Nitrogen Cycle & How Do Human Activities Affect the Ecosystem by Divine Garcia

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Published on March 8, 2014

Author: FumisaDivineChan

Source: slideshare.net

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Report in science :D

Report By: Divine D. Garcia

Nitrogen  Symbol: N Atomic No: 7 Atomic Weight: 14.0067  Gas: colorless, odorless and generally inert  Liquid: colorless, and odorless  A gas that made up 79 % of the gases in the atmosphere.  Its compounds are vital components of foods, fertilizers, and explosives.  Organisms use nitrogen to build proteins and nucleic acids.

Nitrogen Cycle  Is the cycling of nitrogen between living organisms and their environment.  Is the process of converting nitrogen into compounds that can be used by plants and animals.  Is a complex process with four important stages:  Nitrogen Fixation  Ammonification/Decay  Nitrification  Denitrification

Nitrogen Fixation  Is when the nitrogen gets “fixed” and combines with oxygen or hydrogen.  There are 3 Ways that Nitrogen gets “fixed”:  Atmospheric Fixation  Industrial Fixation  Biological Fixation

Atmospheric Fixation (5 % - 8 %)  Lightning breaks nitrogen molecules apart and combines with oxygen forming nitrogen oxides (N₂O). Nitrogen oxides dissolve in rain, forming nitrates. Nitrates (NO₃) are carried to the ground with the rain.

Industrial Fixation  Under great pressure, at a temperature of 600 C˚, and with the use of catalyst, atmospheric nitrogen (N₂) and hydrogen are combined to form ammonia (NH₃). Ammonia can be used as fertilizers.

Biological Fixation  Some symbiotic bacteria (most often associated with leguminous plants) and some free-living bacteria are able to fix nitrogen as organic nitrogen.

Ammonification/ Decay  Bacteria decomposers break down amino acids from dead animals and wastes into nitrogen ammonium.  Because plants cannot use the organic forms of nitrogen that are in the soil as a result of:  wastes ( manure and sewage)  compost and decomposing roots and leaves  Microorganisms convert the organic nitrogen to ammonium. The ammonium is either taken up by the plants or is absorbed into the soil particles.

 Ammonium (NH₄) in the soil is stored up to later be changed into inorganic nitrogen, the kind of nitrogen that most plants can used.

Nitrification  Nitrifying bacteria in the ground first combine ammonia with oxygen to form nitrites. Then another group of nitrifying bacteria convert nitrites to nitrates which green plants can absorb and use.

Denitrification  Converts nitrates (NO₃) in the soil to atmospheric nitrogen (N₂) replenishing atmosphere.  Other ways that nitrogen returns to the atmosphere:

 Humans are top consumers in many food pyramids. To increase food production, they use methods that have an effect on food webs.  Monoculture – is the cultivation of a single crop in large areas. Vast tracts of land are converted to rice farms, sugar farms, and coconut farms.

 Herbicides and Insecticides – farmers spray their crops with insecticides to kill insect pests, and with herbicides to kill weeds. However, the chemicals also destroy other organisms, including beneficial insects and soil organisms which help in decay.

 Chemical Fertilizers – monocrops usually require large amounts of chemical fertilizers. Continuous and uncontrolled used of chemical fertilizers may increase soil acidity, thus destroying soil structure. Findings show that more fertilizers are needed for the same amount of yield after years of monoculture.

 Fertilizers in the water will cause increased growth of algae and other plants. They cover the water’s surface and block the passage of oxygen. Thus, less oxygen is dissolved in water. Furthermore, when algae and aquatic plants die, decay microorganism use oxygen. Dissolved oxygen becomes insufficient, causing fish and other aquatic animals to die.

 To conserve the environment, some desirable practices are described below:  Grow a variety of crops instead of only one crop.  Use insects to fight other insects (known as biological control of insect pests).  Instead of chemical fertilizers, try organic farming using natural fertilizers for crops. Some natural fertilizers are compost and animal manure.

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