1. Outline 1-2 How Scientists Work
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2. 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
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3. Designing an Experiment
Setting Up a Controlled Experiment
A controlled experiment involves:
Experimental group(s)
These receive some type of treatment: what you are testing
2. Control group
Does NOT get the treatment. This will be compared to the experimental group(s).
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4. Designing an Experiment
Experimental Variables:
The control and experimental groups should be identical except for one factor that is deliberately manipulated. This is called the manipulated variable, or independent variable.
The variable that is observed or measured and that changes in response to the manipulated variable is called the responding, or dependent, variable. 
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5. Designing an Experiment
Experimental Variables (continued):
The controlled variables are those that must remain the same between the control and experimental groups.
For example:
Effect of differing amounts of fertilizer on plant growth
Each plant must be exposed to the same conditions except for the amount of fertilizer:
Same temperature, light, soil, water, etc.
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6. Designing an Experiment
Recording and Analyzing Results
Scientists keep written records of their observations, or data.
Sometimes drawings are used to record certain kinds of observations.
Today, researchers use computers to record their work.
Online storage makes it easier for other researchers to review the data.
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7. Designing an Experiment
Drawing a Conclusion
Scientists use the data from an experiment to evaluate a hypothesis and draw a valid conclusion.
This might involve mathematical calculations and statistics.
Do the results support or falsify the hypothesis? Remember, hypotheses are NEVER PROVEN, only supported.
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8. Repeating Investigations
Scientists repeat experiments to be sure that the results match those already obtained.
Publishing Results
Write a report to let other scientists know what you did and to allow them to review, criticize and repeat the experiment.
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9. Designing an Experiment
Series of Experiments as an Example of the Scientific Method at Work:
Asking a Question
Many years ago, people wanted to know how living things came into existence.
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10. Designing an Experiment
Forming a Hypothesis
One early hypothesis was spontaneous generation, or the idea that life could come from nonliving matter.
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.
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11. 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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12. 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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13. Designing an Experiment
Redi’s Experiment
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14. Repeating Investigations
Needham's Test of Redi's Findings
Needham challenged Redi’s results by claiming that spontaneous generation could occur under the right conditions.
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15. 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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16. Repeating Investigations
Spallanzani's Test of Redi's Findings 
He did a different experiment to find out if Needham was correct
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?
Gravy is boiled.
Gravy is boiled.
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17. Repeating Investigations
Spallanzani's Test of Redi's Findings 
Flask is open.
Flask is sealed.
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18. Repeating Investigations
Spallanzani's Test of Redi's Findings 
Gravy is teeming with microorganisms.
Gravy is free of microorganisms.
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19. Repeating Investigations
Pasteur’s Experiment - with open curved neck flask
Broth is free of microorganisms for a year.
Curved neck is removed.
Broth is teeming with microorganisms.
Broth is boiled
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.
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20. Repeating Investigations
Louis Pasteur’s experiment conclusively disproved the hypothesis of spontaneous generation.
Pasteur showed that living things come only from other living things.
This idea is now known as biogenesis.
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21. 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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22. 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 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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