Anonymous
Anonymous asked in Science & MathematicsBiology · 1 decade ago

describe the nitrogen cycle?

Describe the nitrogen cycle. Include its reservoir, functions in living systems, and how overloading it is affecting the ecosystem.

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  • Anonymous
    1 decade ago
    Favorite Answer

    The nitrogen cycle is the biogeochemical cycle that describes the transformations of nitrogen and nitrogen-containing compounds in nature.

    Earth's atmosphere is about 78% nitrogen, making it the largest pool of nitrogen. Nitrogen is essential for many biological processes; and is crucial for any life here on Earth. It is in all amino acids, is incorporated into proteins, and is present in the bases that make up nucleic acids, such as DNA and RNA. In plants, much of the nitrogen is used in chlorophyll molecules which are essential for photosynthesis and further growth.[1]

    Processing, or fixation, is necessary to convert gaseous nitrogen into forms usable by living organisms. Some fixation occurs in lightning strikes, but most fixation is done by free-living or symbiotic bacteria. These bacteria have the nitrogenase enzyme that combines gaseous nitrogen with hydrogen to produce ammonia, which is then further converted by the bacteria to make its own organic compounds. Some nitrogen fixing bacteria, such as Rhizobium, live in the root nodules of legumes (such as peas or beans). Here they form a mutualistic relationship with the plant, producing ammonia in exchange for carbohydrates. Nutrient-poor soils can be planted with legumes to enrich them with nitrogen. A few other plants can form such symbioses.

    Other plants get nitrogen from the soil by absorption at 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.

  • Anonymous
    4 years ago

    Describe Nitrogen

  • 5 years ago

    Nitrogen is constantly being recycled in the nitrogen cycle. Here is how: 1. The atmosphere contains about 78% nitrogen gas, N2. This is very unreactive so it can't be used directly by plants or animals. 2. Nitrogen is needed for making proteins for growth, so living organisms have to get it somehow. 3. Plants get their nitrogen from soil, so nitrogen in the air has to be turned into nitrogen compounds before plants can use it. Animals can only get proteins by eating plants or other animals. 4. Decomposers break down proteins in rotting plants and animals, and urea in animal waste, into ammonia. So the nitrogen in these organisms is recycled. 5. Nitrogen fixation is the process of turning N2 from the air into nitrogen compounds in the soil which plants can use. There are two main ways this happens: a) Lightning- there’s so much energy in a bolt of lightning that it’s enough to make nitrogen react with oxygen in the air to give nitrates. b) Nitrogen-fixing bacteria in roots and soil. 6) There are four different types of bacteria involved in the nitrogen cycle: a) Decomposers- decompose proteins and urea and turn them into ammonia. b) Nitrifying bacteria- turn ammonia in decaying matter into nitrates. c) Nitrogen-fixing bacteria- turn atmospheric N2 into nitrogen compounds plants can use. d) Denitrifying bacteria- turn nitrates back into N2 gas. This is of no benefit to living organisms. :) :)

  • Anonymous
    1 decade ago

    Nitrogen is both the most abundant element in the atmosphere and, as a building block of proteins and nucleic acids such as DNA, a crucially important component of all biological life. The nitrogen cycle is a complex biogeochemical cycle in which nitrogen is converted from its inert atmospheric molecular form (N2) into a form that is useful in biological processes.

    Because it takes a great deal of energy to convert atmospheric nitrogen into biologically useful forms, ecosystems have evolved to get by on fairly modest amounts of organic nitrogen. From forest fires to farming to burning fossil fuels, human activities have been altering the natural nitrogen cycle for centuries. Human practices that add reactive nitrogen (nitrogen that has been fixed) to ecosystems can change ecological balances. Farming, for example, is a relatively nitrogen intensive activity. Crops deplete nitrogen in the soil; therefore many farmers use man-made fertilizers in order to augment nitrogen levels. Unfortunately, in its nitrate form, nitrogen is extremely soluble and is readily leached from the soils into ground water reservoirs which feed into lakes and streams. In heavily agricultural areas, fertilizers are the primary source of nitrogen pollution. Where livestock is raised, animal wastes that are rich in nitrogen - if not properly managed - can also be carried by rainwater into nearby bodies of water.

