1. Ecosystems Unit Activity 3.3 Tracing Carbon Through Ecosystems
Carbon: Transformations in Matter and Energy
Environmental Literacy Project Michigan State University
Ecosystems Unit Activity 3.3 Tracing Carbon Through Ecosystems
Image Credit: Craig Douglas, Michigan State University

2. Tracing Carbon in an Ecosystem
Atmosphere CO2
Carnivores organic carbon
Herbivores organic carbon
Producers organic carbon
Soil
Organic Carbon 99 19 70 32 2
In the Carbon Dice Game, we followed individual carbon atoms into and out of carbon pools. We found that the number of carbon atom visits to different organic matter pools followed the same pattern as the organic matter pyramid.
1. Revisit student ideas about the Carbon Fluxes Question.
Use Lesson 3.2 Carbon Pool Presentation, Slides 2 and 3 to discuss the patterns students found in Lesson 3.1 The Carbon Dice Game. Remind them that in the game they followed individual carbon atoms. Now, they will be tracing multiple carbon atoms through an ecosystem.

3. Tracing Carbon in an Ecosystem
In order to understand carbon cycling at the ecosystem scale, though, we need to follow multiple carbon atoms at the same time. Let’s practice doing this on the Tracing Carbon Worksheet.
Carnivores
Atmosphere
Herbivores
1. Revisit student ideas about the Carbon Fluxes Question.
Use Lesson 3.2 Carbon Pool Presentation, Slides 2 and 3 to discuss the patterns students found in Lesson 3.1 The Carbon Dice Game. Remind them that in the game they followed individual carbon atoms. Now, they will be tracing multiple carbon atoms through an ecosystem.
Image Credit: Craig Douglas, Michigan State University
Producers
Soil Carbon

4. Tracing Carbon in an Ecosystem
2. Practice tracing carbon through an ecosystem.
Pass out copies of the Lesson 3.2 Tracing Carbon Worksheet. Have students complete it on their own and then compare with a neighbor to see if they both agree on all of the processes. Show Slide 4 while they work.
Image Credit: Craig Douglas, Michigan State University

5. Tracing Carbon in an Ecosystem
Use Slide 5 of the Presentation to discuss their answers. Students should have the following arrows on their Worksheet: P: These arrows represent photosynthesis, or the transformation of inorganic CO2 from the atmosphere into organic matter making up organisms. E: These arrows represent carbon atoms in organic matter moving through an ecosystem during the process of eating. D: These arrows represent carbon atoms in organic matter moving through an ecosystem during the process of death. CR: These arrows represent cellular respiration. During cellular respiration, carbon is transformed from organic molecules into CO2 (water is also produced), which is released into the atmosphere. This is also the transformation of organic carbon into inorganic carbon.
Image Credit: Craig Douglas, Michigan State University

6. Tracing Carbon Observations
Why are there no arrows that go from the atmosphere to the rabbits or the fox?
Why are there no arrows that go from the soil to the grass?
Why are there no arrows that go directly from rabbits to grass?
Let’s try tracing carbon through a few different pathways…
Have students use their Worksheets to discuss the questions as a class on Slide 6.

7. What is the path a carbon atom would take to move from the atmosphere to a flower?
Step 1: A carbon atom is in the atmosphere. What happens next?
Step 2:
Step 3:
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With the class as a whole, practice tracing carbon in the scenarios in Slides 7, 8 and 9. Ask: What is the path a carbon atom would take to move from the atmosphere to a flower? What is the path a carbon atom would take to move from the atmosphere to the muscle of a rabbit? What is the longest path a carbon atom would take to move from the atmosphere to a decomposer?

8. What is the path a carbon atom would take to move from the atmosphere to the muscle of a rabbit?
Step 1: A carbon atom is in the atmosphere. What happens next?
Step 2:
Step 3:
Step 4:
Step 5:
Step 6:
With the class as a whole, practice tracing carbon in the scenarios in Slides 7, 8 and 9. Ask: What is the path a carbon atom would take to move from the atmosphere to a flower? What is the path a carbon atom would take to move from the atmosphere to the muscle of a rabbit? What is the longest path a carbon atom would take to move from the atmosphere to a decomposer?

