Develop some hypotheses explaining why only eukaryotic cells have evolved into multi-cellular organisms.

Essay by toyaplayUniversity, Bachelor'sA+, April 2005

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Prokaryotic cells are structurally simple. They are found only in single-celled and colonial organisms. Eukaryotic cells have organelles with their own membranes. Single-celled eukaryotic organisms are very diverse, but many colonial and multicellular forms also exist. The first of eukaryotic cells probably evolved or split off from Archeans, which have attributes of both prokaryotes (oxygen haters, e.g. bacteria), but also contain genes that are more like what you'd find in eukaryotes (oxygen lovers e.g. plants and animals). The first eukaryote cells probably lived near oxygen producing stromatolites. Indicators suggest that precursors evolved a 2.6 billion years ago--a billion years before the oldest fossil cells. Early single celled eukaryotes probably include amoeba, dinoflagellates, and ciliates (pictured top down to the right). They get food by surrounding and absorbing it, or through mouth-like openings, or other means. Some have internal skeletons cysts. The cysts are found fossilized, but of course you need a microscope to see them.

Eukaryotes are larger than prokaryotes and were bigger right from the beginning. They needed to be larger to hold new parts: a nucleus, gene DNA package, and organelles. Life evolved in the sea. It stayed there for the majority of the history of earth. The first fossilized evidence of multi-cellular cells goes back to about 1.5 billion years ago. There was a price to pay for the advantages gained from specialization--death. Prokaryotes cells didn't die--they continued to live by splitting and forming two clones. Only environmental hazards like being eaten or physically destroyed killed them. However, when eukaryotic cells grouped together and specialized, the cells gave up the ability to reproduce by division and began dying. The first replicating molecules were most likely RNA. RNA is a nucleic acid similar to DNA. In laboratory studies it has been shown that some RNA sequences have catalytic...



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