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Redi, Needham, Spallanzani, and Pasteur  For much of history, people believed that animals could come from non-living sources. They thought:  Frogs.

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Presentation on theme: "Redi, Needham, Spallanzani, and Pasteur  For much of history, people believed that animals could come from non-living sources. They thought:  Frogs."— Presentation transcript:

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2 Redi, Needham, Spallanzani, and Pasteur

3  For much of history, people believed that animals could come from non-living sources. They thought:  Frogs developed from falling drops of rain  mice arose from sweaty underwear  and flies arose from decaying meat.  This is called abiogenesis  Also known as spontaneous generation

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7  One “scientist” put forward the belief that mice could be generated spontaneously from wheat and a sweaty shirt.  The wheat provided the “nutritive power” and the shirt provided the “active principle.”  “active principle” = a mysterious “life-force” that allowed spontaneous generation to occur.

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9  Put dead snakes, eels, and veal in large wide mouthed vessels. Sealed one set with wax and left the other set open to air.  Decaying meat was teeming with maggots, sealed meat had no maggots  Wax sealed vessels failed to produce maggots because flies were unable to reach the meat

10  You have too many variables  There is a lack of access and a lack of air.  We ALL know that everything needs air  Of course no flies grew!  You haven’t proven anything.

11 flies laid eggs on top of mesh no maggots in meat fine mesh allows in air, but not flies

12  “All living beings come from seeds of the plants or animals themselves”  However, if someone were to demonstrate even one exception to this hypothesis, then Redi’s hypothesis would be rejected.

13  used swan-necked flask  flask allowed in air, but trapped dust (and microbes)  boiled infusion  showed that NO growth occurred, even after many days  BUT -- what about damaging the “active principle”? (French chemist) entered a contest sponsored by French Academy of Sciences to prove or disprove Spontaneous generation.

14  Pasteur showed that the active principle was NOT damaged  at any later time, he could tip the flask  this allowed nutrient broth to contact the dust  this carried microbes into the broth  result: growth! area where dust had been trapped

15  Since then, no one has been able to refute Pasteur’s experiment  scientists everywhere soon came to accept that abiogenesis did NOT EXIST.  but: then how did life on this planet start in the first place?

16  Molecule that contained carbon must have formed  These molecules had to become organized into complex molecules like proteins, carbohydrates, and nucleic acids  Scientists mixed water vapor, methane, and hydrogen gasses in simulated early earth conditions  They formed several kinds of amino acids, sugars, and other small organic molecules

17  Amino acids were heated without oxygen and they linked to form proteins  These experiments convinced many scientists that organic molecules could have originated from early earth conditions

18  Protocell – large, ordered structure, enclosed by a membrane, that carries out some life activities such as growth and division  Were created by heating solutions of amino acids and could have been the origins of modern cells  Archaebacteria – prokaryotes that live in harsh environments, such as deep-sea vents and hot springs  May have been first true cells able to survive in harsh conditions found on earth

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