importance of nitrogen biology essay

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What Is the Nitrogen Cycle and Why Is It Key to Life?

Nitrogen, the most abundant element in our atmosphere, is crucial to life. Nitrogen is found in soils and plants, in the water we drink, and in the air we breathe. It is also essential to life: a key building block of DNA, which determines our genetics, is essential to plant growth, and therefore necessary for the food we grow. But as with everything, balance is key: too little nitrogen and plants cannot thrive, leading to low crop yields; but too much nitrogen can be toxic to plants, and can also harm our environment. Plants that do not have enough nitrogen become yellowish and do not grow well and can have smaller flowers and fruits. Farmers can add nitrogen fertilizer to produce better crops, but too much can hurt plants and animals, and pollute our aquatic systems. Understanding the Nitrogen Cycle—how nitrogen moves from the atmosphere to earth, through soils and back to the atmosphere in an endless Cycle—can help us grow healthy crops and protect our environment.

Introduction

Nitrogen, or N, using its scientific abbreviation, is a colorless, odorless element. Nitrogen is in the soil under our feet, in the water we drink, and in the air we breathe. In fact, nitrogen is the most abundant element in Earth’s atmosphere: approximately 78% of the atmosphere is nitrogen! Nitrogen is important to all living things, including us. It plays a key role in plant growth: too little nitrogen and plants cannot thrive, leading to low crop yields; but too much nitrogen can be toxic to plants [ 1 ]. Nitrogen is necessary for our food supply, but excess nitrogen can harm the environment.

Why Is Nitrogen Important?

The delicate balance of substances that is important for maintaining life is an important area of research, and the balance of nitrogen in the environment is no exception [ 2 ]. When plants lack nitrogen, they become yellowed, with stunted growth, and produce smaller fruits and flowers. Farmers may add fertilizers containing nitrogen to their crops, to increase crop growth. Without nitrogen fertilizers, scientists estimate that we would lose up to one third of the crops we rely on for food and other types of agriculture. But we need to know how much nitrogen is necessary for plant growth, because too much can pollute waterways, hurting aquatic life.

Nitrogen Is Key to Life!

Nitrogen is a key element in the nucleic acids DNA and RNA , which are the most important of all biological molecules and crucial for all living things. DNA carries the genetic information, which means the instructions for how to make up a life form. When plants do not get enough nitrogen, they are unable to produce amino acids (substances that contain nitrogen and hydrogen and make up many of living cells, muscles and tissue). Without amino acids, plants cannot make the special proteins that the plant cells need to grow. Without enough nitrogen, plant growth is affected negatively. With too much nitrogen, plants produce excess biomass, or organic matter, such as stalks and leaves, but not enough root structure. In extreme cases, plants with very high levels of nitrogen absorbed from soils can poison farm animals that eat them [ 3 ].

What Is Eutrophication and can It Be Prevented?

Excess nitrogen can also leach—or drain—from the soil into underground water sources, or it can enter aquatic systems as above ground runoff. This excess nitrogen can build up, leading to a process called eutrophication . Eutrophication happens when too much nitrogen enriches the water, causing excessive growth of plants and algae. Too much nitrogen can even cause a lake to turn bright green or other colors, with a “bloom” of smelly algae called phytoplankton (see Figure 1 )! When the phytoplankton dies, microbes in the water decompose them. The process of decomposition reduces the amount of dissolved oxygen in the water, and can lead to a “dead zone” that does not have enough oxygen to support most life forms. Organisms in the dead zone die from lack of oxygen. These dead zones can happen in freshwater lakes and also in coastal environments where rivers full of nutrients from agricultural runoff (fertilizer overflow) flow into oceans [ 4 ].

