4Early ScienceFor centuries, people based their beliefs on their interpretations of what they saw going on in the world around them without testing their ideasThey didn’t use the scientific method to arrive at answers to their questionsTheir conclusions were based on untested observations
5Example of Observations Observation: Every year in the spring, the Nile River flooded areas of Egypt along the river, leaving behind nutrient-rich mud that enabled the people to grow that year’s crop of food. However, along with the muddy soil, large numbers of frogs appeared that weren’t around in drier times
6Example cont…Conclusion: It was perfectly obvious to people back then that muddy soil gave rise to the frogs
7John NeedhamBy 1745 an English scientist used microscopic observations to support the theory of abiogenesis.To test the theory he boiled meat broth for several minutes in a loosely sealed flask. ( allow to cool down the flask)Immediately after boiling he saw under the microscope that the broth had no living things.After a few days he examined the flask and found microrganism.
10Francesco Redi (1668)In 1668, Francesco Redi, an Italian physician, did an experiment with flies and wide-mouth jars containing meat
11Redi’s Experiment Redi used open & closed flasks which contained meat. His hypothesis was that rotten meat does not turn into flies.He observed these flasks to see in which one(s) maggots would develop.
12Redi’s (1626-1697) Experiments Evidence against spontaneous generation: 1. Unsealed – maggots on meat 2. Sealed – no maggots on meat 3. Gauze – few maggots on gauze, none on meat
13Redi’s FindingsHe found that if a flask was closed with a lid so adult flies could not get in, no maggots developed on the rotting meat within.In a flask without a lid, maggots soon were seen in the meat because adult flies had laid eggs and more adult flies soon appeared.
15Lazzaro Spallanzani’s (1765) Boiled soups for almost an hour and sealed containers by melting the slender necks closed.The soups remained clear.Later, he broke the seals & the soups became cloudy with microbes.
17ConclusionCritics said sealed vials did not allow enough air for organisms to survive and that prolonged heating destroyed “vital force”“Vital force” needed to life to form.Therefore, spontaneous generation remained the theory of the time
20Pasteur's ExperimentHypothesis: Microbes come from cells of organisms on dust particles in the air; not the air itself.Pasteur put broth into several special S-shaped flasksEach flask was boiled and placed at various locations
21Pasteur's Experiment - Step 1 S-shaped FlaskFilled with brothThe special shaped wasintended to trap any dust particles containingbacteria
27Evidence Pro and Con1668: Francisco Redi filled six jars with decaying meat.Conditions: Results:3 jars covered with fine net - No maggots3 open jars - Maggots appearedFrom where did the maggots come?What was the purpose of the sealed jars?Spontaneous generation or biogenesis?
28Evidence Pro and Con Conditions: Results: 1765: Lazzaro Spallanzani boiled nutrient solutions in flasks.Conditions:Results:Nutrient broth placed in flask, heated, then sealedNo microbial growthSpontaneous generation or biogenesis?
29Evidence Pro and Con Conditions: Results: 1861: Louis Pasteur demonstrated that microorganisms are present in the air.Conditions:Results:Nutrient broth placed in flask, heated, not sealedMicrobial growthNutrient broth placed in flask, heated, then sealedNo microbial growthSpontaneous generation or biogenesis?