Presentation on theme: "spontaneous generation"— Presentation transcript:
1spontaneous generation Redi, Needham, Spallanzani, and Pasteur
2Spontaneous Generation For much of history, people believed that animals could come from non-living sources. They thought:Frogs developed from falling drops of rainmice arose from sweaty underwearand flies arose from decaying meat.This is called abiogenesisAlso known as spontaneous generation
6One “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.
7Francisco Redi (Italian physician & poet)-- attempted to disprove the theory of Spontaneous Generation.
8“The flesh of dead animals cannot engender worms unless the eggs of the living being deposited therein”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 maggotsWax sealed vessels failed to produce maggots because flies were unable to reach the meat
9Redi’s critics said: You have too many variables There is a lack of access and a lack of air.We ALL know that everything needs airOf course no flies grew!You haven’t proven anything.
10Redi part 2 – answer to critics fine mesh allows in air, but not fliesflies laid eggs on top of meshno maggots in meat
11Redi’s Conclusions:“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.
12Louis Pasteur 1859– used swan-necked flask (French chemist) entered a contest sponsored by French Academy of Sciences to prove or disprove Spontaneous generation.used swan-necked flaskflask allowed in air, but trapped dust (and microbes)boiled infusionshowed that NO growth occurred, even after many daysBUT -- what about damaging the “active principle”?
13Pasteur showed that the active principle was NOT damaged at any later time, he could tip the flaskthis allowed nutrient broth to contact the dustthis carried microbes into the brothresult: growth!area where dust had been trapped
14Pasteur squashes the idea of abiogenesis completely! Since then, no one has been able to refute Pasteur’s experimentscientists everywhere soon came to accept that abiogenesis did NOT EXIST.but: then how did life on this planet start in the first place?
15Simple Organic Molecules Molecule that contained carbon must have formedThese molecules had to become organized into complex molecules like proteins, carbohydrates, and nucleic acidsScientists mixed water vapor, methane, and hydrogen gasses in simulated early earth conditionsThey formed several kinds of amino acids, sugars, and other small organic molecules
16Then:Amino acids were heated without oxygen and they linked to form proteinsThese experiments convinced many scientists that organic molecules could have originated from early earth conditions
17Early CellsProtocell – large, ordered structure, enclosed by a membrane, that carries out some life activities such as growth and divisionWere created by heating solutions of amino acids and could have been the origins of modern cellsArchaebacteria – prokaryotes that live in harsh environments, such as deep-sea vents and hot springsMay have been first true cells able to survive in harsh conditions found on earth