Biology · Biological Classification · NEET
Archaebacteria are prokaryotes. They have no nucleus and no membrane-bound organelles, just like eubacteria. They are placed in Kingdom Monera. The word 'archae' means ancient or old, so they are seen as the oldest, most primitive living cells. Do not confuse 'ancient' with 'advanced' or 'eukaryotic'.
Both are prokaryotes in Kingdom Monera, but archaebacteria differ in their cell wall structure. Archaebacteria have a special (different) cell wall that has no peptidoglycan, and this is exactly why they survive extreme salt, heat, acid and no-oxygen conditions. Eubacteria are the 'true bacteria' with a rigid cell wall containing peptidoglycan and live in normal habitats. Simple rule: extreme habitat = archaebacteria; normal habitat = eubacteria.
Halophiles live in extreme salty areas (halo = salt, phile = loving). Examples of such places are salt lakes and very salty ocean edges. So if a NEET question asks about extreme saline (salty) conditions, the answer is archaebacteria, and the exact group is halophiles. NEET 2017 asked this directly.
No. Methanogens are strictly anaerobic, which means they die in the presence of oxygen. They live without oxygen in the gut of ruminant animals (cows, buffaloes) and in marshy areas. In this oxygen-free place they break down food and dung and release methane gas (biogas). A common NEET trap says methanogens 'grow aerobically' which is WRONG.
Methanogens produce methane. They live in the gut (rumen) of ruminant animals like cows and buffaloes, and in the dung. They break down cellulose-rich food without oxygen and give out methane gas. This methane is collected as biogas or gobar gas. NEET 2016 asked exactly this.
Thermoacidophiles live in hot springs. The name explains it: 'thermo' = heat and 'acido' = acid, so they survive both high temperature and high acidity together. Do not mix them with methanogens (gut) or halophiles (salty water). Habitat matching is a favourite NEET question type.
The primitive prokaryotes responsible for the production of biogas from the dung of ruminant animals, include the:
Which of the following statements about methanogens is not correct?
Match Column I with Column II: (a) Halophiles (b) Thermoacidophiles (c) Methanogens (d) Cyanobacteria (i) Hot springs (ii) Aquatic environment (iii) Guts of ruminants (iv) Salty area
Try the real previous-year questions from this chapter — each with the answer and a full solution.
'Archae' means ancient. Archaebacteria are believed to be among the first cells to appear on early Earth, which had harsh conditions like high heat, no oxygen and high salt. They still live in such extreme places today, so they are called the most primitive (oldest) living organisms.
Their special cell wall structure, which is different from all other bacteria and lacks peptidoglycan. This different wall protects them from extreme salt, heat, acid and oxygen-free environments where normal bacteria die.
No, they are useful. In the cow's gut they help digest cellulose, and the methane they release is collected as biogas (gobar gas), a clean cooking and lighting fuel. Read the next concept on methanogens and biogas production to see how this is used.
Yes, all three are archaebacteria, so all three share the special archaebacterial cell wall without peptidoglycan. Only their habitats differ: salty (halophile), hot springs (thermoacidophile), and gut/marsh (methanogen).
Yes. In Whittaker's Five Kingdom system, all bacteria including archaebacteria and eubacteria are placed in Kingdom Monera because they are prokaryotes (no true nucleus).
