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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