1. Slide 1 of 32 Copyright Pearson Prentice Hall 1-2 How Scientists Work Mystery Worms A teacher collected some beetles from a rotting log and placed them in a container of dry oatmeal in her classroom. She kept the box covered with a light cloth so that the beetles could not escape. She also asked one of her students to add potato and apple pieces once a week to provide food and moisture for the beetles. After several weeks, the student reported that there were some strange-looking, wormlike organisms in the container.

2. Slide 2 of 32 Copyright Pearson Prentice Hall 1.Formulate a hypothesis that might explain the presence of the “worms” in the container. 2.How could you test your hypothesis? 3.Identify the variables in your proposed experiment. Identify the control in your proposed experiment.

3. Slide 3 of 32 Copyright Pearson Prentice Hall Definitions: Hypothesis – a possible explanation for something observed. Inference – A conclusion made based on something you already know.

4. 1-2 How Scientists Work Slide 4 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.

5. 1-2 How Scientists Work Slide 5 of 32 Copyright Pearson Prentice Hall Designing an Experiment The process of testing a hypothesis includes: 1. Asking a question 2. Forming a hypothesis 3. Setting up a controlled experiment 4. Recording and analyzing results 5. Drawing a conclusion

6. 1-2 How Scientists Work Slide 6 of 32 Copyright Pearson Prentice Hall Designing an Experiment 1. Asking a Question (What do you want to know?) Many years ago, people wanted to know how living things came into existence. They asked: How do organisms come into being?

7. 1-2 How Scientists Work Slide 7 of 32 Copyright Pearson Prentice Hall Designing an Experiment 2. Forming a Hypothesis One early hypothesis was spontaneous generation (aka: abiogenesis), 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.

8. 1-2 How Scientists Work Slide 8 of 32 Copyright Pearson Prentice Hall Designing an Experiment 3. Setting Up a Controlled Experiment The variables that are not changed are called the controlled variables. The variable that is deliberately changed is called the manipulated variable. The variable that is observed and that changes in response to the manipulated variable is called the responding variable.

9. 1-2 How Scientists Work Slide 9 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

10. 1-2 How Scientists Work Slide 10 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.

11. 1-2 How Scientists Work Slide 11 of 32 Copyright Pearson Prentice Hall Designing an Experiment Redi’s Experiment

12. 1-2 How Scientists Work Slide 12 of 32 Copyright Pearson Prentice Hall Designing an Experiment 4. Recording and Analyzing Results Scientists keep written or electronic records of their observations, or data, so that the experiment can be repeated.

13. 1-2 How Scientists Work Slide 13 of 32 Copyright Pearson Prentice Hall Designing an Experiment 5. Drawing a Conclusion Scientists use the data from an experiment to evaluate a hypothesis and draw a valid conclusion. Redi’s results supported the hypothesis that maggots were produced by flies, not spontaneous generation.

14. 1-2 How Scientists Work Slide 14 of 32 Copyright Pearson Prentice Hall Repeating Investigations Scientists repeat experiments to be sure that the results match those already obtained.

15. 1-2 How Scientists Work Slide 15 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.

16. 1-2 How Scientists Work Slide 16 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.

17. 1-2 How Scientists Work Slide 17 of 32 Copyright Pearson Prentice Hall Repeating Investigations Spallanzani's Test of Redi's Findings Gravy is boiled. Flask is open. Gravy is teeming with microorganisms. Gravy is boiled. Flask is sealed. Gravy is free of microorganisms.

18. 1-2 How Scientists Work Slide 18 of 32 Repeating Investigations Copyright Pearson Prentice Hall Spallanzani found that if the gravy in Needham’s experiment was boiled and sealed, it would not produce microorganisms. He showed that Needham wrongly assumed he had heated the gravy enough to kill any living microorganisms.

19. 1-2 How Scientists Work Slide 19 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.

20. 1-2 How Scientists Work Slide 20 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.

21. 1-2 How Scientists Work Slide 21 of 32 Copyright Pearson Prentice Hall Pasteur’s Experiment Pasteur showed that spontaneous generation would not even occur if air was available. His experiment showed that living things can only come from living things (biogenesis) and he finally put the theory of spontaneous generation to rest.

22. 1-2 How Scientists Work Slide 22 of 32 Copyright Pearson Prentice Hall 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.

23. 1-2 How Scientists Work Slide 23 of 32 Copyright Pearson Prentice Hall How a Theory Develops How does a scientific theory develop?

24. 1-2 How Scientists Work Slide 24 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. In science, the word theory applies to a well-tested explanation that unifies a broad range of observations.

25. 1-2 How Scientists Work Slide 25 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.

26. - or - Continue to: Click to Launch: Slide 26 of 32 Copyright Pearson Prentice Hall 1–2

27. Slide 27 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.

28. Slide 28 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.

29. Slide 29 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

30. Slide 30 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.

31. Slide 31 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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