3. Follow the Carbon
Notes to faculty
Outcomes: In general, students should better articulate the details of the C cycle
in an ecosystem from the atmosphere and through plants and animals. The
scenario should specifically help them better follow transformations of C in
photosynthesis, to starch within plants and then to fat in an animal, which is used
for cellular respiration. They should connect the transformations with the
processes of photosynthesis, synthesis of starch in plants, assimilation of organic
C in plants by animals, and synthesis of fat in animals and its use for respiration.
Students should show that they must “keep track of the carbon” (conservation of
mass). Their understanding of the distinctions between energy and carbon
transformations should be clear.
What students do: Students are given the “you are a carbon atom” scenario
below and asked to follow the C from the air, to an oak tree/seed and then to a
hibernating squirrel. They are asked to describe and explain this pathway in both
words and in drawing(s) with specific requests (e.g. what happens between the
steps in the scenario) in a bulleted list.
What to pay particular attention to: This simple scenario is an example of
something that looks so simple to us but may well bring out
misunderstandings/poor thinking in students (see Carbon Cycling DQCs). There
are numerous steps here that students could get stuck on, but students who
understand the principles below would be able to identify the core ideas at each
step and not get hung up on the details.
Logistics:
o The several ways you could use this scenario, or another one like it that
you develop, include: groupwork followed by presentation/discussion,
homework, peer review. The directions ask students to distinguish
between steps identified in the scenario and ones that happen in between;
you may well need to explain/demonstrate what this means and the
degree of detail you are looking for (e.g. a very knowledgeable student
might think you are looking for the details of starch production and storage
in animals).
o Other scenarios: 1) You are taken in by a pineapple plant, stored in fruit as
a sugar (fructose), then the fruit is eaten by a human, then the sugar
molecule is used by the human for energy, which leaves you where? 2)
You are taken in by a grass, converted to cellulose, eaten by a cow, and
defecated. , Decomposition follows, which leaves you where? 3) You are
taken in by a cypress tree, converted to starch, covered by swamp water
and mud when the tree dies, covered by more layers of mud which are
eventually compressed into sedimentary rock, converted to oil, pumped
out of the ground, converted to gasoline, used to run a car, which leaves
you where?
Resources: From The University Corporation for Atmospheric Research
http://www.ucar.edu/learn/1_4_2_15t.htm
Hidden Curriculum
• Principles: Conservation of matter, conservation of energy, conversion/
transfer of energy; distinction between matter and energy.
• Processes: Generation (photosynthesis); Transformation (movement of
C from one organism to another; building of biomolecules within an organism,
storage, consumption of one organism by another); Oxidation (heterotrophic
respiration)
• Scale & Time: Movement and transformations of C across
atomic/molecular-organismal-ecosystem scales
• Forms & Representations: Flow of matter; glucose and other organic
molecules such as starch are a form of potential chemical energy; different forms
energy can assume in ecosystems (sunlight, chemical potential energy).
Student Directions
Read the scenario below. Then in 1) words and 2) drawing(s) describe and
explain what happens to the carbon atom on this journey.
You are a carbon atom and you are taken in by an oak tree, converted to starch,
stored in a seed, which is eaten by a squirrel. In the squirrel, you are stored in
fat; the squirrel uses up all of its fat during winter hibernation, which leaves you
where?
Both your written explanation and sketch(es) must address the following:




What happens within the steps provided in the scenario
What happens between the steps provided
Where you (the carbon atom) end up
What the typical time scale would be for that path