Q.Why are Archaebacteria called the organisms of abnormal (extreme) conditions? OR Write the definition of indirect development in animals.

Methanobacterium is a methanogenic archaebacterium, distinct from the true (eu)bacteria listed among the other options.

Archaebacteria are structurally and biochemically distinct from ordinary (eu)bacteria, differing in their cell wall composition (lacking true peptidoglycan/muramic acid) and membrane lipids, and they typically live in extreme environments. The methanogens are one major archaebacterial group: they live in anaerobic conditions such as marshy soil, sewage, and the rumen of cattle, and produce methane gas (marsh gas / biogas) as a metabolic by-product from the anaerobic breakdown of organic matter. Methanobacterium is a well-known example of such a methanogenic archaebacterium.

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Archaebacteria adapted to extreme salinity are called halophiles.

Archaebacteria are a distinct group of bacteria (differing from eubacteria in cell wall composition and other features) that are able to survive in some of the harshest habitats on Earth. Based on the extreme condition they are adapted to, three major groups are recognised:

• Methanogens — found in marshy areas and in the guts of ruminant animals (e.g., cattle), where they produce methane gas from organic matter.
• Thermoacidophiles — survive in hot, acidic environments such as hot sulphur springs. …

Extreme saline (high-salt) conditions are the home of halophilic archaebacteria, so the answer is (A) Archebacteria.

Concept. In the five-kingdom system, the Kingdom Monera includes bacteria. The archaebacteria are special bacteria that live in some of the most extreme (harsh) habitats on Earth. They are divided according to habitat into:

• Halophiles - live in extreme salty (saline) areas.
• Methanogens - live in marshy areas and the gut of ruminants; produce methane.
• Thermoacidophiles - live in hot springs (high temperature and acidic conditions).

Evaluating the options:

• (A) Archebacteria - correct; halophilic archaebacteria live in extreme saline conditions.
• (B) Eubacteria - the 'true bacteria', not specialised for extreme salt. …