Designing an Experiment What is Science? Science is the method that people use to answer questions Copyright Pearson Prentice Hall

Designing an Experiment What is Biology? If science is the method people use to answer questions… …Biology attempts to answer questions about living organisms Copyright Pearson Prentice Hall

Designing an Experiment Asking a Question Science helps us answer questions of how and why. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

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 Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

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. Copyright Pearson Prentice Hall

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 Copyright Pearson Prentice Hall

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. 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

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. Copyright Pearson Prentice Hall

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. 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  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? 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 Test of Spontaneous Generation Louis Pasteur conclusively disproved the hypothesis of spontaneous generation. Pasteur showed that all living things come from other living things. Copyright Pearson Prentice Hall

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 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 does a scientific theory develop? 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

Copyright Pearson Prentice Hall 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. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 1–2 Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 1–2 In an experiment, the variable that is deliberately changed is called the control. manipulated variable. responding variable. constant control Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 1–2 The mistaken belief that living organisms can arise from nonliving matter is called biogenesis. Pasteur's theory. spontaneous generation. Spallanzani’s hypothesis. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 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 Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 1–2 A well-tested explanation that unifies a broad range of observations is a hypothesis. variable. control. theory. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 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. Copyright Pearson Prentice Hall

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