Designing an Designing an Experiment Experiment

The idea that life can arise from The idea that life can arise from nonliving matter is called.nonliving matter is called.

Spontaneous generationSpontaneous generation

What was Francesco Redi’s What was Francesco Redi’s hypothesis about the hypothesis about the

appearance of maggots?appearance of maggots?

Flies produce maggots.Flies produce maggots.

What are variables in an What are variables in an experiment?experiment?

They are factors that can change.They are factors that can change.

Ideally, how many variables should Ideally, how many variables should an experiment test at a time?an experiment test at a time?

It should test only oneIt should test only onevariable at a time.variable at a time.

When a variable is kept unchanged When a variable is kept unchanged in an experiment, it is said to be. in an experiment, it is said to be.

Control variableControl variable

6. 6. What is a controlled experiment? What is a controlled experiment?

A controlled experiment is an A controlled experiment is an experiment in which one variable is experiment in which one variable is changed while the other variables changed while the other variables are controlled.are controlled.

Redi’s ExperimentRedi’s Experiment

In Redi’s experiment, what were the manipulated In Redi’s experiment, what were the manipulated variable and the responding variable?variable and the responding variable?

The manipulated variable was the The manipulated variable was the presence or absence of the gauze presence or absence of the gauze covering, and the responding covering, and the responding variable was whether maggots variable was whether maggots appear.appear.

For what do scientists use the data For what do scientists use the data from a controlled experiment? from a controlled experiment?

They use it to evaluate the They use it to evaluate the hypothesis and draw a conclusion.hypothesis and draw a conclusion.

When scientists look for explanations for specific When scientists look for explanations for specific observations, what do they assume about nature? observations, what do they assume about nature?

They assume that the patterns in They assume that the patterns in nature are consistent.nature are consistent.

Why do scientists assume that Why do scientists assume that experimental results can be experimental results can be

reproduced?reproduced?

A key assumption in science is that A key assumption in science is that nature behaves in a consistent nature behaves in a consistent manner.manner.

What did Anton van Leeuwenhoek What did Anton van Leeuwenhoek discover? discover?

He discovered a world of tiny moving He discovered a world of tiny moving objects in rainwater, pond water, and objects in rainwater, pond water, and dust that he called “animalcules.”dust that he called “animalcules.”

14. 14. What did John Needham What did John Needham conclude from his test of Redi’s conclude from his test of Redi’s

findings?findings?

He concluded that theHe concluded that thelittle animals in a bottle of gravy little animals in a bottle of gravy could only have come from the juice could only have come from the juice of the gravy.of the gravy.

What did Spallanzani do to What did Spallanzani do to improve upon Redi’s and improve upon Redi’s and

Needham’s work?Needham’s work?

He boiled two containers of gravy, He boiled two containers of gravy, assuming that the boiling would kill assuming that the boiling would kill any microorganisms that were any microorganisms that were present.present.

How did Pasteur settle the How did Pasteur settle the spontaneous generation argument?spontaneous generation argument?

He designed a special flask that He designed a special flask that showed as long as broth was showed as long as broth was protected from microorganisms, it protected from microorganisms, it remained free of livingremained free of livingthings.things.

Type of Variable DefinitionType of Variable Definition

Manipulated variable The variable that Manipulated variable The variable that is deliberately changed in an is deliberately changed in an experimentexperiment

Responding variable The variable that Responding variable The variable that is observed and changes in response is observed and changes in response to the manipulated variableto the manipulated variable

VARIABLESVARIABLES

In animal field studies, why do scientists In animal field studies, why do scientists usually try to work without making the usually try to work without making the

animals aware that humans are present? animals aware that humans are present?

To learn how animals in the wild interact, it is To learn how animals in the wild interact, it is necessary to observe the animals without necessary to observe the animals without disturbing them.disturbing them.

When a controlled experiment is not possible, why When a controlled experiment is not possible, why do scientists try to identify as manydo scientists try to identify as many

relevant variables as possible?relevant variables as possible?

They identify as many as possible so that most variables They identify as many as possible so that most variables are controlled.are controlled.

The theory that new organisms come The theory that new organisms come from existing organisms is called.from existing organisms is called.

biogenesisbiogenesis

In science, what is a theory? In science, what is a theory?

A theory is a well-tested explanation A theory is a well-tested explanation that unifies a broad range of that unifies a broad range of observations.observations.

Is the following sentence true or Is the following sentence true or false? false?

A theory may be revised or replaced A theory may be revised or replaced by a more useful explanation.by a more useful explanation.

TrueTrue