A free-living nitrogen-fixing cyanobacterium which can also form symbiotic association with the water fern Azolla is
(a) Tolypothrix
(b) Chlorella
(c) Nostoc
(d) Anabaena
Correct Option (d) Anabaena
Explanation:
Anabaena is a free-living nitrogen fixing cyanobactenum which can form symbiotic association with water fern Azolla.
