Describe the nitrogen cycle.

Answer:

•During thunderstorms/lightning nitrogen gas combines with oxygen to form nitrogen oxides
•Nitrogen oxides dissolve in water to form nitric acid
•Acid is deposited in the soil by rain
•Nitric acid combines with chemical substances to form nitrates or nitric acid dissociates to form nitrates which are absorbed by plants
•Symbiotic bacteria (Rhizobium) which are found in root nodules of leguminous plants fix free nitrogen to nitrates
•Free living bacteria (clostridium and Azotobacter) fix nitrogen to nitrates
•Nostoc algae (Anabaema chlorella) fix nitrogen to nitrates
•Plants use nitrates to form plant proteins
•Animals feed on plants and convert plant proteins into animal proteins
•Plants and animals die and are decomposed by putrefying bacteria, fungi(saprophytes)
•Decomposing plants, animals and nitrogenous wastes release ammonia which is converted to nitrites by Nitrosomonas and nitrococcus bacteria
•Nitrites are converted to nitrates by nitrobacter bacteria
•Nitrates in the soil can be converted to free nitrogen (denitrification) by some fungi, pseudomonas and theobaccilus bacteria generally called denitrifying bacteria

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