Question

Which organisms are classified as nitrogen-fixing microbes that convert atmospheric nitrogen into usable forms?

Options

• Rhizobium, Azotobacter, Azospirillum, and Frankia

• Mycorrhizal fungi and cyanobacteria only

• Azolla, Anabaena, and phosphate-solubilizing bacteria

• Only Rhizobium and Azolla

Answer 1

The key nitrogen-fixing microbes are Rhizobium, Azotobacter, Azospirillum, and Frankia. These organisms convert atmospheric nitrogen into usable forms, enriching the soil with available nitrogen for plant uptake. While Anabaena is also nitrogen-fixing, it is classified as a cyanobacterium, and Azolla is a host organism, not a nitrogen-fixing microbe itself.