Cells
Light Microscope
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Can observe living cells
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Magnification
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Eyepiece (10x)
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Objective lens (DIN)
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Red= DIN 4 = 4x
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Yellow= DIN 10 = 10x
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Blue= DIN 40 = 40x
Magnification =
Eyepiece X Objective
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low power
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medium power
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4x * 10x = 40x
10x * 10x = 100x
high power
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40x * 10x = 400x
Electron Microscopes
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Can magnify much higher than
light microscopes
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Very expensive

Big and non-portable
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2 types
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S.E.M. (scanning)
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T.E.M. (transmission)
Scanning Electron
Microscope (S.E.M.)
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Shows an image of the
scanned surface
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Useful for looking at “3-D”
structure of specimens
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Butterfly Eye S.E.M. 22,000X
Transmission Electron
Microscope (T.E.M.)
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Shows a cross section
view of specimens
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Useful for viewing the
“insides”
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Plant Leaf T.E.M. 42,000x
Discovery of Cells

1665- English Scientist, Robert
Hooke, discovered cells while
looking at a thin slice of cork.
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He described the cells as tiny
boxes or a honeycomb
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He thought that cells only
existed in plants and fungi
Anton van Leuwenhoek
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1673- Used a handmade
microscope to observe pond
scum & discovered singlecelled organisms
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He called them “wee beasties”
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He also observed blood cells
from fish, birds, frogs, dogs, and
humans
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Therefore, it was known that
cells are found in animals as
well as plants
150-200 Year Gap???

Between the Hooke/Leuwenhoek
discoveries and the mid 19th
century, very little cell
advancements were made.

This is probably due to the widely
accepted, traditional belief in
Spontaneous Generation.
Spontaneous Generation

For much of history, people believed that
animals could come from non-living sources.

Historical documents contain “recipes”
for creating creatures such as: bees,
frogs, mice, etc.
 These
“recipes” were based on
observations.

When the Nile river flooded, soon many frogs
appeared in the mud.

If damp rags were left in a pile of wheat grain, many
mice appeared 21 days later.
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
Jar-1
Left open:
Maggots
developed
Flies were
observed
laying eggs
on the meat
in the open
jar
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Jar-2
Covered with
netting:
Maggots
appeared on
the netting
Flies were
observed laying
eggs on the
netting
Francisco Redi
• Jar-3
• Sealed: No
maggots
developed
Lazzaro Spallanzani (1767)
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Set up an experiment to test whether a “vital
force” in the air could give rise to microorganisms.
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Spallanzani’s hypothesis:
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Beef broth becomes cloudy due to bacteria
present in the air. The bacteria from the air enter
the broth and contaminate it, rather than the
bacteria arising from the air or broth itself.
Spallanzani’s Experiment
The Big Prize

The Paris Academy of Science offered a
prize to the person who could best
resolve the spontaneous generation
debate once and for all.
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And the winner was…
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Louis Pasteur (1864):
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A scientist who designed an experiment
using a flask that would allow air containing
the “vital force” to enter the flask, but would
keep microorganisms out.
Louis Pasteur Broth
Experiment
Development of Cell Theory
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1838- German Botanist, Matthias
Schleiden, concluded that all plant
parts are made of cells
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1839- German physiologist, Theodor
Schwann, who was a close friend of
Schleiden, stated that all animal
tissues are composed of cells.
Development of Cell Theory

1858- Rudolf Virchow, German
physician, after extensive study of
cellular pathology, concluded that
cells must arise from preexisting cells.
The Cell Theory Complete
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The 3 Basic Components of The Cell Theory
were now complete:
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1. All organisms are composed of one or more
cells. (Schleiden & Schwann)(1838-39)
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2. The cell is the basic unit of life in all living
things. (Schleiden & Schwann)(1838-39)

3. All cells are produced by the division of
preexisting cells. (Virchow)(1858)
Prokaryotes vs. Eukaryotes
Prokaryotes
Eukaryotes
No Nucleus: DNA (the
genetic material) floats
around in cytoplasm
(forms a nucleoid)
Yes Nucleus: Membrane
bound organelle that
contains DNA (the
genetic material)
No membrane-bound
organelles
Yes membrane-bound
organelles
Much smaller in size
Generally larger in size
Very simple structure
More complex structure