1. 1.2 – Publishing and Repeating Investigations

2. Redi’s Experiment on Spontaneous Generation
Section 1-2
OBSERVATIONS: Flies land on meat that is left uncovered. Later, maggots appear on the meat.
HYPOTHESIS: If the jars are left uncovered, maggots will appear.
PROCEDURE
Uncovered jars
Covered jars
Controlled Variables:
jars, type of meat,
location, temperature,
time
Several
days pass
Manipulated Variables:
gauze covering that
keeps flies away from
meat
Responding Variable:
whether maggots
appear
Maggots appear
No maggots appear
CONCLUSION: Maggots form only when flies come in contact with meat. Spontaneous generation of maggots did not occur.
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3. Publishing and Repeating Investigations
Results of experiments should always be the same if the same variables are manipulated
This is why experiments are published and why they can be performed and tested by others
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4. Anton van Leeuwenhoek
Later tests of Redi’s experiment were influenced by Leeuwenhoek’s making of lenses that could magnify things
He discovered tiny moving objects in rainwater, pond water and dust
He called the “animalcules”
The discovery had major implications on spontaneous generation
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5. Needham
In the mid-1700’s John Needham worked with animalcules to attack Redi’s work
He heated a flask of gravy, sealed it and waited several days
After the wait he found that the gravy was swarming with activities
Spontaneous generation
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6. Figure 1-10 Spallanzani’s Experiment
Section 1-2
Spallanzani did not believe that Needham heated the broth enough to kill all the organisms in it.
Gravy is boiled.
Flask is
open.
Gravy is teeming
with microorganisms.
Flask is
sealed.
Gravy is free of
microorganisms.
Gravy is boiled.
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7. Section 1-2 How Scientists Work
Publishing and Repeating Investigations
16. He designed a special S shaped tube that allowed air into the flask but protected microorganisms from entering the flask. Microorganisms got stuck in the tube.
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8. Louis Pasteur
In the 1800’s arguments were still being tested for spontaneous generation
They believed air was the “life force” needed
Pasteur came up with an experiment with a curved neck added to test the air idea
Because of this he solved many problems – souring of wine and the biggest was the idea of infectious disease
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9. Figure 1-11 Pasteur’s Experiment
Section 1-2
Broth is boiled.
Broth is free of
microorganisms
for a year.
Curved neck
is removed.
Broth is
teeming with microorganisms.
(just like
Spallanzani)
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10. Figure 1-11 Pasteur’s Experiment
Section 1-2
Broth is boiled.
Broth is free of
microorganisms
for a year.
Curved neck
is removed.
Broth is
teeming with microorganisms.
Go to Section:
12/4/2018

11. Figure 1-11 Pasteur’s Experiment
Section 1-2
Broth is boiled.
Broth is free of
microorganisms
for a year.
Curved neck
is removed.
Broth is
teeming with microorganisms.
Go to Section:
12/4/2018

12. Figure 1-11 Pasteur’s Experiment
Section 1-2
Broth is boiled.
Broth is free of
microorganisms
for a year.
Curved neck
is removed.
Broth is
teeming with microorganisms.
Go to Section:
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13. When Experiments Are not Possible
When subjects need to not be disturbed
Ethical issues
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14. When experiments are not possible?
18. They identify as many as possible so that most variables are controlled.
Example: It is difficult to run a controlled experiment during human medical studies….WHY?
Different ages
Different races
Different genetic makeup
Different pre existing medical conditions
Goal would be to try to find subjects that are as similar as possible (but it
never will be truly controlled)
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15. How a Theory Develops
Theory occurs when a hypothesis becomes very well supported
In science, the word theory applies to a well tested explanation that unifies a broad range of observations
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16. How a Theory Develops
Oh, that is just one person’s theory! (Poor use of the word theory)
A theory is a well tested explanation that explains many observations
Theory of evolution explains the following observations…
Why our DNA is so similar to other humans (99.9%)
Why our DNA is so similar to other species (>98%)
Why fossils deep in layers are extinct and less complex
Why medicine that use to work on bacteria doesn’t anymore (resistance)
Why things are so adapted to their environment
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