A free living nitrogen fixing cyanobacterium which also forms symbiotic association with Azolla is

Options

(a) Anabaena
(b) Nostoc
(c) Chlorella
(d) Tolypothrix

Correct Answer:

Anabaena

Explanation:

Anabaena azollae resides in the leaf cavities of the fern Anabaena. It fixes nitrogen. A part of the fixed nitrogen is excreted in the cavities and becomes available to the fern. The decaying fern plants release the same for utilization of the rice plants.

Anabaena is a genus of filamentous cyanobacteria that exist as plankton. They are known for nitrogen-fixing abilities, and they form symbiotic relationships with certain plants, such as the mosquito fern.