What is Nitrogen Cycle? CBSE Class 8 Science Notes

The Nitrogen Cycle is an earth’s natural process which converts inert nitrogen in the atmosphere towards a more useful form for living organisms.” Nitrogen is an important nutrient plant nutrient. However, plants and animals cannot directly use the plentiful nitrogen in the atmosphere. Passing from the ambience to soil to the organism and then returning to the atmosphere, nitrogen nitrification, nitrogen fixation, decay, and putrefying are among the mechanisms involved. Nitrogen gas can be found in both inorganic forms. Organic nitrogen is found in living organisms and is passed up the food chain through the usage of many other living organisms. Nitrogen Inorganic forms are present in the atmosphere. Symbiotic bacteria that can convert inert nitrogen into usable forms – such as nitrites – make this nitrogen available to plants. Nitrogen undergoes a variety of transitions to maintain ecosystem balance. This process also extends to different biomes, with marine nitrogen being among the most complex biogeochemical.

Nitrogen Cycle Stages

Nitrification, Nitrogen fixation, Assimilation, Ammonification, and Denitrification are the steps in the Nitrogen Cycle process. These processes occur in phases, which are described below:

1. Nitrogen Fixation Method
2. Nitrification
3. Assimilation
4. Ammonification
5. Denitrification

Nitrogen Fixation method: It’s the first step in the nitrogen cycle. Atmospheric nitrogen (N2), which is primarily available inside an inert shape, is transformed into the useful form of ammonia in this process (NH3). The inanimate form of nitrogen is placed into soil and water from the atmosphere and surface bodies of water during the nitrogen fixation process, primarily through precipitation. Later, this same nitrogen undergoes a series of changes that result in the separation of two nitrogen atoms, which incorporate hydrogen to produce ammonia (NH4+). The entire nitrogen fixation procedure is finished by symbiotic bacteria known as Diazotrophs. Azotobacter and Rhizobium are also important players in this process. These bacteria contain a nitrogenase enzyme, combining gaseous ammonia with hydrogen to form nitrogenase.

Nitrogen fixation could take place in three ways. 

• Atmospheric Nitrogen Fixation: Because of the elevated -temperature present during lightning, inert nitrogen inside the atmosphere is converted to nitrogen oxide. Nitrous oxide, ammonia peroxide, and nitric oxide are formed by the breakdown of nitrogen into nitrogen atoms, which react with oxygen to create nitrogen oxides, nitrogen oxidants, and nitric oxide. These compounds eventually dissolve in the rain, forming dilute nitric acid. When concentrated nitric chemical reaches the Earth, it needs to react with the alkalies to form nitrates, which plants can easily accommodate.
• Biological Nitrogen Fixation: Nitrogen-fixing microbes and blue-green algae exist and convert atmospheric nitrogen into nitrates. Nitrogen-fixing bacteria are classified into two types: Bacteria that are unrestricted, such as Azotobacter and Clostridium.
• Free-living bacteria, such as Azotobacter and Clostridium. 
• Symbiotic Bacteria include Rhizobium, which is found in the rhizosphere soil of personal leguminous plants such as Nostoc and Anabaena. 
• Industrial Nitrogen Fixation: This is an artificial alternative in which Earth’s atmosphere material is converted into nitrogen and then into nitrates in varied fertilisers via Haber’s process.

Nitrification: Microbes in the soil convert ammonia to nitrate during this process. Nitrites are formed through the oxidation of ammonia by Nitrosomonas bacteria species. Nitrobacter then converts the nitrites produced into nitrates. This conversion is critical because ammonia is toxic to plants.

Assimilation: Plants use their roots to absorb nitrogen from the soil, which is available as part of acetone, ammonia ions, nitrate ions, or ammonium salts and are used in the creation of animal and plant enzymes. When the secondary consumers eat the plants, it enters the food web.

Ammonification: When plants and animals die, the ammonia in the organic material returns to the soil. Organic matter is converted back into ammonium by decomposers, bacteria or fungi found in the soil. This decomposition process generates ammonia, used in other biological processes.

Denitrification: Denitrification is when nitrogen compounds return to an atmosphere to convert nitrate (NO3-) into gaseous nitrogen (N). This is the final step of the nitrogen and causes a loss of hydrogen. The deposition is carried out by denitrifying bacterial species such as Clostridium and Bacterial infections, which process nitrate to obtain oxygen and produce free nitrogen gas as a side effect.

