Transcript Grade 10 Cycling of Matter

Cycling of Matter
Biology: The Sustainability of
Ecosystems
(Grade 10)
Expectations
By the end of this lesson, students will:
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Illustrate the cycling of matter through biotic and
abiotic components of an ecosystem by tracking
nitrogen
Nitrogen
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Nitrogen has the
chemical symbol “N”
A nitrogen atom has
seven protons and
seven electrons
Most abundant element
in the Earth’s
atmosphere
Source: http://commons.wikimedia.org/wiki/
Investigating Air
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Source: http://stloe.most.go.th/
Mid-1700’s, chemists
had separated air into
two components: “fire
air” (oxygen) and “foul”
or “noxious” (nitrogen)
air
Nitrogen exists
naturally in the planet’s
atmosphere as nitrogen
gas or diatomic
nitrogen (N2)
Nitrogen
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All life on Earth requires
nitrogen compounds
(e.g. proteins, nucleic
acids)
Approximately, 78% of
our atmosphere is
nitrogen gas (N2)
However, most
organisms can not use
nitrogen in this form!
Source: http://herokids.files.wordpress.com/
Source: http://www.nicksnowden.net/images/Nutrient_Cycles/
Nitrogen Fixation
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Large amounts of energy are required to convert N2
into a more usable form, such as: ammonium ions
(NH4+) or nitrate ions (NO3-)
This process is called “fixing”
Three processes are responsible for the majority of
nitrogen fixation in the biosphere:
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Atmospheric fixation
Biological fixation
Industrial fixation
Atmospheric Fixation
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Source: http://www.moonraker.com.au/techni/lightning.jpg
In the presence of
enormous energy, N2 and
O2 react, to eventually
produce nitric acid (HNO3)
The HNO3 dissolves in the
precipitation forming
nitrates (NO3-) and are
carried to the ground
This process is responsible
for ~ 5-8% of nitrogen
fixation
Biological Fixation
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Colonies of certain
bacteria are found in
the roots of various
plants and have the
ability to fix nitrogen
from the atmosphere
E.g., the symbiotic
relationship between
Rhizobium and
legumes
Source: http://overton.tamu.edu/clover/
Industrial Fixation
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Source: http://www.dextersfarm.com/
Ammonia, NH3, (gas or
liquid) can be injected
directly into the soil
Ammonium nitrate is a
powder which is spread
on the soil and reacts
with water to form ions
Source: http://www.nicksnowden.net/images/Nutrient_Cycles/
Decomposition
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The waste from
animals, as well as the
decay of their bodies
after death, return
nitrogen to the soil
Micro-organisms and
fungi break down the
molecules in wastes
and dead organisms
into ammonia (NH3)
Source: http://extension.usu.edu/
Nitrification
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Source: http://www.anoxkaldnes.com/Bilder/jpg/RD7.jpg
Ammonia can be taken
up directly by plants
However, most of the
ammonia is converted
into nitrates by nitrifying
bacteria
Nitrification makes
nitrogen more readily
available for plants
Denitrification
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Denitrifying bacteria
convert nitrates (NO3-)
to nitrites (NO2-) and
then to nitrogen gas
(N2)
Denitrification
completes the nitrogen
cycle
Source: http://staffwww.fullcoll.edu/tmorris/
Source: http://www.nicksnowden.net/images/Nutrient_Cycles/
Eutrophication
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Source: http://www.umanitoba.ca/institutes/fisheries/eutro.html
Anthropogenic
eutrophication caused
by runoff from
agricultural farms,
urban lawns, and golf
courses
Nitrous Oxide (N2O)
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Average life span of a
N2O molecule = 120
years!
A molecule of N2O
traps 206 times more
heat than a molecule of
CO2!
Source: http://tn3-1.deviantart.com/