• Figure 1 - Eutrophication at a waste water outlet in the Potomac River, Washington, D.C.
• The water in this river, is bright green because it has undergone eutrophication, due to excess nitrogen and other nutrients polluting the water, which has led to increased phytoplankton and algal blooms, so the water has become cloudy and can turn different colors, such as green, yellow, red, or brown, depending on the algal blooms (Wikimedia Commons: https://commons.wikimedia.org/wiki/Category:Eutrophication#/media/File:Potomac_green_water.JPG ).

Figure 2 shows the stages of Eutrophication (open access Wikimedia Commons image from https://commons.m.wikimedia.org/wiki/File:Eutrophicationmodel.svg ).

• Figure 2 - Stages of eutrophication.
• (1) Excess nutrients end up in the soil and ground. (2) Some nutrients become dissolved in water and leach or leak into deeper soil layers. Eventually, they get drained into a water body, such as a lake or pond. (3) Some nutrients run off from over the soils and ground directly into the water. (4) The extra nutrients cause algae to bloom. (5) Sunlight becomes blocked by the algae. (6) Photosynthesis and growth of plants under the water will be weakened or potentially stopped. (7) Next, the algae bloom dies and falls to the bottom of the water body. Then, bacteria begin to decompose or break up the remains, and use up oxygen in the process. (8) The decomposition process causes the water to have reduced oxygen, leading to “dead zones.” Bigger life forms like fish cannot breathe and die. The water body has now undergone eutrophication.

Can eutrophication be prevented? Yes! People who manage water resources can use different strategies to reduce the harmful effects of algal blooms and eutrophication of water surfaces. They can re-reroute excess nutrients away from lakes and vulnerable costal zones, use herbicides (chemicals used to kill unwanted plant growth) or algaecides (chemicals used to kill algae) to stop the algal blooms, and reduce the quantities or combinations of nutrients used in agricultural fertilizers, among other techniques [ 5 ]. But, it can often be hard to find the origin of the excess nitrogen and other nutrients.

Once a lake has undergone eutrophication, it is even harder to do damage control. Algaecides can be expensive, and they also do not correct the source of the problem: the excess nitrogen or other nutrients that caused the algae bloom in the first place! Another potential solution is called bioremediation , which is the process of purposefully changing the food web in an aquatic ecosystem to reduce or control the amount of phytoplankton. For example, water managers can introduce organisms that eat phytoplankton, and these organisms can help reduce the amounts of phytoplankton, by eating them!

What Exactly Is the Nitrogen Cycle?

The nitrogen cycle is a repeating cycle of processes during which nitrogen moves through both living and non-living things: the atmosphere, soil, water, plants, animals and bacteria . In order to move through the different parts of the cycle, nitrogen must change forms. In the atmosphere, nitrogen exists as a gas (N 2 ), but in the soils it exists as nitrogen oxide, NO, and nitrogen dioxide, NO 2 , and when used as a fertilizer, can be found in other forms, such as ammonia, NH 3 , which can be processed even further into a different fertilizer, ammonium nitrate, or NH 4 NO 3 .

There are five stages in the nitrogen cycle, and we will now discuss each of them in turn: fixation or volatilization, mineralization, nitrification, immobilization, and denitrification. In this image, microbes in the soil turn nitrogen gas (N 2 ) into what is called volatile ammonia (NH 3 ), so the fixation process is called volatilization. Leaching is where certain forms of nitrogen (such as nitrate, or NO 3 ) becomes dissolved in water and leaks out of the soil, potentially polluting waterways.

Stage 1: Nitrogen Fixation

In this stage, nitrogen moves from the atmosphere into the soil. Earth’s atmosphere contains a huge pool of nitrogen gas (N 2 ). But this nitrogen is “unavailable” to plants, because the gaseous form cannot be used directly by plants without undergoing a transformation. To be used by plants, the N 2 must be transformed through a process called nitrogen fixation. Fixation converts nitrogen in the atmosphere into forms that plants can absorb through their root systems.

