Chapter 14* Origin of Life

Principle that all living things come from
other living things.
 Before the 17th century (1600s), another
idea was widely accepted.
 Spontaneous generation
› The idea that living things could arise (come
from) nonliving things.
 i.e., maggots appeared on rotting meat;
 fish appeared in ponds that had been dry the
previous season – people thought the mud
gave rise or life to the fish.
Italian scientist
 noticed, described different
developmental forms of flies.
› Wormlike maggots – sturdy oval cases.
› Flies emerged from cases.
› Observed that maggots always appeared
where adult flies had previously landed.
Caused him to question spontaneous
generation from rotting meat.
Redi’s experiment conducted in 1668 to
test his hypothesis.
› Meat kept away from adult flies would
remain free of maggots.
He performed a controlled experiment.
 Experimental Group
› Jars contained meat – covered with nets
Control Group
› Uncovered jars which also contained meat
In the experimental group
› The netting allowed air to enter, yet prevented
the adult flies from landing on the meat.
After a few days
› Maggots swarmed over the meat in the
uncovered jars.
› The net covered jars remained free of maggots.
Redi’s experiment showed flies come only
from eggs laid by other flies.
 Redi’s hypothesis was confirmed.
 Major strike against the hypothesis of
spontaneous generation.
A new tool enters the picture about the
same time that Redi was performing his
 Microscope
 New revelation
› World teeming with tiny creatures
› microorganisms are simple in structure
› amazingly numerous and widespread
Microorganisms believed to arise from a
“vital force” in the air.
Italian scientist
 designed an experiment to test
hypothesis of spontaneous generation of
 Knew that microorganisms grew easily in
 Tested their growth in meat broth.
Boiled meat broth
 This was to kill all microorganisms already
present in the broth, on the glass of the
flask and in the air within the flask.
 Experimental Group
› Boiled clear, fresh broth in a straight neck
flask until flask filled with steam.
› Sealed the flasks by melting their glass necks
closed while the broth was hot.
Control Group
› Flasks were left open
› Broth in the experimental group remained
clear, free of microorganisms.
› Broth in the control group became cloudy
› Contamination with microorganisms
Spallanzani’s Conclusion
› Boiled broth contaminated when
microorganisms in the air entered the flask.
Opponents objected to his method.
 They disagreed with his conclusions.
 Said he had heated the flasks too long
 This destroyed the “vital force” in the air
inside the flasks.
 Because of this, no microorganisms
would form in the broth.
 Because of opposition, spontaneous
generation was kept alive for another
 Spontaneous
controversy grew intense by the
 Paris Academy of France
› Offered prize to anyone who
could solve this dilemma.
› The winner was Louis Pasteur.
Pasteur expanded on Spallanzani’s
 Instead of using a straight-neck flask, he
made a curved-neck flask.
› This allowed air inside the flask to mix with the
air outside the flask.
The curve in the neck of the flask
› prevented solid particles, such as
microorganisms, from entering the body of
the flask.
Experimental Group
› Curved-neck flasks
› Broth remained clear up to a year
Pasteur broke off the curved necks
 Broth became cloudy & contaminated
with microorganisms in a day.
 Pasteur’s Conclusion
› In comparing his experimental group to
Spallanzani’s control group, Pasteur
reasoned that the contamination was
caused by microorganisms in the air.
Those who believed in spontaneous
generation conceded and gave up their
The principle of biogenesis became a
cornerstone of biology.

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