How Science Works

1. How Science Works

2. Objectives • How do scientists test hypothesis? • How does a scientific theory develop?

3. Testing Hypothesis • Ask a Question • Form a Hypothesis • Educated guess • Design experiment • Gather data • Conclusion or retest • Ex: Spontaneous Generation – beginning of experimental science.

4. Spontaneous Generation • Idea that life came from nonliving matter • In 1668 Francesco Redi observed maggots and flies on meat after a few days. • Produced new hypothesis that flies produce maggots. • Designed experiment • Contained 2 variables • Manipulated variable – deliberately changed • Responding variable – changes in response to manipulated variable

6. Needham’s Test of Redi’s Findings • Mid-1700’s used van Leevenhoek’s microscope to view small “animalcules”. • Claimed spontaneous generation could occur under right conditions • Sealed a bottle of gravy and heated it. • He claimed the heat killed the animalcules • Several days later he found animalcules in the gravy – concluded spontaneous generation can happen.

7. Spallanzani’s Test • Thought Needham did not heat the gravy long enough • Boiled two containers of gravy • Sealed one jar immediately • Second jar left open • Examined a few days later • Sealed – No life • Open – Life came from air

9. Pasteur’s Test • 1800’s added to Spallanzani’s experiment • Designed a long neck flask which allowed air in with no microorganisms. • After heating – no life existed • 1 year later – broke the neck and then microorganisms grew • Final experiment to disprove spontaneous generation.

11. If Experiments Not Possible • Some research has to be conducted in wild • Studying wild animals • Ethical considerations • Can not conduct experiments on people unless they volunteer and is not illegal.

12. Theory Development • A well supported hypothesis that has been tested numerous times • No theory is absolute truth • It is continually analyzed, reviewed, and critiqued • With new technology and evidence it can be revised