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Carbon Cycle
Science
Teaching Notes and Answer Keys
Subject area: Science / Biology / Earth Science
Topic focus: The Carbon Cycle
Learning Aims:
• what carbon is and why it is important
• carbon is in all four of the Earth’s spheres
• how carbon moves from one sphere to another
• how carbon cycles work in both the short term and
the long term
• carbon sources and carbon sinks
• how humans influence / change the carbon cycle
and contribute to climate changes
• what a carbon footprint is and how to calculate it
Skills:
Reading: defining and describing; scanning for specific
information; researching and evaluating information
Writing: taking notes; writing an essay
Speaking: planning and making a presentation
Carbon, p. 16
TR 3 - CLIL_Carbon Cycle_1
1 Review with your students that carbon is a common
element on Earth:
- have students brainstorm some of the things in their
daily lives that contain carbon (e.g. trees, cars,
paper, meat, plastic objects, etc.) make a list of
these items on the board
- double check by eliciting a list of the things that don’t
contain carbon (e.g. metals, table salt, water)
- have students work in pairs or small groups following
the instructions
- have them go through the definitions, compare and
discuss
- let students consider the fact that there is a limited
amount of carbon on Earth, but that the carbon
contained in any one thing doesn’t stay there forever.
The Carbon Cycle, pp. 16-17
2 Focus on the picture and go over it with the students,
pointing out how carbon moves from one place to
another. Point out that the possible solutions or
information can be found in the text on p. 17. Make sure
the students realize that carbon atoms move from one
thing to another in the carbon cycle. Explain that parts
of the carbon cycle happen very quickly, like when
plants take in carbon dioxide from the atmosphere for
photosynthesis, but that other parts of the carbon cycle
happen very slowly, like when carbon is released from
natural geological processes.
2 1 Fossil fuel burning, 2 Photosynthesis, 3 Decomposition,
4 Respiration, 5 Biomass, 6 Aquatic biomass, 7 Coal & oil,
8 Sediments.
Balance at Risk, pp. 17-19
3 Spend some time analysing the picture in activity 3 in
order to elicit from students the difference between
source (origin) and sink (container/depository).
TR 4 - CLIL_Carbon Cycle_4
4 First have students fill in the headings, next have them
read and listen to the text in activity 4.
5 Have students work in pairs or small groups to fill in the
chart.
6 Plan enough lesson time to let students organise the
poster as suggested in activity 6 in order to let them
visualise what they have learnt about alterations of the
carbon cycle; give them time to prepare for a
presentation to the class. The task should be assigned
before the lesson so that students can gather and
organize visual materials for the poster.
4 1 Human Alterations, 1.1 Burning Fossil Fuels, 1.2 Deforestation,
1.3 Farming;
2 Dangers; 3 Researching ways to find equilibrium.
5 Model answers
Carbon Sources: Deforestation, Decomposing plants, Volcanoes
and other volcanic phenomena, Using cars,, Photosynthesis,
Heating, Transportation, Building houses (constructions sites),
Cement manufacturing, Farming, Cell respiration, Preparing
meals.
Carbon Sinks: Oceans, Plants, Soil, The Earth, Lakes,
Underground rocks
Your Carbon Footprint, p. 19
7+8 Encourage students to plan individual actions to cut
down on emissions (e.g. turn down heating by one or
two degrees, etc.)
Check your Knowledge, p. 20
The Carbon Cycle Test (test A) is focused on subject
knowledge, while the crossword activity (test B) checks
students’ subject- specific vocabulary.
A Model answers
1 It’s the constant flowing of carbon between the Earth’s
spheres; 2 It combines sunlight, water, and carbon dioxide to
produce oxygen and glucose (sugar / energy) through
chlorophyll; 3 Terrestrial and aquatic plants; 4 Through
respiration because they use the oxygen produced by the plants;
5 Non-renewable energy sources (oil, coal and natural gas)
formed from the compressed sediments of decomposed plants
and animals that died long ago; 6 By combustion and volcanic
eruption; 7 Burning fossil fuels, deforestation, cattle and rice
farming; 8 Burned trees, stability and temperature of soil and
tillage; 9 Global warming, i.e., temperature increases, rising sea
level, changes in rainfall patterns, increased storms and
organism extinction; 10 Alternative energy sources (solar, wind,
etc.), reconsidering your lifestyle (driving less, saving electricity,
etc.), carbon capture and storage.