A small amount of nitrogen can be fixed when lightning provides the energy needed for N 2 to react with oxygen, producing nitrogen oxide, NO, and nitrogen dioxide, NO 2 . These forms of nitrogen then enter soils through rain or snow. Nitrogen can also be fixed through the industrial process that creates fertilizer. This form of fixing occurs under high heat and pressure, during which atmospheric nitrogen and hydrogen are combined to form ammonia (NH 3 ), which may then be processed further, to produce ammonium nitrate (NH 4 NO 3 ), a form of nitrogen that can be added to soils and used by plants.

Most nitrogen fixation occurs naturally, in the soil, by bacteria. In Figure 3 (above), you can see nitrogen fixation and exchange of form occurring in the soil. Some bacteria attach to plant roots and have a symbiotic (beneficial for both the plant and the bacteria) relationship with the plant [ 6 ]. The bacteria get energy through photosynthesis and, in return, they fix nitrogen into a form the plant needs. The fixed nitrogen is then carried to other parts of the plant and is used to form plant tissues, so the plant can grow. Other bacteria live freely in soils or water and can fix nitrogen without this symbiotic relationship. These bacteria can also create forms of nitrogen that can be used by organisms.

• Figure 3 - Stages of the nitrogen cycle.
• The Nitrogen Cycle: Nitrogen cycling through the various forms in soil determines the amount of nitrogen available for plants to uptake. Source: https://www.agric.wa.gov.au/soil-carbon/immobilisation-soil-nitrogen-heavy-stubble-loads .

Stage 2: Mineralization

This stage takes place in the soil. Nitrogen moves from organic materials, such as manure or plant materials to an inorganic form of nitrogen that plants can use. Eventually, the plant’s nutrients are used up and the plant dies and decomposes. This becomes important in the second stage of the nitrogen cycle. Mineralization happens when microbes act on organic material, such as animal manure or decomposing plant or animal material and begin to convert it to a form of nitrogen that can be used by plants. All plants under cultivation, except legumes (plants with seed pods that split in half, such as lentils, beans, peas or peanuts) get the nitrogen they require through the soil. Legumes get nitrogen through fixation that occurs in their root nodules, as described above.

The first form of nitrogen produced by the process of mineralization is ammonia, NH 3 . The NH 3 in the soil then reacts with water to form ammonium, NH 4 . This ammonium is held in the soils and is available for use by plants that do not get nitrogen through the symbiotic nitrogen fixing relationship described above.

Stage 3: Nitrification

The third stage, nitrification, also occurs in soils. During nitrification the ammonia in the soils, produced during mineralization, is converted into compounds called nitrites, NO 2 − , and nitrates, NO 3 − . Nitrates can be used by plants and animals that consume the plants. Some bacteria in the soil can turn ammonia into nitrites. Although nitrite is not usable by plants and animals directly, other bacteria can change nitrites into nitrates—a form that is usable by plants and animals. This reaction provides energy for the bacteria engaged in this process. The bacteria that we are talking about are called nitrosomonas and nitrobacter. Nitrobacter turns nitrites into nitrates; nitrosomonas transform ammonia to nitrites. Both kinds of bacteria can act only in the presence of oxygen, O 2 [ 7 ]. The process of nitrification is important to plants, as it produces an extra stash of available nitrogen that can be absorbed by the plants through their root systems.

Stage 4: Immobilization

The fourth stage of the nitrogen cycle is immobilization, sometimes described as the reverse of mineralization. These two processes together control the amount of nitrogen in soils. Just like plants, microorganisms living in the soil require nitrogen as an energy source. These soil microorganisms pull nitrogen from the soil when the residues of decomposing plants do not contain enough nitrogen. When microorganisms take in ammonium (NH 4 + ) and nitrate (NO 3 − ), these forms of nitrogen are no longer available to the plants and may cause nitrogen deficiency, or a lack of nitrogen. Immobilization, therefore, ties up nitrogen in microorganisms. However, immobilization is important because it helps control and balance the amount of nitrogen in the soils by tying it up, or immobilizing the nitrogen, in microorganisms.

