Chapter01 Section02 Meredith

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Copyright Pearson Prentice Hall

Biology


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1-2 How Scientists Work


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Designing an Experiment

How do scientists test hypotheses?

A hypothesis should be tested by anexperiment in which only one variable ischanged at a time.


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Designing an ExperimentThe process of testing a hypothesis includes:

Asking a question

Forming a hypothesis

Setting up a controlled experiment

Recording and analyzing results Drawing a conclusion


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Asking a Question

Many years ago, people wanted to know how livingthings came into existence. They asked:

How do organisms come into being?


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Forming a Hypothesis

One early hypothesis was spontaneousgeneration.

For example, most people thought that maggotsspontaneously appeared on meat.

In 1668, Redi proposed a different hypothesis: thatmaggots came from eggs that flies laid on meat.


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Setting Up a Controlled Experiment

manipulated variable

responding variable
http://resources/ActiveArt/redi_pasteur_experiment.swf


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Redis Experiment

Controlled Variables:jars, type of meat,Location, temperature,time

Covered jarsUncovered jars
http://resources/ActiveArt/redi_pasteur_experiment.swfhttp://resources/ActiveArt/redi_pasteur_experiment.swf


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Redis Experiment

Manipulated Variable:Gauze covering that keepsflies away from meat

Responding Variable:whether maggots appear Maggots appear.

Severaldays pass.

No maggots appear.


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Drawing a Conclusion

Scientists use the data from an experiment toevaluate a hypothesis and draw a valid conclusion.


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Repeating Investigations

Spallanzani's Test of Redi's Findings

Gravy is boiled. Gravy is boiled.


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Flask is open. Flask is sealed.


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Gravy is teemingwith microorganisms.

Gravy is free ofmicroorganisms.


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Pasteur's Test of Spontaneous Generation

Louis Pasteur conclusively disproved thehypothesis of spontaneous generation.

Pasteur showed that all living things come fromother living things.

2 H S i i W k R i I i i


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Pasteurs Experiment

Broth isboiled

Broth is freeof microorganismsfor a year.

Curved neck is

removed.

Broth is

teeming withmicroorganisms.

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The Impact of Pasteurs Work

Pasteur saved the French wine industry, whichwas troubled by unexplained souring of wine.

He began to uncover the nature of infectiousdiseases, showing that they were the result ofmicroorganisms.

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How a Theory Develops

How does a scientific theory develop?

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As evidence from numerous investigations

builds up, a hypothesis may become so wellsupported that scientists consider it a theory.

In science, the word theoryapplies to a

well-tested explanation that unifies abroad range of observations.


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Major Theories in Biology

Germ Theory

Evolutionary Theory

Cell Theory

Gene Theory


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- or -

Continue to: Click to Launch:

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http://resources/ch01_sectn02_quiz.qtbhttp://resources/ActiveArt/index.htmlhttp://resources/ActiveArt/index.html


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In an experiment, the variable that is deliberatelychanged is called the

a. control.

b. manipulated variable.c. responding variable.

d. constant control


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The mistaken belief that living organisms canarise from nonliving matter is called

a. biogenesis.

b. Pasteur's theory.c. spontaneous generation.

d. Spallanzanis hypothesis.


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Which of the following was the manipulatedvariable in Redis experiment?

a. the kind of meat used

b. the temperature the jars were kept atc. the gauze covering on some jars

d. the kind of fly that visited the jars


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A well-tested explanation that unifies a broadrange of observations is a

a. hypothesis.

b. variable.c. control.

d. theory.


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A scientific explanation does not become atheory until

a. a majority of scientists agree with it.

b. it has been supported by evidence fromnumerous investigations and observations.

c. it is first proposed as an explanation.

d. it is published in a textbook.


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Chapter01 Section02 Meredith

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