Question

What of the following characteristics is true for archaebacteria? 
(1) Extreme halophiles
(2) Extreme thermophiles 
(3) Methanogens 
(4) The occurrence of peptidoglycan in the cell wall 
(a) 1, 2, and 3 are correct 
(b) 1 and 2 are correct
(c) 2 and 4 are correct 
(d) 1 and 3 are correct 

Answer 1

Hint: Archaebacteria have the ability to live in extreme conditions, including very salty, very acidic, and very hot environments. Methanobacterium bryantii, Haloarcula hispanica, Halobacterium salinarum are some of the examples of archaebacteria.

Complete answer:
Archaebacteria is composed of three groups: halophiles, thermophiles, and methanogens. Peptidoglycan is a pigment that most bacteria use in the cell wall. Often known as Murein. Archaebacteria in its wall is therefore devoid of peptidoglycan. Rather, they are composed of the polysaccharide called pseudomurein. In 1977 Carl Woese and George E. Fox had experimentally proved wrong about the theory on the fundamental structure of the tree of life. Woese and Fox discovered "archaebacteria" (Archaea) . They claimed that as distinct from bacteria as plants and animals the archaebacteria constituted "a third kingdom" of life. Having described Archaea as a new, neither bacteria nor eukaryotes, "urkingdom" (later domain) , Woese redrew the taxonomic tree. The three- domain of classification, made by Woese is based on phylogenetic rather than morphological similarities, divided life into 23 major groups, integrated into three domains called bacteria, archaea, and eukarya.
- Archaebacteria are a type of single- cell organism so distinct from other typical life- forms that they have challenged the way scientists classify life. Another noteworthy characteristic of archaebacteria is their ability to live in extreme conditions, including very salty, very acidic, and very hot environments.
- Cell wall: Archaebacteria have cell membranes composed of ether- linked phospholipids, whereas bacteria and eukaryotes all incorporate the ester- linked phospholipids into their cell membranes. 
- Transcription: Archaebacteria have a single, circular chromosome, similar to bacteria, but their gene transcription is identical to what happens in eukaryotic cell nuclei.
- Archaebacteria use a sugar similar to the peptidoglycan sugar found in cell membranes of bacteria but not the same as.
- Methanogenesis is only possible with archaebacteria – a type of anaerobic respiration that produces methane. There are also archaebacteria that use other means of cellular respiration, but cells that contain methane are not present in either Bacteria or Eukarya.
- Differences in ribosomal RNA indicating divergence from both Bacteria and Eukarya at a distant point in the past.
So, the correct answer is ‘1, 2, and 3 are correct’.


Note: Methanogenic archaea are a critical part of sewage treatment, as it is part of the microorganism culture that performs anaerobic digestion and produces biogas. Acidophilic archaea show potential in mineral processing for the extraction of metals from ores, including gold, cobalt, and copper. Also, some archaea are used to obtain a class of antibiotics.