Origin of life


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Origin of life

  1. 1. Origin of Life copyright cmassengale 1
  2. 2. Aristotle (384 –322 BC)Proposed the theory ofspontaneous generationAlso called abiogenesisIdea that living things canarise from nonliving matterIdea lasted almost 2000years copyright cmassengale 2
  3. 3. copyright cmassengale 3
  4. 4. Spontaneous GenerationFor centuries, people based theirbeliefs on their interpretations ofwhat they saw going on in the worldaround them without testing theirideas They didn’t use the scientificmethod to arrive at answers to theirquestionsTheir conclusions were based onuntested observations copyright cmassengale 4
  5. 5. Examples ofSpontaneous Generation copyright cmassengale 5
  6. 6. Example #1Observation: Every year in thespring, the Nile River floodedareas of Egypt along the river,leaving behind nutrient-rich mudthat enabled the people to growthat year’s crop of food.However, along with the muddysoil, large numbers of frogsappeared that weren’t around indrier times copyright cmassengale 6
  7. 7. Example #1Conclusion: It was perfectlyobvious to people back thenthat muddy soil gave rise tothe frogs copyright cmassengale 7
  8. 8. Example #2Observation: In many parts ofEurope, medieval farmers storedgrain in barns with thatchedroofs (like Shakespeare’s house).As a roof aged, it was notuncommon for it to start leaking.This could lead to spoiled ormoldy grain, and of course therewere lots of mice around. copyright cmassengale 8
  9. 9. Example #2Conclusion: It was obvious tothem that the mice camefrom the moldy grain. copyright cmassengale 9
  10. 10. Example #3Observation: In the citiescenturies ago, there were nosewers, no garbage trucks, noelectricity, and no refrigeration.Sewage flowed down the streets,and chamber pots and left overfood were thrown out into thestreets each morning. Manycities also had major ratproblems and a disease calledBubonic plague. copyright cmassengale 10
  11. 11. Example #3Conclusion: Obviously, allthe sewage and garbageturned into the rats. copyright cmassengale 11
  12. 12. Example #4Observation: Since there were norefrigerators, the mandatory,daily trip to the butcher shop,especially in summer, meantbattling the flies around thecarcasses. Typically, carcasseswere “hung by their heels,” andcustomers selected which chunkthe butcher would carve off forthem. copyright cmassengale 12
  13. 13. Example #4Conclusion: Obviously, therotting meat that had beenhanging in the sun all day wasthe source of the flies. copyright cmassengale 13
  14. 14. Abiogenesis RecipesRecipe for bees: Kill a young bull, and bury it in an upright position so that its horns protrude from the ground. After a month, a swarm of bees will fly out of the corpse. copyright cmassengale 14
  15. 15. Abiogenesis RecipesRecipe for mice:Place a dirty shirt or some rags in an open pot or barrel containing a few grains of wheat or some wheat bran, and in 21 days, mice will appear. There will be adult males and females present, and they will be capable of mating and reproducing more mice. copyright cmassengale 15
  16. 16. DisprovingSpontaneous Generation copyright cmassengale 16
  17. 17. Francesco Redi (1668)In 1668, Francesco Redi, anItalian physician, did anexperiment with flies and wide-mouth jars containing meat copyright cmassengale 17
  18. 18. Redi’s ExperimentRedi used open & closedflasks which contained meat. His hypothesis was thatrotten meat does not turninto flies. He observed these flasks tosee in which one(s) maggotswould develop. copyright cmassengale 18
  19. 19. Redi’s FindingsHe found that if a flask wasclosed with a lid so adult fliescould not get in, no maggotsdeveloped on the rotting meatwithin. In a flask without a lid,maggots soon were seen in themeat because adult flies had laideggs and more adult flies soonappeared. copyright cmassengale 19
  20. 20. Redi’s (1626-1697) ExperimentsEvidence against spontaneous generation: 1. Unsealed – maggots on meat 2. Sealed – no maggots on meat 3. Gauze – few maggots on gauze, none on meat copyright cmassengale 20
  21. 21. Results of Redi’s ExperimentsThe results of thisexperiment disproved the ideaof spontaneous generation forlarger organisms, but peoplestill thought microscopicorganisms like algae orbacteria could arise that way. copyright cmassengale 21
  22. 22. Francesco Redi copyright cmassengale 22
  23. 23. Did Redi Use theScientific Method? copyright cmassengale 23
  24. 24. The Scientific MethodObservationHypothesisExperimentAccept, Reject, or Modify hypothesis copyright cmassengale 24
  25. 25. Step 1 - ObservationThere were flies around meatcarcasses at the Butchershop.Where do the flies comefrom?Does rotting meat turn intoor produce rotting flies? copyright cmassengale 25
  26. 26. Step 2 - HypothesisRotten meat does not turninto flies. Only flies canmake more flies. copyright cmassengale 26
  27. 27. Step 3 - TestingWide-mouth jars each containing a piece ofmeat were subjected to several variations of“openness” while all other variables werekept the same.Control group — These jars of meat wereset out without lids so the meat would beexposed to whatever it might be in thebutcher shop.Experimental group(s) — One group of jarswere sealed with lids, and another group ofjars had gauze placed over them. copyright cmassengale 27