9. What is the longest path a carbon atom would take to move from the atmosphere to a decomposer?
Step 1: A carbon atom is in the atmosphere. What happens next?
Step 2:
Step 3:
Step 4:
Step 5:
Step 6:
With the class as a whole, practice tracing carbon in the scenarios in Slides 7, 8 and 9. Ask: What is the path a carbon atom would take to move from the atmosphere to a flower? What is the path a carbon atom would take to move from the atmosphere to the muscle of a rabbit? What is the longest path a carbon atom would take to move from the atmosphere to a decomposer?

10. How can we explain the organic matter pyramid by tracing carbon atoms through the ecosystem?
Let's follow 500 carbon atoms through the ecosystem.
The organic matter pyramid: Comparing the organic matter of producers, herbivores, and carnivores.
Carnivores 1 10
In these slides we are counting individual carbon atoms, but real ecosystems have far too many carbon atoms to count.  For example, the organic matter of a small meadow contains more than 10,000,000,000,000,000,000,000,000,000 carbon atoms!
Note: The pathways of carbon atoms are the same in all ecosystems, but the numbers of atoms are different.
Atmosphere
Herbivores
3. Introduce the organic matter pyramid animation.
Tell students that they will follow a computer simulation that tracks 500 carbon atoms through an ecosystem to evaluate their predictions about how carbon-transforming processes impact organic carbon pool sizes.
Show Slide 10 to begin the Presentation. Be sure to show the Presentation in “presentation mode” so the animations are visible. Click one time to advance the animation so students can see the “organic matter pyramid,” which shows one hundred carbon atoms in the producer pool, ten carbon atoms in the herbivore pool, and one carbon atom in the carnivore pool. Remind students that these numbers are used to show relative size.
Click a second time so that the arrows appear and the molecules start moving from pool to pool.
Image Credit: Craig Douglas, Michigan State University
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Soil Carbon
Producers

11. 100 What happens to carbon atoms in producers? - Photosynthesis
Carnivores
- Cellular Respiration/Biosynthesis
200 carbon atoms go back to the atmosphere when plants use the sugar for cellular respiration.
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- Being Eaten/Death
Note: The pathways of carbon atoms are the same in all ecosystems, but the numbers of atoms are different.
Atmosphere
100 40 50 30 20 10 70 60 80 90
Herbivores
500 carbon atoms become part of sugar molecules through photosynthesis.
100 carbon atoms go to herbivores when they eat plants.
4. Have students watch the animations.
Go through the animations as a class.
Display Slide 11. Click through the animations until all of the processes moving carbon into and out of the Producer pool are complete.
Image Credit: Craig Douglas, Michigan State University
300 carbon atoms become part of the plant through biosynthesis.
100 carbon atoms stay in the living plants.
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100 carbon atoms go to the soil when plants or leaves die.
Soil Carbon
Producers

12. 100 10 What happens to carbon atoms in herbivores?
Note: The pathways of carbon atoms are the same in all ecosystems, but the numbers of atoms are different.
What happens to carbon atoms in herbivores?
What happens to carbon atoms in producers?
15 carbon atoms go to carnivores when they eat herbivores. 10 12 11 13 14 15 4 2 3 5 7 1 9 6 8
- Undigested food/Defecation
Carnivores
- Cellular Respiration/Biosynthesis
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- Being Eaten/Death
34 carbon atoms become part of the herbivore through biosynthesis.
Atmosphere
50 carbon atoms go back to the atmosphere when herbivores use the food for cellular respiration.
10 carbon atoms stay in the living herbivores.
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Herbivores
9 carbon atoms go to the soil when herbivores die.
16 carbon atoms go to the soil when herbivores defecate.
100 carbon atoms go to herbivores when they eat plants.
Click through the animations until all of the processes moving carbon into and out of the Producer pool are complete.
Repeat this process with Slides with the herbivore, carnivore, soil carbon, and atmosphere pools. Note: Students may come up with ideas that are not represented in the ecosystem model. For example, CO2 molecules can be dissolved into the oceans. However, because we do not have an ocean pool in this model, the ocean pool is not discussed. This might be an appropriate time to discuss the fact that all models have limitations. Congratulate students for thinking of ways carbon atoms can move that were not represented in the model!
Image Credit: Craig Douglas, Michigan State University
100 carbon atoms stay in the living plants.
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100 carbon atoms go to the soil when plants die.
Soil Carbon
Producers

