Ecological Cycles

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Ecological Cycles

• The Water, Carbon and Nitrogen Cycle

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Water Cycle
Water never leaves the Earth. It is constantly
being cycled through the atmosphere, ocean, and
land.
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• Water never leaves the Earth. It is constantly
  being cycled through the atmosphere, ocean, and
  land. This process, known as the water cycle, is
  driven by energy from the sun. The water cycle is
  crucial to the existence of life on our planet.

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Evaporation
Evaporation Process by which the sun heats up
liquid water and changes it to a gas Where does
the water come from via this process? What speeds
up the process of evaporation?
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Condensation
Condensation Process by which water rises into
the atmosphere, cools and becomes a liquir
again. In what form is water as it rises? What
does it become as it condenses?
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Precipitation
Precipitation Process by which water condenses
and falls back to the earth. Where do you think
most Precipitation occurs? What is the difference
between rain and snow in the context of the bonds
between water molecules? What are these bonds
called?
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Transpiration
Transpiration The process of evaporation from
plants Why would plants release water? Think
back to your properties of water.
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Runoff
Runoff Water that collects in rivers, streams,
and oceans What could contribute to greater
amounts of runoff?
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Practice!
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The Nitrogen Cycle
(1) Nitrogen Fixation
(4) Denitrification
Nitrogen Cycle
(3) Nitrification
(2) Ammonification
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Atmospheric nitrogen (about 78 of our air) is
converted to ammonia or nitrates.
N
N
Atmospheric Nitrogen (N2)
N
N
Nitrates (NO3) Nitrogen combines with Oxygen to
make Nitrates
Ammonia (NH3) Nitrogen combines with Hydrogen to
make Ammonia
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It is one of natures great ironies

• Nitrogen is an essential component of DNA, RNA,
  and proteins
• the majority of the air we breathe is nitrogen
  yet most living organisms are unable to use
  nitrogen as it exists in the atmosphere.

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Nitrogen Fixation is the process that causes
the strong two-atom nitrogen molecules found in
the atmosphere to break apart so they can combine
with other atoms. Nitrogen gets
fixed when it is combined with oxygen or
hydrogen.
N
N
Oxygen
Hydrogen
Hydrogen
N
N
N
N
Oxygen
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Free Living Bacteria (ex of nitrogen
fixation)Highly specialized bacteria live in the
soil and have the ability to combine atmospheric
nitrogen with hydrogen to make ammonia (NH3).
N
N
H
N
H3
Free-living bacteria live in soil and combine
atmospheric nitrogen with hydrogen
(NH3)
Nitrogen changes into ammonia
Bacteria
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Symbiotic Relationship BacteriaBacteria live in
the roots of legume family plants and provide the
plants with ammonia (NH3) in exchange for the
plants carbon and a protected home.
Legume plants
N
NH3
N
Roots with nodules where bacteria live
Nitrogen changes into ammonia.
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Ammonification Bacteria decomposers break down
amino acids from dead animals and wastes into
nitrogen ammonium.
Bacteria decomposers break down amino acids into
ammonium
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Plants cannot use the organic forms of nitrogen
that are in the soil as a result of(1) wastes
(manure and sewage)(2) compost and decomposing
roots and leaves
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Microorganisms convert the organic nitrogen to
ammonium. The ammonium is either taken up by the
plants (only in a few types of 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 use.
Bacteria converts organic nitrogen to ammonium
(NH4)
Ammonium (NH4) is used by some plants
Bacteria
Ammonium (NH4) is stored in soil.
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Nitrification Nitrifying bacteria in the ground
combine ammonia with oxygen to form nitrites.
Then another group of nitrifying bacteria convert
nitrites to nitrates which green plants can
absorb and use.
Nitrifying bacteria in soil combine ammonia with
oxygen
Ammonia changes to nitrites
Nitrifying bacteria in soil convert nitrites to
nitrates
Ammonia
Nitrites
Nitrates
Plants absorb nitrates and grow!
(NH3)
(NO3)
(NO2)
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Denitrification The conversion of nitrates (NO3)
in the soil to atmospheric nitrogen (N2) thereby
replenishing the atmosphere.
Nitrogen in atmosphere (N2)
Nitrates (NO3) in Soil
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Denitrifying bacteria live deep in soil and in
aquatic sediments where conditions make it
difficult for them to get oxygen. The
denitrifying bacteria use nitrates as an
alternative to oxygen, leaving free nitrogen gas
as a byproduct. They close the nitrogen cycle!
Nitrogen in atmosphere closes the nitrogen cycle!
(N2)
(NO3)
Denitrifying bacteria live deep in soil and use
nitrates as an alternative to oxygen making a
byproduct of nitrogen gas.
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(a)
(b)
N2
N2O
(1) _____________
(4) _____________
(c)
Nitrogen Cycle
(3) ____________
(2) _____________
NO3
NH3
Ammonia is converted to nitrites and nitrates.
Organic nitrogen is converted to ammonium.
Nitrates in Soil
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Carbon Cycle
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Summary

• Carbon (as CO2) is accumulated
• Photosynthesis uses sunlight to make carbohydrate
  from CO2.
• Carbon (as CO2) is released
• Respiration - carbon is oxidized for energy.
• Combustion - carbon is burned
• Weathering - rain (slightly acidic) weathers
  calcium carbonate rocks
• Get out a blank piece of paper for a practice
  quiz

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In July, a student tested the soil in two plots
and calculated the concentration of nitrogen
compounds present in each plot. The student then
planted 20 seedlings in the first plot and
allowed them to grow. Nothing was planted in the
second plot. The student tested the soil in both
plots again after one month. The concentration of
nitrogen compounds had decreased in the first
plot but had remained the same in the second plot.
Which of the following best explains the decrease
in nitrogen compounds in the first plot? A.The
nitrogen compounds had broken down into
elements. B.The nitrogen compounds were absorbed
by the seedlings for their growth. C.The nitrogen
compounds escaped through air pockets created by
the seedlings roots. D.The nitrogen compounds
had evaporated because of the warm summer
temperatures.
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• Leaves fall from deciduous trees in autumn.
  The carbon in these leaves is returned to the
  atmosphere through which of the following
  processes?
• A. condensation
• B. decomposition
• C. photosynthesis
• D. transpiration

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• Which of the following processes
• releases primarily oxygen into the
• atmosphere?
• A. combustion
• B. osmosis
• C. photosynthesis
• D. respiration

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If many trees are removed from a forest by
logging, what is the most immediate effect on the
carbon cycle in that forest?

• A. increased rates of decomposition
• B. decreased use of atmospheric CO2
• decreased combustion of fossilfuels
• increased production of organic compounds

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• The water cycle would not occur if which of the
  following were missing?
• A. animals
• B. bacteria
• C. ice caps
• D. solar energy

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• Which of the following explains why legume plants
  are less likely than other terrestrial plants to
  experience nitrogen limitation?
• A. Legume plants need less nitrogen than other
  plants do.
• B. Legume plants have nitrogen-fixing bacteria on
  their roots.
• C. Legume plants catch insects to supply
  themselves with nitrogen.
• D. Legume plants can absorb nitrogen directly
  from the atmosphere.