Francesco Redi

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Chapter 1

• Section 1-2

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Francesco Redi

• Designed experiment that challenged spontaneous
  generation
• Used a controlled experiment to test his
  hypothesis that maggots come from flies.
• Hypothesis was supported by the data and
  spontaneous generation began to be questioned by
  other scientists

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Anton van Leeuwenhoek

• Scientist in the Netherlands
• About the same time as Redi, he was experimenting
  with lenses that were able to see tiny things
• Discovered animalcules in rainwater, pond
  water, and dust
• The first microbiologist?

4
Anton van Leeuwenhoek

• His discovery of animalcules fueled a new
  argument about spontaneous generation
• Scientists could not agree on whether the
  animalcules were alive or how they came to exist

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John Needham

• English scientist who wanted to prove spontaneous
  generation
• Direct challenge to Francesco Redis work
• His hypothesis spontaneous generation occurs
  under the right conditions

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Needhams Experiment

• Step 1 Seal gravy in a flask
• Step 2 Heat the gravy
• Step 3 Watch for appearance of animalcules

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Needhams Experiment

• Result After several days, the bottle is teeming
  with tiny organisms
• His claim These little animals can only have
  come from the juice of the gravy

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Lazzaro Spallazani

• Challenges the work of both Redi Needham
• Designs a more controlled experiment for more
  accurate results
• Figure 1-10 on page 11 of text

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Spallazanis Experiment

• Step 1 Boils gravy in two open flasks
• Step 2 Leaves one flask open and seals the
  other
• Step 3 Observe after a few days
• Result Open flask teeming with microorganisms
  sealed flask has no microorganisms

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Lets Compare Their Work

• How were Needhams experiment and Spallazanis
  experiment similar?
• How were they different?
• Which one was more accurate?
• Why?

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Louis Pasteur

• French genius from the 1800s
• Designed an even better experiment to prove that
  spontaneous generation was not possible

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Pasteurs Experiment

• Scientists argued that air was a life force
  necessary to bring about spontaneous generation
• Used this theory to try to discredit Spallazanis
  work
• Pasteur designs a flask with a long curved neck
  so that air will be able to enter the flask

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Pasteurs Experiment

• Figure 1-11 on page 12 in text
• Step 1 broth is boiled
• Step 2 broth is kept in flask for one year
• Step 3 After a year, the curved neck is broken
  off, and the flask is exposed to the atmosphere
• Step 4 After a few days, broth is teeming with
  microorganisms

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Why the curved neck?

• The curved neck on Pasteurs flask allowed air to
  pass into the flask
• But the shape of the flask, caused any dust
  particles to settle at the bottom of the curve
  and, therefore, not make contact with the broth
  itself

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Why does it matter?

• Scientists constantly challenge, grow from, and
  build upon each others work
• It takes the work of multiple scientists, for a
  theory to develop

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Whats a Theory?

• A theory is NOT the same as a guess
• In science, a theory is a well tested explanation
  that unifies a broad range of observations
• No theory is absolute truth

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How a Theory is Developed

• The Scientific Method
• Collaboration
• Publication

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The Scientific Method

• Identify the problem/question
• Research information
• Formulate a hypothesis
• Conduct an experiment
• Analyze data
• Draw conclusions