The Cell Theory

Discovery of the cells
Some Random Cell Facts
The average human being is composed
of around 100 Trillion individual cells!!!
 It would take as many as 50 cells to
cover the area of a dot on the letter “i”
Previous to the Discovery of
the cell…
What was happening at that time?
Spontaneous Generation
For much of history, people believed that animals could come
from non-living sources. They thought:
Frogs developed from falling drops of rain
mice and snakes came from hay barns and grain bins
flies arose from decaying meat.
This is called abiogenesis
 Also known as spontaneous generation
These ideas
were followed
because people
accepted what
they were told
The Power of Authority
In the past, people
believed what they were
told by “authorities” such
as the Church, or the
ancient Greek philosopher
 Questioning Aristotle was
like questioning the
Discovery of Cells
1665- English Scientist, Robert Hooke, discovered
cells while looking at a thin slice of cork.
He described the cells as tiny boxes or a honeycomb
He thought that cells only existed in plants and fungi
Anton van Leuwenhoek
1673- Used a handmade microscope to observe pond
scum & discovered single-celled organisms
He called them “animalcules”
He also observed blood cells from fish, birds, frogs,
dogs, and humans
 Therefore, it was known that cells are found in
animals as well as plants
HOW MANY YearS 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.
 Examples:
-Mice from dirty clothes/corn husks
-Maggots from rotting meat
Italian doctor poet, Francesco Redi. In the mid-1600s,
i designed a controlled experiment
It took hundreds of years
of experiments to
convince people that
spontaneous generation
does not occur.
1668 -- Francisco Redi (Italian physician & poet)-attempted to disprove the theory of Spontaneous
“The flesh of dead animals cannot engender
worms unless the eggs of the living being
deposited therein”
Put dead snakes, eels, and veal in large wide
mouthed vessels. Sealed one set with wax
and left the other set open to air.
 Decaying meat was teeming with maggots,
sealed meat had no maggots
 Wax sealed vessels failed to produce maggots
because flies were unable to reach the meat
Redi’s critics said:
You have too many variables
There is a lack of access and
a lack of air.
We ALL know that everything
needs air
Of course no flies grew!
You haven’t proven
Redi part 2 – answer to critics
fine mesh allows in air,
but not flies
flies laid eggs on top of mesh
no maggots in meat
Redi’s Conclusions:
“All living beings come from seeds of
the plants or animals themselves”
 However, if someone were to
demonstrate even one exception to this
hypothesis, then Redi’s hypothesis
would be rejected.
19th Century Advancement
Much doubt existed around Spontaneous Generation
Conclusively disproved by Louis Pasteur
Pasteur: Ummm, I
don’t think so!!!
(French chemist) entered a contest sponsored by French Academy
of Sciences to prove or disprove Spontaneous generation.
used swan-necked
flask allowed in air, but
trapped dust (and
boiled infusion
showed that NO
growth occurred,
even after many days
BUT -- what about
damaging the “active
Pasteur squashes the idea of abiogenesis
Since then, no one has been able to refute Pasteur’s
scientists everywhere soon came to accept that
abiogenesis did NOT EXIST.
but: then how did life on this planet start in the first
The Cell Theory
Development of Cell Theory
1838- German Botanist, Matthias Schleiden,
concluded that all plant parts are made of cells
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
The 3 Basic Components of the Cell Theory
were now complete:
1. All organisms are composed of one or more
cells. (Schleiden & Schwann)(1838-39)
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)
.1. All organisms are composed
of one or more cells.
2. The cell is the basic unit of
life in all living things.
3. All cells are produced by the
division of preexisting cells.
Can you imagine…donut’s are
produced by the division of
preexisting donuts!
Modern Cell Theory
Modern Cell Theory contains 4 statements, in
addition to the original Cell Theory:
The cell contains hereditary information(DNA) which
is passed on from cell to cell during cell division.
 All cells are basically the same in chemical
composition and metabolic activities.
 All basic chemical & physiological functions are
carried out inside the cells.(movement, digestion,etc)
 Cell activity depends on the activities of sub-cellular
structures within the cell(organelles, nucleus, plasma
How Has The Cell Theory Been Used?
The basic discovered truths about cells, listed
in the Cell Theory, are the basis for things
such as:
Disease/Health/Medical Research and Cures(AIDS,
Cancer, Vaccines, Cloning, Stem Cell Research, etc.)
Some Parting Thoughts
It is amazing to think that the cells that make
up our bodies are just as alive as we are.
Humans are just an intricately designed
community of cells, which must work
together to survive.
 Cells, in my opinion, are one of the strongest
cases for intelligent design.
Stem cells (embryonic stem cells)
distinguished from other cell types by two important
First, they are unspecialized cells capable of renewing
themselves through cell division, sometimes after
long periods of inactivity.
Second, under certain physiologic or experimental
conditions, they can be induced to become tissue- or
organ-specific cells with special functions.