Nitrogen Cycle Nitrogen Facts The growth of all organisms

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Nitrogen Cycle
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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
  constituents.
• 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
  slowly!
• Since it is hard to obtain, Nitrogen is often the
  Limiting factor for growth biomass production
  in all Environments!

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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
  organisms!
• Other stores of N include organic matter in soil
  oceans.
• N-containing substances like ammonia, nitrates
  and nitrites are found in the wastes produced by
  many organisms and in dead decaying organic
  matter.

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Plants

• 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
  plants)
• 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?

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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
  bacteria).
• Others live in close symbiotic associations
  w/plants or w/other organisms like protozoa.
• Examples
• Aerobic bacteria Cyanobacteria
• Anaerobic bacteria Clostirdium, Green sulphur
  bacteria
• Symbiotic w/other organisms Rhizobium
  (Legumes-peas, beans, etc.)

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N Cycle

• http//upload.wikimedia.org/wikipedia/en/thumb/d/d
  e/Nitrogen_Cycle.jpg/320px-Nitrogen_Cycle.jpg
• 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
  matter).
• 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.

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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
cycle?

• 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
  fertilizers.

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Environmental problems with fertilizers?

• The main environmental problem with fertilizer
  use is contamination of water with nitrates and
  phosphates.
• 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.

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http//www.bbc.co.uk/schools/gcsebitesize/img/bieu
trophication.jpg
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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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