CBSE Class 11-science Answered

Origin of Archaebacteria:

• It is said that archaebacteria evolved immediately after the origin of life on the Earth.
• They are considered one of the most primitive forms of living organisms
• They live in extreme habitats such as salty areas, hot springs and marshy places and hence are also termed evolutionary relics or living fossils.

General Characters of Archaebacteria:

• Cell wall is non-cellulosic formed of polysaccharaides or proteins.
• Cell membrane lipids are arranged in monolayer. The lipids have long, branched hydrocarbon chains linked to glycerol which enable these forms to tolerate extremes of heat and acidity.
• Characteristic chemical composition enables them to bear extremes of heat and pH.

Classification of Archaebacteria:

Based on the kind of environmental conditions in which archaebacteria survive, they are categorised into three major groups.

Methanogens

• Occur in marshy areas
• Convert CO₂ into methane
• Obligate anaerobes
• Used in gobar gas plants for the production of methane and fuel gas
• Also found in the stomach of ruminants
• Examples: Methanobacterium, Methanococcus

Halophiles

• Grow in salt-rich conditions
• Grow in salt pans, sea, salted fish
• They give unpleasant odour and undesirable pigmentation to salt
• Examples: Halobacterium, Halococcus 

Thermoacidophiles

• Can live in high termperature as well as acidic conditions
• Found in hot sulphur springs (temperature: 80 °C, pH: 2)
• Chemosynthetic in nature
• Examples: Thermoproteus, Thermoplasma

Economic Importance of Archaebacteria:

• Methanogens are used in the generation of gobar gas from dung and sewage to be used as cooking gas.
• Heat resistant thermophilic enzymes and restriction enzymes obtained from thermoacidophiles are used in biotechnology.
• Halophiles are used in bioleaching of poor mines.
• Archaebacteria are used in biosensors.