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•  Materials in ecosystems are constantly reused
•  Three cycles:
•  The Carbon Cycle
•  The Nitrogen Cycle
•  The Phosphorus Cycle
•  Carbon is essential in proteins, fats, and
carbohydrates, which make up all organisms
•  Carbon cycle – a process by which carbon is
cycled between the atmosphere, land, water
and organisms
•  Carbon enters an
ecosystem when
producers
convert carbon
dioxide in the
atmosphere into
carbohydrates
•  Consumers get
carbon from
producers and
release as CO2
* Carbon ENTERS biotic environment through: Photosynthesis: changes light energy to
chemical energy •  Carbon RETURNS to atmosphere by: 1. Respiration CO2
2. Decomposition / Decay 3. Burning * Carbon Cycle and Humans: 1. Removal of photosynthesizing plants 2. Combustion of fossil fuels 1
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•  Fossil fuels are stored carbon left over from
bodies of plants and animals that died
millions of years ago
•  When we burn fossil fuels, we release carbon
into the atmosphere
•  Carbon returns to atmosphere as CO2
•  6 billion metric tons of carbon a year are
released into the atmosphere as carbon dioxide
• ½ of this carbon stays in atmosphere
•  Increased levels of carbon dioxide may
contribute to global warming
•  Global warming – an overall increase in the
temperature of the Earth
•  Scientists estimate that over a billion tons of
carbon dioxide dissolves into the ocean
•  Atmosphere is 78% nitrogen
•  All organisms need nitrogen to build proteins
(which are used to build new cells)
•  Can’t use atmospheric nitrogen
•  Has to be altered or “fixed”
•  Can only be done by nitrogen-fixing bacteria
•  Nitrogen-fixing bacteria are a crucial part of
the nitrogen cycle
•  A process in which nitrogen is cycled between the
atmosphere, bacteria, and other organisms
•  Bacteria take nitrogen from gas in the air and
transform it into molecules that living things can use
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Nitrogen
Cycle
Fixation
means:
•  Live within nodules on the roots of plants
called legumes (some live in the soil)
•  Beans, peas, clover
•  Extra nitrogen is released into soil
•  Plants get nitrogen from their nitrogen-fixing
bacteria or the soil
•  Animals get nitrogen from eating the plants
to chemically
change
Nitrogen
in the a compound
atmosphere
into another similar compound
e.g. N3 to NH3
Nitrogen
consumption
Denitrifying
bacteria
Fixation by bacteria,
or lightning
Decomposing
dead matter
Nitrogen in
the soil
•  Nitrogen moves between atmosphere and
living things
•  Decomposers break down waste and return
nitrogen to the soil
•  Without decomposers, most nitrogen would
be stored in waste
•  Nitrogen stays within ecosystem, cycling
between organisms and the soil and is
constantly reused
* Nitrogen RETURNS to soil by: 1. decomposition of once living things
- done by fungi and bacteria
2. exists in soil as nitrate (NO3-), nitrite (NO2-),
and ammonia (NH3) * Nitrogen returns to atmosphere by: 1. denitrifying bacteria * Nitrogen Cycle and Humans: 1. Nitrogen required for genetic materials
(DNA, RNA, amino acids)
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•  Phosphorus is an element that is part of
many molecules that make up cells •  Plants get from soil and water
•  Animals get from eating plants
•  Phosphorus cycle
•  The movement of phosphorus from the
environment to organisms and then back to the
environment •  Slow cycle •  Doesn’t occur in atmosphere
•  Phosphorus is rarely a gas
Phosphorus
Cycle
Detritivores
are:
organisms that obtain nutrients by
feeding off decomposing plant and
consumed by
animal matter (inc. faeces)
animals
Phosphorus
stored in rocks
released by
weathering
decomposed
by detritivores
Phosphorus
in the soil
absorbed
by plants
•  Rocks erode, small amounts of phosphorus
dissolve as phosphate in soil and water
•  Plants absorb phosphates
•  Phosphorus is also added by dead organisms
and waste
•  Phosphorus also washes off land and ends up
in ocean, sink to bottom
•  1. Leaching: water dissolves phosphates in
rocks and carries to lake, stream, etc. •  2. Dissolved phosphate: used by plants and
passed through food chain •  3. Animals return phosphorus to environment by: * excretion * death and decay * Phosphorus Cycle and Humans: 1. Phosphates mined for fertilizers returns P to
soil 2. Erosion: P in soil and rocks washed away into
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•  Fertilizers are used to stimulate and maximize
plant growth and contain phosphorus and
nitrogen •  The more phosphorus and nitrogen available
to a plant, the bigger and faster it will grow
•  Fertilizer is bad too – can run off into
waterways and cause overpopulation of algae
•  When fertilizer runs off into the waterways,
it causes an overgrowth of algae
•  Algal blooms are dense visible patches of
algae that occur near the surface of water
•  They can deplete an aquatic ecosystem of
important nutrients •  We affect the nitrogen cycle every time we
burn coal, wood, or oil •  Nitric oxide is a harmful gas released when
burning
•  Combines with oxygen and water vapor to
form nitric acid
•  Can dissolve in rain or snow and cause acid
precipitation 1.  Describe the three stages of the carbon cycle.
2.  Describe how the burning of fossil fuels affects the
carbon cycle
3.  Explain how the excess use of fertilizer affects the
nitrogen cycle and phosphorus cycle
4.  Explain why the phosphorus cycle occurs more
slowly than both the carbon cycle and nitrogen
cycle.
5.  Write a short paragraph that describes the
importance of bacteria in the carbon, nitrogen, and
phosphorus cycles. What role does bacteria play in
each cycle?
6.  What is one way that a person can help reduce the
level of carbon dioxide in the atmosphere? Can you
think of more than one way?
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