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!

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