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Biogenesis vs. Abiogenesis Biology 11. “The secret to reaching my goals lies solely in my tenacity” -Louis Pasteur.

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Presentation on theme: "Biogenesis vs. Abiogenesis Biology 11. “The secret to reaching my goals lies solely in my tenacity” -Louis Pasteur."— Presentation transcript:

1 Biogenesis vs. Abiogenesis Biology 11

2 “The secret to reaching my goals lies solely in my tenacity” -Louis Pasteur

3 Abiogenesis vs. Biogenesis Introduction: Biology as a Science progressed by observation. The hypotheses proposed by early scientists were rarely tested by experiments.

4 Abiogenesis continued… Example: Pond dries up – no fish or frogs Rain comes – fish and frogs Therefore: It rained fish and frogs

5 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

6 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!

7 Redi In 1668 Francesco Redi (Italian physician) tested Aristotle’s hypothesis (meat  flies)

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9 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.

10 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…

11 Needham John Needham (1713 – 1781) English botanist Reexamined theory of Abiogenesis Observed meat broth left unsealed soon changed colour (evidence of microorganisms).

12 Needham continued… Experiment: Boiled flasks of meat broth to kill microorganisms Left the flasks (unsealed) Flasks soon become murky and full of microbes

13 Needham continued… Conclusion: Abiogenesis AHHHHHHHHH!!! Sent many Scientists down the wrong path.

14 Lazzaro Spallanzani ( ) 25 years later Spallanzani repeated experiment more carefully Boiled flasks longer and sealed flasks Critics again objected to sealed flasks!

15 The Final Blow! Louis Pasteur ( ) 1864 – Pasteur developed a swan-neck flask

16 Pasteur continued… Experiment: Boiled broth, air could enter but microbes were trapped in curved flask Broth remained clear  Biogenesis finally proven!

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18 The End! Now here is your assignment: List and explain three “flaws” in experimental design that you have heard about during this presentation.


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