Earthlabs: Carbon Cycle– Lab 1 STUDENT ANSWERS
http://serc.carleton.edu/eslabs/carbon/lab1.html
Living in a Carbon World
PART A. Trees - The Carbon Storage Experts
1: Using the tree diagram above to help you, explain why trees
(and all plants) represent a small but complete carbon cycle.
Draw your own diagram to help you illustrate your answer.
Key Points:
Trees take in carbon when they absorb CO2 from the air for
photosynthesis. In cell respiration, CO2 is produced as a byproduct moving from leaves into the atmosphere. That CO2
released via respiration can be used by plants for
photosynthesis.
Earthlabs: Carbon Cycle– Lab 1
http://serc.carleton.edu/eslabs/carbon/lab1.html
PART B. Carbon Storage in Local Trees
1: Carbon dioxide (CO2) is a greenhouse gas that naturally warms
the atmosphere as part of the greenhouse effect. Unfortunately,
the amount of CO2 in the atmosphere has been increasing over the
past hundred years. According to scientists, this increase in
atmospheric CO2 has caused the average global temperature on
Earth to increase by about 0.8° Celsius (1.4° Fahrenheit) since
1880. Two-thirds of the warming has occurred since 1975, at a
rate of roughly 0.15-0.20°C per decade. (NASA)

Explain how planting and growing more trees could mitigate
(slow down ) this warming trend in global temperature.
Key Points:
CO2 is a greenhouse gas that naturally warms the atmosphere.
Trees not only absorb a lot of CO2 for photosynthesis, they store
that carbon in their cells and tissues for hundreds of years. Thus,
photosynthesis and carbon storage reduce the amount of fossil
fuel CO2 emitted to the atmosphere.
Earthlabs: Carbon Cycle– Lab 1
http://serc.carleton.edu/eslabs/carbon/lab1.html
PART C. Building Carbon Compounds
1. Explain why the carbon atoms in carbon compounds such as
proteins and DNA originally came from CO2 molecules in the
atmosphere.
Key points:
Plants absorb CO2 from the atmosphere during photosynthesis
and use those carbon atoms to make glucose molecules. When
glucose molecules are broken down, plants use these carbon
atoms to build all of their other carbon compounds – including
DNA and proteins. The only source of carbon to make all of the
new carbon compounds is the CO2 –photosynthesis-glucose
pathway.
2. Explain why a lack of soil nutrients (ex. nitrogen,
phosphorus, sulfur and magnesium) limits a tree's ability to
grow and store carbon.
Key Points:
Important biomolecules such as proteins and DNA are
required for carrying out all of life’s activities (including
growing). Plants need nitrogen atoms to build their proteins
and nitrogen, phosphorus and sulfur atoms to build their
DNA molecules.
Chlorophyll is a pigment that plants use to absorb the sunlight
needed to power photosynthesis. Plants need magnesium
atoms to build their chlorophyll pigment molecules. Lack of
chlorophyll means that photosynthesis does not occur and
glucose is not produced.
3. Explain how trees and all other organisms in the biosphere
are able to make millions of different configurations of
carbon compounds.
Key Points:
Because carbon atoms can form 4 bonds and can bond easily
with hydrogen and oxygen atoms, producing many different
structures and sizes of carbon compound molecules. The atoms
in these carbon compounds can be continually rearranged into
new configurations. By bonding with nitrogen, phosphorus and
sulfur atoms, even more configurations are possible, producing
biomolecules that can be very large and very complex (ex.
Proteins, DNA).
Earthlabs: Carbon Cycle– Lab 1
http://serc.carleton.edu/eslabs/carbon/lab1.html
PART D. Fossil Fuels, Hydrocarbons and CO2
1: Describe how combustion can move carbon atoms from being
stored deep in the ground to the atmosphere.
Key Points:
Fossil fuels (oil, natural gas, coal) have been stored for millions
of years deep within the ground. Fossil fuels are made of
hydrocarbon molecules. When hydrocarbons are burned
(combustion) in the presence of oxygen, the carbon, hydrogen
and oxygen atoms are rearranged producing CO2 and H2O
molecules. The CO2 molecules are released to the surrounding
air.
2: Identify and explain at least one piece of evidence supporting or
refuting the claim that humans are changing the carbon chemistry
of the atmosphere.
Key points: (supporting)
Burning fossil fuel produces CO2. Atmospheric CO2 has been
increasing since humans began burning fossil fuels. CO2 that
has been produced by burning fossil fuels has a chemical
signature that differs from CO2 released by photosynthesis,
respiration and volcanoes. This evidence tells scientists how
much of the CO2 increase since the beginning of the industrial
revolution comes directly from the combustion of fossil fuels.