Where do living organisms come from?Biology

Spontaneous Generation• Life can come from non-living things

• Idea persisted up to the 1800s

• Many ideas were based on observations that had never been tested

• Examples:• Frogs appeared in muddy soil when not

present when soil was drier• Mice came from moldy grain• Sewage and garbage turned into rats• Rotting meat was the source of flies

Francesco Redi1668-Experiment to challenge the idea of spontaneous generation, considered 1st true scientific experiment that contained a control

Apply “Scientific Method” to Redi’s experiment

Question:

Hypothesis:

IV:

DV:

Control:

Conclusion:

Apply “Scientific Method” to Redi’s experiment

Question: Where do flies come from? Can rotting meat produce flies?

Hypothesis: Rotting meat does not turn into flies. Only flies can produce other flies.

IV: jars of meat sealed with either lids or gauze covering

DV: record presence or absence of flies and maggots

Control: jars containing meat without covers on them

Conclusion: Maggots arose only where flies were able to lay eggs. The sealed container had no flies/maggots/eggs. Therefore, only flies can produce more flies.

What happened next?• Many people still felt that spontaneous

generation was possible in certain circumstances...including Redi.

• By the 1700s it was known the boiling substances killed microorganisms. In 1745, John Needham performed an experiment to test whether or not microoganisms appeared spontaneously after boiling some meat broth. He boiled the broth, placed it in a flask and sealed the container. Microoganisms grew in the broth so Needham considered his results to be support for spontaneous generation.

• Why do you think Needham got these results?

“Life force” in air and/or oxygen that enable the

bacteria to form in the flask

Lazzaro Spallanzani Repeated John Needham’s

experiment but boiled the broth in a sealed flask in which the air had been removed.

No microorganisms formed which provided evidence against spontaneous generation.

Why do you think he got these results?

Pasteur1859 experiment to provide evidence against spontaneous generation

Performed a variation of Needham and Spallanzani’s experiments

Apply “Scientific Method” to Pasteur’s experiment

• Question:

• Hypothesis:

• IV:

• DV:

• Control:

• Conclusion:

Apply “Scientific Method” to Pasteur’s experiment

• Question: Is there a “life force” in air/oxygen that can allow for bacteria to form through spontaneous generation? Is it possible to let air into a container but not the bacteria in the air?

• Hypothesis: Broth that has been boiled in a flask that is exposed to air will remain sterile, as long as bacteria are not able to enter the flask.

• IV: used flasks with long, S-shaped necks; some flasks were closed with cotton plugs

• DV: presence or absence of bacterial growth in the flasks based on observations of odor, cloudy appearance of broth and microscope

• Control: some flasks that were used opened straight up so bacteria and air had access to the broth in the flask

• Conclusion: There is no “life force” and organisms do not arise via spontaneous generation.