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1. origin of life.ppt

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1. origin of life.ppt

  1. 1. Biochemical evolution
  2. 2. Biochemical evolution Life appeared after a period of chemical reactions According to physical and chemical laws.
  3. 3. The big bang is how astronomers explain the way the universe began. It is the idea that the universe began as just a single point, then expanded and stretched to grow as large as it is right now—and it is still stretching!
  4. 4. Prebiotic Earth Conditions on the primitive Earth were not the same as those present today No spontaneous generation of life today (Pasteur)… because the necessary conditions no longer exist.
  5. 5. Conditions on early Earth  Reducing atmosphere on the primitive Earth. No free oxygen (O2)  Free hydrogen (H2) and saturated hydrides (CH4, NH3 and H2O)  Energy for chemical reactions between these gases could come from electric discharge in storms or solar energy (no ozone layer)  The Earth’s surface temperature probably hotter than today.
  6. 6. The formation of monomers  Miller and Urey recreate these conditions in vitro  The water is heated and the mixture circulates for many days. H2 NH3 CH4 H2O H2O Heat Electric discharge Samples
  7. 7. Results  After a week 15 amino acids in the mixture  Other biologically important molecules had been formed including ethanoic acid, lactic acid and urea  Later similar experiments were done using CO2 that produced nucleotides.
  8. 8. Conclusion  These experiments cannot reproduce the exact conditions on the primitive Earth  We shall never know exactly what happened  But it can be shown that the basic building blocks for the large macromolecules can be synthesised in vitro from inorganic compounds.
  9. 9. How Do Microbes Arise?  By 1860, the debate had become so heated that the Paris Academy of Sciences offered a prize for any experiments that would help resolve this conflict  The prize was claimed in 1864 by Louis Pasteur, as he published the results of an experiment he did to disproved spontaneous generation in microscopic organisms
  10. 10. Spontaneous Generation  For centuries, people based their beliefs on their interpretations of what they saw going on in the world around them without testing their ideas  They didn’t use the scientific method to arrive at answers to their questions  Their conclusions were based on untested observations
  11. 11. Aristotle (384 –322 BC) Proposed the theory of spontaneous generation Also called abiogenesis Idea that living things can arise from nonliving matter Idea lasted almost 2000 years
  12. 12. Disproving Spontaneous Generation
  13. 13. Francesco Redi (1668) In 1668, Francesco Redi, an Italian physician, did an experiment with flies and wide-mouth jars containing meat
  14. 14. Redi’s Experiment  Redi used open & closed flasks which contained meat.  His hypothesis was that rotten meat does not turn into flies.  He observed these flasks to see in which one(s) maggots would develop.
  15. 15. Redi’s (1626-1697) Experiments  Evidence against spontaneous generation: 1. Unsealed – maggots on meat 2. Sealed – no maggots on meat 3. Gauze – few maggots on gauze, none on meat
  16. 16. Redi’s Findings  He found that if a flask was closed with a lid so adult flies could not get in, no maggots developed on the rotting meat within.  In a flask without a lid, maggots soon were seen in the meat because adult flies had laid eggs and more adult flies soon appeared.
  17. 17. Results of Redi’s Experiments  The results of this experiment disproved the idea of spontaneous generation for larger organisms, but people still thought microscopic organisms like algae or bacteria could arise that way.
  18. 18. Needham’s Experiment
  19. 19. 22 Needham’s Results copyright cmassengale  Needham’s experiments seemed to support the idea of spontaneous generation  People didn’t realize bacteria were already present in Needham’s soups  Needham didn’t boil long enough to kill the microbes
  20. 20. Lazzaro Spallanzani Experiment (1765)
  21. 21. Microbes come from cells of organisms on dust particles in the air; not the air itself. Pasteur put broth into several special S-shaped flasks Each flask was boiled and placed at various locations Pasteur's Hypothesis
  22. 22. Pasteur's Experiment S-shaped Flask Filled with broth The special shaped was intended to trap any dust particles containing bacteria Flasks boiled Microbes Killed
  23. 23. Flask left at various locations Did not turn cloudy Microbes not found Notice the dust that collected in the neck of the flask
  24. 24. Pasteur's Experiment  Pasteur’s S-shaped flask kept microbes out but let air in.  Proved microbes only come from other microbes (life from life) - biogenesis

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