Honors Biology Chapter 1 Section 2 How Scientists

Honors Biology Chapter 1 Section 2 How Scientists Work Essential Question: How would you explain the scientific method?

Designing an Experiment: back in time

Spontaneous Generation �Life can spring from nonliving things �Based on many observations �People were convinced it worked �No one tested this hypothesis

Controlled Experiments �An experiment in which only one variable is changed at a time; all other variables are kept “controlled” or unchanged, or constant.

Variables �manipulated variable: variable that is changed by experimenter, aka: independent variable �responding variable: variable that is observed or measured in the experiment, aka: dependent variable

Redi (1678) 1 st to test spontaneous generation �New Hypothesis: flies produce maggots �Prediction: keep flies away from meat & no maggots will appear

Redi’s. Experiment �Working in pairs identify the following: �Manipulated Variable �Responding Variable �Was this a controlled experiment?

Redi’s Experiment

Redi’s Experiment �Results: �+ maggots on control meat � - maggots on jar covered with gauze �Conclusion: � Redi’s hypothesis supported…………… So: spontaneous generation refuted

Repeating the Experiment �When 1 variable manipulated in experiment then repeating the experiment should always give you the same results �Scientists repeat their experiments to verify results then communicate with others �expectedthat other scientists will repeat each other’s work: it adds confidence to conclusions

Needham Tests Redi’s Work � Mid 1700’s English scientist John Needham tried to prove spontaneous generation could occur under certain conditions

Spallazani Tests Redi’s Work �Italian scientist who read Redi’s & Needham papers �hypothesized that Needham had not heated samples sufficiently

Spallazani’s Conclusion �organisms came from the air not from the gravy…. . There is no spontaneous generation

Pasteur’s Final test of Spontaneous Generation �mid-1800’s arguments still going on for/against spontaneous generation � Louis Pasteur designed experiment that finally put the arguments to rest

Louis Pasteur � 1 year later Pasteur broke neck of flask and microrganisms appeared in the broth � Confirmed “all living things come from other living things”

When experiments are not possible � Not all hypotheses can be easily tested � Examples: �? � Studies: � Not experiments in true sense � Observations � Use large #s or long periods of time to minimize risk of misleading results

Scientific Theories � Theory: well-tested explanation that unifies a broad range of observations � Enable scientists to make accurate predictions about new situations � Cannot be absolutely proven � Can change if new evidence disproves theory