Biogenesis vs. Abiogenesis

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
  Aristotles hypothesis (meat ? flies)

8
(No Transcript)
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 (1729-1799)

• 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 (1822-1895)
• 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!

17
(No Transcript)
18

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