Download Activity 8 Photosynthesis, Respiration, and the Carbon Cycle

CS_Ch9_Environment
2/28/05
4:42 PM
Page 591
Activity 8 Photosynthesis, Respiration, and the Carbon Cycle
Activity 8
Photosynthesis, Respiration,
and the Carbon Cycle
GOALS
What Do You Think?
In this activity you will:
Consider the mass of a seed from a giant redwood tree and
the tree itself. It is hard to believe that a giant of a tree began
as a small seed.
• Learn how oxygen cycles
through photosynthesis and
respiration.
• Practice safe laboratory
techniques for using
chemicals in a laboratory
situation.
• Describe the cycling of
carbon in an ecosystem.
• Speculate how human
activities can affect the
carbon cycle.
• From where do the materials come to make up the
mass of a mature tree?
Write your answer to this question in your Active Biology log.
Be prepared to discuss your ideas with your small group and
other members of your class.
For You To Do
In this activity you will investigate what happens when the
exchange of carbon dioxide between a leaf and the
atmosphere is blocked.
1. Three days before this activity, one plant was placed in
the dark. A second plant of the same species was placed
in sunlight.
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A Vote for Ecology
a) Predict what you will find when you
test a leaf from each plant for the
presence of starch.
Day 1
Isopropyl
alcohol is
flammable
and toxic. Do
not expose
the liquid or
its vapors to
heat or flame.
Do not ingest;
avoid skin/eye
contact. In
case of spills,
flood the area
with water
and then call
your teacher.
Make sure you
wear goggles,
apron, and
gloves
2. Remove one leaf from each plant. Use
scissors to cut a small notch in the
margin of the one placed in sunlight.
Using forceps, drop the leaves into a
beaker of hot (60°C) tap water.
3. When the leaves are limp, use forceps
to transfer the leaves to a screw-cap
jar about half full of isopropyl
alcohol. Label the jar with your team
symbol and store it overnight as
directed by your teacher.
4. Select four similar leaves on the plant
that has been kept in the dark, but
do not remove them from the plant.
Using a fingertip, apply a thin film of
petroleum jelly to the upper surface
of one leaf. Check to be sure the
entire surface is covered. (A layer of
petroleum jelly, although transparent,
is a highly effective barrier across
which many gases cannot
pass.) Cut one notch in the
leaf’s margin.
5. Apply a thin film to the
lower surface of a second
leaf and cut two notches
in its margin.
6. Apply a thin film to both
upper and lower surfaces
of a third leaf and cut
three notches in its
margin.
7. Do not apply petroleum
jelly to the fourth leaf, but
cut four notches in its
margin; Place the plant in
sunlight.
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Active Biology
a) What is the purpose of the leaf
marked with four notches?
8. Wash your hands thoroughly before
leaving the laboratory.
Day 2
9. Obtain your jar of leaf-containing
alcohol from Day 1. Using forceps,
carefully remove the leaves from
the alcohol and place them in a
beaker of room-temperature water.
(The alcohol extracts chlorophyll
from the leaves but also removes
most of the water, making them
brittle.) Recap the jar of alcohol
and return it to your teacher.
10. When the leaves have softened,
place them in a screw-cap jar about
half full of Lugol’s iodine solution.
Lugol’s iodine solution is used to
test for the presence of small
amounts of starch. Starch gives a
blue-black color.
11. After several minutes, use forceps to
remove both leaves, rinse them in a
beaker of water, and spread them
out in open Petri dishes of water
placed on a sheet of white paper.
a) Record the color of each leaf.
Recap the jar of Lugol’s iodine
solution and return it to your
teacher.
b) What was the purpose of the
iodine test on Day 2?
c) If you use these tests as an
indication of photosynthetic
activity, what are you assuming?
Lugol's iodine solution is poisonous
if ingested, irritating to skin and
eyes, and can stain clothing. Should
a spill or splash occur, call your
teacher immediately; flush the area with
water for 15 minutes; rinse mouth with water.
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Activity 8 Photosynthesis, Respiration, and the Carbon Cycle
12. Wash your hands thoroughly before
leaving the laboratory.
14. Repeat Steps 10 and 11.
a) Compare the color reactions of
the four leaves and record your
observations.
Day 4
13. Remove from the plant the four
notched leaves prepared on Day 1
and place them on paper towels.
To remove the petroleum jelly, dip
a swab applicator in the
HistoclearTM and gently rub it over
the surface of the film once or
twice. Then gently use a paper
towel to remove any residue of
petroleum jelly. Discard the swab
applicator and the paper towel in
the waste bag.
b) In which of the leaves coated
with petroleum jelly did
photosynthetic activity appear to
have been greatest? Least?