B 1 greenhouse effect, 2 carbon, 3 carbon cycle, 4 biosphere,
5 carbon footprint, 6 lithosphere, 7 atmosphere, 8 carbon sink,
9 carbon dioxide, 10 hydrosphere.
15
Science
Carbon
1
TR 3 - CLIL_Carbon Cycle_1 What is the answer to the following questions? Match them to the answers below.
Next, read and listen to the answers provided and compare them with your own.
1
2
3
What is Carbon (C)?
Where is Carbon found?
What is the Carbon Cycle and why is it important?
I A Carbon is an element that is essential for life as we know it. Put very simply, living organisms take
I
I
carbon from their environment. When they die, carbon is returned to the non-living environment. The
carbon cycle includes the processes of production, consumption, decomposition and storage of carbon.
B Carbon is a naturally abundant, non-metallic element that occurs in all organic compounds and can
be found in all known forms of life.
C Carbon exists in the non-living environment as: carbon dioxide (CO2) in the atmosphere and
dissolved in water (forming HCO3¯, bicarbonate ion), carbonate rocks (limestone and coral =
CaCO3), deposits of coal, petroleum, and natural gas derived from once-living things, dead organic
matter, e.g. humus in the soil.
The Earth
System
Biogeochemistry studies how our
planet’s spheres interact. The carbon
cycle is one of the processes which
involves the whole of the Earth
system: it describes the storage and
exchange of carbon between the
Earth’s spheres.
The Carbon Cycle
2
Look at this picture then
read the text on p. 17 and
fill in the blank labels with
words from the box.
Aquatic Biomass
Biomass
Coal and Oil
Decomposition
Fossil Fuel Burning
Photosynthesis
Respiration
Sediments
1
CO2 in
Atmosphere
CO2 in
Biosphere
2
3
4
CO2 in
Hydrosphere
6
5
7
CO2 in
Lithosphere
Limestone
8
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Photocopiable Science – Carbon Cycle
Introduction to CLIL – Change Up! © ELI
Science
The Carbon Cycle
The carbon cycle naturally consists of two parts, the terrestrial and the aquatic.
In the aquatic carbon cycle carbon moves through marine ecosystems and in the terrestrial carbon
cycle moves through terrestrial ecosystems. The carbon cycle is based on the creation of carbon
dioxide (CO2), which can be found in the air in gaseous form, and in water in dissolved form.
Terrestrial plants use carbon dioxide from the atmosphere to generate oxygen that sustains animal
life. In much the same way, aquatic plants also generate oxygen through photosynthesis, a process
by which plants and other carbon producers transform carbon dioxide and water into a complex
carbohydrate (glucose C6H12O6), under the influence of sunlight. Only plants and some bacteria have
the ability to carry out this process because they possess chlorophyll, a pigment molecule found
primarily in green leaves, that makes it possible to “capture” solar energy and transform it.
The basic chemical reaction that makes up the process of photosynthesis is:
carbon dioxide + water + solar energy —> glucose + oxygen
6CO2
+ 6H2O + solar energy —> C6H12O6 + 6O2
Carbon dioxide is released back into the atmosphere during respiration of carbon consumers, which
breaks down glucose and other complex organic compounds and converts the carbon back to carbon
dioxide for reuse by carbon producers.
Carbon that is used by producers (green plants), consumers (animals and humans) and
decomposers (fungi and bacteria) cycles fairly rapidly through air, water and biosphere. But carbon
can also be stored as biomass in the roots of trees and other organic matter for many decades. This
carbon is released back into the atmosphere by decomposition. Not all organic matter is immediately
decomposed. Under certain conditions dead plant matter accumulates faster than it is decomposed
within an ecosystem. The remains are locked away in underground deposits. When layers of
sediment compress this matter, fossil fuels will be formed after many centuries. The carbon in these
fossil fuels is slowly released into the air during long-term geological processes and volcanic eruptions;
it is also released during combustion processes related to human activity.
