1. The document discusses the history of theories on the origins of life, from early ideas of spontaneous generation to modern scientific understanding. 2. It describes key experiments that helped disprove spontaneous generation, including Redi's experiments showing that maggots come from flies rather than rotting meat, and Pasteur's experiments showing that microbes could infiltrate supposedly sterile environments. 3. Pasteur's experiments, which demonstrated that sterile broth remained microbe-free unless exposed to air, definitively disproved spontaneous generation and supported the theory that all life arises from pre-existing life, known as biogenesis.

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Introduction to
Biological Sciences
Type in the chat box ‘present sir’ for your attendance this afternoon.

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Introduction to
Biological Sciences

4. Objectives:
 Explore the different theories on
the origin of life.
 Understand the events that lead
to the understanding of how life
came from life.
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Biology – The Study of Life
 Life arose more than
3.5 billion years ago
 First organisms (living
things) were single
celled
 Only life on Earth for
millions of years
 Organisms changed
over time (evolved)

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 New organisms arose
from older kinds
 Today there are millions
of species
 They inhabit almost
every region of Earth
today

7. Question:
What does it mean
to be alive?
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8. Short Activity
Look around you and make a list of 2
objects you consider as living things.
Record your answers on a paper and give
the reason/s as to why you considered
the identified objects as living things.
Share this with the class.
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9. Definitions of Life
 Life is the aspect of existence that
processes, acts, reacts, evaluates, and evolves
through growth (reproduction and
metabolism). (Tom Baranski)
 Life is self-organising chemistry which
reproduces itself and passes on its evolved
characteristics, encoded in DNA. (Dr. Harry
Fuchs)
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10.  Life is an arrangement of molecules with
qualities of self-sustenance and self-
replication. (John Talley)
 Life is self-reproduction with variations.
(Edward Trifonov)
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11. Characteristics of Life
 Life is Organized
 Life maintains Internal Constancy
 Life requires and uses Energy
 Life Evolves
 Life Reproduces
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12. How did life
begin?
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13. Panspermia and
Primordial Soup Theory
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14. Primordial Soup Theory
 When the earth was young, the oceans were filled
with simple chemicals important for life which
would eventually self-assemble into simple living
cells.
 proposed in the 1920's by two researchers working
independently: Alexander Oparin in the USSR and
British geneticist J. B. S. Haldane.
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15. The Miller-Urey Experiment
Stanley Miller, supervised by Harold Urey, mixed
four simple chemicals (CH4, NH3, H2O, H2) in glass
tubes, which were heated and shocked with electrical
sparks to mimic lightning. The experiment made
several amino acids, the building blocks of proteins.
The Miller-Urey experiment showed that the
chemicals of life could form naturally.
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17. Panspermia Theory
 An idea that life must have begun elsewhere in the
universe and was carried to Earth by meteoroids.
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18. Where?
As to the location,
many still favor the sea
but not necessarily the
open sea: a vocal minority
of researchers think life
began in alkaline vents on
the sea floor. Others
think life began in ponds
on land, perhaps
geothermal pools like
those in Yellowstone.
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19. Where does new
life come from?
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20. The Spontaneous Generation Theory
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21. Spontaneous Generation Theory
 Proposed by Greeks including Aristotle.
 The notion that life can arise from non-
living matter. (Life came from nothing.)
 Life arose from non-living material if
the material contained pneuma (“vital
heat”).
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22. Examples of Spontaneous Generation
 Bougonia
 Written by the Roman poet Virgil as a recipe in
which one could make synthetic bees.
 The readers were instructed to beat a bovine
calf to death, block up its mouth and nose,
before leaving the carcass on a bed of cinnamon
sticks and thyme.
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23.  How mice came to life
 The “recipe” for making a mouse requires that
sweaty underwear should be placed over an open-
mouth jar containing husks of wheat inside for
around 21 days.
 A simple explanation: mice like to eat wheat and,
with ease of entering a jar and finding a dark and
safe space, would be most likely to find
themselves at home and have a few offspring in
the new nest.
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24.  Wet soil after a flood was believed to create
amphibians such as frogs and toads.
 Maggots came from meat.
 Salamanders were thought to be borne within fire
(they often hide inside logs and were probably trying
to escape the blaze!).
 Oyster shells were believed to form as the earth
solidified around them and the “vital heat” grew the
creature within.
 Crocodiles in Egypt were thought to have emerged
from the mud with the sunshine as a catalyst.
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25. !!!
Spontaneous generation (also referred
to as abiogenesis) is an incorrect and
obsolete hypothesis about the possibility
of life forms being able to emerge from
non-living things. This theory peristed
until the 17th century.
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26. Disproving the
Spontaneous Generation Theory
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27. Francesco Redi
 An Italian physician who performed an experiment in
1668 that was one of the first to refute the idea that
maggots (the larvae of flies) spontaneously generate
on meat left out in the open air.
 He predicted that preventing flies from having direct
contact with the meat would also prevent the
appearance of maggots. Redi left meat in each of the
six containers
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28. Redi's Experiment
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29. His hypothesis was supported when
maggots developed in the uncovered jars, but
no maggots appeared in either the gauze-
covered or the tightly sealed jars. He
concluded that maggots could only form when
flies were allowed to lay eggs in the meat,
and that the maggots were the offspring of
flies, not the product of spontaneous
generation
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30. John Needham
 A known supporter of SGT
 He briefly boiled broth infused with plant or animal
matter, hoping to kill all pre-existing microbes. He
then sealed the flasks. After a few days, Needham
observed that the broth had become cloudy, and a
single drop contained numerous microscopic creatures.
He argued that the new microbes must have arisen
spontaneously.
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32. Lazzaro Spallanzani
 Did not agree with Needham's experiment.
 As in Needham’s experiment, broth in sealed jars and
unsealed jars was infused with plant and animal
matter. Spallanzani’s results contradicted the findings
of Needham: Heated but sealed flasks remained clear,
without any signs of spontaneous growth, unless the
flasks were subsequently opened to the air.
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33. Spallanzani's
Experiment
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34. The debate continues....
Spallanzani: Microbes were introduced into these
flasks from the air.
Needham: Life originates from a “life force” that
was destroyed during Spallanzani’s extended
boiling. Any subsequent sealing of the flasks then
prevented new life force from entering and
causing spontaneous generation.
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35. French Academy of Science
 Offered a prize for the
resolution of the debate.
 Setup a contest to prove or
disprove Spontaneous Generation.
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36. Louis Pasteur
Pasteur filtered air through a gun-cotton filter
and, upon microscopic examination of the
cotton, found it full of microorganisms,
suggesting that the exposure of a broth to air
was not introducing a “life force” to the broth
but rather airborne microorganisms.
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38. Felix Archimede Pouchet
 “animals and plants could be generated in a
medium absolutely free from atmospheric air
and in which therefore no germ of organic
bodies could have been brought by air.
 He used hay medium in his experiments.
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39. Pouchet's experiment still had growth
even when he followed Pasteur's
methods. What might be the cause?
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40. What's the difference?
The yeast extract and sugar broth of
Pasteur could be sterilized with just a
few minutes of boiling, whereas the hay
medium of Pouchet required heating for
several hours to accomplish sterilization.
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41. Pasteur’s set of experiments
irrefutably disproved the theory of
spontaneous generation and earned
him the prestigious Alhumbert Prize
from the Paris Academy of Sciences
in 1862.
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42. "Omne vivum ex vivo"
Life only comes from life.
(biogenesis)
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