1. Chapter 1 Section 2 How Scientists Work
Objectives:
Describe how scientists test hypotheses.
Explain how a scientific theory develops.

2. Vocabulary
spontaneous generation: hypothesis stating that life could arise from nonliving matter
controlled experiment: a test of the effect of a single variable by changing it while keeping all other variables the same

3. Vocabulary
manipulated variable: factor in an experiment that a scientist purposely changes; also known as independent variable
responding variable: factor in an experiment that a scientist wants to observe, which may change in response to the manipulated variable; also known as a dependent variable

4. theory: well-tested explanation that unifies a broad range of observations

5. Designing an Experiment
Asking a Question
Forming a Hypothesis
Setting Up a Controlled Experiment
Recording and Analyzing Results
Drawing a Conclusion

6. Designing an Experiment
Whenever possible, a hypothesis should be tested by an experiment in which only one variable is changed at a time. All other variables should be kept unchanged, or controlled.

7. Redi’s Experiment on Spontaneous Generation

8. Repeating Investigations
A key assumption in science is that experimental results can be reproduced because nature behaves in a consistent manner.

9. How a Theory Develops
As evidence from numerous investigations builds up, a particular hypothesis may become so well supported that scientists consider it a theory.

10. How a Theory Develops
In science, the word theory applies to a well-tested explanation that unifies a broad range of observations.