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Heterocyst Many of the Blue Green Algae (BGA) have the power of Nitrogen fixation, and for this nature has provided them a very special enlarged cell, which is called as Heterocyst ( Hetero - different; Cyst - swollen and encapsulated cell). Heterocyst is the site for Cyanobacterial Nitrogen Fixation which is an enlarged cell, and may be present terminally or intercalary in the Filamentous cyanobacterial cell. Heterocyst is very much enlarged than its other body cells (Vegetative cells). Heterocysts are terminally differentiated cells that form in a semi-regular pattern in filaments starved for a source of fixed nitrogen. These cells, occurring about every 10 - 15 cells in a filament are evident by differences in structure compared to Vegetative cells.   Figure – 1: Heterocyst and Vegetative cells in BGA   Heterocysts typically somewhat larger than Vegetative cells with a thicker cell envelope. The Heterocyst is made up of three different cell wall layers - t

Azolla – Anabaena SYMBIOSIS Azolla Azolla is a free-floating water fern (only know Pteridophyte that lives in Symbiosis) that floats in water and fixes atmospheric nitrogen in association with nitrogen fixing Blue Green Algae Anabaena azollae . Fern is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via Spores and have neither Seeds nor Flowers. Azolla is also called as Mosquito fern, Duckweed fern, Fairy moss or Water fern. Azolla belongs to the family Salviniaceae. Azolla is Omnipresent in nature that means it is present in all places at all times. Azolla is found on water in ponds, lakes, swamps, ditches and paddy fields of temperate and tropical regions. Because of its rapid growth, high Nitrogen content and ability to grow in water, it has been exploited as a fertilizer for Rice. Figure – 1: Azolla Azolla is