The Evolution of the Eukaryotic Cell

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In the Proterozoic Era, 2.5 billion to 544 million years ago, the atmospheric level of oxygen increased to 15% due to oxygen producing cyanobacteria. The levels of oxygen in the atmosphere produced a fatal environment in which anaerobic organisms needed to evolve methods of coping with the presence of oxygen.


This theory maintains that advantageous mutations, which enabled organisms to survive with oxygen in the atmosphere, were the basis for evolutionary change in prokaryotes. (Conduah, 2005).
The second theory, referred to as the "botanical myth" by Lynn Margulis states that primitive photosynthetic bacteria evolved gradually into algae and plants, and some of these lost photosynthetic competence and evolved into fungi and animals. Due to the abundance of oxygen in the atmosphere, the fungi and animals evolved mitochondria, which utilize oxygen instead of light, as the energy producing organelle. (Conduah, 2005).
The third theory of serial endosymbiosis relies on symbiogenesis, or long term symbiotic relationships between different species that lead to new forms of life states the following: blue green algae produced oxygen as a by-product of photosynthesis, allowing oxygen to buildup in the atmosphere; other bacteria, prokaryotic cells, developed and grew, some of them with aerobic capabilities; anaerobic, heterotrophic cells known as proto- eukaryotes, ingested these aerobes and developed a mutually beneficial relationship. ...
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