Stage 5: Denitrification

In the fifth stage of the nitrogen cycle, nitrogen returns to the air as nitrates are converted to atmospheric nitrogen (N 2 ) by bacteria through the process we call denitrification. This results in an overall loss of nitrogen from soils, as the gaseous form of nitrogen moves into the atmosphere, back where we began our story.

Nitrogen Is Crucial for Life

The cycling of nitrogen through the ecosystem is crucial for maintaining productive and healthy ecosystems with neither too much nor too little nitrogen. Plant production and biomass (living material) are limited by the availability of nitrogen. Understanding how the plant-soil nitrogen cycle works can help us make better decisions about what crops to grow and where to grow them, so we have an adequate supply of food. Knowledge of the nitrogen cycle can also help us reduce pollution caused by adding too much fertilizer to soils. Certain plants can uptake more nitrogen or other nutrients, such as phosphorous, another fertilizer, and can even be used as a “buffer,” or filter, to prevent excessive fertilizer from entering waterways. For example, a study done by Haycock and Pinay [ 8 ] showed that poplar trees ( Populus italica ) used as a buffer held on to 99% of the nitrate entering the underground water flow during winter, while a riverbank zone covered with a specific grass ( Lolium perenne L.) held up to 84% of the nitrate, preventing it from entering the river.

As you have seen, not enough nitrogen in the soils leaves plants hungry, while too much of a good thing can be bad: excess nitrogen can poison plants and even livestock! Pollution of our water sources by surplus nitrogen and other nutrients is a huge problem, as marine life is being suffocated from decomposition of dead algae blooms. Farmers and communities need to work to improve the uptake of added nutrients by crops and treat animal manure waste properly. We also need to protect the natural plant buffer zones that can take up nitrogen runoff before it reaches water bodies. But, our current patterns of clearing trees to build roads and other construction worsen this problem, because there are fewer plants left to uptake excess nutrients. We need to do further research to determine which plant species are best to grow in coastal areas to take up excess nitrogen. We also need to find other ways to fix or avoid the problem of excess nitrogen spilling over into aquatic ecosystems. By working toward a more complete understanding of the nitrogen cycle and other cycles at play in Earth’s interconnected natural systems, we can better understand how to better protect Earth’s precious natural resources.

DNA : ↑ Deoxyribonucleic acid, a self-replicating material which is present in nearly all living organisms as the main component of chromosomes, and carrier of genetic information.

RNA : ↑ Ribonucleic acid, a nucleic acid present in all living cells, acts as a messenger carrying instructions from DNA.

Eutrophication : ↑ Excessive amount of nutrients (such as nitrogen) in a lake or other body of water, which causes a dense growth of aquatic plant life, such as algae.

Phytoplankton : ↑ Tiny, microscopic marine algae (also known as microalgae) that require sunlight in order to grow.

Bioremediation : ↑ Using other microorganisms or tiny living creatures to eat and break down pollution in order to clean a polluted site.

Bacteria : ↑ Microscopic living organisms that usually contain only one cell and are found everywhere. Bacteria can cause decomposition or breaking down, of organic material in soils.

Leaching : ↑ When a mineral or chemical (such as nitrate, or NO 3 ) drains away from soil or other ground material and leaks into surrounding area.

Legumes : ↑ A member of the pea family: beans, lentils, soybeans, peanuts and peas, are plants with seed pods that split in half.

Microorganism : ↑ An organism, or living thing, that is too tiny to be seen without a microscope, such as a bacterium.

