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The Carbon Cycle
Why is Carbon important?
All living things are made of carbon!!!
• Calcium carbonate (CaCO3) makes up
animal skeletons
• Carbon Dioxide gas which makes
photosynthesis and respiration work
together
Carbon Does Not Stay Still – It Is
On the Move!
1. In the atmosphere, carbon is attached to some oxygen in
2.
3.
4.
5.
a gas called carbon dioxide.
Plants use carbon dioxide and sunlight to make their own
food and grow. The carbon becomes part of the plant.
Animals consume plants. The carbon becomes part of the
animal.
Plants that die and are buried may turn into fossil fuels
made of carbon like coal and oil over millions of years.
When humans burn fossil fuels, most of the carbon
quickly enters the atmosphere as carbon dioxide.
PHOTOSYNTHESIS
Using light energy, plants combine
carbon dioxide (CO2) from the
atmosphere and water (H20) to form
sugar and oxygen in the process of
photosynthesis.
sunlight
(CO2) + (H2O) →
(C6H12O6 ) + (O2)
What is Sugar (Glucose)
Used For?
1. Source of energy
2. Building block for
other compounds such
as proteins, oils, and
starches.
RESPIRATION
• In respiration, the compounds
containing carbon (the organic
compounds) are broken down, and carbon
dioxide is released.
Plants, animals, and
microorganisms all
carry out respiration!
IS THE CARBON-OXYGEN CYCLE
BALANCED?
• The Carbon-Oxygen cycle is out of
balance.
• There is more carbon dioxide being
released into the atmosphere than is being
removed.
COMBUSTION
• Most of the carbon dioxide is
produced during the process
of burning called
combustion.
• When compounds containing
carbon (wood, coal, or oil) are
burned, the carbon is
chemically combined with
oxygen, and carbon dioxide is
released.
• The use of carbon dioxide by plants during
photosynthesis is a much slower process.
• As a result of the imbalance between
these two processes, the level of carbon
dioxide in the atmosphere is increasing.
• “Even if human emissions of CO2 magically dropped to
zero, the gas already in the air would linger for many
centuries, trapping heat. Global temperatures would
continue to creep upward until the ocean depths
reached equilibrium with the heated air, until biological
systems finished adapting to the new conditions, and
until Arctic icecaps melted back to their own equilibrium”
Decomposers
• When organisms die,
decomposers break down the
carbon compounds in their
bodies, and carbon dioxide is
returned to the atmosphere.
• During decomposition
(decay), other chemicals are
also returned to the soil or
released into the air. One of
these chemicals is nitrogen.
The Nitrogen Cycle
NITROGEN
• Plants and animals need
nitrogen to make amino
acids (proteins)
• The atmosphere is about
78% nitrogen gas, but
plants and animals cannot
use nitrogen directly from
the air.
How Do Plants Get Nitrogen?
• Special bacteria, in the soil
and water, must change or
“fix” nitrogen gas (N2) into
nitrogen fertilizers (NO3-) or
ammonium ions (NH4+) that
plants can use.
• These bacteria are called
nitrogen-fixers.
N=N → 2NH3
Nitrogen Fixers
Most nitrogen-fixing bacteria live
in little houses, or nodules, on
the roots of plants called
legumes.
• Legumes - members of a large family of
plants that include peas, beans, alfafa,
and clover.
• Convert nitrogen gas to ammonia
Nitrogen Fixers
• Mutualistic Relationship
– The plants provide food and cover for the
bacteria, and the bacteria convert nitrogen
gas into fertilizer for the plant.
How Do Animals Get Nitrogen?
• Animals get nitrogen from plants or from other
plant-eating animals, in the form of protein.
Animals must
eat protein to
get our nitrogen
requirements!
We can’t breathe
in nitrogen.
How is Nitrogen Recycled?
Nitrogen is recycled by special bacteria (legumes) that
break down the nitrogen compounds (proteins) in dead
plants and animals, and in animal wastes.
If plants do not use the nitrogen compounds as
fertilizer, special forms of bacteria may recycle it.
These bacteria convert the unused fertilizer into
nitrogen gas and release it into the atmosphere.
All natural ecosystems
depend upon
bacteria to keep the
nitrogen cycle going!
Lightning and the Nitrogen Cycle
• Lightning plays a small
role in the nitrogen cycle.
• The high temperature and
pressure from lightning
combines nitrogen and
oxygen (nitrogen oxides)
in the atmosphere.
– The “fixed” nitrogen,
(which is dissolved in the
rain making nitrates)
enters the soil