Answer: Anabaena, Nostoc and Cyanobacteria
Nitrogen fixation is a mechanism in which atmospheric nitrogen is fixed into the form in which plants can easily absorb nitrogen.
There are two types of nitrogen-fixing species.
(1) symbiotic species – They are non-free living bacteria.
Examples – Bradyrhizobium and Rhizobium
(2) Nonsymbiotic species – They are free-living bacteria.
Examples – Anabaena, Nostoc and Cyanobacteria
