Archaebacteria

Among the prokaryotes, archaebacteria are presented in NCERT Class 11, Chapter 2 (Biological Classification) as special forms living in some of the harshest habitats: halophiles in extremely salty areas, thermoacidophiles in hot acidic springs, and methanogens in the guts of ruminant animals. What enables this remarkable tolerance is the different chemical structure of their cell wall, which contains branched-chain lipids that make the wall and membrane highly resistant to heat, acidity and high salinity. Peptidoglycan strengthened by teichoic acids is characteristic of true bacteria, the eubacteria, not archaebacteria, so that option is wrong. Cellulose microfibrils in pectin describe plant and some algal walls, which are eukaryotic features absent in prokaryotes. Chitin reinforced with calcium carbonate is not a bacterial wall component at all; chitin instead occurs in fungal walls and arthropod exoskeletons. Methanogens among archaebacteria carry additional significance because they produce methane, or biogas, from the dung of cattle and contribute to ruminant digestion. A consistency check supports the answer: organisms inhabiting boiling, acidic or hypersaline environments require a membrane and wall chemistry that stays stable under such extreme stress, a stability that the branched lipid architecture uniquely provides.