Transcript File - Siegel Science

Where do living organisms
come from?
Biology
Spontaneous Generation
• Life can come from non-living things
• Idea persisted up to the 1800s
• Many ideas were based on observations that had
never been tested
• Examples:
• Frogs appeared in muddy soil when not present
when soil was drier
• Mice came from moldy grain
• Sewage and garbage turned into rats
• Rotting meat was the source of flies
Francesco Redi
1668-Experiment to challenge the idea of
spontaneous generation, considered 1st true scientific
experiment that contained a control
Apply “Scientific Method” to
Redi’s experiment
 Question:
 Hypothesis:
 IV:
 DV:
 Control:
 Conclusion:
Apply “Scientific Method” to
Redi’s experiment
 Question: Where do flies come from? Can rotting meat
produce flies?
 Hypothesis: Rotting meat does not turn into flies. Only flies
can produce other flies.
 IV: jars of meat sealed with either lids or gauze covering
 DV: record presence or absence of flies and maggots
 Control: jars containing meat without covers on them
 Conclusion: Maggots arose only where flies were able to lay
eggs. The sealed container had no flies/maggots/eggs.
Therefore, only flies can produce more flies.
What happened next?
• Many people still felt that spontaneous generation was
possible in certain circumstances...including Redi.
• By the 1700s it was known the boiling substances killed
microorganisms. In 1745, John Needham performed an
experiment to test whether or not microoganisms
appeared spontaneously after boiling some meat broth.
He boiled the broth, placed it in a flask and sealed the
container. Microoganisms grew in the broth so
Needham considered his results to be support for
spontaneous generation.
• Why do you think Needham got these results?
“Life force” in air and/or oxygen
that enable the bacteria to form in
the flask
Lazzaro Spallanzani
 Repeated John Needham’s experiment but
boiled the broth in a sealed flask in which
the air had been removed.
No microorganisms formed which provided
evidence against spontaneous generation.
Why do you think he got these results?
Pasteur
1859 experiment to provide evidence against
spontaneous generation
Performed a variation of Needham and Spallanzani’s
experiments
Apply “Scientific Method” to
Pasteur’s experiment
• Question:
• Hypothesis:
• IV:
• DV:
• Control:
• Conclusion:
Apply “Scientific Method” to
Pasteur’s experiment
•
Question: Is there a “life force” in air/oxygen that can allow for
bacteria to form through spontaneous generation? Is it possible to let
air into a container but not the bacteria in the air?
•
Hypothesis: Broth that has been boiled in a flask that is exposed to
air will remain sterile, as long as bacteria are not able to enter the
flask.
•
IV: used flasks with long, S-shaped necks; some flasks were closed
with cotton plugs
•
DV: presence or absence of bacterial growth in the flasks based on
observations of odor, cloudy appearance of broth and microscope
•
Control: some flasks that were used opened straight up so bacteria
and air had access to the broth in the flask
•
Conclusion: There is no “life force” and organisms do not arise via
spontaneous generation.