42. NCERT Exemplar XXIV

 

Leguminous plants, such as rose and mangopeas and beans jasmine and hibiscus have root nodules. These root nodules contain symbiotic oxygen-fixing bacterianitrogen-fixing bacteriadenitrifying bacteria like Rhizobium, etc. These symbiotic bacteria are beneficial to plants because they absorb free atmospheric nitrogen, which plants and animals cannot utilise and must be transformed into biologically suitable forms.

 

They convert it into ammonia. Most ammonium compounds are oxidised by nitrate bacteria nitrite bacteria ammnia bacteria (Nitrosomonas and Nitrosococcus) to soluble carbidessoluble nitritiessoluble nitrates, which are further oxidised by nitrate bacteria ammonia bacterianitrite bacteria  (Nitrobacter and Nitrocystis) to soluble nitritiessoluble nitratessoluble carbides. This process is called biological nitrogen fixation. Farmers cultivate these leguminous plants containing root nodules after wheat to replenish the nitrogen in the soil as nitrates.