15. Wash your hands thoroughly before
leaving the laboratory.
Histoclear is a combustible liquid. Do not
expose to heat or flame. Do not ingest;
avoid skin/eye contact. Should a spill or
splash occur, call your teacher
immediately; wash skin area with soap and water.
The Carbon Cycle
You take in carbon in all the foods you eat.You return carbon dioxide
to the air every time you exhale. A plant also returns carbon dioxide
to the air when it uses its own sugars as a source of energy.When
another plant takes in the carbon dioxide during photosynthesis, the
cycle of carbon through the community is complete. In this activity
you observed what happens when this exchange of carbon dioxide
does not take place. However, when the exchange does take place, the
plant can use the carbon from the carbon dioxide to live and grow.
Carbon dioxide is also returned to the air by decomposers.When
producers or consumers die, decomposers begin their work. As its
source of energy, a decomposer uses the energy locked in the bodies
of dead organisms. It uses the carbon from the bodies to build its own
body. Carbon that is not used is returned to the air as carbon dioxide.
Eventually, almost all the carbon that is taken in by plants during
photosynthesis is returned to the air by the activity of decomposers.
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OXYGEN CYCLE THROUGH
PHOTOSYNTHESIS AND
RESPIRATION
oxygen
photosynthesis
(green plants)
respiration
(plants and animals
animals)
respiration
((decomposers))
carbon
dioxide
Hundreds of millions of years ago, many energy-rich plant bodies
were buried before decomposers could get to them.When that
happened, the bodies slowly changed during long periods of time.They
became a source of fuels like coal, oil, and natural gas.Today, when
these fuels are burned, energy is released.The carbon in the fuels is
returned to the air as carbon dioxide.You can see that even the energy
obtained from fuels is a result of photosynthesis.The process in which
carbon is passed from one organism to another, then to the abiotic
community, and finally back to the plants is called the carbon cycle.
The Cycling of Matter
The energy from the Sun flows through the ecosystem in the form of
carbon-carbon bonds in organic matter.When respiration occurs, the
carbon-carbon bonds are broken and energy is released.The carbon is
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Activity 8 Photosynthesis, Respiration, and the Carbon Cycle
combined with oxygen to form carbon dioxide.The energy that is
released is either used by the organism (to move, digest food, excrete
wastes, etc.) or the energy may be lost as heat. In photosynthesis
energy is used to combine the carbon molecules from the carbon
dioxide, and oxygen is released.This is illustrated in the diagram. All
the energy comes from the Sun.The ultimate fate of all energy in
ecosystems is to be lost as heat. Energy does not recycle!
Bio Words
carbon cycle: the
process in which
carbon is passed from
one organism to
another, then to the
abiotic community,
and finally back to
the plants
However, inorganic nutrients do recycle.They are inorganic because
they do not contain carbon-carbon bonds.These inorganic nutrients
include the phosphorous in your teeth, bones, and cell membranes.
Also, nitrogen is found in your amino acids (the building blocks of
protein). Iron is in your blood.These are just a few of the inorganic
nutrients found in your body. Autotrophs obtain these inorganic
nutrients from the inorganic nutrient pool.These nutrients can usually
be found in the soil or water surrounding the plants or algae.These
inorganic nutrients
are then passed
THE CARBON
from organism to
CYCLE
atmospheric
carbon dioxide
organism as one
photosynthesis
animal
respiration
organism is
consumed by
another. Ultimately,
plan
exchange of CO2
respiration
all organisms die.
between atmosph
and water
They become
detritus, food for
burn
the decomposers.
At this stage, the
last of the energy is
extracted (and lost
as heat).The
inorganic nutrients
decay
are returned to the
decay
soil or water to be
taken up again.The
inorganic nutrients
carbon
are recycled; the
compounds
energy is not.
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Reflecting on the Activity and the Challenge
In this activity you learned that carbon
is the key element in all organic matter.
You investigated the process of
photosynthesis and then related this
process to respiration in the carbon-
oxygen cycle. The cycling of matter like
carbon is essential to the survival of any
ecosystem. You will need to explain this
cycle in your booklet.
1. Explain why photosynthesis and cellular respiration are considered to be paired
processes.
2. What is the importance of decomposers in the carbon cycle?
3. What effect does the burning of fossil fuels have on the carbon cycle?
4. Scientists have expressed concerns about the burning of the rainforests to clear
the land for the planting of crops.
a) Explain how the burning of the forests could change oxygen levels.
b) What impact would the change in oxygen levels have on living things?
Inquiring Further
The greenhouse effect
The term greenhouse effect was coined
in the 1930s to describe the heatblocking action of atmospheric gases.
Research and report the connection
between the greenhouse effect and the
carbon cycle.
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