SNC 1D/2D
Name: _______________________
Date: _______________________
Unit 1: Sustainable Ecosystems
The Carbon Cycle in More Detail
A) Diagram of the Major Carbon Cycle Processes
Human activities
like burning
fossil fuels
Water and
Energy for
Cells
Water
Carbon Dioxide Gas*
in the atmosphere
Cellular
Respiration

Happens in the
mitochondria
inside all living
cells all the
time.

Is the process
that releases
energy from
glucose in the
presence of
oxygen.
[Fermentation is
another process that
does the same thing in
organisms where oxygen
is unavailable.]
Glucose
(a carbohydrate
stored in tissue; used
as food energy
source) AND
Oxygen Gas
PHOTOSYNTHESIS

Happens only in
producers

Requires
ENERGY from
SUNLIGHT so
can only happen
during the day

Requires the
green pigment,
chlorophyll found
in the
chloroplasts of
green plants
* carbon can also be stored in coal,
oil, rock, fossils and water bodies
B) Word Descriptions of the Major Carbon Cycle Processes
 The chemical equation for photosynthesis looks like this:
Carbon dioxide gas
from atmosphere
+
water ----------------------------------
in the presence of Sun energy
and chlorophyll in green plants
glucose (stored in +
plants and animals
for use in tissues)
oxygen
gas
 The chemical equation for cellular respiration looks like this:
Glucose + oxygen gas  carbon dioxide gas + water + energy for cells


Photosynthesis and respiration are called complementary processes because the
materials made in one of them are used up in the other one.
Photosynthesis and respiration each make up half of the bulk of the carbon cycle.
C) Important Challenges Involving the Carbon Cycle
 Carbon dioxide is a greenhouse gas – as are water vapour, methane, nitrous oxide
and ozone.
 Greenhouse gases are essential to Earth’s atmosphere because they prevent some
of the heat that reaches Earth from the Sun from leaving the atmosphere. This


ensures that most of the Earth’s surface is warm enough for life. This natural
insulating capacity of greenhouse gases is called the greenhouse effect.
Because humans have “suddenly” released much of the carbon dioxide that was
converted into fossil fuels, this has increased the total amount of carbon dioxide
(and other greenhouse gases) in the atmosphere. This means these gases are not
being recycled fast enough so their greenhouse effect is increasing. The result,
suggest many scientists, is global warming. Global warming is the increase in Earth’s
average surface temperature.
Burning carbon-containing fossil fuels like coal and oil produces nitrogen oxides and
sulphur dioxide compounds. These compounds mix with water in the air to form
acids. Eventually, the acid materials fall to the ground as acid precipitation. Acid
precipitation has a pH level measuring less than 7 on a scale of 0 to 14. The pH of
rainwater is usually around 5.6. The pH of acid precipitation can be as low as 4.2.
Some effects of acid precipitation include:
a) Calcium and other soil nutrients dissolve in acids and wash away while other
materials, like aluminum, settle into acidic soil and kill some species of trees.
b) Tree leaves are “pock-marked” and statues are eroded by acidic precipitation.
c) Many aquatic organisms (e.g. snails, clams, insects, corals) are very sensitive to
acid levels and their populations decline as acidity increases. This, in turn,
affects other species which rely on them for food.
D) Positive Developments Involving the Carbon Cycle
 In landfills, bacteria put carbon dioxide into the carbon cycle using fermentation (a
process like cellular respiration but one that does not use oxygen). The leftover
carbon material ends up as methane gas. Ontario has introduced a law requiring all
large landfill sites to install pipes to collect methane gas. Many Canadian homes now
run on electricity that is at least partially generated by burning methane gas
collected at their local landfill!
 Canada has reduced it emissions of the sulphur and nitrogen compounds involved in
acid rain formation since 1990 and this has led to less acid rain damage. Improved
technologies, such as scrubbers in smoke stacks, are designed to remove undesirable
gases from industrial emissions. International agreements with the United States
have also contributed to fewer emissions originating south of the border and blowing
across to Canada.
 Recently (December 2009), Canada and many other countries joined forces to try to
come up with an international agreement on climate change in Copenhagen. Some
possible “targets” for reducing carbon dioxide and other greenhouse gas emissions
are in the works. Previous international agreements like the Kyoto Protocol have also
attempted to encourage international cooperation on these issues.
 In July 2008, Ontario announced that roughly half of its forests
(about 225 000 km2) will be used only for tourism and Aboriginal purposes and will
be protected from logging, mining and oil and gas exploration. The boreal forests of
Ontario absorb about 12 million tonnes of carbon dioxide per year for
photosynthesis.
 Through recycling programs in Ontario, more than 2.3 million tonnes of waste are
recycled or composted each year. Recycling helps to cut carbon dioxide emissions
because, in most cases, more energy is needed to make something from new
materials than from recycled ones.
Practice
Except for #2, answer these questions at the bottom of this page, or on a separate sheet,
please. Do not try to squish an answer in between the questions.
1.
Photosynthesis and cellular respiration happen in all cells all the time.” Is this statement
true or false? Explain.
2. Fill in the following table.
Process 
Photosynthesis
Respiration
Organisms in which this
process occurs
Materials needed for the
process to occur
Materials made during the
process
Is energy absorbed or is it
released in this process?
(Choose one.)
3. Why are photosynthesis and cellular respiration called complementary processes?
4. Two processes can be used to extract energy from the glucose produced in
photosynthesis. One uses oxygen gas, the other does not. Name the two processes and
identify which one requires oxygen gas.
5. What is the greenhouse effect? Is the greenhouse effect always a ‘bad” thing? Explain.
6. What is global warming? How is global warming connected to the greenhouse effect?
7. Name two kinds of compounds involved in the formation of acid precipitation. What one
substance in the air must each of these compounds react with in order to form their
acid?
8. List three activities individuals can take part in to help alleviate some of the human
effects on the carbon cycle.
9. In the winter, very little photosynthesis occurs in Canada. Explain how, on a January
day, you might directly benefit from tropical forests.