NAME:______________________PERIOD:_____DATE:________
Scientific Method
Directions: Science is based on the objective, careful observation of nature. People who work in
science follow the research method, which is a logical process that involves observation, formation
of hypotheses, and experimentation. Consider how the research method was carried out in the
following example. A scientist observed that tobacco plants flower only at certain times of the year.
After careful consideration of this phenomenon, the scientist conducted an experiment. She grew
five tobacco plants and exposed each to a specific amount of daily light. Study the diagrams below,
which show the result of this experiment. Then complete the sentences that follow and fill in the
chart, explaining how a scientist would apply the research method to this problem.
1.
Since only one factor changed in this experiment, it is called a _________________ experiment.
2. The variable in this experiment is ____________________.
3. List some conditions of the experiment that were probably held constant.
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Research Method Step
Application to this Problem
Observation
Defining the Problem
Forming a Hypothesis
Testing the Hypothesis
Observing and Recording
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Results
Drawing Conclusions
Reporting the Results
Directions: Many significant problems in science have been solved through the use of the research
method. The following describes on such problem. Read the description and answer the questions
that follow.
Anthrax is a severe, contagious disease of animals and people. Animals with anthrax usually die
suddenly. Robert Koch discovered a bacterium responsible for anthrax. When outside a living body,
anthrax bacteria form spores, reproductive cells that can exist for long periods of time with no food or
water. Spores can be killed only by burning. If any animal with anthrax did not die, it never caught
anthrax again. If a mild form of anthrax had existed, it could have been deliberately given to an animal as
a vaccine to make the animal immune. But a mild form of anthrax did not exist.
Louis Pasteur had an idea for immunizing animals from anthrax. He collected some anthrax bacteria from
infected animals. He then heated the bacteria to weaken, but not kill them. In 1881, Pasteur inoculated
half of a herd of sheep with the anthrax bacteria he had weakened. After a period of time, he inoculated
the whole herd with full-strength anthrax bacteria. The animals that had not previously received the
weakened form of anthrax became ill and died. Those that had previously received the weakened anthrax
bacteria remained healthy.
1.
Animals that died of anthrax were burned before they were buried. Why do you think this was
done?
2. Complete this three hypotheses that Pasteur made:
a. If burning kills anthrax bacteria, then __________________________________
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b. If an animal that survives anthrax can never get it again, then _______________
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c. If full-strength bacteria either kill an animal or make it immune, then ________
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3. What conclusions did Pasteur come to as a result of his experiment?
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4. Would Pasteur’s experiment have been as effective if he had used only two sheep? Explain you
answer.
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