theory of origin of life.pptx

origin of microrganisim

1. 1.2.1. Theories on the origin of life ( spontaneous generation theory) Where did microbes come from? The hypothesis that living organisms arise from nonliving matter is called spontaneous generation Spontaneous Generation theory is belief that all living things originated spontaneously from inanimate/non-living matter, without the need for a living progenitor to give them life. Spontaneous generation also called abiogenesis, It became difficult to disprove this doctrine, because of lack of experimental proof. Later, Francesco Redi in 1665 performed experiments and showed that maggots that develop in putrefying meat are the larval stages of flies and will never develop in putrefying meat if it is protected from flies laying eggs. He was the first to disprove SG of animals .

2. Where did microbes come from? The hypothesis that living organisms arise from nonliving matter is called spontaneous generation. Spontaneous Generation is the Theory that belief life come from inanimate objects or non-living things . Spontaneous generation also called abiogenesis . The belief in the spontaneous generation theory was introduced by Aristotle , who lived around 350 BC. According to Aristotle, it was: "readily observable that aphids arise from the dew which falls on plants, mice from dirty hay .” This theory is NOT true but it was believed for almost for 2000 years . Even in1700's and 1800's It became difficult to disprove this doctrine, because of lack of experimental proof. This theory was disproven by the experiments that used the scientific method as early as the 17th century and completely rejected in the 19th century 1.2.1. Theories on the origin of life ( spontaneous generation theory)

3. Spontaneous Generation/ Abiogenesis… In 1665 Francesco Redi disproved abiogenesis theory for the first time at the macroscopic level by demonstrating flies did not arise spontaneously from decaying meat. Hypothesis : maggots came from the eggs of flies Experiment procedure He put some meat inside jars and covered them. No maggots grew. Antagonists claimed life needed fresh air to grow so the experiment was invalid. Redi repeated the experiment but used gauze to cover the jars allowing fresh air in, but keeping flies out. No maggots grew . Conclusion: Because there were no maggots in or around the jar it was concluded that the maggots came from the fly eggs. Open jar Covered jar Sealed jar

4. Spontaneous Generation/ Abiogenesis theory… John Needham (1713 –1781 ) In England, John Needham challenged Redi's findings by conducting an experiment in which he placed a broth , or “gravy,” into a bottle, heated the bottle to kill anything inside, then sealed it. Days later, he reported the presence of life in the broth and announced that life had been created from nonlife. In actuality, he did not heat it long enough to kill all the microbes . Conclusion : He thought organic matter contained a vital force that could confer the properties of life on nonliving matter. He supports or prove abiogenesis

5. In 1670 Jablot conducted an experiment in which he divided a hay infusion that had been boiled into two containers: a heated container that was closed to the air and a heated container that was freely open to the air. Only the open vessel developed microorganisms. This further helped to disprove abiogenesis. Spontaneous Generation/ Abiogenesis theory…

6. Procedure/ : Spallanzani put broth /gravy into four flasks Flask 1 – left open to the air Flask 2 – was sealed Flask 3 – was boiled and left open Flask 4 – was boiled then sealed Results Flask 1 – left open to the air– Turned cloudy (microbes found) Flask 2 – was sealed – Turned cloudy (microbes found) Flask 3 – was boiled and left open – Turned cloudy (microbes found) • Flask 4 – was boiled then sealed – Did not turn cloudy (NO MICROBES ) Spontaneous Generation theory … Lazzaro Spallanzani (1729-1799): He refused the Needham’s experiment. Hypothesis: Microbes come from the air. Boiling will kill microbes. was the first to provide evidence that MO do not develop spontaneously. He believed microbes move through the air and could be killed by boiling. He boiled beef broth for an hour and then sealed the flasks. No microbes appeared following incubation.

7. Spontaneous Generation/ Abiogenesis theory… These assumptions provoked Louis Pasteur (1822- 1895) to settle the matter once and for all. In 1862, Louis Pasteur conducted experiments to disprove the theory of Spontaneous Generation . He prepared flasks, with long, narrow, goose-neck openings heated the nutrient broth in the flask and thus the air carrying the germs were allowed to settle in the goose-neck. When the flasks were cooled, the air entering through the gooseneck retained the germs, and under these conditions the broth remained clear. He also showed by further studies that ‘used’ cotton filters, when examined under the microscope, revealed the presence of microscopic organisms . However, Spallanzani couldn’t convince people because it was thought that air was necessary for spontaneous generation and he couldn’t figure out how to let in air without also letting in microbes.

8. Louis Pasteur experiment Pasteur’s Swan/goose neck flasks could supply air but could also trap ambient germs from entering broth

9. Set of experiments involving a goose necked flask. Boiled broth in a flask with a straight neck and left it exposed to air, organisms grew Boiled with his goose- necked flask, nothing grew The S- shape of this second flask trapped dust particles from the air Preventing the air from reaching the broth He could allow air to get into the flask but not the particles in the air, Pasteur proved that it was the organisms in the dust that were growing in the broth Resolved the controversy of Abiogenesis versus biogenesis Established the theory of Biogenesis Pasteur’s Experiment in Flow Chart

10. Conclusion of Pasteur's experiment The hypothesis was supported by the data therefore it was accepted. Because the broth did not turn cloudy and dust was observed trapped in the neck of the S-Shaped flask , it was concluded that the microbes came from cells of organisms riding on dust particles . Louis Pasteur experiment…. Pasteur is called father of microbiology because of his enormous contribution. Father of “Modern Bacteriology” and “Founder of microbiology” Father of Pasteurization and Fermentation

11. John Tyndall (1820-1923) proved that dust carried the germs. He showed that sterile infusions placed in a dust free chamber could remain sterile indefinitely even if kept exposed to air. During his experimentation he concluded that bacteria have phases one relatively thermo labile (growing phase destroyed by boiling for 5 min.) and One thermo resistant (bacterial spores cannot be destroyed even by boiling for 5 ½ hours). He developed a method of sterilization by discontinuous heating, later called Tyndallization , which could be used to kill all bacteria in infusions. He found that discontinuous boiling for 1 min on 5 successive occasions would make the infusion sterile whereas continuous boiling for 1 hr. would not. Pasteur and Tyndall’s experiments finally disproved the Doctrine of Spontaneous generation (S.G .). Spontaneous Generation/ Abiogenesis theory…