NEET Biology Microbes In Human Welfare Revision Notes

Bacteria
 
(1) Study of bacteria is called bacteriology.
(2) Linnaeous placed them under genus vermes.
(3) Nageli classified bacteria under schizomycetes.
(4) Bacteria are unicellular, microscopic organisms.
(5) These are the smallest cell wall having prokaryotic cell.
(6) They differ from animals in having a rigid cell wall and being capable to synthesize vitamins.
 
Size:
 
(i) Bacteria are the smallest of all known cellular organisms which are visible only with the aid of microscope.
(ii) They are 3 to 5 microns (1 m = 1/1000 millimetre or about 1/25,000 inch) in length.
(iii) A few species of bacteria are approximately 15m in diameter.
 
Shape:
 
(i) The shape bacteria usually remain constant.
(ii) Some of them are able to change their shape and size with changes in environmental conditions. Such bacteria, which change their shape, are called pleomorphic.
 
(e) Filament: The body of bacterium is filamentous like a fungal mycelia. The filaments are very small e.g.Beggiota, Thiothrix etc.
 
(f) Stalked: The body of bacterium posses a stalk e.g. Caulobacter.
 
(g) Budded: The body of bacterium is swollen at places e.g. Retrodomicrobiom.
 
Role of Bacteria in nitrogen cycle:

Nitrogen cycle existing in nature, comprises of –
 
Nitrogen fixation:

(1) Many free-living soil inhabiting bacteria such as, Azotobacter (aerobic), Clostridium (anaerobic), etc. have ability to fix atmospheric nitrogen into ammonia.
(2) The other group of nitrogen fixing bacteria lives in symbiotic association with other plants.
(3) The most important symbiotic nitrogen fixing bacteria is Rhizobium spp.
(4) The various species of Rhizobium inhabit different leguminous plants. For example, R. leguminosarium infects soyabeans, etc.


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