1. Slide 1 of 32 Copyright Pearson Prentice Hall Biology

2. Slide 2 of 32 Copyright Pearson Prentice Hall 1-2 How Scientists Work

3. Slide 3 of 32 Copyright Pearson Prentice Hall Designing an Experiment 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. All other variables should be kept unchanged, or controlled.

4. 1-2 How Scientists Work Slide 4 of 32 Copyright Pearson Prentice Hall Designing an Experiment SCIENTIFIC METHOD The process of testing a hypothesis includes: Asking a question Forming a hypothesis Setting up a controlled experiment Recording and analyzing results Drawing a conclusion

5. 1-2 How Scientists Work Slide 5 of 32 Copyright Pearson Prentice Hall Designing an Experiment Asking a Question Many years ago, people wanted to know how living things came into existence. They asked: How do organisms come into being?

6. 1-2 How Scientists Work Slide 6 of 32 Copyright Pearson Prentice Hall Designing an Experiment Forming a Hypothesis One early hypothesis was spontaneous generation, or the idea that life could come from nonliving matter. For example, most people thought that maggots spontaneously appeared on meat. In 1668, Redi proposed a different hypothesis: that maggots came from eggs that flies laid on meat.

7. 1-2 How Scientists Work Slide 7 of 32 Copyright Pearson Prentice Hall Designing an Experiment Setting Up a Controlled Experiment There are 3 types of variables: 1.Controlled: things that stay the same ex: 2.Manipulated: variable you deliberately change ex: 3. Responding: variable that changes in response to the manipulated variable (the thing you changed) ex:

8. 1-2 How Scientists Work Slide 8 of 32 Copyright Pearson Prentice Hall Designing an Experiment Redi’s Experiment Controlled Variables: jars, type of meat, location, temperature, time Covered jars Uncovered jars

9. 1-2 How Scientists Work Slide 9 of 32 Copyright Pearson Prentice Hall Designing an Experiment Redi’s Experiment Manipulated Variable: Gauze covering that keeps flies away from meat Responding Variable: whether maggots appear Maggots appear. Several days pass. No maggots appear.

10. 1-2 How Scientists Work Slide 10 of 32 Copyright Pearson Prentice Hall Designing an Experiment Redi’s Experiment

11. 1-2 How Scientists Work Slide 11 of 32 Copyright Pearson Prentice Hall 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.

12. 1-2 How Scientists Work Slide 12 of 32 Copyright Pearson Prentice Hall 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.

13. 1-2 How Scientists Work Slide 13 of 32 Copyright Pearson Prentice Hall Repeating Investigations Spallanzani's Test of Redi's Findings Gravy is boiled.

14. 1-2 How Scientists Work Slide 14 of 32 Copyright Pearson Prentice Hall Repeating Investigations Spallanzani's Test of Redi's Findings Flask is open. Flask is sealed.

15. 1-2 How Scientists Work Slide 15 of 32 Copyright Pearson Prentice Hall Repeating Investigations Spallanzani's Test of Redi's Findings Gravy is teeming with microorganisms. Gravy is free of microorganisms.

16. 1-2 How Scientists Work Slide 16 of 32 Copyright Pearson Prentice Hall 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.

17. 1-2 How Scientists Work Slide 17 of 32 Copyright Pearson Prentice Hall 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.

18. 1-2 How Scientists Work Slide 18 of 32 Copyright Pearson Prentice Hall How a Theory Develops How does a scientific theory develop?

19. 1-2 How Scientists Work Slide 19 of 32 Copyright Pearson Prentice Hall How a Theory Develops As evidence from numerous investigations builds up, a hypothesis may become so well supported that scientists consider it a theory. A theory is a well-tested explanation that pulls together a broad range of observations.

20. 1-2 How Scientists Work Slide 20 of 32 Copyright Pearson Prentice Hall 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. Law: a theory that has been proven and has upheld the test of time.

21. - or - Continue to: Click to Launch: Slide 21 of 32 Copyright Pearson Prentice Hall 1–2

22. Slide 22 of 32 Copyright Pearson Prentice Hall 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.

23. Slide 23 of 32 Copyright Pearson Prentice Hall 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.

24. Slide 24 of 32 Copyright Pearson Prentice Hall 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

25. Slide 25 of 32 Copyright Pearson Prentice Hall 1–2 A well-tested explanation that unifies a broad range of observations is a a.hypothesis. b.variable. c.control. d.theory.

26. Slide 26 of 32 Copyright Pearson Prentice Hall 1–2 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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