Question

Nitrogen cycle - Explain the cycle in your own words with suitable diagrams.

Answer 1

The cycle of nitrogen is described below :

(i) Nitrogen is very vital molecule as it is a part of proteins, DNA and RNA, vitamins, etc.

(ii) In our atmosphere, the air consists about 78% nitrogen. But this cannot be used by plants as well as animals directly. So, for using it, it has to be first fixed by the nitrogen fixing bacteria.

(iii) First the nitrogen is transformed into ammonia by those microbes. Then occurs the process of nitrification where the ammonia is transformed into nitrate.  Plants are now able to use nitrate.

(iv) By denitrification, the nitrate is then converted back into nitrogen which then goes in the atmosphere. This way the cycle gets completed.

Answer 2

Answer:

Explanation:

Nitrogen cycle as you know, is the continuous exchange of nitrogen between the atmosphere and the biosphere. Though, the atmosphere contains large reserves of nitrogen, most plants and animals cannot utilise it in the elemental form. Plants can utilise nitrogen in the form of ammonium salts or as nitrates, so atmospheric nitrogen has to be converted to this form or 'fixed' so that plants can utilise it.

One way of nitrogen fixation is by lightning discharges in the atmosphere, when nitrogen gets converted to nitric oxide and then to nitric acid. This nitric acid is washed down by rain into the soil, where it is neutralized by lime present in the soil to form calcium nitrate.

There is also a biological mode of nitrogen fixation. Certain bacteria, both free living or symbiotic convert atmospheric nitrogen into ammonium salts. In the latter category is rhizobium which lives in the root nodules of leguminous plants like peas, beans, soya , ect. Such bacteria are called nitrogen fixation bacteria. It has been estimated that about 90-175×10^6 tonnes of nitrogen is fixed biologically per year. The comparable figures for industrial fixation are about 85×10^6 tonnes per annum.

The ammonium salt and nitrates are taken up from the soil by plants which convert them into proteins and nucleic acids, essential components of all living beings. From plants these are passed on to the herbivorous, the animals which live on plants and then on to the carnivores along the food chain.

When the plants and animals die, their body decay the nitrogenous compounds in their bodies get decomposed to ammonia and ammonium compounds by ammonifying bacteria present in the soil. The ammonium salts are converted to the nitrites by nitrosifying bacteria, and the nitrites oxidised to nitrates by nitrifying bacteria. An alternate path way in the is the conversion of nitrogenous compounds to elementary nitrogen by denitrifying bacteria. Release of Nitrogen into the atmosphere, in a way, completes this cycle