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Nutrient Cycles
Nitrogen and Phosphorus
Step 1: Nitrogen fixation
•Since nitrogen doesn’t naturally react with
other molecules, several sources must fixes
gaseous nitrogen (N2 ) to ammonia (NH3 )
requiring intense heat, pressure and energy
•Bacteria (use the enzyme nitrogenase) and
are found in the roots (nodules) of legumes
such as beans or peas or under oxygen rich
slime on other roots.
•Burning fossil fuels
•Volcanic eruptions
•Lightning
•Industrial manufacturing of fertilizers
•Cyanobacteria- aquatic bacteria that fix
oxygen in heterocysts (oxygen rich cells)
Step 1: Nitrogen fixation: transfers
nitrogen from the air
(78%) to the soil
Accomplished by: bacteria found in legume (bean)
roots, volcanoes, burning fossil fuels, lightning, ocean
bacteria, and fertilizers
Step 2: Nitrification
• Soil bacteria convert ammonia (NH4)
to ammonium (NH3) in two steps in
order to create energy for themselves:
Chemosynthesis!
Step 1: Nitrogen fixation: transfers nitrogen from the air to the soil
Accomplished by: bacteria found in legume (bean) roots,
volcanoes, burning fossil fuels, lightning, cyanobacteria, fertilizers
Step 2: Nitrification: bacteria use the
nitrogen for chemosynthesis and convert it
to a form that animals and plants can use.
Step 3: Assimilation
•Plant roots absorb nitrate ammonia or
ammonium and incorporate them into
proteins and nucleic acids
•Animals that eat plants covert these
proteins and nucleic acids to animal
forms
•Example- folic acid
Step 2: Nitrification: bacteria change ammonia to ammonium
Step 3: Assimilation: plants and animals
absorb ammonium from their food sources
and convert it to nucleic acids (DNA or
RNA) and protein
Step 4: Ammonification
•Organisms covert glucose to energy
and create a waste product of ammonia
•Organisms convert this to urine.
•It is also absorbed in the soil when an
animal dies.
•Bacteria recycle the ammonia for
nitrification or assimilation
Step 2: Nitrification: bacteria change ammonia to ammonium
Step 3: Assimilation: plants and animals absorb ammonium from
their food sources and convert it to nucleic acids and protein
Step 4: Ammonification: animals create
nitrogen-containing urine as a waste
product which returns to the soil and is
recycled by bacteria back to step 2
Step 5: Denitrification
•Nitrate is reduced to gaseous nitrogen
and returns to the atmosphere
•Denitrifying (anaerobic) bacteria
reverse the process of nitrogen fixation
deep in the soil
Step 3: Assimilation: plants and animals absorb ammonium from
their food sources and convert it to nucleic acids and protein
Step 4: Ammonification: animals create nitrogen-containing urine as
a waste product which returns to the soil and is recycled by bacteria
back to step 2
Step 5: Denitrification: anaerobic bacteria
ingest nitrogen products in the soil and
convert it to a gas.
Human Influence:
•Agriculture- fertilizers produced from nitrogen
gas are used to increase crop yields but add too
much nitrogen to the earth.
•When it enters ponds and lakes, the fertilizer
increases algae growth… the overgrowth
(eutrophication) dies and settles on the bottom
of the body of water. Then bacteria decompose
it, using all of the available oxygen dissolved in the
water. This causes other aquatic life to suffocate.
•Leach through soil and contaminate
groundwater.
•Burning fossil fuels adds more to the
atmosphere causing photochemical smog, global
warming and acid rain.
Step 4: Ammonification: animals create nitrogen-containing urine as
a waste product which returns to the soil and is recycled by bacteria
back to step 2
Step 5: Denitrification: anaerobic bacteria ingest nitrogen products
in the soil and convert it to a gas.
Human Influence: agriculture (causes algae
blooms, kills fish and fertilizers leach in soil
contaminating groundwater), burning fossil
fuels causes air pollution
The Phosphorus Cycle
The phosphorus cycle has two loops or
circuits◦ Rocks with phosphorus contained in them
weather and erode to become soil.
1. If the soil stays on land, it will be used by plants,
passed to animals and returned to the soil via
decomposition.
2. If the soil is compressed over time, it will
become sedimentary rock, again.
…or it could be washed into bodies of water
where it will become sediment on the seafloor
The Phosphorus Cycle
Phosphorus is an important nutrient for
plants and animals
◦ Used by cells to make ATP and DNA
It must be present in soil for plant growth
Too much can also cause problems- it can
be toxic in high amounts
The Phosphorus Cycle
The phosphorus cycle does not involve the
atmospherePhosphorus is found in the:
• Ocean- dissolved in the water
•Ocean bottom as sediments
•Land soils- carried during erosion
•Plants and animals
Erosion of rock
releases
phosphorus into
the soil for plant
roots
The Phosphorus Cycle
Inside cells, it is
used to make
nucleic acids and
ATP
Decomposers
recycle waste
products
The Phosphorus Cycle
Differences between phosphorus and other
matter cycles:
• the atmosphere is not involved
•Phosphate can be “lost” when it settles to the
bottom of the ocean it may not be used for
millions of years
•Once in the aquatic system, it rarely returns
back to land.
The Phosphorus Cycle
Human Influence:
1. Humans spread phosphorus more through
agriculture and shipments of food around the
country- causing loses of it on crops. More is
added through fertilizers.
2. Human waste (sewage) is not treated for
phosphorus so it is concentrated in rivers and
lakes.
3. Phosphorus is lost by deforestation and
development.
The Phosphorus Cycle
Description of the phosphorus cycle:
After rock is weathered and erodes it will:
1.
2.
Importance to phosphorus to plants and animals:
Differences between this cycle and other nutrient cycles
Human influences:
The Phosphorus Cycle
Step 1: Nitrogen fixation:
Accomplished by:
Step 2: Nitrification:
Step 3: Assimilation:
Step 4: Ammonification:
Step 5: Denitrification
Human Influence