Conflict of Interest Statement

The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

[1] ↑ Britto, D. T., and Kronzuker, H. J. 2002. NH 4 + toxicity in higher plants: a critical review. J. Plant Physiol . 159:567–84. doi: 10.1078/0176-1617-0774

[2] ↑ Weathers, K. C., Groffman, P. M., Dolah, E. V., Bernhardt, E., Grimm, N. B., McMahon, K., et al. 2016. Frontiers in ecosystem ecology from a community perspective: the future is boundless and bright. Ecosystems 19:753–70. doi: 10.1007/s10021-016-9967-0

[3] ↑ Brady, N., and Weil, R. 2010. “Nutrient cycles and soil fertility,” in Elements of the Nature and Properties of Soils, 3rd Edn , ed V. R. Anthony (Upper Saddle River, NJ: Pearson Education Inc.), 396–420.

[4] ↑ Foth, H. 1990. Chapter 12: “Plant-Soil Macronutrient Relations,” in Fundamentals of Soil Science , 8th Edn , ed John Wiley and Sons (New York, NY: John Wiley Company), 186–209.

[5] ↑ Chislock, M. F., Doster, E., Zitomer, R. A., and Wilson, A. E. 2013. Eutrophication: causes, consequences, and controls in aquatic ecosystems. Nat. Educ. Knowl . 4:10. Available online at: https://www.nature.com/scitable/knowledge/library/eutrophication-causes-consequences-and-controls-in-aquatic-102364466

[6] ↑ Peoples, M. B., Herridge, D. F., and Ladha, J. K. 1995. Biological nitrogen fixation: an efficient source of nitrogen for sustainable agricultural production? Plant Soil 174:3–28. doi: 10.1007/BF00032239

[7] ↑ Manahan, S. E. 2010. Environmental Chemistry , 9th Edn . Boca Raton, FL: CRC Press, 166–72.

[8] ↑ Haycock, N. E., and Pinay, G. 1993. Groundwater nitrate dynamics in grass and poplar vegetated riparian buffer strips during the winter. J. Environ. Qual . 22:273–8. doi: 10.2134/jeq1993.00472425002200020007x

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Biology library

Course: biology library   >   unit 28.

• Intro to biogeochemical cycles
• Biogeochemical cycles overview
• The water cycle
• The carbon cycle

The nitrogen cycle

• The phosphorus cycle
• Phosphorus cycle
• Eutrophication and dead zones
• Biogeochemical cycles
• Nitrogen is a key component of the bodies of living organisms. Nitrogen atoms are found in all proteins and DNA ‍   .
• Nitrogen exists in the atmosphere as N 2 ‍   gas. In nitrogen fixation , bacteria convert N 2 ‍   into ammonia, a form of nitrogen usable by plants. When animals eat the plants, they acquire usable nitrogen compounds.
• Nitrogen is a common limiting nutrient in nature, and agriculture. A limiting nutrient is the nutrient that's in shortest supply and limits growth.
• When fertilizers containing nitrogen and phosphorus are carried in runoff to lakes and rivers, they can result in blooms of algae—this is called eutrophication .

Introduction

Bacteria play a key role in the nitrogen cycle., nitrogen cycling in marine ecosystems, nitrogen as a limiting nutrient.

• When a nutrient is limiting, adding more of it will increase growth—e.g., it will cause plants to grow taller than if nothing were added.
• If a non-limiting nutrient is instead added, it won't have an effect—e. g., plants will grow to the same height whether the nutrient is present or absent.

Human activity affects cycling of nitrogen.

Attribution.

• " Biogeochemical cycles " by Robert Bear, David Rintoul, Bruce Snyder, Martha Smith-Caldas, Christopher Herren, and Eva Horne, CC BY 4.0 ; download the original article for free at http://cnx.org/contents/[email protected]
• " Biogeochemical cycles " by OpenStax College, Concepts of Biology, CC BY 4.0 ; download the original article for free at http://cnx.org/contents/[email protected] .

