Cycles in Nature………Standard 1
Objective 2:
Explain relationships between matter cycles and Energy
a) use diagrams to trace the movement of matter through a cycle
b) Explain how water is a limiting factor in various Ecosystems
HS Biology
Energy Flow Through an Ecosystem
 Introduction
to Cycles of Matter
& Energy Transfer
Food Webs &
Food Pyramids
Earth Cycles
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Video Mr. Anderson
Earth’s biosphere contains a fixed amount of
water, carbon, nitrogen, oxygen, and other
materials that cycle through the environment
and are reused by different organisms.
Water Cycle

How water moves from the Earth’s surface to
the atmosphere and back to the surface
again
2. condensation
2. condensation
1. Evaporation
e
3. Precipitation
5. snow Runoff
3. Precipitation
4. Transpiration
1. Evaporation
6. Groundwater flow
Components of the Water Cycle
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Evaporation: when liquid water changes into
water vapor and enters the atmosphere
Condensation: the process of changing water
from a gas to a liquid
Precipitation: when water drops become
large enough and fall to the ground as rain,
snow, sleet, etc.
Transpiration: Transpiration is the process by
which plants lose water out of their
leaves. Transpiration gives evaporation a bit
of a hand in getting the water vapor back up
into the air.
Nitrogen cycle
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The transfer of nitrogen from the atmosphere
to the soil, to living organisms, and back to
the atmosphere
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.
Nitrogen Cycle (cont.)

There is an abundant supply of nitrogen in
the earth's atmosphere - nearly 79% in the
form of N2 gas. However, N2 is unavailable
for use by most organisms because there is a
triple bond between the two nitrogen atoms,
making the molecule almost inert.
Nitrogen Fixation
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In order for nitrogen to be used for growth it
must be "fixed" (combined) in the form of
ammonium (NH3) or nitrate (NO3) ions.
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)
Nitrogen-fixing bacteria can be found in the
soil as well as on submerged objects in lakes
and ponds. These are called cyanophytes
(blue-green algae).
Legume symbioses

The most familiar
examples of nitrogenfixing symbioses are
the root nodules of
legumes (peas, beans,
clover, etc.).
More ammonia
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A small amount of nitrogen fixation also
results from the passage of ultraviolet light
and lightning through the air, causing
nitrogen to react with oxygen to form nitrate
ions.
Additional amounts of nitrate and ammonia
are put into the atmosphere by volcanoes, by
combustion of fossil fuels, and by forest fires.
Other nitrogen
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Farmers replace nitrogen in the soil by
growing nitrogen-fixing crops or using
fertilizers that contain nitrogen compounds
that plants need for growth.
Ammonification
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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.
The excretions of animals and dead bodies
are broken down in the soil by decomposers
This produces ammonia.
Nitrification
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Some bacteria called nitrifying bacteria take
the ammonia and change it to a nitrite ion,
and then a different group of nitrifying
bacteria change that nitrite ion to a nitrate
ion.
This then can be taken up into the roots of
the plant and be used.
Problems of nitrification
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The ammonium ion is readily adsorbed onto
the clay soil and soil organic matter,
preventing it from being washed out of the
soil by rainfall.
In contrast, the nitrate ion is not held on soil
particles and so can be washed down the soil
- the process termed leaching
In this way, valuable nitrogen can be lost
from the soil, reducing the soil fertility.
The problems with too many nitrates
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The nitrates can then accumulate in
groundwater, and ultimately in drinking water.
There are strict regulations governing the
amount of nitrate that can be present in
drinking water, because nitrates can be
changed to nitrites by microorganisms in the
gut.
Nitrites are absorbed from the gut and bind to
haemoglobin in your blood, reducing its
oxygen-carrying capacity.
Denitrification
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If the soil becomes too compacted or gets too
wet, air cannot penetrate.
This allows bacteria called denitrifying
bacteria to convert nitrate to nitrous oxide or
nitrogen gas which is then lost to the
atmosphere.
That is why it is important for farmland to be
kept well drained and plowed. video
Carbon Cycle
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How carbon molecules move between the
living and nonliving world
The same carbon atoms in your body today
have been used in countless other molecules
since time began.
Plants absorb carbon dioxide from the
atmosphere and use it, combined with water
they get from the soil, to make the
substances they need for growth.
Carbon Cycle (cont.)
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Animals, like a rabbit, eat the plants and use
the carbon to build their own tissues.
Other animals, such as the fox, eat the rabbit
and then use the carbon for their own needs.
These animals return carbon dioxide into the
air when they breathe, and when they die,
since the carbon is returned to the soil during
decomposition.
Carbon cycle (cont.)
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The carbon atoms in soil may then be used in
a new plant or small microorganisms.
Ultimately, the same carbon atom can move
through many organisms and even end in the
same place where it began.
video
Video II