Question

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

Answer 1

The correct option is D Anabaena

Anabaena is a free living nitrogen fixing cyanobacterium which can form symbiotic association with water fern Azolla. Azolla and Anabaena have formed a symbiotic relationship in which the cyanobacterium receives carbon and nitrogen sources from the plant in exchange for fixed nitrogen. This relationship has proven to be useful to humans in the production of food; specifically in the fertilization of rice paddies. Azolla is used as an organic biofertilizer to increase the nitrogen levels in the rice paddies.