Chapter 1 Section 1-2: How Scientists Work

Objectives Describe how scientists test hypotheses. Describe how scientists test hypotheses. Explain how a scientific theory develops. Explain how a scientific theory develops.

Designing an Experiment People’s ideas about the origin of living things have changed over centuries. People’s ideas about the origin of living things have changed over centuries. Throughout time, Scientists have been challenging established ideas on where living things came from. Throughout time, Scientists have been challenging established ideas on where living things came from. Exploring this change is one example of how science works. Exploring this change is one example of how science works.

Asking a Question For years, observations seemed to show that living things could just suddenly “appear.” For years, observations seemed to show that living things could just suddenly “appear.” Example: Maggots “appearing” on meat that was left to rot. Example: Maggots “appearing” on meat that was left to rot. In wondering how these events happened, people were identifying a problem to be solved: “How do living things come into being?” In wondering how these events happened, people were identifying a problem to be solved: “How do living things come into being?”

Forming a Hypothesis The idea of SPONTANEOUS GENERATION, or life arising from non-living matter was accepted for centuries. The idea of SPONTANEOUS GENERATION, or life arising from non-living matter was accepted for centuries. In 1668, Francesco Redi proposed a different hypothesis for the appearance of maggots. In 1668, Francesco Redi proposed a different hypothesis for the appearance of maggots. “Maggots come from FLIES.” “Maggots come from FLIES.”

Setting Up a Controlled Experiment Testing a hypothesis often involves setting up an experiment. Testing a hypothesis often involves setting up an experiment. Factors in an experiment that can change are called VARIABLES. Factors in an experiment that can change are called VARIABLES. Examples of variables: equipment used, type of material, amount of material, temperature, light, time. Examples of variables: equipment used, type of material, amount of material, temperature, light, time.

Setting Up a Controlled Experiment WHENEVER POSSIBLE: A hypothesis should be tested by an experiment in which only one variable is changed at a time. (Too many variables = cannot tell which effected the outcome) WHENEVER POSSIBLE: A hypothesis should be tested by an experiment in which only one variable is changed at a time. (Too many variables = cannot tell which effected the outcome)

Setting Up a Controlled Experiment A type of experiment in which ONE variable is changed is a CONTROLLED EXPERIMENT. A type of experiment in which ONE variable is changed is a CONTROLLED EXPERIMENT. The variable that is CHANGED is called the MANIPULATED VARIABLE. The variable that is CHANGED is called the MANIPULATED VARIABLE. The variable that CHANGES in response to the manipulated variable is called the RESPONDING VARIABLE. The variable that CHANGES in response to the manipulated variable is called the RESPONDING VARIABLE.

Redi’s Experiment Draw and label Redi’s Experiment Below:

Recording and Analyzing Results Scientists keep written records of their observations. Scientists keep written records of their observations. Records are kept in journals, notebooks, computers, etc. Records are kept in journals, notebooks, computers, etc.

Drawing a Conclusion Data from experiments is used by scientists to draw a valid conclusion. Data from experiments is used by scientists to draw a valid conclusion. Evidence leads to hypotheses being supported or refuted. Evidence leads to hypotheses being supported or refuted. Redi’s evidence supported his hypothesis, so he concluded that maggots were produced by flies. Redi’s evidence supported his hypothesis, so he concluded that maggots were produced by flies.

Why should we care about this? Not only did Redi’s results show that maggots were produced by flies… Not only did Redi’s results show that maggots were produced by flies… His results ALSO refuted the hypothesis of SPONTANEOUS GENERATION. His results ALSO refuted the hypothesis of SPONTANEOUS GENERATION.

Repeating Investigations KEY: In science, one must be able to reproduce experimental results. KEY: In science, one must be able to reproduce experimental results. Scientists are continuously retesting one another’s investigations, so it is important to communicate descriptions of experiments accurately. (via publishing them in journals, etc.) Scientists are continuously retesting one another’s investigations, so it is important to communicate descriptions of experiments accurately. (via publishing them in journals, etc.)

Needham Tests Redi’s Experiment After van Leeuwenhoek discovered microorganisms in pond water, scientists spent the next 200 years trying to figure how these tiny organisms came to be. After van Leeuwenhoek discovered microorganisms in pond water, scientists spent the next 200 years trying to figure how these tiny organisms came to be. Mid-1700s: John Needhan used these microorganisms to test Redi’s work. Needham thought these microorganisms could be created through Spontaneous Generation. Mid-1700s: John Needhan used these microorganisms to test Redi’s work. Needham thought these microorganisms could be created through Spontaneous Generation.

Needham Tests Redi’s Experiment 1. Sealed bottle of gravy and heated it. (to kill microorganisms) 2. Unsealed bottle and left it to sit for a few days. 3. When he came back, the gravy was swarming with microorganisms. 4. Concluded that animals came from the gravy.

Spallanzani’s Test of Redi’s Findings 1. Boiled two flasks of gravy. 2. Sealed one and left the other one open. 3. After a few days, the gravy in the open flask was teeming with microorganisms, but the sealed flask was free of microorganisms. 4. Conclusion: Microorganisms were offspring of microorganisms that entered through the air.

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Pasteur’s Test of Spontaneous Generation Well into the 1800s, scientists still supported spontaneous generation, arguing that AIR was a necessary ingredient for live to arise. Well into the 1800s, scientists still supported spontaneous generation, arguing that AIR was a necessary ingredient for live to arise. Pasteur used air to further refute SPONTANEUS GENERATION. Pasteur used air to further refute SPONTANEUS GENERATION.

Pasteur’s Test of Spontaneous Generation Draw and label Pasteu’s Experiment:

Pasteur’s Test of Spontaneous Generation 1. Designed a flask with a curved neck. 2. Flask remained open to air. 3. Microorganisms did not make their way through the curved neck. 4. Conclusion: As long as the broth was protected from microorganisms, it would remain free of living things.

The Impact of Pasteur’s Work Saved French wine industry from contamination by microorganisms. Saved French wine industry from contamination by microorganisms. Began to uncover nature of infectious disease (a result of microorganism entering the body). Began to uncover nature of infectious disease (a result of microorganism entering the body).

When Experiments are NOT Possible Researchers carry out field studies, observing organisms in their natural environments. Researchers carry out field studies, observing organisms in their natural environments. This entails identifying related variables, and exerting great care in carrying out investigations. This entails identifying related variables, and exerting great care in carrying out investigations.

How a Theory Develops Theory: well-tested explanation that unifies a broad range of observations. Theory: well-tested explanation that unifies a broad range of observations. Theories enable scientists to make predictions about new situations. Theories enable scientists to make predictions about new situations. Theories are constantly being analyzed, reviewed and retested. Theories are constantly being analyzed, reviewed and retested.