What is Science?

1. What is Science? Ms. Hirsh Honors Biology

2. Scientific Method (5 Steps) • An organized plan for gathering, organizing and communicating information • Used to solve a problem or better understand an observed event Observation/Question  Hypothesis  Controlled Experiment  Data Collection  Conclusion

3. Parts to a Good Experiment Whenever possible, a hypothesis should be tested by an experiment in which only one variable is changed at a time. All other variables should be kept unchanged or controlled • Controlled Experiment – Only 1 variable • Control – the factors in an experiment that remain the same and do not change • Variable – the factors in a experiment that change • Manipulated Variable – Variable that deliberately changes • Responding Variable – Variable that changes in response to the manipulated variable

4. Theory verse Law • As evidence from an investigation builds up, a hypothesis may become so supported that scientists consider it a theory • Theory – Well tested explanation for a set of observations • Subject to change, may be revised • Never proved, only disproved • Widely accepted by scientific community • Law – Statement that summarizes a pattern in nature • Law states how something will behave and a theory explains how it works

5. Redi and Spontaneous Generation • Spontaneous Generation – primitive theory that states life “arose” from non-living matter. Is now considered a hypothesis maggots from meat, mice from grain, beetles from dung • Francesco Redi (Italian physician) prediction – keeping flies away from meat would prevent the appearance of maggots. Set up a controlled experiment

6. Redi and Spontaneous Generation OBSERVATIONS: Flies land on meat that is left uncovered. Later, maggots appear on the meat. HYPOTHESIS: Flies produce maggots. PROCEDURE Uncovered jars Covered jars Controlled Variables: jars, type of meat, location, temperature, time Several days pass Manipulated Variables: gauze covering that keeps flies away from meat Responding Variable: whether maggots appear Maggots appear No maggots appear CONCLUSION: Maggots form only when flies come in contact with meat. Spontaneous generation of maggots did not occur.

7. Leeuwenhoek and Needham’s Test of Redi’s Findings • Leeuwenhoek discovered a world of tiny organisms in rainwater and pond water. Noted that they were alive and called them “animalcules” or tiny animals. • John Needham (English scientist in 1700’s) suggested spontaneous generation could exist under the correct conditions. He sealed a bottle of gravy, heated it and claimed he had killed all tiny organisms. After several days it was swarming with activity. “These little animals can only have come from the juice of this gravy!”

8. Spallanzani’s Test of Redi’s Findings • Lazzaro Spallanzani (Italian Scholar) thought Needham had not heated samples enough and decided to improve on his experiment • Boiled 2 containers of gravy to kill all microorganisms and immediately sealed one of them. After several days, the open flask is teeming with microorganisms while the sealed mask is microorganism free. • Concluded that spontaneous generation did not exist and that new organisms are produced only by existing organisms

9. Spallanzani’s Test of Redi’s Findings

10. Pasteur’s Test of Spontaneous Generation • Some scientists still supported spontaneous generation and argued that the air was a necessary factor and contained a “life force”. Spallanzani’s test excluded the air. • Louis Pasteur (French scientist in 1800’s) decided to settle the argument and created a special flask with a long curved neck. The flask contained gravy but the curved neck prevented microorganisms from entering the broth. He let the boiled broth and let sit for a year and it still remained free of microorganisms. Broke off the curved neck and within several days was teeming with microorganisms

11. Pasteur’s Test of Spontaneous Generation