CBSE Class 9 Answered

please explain nitrogen cycle. And please elaborate to get me out of confusion

Asked by nimishagupta0409 | 20 Feb, 2015, 11:33: PM

Expert Answer

Nitrogen cycle:

The cycle in which nitrogen passes from its elemental form in the atmosphere into simple molecules in the soil and water, then to more complex molecules in living beings and back again to the simple atmospheric nitrogen molecule is called nitrogen cycle.

Process

(i)Nitrogen is a vital element found in all living organisms.

(ii)It is a part of proteins, nucleic acids, some vitamins as well as alkaloids and urea.

(iii)A few nitrogen fixing bacteria can fix atmospheric nitrogen into usable forms like nitrates and nitrites. These bacteria may be free living (eg. Azotobacter) or found mainly in root nodules of leguminous plants (eg. Rhizobium).

(iv)The high temperatures and pressures created in the air during lightning convert nitrogen into oxides of nitrogen, which then dissolve in water to give nitric and nitrous acids and fall on land along with rain. These can then be utilised by the living organisms.

(v)Plants utilise nitrates and nitrites to produce amino acids, which are then used to form proteins. In addition, they also form nucleic acids and vitamins using the nitrates and nitrites.

(vi)These complex compounds are then passed on to the consumers when they eat the plants. When plants and animals die, their proteins are decomposed by certain microorganisms to ammonia. This process is called ammonification and is carried out by ammonifying bacteria.

(vii)Certain soil bacteria oxidise the ammonia into nitrites and then into nitrates. This process is called nitrification and is carried out by nitrifying bacteria like Nitrosomonas and Nitrobacter.

(viii)Another type of anaerobic bacteria converts the nitrates and nitrites into elemental nitrogen in a process called denitrification. The bacteria carrying out this process is called denitrifying bacteria (eg. Pseudomonas species). This nitrogen gas is released back to atmosphere.

Answered by Sivanand Patnaik | 21 Feb, 2015, 10:21: AM