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Unicellular Organisms


Archaebacteria (Ancient Bacteria)

archaea archaea env. Many years ago archaebacteria were believed to be the earliest prokaryotes (cells without nucleus, i.e., the bacteria). Molecular evidence now indicates an extremely ancient separation between Bacteria and Archaea. Though they lack a nuclear membrane and are therefore prokaryotes, archaea resemble eukaryotes (cells with nucleus) in several aspects of their genetic system, including an intron / exon gene structure,

Figure 11-38 Archaea [view large image]

Figure 11-39 Environment for Archaea [view large image]

and membrane infolding. Eukaryotic cells were derived from the archaean branch approximately 1.7 billion years ago (see Figure 10-02).
Modern archaea are found in extreme environments requiring methanogenic, halophilic, or thermophilic metabolisms. While they are able to live elsewhere, they are usually not found there because outside of extreme environments they are competitively excluded by other organisms. Figure 11-38 shows some of the archaebacteria and Figure 11-39 shows the various environments where the archaea are thriving: (1) Halophiles in salty lakes, (2) Thermoproteus in deep-sea hydrothermal vents, (3) Sulfolobus in hot sulfur springs, (4) Methanococcus in swamps and marshes, and (5) Acidianus in acidic ponds.

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