The Earth is surrounded by organisms that have independent roles to maintain various life processes. Microorganisms can be defined as living beings invisible to our naked eyes and present in abundance in our environments. Based on ribosomal RNA (ribonucleic acid) sequencing, microorganisms are divided into three phylogenetically distinct domains, which include Archaea, Bacteria, and Eukarya (Madigan, Martinko, Stahl, & Clark, 2012) (refer to Figure 1 in Appendix 1 ).Archaea is the first domain of microorganisms. Archaea are single-celled prokaryotes that vary from bacteria and eukaryotes (Pack, 2007). Pack (2007) stated that the cell walls of Archaea are made up of polysaccharides while the plasma membranes are made up of phospholipids. According to Cohen (2011), the cell walls of archaea do not contain peptidoglycan, cellulose, or chitin. There are four main differences between the archaeal membrane and other cells (Cohen, 2011). For example, the hydrophobic chains of phospholipids are highly branched and etherally bonded to glycerol (Pack, 2007). Archaea have irregular shapes such as spheres, rods or spirals (Levy, 2011) and some are triangular or square (Soloman, Berg & Martin, 2011). In addition to this, Archaea reproduce asexually through binary fission but not mitosis because the nucleus is absent (Hogan, 2011). Bej, Aislabie, and Atlas (2010) stated that the two main phyla of Archaea are Crenarchaeota and Euryarchaeota. According to Kratz (2005), most Crenarchaeota are hyperthermophiles that grow at temperatures above 80°C. Kratz (2005) also mentioned that hyperthermophiles prefer to live in warm habitats with high sulfur content such as volcanoes. Sulfolobe was the first type of hyperthermophy......middle paper......Ed.). (2011). Bacteria and viruses. New York, NY: Britannica Educational Publishing.Salton, M.R.J. (1953). Bacterial cell wall studies: IV. The composition of the cell walls of some gram-positive and gram-negative bacteria. Biochimica et Biophysica Acta, 10, 512-523. Solomon, E. P., Berg, L. R., & Martin, D. W. (2011). Biology. Belmont, CA: Brooks/Cole, Cengage Learning. Srivastava, S. (2012). Understanding bacteria. Dordrecht, Netherlands: Kluwer Academic Publishers.Vellai, T., & Vida, G. (1999). The origin of eukaryotes: the difference between prokaryotic and eukaryotic cells. Proceedings of the Royal Society of London. Series B: Biological Sciences, 266(1428), 1571-1577. Whitman, W. B., Coleman, D. C., & Wiebe, W. J. (1998). Prokaryotes: the invisible majority. Proceedings of the National Academy of Sciences of the United States of America, 95(12), 78-83.