1. Human Energy Systems Unit Activity 4.3: Carbon Fluxes
Carbon: Transformations in Matter and Energy
Environmental Literacy Project Michigan State University
Human Energy Systems Unit Activity 4.3: Carbon Fluxes

2. Explaining the seasonal cycle
The Keeling Curve
Explaining the seasonal cycle

3. The Carbon Movement Question
How are carbon atoms cycling among pools? How are the pools getting larger or smaller? What makes carbon move from one pool to another?

4. During photosynthesis which way does carbon move?
Question:
During photosynthesis which way does carbon move?
Which pool(s) increase and decrease when photosynthesis happens?
Atmosphere
CO2
Soil
organic carbon
Biomass
Fossil Fuels

5. Which pool(s) increase and decrease when cellular respiration happens?
Question:
During cellular respiration (in plants, animals and decomposers) which way does carbon move?
Which pool(s) increase and decrease when cellular respiration happens?
Atmosphere
CO2
Soil
organic carbon
Biomass
Fossil Fuels

6. Carbon pools change size over time
Atmosphere
CO2
Soil
organic carbon
Biomass
Fossil Fuels
Different amounts of carbon move between the atmosphere and the biomass or soil pools in the summer versus in the winter.
Photosynthesis
Cellular Respiration
Cellular Respiration
The amount of carbon that moves per unit of time is called a “flux”.

7. Carbon moving from pool to another relates to energy
Why does photosynthesis happen in plants?
Why does cellular respiration happen in the biomass pool?
Why does cellular respiration happen in the soil pool?
How are these things connected to energy?

8. Energy enters the biomass pool from the sun
How does energy enter the biomass pool?
(Remember our third rule: Energy flows! Energy can never be created or destroyed. It has to come from somewhere).
Through the process of photosynthesis, plants absorb sunlight energy and sequester it in C-C and C-H bonds of glucose molecules. This energy may be stored in the plant’s body (and might even be eaten by an animal). This is how energy enters the biomass pool.

9. Energy flows out of the biomass pool
How does chemical energy leave the biomass pool?
Plants, animals and decomposers do cellular respiration for all of their life processes. During cellular respiration, organic molecules like sugar are broken apart. High energy bonds in sugar (C-C and C-H) are replaced by low energy bonds (C-O and H-O) and the chemical energy is released. This energy can be transformed into:
work or motion energy and eventually to
heat radiated into space

10. Where does the energy go?
When the energy leaves the biomass pool and enters the atmosphere pool, what happens to it? (Remember, energy can never be created or destroyed. It has to go somewhere).
Heat energy is lost from the biomass pool (and eventually radiates into outer space). Some of this heat energy is trapped in greenhouse gases and remains in the atmosphere. Most of this heat radiates back into outer space.
As greenhouse gases increase, more of this heat is trapped in the atmosphere, causing the global temperatures to rise.

11. Example scenario card
Round 1: Decide as a group what will happen to the organic and inorganic pools of carbon according to the scenario below:
It is summer in the northern hemisphere and annual flowers begin to grow.
Winter comes and the annual plants die and are digested by decomposers.
Round 2: Explain how energy is transformed in the scenarios above.