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Biogenesis vs. Abiogenesis. Biology 11. “The secret to reaching my goals lies solely in my tenacity” -Louis Pasteur. Abiogenesis vs. Biogenesis. Introduction: Biology as a Science progressed by observation. The hypotheses proposed by early scientists were rarely tested by experiments.
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Biogenesis vs. Abiogenesis Biology 11
“The secret to reaching my goals lies solely in my tenacity” -Louis Pasteur
Abiogenesis vs. Biogenesis Introduction: • Biology as a Science progressed by observation. • The hypotheses proposed by early scientists were rarely tested by experiments.
Abiogenesis continued… Example: • Pond dries up – no fish or frogs • Rain comes – fish and frogs Therefore: It rained fish and frogs
Abiogenesis continued… Theory of Abiogenesis (aka spontaneous generation) • Nonliving things can be transformed into living things. • Proposed by Aristotle who observed rotting meat and flies. • Existed for nearly 2000 years
Van Helmont continued… • ~300 years ago Belgian doctor Jean van Helmont – concluded that mice could be created from a dirty shirt. • He placed grains of wheat and a dirty shirt in a container and in 21 days mice appeared. • Conclusion: Sweat caused wheat to ferment into mice. Abiogenesis!
Redi • In 1668 Francesco Redi (Italian physician) tested Aristotle’s hypothesis (meat flies)
Redi continued… • 4 sets of jars with meat (snake, eel, fish, veal) one set was open (experimental group) one set was sealed (control group) • Maggots appeared on open jars of meat • Conclusion: Flies come from flies! Biogenesis – life from life.
Redi continued… • Bad news lots of critics • No air in jar, therefore life could not survive. • Redi repeated his experiment with a fine mesh wire – supported Biogenesis again! • Critics still objected…
Needham • John Needham (1713 – 1781) English botanist • Reexamined theory of Abiogenesis • Observed meat broth left unsealed soon changed colour (evidence of microorganisms).
Needham continued… Experiment: • Boiled flasks of meat broth to kill microorganisms • Left the flasks (unsealed) • Flasks soon become murky and full of microbes
Needham continued… Conclusion: • Abiogenesis AHHHHHHHHH!!! • Sent many Scientists down the wrong path.
Lazzaro Spallanzani (1729-1799) • 25 years later Spallanzani repeated experiment more carefully • Boiled flasks longer and sealed flasks • Critics again objected to sealed flasks!
The Final Blow! Louis Pasteur (1822-1895) • 1864 – Pasteur developed a swan-neck flask
Pasteur continued… Experiment: • Boiled broth, air could enter but microbes were trapped in curved flask • Broth remained clear Biogenesis finally proven!
The End! Now here is your assignment: List and explain three “flaws” in experimental design that you have heard about during this presentation.