Theories about the evolution of organic molecules

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Theories about the evolution of organic molecules

• Year 11Biology

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• Describe two scientific theories relating to the
  evolution of the chemicals of life and discuss
  their significance in understanding the origin of
  life

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Spontaneous generation

• As far back as the time of Aristotle, humans
  thought that life spontaneously arises from
  non-living matter.
• They saw maggots appear in rotting meat

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• This concept of spontaneous generation was an
  accepted fact and was not scientifically tested
  until 1668.
• Francesco Redi an Italian physician, demonstrated
  that maggots in decaying meat came from eggs laid
  by flies

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• About 100 years later Lazzaro Spallanzani showed
  that the microorganisms that appeared in broth
  came from the air
• However his experimental technique was not
  sufficient to exclude spontaneous generation

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• It was almost another 100 years, 1862, before
  French scientist Louis Pasteur convinced people
  that the spontaneous generation did not occur
• DIAGRAMS

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• Pasteurs work and work of others such as
  Virchow established the statement that all life
  comes from pre-existing life
• This presumed that first living thing or things
  had to arise somewhere, sometime, somehow

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