Name
Class
Section 1-2 How Scientists Work
Date
(pages 8-14)
Answer each of the following questions:
 In your head first
 Look back into the book/your notes and check to see if what you are
thinking is correct
 Write your answer on the paper
Designing an Experiment (pages 8-10)
1. The idea that life can arise from nonliving matter is called
2. What was Francesco Redi’s hypothesis about the appearance of maggots?
3. What are variables in an experiment?
4. Ideally, how many variables should an experiment test at a time?
5. What is a controlled experiment?
6. The illustration below shows the beginning of Redi’s experiment. Complete the
illustration by showing the outcome.
Redi’s Experiment on Spontaneous Generation
Uncovered jars
Covered jars
Several
days pass.
Variables
In a controlled experiment, only one variable is changed. This is called the
manipulated variable. The variable that changes in response to the manipulated
variable is called the responding variable. The variables that are kept constant are
called controlled variables.
Identify the manipulated variable, the responding variable, and two of the controlled
variables in the experiment shown.
Types of Variables
Manipulated
Variable
Responding
Variable
Gravy is boiled.
Gravy is boiled.
Flask is open.
Flask is sealed.
Controlled
Variables
Gravy is teeming
with microorganisms.
Gravy is free
of microorganisms.
Use the diagram and table to answer the question.
7. Suppose the scientist had put one type of gravy in the flask he left open and
another in the flask he sealed. Would this be a well-designed controlled
experiment? Explain. ______________________________________________
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8. In Redi’s experiment, what were the manipulated variable and the responding variable?
9. For what do scientists use the data from a controlled experiment?
10. When scientists look for explanations for specific observations, what do they assume about
nature?
Repeating Investigations (pages 10-12)
11. Why do scientists assume that experimental results can be reproduced?
12. What did Anton van Leeuwenhoek discover?
13. What did John Needham conclude from his test of Redi’s findings?
14. What did Spallanzani do to improve upon Redi’s and Needham’s work?
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Pasteur’s Test of Spontaneous Generation
The theory of spontaneous generation stated that life could arise from nonliving matter.
Louis Pasteur did an experiment that disproved this theory. He put boiled broth in a flask
that allowed air but not microorganisms to reach the broth. A year later, he broke the
neck of the flask.
Color the broth in the flask in which microorganisms grew.
1 Year Passes
Use the diagram to answer the questions.
15. Would the results of this experiment have changed if Pasteur had let the
unbroken flask sit for three years instead of one? Why or why not?
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When Experiments Are Not Possible (page 13)
16.
In animal field studies, why do scientists usually try to work without making the animals aware that
humans are present?
17.
When a controlled experiment is not possible, why do scientists try to identify as many
relevant variables as possible?
How a Theory Develops (pages 13-14)
18.
19.
In science, what is a theory?
Is the following sentence true or false? A theory may be revised or replaced by a more useful
explanation.