Uploaded byHARINATHA REDDY ASWARTHAGARI
Biogenesis
This document discusses the history of the theory of biogenesis. It describes experiments by Redi, Needham, Spallanzani, and Pasteur that provided evidence against spontaneous generation and in favor of biogenesis, the idea that life only arises from preexisting life. Redi's experiments with flies and meat in jars showed that maggots only appeared in open jars where flies could lay eggs. Spallanzani and Pasteur's experiments boiling broth in sealed flasks found no new life developed, supporting biogenesis over abiogenesis. Pasteur's famous experiment using flasks with S-shaped necks conclusively demonstrated that microbes arise from other microbes, not from non-living matter.
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Dr. Harinatha Reddy A introduces biogenesis, highlighting it as the production of life from pre-existing life, opposing abiogenesis.
Francesco Redi (1668) conducted experiments with meat in jars to demonstrate that maggots arise from eggs laid by flies, not spontaneously.
John Needham (1745) boiled meat broth but found microorganisms later, supporting abiogenesis, suggesting life can originate spontaneously.
Lazzaro Spallanzani (1765) sealed boiled soups and observed no microbial growth, challenging abiogenesis; however, critics questioned his methods.
Louis Pasteur (1864) proved that life arises from life using S-shaped flasks, showing microbes enter from the air, confirming biogenesis.
Various experiments over time (Redi, Spallanzani, Pasteur) are reviewed, contrasting spontaneous generation and biogenesis with experimental results.
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Biogenesis
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- 2. • Biogenesis isthe formation (production) of new living organisms or organelles. • According to Louis Pasteur living things come only from other living things, by means of reproduction. • That is, life does not spontaneously arise from non-living material. Biogenesis:
- 3. Francesco Redi (1668) •In 1668, Francesco Redi, an Italian physician, did an experiment with flies and wide-mouth jars containing meat. • He took rotting meat pieces in jars. He sealed some of these jars tightly and other left open.
- 4. • After fewdays maggots appeared in open jars in which the flies went freely in and out and laid their eggs on meat. • But in sealed jars in which the flies could not enter did not show any maggots. • Redi concluded that the maggots arise from the eggs laid down by the parent flies and that the maggots can not appear spontaneously.
- 5. • Redi setup new experiment in which he covered jars with fine muslin cloth of sealing them tightly and allow free air in out of the jars. • After some time maggots appeared only in some jars. • Redi concluded that free air considered as vital force necessary for spontaneous origin.
- 6. John Needham By 1745an English scientist used microscopic observations to support the theory of abiogenesis. To test the theory he boiled meat broth for several minutes in a loosely sealed flask. ( allow to cool down the flask) Immediately after boiling he saw under the microscope that the broth had no living things. .
- 7. • After afew days he examined the flask and found microorganism. • He concluded that the organisms originated spontaneously form the nutrient fluids.
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- 9. Lazzaro Spallanzani (1765) •Boiled soups for almost an hour and sealed containers by melting the slender necks closed. • The soups remained clear. • Later, he broke the seals & the soups became cloudy with microbes.
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- 11. Conclusion • Critics saidsealed vials did not allow enough air for organisms to survive and that prolonged heating destroyed “vital force”. • “Vital force” needed to life to form. • Therefore, spontaneous generation remained the theory of the time
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- 14. Pasteur's Experiment • Hypothesis: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
- 15. Pasteur's Experiment -Step 1 • S-shaped Flask • Filled with broth • The special shaped was • intended to trap any dust particles containing • bacteria
- 16. Pasteur's Experiment - Step2 • Flasks boiled • Microbes Killed
- 17. Pasteur's Experiment - Step3 • Flask left at various locations • Did not turn cloudy • Microbes not found • Notice the dust that collected in the neck of the flask
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- 19. The Theory ofBiogenesis 1864 • Pasteur’s S-shaped flask kept microbes out but let air in. • Proved microbes only come from other microbes (life from life) – biogenesis Life come from life
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- 21. Evidence Pro andCon • 1668: Francisco Redi filled six jars with decaying meat. Conditions: Results: 3 jars covered with fine net - No maggots 3 open jars - Maggots appeared From where did the maggots come? What was the purpose of the sealed jars? Spontaneous generation or biogenesis?
- 22. Evidence Pro andCon • 1765: Lazzaro Spallanzani boiled nutrient solutions in flasks. Conditions: Results: Nutrient broth placed in flask, heated, then sealed No microbial growth Spontaneous generation or biogenesis?
- 23. Evidence Pro andCon • 1861: Louis Pasteur demonstrated that microorganisms are present in the air. Conditions: Results: Nutrient broth placed in flask, heated, neck broken Microbial growth Nutrient broth placed in flask, heated, then neck not broken. No microbial growth Spontaneous generation or biogenesis?