NITROGENCYCLE

By- Siddhant Sethi and Vibhor SharmaClass- 9th - A

NITROGEN• Nitrogen is a constituent element of

amino acids and thus of proteins, and of nucleic acids, DNA and RNA. • Majority of air we breath is N2. • Many industrially important compounds, such as ammonia, nitric acid and cyanides, contain nitrogen. •Composes about four-fifths (78.03 percent) by volume of the atmosphere.

•Nitrogen occurs in all living organisms, and the nitrogen cycle describes movement of the element from air into the biosphere and organic compounds, then back into the atmosphere.•In order for plants and animals to be able to use nitrogen, N2 gas must first be converted to a more a chemically available form.

NITROGEN IN NITROGEN CYCLE

What is Nitrogen Cycle ?The nitrogen cycle is the process

by which nitrogen is converted between its various chemical forms. This transformation can be carried out via both biological and non-biological processes. Important processes in the nitrogen cycle include fixation, ammonification, nitrification, and denitrification.

Steps of Nitrogen Cycle1)Nitrogen Fixation2)Nitrogen Assimilation3)Ammonification4)Nitrification5)Denitrification

1) Nitrogen FixationNitrogen fixation is the natural process, either biological or abiotic, by which nitrogen (N2) in the atmosphere is converted into ammonia (NH3). It is mostly done by nitrogen fixing bacteria in legume root.

FIXATION BY LIGHTNINGDuring lightning atmospheric nitrogen and oxygen combine to form nitrogen oxides during high- energy electrical discharge in the atmosphere. These dissolve in rain to form nitric acid. When natural minerals like limestone present in soil react with nitric acid, soluble nitrates(such as calcium nitrate) are formed, which can be absorbed by the plants. The high energies provided by lightning and cosmic radiation serve to combine atmospheric nitrogen and oxygen into nitrates, which are carried to the Earth’s surface in precipitation.

BIOLOGICAL NITROGEN FIXATIONNitrogen fixation can also be accomplished by nitrogen fixing bacteria present in the root nodules of leguminous plants(such as peas and beans). These bacteria can convert atmospheric nitrogen directly to ammonia through a nitrogen fixing bacteria such as Rhizobium. The ammonia is subsequently used by plants for the synthesis of biological molecules such as amino acids, proteins, and nucleic acids.

2) Nitrogen AssimilationSome plants get nitrogen from the soil, and by absorption of their roots in the form of either nitrate ions or ammonium ions. All nitrogen obtained by animals can be traced back to the eating of plants at some stage of the food chain.

3) AmmonificationWhen a plant dies, an animal dies, or an animal expels waste, the initial form of nitrogen is organic. Bacteria, or in some cases, fungi, convert the organic nitrogen within the remains back into ammonium (NH4

+), a process called ammonification.

Step

3

4) NitrificationNitrification is the biological oxidation of ammonia with oxygen into nitrite followed by the oxidation of these nitrites into nitrates. Degradation of ammonia to nitrite is usually the rate limiting step of nitrification. Nitrification is an important step in the nitrogen cycle in soil.

5) DenitrificationThe process where nitrates are metabolized by denitrifying bacteria to free nitrogen and returned to the atmosphere.

Human Intrusion and It’s Effects

Declination of nitrogen in the soil• cultivation of croplands • harvesting of crops• cutting of forests

Over supply of Nitrogen• the production and use of nitrogen

fertilizers • burning of fossil fuels in

automobiles, power generation plants, and industries

Effects of Over Supply of Nitrogen

• acidification of soils and of the waters of streams and lakes

• acid rain • Increased global concentrations of nitrous

oxide (N2O), a potent greenhouse gas.

Effects of Over Supply of Nitrogen

• stratospheric ozone depletion • greatly increased transport of

nitrogen by rivers into estuaries and coastal waters where it is a major pollutant.

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