13. 100 1 10 What happens to carbon atoms in carnivores?
8 carbon atoms go back to the atmosphere when carnivores use the food for cellular respiration.
Note: The pathways of carbon atoms are the same in all ecosystems, but the numbers of atoms are different.
What happens to carbon atoms in carnivores?
What happens to carbon atoms in herbivores?
1 carbon atom stays in the living carnivores.
15 carbon atoms go to carnivores when they eat herbivores. 13 14 11 12 10 15 6 8 9 7 4 2 3 5 1
- Undigested food/Defecation
3 carbon atoms become part of carnivores through biosynthesis.
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- Cellular Respiration/Biosynthesis 10
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10 carbon atoms stay in the living herbivores. 10
4 carbon atoms go to the soil when carnivores defecate.
2 carbon atoms go to the soil when carnivores die.
Herbivores
9 carbon atoms go to the soil when herbivores die.
Click through the animations until all of the processes moving carbon into and out of the Producer pool are complete.
Repeat this process with Slides with the herbivore, carnivore, soil carbon, and atmosphere pools. Note: Students may come up with ideas that are not represented in the ecosystem model. For example, CO2 molecules can be dissolved into the oceans. However, because we do not have an ocean pool in this model, the ocean pool is not discussed. This might be an appropriate time to discuss the fact that all models have limitations. Congratulate students for thinking of ways carbon atoms can move that were not represented in the model!
Image Credit: Craig Douglas, Michigan State University
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Producers

14. 100 1 10 What happens to carbon atoms in carnivores?
Note: The pathways of carbon atoms are the same in all ecosystems, but the numbers of atoms are different.
What happens to carbon atoms in carnivores?
What happens to carbon atoms in the soil?
1 carbon atom stays in the living carnivores. 1
- Cellular Respiration/Biosynthesis
Carnivores 1 10
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66 carbon atoms go back to the atmosphere when decomposers use the soil carbon for cellular respiration. 10
6 carbon atoms go to the soil when carnivores die.
Herbivores
Click through the animations until all of the processes moving carbon into and out of the Producer pool are complete.
Repeat this process with Slides with the herbivore, carnivore, soil carbon, and atmosphere pools. Note: Students may come up with ideas that are not represented in the ecosystem model. For example, CO2 molecules can be dissolved into the oceans. However, because we do not have an ocean pool in this model, the ocean pool is not discussed. This might be an appropriate time to discuss the fact that all models have limitations. Congratulate students for thinking of ways carbon atoms can move that were not represented in the model!
Image Credit: Craig Douglas, Michigan State University
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65 carbon atoms stay in the soil.
Producers

15. Note: The pathways of carbon atoms are the same in all ecosystems, but the numbers of atoms are different.
How can we explain the organic matter pyramid by tracing carbon atoms through the ecosystem?
Carnivores 1
Plants, animals, and decomposers create the organic matter pyramid through their carbon-transforming processes--when they photosynthesize, eat, grow, live, and die. 10
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Atmosphere
Herbivores
Click through the animations until all of the processes moving carbon into and out of the Producer pool are complete.
Repeat this process with Slides with the herbivore, carnivore, soil carbon, and atmosphere pools. Note: Students may come up with ideas that are not represented in the ecosystem model. For example, CO2 molecules can be dissolved into the oceans. However, because we do not have an ocean pool in this model, the ocean pool is not discussed. This might be an appropriate time to discuss the fact that all models have limitations. Congratulate students for thinking of ways carbon atoms can move that were not represented in the model!
5. Have students share reflections on the animations.
Have students share their reflections on the animations
By the end of the presentation, there will be 100 atoms in the producers, 10 atoms in the herbivore pool, and 1 in the carnivore pool, and students should begin to have an answer for why carnivores need so much grass to support them.
At this point, you may want to watch the animation again, so students can see the carbon atoms moving through the pools without pausing to examine their predictions.
Image Credit: Craig Douglas, Michigan State University
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Soil Carbon
Producers

16. Tracing Carbon in an Ecosystem
So, to recap:
Producers are the only organisms that can take up inorganic carbon. This is why there is so much carbon in this pool.
All other organic pools are dependent on the carbon atoms in the Producer pool to carry out their life processes, like eating, growing, defecating, and cellular respiration.
6. Discuss the results.
Show Slides 16 and 17 to recap some of the main points of carbon transfer through an ecosystem.

17. Tracing Carbon in an Ecosystem
Every time organisms do their life processes, carbon atoms are lost from that pool and enter a different carbon pool.
This continual loss of carbon atoms from organic pools is one reason the organic matter pyramid looks the way it does.
6. Discuss the results.
Show Slides 16 and 17 to recap some of the main points of carbon transfer through an ecosystem.