HISTORY OF LIFE

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HISTORY OF LIFE

• (Chapter 14)

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? Spontaneous Generation

• Before the 17th century it was believed that
  living things arise from nonliving things through
  a process called Spontaneous Generation

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• 6th century BC Greek philosophers propose life
  arose when sunlight was shined onto mud
• Why?

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• 1600s It was believed that mice appeared from
  rotten grain

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? Francesco Redi (1626-1697)

• Mid-17th century people believed flies were
  spontaneously generated from rotting meat
• Redi was a scientist who noticed a life stage to
  the flies on the rotten meat
• 1. Maggots
• 2. Pupa
• 3. Flies
• He observed that the maggots appeared where flies
  had landed first

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• Redi predicted that if the meat could be kept
  away from the flies, then there would be no
  maggots on the meat
• He did not believe that flies spontaneously
  generated from meat!!!
• So he set up his experiment

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• Control Group uncovered jar of meat, flies
  layed eggs, which hatched into maggots, which
  turned into more flies
• Experimental Group covered jars of meat, flies
  have no chance to lay eggs, new flies do not
  appear

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? Lazzaro Spallanzani (1729-1799)

• Experimented around the time the microscope was
  created
• Microscope allowed scientists to view
  microorganisms for the first time

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• People believed microorganisms that made you sick
  (what we now know as bacteria viruses)
  spontaneously generated in the air
• Air held vital force that could generate life

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• Spallanzanis experiment he knew microorganisms
  grew easily in food (ex broth), he also knew
  that boiling the broth would kill the
  microorganisms

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• Growth occurred in boiled broth only when the
  flask was uncorked exposed to air
• Exposure to air allows microorganisms to fall in
  and land in the broth to grow
• But many people still believed in spontaneous
  generation!!! Boiling destroyed the vital force

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? Louis Pasteur (1822-1895)

• Continued with Spallanzanis experiments to
  finally disprove spontaneous generation
• Pasteur set up an experiment where boiled broth
  was exposed to air, but microorganisms couldnt
  fall in

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• Boiled broth was exposed to air over a period of
  time but nothing grew
• Once the neck was broken off bacteria grew in the
  broth
• Bacteria did not spontaneously grow from the
  air!!!