The Slow Death of Spontaneous Generation

Spontaneous Generation What do you think this means?

+ = Horse Hair Water Snake

Francesco Redi (1626 – 1697) “Founder of Experimental Biology” and first to challenge the theory of Spontaneous Generation

At the time of Francesco Redi it was believed that rotting meat gave rise to maggots.

What kind of experiment do you think Redi designed to prove that maggots come from flies that visit the rotting meat? If you were Redi, what procedure would your procedure be? (remember: He lived in the 17 th century!)

What was the independent variable in Redi’s experiment? Type of lid on the container

Lazzaro Spallanzani (1729 – 1799) One hundred years after Redi another Italian scientist took on spontaneous generation. Spallanzani experimented with microorganisms in gravy. Where did the microorganisms in the flask on the left come from? What is a limitation of this experiment in disproving spontaneous generation?

Louis Pasteur (1822 – 1895) This French scientist contributed much of what we know about microorganisms and disease. His experiments, among many other important things, disproved the idea of spontaneous generation.

Designing Pasteur’s Experiment Using beef broth and glass flasks, what scientific design do you think Pasteur used that was different from Spallanzani? Remember: This is what Spallanzani’s experiment looked like:

Designing Pasteur’s Experiment What was the purpose of the “S” shaped tube on the top of the flask? This shape allowed air to continue to enter the flask but prevented air- borne microorganisms from coming into contact with the broth.

Parts of a controlled experiment: How many independent variables should be tested for in an experiment at one time? – Only one What part of an experiment has the independent variable? – The experimental group What part of an experiment does not have the independent variable? – The control group

Parts of a controlled experiment: What is the purpose of the control group? – To use as a comparison, so you know what would normally happen in the experiment if the independent variable was not introduced In Pasteur’s experiment what was the control group? – The flask with the unbroken tube

Parts of a controlled experiment: In Redi’s experiment what was the control group? – The jar open to the air

Parts of a controlled experiment: Pick one of the three experiments and list as many controlled variables (constants) as you can think of.

One Last Note: Louis Pasteur developed the process by which food is heated to a high temperature for a short amount of time and then cooled. What is this process called? Pasteurization