Works Cited

• "Atmosphere of Earth," Wikipedia, last modified June 9, 2016, https://en.wikipedia.org/wiki/Atmosphere_of_Earth .
• Scott L. Morford, Benjamin Z. Houlton, and Randy A. Dahlgren, “Increased Forest Ecosystem Carbon and Nitrogen Storage from Nitrogen Rich Bedrock,” Nature 477, no. 7362 (2011): 78–81.
• "Limiting Nutrient," accessed June 10, 2016, https://www.rpi.edu/dept/chem-eng/Biotech-Environ/GrowPresent/limiting.htm .
• "Haber Process," Wikipedia, last modified June 10, 2016, https://en.wikipedia.org/wiki/Haber_process .
• "Eutrophication," Wikipedia, last modified June 6, 2016, https://en.wikipedia.org/wiki/Eutrophication .

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• Biology Article

Nitrogen Cycle

Nitrogen cycle is an important part of the ecosystem. In this article, we shall explore its implications on the environment in detail.

Table of Contents

• What is Nitrogen Cycle
• In Marine Ecosystem

Nitrogen Cycle Definition

“Nitrogen Cycle is a biogeochemical process which transforms the inert nitrogen present in the atmosphere to a more usable form for living organisms.”

Furthermore, nitrogen is a key nutrient element for plants. However, the abundant nitrogen in the atmosphere cannot be used directly by plants or animals. Read on to explore how the Nitrogen cycle makes usable nitrogen available to plants and other living organisms.

What is the Nitrogen Cycle?

Nitrogen Cycle is a biogeochemical process through which nitrogen is converted into many forms, consecutively passing from the atmosphere to the soil to organism and back into the atmosphere.

It involves several processes such as nitrogen fixation, nitrification, denitrification, decay and putrefaction.

Nitrogen gas exists in both organic and inorganic forms. Organic nitrogen exists in living organisms, and they get passed through the food chain by the consumption of other living organisms.

Inorganic forms of nitrogen are found in abundance in the atmosphere. This nitrogen is made available to plants by symbiotic bacteria which can convert the inert nitrogen into a usable form – such as nitrites and nitrates.

Nitrogen undergoes various types of transformation to maintain a balance in the ecosystem. Furthermore, this process extends to various biomes, with the marine nitrogen cycle being one of the most complicated biogeochemical cycles.

Nitrogen Cycle Explained – Stages of Nitrogen Cycle

Process of the Nitrogen Cycle consists of the following steps – Nitrogen fixation, Nitrification, Assimilation, Ammonification and Denitrification. These processes take place in several stages and are explained below:

Nitrogen Fixation Process

It is the initial step of the nitrogen cycle. Here, Atmospheric nitrogen (N 2 ) which is primarily available in an inert form, is converted into the usable form -ammonia (NH 3 ).

During the process of Nitrogen fixation, the inert form of nitrogen gas is deposited into soils from the atmosphere and surface waters, mainly through precipitation.

The entire process of Nitrogen fixation is completed by symbiotic bacteria, which are known as Diazotrophs. Azotobacter and Rhizobium also have a major role in this process. These bacteria consist of a nitrogenase enzyme, which has the capability to combine gaseous nitrogen with hydrogen to form ammonia.

Nitrogen fixation can occur either by atmospheric fixation- which involves lightening, or industrial fixation by manufacturing ammonia under high temperature and pressure conditions. This can also be fixed through man-made processes, primarily industrial processes that create ammonia and nitrogen-rich fertilisers.

Recommended Video:

Types of Nitrogen Fixation

• Atmospheric fixation: A natural phenomenon where the energy of lightning breaks the nitrogen into nitrogen oxides, which are then used by plants.
• Industrial nitrogen fixation:  It is a man-made alternative that aids in nitrogen fixation by the use of ammonia. Ammonia is produced by the direct combination of nitrogen and hydrogen. Later, it is converted into various fertilisers such as urea.
• Biological nitrogen fixation: We already know that nitrogen is not used directly from the air by plants and animals. Bacteria like Rhizobium and blue-green algae transform the unusable form of nitrogen into other compounds that are more readily usable. These nitrogen compounds get fixed in the soil by these microbes.

