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Nitrogen Cycle – Introduction, Types and Importance

Grade 10
Aug 24, 2022


Energy flow in ecosystem 

The food chain and food web facilitate the movement of energy. Plants collect sunlight with the aid of chloroplasts during the process of energy flow in the ecosystem, and a portion of it is turned into chemical energy in the process of photosynthesis. When herbivores eat (primary consumers) the plants as food, this energy is stored in various organic products in the plants and passed on to the primary consumers in the food chain. The chemical energy contained in plant products is then converted into kinetic energy, and energy is released by heat conversion.  

The flow of energy in the ecosystem is one of the most important variables in the survival of such a large number of creatures. Solar energy is the principal source of energy for practically all species on Earth. It’s interesting to learn that we only receive around half of the sun’s effective radiation on Earth. When we say effective radiation, we mean radiation that plants can employ to perform photosynthesis. 

 Energy flow 

Nitrogen cycle 

Nitrogen is one of the most important nutrients for the existence of all living species. It is required for the formation of several biomolecules, including proteins, DNA, and chlorophyll. Despite the fact that nitrogen is abundant in the atmosphere as dinitrogen gas (N2), it is mostly inaccessible to most species in this form, making nitrogen a rare resource and frequently restricting primary production in many ecosystems. Nitrogen becomes accessible to primary producers such as plants only after it has been transformed from dinitrogen gas to ammonia (NH3). In addition to N2 and NH3, nitrogen may be found in a variety of inorganic. 
(e.g., ammonia, nitrate) and organic  
(e.g., amino and nucleic acids) forms.  

As a result, nitrogen undergoes several transformations in the environment, moving from one form to another as organisms utilize it for growth and, in some circumstances, energy. Nitrogen fixation, nitrification, denitrification, assimilation, and ammonification are the principal nitrogen reactions in the nitrogen cycle. During the last phases of the nitrogen cycle, bacteria and fungi help in the decomposition of organic matter, allowing nitrogenous chemicals to be dissolved into the soil and utilized by plants again.  

Nitrogen-fixing bacteria are critical in converting atmospheric nitrogen into nitrogen molecules that plants can utilize. Through their roots, the plants receive useable nitrogen molecules from the soil. These nitrogen molecules are then utilized in the cell to produce proteins and other substances. 


Animals absorb nitrogen through ingesting nitrogen-containing plants or other animals. Humans ingest the proteins from these plants and animals, and the nitrogen is subsequently assimilated into our system. 

Nitrogen cycle 

Nitrogen cycle steps 

 steps of Nitrogen cycle 

Nitrogen fixation 

  • It is the first phase in the nitrogen cycle. Atmospheric nitrogen (N2), which is predominantly accessible in an inert state, is transformed into the useful form -ammonia in this process (NH3). 
  • The inert form of nitrogen gas is deposited into soils from the atmosphere and surface waters during the nitrogen fixation process, mostly by precipitation. Later, the nitrogen undergoes a series of modifications that result in the separation of two nitrogen atoms, which mix with hydrogen to produce ammonia (NH3+). 
  • Diazotrophs is a kind of symbiotic bacteria that complete the nitrogen fixation process. 
  • Other essential participants in this process are Azotobacter and Rhizobium. These bacteria have a nitrogenize enzyme that can mix gaseous nitrogen with hydrogen to produce ammonia. 

N2+8H++8 e  → 2 NH3+H2


  • The presence of microorganisms in the soil converts ammonia to nitrate throughout this process. 
  • Nitrites are generated by the oxidation of ammonia by Nitrosomonas bacteria species. Nitrobacteria then converts the nitrites generated into nitrates. This reaction is critical since ammonia gas is poisonous to plants 
  • Reaction 1 is performed by the enzyme ammonia monooxygenase and transforms ammonia to the intermediate hydroxylamine. 
  • Reaction 2 is performed by the enzyme hydroxylamine oxidoreductase and transforms hydroxylamine to nitrite.  
  1. NH3+O2+2 e     →       NH2OH+H2
  1. NH2OH+H2O      →         NO2−+5 H++4 e


  • Plants utilize their roots to absorb nitrogen molecules from the soil, which are accessible in the form of ammonia, nitrite ions, nitrate ions, or ammonium ions and are employed in the production of plant and animal proteins. 
  • Nitrogen enters the food web when the plants are eaten by the primary consumers. 


  • When plants or animals die, the nitrogen in the organic matter returns to the soil. Organic matter is converted back into ammonium by decomposers, which are bacteria or fungus found in the soil. 
  • This breakdown process generates ammonia, which is then utilized in other biological activities. 


  • Denitrification is the process by which nitrogen compounds return to the environment by turning nitrate (NO−3)NO3− into gaseous nitrogen (N). This is the last step of the nitrogen cycle and happens in the absence of oxygen. 
  • Denitrification is carried out by denitrifying bacterial species such as Clostridium and Pseudomonas, which consume nitrate to get oxygen and produce free nitrogen gas as a byproduct. 

Nitrogen cycle in marine ecosystem 

  • The nitrogen cycle process happens in the marine environment in the same way that it does in the terrestrial ecosystem. The only difference is that it is carried out by sea microbes rather than humans. 
  • As sediments are compacted over extended periods of time and form sedimentary rock, nitrogen-containing chemicals 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 sedimentary rocks provide an important source of nitrogen. However, subsequent studies have shown that the nitrogen from these rocks is released into the plants as a result of weathering. 
Marine nitrogen cycle 

Importance of nitrogen cycle 

  • Helps plants in the production of chlorophyll from nitrogen molecules. 
  • Through the metabolic process, it helps in the conversion of inert nitrogen gas into a useful form for plants. 
  • Bacteria aid in the decomposition of animal and plant materials during the ammonification process, which indirectly helps to clean up the environment. 
  • Nitrates and nitrites are released into the soil, which helps in the enrichment of the soil with the nutrients essential for agriculture. 
  • Nitrogen is an essential component of the cell, forming several vital chemicals and biomolecules. 
Nitrogen cycle 




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