    In areas with large human populations, most of the reactive nitrogen that is introduced into the environment by human activity comes from food and food processing. As with other animals, human wastes are nitrogen rich. This is especially the case with the large amounts of food protein that most Americans consume. Waste treatment facilities permit significant quantities of reactive nitrogen from human wastes to reenter the water cycle.

    There are a variety of consequences of nitrogen pollution. A major source of reactive nitrogen is atmospheric deposition which comes largely from transportation emissions, as nitrogen oxides (NO x ) are released through the exhaust. These emissions are a key ingredient in the formation of ground level ozone (smog). Another form of reactive nitrogen - nitric acid (HNO 3 ) - is an important ingredient in the creation of acid rain.

    One of the most serious consequences of nitrogen pollution is over-nutrition, or eutrophication, of aquatic ecosystems. Nitrogen leaches into the soil, and eventually into standing bodies of water, causing an unnaturally high level of nitrogen in the water. This eutrophication harms aquatic ecosystems by fueling excessive algae growth, which overshadows the water surface and deprives other aquatic organisms of necessary sunlight. When the algae dies, the oxygen consumed in the decomposition process can further deprive other aquatic organisms of needed oxygen. In extreme cases, eutrophication can result in the total die-off of fish in lakes and ponds.

    The nitrogen cycle contains several stages:

    Nitrogen fixation

    Atmospheric nitrogen occurs primarily in an inert form (N2) that few organisms can use; therefore it must be converted to an organic - or fixed - form in a process called nitrogen fixation. Most atmospheric nitrogen is 'fixed' through biological processes. First, nitrogen is deposited from the atmosphere into soils and surface waters, mainly through precipitation. Once in the soils and surface waters, nitrogen undergoes a set of changes: its two nitrogen atoms separate and combine with hydrogen to form ammonia (NH4+). This is done by microorganisms that fall into three broad categories: bacteria living in symbiotic relationships with certain plants, free anaerobic bacteria, and algae. Crops, such as alfalfa and beans, are often planted in order to remedy the nitrogen-depletion in soils, and nitrogen-fixing bacteria employ an enzyme, known as nitrogenase, to split atmospheric nitrogen molecules into individual atoms for combination into other compounds.

    A small amount of nitrogen is 'fixed' through a process of high energy fixation that occurs primarily as lighting strikes converting atmospheric nitrogen into ammonia (NH4+) and nitrates (NO3-). Nitrogen can also be fixed through man-made processes, primarily industrial processes that create ammonia and nitrogen-rich fertilizers.

    Nitrification

    While ammonia can be used by some plants, most of the nitrogen taken up by plants is converted by bacteria from ammonia - which is highly toxic to many organisms - into nitrite (NO2-), and then into nitrate (NO3-). This process is called nitrification, and these bacteria are known as nitrifying bacteria.

    Assimilation

    Nitrogen compounds in various forms, such as nitrate, nitrite, ammonia, and ammonium are taken up from soils by plants which are then used in the formation of plant and animal proteins.

    Ammonification

    When plants and animals die, or when animals emit wastes, the nitrogen in the organic matter reenters the soil where it is broken down by other microorganisms, known as decomposers. This decomposition produces ammonia which is then available for other biological processes.

    Denitrification

    Nitrogen makes its way back into the atmosphere through a process called denitrification, in which nitrate (NO3-) is converted back to gaseous nitrogen (N2). Denitrification occurs primarily in wet soils where the water makes it difficult for microorganisms to get oxygen. Under these conditions, certain organisms - known as denitrifiying bacteria - will process nitrate to gain oxygen, leaving free nitrogen gas as a byproduct.

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