Also Read: Nitrogen Fixation And Nitrogen Metabolism

• Nitrification

In this process, the ammonia is converted into nitrate by the presence of bacteria in the soil. Nitrites are formed by the oxidation of ammonia with the help of Nitrosomonas bacteria species. Later, the produced nitrites are converted into nitrates by Nitrobacter . This conversion is very important as ammonia gas is toxic for plants.

The reaction involved in the process of Nitrification is as follows:

2NH 3 + 3O 2  → 2NO 2 – + 2H +  + 2H 2 O

2NO 2 – + O 2  → 2NO 3 –

• Assimilation

Primary producers – plants take in the nitrogen compounds from the soil with the help of their roots, which are available in the form of ammonia, nitrite ions, nitrate ions or ammonium ions and are used in the formation of the plant and animal proteins. This way, it enters the food web when the primary consumers eat the plants.

• Ammonification

When plants or animals die, the nitrogen present in the organic matter is released back into the soil. The decomposers, namely bacteria or fungi present in the soil, convert the organic matter back into ammonium. This process of decomposition produces ammonia, which is further used for other biological processes.

• Denitrification

Denitrification is the process in which the nitrogen compounds make their way back into the atmosphere by converting nitrate (NO 3 -)  into gaseous nitrogen (N). This process of the nitrogen cycle is the final stage and occurs in the absence of oxygen. Denitrification is carried out by the denitrifying bacterial species- Clostridium and Pseudomonas , which will process nitrate to gain oxygen and gives out free nitrogen gas as a byproduct.

Nitrogen Cycle in Marine Ecosystem

The process of the nitrogen cycle occurs in the same manner in the marine ecosystem as in the terrestrial ecosystem. The only difference is that it is carried out by marine bacteria.

The nitrogen-containing compounds fall into the ocean as sediments get compressed over long periods and form sedimentary rock. Due to the geological uplift, these sedimentary rocks move to land. Initially, it was not known that these nitrogen-containing sedimentary rocks are an essential source of nitrogen. But, recent researches have proved that the nitrogen from these rocks is released into the plants due to the weathering of rocks.

Importance of Nitrogen Cycle

The importance of the nitrogen cycle are as follows:

• Helps plants to synthesise chlorophyll from the nitrogen compounds.
• Helps in converting inert nitrogen gas into a usable form for the plants through the biochemical process.
• In the process of ammonification, the bacteria help in decomposing the animal and plant matter, which indirectly helps to clean up the environment.
• Nitrates and nitrites are released into the soil, which helps in enriching the soil with the necessary nutrients required for cultivation.
• Nitrogen is an integral component of the cell and it forms many crucial compounds and important biomolecules.

Nitrogen is also cycled by human activities such as the combustion of fuels and the use of nitrogen fertilisers. These processes increase the levels of nitrogen-containing compounds in the atmosphere. The fertilisers containing nitrogen are washed away in lakes, rivers and result in eutrophication.

• Nitrogen is abundant in the atmosphere, but it is unusable to plants or animals unless it is converted into nitrogen compounds.
• Nitrogen-fixing bacteria play a crucial role in fixing atmospheric nitrogen into nitrogen compounds that can be used by plants.
• The plants absorb the usable nitrogen compounds from the soil through their roots. Then, these nitrogen compounds are used for the production of proteins and other compounds in the plant cell.
• Animals assimilate nitrogen by consuming these plants or other animals that contain nitrogen. Humans consume proteins from these plants and animals. The nitrogen then assimilates into our body system.
• During the final stages of the nitrogen cycle, bacteria and fungi help decompose organic matter, where the nitrogenous compounds get dissolved into the soil which is again used by the plants.
• Some bacteria then convert these nitrogenous compounds in the soil and turn it into nitrogen gas. Eventually, it goes back to the atmosphere.
• These sets of processes repeat continuously and thus maintain the percentage of nitrogen in the atmosphere.

