Science 10 Sustainability of Ecosystems
Carbon-Oxygen Cycle in Ecosystems
Carbon is a basic building block of all living materials. Atmospheric carbon dioxide is
one of the most important forms of carbon found in our biosphere. The carbon-oxygen
cycle is very dependent on plants that photosynthesize solar radiation. Green land
plants take in carbon dioxide from the atmosphere. During photosynthesis, they use the
sun's energy, carbon dioxide and water to make carbohydrates for food and release
oxygen and water. In oceans, atmospheric carbon dioxide is dissolved into bicarbonate
ions which can be used by marine algae and bacteria for photosynthesis. These
organisms are the autotrophic life that supports marine food webs. The carbon in the
ocean is also a required component in the formation of the shells of aquatic animals
such as snails and clams.
When plants or animals die, their remains are broken down and carbon dioxide is again
released into the biosphere. Under suitable conditions, in swamp-like areas, peat can
be compressed and slowly transformed into carbon-rich fossil fuels such as coal, natural
gas and petroleum.
Animals use the oxygen released by the plants for breathing and release carbon dioxide
into the atmosphere.
Science 10
Sustainability of Ecosystems – Nutrient Cycles
Prior to human influence, the carbon-oxygen cycle was balanced. There was enough
carbon dioxide released to maintain the photosynthesis processes and enough carbon
dioxide absorbed to decrease the amounts in the atmosphere. However, human
activities have abnormally increased the amount of carbon dioxide in the air.
Deforestation, the burning of fossil fuels, the use of aerosols have all had a huge impact
on the stability of the carbon-oxygen cycle. The adverse effects of this instability is the
increase in global warming and the destruction of the protective ozone layer in the
stratosphere.
When considering the sustainability of our ecosystem, namely the Earth, we must
consider the long range effects that we have on the planet.
Vocabulary
abiotic - non-living components (sunlight, temperature, wind, water, and rock) of an
ecosystem
aerosols - a suspension of small particles in a gas. The particles may be solid or liquid
or a mixture of both
biosphere - the life zone of Earth, including the lower part of the atmosphere,
hydrosphere and upper part of Earth's crust
biotic - living components (animals and plants) of an ecosystem
carbon sink - a sink absorbs more carbon than it gives off
fossil fuels - are hydrocarbons found within the top layer of the earth’s crust. Fossil fuels
are non-renewable resources because they take millions of years to form and reserves
are being depleted much faster than new ones are being formed.
global warming - the increase in the average Earth's temperature due to an increased
concentration of greenhouse gases in the atmosphere that amplifies the Greenhouse
Effect.
ozone layer - (O3)is a gas that consists of three oxygen atoms that forms a layer
surrounding the Earth and absorbs ultraviolet radiation from the sun.
peat - is an accumulation of partially decayed vegetation matter. Peat forms in wetlands
called bogs, moors, or muskegs
photosynthesis - is the process by which green plants and other producers use energy
from the sun, and carbon dioxide and water to produce sugars and oxygen
solar radiation - energy that is radiated or transmitted in the form of rays or waves or
particles
stratosphere - the region of the atmosphere between 10 km and 50 km above the
Earth's surface
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Science 10
Sustainability of Ecosystems – Nutrient Cycles
Comparing Carbon and Nitrogen Cycles Activity
You have learned that the carbon-oxygen and the nitrogen cycles are very important of
life on Earth. You have also learned that human activities have caused a serious impact
on these cycles. In nature, these cycles are balanced, however, now they have become
unbalanced. In this exercise, you will draw concept maps to illustrate both the cycle
itself and the human impact on the cycles.
Procedure: 1. Make a concept map illustrating the carbon-oxygen cycle.
2. Include aquatic and terrestrial ecosystems.
3. Include human activities and how they have altered the cycle.
4. Include how human impact has changed the biotic and abiotic
components of the ecosystem.
5. Include diagrams or pictures in your concept map.
Analysis: 1. What technologies have played a major role in changing these two
cycles?
2. How is it possible that the tropical rain forests can affect the carbon
cycle in Canada?
3. How might forests in Canada affect the nitrogen cycle in the tropics?
4. Which country has the greatest impact on the carbon cycle?
5. What is meant by the term carbon sink?
6. Why are forests and oceans considered to be carbon sinks?
Repeat the above procedure for the nitrogen cycle.
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Science 10
Sustainability of Ecosystems – Nutrient Cycles
Comparing Carbon and Nitrogen Cycles Activity (Answer Key)
You have learned that the carbon-oxygen and the nitrogen cycles are very important of
life on Earth. You have also learned that human activities have caused a serious impact
on these cycles. In nature, these cycles are balanced, however, now they have become
unbalanced. In this exercise, you will draw concept maps to illustrate both the cycle
itself and the human impact on the cycles.
Procedure: 1. Make a concept map illustrating the carbon-oxygen cycle.
2. Include aquatic and terrestrial ecosystems.
3. Include human activities and how they have altered the cycle.
4. Include how human impact has changed the biotic and abiotic
components of the ecosystem.
5. Include diagrams or pictures in your concept map.
Analysis: 1. What technologies have played a major role in changing these two
cycles?
Technologies that rely on the combustion of fossil fuels have contributed
largely to the changes in these two cycles. Industrialization, automobiles,
pulp and paper mills are just some examples of technologies that increase
the burning of fossil fuels.
2. How is it possible that the tropical rain forests can affect the carbon
cycle in Canada?
A tropical rain forest would lower the levels of carbon in the atmosphere in
Canada significantly because a tropical rain forest is a large store of
carbon.
3. How might forests in Canada affect the nitrogen cycle in the tropics?
Forests in Canada could increase nitrogen levels in the tropics. Canadian
forests have greater levels of nitrates than do tropical rain forests.
4. Which country has the greatest impact on the carbon cycle?
The countries that have the greatest impact on the carbon and nitrogen
cycles would be those that have the greatest amount of industrialization,
and populations -- Canada, USA, Japan, and Britain. These countries
have larger quantities of pollution that unbalances the cycles than
countries that are still developing industrialization.
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Science 10
Sustainability of Ecosystems – Nutrient Cycles
5. What is meant by the term carbon sink?
A carbon sink is an ecosystem that can store great quantities of carbon.
6. Why are forests and oceans considered to be carbon sinks?
As carbon sinks, forests and oceans can absorb vast quantities of carbon
from the atmosphere. As long as the ocean temperatures remain relatively
constant and the forests remain in existence, the levels of carbon can
remain fairly constant within these ecosystems.
Repeat the above procedure for the nitrogen cycle.
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