1. The Scientific Method

2. The scientific method
Is how scientists as questions about the world and test the answers
In other fields: art, philosophy, music, history, specialists ask questions about the world
The scientific method is different

3. The scientific method defined:
Is a system of asking questions and then
Developing explanations and then
Testing these explanations against the reality of the natural world

4. Steps in the scientific method (1)
State a specific problem or question based on an observation of the natural world
A fact is a repeatable observation
With the problem in mind propose an explanation for what you observe. This explanation is the hypothesis

5. Steps in the scientific method (2)
Test the hypothesis
One way is to make more observations and see if they are ALL consistent with your hypothesis
Another way is set up a controlled test of the hypothesis. This is called the experiment
Controlled test means you have a control group of test subjects and an experimental group of test subjects

6. Steps in the scientific method (3)
Analyze the results of the experiment
Sometimes the results are clear cut and obvious; your hypothesis stands up (=correct) or it does not (=incorrect)
Sometimes the results suggest a new hypothesis; you start the process over again until your hypothesis is correct

7. The experiment Control group: the benchmark Experimental group
You treat the subjects or articles in the control group exactly the same as those in the experimental group but without the treatment you are testing
Experimental group
You vary one condition (the variable) and keep all other conditions the same as in the control group

8. The experiment You collect data in an experiment
You summarize the data mathematically
Mean, mode, medium, range
You compare the data summary of the experimental group with the control group
Statistical tools are used
Compare means, standard deviations, variances

9. Three experiments to consider
Tomato experiment
Text page 14, see figure 1.10
Yellow fever experiment
Text page 17-19
Pasteur’s experiment

10. Louis Pasteur’s experiment
Hypothesis: “omnis cellula e cellua”
Famous goose neck flask experiment
Control flasks
Experimental flasks
Results confirm hypothesis (now theory) of biogenesis
Disproved hypothesis of spontaneous generation

11. Spontaneous Generation (1)
Up until the 17th century biologists thought that simple living things appeared spontaneously
Francisco Redi did the famous decaying meat experiment
Control: decaying meat covered with a cloth
Experimental: decaying meat open to the air
No maggots in the control

12. Spontaneous Generation (2)
Spontaneous generation idea was revived with the invention of the microscope
Microorganisms and small animals seemed to appear spontaneously in water or broth
Pasteur’s experiment disproved spontaneous generation for the second time