Outline 1-2 How Scientists Work Copyright Pearson Prentice Hall

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 Copyright Pearson Prentice Hall

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). Copyright Pearson Prentice Hall

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.  Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

Designing an Experiment Redi’s Experiment Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

Repeating Investigations Spallanzani's Test of Redi's Findings  Flask is open. Flask is sealed. Copyright Pearson Prentice Hall

Repeating Investigations Spallanzani's Test of Redi's Findings  Gravy is teeming with microorganisms. Gravy is free of microorganisms. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 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. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 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. Copyright Pearson Prentice Hall

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