A teacher collected some beetles from a rotting log and placed them in a container of dry oatmeal in her classroom. She kept the box covered with a light cloth so that the beetles could not escape. She also asked one of her students to add potato and apple pieces once a week to provide food and moisture for the beetles. After several weeks, the student reported that there were some strange-looking, wormlike organisms in the container.
1 – 2 How Scientists Work
The Scientific Method
The Steps of the Scientific Method
Designing an Experiment
State the Problem
Form a Hypothesis
Draw a Conclusion
Set Up a Controlled Experiment
group, constants and variables
What have I observed?
What do I want to know?
Has anyone asked this before?
Did they discover an answer?
How did they go about looking for an answer?
What other things do I need to understand to answer my question?
Based on the research you have done, write a possible answer or solution – your best educated guess – to your question.
What was expected? What was unexpected?
What trends did you notice in the data?
Indicate whether or not the data supports the hypothesis and explain why or why not.
Suggest possible improvements to the experiment.
Suggest further avenues of research or uses for the information discovered.
1st Experiment- 1668, Francesco Redi:
Figure 1-8 Redi’s Experiment on Spontaneous Generation
OBSERVATIONS: Flies land on meat that is left uncovered. Later, maggots appear on the meat.
HYPOTHESIS: Flies produce maggots.
jars, type of meat,
gauze covering that
keeps flies away from
No maggots appear
CONCLUSION: Maggots form only when flies come in contact with meat. Spontaneous generation of maggots did not occur.
2nd Experiment- Mid 1700s, John Needham:
under the right conditions.
3rd Experiment- Lazzaro Spallanzani:
Figure 1-10 Spallanzani’s Experiment
Gravy is teeming
Gravy is boiled.
Needham tried first but didn’t bring gravy to hot enough temperature.
Gravy is free of
Gravy is boiled.
4th Experiment- 1864, Louis Pasteur:
can only come from living things.
and is now considered a theory
Figure 1-11 Pasteur’s Experiment
Broth is boiled.
Broth is free of
for a year.
teeming with microorganisms.
What can you conclude?
What other factors may affect the growth?