Biological Classification

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2. Biological Classification
Classification  The process of grouping living organisms into convenient categories based on simple characters is known as classification. 1. Two kingdom classification  Carolus Linnaeus divided all living things into two kingdoms- Plantae and Animalia. 2. Five kingdom classification  R.H. Whittaker divided all living things into five kingdoms- Monera, Protista, Fungi, Plantae, and Animalia.  The main criteria for classification included o cell structure o thallus organisation o mode of nutrition o reproduction o phylogenetic relationship (evolutionary relationship) Kingdom Monera  It includes all prokaryotes. Bacteria are the sole members of this kingdom.  They have autotrophic (photosynthetic or chemosynthetic) or heterotrophic mode of nutrition.  Bacteria can be classified into four categories based on their shapes.  Spirillum – spiral-shaped  Coccus – spherical-shaped  Bacillus – rod-shaped  Vibrium – comma-shaped 1. Archaebacteria  It includes halophiles that are found in extreme salty areas; thermoacidophiles that are found in hot springs; and methanogens that are found in marshy areas.  Methanogens are found in the gut of ruminants and are used for the production of biogas from cow dung. 2. Eubacteria (also known as true bacteria)  It includes blue-green algae (cyanobacteria) such as Nostoc, Anabaena, etc.

 Photosynthetic bacteria contain chlorophyll a. Chemosynthetic bacteria oxidise various inorganic compounds and use the released energy for their ATP production.  They have rigid cell wall and flagellum (if motile) for locomotion.  They have specialised cells known as heterocysts that are involved in nitrogen fixation.  Bacteria reproduce mainly by binary fission. Spore formation and primitive type of DNA transfer techniques from one bacterium to another are also seen for reproduction.  Mycoplasma is the smallest cell that can survive in the absence of oxygen and completely lacks a cell wall. Many of...
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