– Aristotle classified organisms for the first time.

– Two kingdom system includes – Plantae & Animalia.


Demerits of Two Kingdom system

– No difference in Eukaryotes and Prokaryotes.

– Heterotrophic Fungi kept in Plantae.

– Five kingdom system is given by R.H Whittaker (1969) viz. Monera, Protista, Fungi, Plantae and Animalia.

Kingdom Monera –

– Prokaryotic unicellular organisms.

– Most abundant.

– Also live in extreme habitats viz. Hotsprings, Snow etc. as endoparasite etc.

–  eg. Bacteria.

– Some bacteria are autotrophic others are heterotrophic.

Archaebacteria –

– Cellwall different from other bacteria.

– Live in most harsh habitats eg. Halophile.

– Methanogens are found in the gut of ruminants and produce methane (CH4) gas.

Eubacteria –

– True bacteria.

– Rigid cellwall with or without flagellum.

– Cyanobacteria( Blue green algae) are also included in this group.

– Cyanobacteria are Photosynthetic autotrophs, unicellular, colonial or filamentous, with gelatinous sheath.

– Have Heterocyst for N2fixation eg. Nostoc, Anabaena, Oscillatoria, Rivularia, Gloeotrichia etc.

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