It is necessary for students to understand the history of cell theory development for several reasons. Learning about the early scientists who discovered cells and contributed ideas that led to the modern cell theory provides context for why we accept cells as the fundamental unit of life. Understanding the process of how the cell theory was developed and built upon over time shows how scientific knowledge advances through experiments, observations, and collaboration between scientists. Tracing the key experiments that helped reject ideas like spontaneous generation helps students appreciate how scientific understanding progresses. A brief overview of the history helps students grasp the full significance and universal acceptance of the modern cell theory in biology.

1. Spontaneous
generation

2. Learning competency
✗ explain the postulates of the cell
theory.
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3. Arrange the jumbled words into meaningful words
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1. ONEOUNTSPAS
2. CLEL
3. CLEL TEROHY
4. LNVINNOIG
5. IONSGABEEIS
6. PUNEMA
7. MOAGGTS
8. CMIOROCSPE
9. NCLEUUS
10. ESTXNIIG

4. Arrange the jumbled words into meaningful words
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1. SPONTANEOUS
2. CELL
3. CELL THEORY
4. NONLIVING
5. ABIOGENESIS
6. PNEUMA
7. MAGGOTS
8. MICROSCOPE
9. NUCLEUS
10. EXISTING

5. !
A. Where does life come from?
B. In the past, what is the
people’s understanding about cell?

6. SPONATEOUS GENERATION
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✗ For much of history, people believed that animals could
come from non-living sources. They thought:
✗ Frogs developed from falling drops of rain
✗ mice arose from sweaty underwear
✗ and flies arose from decaying meat.
✗ This is called abiogenesis
✗ Also known as spontaneous generation

7. SPONATEOUS GENERATION
7
Before 1860s many scientists believed in
Spontaneous generation, i.e.: That living
organisms could arise spontaneously from
nonliving matter:
✗ Mice come from rags in a basket.
✗ Maggots come from rotting meat.
✗ Ants come from honey.
✗ Microbes come from spoiled broth.

8. SPONATEOUS GENERATION
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✗ In the past, people
believed what they were
told by “authorities” such
as the Church, or the
ancient Greek philosopher
Aristotle
✗ Questioning Aristotle was
like questioning the
Church..

9. SPONATEOUS GENERATION
9
✗ One “scientist” put forward the
belief that mice could be
generated spontaneously from
wheat and a sweaty shirt.
✗ The wheat provided the
“nutritive power” and the shirt
provided the “active principle.”
✗ “active principle” = a mysterious
“ life-force ” that allowed
spontaneous generation to
occur.

10. SPONATEOUS GENERATION
10
The first serious attack on the idea of
spontaneous generation was made in 1668
by Francesco Redi, an Italian physician and
poet.

11. SPONATEOUS GENERATION
11
At that time, it was widely held that maggots
arose spontaneously in rotting meat. Redi
believed that maggots developed from eggs
laid by flies.

12. SPONATEOUS GENERATION
12
To test his hypothesis, he set out meat in a
variety of flasks, some open to the air, some
sealed completely, and others covered with
gauze. As he had expected, maggots
appeared only in the open flasks in which the
flies could reach the meat and lay their eggs.

13. SPONATEOUS GENERATION
13

14. SPONATEOUS GENERATION
14

15. SPONATEOUS GENERATION
15
“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

16. SPONATEOUS GENERATION
16
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 anything.

17. SPONATEOUS GENERATION
17

18. SPONATEOUS GENERATION
18
Redi’s Conclusion
• “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.

19. SPONATEOUS GENERATION
19
John Needham (English Clergyman)
wondered if this would work with
micro organisms in1745.
Everyone knew that boiling killed
organisms.
Needham prepared various broths
and showed that they contained
microbes.

20. SPONATEOUS GENERATION
20
Then he boiled them, and showed that
there were no longer any microbes.
He ensured the stoppers were loose,
so that air would not be excluded
Then, after a few days, microbes had
reappeared!
This was “proof” that the microbes
had spontaneously generated from
the non-living broth.

21. SPONATEOUS GENERATION
21
BUT: how was this evidence of a faulty
experiment?
what ERROR in experimental method is shown here?
Hypothesis: microbes MUST HAVE arisen
spontaneously from the broth.
Assumption: there is no other place the microbes
could come from (other than the broth).
error: microbes could have come from the air!

22. SPONATEOUS GENERATION
22
An Italian priest, Lazzaro Spallanzani, was not convinced, and he
suggested that perhaps the microorganisms had entered the
broth from the air after the broth was boiled, but before it was
sealed.
To test his theory, he modified Needham's experiment - he
placed the chicken broth in a flask, sealed the flask, drew off the
air to create a partial vacuum, then boiled the broth. No
microorganisms grew. Proponents of spontaneous generation
argued that Spallanzani had only proven that spontaneous
generation could not occur without air.

23. SPONATEOUS GENERATION
23

24. SPONATEOUS GENERATION
24
Needham criticizes Spallanzani’s first experiment
BUT Needham said: you boiled it TOO
LONG, and:
You spoiled the vegetative power by boiling.
You killed the ability of the broth to give life.
Life can still come from broth -- but the broth
must not be “damaged” by boiling.

25. SPONATEOUS GENERATION
25
Spallanzani’s second experiment
he did TIMED BOILINGS
then left them partially sealed
some partially sealed, some hermetically
sealed as in his previous experiment
hypothesized that more boiling should
lead to less life
he left some jars as Needham had (leaky
seals), to ensure “active principle” was not
damaged

26. SPONATEOUS GENERATION
26
Spallanzani ’ s second experiment
results:
this showed TWO main things:
boiling did NOT damage broth’s ability to
support life
growth depended on the SEAL only

27. SPONATEOUS GENERATION
27
Louis Pasteur 1859– ✗ used swan-necked flask
✗ flask allowed in air, but
trapped dust (and microbes)
✗ boiled infusion
✗ showed that NO growth
occurred, even after many
days
✗ BUT -- what about damaging
the “active principle”?
(French chemist) entered a
contest sponsored by
French Academy of
Sciences to prove or
disprove Spontaneous
generation.

28. SPONATEOUS GENERATION
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29. SPONATEOUS GENERATION
29
✗ Pasteur showed that the
active principle was NOT
damaged
✗ at any later time, he could tip
the flask
✗ this allowed nutrient broth to
contact the dust
✗ this carried microbes into the
broth
✗ result: growth!

30. SPONATEOUS GENERATION
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✗ Pasteur showed that the
active principle was NOT
damaged
✗ at any later time, he could tip
the flask
✗ this allowed nutrient broth to
contact the dust
✗ this carried microbes into the
broth
✗ result: growth!

31. Discovery
of the Cell
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32. History of cell
32

33. Development of cell theory
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• In 1838 and 1839, a German botanist by the name
of Matthias Schleiden and German zoologist by
the name of Theodore Schwann viewed plants
and animals under a microscope and discovered
that plants and animals are both made of cells.
• In 1855 a Prussian (modern day German)
physician by the name of Rudolph Virchow
collaborated his ideas with the other two scientists
and they developed the Cell Theory.

34. cell theory
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• The ideas of these three men led to the creation of
the cell theory. These are the three main principles
of cell theory.
1. All living organisms are made up of cells.
2. Cells are the most basic unit of life.
3. Cells only come from the division of pre-existing
cells. In other words, spontaneous generation of cells
does not occur.

35. Write a short paragraph discussing why
is it necessary for a student like you to
understand and to look back on the
history of the development of the cell
theory. Make your answer brief and
concise, express your answer using 5-10
sentences only.
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