The Story of Spontaneous Generation

Objectives I can… Argue that science is not about proving ideas correct but rather disproving bad ideas (understanding the Nature of Science) Use the story of spontaneous generation as an example of the scientific method bringing us to more reliable knowledge.

Spontaneous generation Spontaneous generation is the idea that living things can be produced from non-living things. From the time of the ancient Romans, through the Middle Ages, and until the late nineteenth century, it was generally accepted that some life forms arose spontaneously from non-living matter.

The Question Where did life forms such as mice, maggots, and microorganisms come from?

Different Theories of Spontaneous Generation Theory 1 = the spontaneous production of mice required placing sweaty clothes and husks of wheat in an open-mouthed jar, then waiting for about 21 days, during which time it was alleged that the sweat from the clothing would penetrate the husks of wheat, changing them into mice.

The Theories T2 = maggots arise spontaneously in rotting meat T3 = microorganisms arise spontaneously in broth.

Different scientist tested theses theories over the years Francesco Redi An Italian doctor Louis Pasteur A French Scientist Lazzaro Spallanzani An Italian Scientist

Redi’s Experiment Question: where did maggots come from Hypothesis: maggots came from the eggs of flies

Redi’s Experiment Procedure: Redi put rotting meat into three jars. Jar 1 – open to the air Jar 2 – covered with netting Jar 3 – sealed off completely from outside

Redi’s Experiment Results: Jar 1 = maggots developed on rotting meat Flies were observed on meat

Redi’s Experiment Results Jar 2 = maggots appeared on netting Flies were observed on netting

Redi’s Experiment Results Jar 3 = maggots did not appear at all in or around the sealed jar No flies were observed near jar 3

Redi’s Experiment Conclusion: The hypothesis was supported by the data and therefore accepted Because there were no maggots in or around the jar it was concluded the maggots came from the fly eggs.

Spallanzani’s Experiment Question: What causes microbes to form from decaying broth? Hypothesis: Microbes come from the air. Boiling will kill microbes.

Spallanzani’s Experiment Procedure: Spallanzani put broth into four flasks Flask 1 – left open to the air Flask 2 – was sealed Flask 3 – was boiled and left open Flask 4 – was boiled then sealed

Spallanzani’s Experiment Results Flask 1 – left open to the air Turned cloudy (microbes found) Flask 2 – was sealed Flask 3 – was boiled and left open Flask 4 – was boiled then sealed Did not turn cloudy (NO MICROBES)

Spallanzani’s Experiment Conclusions: The hypothesis was accepted Because the combination of boiling the broth (killing bacteria that were in the jar to start) and sealing the jar (keeping bacteria in the air out) it was concluded that boiling does kill bacteria and that Microbes come from the air.

Pasteur’s Experiment Question: Where do microbes come from to cause chicken broth to decay? Hypothesis: Microbes come from cells of organisms on dust particles in the air; not from the air itself.

Pasteur’s Experiment Procedures: Control Group Experimental group One flask of broth open to the air Experimental group One S-shaped flask that prevents dust from entering the flask.

Pasteur’s Experiment Procedure: Pasteur put broth in both the open flask and into special S-Shaped flasks and boiled it. S-shaped flask was used to trap any dust particles Boiling was done to kill all the microbes already in the flask.

Pasteur’s Experiment Procedure (cont.) Pasteur then watched to see if any changes took place with the appearance of the broth in the flasks. If the broth became cloudy that meant microbes were present

Pasteur’s Experiment Results: Open flask – the broth became cloudy S-shaped flask – the broth remain clear Dust was observed in the neck of the S-shaped neck of the flask.

Pasteur’s Experiment Conclusion: The hypothesis was supported by the data therefore it was accepted. Because the broth did not turn cloudy and dust was observed trapped in the neck of the S-Shaped flask, it was concluded that the microbes came from cells of organisms riding on dust particles.

The Scientific Method Each of these scientist used the scientific method of investigation to successfully disprove spontaneous generation. Remember Science is not just a body of facts but a method of investigation. Science is a process that allows us to obtain reliable knowledge by disproving bad ideas.

Summary Write a summary of your notes in the space provided. What are you supposed to know? What point are we trying to make? What were some important details? How do these details support the main point? What were your personal thoughts? What was confusing or what made a lot of sense?