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Nitrogen Cycle Nitrogen Facts The growth of all organisms


Nitrogen Cycle Nitrogen Facts The growth of all organisms depends on the availability of mineral nutrients, and none is more important than NITROGEN, which is ... – PowerPoint PPT presentation

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Title: Nitrogen Cycle Nitrogen Facts The growth of all organisms

Nitrogen Cycle
Nitrogen Facts
  • The growth of all organisms depends on the
    availability of mineral nutrients, and none is
    more important than NITROGEN, which is required
    in large amounts as an essential component of
    proteins, nucleic acids and other cellular
  • 79 of the atmosphere consists of N2
  • N2 in the atmosphere isnt available for use by
    most organisms b/c it is held together by a
    strong triple bond!
  • Sometimes when Rocks weather these release N ions
  • Since it is hard to obtain, Nitrogen is often the
    Limiting factor for growth biomass production
    in all Environments!

N facts continued
  • Nitrogen is used by living organisms to produce
    organic molecules (amino acids, proteins and
    nucleic acids).
  • N2 found in the atmosphere is about one million
    times larger than the total N contained in living
  • Other stores of N include organic matter in soil
  • N-containing substances like ammonia, nitrates
    and nitrites are found in the wastes produced by
    many organisms and in dead decaying organic

  • Plants can only obtain Nitrogen in 2 forms
    ammonium (NH4) and the ion nitrate (NO3-). (In
    large quantities ammonium can be extremely toxic
    to plants so nitrates are used more often by
  • Once Ammonium and Nitrates are available,
    producers like Plants can use these materials to
    make Proteins!
  • Consumers then eat the producers and reuse the
    nitrogen to make their own protein.
  • (Animals receive the N they need for Metabolism,
    growth and reproduction by the consumption of
    living/dead organic matter containing molecules
    composed of Nitrogen!)
  • So How do plants get ammonium and nitrates?

How do we obtain Nitrogen?
  • Microorganisms have a key role in helping us
    obtain nitrogen and thus for life support on
    earth! They can convert atmospheric N into a
    form that can be used by plants and then
    transferred to other organisms via the food web.
  • Some bacteria can convert N2 into ammonia by the
    process termed nitrogen fixation these bacteria
    are either free-living or form symbiotic
    associations with plants or other organisms (e.g.
    termites, protozoa).
  • many bacteria and fungi degrade organic matter,
    releasing fixed nitrogen for reuse by other
    organisms. (Decomposers!)
  • All of these processes contribute to the
  • N cycle

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Example of N-fixing organisms
  • N-fixing organisms are prokaryotes (Bacteria).
  • Some live independently (free-living N-fixing
  • Others live in close symbiotic associations
    w/plants or w/other organisms like protozoa.
  • Examples
  • Aerobic bacteria Cyanobacteria
  • Anaerobic bacteria Clostirdium, Green sulphur
  • Symbiotic w/other organisms Rhizobium
    (Legumes-peas, beans, etc.)

N Cycle
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  • At any one time a large proportion of the total
    fixed nitrogen will be locked up in the biomass
    or in the dead remains of organisms (organic
  • So the only Nitrogen available to support new
    growth will be whatever is supplied by Nitrogen
    fixation from the atmosphere or by the release of
    organic nitrogen compounds through the
    decomposition of organic matter.

Decomposition Denitrification
  • When organisms die, decomposers return Nitrogen
    to the soil as ammonia (NH3).
  • (The NH3 may be taken up again by producers.)
  • Other soil bacteria convert nitrates (NO3-) into
    nitrogen gas (N2 ) Denitrification
  • Denitrification releases N into the atmosphere
    once again!

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What role do humans lightning have on the N
  • Lightning can break the triple bond of N2 in an
    action called Atmospheric nitrogen fixation and
    convert N2 into nitrates nitrites.
  • Human activity adds nitrogen to the biosphere in
    the form of nitrate- a major component of plant

Environmental problems with fertilizers?
  • The main environmental problem with fertilizer
    use is contamination of water with nitrates and
  • Nitrates can be leached into the groundwater or
    be washed out of the soil surface into streams
    and rivers. High nitrate levels in drinking water
    are considered to be dangerous to human health
  • Phosphorus can also be washed into surface waters
    together with the soil that is being eroded. The
    phosphorus stimulates the growth of algae in slow
    moving water.
  • Algae then reproduce (algal bloom ) and
    eventually die and decompose, the decaying, which
    removes the oxygen from the water causes fish
    kills . This process is called eutrophication.

Eutrophicationwhat exactly is going on?
  • Algae are a group of plantlike organisms that
    live in water and can make their own food through
    photosynthesis (using sunlight to make food from
    simple chemicals). When additional phosphates are
    added to a body of water, the plants begin to
    grow explosively and algae takes off or "blooms.
  • The algae consume greater amounts of oxygen in
    the water, robbing fish and other species of
    necessary oxygen. All algae eventually die, and
    when they do, oxygen is required by bacteria in
    order for them to decompose or break down the
    dead algae.
  • A cycle then begins in which more bacteria
    decompose more dead algae, consuming even more
    oxygen in the process. The bacteria then release
    more phosphates back into the water, which feed
    more algae. As levels of oxygen in the body of
    water become lower, species such as fish and
    mollusks literally suffocate to death.
  • Eventually, the lake or pond begins to fill in
    and starts to be choked with plant growth. As the
    plants die and turn to sediment that sinks, the
    lake bottom starts to rise. The waters grow
    shallower and finally the body of water is filled
    completely and disappears.

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