- A Rhizobium
- B Azotobacter
- C Anabaena
- D Nitrosomonas
Correct answer: C. Anabaena
Explanation: Anabaena (and Nostoc) are cyanobacteria (blue-green algae) that fix atmospheric nitrogen. Anabaena azollae grows in symbiosis with Azolla (water fern) in rice paddies, naturally fertilizing the water.
Concept context
Essential mineral elements, their roles and deficiency symptoms. Nitrogen fixation and soil nutrition.