Question

Nostoc is
A. A bacteriophage
B. A beaded bacterium
C. A cyanobacteria
D. A parasite

Answer 1

Hint: Nostoc is a photosynthetic bacterium. It is mainly associated with the nitrogen fixation. Cyanobacteria is also a class of oxygenic photosynthetic bacteria. It has the most variety of species in it and is extremely diverse.

Complete answer:
To solve the question, we must be well aware of nostoc. Nostoc is a filamentous bacterium which has a beaded structure. It is often found to be associated symbiotically with Anabaena. It can perform photosynthesis and hence is placed in the Class Cyanobacteria. Hence, the correct answer to the question is cyanobacteria.
Further, bacteriophage is a virus which attacks and kills only bacteria. They have double stranded DNA. While parasites are organisms which draw nutrition from other organisms and harm the host on which they live.

Additional information-
Cyanobacteria are prokaryotes.
They reproduce by binary fission, budding, and fragmentation. Some species also have thick-walled akinetes due to the deposition of food material.
They are capable of tolerating extreme environmental stresses.
They have a gram negative type cell wall.
They do not have flagella.
Oscillatoria is also a cyanobacteria which is an indicator of water pollution.

Note:
> Nostoc is also beaded in shape but a better and clearer answer would be that it is a cyanobacterium.
> Nostoc forms colonies of cells that are filamentous and are enclosed inside a gelatinous sheath.
> The cyanobacteria Spirulina and Nostoc are consumed in various countries.