1. RHP 5: Controlled Experiment
21 February 2019
LHP 4: Variables
RHP 5: Controlled Experiment
Compare and Contrast:
Manipulated / Responding / Controlled Variables

2. Experiments
Used to test a hypothesis
Generate data

3. Designing an Experiment
State the problem/ask a question.
Form a hypothesis [null hypothesis].
Set up a controlled experiment.
Record and analyze results.
Draw a conclusion
But…..
It doesn’t stop there!
Retest and share the results.

4. In a controlled experiment a scientist isolates and tests a single variable.
Manipulated variable (Independent variable)
This is changed by the experimenter. Only one variable should be manipulated by the scientist.
Responding variable (Dependent variable)
This is the variable measured by the experimenter
Controlled variables
All other variables are kept the same

5. IAN LHP Create a Venn Diagram
Compare and contrast manipulated, responding, and controlled variables.
Give at least 3 bullet points for each

6. RHP 7: Famous Experiments
21 February 2019
LHP 6: Variables
RHP 7: Famous Experiments
Create a chart that identifies the independent, dependent, and controlled variables for Redi’s, Spallanzani’s, and Pasteur’s experiments.

7. Famous Experiments

8. Francisco Redi
1600s popular belief was that flies and other creatures would spontaneously generate from nonliving matter.
1668 Redi proposed a different hypothesis.
Observed flies landing on chunks of meat, then several days later maggots appear.
Hypothesized that maggots came from the flies, not the dead meat.
In other words, life only comes from living organisms.

9. 1668

10. Needham’s Experiment
Heated gravy to kill microorganisms, then sealed the flask
After several days gravy was teeming with microbes
Claimed organisms spontaneously generated

11. Spallanzani’s Experiment
Didn’t think Needham heated flask enough to kill microorganisms
Repeated experiment, but boiled broth thoroughly
Sealed flask did not grow microbes, open flask did
Findings not accepted by many scientists because sealed flask did not allow “life force” in

12. Pasteur’s Experiment (1864)
Repeated experiment using a flask with a special neck that allowed air into it
Remained free of microorganisms until the neck was removed

13. Why do scientists publish their procedures and results of their experiments?
So their work can be repeated.
Their procedures can be reviewed.
And, others can try to reproduce their results.

14. Hypothesis vs. Theory
A hypothesis is a possible explanation for a problem.
A theory has been well tested and unifies many observations.
What started as Redi’s hypothesis in the 1600’s eventually became the theory of biogenesis [life must come from other living things].

15. IAN LHP
Create a chart that identifies the independent, dependent, and controlled variables for Redi’s, Spallanzani’s, and Pasteur’s experiments.