  28. 28. Step 4 - DataPresence or absence of fliesand maggots observed in eachjar was recorded.Control group – flies entered,laid eggs, & maggots emergedGauze covered – flies on gauze,but not in jarSealed jars – No maggots orflies on the meat copyright cmassengale 28
  29. 29. Step 5 - ConclusionOnly flies can make more flies. In theuncovered jars, flies entered and laid eggson the meat. Maggots hatched from theseeggs and grew into more adult flies. Adultflies laid eggs on the gauze on the gauze-covered jars. These eggs or the maggotsfrom them dropped through the gauze ontothe meat. In the sealed jars, no flies,maggots, nor eggs could enter, thus nonewere seen in those jars. Maggots arose onlywhere flies were able to lay eggs. Thisexperiment disproved the idea ofspontaneous generation for larger organisms. copyright cmassengale 29
  30. 30. Disproving SpontaneousGeneration of Microbes copyright cmassengale 30
  31. 31. Anton van Leeuwenhoek (1674)Leeuwenhoek began making andlooking through simple microscopesHe often made a new microscopefor each specimenHe examined water and visualizedtiny animals, fungi, algae, andsingle celled protozoa;“animalcules”By end of 19th century, theseorganisms were called microbes copyright cmassengale 31
  32. 32. Anton van Leeuwenhoek 1632-1723 copyright cmassengale 32
  33. 33. Leeuwenhoek’s Microscope copyright cmassengale 33
  34. 34. John Needham (1745)Showed that microorganismsflourished in various soups thathad been exposed to the airClaimed that there was a “lifeforce” present in the moleculesof all inorganic matter, includingair and the oxygen in it, thatcould cause spontaneousgeneration to occur copyright cmassengale 34
  35. 35. Needham’s ResultsNeedham’s experimentsseemed to support the ideaof spontaneous generationPeople didn’t realize bacteriawere already present inNeedham’s soupsNeedham didn’t boil longenough to kill the microbes copyright cmassengale 35
  36. 36. Needham’s Experiment copyright cmassengale 36
  37. 37. Lazzaro Spallanzani’s (1765)Boiled soups for almost an hourand sealed containers by meltingthe slender necks closed.The soups remained clear.Later, he broke the seals & thesoups became cloudy withmicrobes. copyright cmassengale 37
  38. 38. Spallanzani’s Results copyright cmassengale 38
  39. 39. ConclusionCritics said sealed vials didnot allow enough air fororganisms to survive and thatprolonged heating destroyed“life force”Therefore, spontaneousgeneration remained thetheory of the time copyright cmassengale 39
  40. 40. The TheoryFinally Changes copyright cmassengale 40
  41. 41. How Do Microbes Arise?By 1860, the debate had become soheated that the Paris Academy ofSciences offered a prize for anyexperiments that would help resolvethis conflictThe prize was claimed in 1864 byLouis Pasteur, as he published theresults of an experiment he did todisproved spontaneous generation inmicroscopic organisms copyright cmassengale 41
  42. 42. Louis Pasteur (1822-1895) copyright cmassengale 42
  43. 43. Pasteurs ProblemHypothesis: Microbes comefrom cells of organisms on dustparticles in the air; not the airitself.Pasteur put broth into severalspecial S-shaped flasksEach flask was boiled and placedat various locations copyright cmassengale 43
  44. 44. Pasteurs Experiment - Step 1 S-shaped Flask Filled with broth The special shaped was intended to trap any dust particles containing bacteria copyright cmassengale 44
  45. 45. Pasteurs Experiment - Step 2 Flasks boiled Microbes Killed copyright cmassengale 45
  46. 46. Pasteurs Experiment - Step 3 Flask left at various locations Did not turn cloudy Microbes not found Notice the dust that collected in the neck of the flask copyright cmassengale 46
  47. 47. Pasteurs Experimental Results copyright cmassengale 47
  48. 48. The Theory of BiogenesisPasteur’s S-shaped flask kept microbesout but let air in.Proved microbes only come from othermicrobes (life from life) - biogenesis copyright cmassengale Figure 1.3 48
  49. 49. Review copyright cmassengale 49
  50. 50. Evidence Pro and Con 1668: Francisco Redi filled six jars with decaying meat. Conditions: Results:3 jars covered with fine No maggotsnet3 open jars Maggots appearedFrom where did the maggots come?What was the purpose of the sealed jars?Spontaneous generation or biogenesis? copyright cmassengale 50
  51. 51. Evidence Pro and Con1745: John Needham put boilednutrient broth into covered flasks. Conditions: Results:Nutrient broth Microbial growthheated, then placedin sealed flaskFrom where did the microbes come?Spontaneous generation or biogenesis? copyright cmassengale 51
  52. 52. Evidence Pro and Con 1765: Lazzaro Spallanzani boiled nutrient solutions in flasks. Conditions: Results:Nutrient broth No microbialplaced in flask, growthheated, thensealedSpontaneous generation orbiogenesis? copyright cmassengale 52
  53. 53. Evidence Pro and Con 1861: Louis Pasteur demonstrated that microorganisms are present in the air. Conditions: Results:Nutrient broth placed in Microbial growthflask, heated, notsealedNutrient broth placed in No microbial growthflask, heated, thensealedSpontaneous generation or biogenesis? copyright cmassengale 53
  54. 54. copyright cmassengale 54