In the hydrosphere, carbon dioxide can be stored in deep sea sediments and in rocks in the
lithosphere. It will take a long time before this carbon dioxide will be released, through the natural
weathering of rocks or geologic processes that bring sediment to the surface of water. Carbon dioxide
that is stored in water will be present as either carbonate or bicarbonate ions; when the sun warms
up the water, carbonate and bicarbonate ions will be returned to the atmosphere as carbon dioxide.
Carbon moves through two cycles. The two systems move hundreds of billions of tons of carbon
dioxide into and out of the atmosphere each year.
• The short-term cycle carries carbon through surface ocean water, the atmosphere, soils and
vegetation, taking tens to hundreds of years to complete.
• The long-term cycle moves carbon very slowly through the atmosphere, oceans, as well as through
underground rocks, deep-sea sediments and volcanoes.
Balance at Risk
3
Considering the text above, look carefully at this picture and take some notes to distinguish between:
- Carbon sources – activities and processes that introduce carbon dioxide into the atmosphere.
- Carbon sinks – places where CO2 goes after it leaves a source.
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Introduction to CLIL – Change Up! © ELI
Science – Carbon Cycle Photocopiable
17
Science
4
TR 4 - CLIL_Carbon Cycle_4 Read the following text and match these headings to the appropriate paragraphs.
Then listen and check.
Dangers
Burning Fossil Fuels Researching ways to find equilibrium
Deforestation Human Alterations Farming
A new and risky equilibrium
A complete carbon cycle can take millions of years. When the cycles are in balance or
‘equilibrium’, atmospheric levels of carbon remain relatively stable.
1 _________________________________________
There are natural fluctuations in the carbon cycle, but humans have been changing the carbon flows on earth at
an unnatural rate. The major human-induced changes in the carbon cycle result in increased carbon dioxide
(CO2) and methane (CH4) in the atmosphere. The largest source of this change is burning fossil fuels, but other
actions such as deforestation, cattle farming, and rice farming also contribute to this change in the carbon cycle.
1.1 _______________________________________
Humans use fossil fuels such as oil, coal, and natural gas for a variety of purposes including powering our
vehicles, producing electricity, heating and cooling our buildings, and producing goods such as plastics. When
we burn these fossil fuels, we take carbon that has been stored underground for a very long time and put it into
the atmosphere.
1.2 _______________________________________
Deforestation causes carbon to be released into the atmosphere for a number of reasons. First, trees that are
cut are often burned, which immediately releases the carbon stored in the trees into the atmosphere. Second,
deforestation impacts both the temperature and stability of the soil. Since soils contain a significant amount of
carbon, changes that affect the soil can affect the carbon stored in the soil. Deforestation results in more soil
erosion because trees are no longer there to stabilize the soil. Eroded soil and the carbon it contains often end
up in rivers and streams and eventually in the oceans, bringing carbon from the land into the hydrosphere.
Soils in deforested areas are not only eroded because of the lack of trees, but they are also often tilled for
agriculture. Tillage* turns over the soil, releasing carbon dioxide gas contained in the soil to the atmosphere.
1.3 _______________________________________
Cattle farming and rice farming both release methane gas to the atmosphere. This also occurs in natural
wetlands. Both cattle and rice farming are on the rise worldwide and thus these sources of greenhouse gases
are becoming more and more of a concern. Methane emissions are also especially concerning because methane
is a much stronger greenhouse gas than carbon dioxide, meaning that each molecule of methane warms the
earth substantially more than each molecule of carbon dioxide.
2 _________________________________________
Carbon dioxide (CO2) and methane (CH4) are ‘greenhouse gases’, that is gases which tend to raise the
temperature of a gaseous atmosphere when irradiated with UV radiation. Therefore, it has been conjectured by
many scientists that human-induced increases in atmospheric carbon levels are resulting in an artificial climate
change on our planet. This change includes temperature increases, rising sea level, changes in rainfall patterns,
increased storms, and organism extinctions.
