Concept:Nitrogen cycle:It is a biogeochemical cycle.It transforms inert nitrogen in the atmosphere into nitrogen that is beneficial to plants and animals.Nitrogen fixation:Nitrogen is a limiting nutrient for both natural and agricultural ecosystems.Nitrogen exists as two nitrogen atoms joined by a very strong triple covalent bond (N ? N).The process of conversion of nitrogen (N2 ) to ammonia is termed nitrogen fixation.Explanation:?Biological nitrogen fixation:Some prokaryotic species are capable of fixing nitrogen.The reduction of nitrogen to ammonia by living organisms is called biological nitrogen fixation.The enzyme, nitrogenase which is capable of nitrogen reduction is present exclusively in prokaryotes.Such microbes are called N2 - fixers. The formula of nitrogen fixation: N?N?NH3.Examples of free-living nitrogen-fixing aerobic microbes are Azotobacter and Beijernickia while Rhodospirillum is anaerobic and Bacillus free-living.A number of cyanobacteria such as Anabaena and Nostoc are also free-living nitrogen-fixers.Symbiotic biological nitrogen fixation:The most prominent symbiotic biological nitrogen-fixing is the legume-bacteria relationship.Species of rod-shaped Rhizobium have such relationship with the roots of several legumes such as alfalfa, sweet clover, sweet pea, groundnut, lentils, garden pea, broad bean, clover beans, etc.The most common association with roots is nodules.These nodules are small outgrowths on the roots.The microbe, Frankia, also produces nitrogen-fixing nodules on the roots of non-leguminous plants.Thus, the Tulsi plant does NOT form Root Nodules having Nitrogen-fixing bacteria in it.Additional InformationTulsi:Tulsi's scientific name is Ocimum sanctum Linn.It is a plant in the Ocimum genus.It has a wide range of therapeutic effects.It is used as a medicinal herb in Indian homes to treat a variety of ailments.Its root does not have nitrogen fixating bacteria.