Transcript Redi`s Famous Experiment Hypothesis, Theory and Inference

Redi’s Famous Experiment
Hypothesis, Theory and Inference
Designing an Experiment
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Observation
Ask a Question
Form a Hypothesis
Set up an Experiment
Record Data
Draw a Conclusion
Repeat…..Repeat…..Repeat
Theory….maybe
Steps of the Scientific Method
Observation
Question
Hypothesis
Experiment
Record Data
Conclusion
Repeat
Theory
Redi’s Experiment - 1668
1. Observation: Something you “see”
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People noticed maggots on meat, mice on grains, and
beetles on cow dung
What could be the Inference ????
2. Question
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How do new living things, organisms, suddenly come
into being?
3. Hypothesis: Proposed explanation for observation…testable!!
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Redi noticed that maggots appeared a few days after
flies were present
Hypothesis = Flies produce maggots
Redi’s Experiment
4. Set up an Experiment
Control: stays constant
(jars, meat, location, temperature, time)
Independent Variable: something scientist changes or manipulates
(gauze covering keeping flies away from meat)
Dependent Variable: changes due to other variables
(whether maggots appear)
(what you measure)
Redi’s Experiment
5. Record Data
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Maggots appeared in jars which were not covered
by gauze
Usually done in tables and graphs
Numbers and observations are recorded
Draw Conclusions: Was the hypothesis correct or incorrect???
• Must be based on data from experiment
• Maggots form only when flies come in contact with
meat.
• Spontaneous generation of maggots did NOT occur.
Redi’s Experiment
7. Repeat….Repeat….Repeat
Other scientists must be able to duplicate results in order
for other to believe it!
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Needham
• Grew “bacteria” in heated gravy containers
• Found “bacteria” in heated, sealed containers of gravy
• Disagreed with Redi
Spallanzani
• Thought gravy was not heated enough
• Repeated & boiled gravy
• The sealed jar remained free of bacteria
• Agreed with Redi
Spallanzani’s Test
Louis Pasteur
 About 200 years later (late 1800’s)
 People argued
 air was the “life force” needed to produce life
 Spallanzani didn’t account for this
 Pasteur repeated the experiment using a
different container
 Protected from microorganisms
 Allowed air “life force” to flow freely
Louis Pasteur
Air Enters
Curved Neck
Broken Neck
Pasteur’s Impact
 Saved the French wine industry
 Unexplained souring of wine
 Saved the silk industry
 Silkworm disease
 Began to uncover the nature of infectious
disease
 Showed how microorganisms enter the body
 “Pasteurization”
Hypothesis vs. Theory
 Theory – A well-tested explanation that unifies
a broad range of observations
 Plate Tectonics
 Evolution
 Hypothesis – A proposed scientific explanation
for a set of observations
How does a hypothesis become a theory??