Name: ______

Pasteur’s Experiment

The Experiment:

You are going to recreate the experiment that Louis Pasteur used to prove that spontaneous generation could not occur and was not the basis for the origin of life.

Spontaneous generation is the hypothetical process by which living organisms develop from non-living matter. According to this theory, pieces of bread or cheese wrapped in rags and left in a dark corner for example, were thus thought to produce mice because after several weeks there were mice in the rags. Many believed in spontaneous generation because it explained such occurrences as the appearance of maggots on decaying meat.

Lab Group #: ______

Group Member: ______

Group Member: ______

Group Member: ______

Do the following as a group:

Hypothesis:

An educated guess written as an “if, then” statement.

Experiment:

Independent Variable (What are we changing?):

Dependent Variable (What are we measuring?):

Constant Variables (What is staying the same?):

Control Group (Our basis for comparison):

Materials:

  • 200 mL of beef broth
  • Hot plate
  • Safety goggles
  • (2) 125 mL Erlenmeyer flasks
  • Wax pencil
  • (1) one-hole rubber stopper with S-tube

Procedure:check off each step so you do not miss anything!!

  1. Obtain two (2) 125 mL Erlenmeyer Flasks.
  2. Inspect them for cracks.
  3. Using a wax pencil, write your group number and class period on each flask.
  4. Pour approximately 100 mL of beef broth from class supply into both flasks.
  5. Insert the S-tube stopper into ONE flask. Leave the other flask open.
  6. Put on your safety goggles and put on an apron.
  1. Place the flasks on the hot plate and set the hot plate to the HIGHEST setting. BE CAREFUL NOT TO TOUCH THE TOP OF THE HOT PLATE!
  2. Bring the broth to a boil and let it continue to boil for 30 minutes.
  3. Turn off the hot plate. (hot plates will remain hot long after they have been turned off!)
  4. Using heatproof gloves carefully remove each flask from the hot plate and place on lab table.
  5. Make observations about the appearance of the liquid in each flask and record your findings in the data table provided.
  6. Place the flasks in a location that is designated.
  7. You will make observations of these flasks again in one week and then again after two weeks.
  8. NOTE: if solution becomes cloudy = bacterial growth. If solution contains thin, threadlike structures = mold growth.

DATA TABLE:

Flask / Description on Day 1 / Description after one week / Description after two weeks
Open Flask
S-Shaped Flask

Analysis Questions:

  1. State the problem that the scientists of Pasteur’s time were trying to address.
  2. What was Pasteur’s hypothesis?
  3. What was the purpose of boiling the broth?
  4. How did Pasteur’s S-tube flask help to end the controversy over spontaneous generation?
  5. Was this recreation of Pasteur’s experiment a controlled experiment? Explain your answer.
  6. Was Pasteur’s hypothesis correct based on your findings? Explain your answer using your observations.
  7. What would happen if the flask with the S-tube was disturbed causing some of the broth to enter into the curve of the S-tube and return back into the flask? Explain.