1. Aim: What are controlled experiments ?
About 2000 years ago, a Roman poet wrote these directions for producing bees
Why do you think individuals accepted this recipe?
Recipe for Bees
Kill a bull during the first thaw of winter
Build a shed
Place the dead bull on branches and herbs inside the shed.
Wait for summer. The decaying body of the bull will produce bees

2. Observations seemed to indicate that living things just suddenly appeared
Maggots on meat
Beetles on cow dung

3. Common Beliefs of the Time
Frogs and Turtles come from mud and rotting wood.
Mice come from straw.
Flies come from rotting meat.
Most of these ideas remained from the time of Aristotle.

4. In 1668 Francesco Redi challenged these ideas. He made observations
Noticed that maggots only appeared on meat a few days after flies were present
He asked a question.
Do flies have any thing to do with the appearance of maggots?

5. Hypothesis Flies produce maggots A good hypothesis is testable
Redi’s next step was to test his hypothesis
How do you test a hypothesis?
Based on his question he developed a hypothesis.
Group work: develop a plan to test a hypothesis.

6. A Controlled Experiment is developed to test a HYPOTHESIS
The independent variable is the one that is changed by the scientist. To insure a fair test, a good experiment has only one independent variable. As the scientist changes the independent variable, he or she observes what happens.
The scientist focuses his or her observations on the dependent variable to see how the organism responds to the change made to the independent variable.
Give examples based on experiments you have done in the past.

7. Redi’s Controlled Experiment
Observation: Flies land on meat that is left uncovered Later maggots appear on meat.
Hypothesis: Flies produce maggots.
Experiment:
Group: Explain the experiment.
Independent variable is the one that changes. Beaker with cover (flies do not smell the meat) and beaker with gauze (flies can smell the meat but cannot get to it)

8. Conclusion: Maggots form only when flies come in contact with meat
Conclusion: Maggots form only when flies come in contact with meat. Spontaneous generation did not occur.

9. Peer Review – Louis Pasteur’s Experiment
Experiments are repeated by other scientists to ensure the results are accurate.
Spontaneous Generation does not occur
Broth is boiled.
Broth is free of microorganisms for a year.
Curved neck is removed.
Broth is teeming with microorganisms.
The curved neck prevented microorganisms from making their way into the flask. Once the neck of the flask was broken, microorganisms could get to the broth, where the microorganisms multiplied.
Group : What did this experiment prove?

10. Controlled Experiment
Observations
Questions
Hypothesis
Experiment – independent and dependent variables (Procedure & Materials)
Data
Analysis of Data – Chart or graph
Conclusion

11. Inquiry-Deformed Frogs
Wetland Discovery
Students will make a list of the questions they have about these deformed frogs, and do what is asked on the handout.
HW 4
Inquiry-Deformed Frogs