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Biology The Invader Within Eukaryotic Term Paper

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In one laboratory experiment, bacteria exposed to high levels of pathogenic bacteria over several hundred generations eventually adapted "their progeny became dependent on having the formerly pathogenic bacteria in food vacuoles...(Jeon, 1991)" (Armstrong) There are several ways in which bacteria may subsume other bacteria, including ingesting them and maintaining them in food vacuoles as in the Jeon experiment, or they may become infected by bacteria that are acting as parasites. Mitochondria, for example, could have been parasitic and fed off the host at the same time that they proved useful to it. Chloroplasts, because they are significantly self-supporting, are more likely to have been introduced as food. This theory continues to suggest that after many generations of true symbiosis, the mitochondria and chloroplasts lost their independence. If the endosymbiosis theory was correct, there are many things which should hypothetically prove true in experimentation. For example, it should be evidenced that single-celled organisms can indeed subsume other organisms and become dependent upon them for survival, and that subsumed organisms can surrender their own DNA and become dependent. These have both been seen to be true. For example, Margulis and Swartz found "an anaerobic organism that has adapted...

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"Gene loss is also known to have happened in other endosymbiotic organisms, like Buchnera aphidicola, a symbiont of aphids that supplies "essential" amino acids and other nutrients to their hosts, and Rickettsia prowazekii, which causes the disease typhus." (Smith et al.) Another test would be to see whether or not the membranes surrounding the organelles appear to have originated as vacuoles formed from the introduction of foreign matter to the cell. Once again, the findings are consistent with the outer membrane surrounding these organelles having what appears to be an exterior side facing inward toward the mitochondria's second membrane, and its interior side touching the rest of the cell. The appearance of differently sized ribosomes, independent reproduction and movement of these organelles, and the lack of intermediate stages all also point to this conclusion.
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Armstrong. Customer supplied source.

Smith, V. et all. "Endosymbiotic theory." EvoWiki. http://wiki.cotch.net/index.php/Endosymbiotic_theory

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Armstrong. Customer supplied source.

Smith, V. et all. "Endosymbiotic theory." EvoWiki. http://wiki.cotch.net/index.php/Endosymbiotic_theory
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