Question

A free living nitrogen fixing cyanobacterium which can also form symbiotic association with the aquatic fern Azolla is

• A. Tolypothrix
• B. Chlorella
• C. Nostoc
• D. Anabaena

Answer 1

The correct option is D Anabaena

Chlorella is a special type of micro algae that is known for its detoxifying & immune benefits. Nostoc is found in various environments that forms colonies composed of filaments of cells in a gelatinous sheath. Any sample of Azolla examined under a microscope will have filaments of Anabaena living within ovoid cavities inside the leaves which fixes nitrogen. It is a free living N${}_2$ fixing cyanobacterium which forms symbiotic association with the aquatic fern Azolla.

So, the answer is D.