Further Reading: Other Biogeochemical Cycles

To explore more about the Nitrogen cycle, or the steps involved, keep visiting BYJU’S Biology website or download the BYJU’S app, for further reference.

Frequently Asked Questions

Why is nitrogen important for life.

Nitrogen constitutes many cellular components and is essential in many biological processes. For instance, the amino acids contain nitrogen and form building blocks that make up various components of the human body such as hair, tissues and muscles.

Why do plants need nitrogen?

Plants need nitrogen as this element is an important component of chlorophyll. Consequently, chlorophyll is vital for the process of photosynthesis, so lack of nitrogen can cause deficiency disorders such as stunted growth and other abnormalities

List the different steps that explain the Nitrogen Cycle process.

• Nitrogen Fixation

What is Ammonification?

Ammonification occurs during the decomposition of organic matter, where ammonifying bacteria convert organic nitrogen into inorganic components like ammonia or ammonium ions.

What is Nitrification?

Nitrification is a process that converts ammonia into nitrate by bacteria. Initially, the ammonia is converted to nitrite (NO 2 − ) by the bacteria Nitrosomonas , or Nitrococcus , etc., and then to nitrate (NO 3 – ) by Nitrobacter .

What is Denitrification?

Denitrification is the process of converting the nitrate back into molecular nitrogen by bacterias such as  Pseudomonas, Thiobacillus, Bacillus subtilis etc.

What is the function of nitrifying bacteria?

Nitrifying bacteria are a small group of aerobic bacteria, which are mainly involved in the conversion of ammonia into nitrates.

Which part of the plant is involved in nitrogen fixation?

The process of nitrogen fixation is carried out naturally in the soil within nodules in the plant’s root systems.

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Your explanation is helpful and interesting! Thank you alot

Thank you Byjus

The information is nice. Keep it up

Thank you byjus

Explanation is very helpful

Your explanation is very interesting and it helps a lot thank you

Your explanation is very helpful and interesting.

Well explained. Loved it and actually very useful.

Yes, I can understand the nitrogen cycle and it’s important. Thank you Byju’s.

thanks for helping me understand this whole concept so well.

Very nicely explained.

Well explained about the nitrogen cycle thank you Byjus

Thanks, it was useful for my project

very useful thanks for the info

Good job! Keep it up!

Ur explanation is very good . But I was also looking for role of agrobacterium in agriculture . But I haven’t find this at ur site . I have look it from another sites but no site is providing related information upon only the uses of agrobacterium in sustainable agriculture. Please if u can provide it

True, Me too was finding about that

I hope this may help you,

Agrobacterium tumefaciens is a soil phytopathogen that naturally infects plant wound sites and causes crown gall disease via delivery of transferred (T)-DNA from bacterial cells into host plant cells through a bacterial type IV secretion system (T4SS). Through the advancement and innovation of molecular biology technology during the past few decades, various important bacterial and plant genes involved in tumorigenesis were identified. With the help of more comprehensive knowledge of how A. tumefaciens interacts with host cells, A. tumefaciens has become the most popular plant transformation tool to date. Any gene of interest can now easily be used to replace the oncogenes in the T-DNA region of various types of binary vectors to perform plant genetic transformation with A. tumefaciens. Arabidopsis, the most-studied model plant with powerful genetic and genomic resources, is readily transformable by A. tumefaciens for stable and transient transformation in several ecotypes tested, although variable transformation efficiencies in different accessions were observed.

It is very useful for my project work

This is very helpful. Its so easy to understand

can you please tell disadvantages of nitrogen

Must include nitrogen cycle

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A-level Biology Model Essay

Subject: Biology

Age range: 16+

Resource type: Worksheet/Activity

Last updated

14 May 2023

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A-level Biology Essay on the importance of nitrogen-containing substances in biological systems (from the 2017 A-level paper).

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