Question

Nostoc is characterized by
(a)Cellulosic cell wall
(b)Uni Flagellated zoospores
(c)Chlorophyll ‘e’
(d)Sexual reproduction

Answer 1

Hint: In nostoc Reproduction is done by fragmentation. A special thick-walled cell (akinete) has the power to face up to desiccation for long periods of your time. After 70 years of dry storage, the akinete of 1 species germinates into a filament when moistened.

Complete answer
Nostoc is free-living nitrogen-fixing cyanobacteria having cells arranged in beadlike chains (trichomes) that are grouped together in a gelatinous mass (Nostoc balls). Each cell is surrounded by a cellulose cell wall. They fix atmospheric nitrogen in specialized cells called heterocysts. Nostoc contains two pigments, blue phycocyanin, and red phycoerythrin, also as chlorophyll. It does not have chlorophyll 'e' which is a characteristic feature of Xanthophyceae. The cells do not possess flagella but are motile by a swaying motion. Reproduction is only by vegetative and asexual methods.

Additional information
Nostoc spp. also occurs in symbiotic associations with liverworts, ferns, and therefore the angiosperm Gunnera. Cells of Nostoc spp. are spherical, barrel-shaped, or oval forming unbranched filaments. Nostoc sp. develops colonies with a variety of characteristic shapes, sizes, smells, textures, and colors. If sufficient water is out there, these colonies can become quite large. For example, colonies of Nostoc pruniforme as large as 25 cm in diameter are reported. Similarly, Nostoc commune may form spheres (“pearls”) from tens of millimeters to three cm in diameter, or discoid and flattened crusts. In these colonies, the Nostoc trichomes are embedded during a thick layer of exopolysaccharide which also contains protein and which serves to guard the cells against the external environment. Colonies are pigmented and may have a variety of colors from dark green to black, yellow-green to red-brown. Extracellular pigments that have been identified include the brownish scytonemin and the violet nostocine.

So the correct answer is ‘Cellulosic cell wall’.

Note: Many species of Nostoc can survive desiccation for very long periods (years), a feature that's largely liable for the success of this genus in many terrestrial habitats. As the Nostoc colony dries, physiological functions gradually shut down On rewetting, they quickly recover. Nostoc sp. can be used in soil rehabilitation and as natural nitrogen fertilizers in rice fields. Nostoc muscorum is a precursor for natural plastics and it has been shown to accumulate polyhydroxy butyrate.