1. Copyright Pearson Prentice Hall
1-2 How Scientists Work
Copyright Pearson Prentice Hall 1

2. Science is a way of thinking, questioning, and gathering evidence.

3. Like all science, biology is a process of inquiry.
Observing-using senses to gather information.
Forming a hypotheses-ask a question and try to explain observations.
Testing hypotheses-collecting data to support or reject hypothesis.
Analyzing data-statistical analysis of data to draw conclusions
Evaluating results-data and conclusions are studied to determine whether they are valid

4. Experimental studies allow scientists to determine what causes a phenomenon.
Independent variables are manipulated.
Dependent variables are observed and measured.
Constants are conditions that are kept the same.

5. A theory explains a wide range of observations.
Theories explain a wide range of observations and experimental results.
A theory is supported by a wide range of scientific evidence.
Theories can change based on new evidence.

6. Copyright Pearson Prentice Hall
How a Theory Develops
How does a scientific theory develop?
Copyright Pearson Prentice Hall

7. Copyright Pearson Prentice Hall
How a Theory Develops
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.
Copyright Pearson Prentice Hall

8. Copyright Pearson Prentice Hall
Major Theories in Biology
Germ Theory
Evolutionary Theory
Cell Theory
Gene Theory
Copyright Pearson Prentice Hall

9. Copyright Pearson Prentice Hall
Germ theory- The germ theory of disease states that many diseases are caused by microorganisms. 
Copyright Pearson Prentice Hall

10. Designing an Experiment
How do scientists test hypotheses?
A hypothesis should be tested by an experiment in which only one variable is changed at a time.
Copyright Pearson Prentice Hall

11. Designing an Experiment
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
Copyright Pearson Prentice Hall

12. 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?
Copyright Pearson Prentice Hall

13. Designing an Experiment
Forming a Hypothesis
One early hypothesis was spontaneous generation.
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.
Copyright Pearson Prentice Hall

14. Designing an Experiment
Setting Up a Controlled Experiment- to find “cause and effect” relationships
Manipulated variable (independent variable)-the condition that is manipulated in an experiment; the “cause”
Responding variable (dependent variable)-the factor that is measured in an experiment; the “effect”
Constant-any condition that is kept the same during an experiment; necessary for determining whether the independent variable produces any change in the dependent variable.
Copyright Pearson Prentice Hall

15. Designing an Experiment
Redi’s Experiment
Uncovered jars
Covered jars
Controlled Variables:
jars, type of meat,
Location, temperature,
time
In a controlled experiment, only one variable is tested at a time. Redi designed an experiment to determine what caused the sudden appearance of maggots. In his experiment, the manipulated variable was the presence or absence of the gauze covering. The results of this experiment helped disprove the hypothesis of spontaneous generation.
Copyright Pearson Prentice Hall

16. Designing an Experiment
Redi’s Experiment
Manipulated Variable:
Gauze covering that keeps flies away from meat
Several days pass.
Responding Variable:
whether maggots appear
Maggots appear.
No maggots appear.
Copyright Pearson Prentice Hall

17. Designing an Experiment
Drawing a Conclusion
Scientists use the data from an experiment to evaluate a hypothesis and draw a valid conclusion.
Copyright Pearson Prentice Hall

18. Repeating Investigations
John Needham decided to attack Redi’s work, claiming that spontaneous generation could occur under the right conditions.
To prove his claim, he sealed a bottle of gravy and heated it to kill any living things that might be in the gravy (Redi did not use heat in his experiment)
After several days, he examined the flask of gravy and found many “animalcules”
Copyright Pearson Prentice Hall

19. Repeating Investigations
Spallanzani's Test of Needham’s Findings 
Gravy is boiled.
Gravy is boiled.
Spallanzani’s experiment showed that microorganisms will not grow in boiled gravy that has been sealed but will grow in boiled gravy that is left open to the air. Interpreting Graphics What variable was controlled in this experiment?
Copyright Pearson Prentice Hall

20. Repeating Investigations
Spallanzani's Test of Needham’s Findings 
Flask is open.
Flask is sealed.
Copyright Pearson Prentice Hall

21. Repeating Investigations
Spallanzani's Test of Needham’s Findings 
Gravy is teeming with microorganisms.
Gravy is free of microorganisms.
Copyright Pearson Prentice Hall

22. Repeating Investigations p 11
What was Spallanzini’s observations of Needham’s experiment?
What was his hypothesis?
Control variables?
Manipulated variables?
Responding variables?
Copyright Pearson Prentice Hall

23. 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.
Copyright Pearson Prentice Hall

24. Repeating Investigations
Pasteur’s Experiment
Broth is free of microorganisms for a year.
Curved neck is removed.
Broth is teeming with microorganisms.
Pasteur’s experiment showed that boiled broth would remain free of microorganisms even if air was allowed in, as long as dust and other particles were kept out.
Broth is boiled
Copyright Pearson Prentice Hall

25. Repeating Investigations p 12
What was Pasteur’s observations?
What was his hypothesis?
Control variables?
Manipulated variables?
Responding variables?
Copyright Pearson Prentice Hall

26. Repeating Investigations
The Impact of Pasteur’s Work
Pasteur saved the French wine industry, which was troubled by unexplained souring of wine.
He began to uncover the nature of infectious diseases, showing that they were the result of microorganisms.
Copyright Pearson Prentice Hall

27. Copyright Pearson Prentice Hall
1–2
Copyright Pearson Prentice Hall

28. Copyright Pearson Prentice Hall
1–2
In an experiment, the variable that is deliberately changed is called the
control.
manipulated variable.
responding variable.
constant control
Copyright Pearson Prentice Hall

29. Copyright Pearson Prentice Hall
1–2
The mistaken belief that living organisms can arise from nonliving matter is called
biogenesis.
Pasteur's theory.
spontaneous generation.
Spallanzani’s hypothesis.
Copyright Pearson Prentice Hall

30. Copyright Pearson Prentice Hall
1–2
Which of the following was the manipulated variable in Redi’s experiment?
the kind of meat used
the temperature the jars were kept at
the gauze covering on some jars
the kind of fly that visited the jars
Copyright Pearson Prentice Hall

31. Copyright Pearson Prentice Hall
1–2
A well-tested explanation that unifies a broad range of observations is a
hypothesis.
variable.
control.
theory.
Copyright Pearson Prentice Hall

32. Copyright Pearson Prentice Hall
1–2
A scientific explanation does not become a theory until
a majority of scientists agree with it.
it has been supported by evidence from numerous investigations and observations.
it is first proposed as an explanation.
it is published in a textbook.
Copyright Pearson Prentice Hall

33. END OF SECTION