1. Designing an Experiment
What is Science?
Science is the method that people use to answer questions
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2. Designing an Experiment
What is Biology?
If science is the method people use to answer questions…
…Biology attempts to answer questions about living organisms
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3. Designing an Experiment
Asking a Question
Science helps us answer questions of how and why.
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4. Designing an Experiment
Forming a Hypothesis
When a scientist proposes an answer to a question they have formed a hypothesis
A hypothesis is a tentative explanation.
In order for the hypothesis to be accepted by others it must be tested.
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5. Designing an Experiment
Setting Up a Controlled Experiment
An experiment is a test for a hypothesis
A controlled experiment is one that has a basis for comparison.
Ex. You have two gardens you decide to try a new fertilizer on one of your gardens. Both gardens are identical. After one month both gardens have grown significantly however, there appears to be no difference between the two.
What can you conclude about the new fertilizer?
What would you conclude if there was only one garden?
The garden in which you did not use the new fertilizer is the control. It is your basis for comparison.
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6. Designing an Experiment
Setting Up a Controlled Experiment
The factors in an experiment are called variables
The variable that is deliberately changed is called the independent variable.
The variable that is observed and that changes in response to the independent variable is called the dependent variable.
Independent = Manipulated
Dependent = Responding
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7. Designing an Experiment
Setting Up a Controlled Experiment
Once an experiment is designed the scientist must collect Data
Data is the measurements and observations collected during the experiment
It must be collected and recorded in an organized manner.
Sometimes drawings are used to record observations.
The more data an experiment produces the more reliable the result.
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8. Designing an Experiment
How Scientists Interpret Data
Scientists use statistics to analyze data
Average (Mean): The central tendency of a data set.
Deviation: How far the average will vary by chance.
N+/- √N
This tells us that in a given set of numbers with an average N. 68% of the numbers in the set should fall within a range of √N
Ex. If the average height of a male human in the United states is 70 inches 68% of the men in the US are between 62 and 78 inches.
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9. Designing an Experiment
How Scientists Interpret Data
Additionally 95% of the time data will range by two standard deviations this is represented by
N+/-2√N
That tells us that in the United States 95% of men are between 53 inches and 87 inches tall.
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10. Designing an Experiment
What makes a good experiment?
Not all experiments will be equally accepted by scientists. The results of an experiment are best if:
The experimental groups are large.
The amount of data collected is large
There is a control
The experiment is repeated several times.
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11. Designing an Experiment
Looking at an old question
“Where do living things come from?”
All living things are called organisms.
Before the 15th century it was believed that organisms came from one of the four “elements” of the universe:
Earth, Fire, Water, Air
Or a combination of these
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12. Designing an Experiment
Looking at an old question
“Where do living things come from?”
In 1688 Francesco Redi ,an Italian physician, proposed that maggots “arose” not from meat but from fly eggs.
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13. 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.
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14. 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.
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15. Designing an Experiment
Redi’s Experiment
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16. Designing an Experiment
Drawing a Conclusion
Scientists use the data from an experiment to evaluate a hypothesis and draw a valid conclusion.
The results either support or refute the hypothesis. If the results refute the hypothesis it is rejected and a new hypothesis is formed.
Redi’s results supported the hypothesis that maggots were produced by flies, not spontaneous generation.
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17. Repeating Investigations
Needham's Test of Redi's Findings
John Needham challenged Redi’s results by claiming that spontaneous generation could occur under the right conditions.
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18. 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.
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19. Repeating Investigations
Spallanzani's Test of Redi'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?
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20. Repeating Investigations
Spallanzani's Test of Redi's Findings 
Flask is open.
Flask is sealed.
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21. Repeating Investigations
Spallanzani's Test of Redi's Findings 
Gravy is teeming with microorganisms.
Gravy is free of microorganisms.
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22. 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.
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23. 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
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24. Repeating Investigations
The Impact of Pasteur’s Work
Pasteur saved the French wine industry, which was troubled by unexplained souring of wine.
He saved the silk industry, which was endangered by a silkworm disease.
He began to uncover the nature of infectious diseases, showing that they were the result of microorganisms.
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25. 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.
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How a Theory Develops
How does a scientific theory develop?
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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.
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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.
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.
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How a Theory Develops
Scientific Laws
Scientific Laws are similar to theories but they are not the same.
Scientific Laws state a relationship observed in nature but do not attempt to explain why it exists
Ex. The Law of Gravity tells us that all objects exert a force on each other proportional to their mass. It does not tell us why this force exists.
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.
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1–2
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1–2
In an experiment, the variable that is deliberately changed is called the
control.
manipulated variable.
responding variable.
constant control
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1–2
The mistaken belief that living organisms can arise from nonliving matter is called
biogenesis.
Pasteur's theory.
spontaneous generation.
Spallanzani’s hypothesis.
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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
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1–2
A well-tested explanation that unifies a broad range of observations is a
hypothesis.
variable.
control.
theory.
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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.
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