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Mindmap von harry_bygraves, aktualisiert more than 1 year ago
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Nitrogen cycle
- The nitorgen cycle ensures that nitrogen bound up within these organic
molecules in the biosphere is constantly recycled so that it may be used
- Saprobiotic nutrition; breaking down dead organisms. Decomposers break down
solid organic matter into soluble substances, first step in the decay of dead organisms
- Ammonification; ammonia from urea and amino acids. Decomposers and
other microorganisms are also involved in the conversion of organic
nitrogen-containing compunds in urea and amino acids into ammonia. This
process is called ammonification. Ammonia can be lost to the atmosphere,
taken up by plants as ammonium ions, or converted to other forms of nitrogen
- Nirtification ; ammonium ions (in soil and water) are oxidises to
nitrites and nitrates by nitrifying bacteria. These bacteria are
chemoautotrophs, obtaining energy from the redox reactions involved
in nitrification. Nitrification requires oxygen, so it happens most
rapidly in well aerated soil or well oxygenated bodyies of water. The
nitrate ions produced by nitrification can be taken up by plants and
used to make proteins
- Nitrogen fixation; nitrogen to nitrogen coumpounds. Before plants and animals can
use nitorgen, it must first be converted to absorbable nitrogen compounds. This is
called nitrogen fixation. A little nitrogen fixation occurs during thunderstorms.
Lightening provides the energy to oxidise nitrogen to nitrogen oxides. More than
95% of nitrogen fixation takes place biologically. The fixation is carried out by
nitrogen - fixing bacteria. Some live free in the soil or water, whereas others live
mutualistically in root nodules of leguminous plants. Nitogen - fixing bacteria
passes nitogenase, an enzyme that enables them to reduce nitrogen to ammonia
or ammonium compounds
- Denitrification; nitrates back to nitrogen. The nitrogen cycle is
completed by denitirfying bacteria. these bacteria live in
conditions of low oxygen and reverse the nitrifying process,
coverting nitrates to nitrites, and nitrites into nitrogen gas. The
process called denitrification, leads to the loss of nitrogen from
the biotic component of an ecosystem to the atmosphere.
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