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1- Spontaneous generation - about 350 B.C

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1- Spontaneous generation - about 350 B.C

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The philosopher Theophrastus affirmed that a plant called Silphium had appeared out of the  ground were there was nothing before and he called this as an example of spontaneous generation.

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Aristotle also wrote about the formation of insects out of meat,  animal feces and other matter.

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By the XVI century, Paracelsus recorded observations of the spontaneous generation of rats, frogs and eagles from water, air or decomposing matter.

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4.Refuting the theory of spontaneous generation - 1665

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4.Refuting the theory of spontaneous generation - 1665

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Francesco Redi demonstrated that fresh air is not needed to generate life, maggots were not the product of decay, it was because flies laid their eggs in roten meat.

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5. Refuting the theory of spontaneous generation. - 1729

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5. Refuting the theory of spontaneous generation. - 1729

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Lazzaro Spallanzani boiled broth in 8 recipients, he sealed completely 4 of them and left the other 4 open. He proved that organisms only grew in open recipients, not closed.

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6. Refuting the theory of spontaneous generation - 1859

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6. Refuting the theory of spontaneous generation - 1859

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Luis Pasteur refuted the spontaneous generation theory with a Swan neck flask theory, which proved completely that spontaneous generation was not possible. When boiling the recipents, bacteria got killed while he left other recipent without boiling and fungi appeared in the non boiling frasks. Later of 36 Hours there was a big quantity of organisms In the broth of sugar and yeast.

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7. Origin of the first cell from non-living matter. - 1953

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7. Origin of the first cell from non-living matter. - 1953

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1- Production of carbon compunds like sugar and aminoacids:
Stanley Miller and Harold Urey passed vapor through a mix of methane, hydrogen and ammonia. They used electric charges to simulate rays and observed that aminoacids and other carbon compunds neccesary for life were produced.

2- Assembly of carbon compunds in polymers:
A possible origin of the first carbon compounds are the vents in the bottom of the ocean. These vents are cracks in the surface of the Earth that characterize by emanating hot water with chemical compounds and inorganic residues. This chemical compounds represent an accesible energy source for the assembly of carbon in polymers.

3-Membrane formation:
If phospholipids or other amphipathic carbon compounds are found in the first carbon compounds they would organize naturally in bilayers. It was proven in experiments that these bilayers easily form vessicles that look like plasmic membrane of a small cell.

4-Development of an inheritance system
Living organisms have compound genes of DNA and they use enzymes as catalysts. To replicate DNA and pass it through generations enzymes are needed, but to make enzymes genes are needed.

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8. Assembly of carbon compounds into polymers.

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8. Assembly of carbon compounds into polymers.

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In the Miller-Urey experiment, the results showed that  simulated primitive Earth helped in the chemical syntheses of the fundamental structures of the cell membrane. When mixing gases like methane, ammonia, hydrogen, and water and then electrically-sparking them resulted in the formation of amino acids.

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9. Endosymbiotic theory including evidence that sustains it. - 1967

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9. Endosymbiotic theory including evidence that sustains it. - 1967

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Lynn Margulis came up with the Endosymbiotic Theory in 1967.
The embyotic theory establishes that mitochondrion was once a prokaryotic organism that lived independently because they had developed the process of aerobic cellular respiration. According to this theory bigger prokaryotes and smaller prokaryotes coexisted for thousands of years of evolution until they became the mitochondria of actual eukaryotic cells.

Some evidence that proves this theory are:
-Chloroplast and mitochondrion have more less the same size as prokaryotes

-Chloroplast and mitochondrion have a same circular DNA

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Allot, A & Mindorff, D. (2015). Biology. IB program. United Kingdom: Oxford University Press

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We, Fátima Villarreal and Regina Cavazos, affirm we have done this activity with academic honesty.