Which of the following statements about the nitrogen cycle are false? 1 . Rhizobium and Frankia cause nitrogen fixation in their independent free-living stage. 2 . Azotobacter and Anabaena are anaerobic, symbiotic, free-living, nitrogen fixers. 3 . Rhodospirillum is an aerobic, nitrogen-fixing microbe found in the root nodules of legumes. 4 . Nitrobacter oxidizes nitrites to nitrates.

Step-by-step solution

Free living nitrogen fixing aerobic microbes are Azobacter and Beijerinckia while Rhodospirillum is anaerobic and free living. Cyanobacteria such as Nostoc are also free living nitrogen fixers. Rhizobium has a symbiotic relationship with roots of legumes like, pea, lentils, alfalfa etc. They produce nodules on the roots. Similar to this is Frankia which also produces nitrogen fixing nodules on the roots of non-leguminous plant Alnus. Ammonia is first oxidised to nitrite by the bacteria Nitrosomonas and/or Nitrococc