give characteristic features of nostoc,and its economic importance.
Answers
Answer:
Nostoc is a genus of blue-green algae or cyanobacteria. They are prokaryotic and perform photosynthesis. They are found mainly in freshwater as free-living colonies or attached to rocks or at the bottom of lakes. They are also found on tree trunks. They are also found as an algal component of lichens in certain bryophytes (Anthoceros). They are capable of nitrogen-fixing and perform photosynthesis. They are also present as an endosymbiont to fungus.
Nostoc Classification
Nostoc are prokaryotic and are grouped with bacteria. The cell lacks membrane-bound organelles and genetic material is found dispersed in the cytoplasm. They are kept in cyanobacteria as they are photosynthetic.
Domain Bacteria
Phylum Cyanobacteria
Class Cyanophyceae
Order Nostocales
Family Nostocaceae
Genus Nostoc
Some of the commonly found Nostoc species are:
Nostoc commune is eaten as a salad
Nostoc azollae forms symbiotic association with water fern
Nostoc punctiforme form symbiotic relationship with Anthceros and other higher plants
Nostoc flagelliforme is known as Fat choy. It is used as a vegetable in China
Nostoc pruniforme forms very big colonies (diameter as large as ~25 cm)
Nostoc Structure
Nostoc are filamentous and unbranched. Numerous filaments are found in a gelatinous mass as a colony. The colonies may be as big as an egg. The filament consists of a chain of cells, which appear like a bead. They are called trichomes
Cells are oval, spherical or cylindrical
Some of the cells in the filament are differentiated, they are called heterocyst. They are sites for nitrogen fixation. Nitrogenase enzyme fixes nitrogen
Each filament is covered in a mucilaginous sheath, which is a protective layer. It absorbs and retains water. The gelatinous sheath is made up of polysaccharides and also contains proteins
Colonies are of different shapes, sizes and colours. They are mostly greenish or bluish-green in colour and also have red-brown or yellow-green colour
Extracellular pigments are also found, e.g. nostocine, scytonemin. These pigments along with some amino acids protect the cells from UV radiation
Each cell has a thick cell wall made up of peptidoglycan
The cytoplasm of a cell is differentiated into outer coloured due to peripherally arranged chromoplast and inner clear cytoplasm
Cells have various pigments. Cells contain chlorophyll (green pigment). Phycocyanin (blue) and phycoerythrin (red) are also present
Inner cytoplasm contains incipient nucleus or a nuclear body, DNA is without histones
Nostoc Reproduction
Nostoc reproduce vegetatively or asexually by spore formation.
The vegetative reproduction is by fragmentation
Explanation:
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Answer:
Nostoc is a genus of cyanobacteria found in various environments that forms colonies composed of filaments of moniliform cells in a gelatinous sheath.
Domain:Bacteria
Phylum:Cyanobacteria
Class:Cyanophyceae
Order:Nostocales
Family:Nostocaceae
Genus:Nostoc
Vaucher, 1888, ex Bornet and Flahaul