3 _________________________________________
People are currently taking many different actions in an attempt to slow climate change. They are
endeavouring both to lessen the amount of carbon that is emitted to the atmosphere and to take carbon out of
the atmosphere and store it elsewhere. Some of the ways we can decrease the amount of carbon emitted into the
atmosphere include driving less, using energy efficient appliances, switching to solar and wind power, and
capturing carbon from power plants and other stationary sources and pumping it underground for storage. This
is called carbon capture and storage. People have been using this technique in oil fields for a long time.
Scientists are currently researching carbon capture and storage methods to try to determine whether this
technique can be used on a large scale. Mitigating climate change by actually taking carbon out of the
atmosphere can be accomplished by several different methods. Simply planting more trees takes carbon out of
the atmosphere, because plants take carbon from the atmosphere to perform photosynthesis. Other methods for
taking carbon dioxide out of the atmosphere include capturing carbon dioxide gas and converting it back into
usable fuel. This is an ongoing research topic and although there are currently many viable options for
decreasing the amount of carbon in the atmosphere, the future may hold other possibilities as well.
___________
* Tillage: working the land by ploughing to make it ready for growing crops
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Photocopiable Science – Carbon Cycle
Introduction to CLIL – Change Up! © ELI
Science
5
6
Fill in the chart taking into consideration your notes from activity 3 and what you read in the text in activity 4.
Carbon Sources
Carbon Sinks
Electricity Generation
_______________________________________________
_______________________________________________
_______________________________________________
_______________________________________________
_______________________________________________
_______________________________________________
_______________________________________________
_______________________________________________
_______________________________________________
_______________________________________________
_______________________________________________
Deposits of Fossil fuels (coal, oil,etc.)
Atmosphere / air
Rivers
_______________________________________________
_______________________________________________
_______________________________________________
_______________________________________________
_______________________________________________
_______________________________________________
_______________________________________________
_______________________________________________
_______________________________________________
Make a poster showing the alterations of the carbon cycle and its consequences for the Earth, then present it
to the class.
Your Carbon Footprint
7
Do you know what is meant by “carbon footprint”? Discuss your ideas with a partner. Next, read this text and
compare with your own answers.
Footprints, in general, can be very
destructive to delicate environments
like nature reserves. A carbon footprint
is a representation of your personal
contribution to global warming. It is
measured by the greenhouse gas
emissions that result from the choices
you make: for instance, when you
choose to drive to school instead of
walking or taking public transport you
are choosing to emit more
greenhouse gases and are thus
increasing your footprint. Being aware
of your footprint will help focus
attention on what you can do to
diminish the negative impacts on our
global environment.
8
How do you and your family use energy?
How do you usually travel?
Calculate your carbon footprint at
http://www.carbonfootprint.com/carbonfootprint.html
and discuss the results:
How can you reduce your carbon footprint?
You should be able to find plenty of
information on reducing your own carbon
footprint on the Internet.
Some suggested starting points are
http://www.safeclimate.net/action/
Essay Writing
What can humans do to decrease the amount of carbon being released into the atmosphere?
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Introduction to CLIL – Change Up! © ELI
Science – Carbon Cycle Photocopiable
19
Science
Check your knowledge
A
The Carbon Cycle Test
1
2
3
4
5
6
7
8
9
10
What is the carbon cycle?
What does photosynthesis do in the carbon cycle?
What are carbon producers?
How do carbon consumers release carbon dioxide into the air ?
What are fossil fuels?
How do fossil fuels release carbon dioxide into the atmosphere?
What human activities can alter the equilibrium of the carbon cycle?
How is deforestation responsible for the release of carbon dioxide?
What are the consequences of changes in the carbon cycle?
What ways have been found to lessen the amount of CO2 being released?
B Crossword
1
2
3
1 The result of excess carbon dioxide in the
atmosphere causing climate changes.
2 Non-metallic chemical element found in
all organic compounds.
3 The continuous process by which carbon
is exchanged between the 4 spheres of
the Earth system.
4 All living things.
5 Refers to the amount of carbon dioxide
emitted.
6 The Earth’s crust.
7 Air surrounding the Earth.
8 Area that absorbs carbon in water or land
and doesn’t recycle.
9 Gas used in plants for photosynthesis.
10 Bodies of water on the Earth.
4
5
6
7
8
9
10
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Photocopiable Science – Carbon Cycle
Introduction to CLIL – Change Up! © ELI