Biology
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1-2 How Scientists Work
Designing an Experiment
1-2 How Scientists work
How do scientists test hypotheses?
Whenever possible, a hypothesis should
be tested by an experiment in which only
one variable is changed at a time
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1-2 How Scientists Work
Designing an Experiment
1. Designing an Experiment
a. The process of testing a hypothesis includes:
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1-2 How Scientists Work
Designing an Experiment
1. Asking a Question
I wonder how many drops of water will fit on a
penny???
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1-2 How Scientists Work
Designing an Experiment
2. Forming a Hypothesis
a. Written as an If…..then…..statement
(A prediction as to what is going to happen)
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1-2 How Scientists Work
3. Supplies Needed:
a. Water
b. Soap Water
c. Cups for water/soap water
d. 2 droppers
e. Penny
f. Paper Toweling
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1-2 How Scientists Work
Designing an Experiment
4. Setting Up a Controlled Experiment
a. only 1 variable can be changed to be a
valid experiment!
b. manipulated variable :
* variable that is deliberately changed
c. responding variable:
*is observed and changes in response to
the manipulated variable
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1-2 How Scientists Work
Designing an Experiment
5. Recording and Analyzing Results
*keep written records of their observations,
or data.
*Sometimes drawings are used to record
certain kinds of observations.
( Create Data Table for water vs soap water, 5
trials for each solution then calculate the ave.)
(Also compare data from other groups before a
conclusion is drawn)
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1-2 How Scientists Work
Designing an Experiment
6. Drawing a Conclusion
a. use the data from an experiment to evaluate
a hypothesis and draw a valid conclusion.
(Based on the data collected, my hypothesis was
correct/incorrect because…….reference the data
to explain)
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1-2 How Scientists Work
Repeating Investigations
7. Repeating Investigations
(repeat experiments to be sure that the
results match those already obtained.)
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1-2 How Scientists Work
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1-2 How Scientists Work
Designing an Experiment
Redi’s Experiment
Uncovered jars
Covered jars
Controlled Variables:
jars, type of meat,
location, temperature,
time
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1-2 How Scientists Work
Designing an Experiment
Redi’s Experiment
Manipulated Variable:
Gauze covering that keeps
flies away from meat
Responding Variable:
whether maggots appear
Several
days pass.
Maggots appear.
No maggots appear.
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1-2 How Scientists Work
Designing an Experiment
Redi’s Experiment
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1-2 How Scientists Work
Designing an Experiment
Today, researchers use computers to record their
work.
Online storage makes it easier for researchers to
review the data.
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1-2 How Scientists Work
Repeating Investigations
Needham's Test of Redi's Findings
Needham challenged Redi’s results by claiming that
spontaneous generation could occur under the right
conditions. *
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Repeating Investigations
Needham’s Test of Redi’s Findings
• Needham sealed a bottle of gravy and heated it.
• After several days, the gravy was swarming with
microorganisms.
• Needham concluded that these organisms came
from the gravy by spontaneous generation.
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Repeating Investigations
Spallanzani's Test of Redi's Findings
Gravy is boiled.
Gravy is boiled.
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1-2 How Scientists Work
Repeating Investigations
Spallanzani's Test of Redi's Findings
Flask is sealed.
Flask is open.
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1-2 How Scientists Work
Repeating Investigations
Spallanzani's Test of Redi's Findings
Gravy is teeming
with microorganisms.
Gravy is free of
microorganisms.
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1-2 How Scientists Work
Repeating Investigations
Pasteur's Test of Spontaneous Generation
• Louis Pasteur conclusively disproved the
hypothesis of spontaneous generation.
• Pasteur showed that all living things come from
other living things.
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1-2 How Scientists Work
Repeating Investigations
Pasteur’s Experiment
Broth is boiled
Broth is free
of microorganisms
for a year.
Curved neck is
removed.
Broth is
teeming with
microorganisms.
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Repeating Investigations
The Impact of Pasteur’s Work
Pasteur saved the French wine industry, which
was troubled by unexplained souring of wine.
He saved the silk industry, which was endangered
by a silkworm disease.
He began to uncover the nature of infectious
diseases, showing that they were the result of
microorganisms.
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1-2 How Scientists Work
When Experiments Are Not Possible
When Experiments Are Not Possible
It is not always possible to do an experiment to test
a hypothesis. For example:
• Wild animals must be observed without
disturbing them.
• Ethical considerations prevent some
experiments.
By carefully planning alternative investigations,
scientists can discover reliable patterns that add to
scientific understanding.
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1-2 How Scientists Work
How a Theory Develops
How does a scientific theory develop?
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1-2 How Scientists Work
How a Theory Develops
How a Theory Develops
As evidence from numerous investigations
builds up, a hypothesis may become so well
supported that scientists consider it a theory.
In science, the word theory applies to a
well-tested explanation that unifies a
broad range of observations.
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How a Theory Develops
No theory is considered absolute truth.
As new evidence is uncovered, a theory may be
revised or replaced by a more useful explanation.
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1–2
Click to Launch:
Continue to:
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1–2
In an experiment, the variable that is deliberately
changed is called the
a. control.
b. manipulated variable.
c. responding variable.
d. constant control.
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1–2
The mistaken belief that living organisms can
arise from nonliving matter is called
a. biogenesis.
b. Pasteur's theory.
c. spontaneous generation.
d. Spallanzani’s hypothesis.
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1–2
Which of the following was the manipulated
variable in Redi’s experiment?
a. the kind of meat used
b. the temperature the jars were kept at
c. the gauze covering on some jars
d. the kind of fly that visited the jars
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1–2
A well-tested explanation that unifies a broad
range of observations is a
a. hypothesis.
b. variable.
c. control.
d. theory.
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A scientific explanation does not become a
theory until
a. a majority of scientists agree with it.
b. it has been supported by evidence from
numerous investigations and observations.
c. it is first proposed as an explanation.
d. it is published in a textbook.
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