Advanced Biology 11
Spontaneous Generation and Biogenesis
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Spontaneous generation: life comes from non-living materials
Biogenesis: life comes from life
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Aristotle (philosopher, Greece, 384-322 BC) believed life could come from sexual reproduction,
asexual reproduction and from interaction of non-living materials (mixture of earth, fire, water,
air and pneuma(Latin word for soul)
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aphids arise from the dew on plants, fleas from rotting matter, and mice from dirty hay
Jan Baptist van Helmont (Chemist, Belgium, 1579-1644)
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developed recipe for making mice.
Place a dirty shirt or some rags in an open pot or barrel containing a few grains of wheat
or some wheat bran, and in 21 days, mice will appear. There will be adult males and
females present, and they will be capable of mating and reproducing more mice.
Francesco Redi, Italian Physician, 1668
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First against abiogenesis
Experimented to proved that maggots did not come from rotting meat
First experiment:
 Used 4 different jars: snake, eel, fish, veal (control group, uncovered)
 Placed the same contents into 4 other jars
(experimental group, sealed)
 Maggots grew in the uncovered jars but not the sealed jars.
 Experimental evidence was not approved because he did not allow air to enter
the jars.
o All experiments MUST consider all aspects of the question.
o Redi redid the experiment and this time used a mesh over the jars.
 No maggots grew in the experimental group
 Spontaneous generation was defeated.
John Needham, English Biologist (1713-1781)
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Took another look at SPONTANEOUS GENERATION with the use of the microscope
Found that microbes grew in a broth that was left open to the air, even after boiling the
broth
o boiling should kill all microbes
o Surmised that the microbes grew from spontaneous generation.
Lazzaro Spallanzani, Italian (1767)
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Repeated Needham’s experiment with slight changes
Boiled the broth longer and sealed the containers of the experimental group
No bacteria grew in experimental group
Spontaneous generation defeated again!!
Scientists were skeptical, Spallanzani had discounted the active principle, AIR.
Advanced Biology 11
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Louis Pasteur, French Scientist, 1864
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Changed Spallanzani’s experiment
He used the broths, but redesigned the flask that was used to an S-shaped flask
The neck of the flask would allow air to enter, but trap the dust particles in its neck
No microbes grew, spontaneous generation was defeated using approved scientific
evidence.
Scientific Method
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today scientists examine all variables carefully and consider each independently
Control variable: the variable that remains the same
Manipulated variable(independent): the variable that we as scientists change
Responding variable(dependant): the variable that we measure for results