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Question

With the help of a labelled diagram show:
(a) Nitrogen cycle in nature
(b) Describe briefly two processes involved in cycling of N2 in environment.

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Solution

The two process are as follows
1.NITROGEN FIXATION

Nitrogen fixation is the process of converting the atmospheric nitrogen (N2) into biological state nitrogen. It is the first process of making nitrogen available for plants. It is defined as an anaerobic (without oxygen) process that catalyzes the reduction of atmospheric nitrogen (N2) into ammonia (NH3).

The process is solely carried out by prokaryotes (bacteria) which have the natural strength to break the triple bond between the nitrogen atoms. These nitrogen-fixing organisms are free-living bacteria whereas others are symbiotic nitrogen fixers. An example of a nitrogen fixer is the Rhizobium bacteria in the roots of legumes (soybeans, peas or clovers).

Other types of nitrogen-fixing prokaryotes are extensively distributed in different environments including terrestrial and aquatic settings. A special enzyme known as dinitrogenase is responsible for the fixation process. Once the nitrogen has been reduced to ammonia, the plants can now use it to make other biological compounds through the synthesis of enzymes, nucleic acids, chlorophyll, and proteins.

2.NITRIFICATION

Nitrification is the process where the ammonium ions (NH4) are converted into nitrides, first into nitrites (NO2–) then into nitrate (NO3–). Still, this process is done by the nitrogen-fixing bacteria. The first step is the oxidation of ammonia to nitrate, done by microbes termed as ammonia-oxidizers.

The second step is the oxidation of nitrite (NO2–) to nitrate (NO3–). The participating bacteria here are termed as nitrogen-oxidizing bacteria and they include nitrococcus, nitrobacters, and nitrosomonas.

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