Domain Archaea is mostly composed of cells that live in extreme environments. 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. Species of the domain Archaea are not inhibited by antibiotics, lack peptidoglycan in their cell wall (unlike bacteria, which have this sugar/polypeptide compound), and can have branched carbon chains in their membrane lipids of the phospholipid bilayer. It is believed that Archaea are very similar to prokaryotes that inhabited the earth billions of years ago. It is also believed that eukaryotes evolved from Archaea, because they share many mRNA sequences, have similar RNA polymerases, and have introns. Therefore, it is believed that the domains Archaea and Bacteria branched from each other very early in history, and membrane infolding produced eukaryotic cells in the archaean branch approximately 1.7 billion years ago.
There are three main groups of Archaea: extreme halophiles, methanogens, and hyperthermophiles.
Answer the following questions:
1. Are Archea bacteria? Explain and compare the three domains.
2. Some archea are "halophilic". What does this mean? Why might one call them "life's extremists"?