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1.3: Scientific Theories

Difficulty Level: At Grade Created by: CK-12
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Theory vs. theory. Is a scientific theory different from the everyday use of the word theory?

A scientific theory is accepted as a scientific truth , supported by evidence collected by many scientists. The theory of evolution by natural selection is a classic scientific theory.

Scientific Theories

With repeated testing, some hypotheses may eventually become scientific theories. Keep in mind, a hypothesis is a possible answer to a scientific question. A scientific theory is a broad explanation for events that is widely accepted as true. To become a theory, a hypothesis must be tested over and over again, and it must be supported by a great deal of evidence.

People commonly use the word theory to describe a guess about how or why something happens. For example, you might say, “I think a woodchuck dug this hole in the ground, but it’s just a theory.” Using the word theory in this way is different from the way it is used in science. A scientific theory is more like a fact than a guess because it is so well-supported. There are several well-known theories in biology, including the theory of evolution, cell theory, and germ theory.

Two videos explaining scientific theories can be seen at http://www.youtube.com/watch?v=S5YGhprR6KE and http://www.youtube.com/watch?v=jdWMcMW54fA .

As you view Know the Difference (Between Hypothesis and Theory) , focus on these concepts:

  1. the controversy surrounding the words "hypothesis" and "theory,"
  2. the scientific use of the words "hypothesis" and "theory,"
  3. the criteria for a "hypothesis,"
  4. the National Academy of Sciences definition of "theory,"
  5. the meaning of the statement, "theories are the bedrock of our understanding of nature."

The Theory of Evolution

Evolution is a change in the characteristics of living things over time. Evolution occurs by a process called natural selection . In natural selection, some living things produce more offspring than others, so they pass more genes to the next generation than others do. Over many generations, this can lead to major changes in the characteristics of living things. The theory of evolution by natural selection explains how living things are changing today and how modern living things have descended from ancient life forms that no longer exist on Earth.

The Cell Theory

According to the cell theory , all living things are made up of cells, and living cells always come from other living cells.

The Germ Theory

The germ theory of disease, also called the pathogenic theory of medicine, is a theory that proposes that microorganisms are the cause of many diseases.

Summary

  • With repeated testing, some hypotheses may eventually become scientific theories. A scientific theory is a broad explanation for events that is widely accepted as true.
  • Evolution is a change species over time. Evolution occurs by natural selection.
  • The cell theory states that all living things are made up of cells, and living cells always come from other living cells.
  • The germ theory proposes that microorganisms are the cause of many diseases.

Practice

Use these resources to answer the questions that follow.

  1. How is the word "theory" used in common language?
  2. How is the word "theory" used in science?
  3. Provide a detailed definition for a "scientific theory."
  1. What is a scientific law?
  2. What is a scientific theory?
  3. Give an example of a scientific theory.
  4. Why is a scientific theory different from the common use of the word "theory"?

Review

1. Contrast how the term theory is used in science and in everyday language.

2. Explain how a hypothesis could become a theory.

Vocabulary

cell theory

cell theory

Theory that states that cells are the basic structural units of all organisms.
germ theory

germ theory

Theory that states that microorganisms are the cause of many diseases.
scientific theory

scientific theory

Broad explanation that is widely accepted as true because it is supported by a great deal of evidence.
hypothesis

hypothesis

Possible answer to a scientific question; must be falsifiable.

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Difficulty Level:

At Grade

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Date Created:

Feb 24, 2012

Last Modified:

Nov 11, 2014
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