The Slow Death of Spontaneous Generation Spontaneous Generation

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 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 airborne 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