The Nitrogen Cycle’s Importance

The Nitrogen Cycle is critical for the following reasons:

• Aids plants in the synthesis of chloroplasts from nitrogen.
• The biochemical process aids in converting inert nitrogen into a usable form for plants.
• Bacteria aid in the decomposition of plants and animal matter during the ammonification process, which indirectly works to help to remove pollutants.
• Nitrates and sulphites are returned to the soil, which aids in the enrichment of the soil with the nutrients required for agriculture.
• Nitrogen is an essential component of the cell, forming many important compounds and biomolecules.
• Chlorophyll is a pigment that is required for photosynthetic activity. The nitrogen cycle aids plants in the production of chlorophyll from nitrogen compounds. It is necessary for plant survival because plants require nitrogen to live and flourish. Bacteria decompose dead and rotted organic matter during the ammonia formation process. This process aids in the removal of organic matter from the environment while also providing essential nutrients to the soil. Carbon dioxide compounds enrich the soil, making it fertile and appropriate for plant growth. 
• Ammonia is a necessary component of living organisms’ cells and tissues. It generates proteins and nucleic acids, which are essential components of life. Life also couldn’t exist without nitrogen.
• Nitrogen is also recirculated by anthropogenic activities such as fuel combustion and nitrogen fertiliser use. The levels of ammonia emissions in the air rise due to these processes. Nitrogen-containing fertilisers are wiped away in lakes, causing eutrophication.

The Nitrogen Cycle in the Marine Ecosystem

The Nitrogen Cycle process occurs inside the marine ecosystem in the same way it does in the terrestrial environment. The only distinction is that this is managed to carry out by cyanobacteria rather than humans. As sediments are condensed over long periods and form sedimentary rock, nitrogen-containing substances fall into the ocean. These sedimentary rocks have moved to land as a result of geological uplift. It was previously unknown that these nitrogen-containing rock layers are an important nitrogen source. However, recent studies have shown that the ammonia from such rocks is published into the plants due to weathering.

Facts About Nitrogen Cycle

• Nitrogen is abundant in the atmosphere, but plants cannot use it directly from the air. Nitrogen has been fixed in three ways: atmospherically, industrially, and biologically. 
• The nitrogen in the atmosphere is converted into ammonia. Nitrogen-fixing bacteria, such as Azotobacter and Rhizobium, are crucial to creating nitrogen. 
• Fungi such as actinomyces decompose dead and rotten plants, releasing ammonia, dioxide, and water. This is known as ammonification. 
• Nitrosomonas use nitrification to convert ammonia to nitrites, converted to nitrates by Anaerobic bacteria. 
• Plants absorb nitrates, and nitrogen is being used to form vital cell organs and biomolecules. 
• Assimilation is the process by which plants take up nitrogen compounds.
• Pseudomonas bacteria convert the nitrates in the soil into free nitrogen. This is known as denitrification. The cycle continues, and the percentage of nitrogen remains constant.
•  Phytoplankton plants and other microbes transform nitrogen into nitrogen compounds in the marine ecosystem, completing the nitrogen cycle. 
• This is an important part of the earth’s natural cycle required for life processes throughout nature.

Conclusion

Nitrogen is an important component of the environment, and nitrification is critical to the ecosystem’s survival. Nitrogen is plentiful in the ambiance, but it is useless to plants and animals unless it has been transformed into nitrogen compounds. Nitrogen-fixing bacteria are critical in converting nitrogen from the atmosphere into nitrogen that plants can use. Through their roots, the plants absorb usable nitrogen from the soil. Such nitrogen compounds are then used to produce proteins and other compounds in the cell. 

Animals absorb nitrogen by consuming nitrogen-containing plants or other animals. Humans consume the proteins from these animals and plants, and the nitrogen is then assimilated into our system. During the final phases of nitrogen, bacteria and fungi aid in decomposing organic matter, allowing nitrogenous compounds to be disintegrated into the soil and used by plants again. Some bacteria in the soil then transform these nitrogen compounds into nitrogen gas. It eventually returns to the atmosphere. These processes are repeated indefinitely, ensuring that the proportion of nitrogen remains constant.

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