1. Ecology: Chapter 2.2
The Carbon Cycle

2. Framing Questions What is photosynthesis? What is the equation for it?
What is cellular respiration? What is the equation for it?
What role does carbon play in these two processes?
Explain the carbon cycle
What happened during the Carboniferous Period? How does this affect us today?

3. Photosynthesis
Recall that we discussed plants capturing energy from the sun and passing it along food chains. How do they do this?
Plants use the sun’s light to make carbohydrates in the process of photosynthesis
6CO H energy -> C6H12O6 + 6O6
Carbon water Sun carbohydrates oxygen
dioxide

4. Photosynthesis, Continued…
So why are we talking about photosynthesis if this lesson is about the carbon cycle?
Photosynthesis is one of the stages in the carbon cycle.
Plants “capture” carbon from the atmosphere in the form of carbon dioxide and combine it with water to make carbohydrates
Plants then use these carbs to make other carbon compounds such as fats and proteins (food/energy to be used and passed on)
Consumers eat the plants (or eat organisms that have eaten plants), gain the carbon compounds, and break them down to build tissue… carbon is an important part of the structure of all living things!

5. The Story So Far…
So, if plants use carbon to create food energy, and consumers use the carbon food energy from plants to live, then why isn’t this gas eventually all used up?
Only 0.03% of the Earth’s atmosphere is carbon dioxide
There must be another process that returns this carbon to the atmosphere to complete the cycle.
Well, we said that the energy consumers gain is partially used up to do things like grow, reproduce and move… and during these processes, the organism’s cells are respirating.

6. Cellular Respiration 6O6 + C6H12O6 -> 6CO2 + 6H20 + energy
What does that mean?
Cells need oxygen and carbohydrates to work, and when they get these, they use them to do the tasks required for daily life.
As they do, they break down the oxygen and carbohydrates and give off waste that looks like this:
6O6 + C6H12O6 -> 6CO2 + 6H20 + energy
oxygen carbohydrates carbon water Sun
dioxide
Look familiar?

7. Let’s Compare: Photosynthesis:
6CO H energy -> C6H12O6 + 6O6
carbon water Sun carbohydrates oxygen
dioxide
Cellular Respiration:
6O6 + C6H12O6 -> 6CO2 + 6H20 + energy
oxygen carbohydrates carbon water dioxide
These make up the two halves of the carbon cycle!

8. The Carbon Cycle in a Nutshell
In the carbon cycle, carbon and oxygen move back and forth between living things (biotic) and their environment (abiotic)
Photosynthesis captures carbon from the air and uses it to make food energy for animals
Animals eat plants and use the food energy to live. Their cells respirate as they carry out their life processes
Cellular respiration breaks apart carbohydrate molecules in cells and releases the carbon
This carbon is returned to surrounding air or water and can be used again for photosynthesis
Decomposers break down dead organisms and waste from animals and absorb the carbon from the cells or waste. They return it back to the environment through cellular respiration
Remember: only producers carry out photosynthesis, but all organisms, including producers, carry out cellular respiration… it is necessary to live!

9. The Carbon Cycle in Aquatic Systems
The worlds oceans and lakes contain up to 50 times the amount of carbon than the atmosphere
Carbon dissolves on the surface of water to form carbonic acid, which is used by water plants for photosynthesis
Shells of underwater creatures use carbon (calcium carbonate – carbon, calcium and oxygen)
When these organisms die, their shells fall to the ocean floor, and harden into sedimentary rock.
Carbon is eventually released back into the system

10. Disrupting the Carbon Cycle
Oh, these cycles are just so delicate, aren’t they?!
Usually, the amount of CO2 produced through cellular respiration equals the amount absorbed for photosynthesis
Thus, the amount of carbon dioxide in the atmosphere has remained fairly constant
When too much carbon is released into the atmosphere, or too little is available, the balance changes.
What do you think happens?

11. The Carboniferous Period
300 million years ago, swamps became filled with decaying plant matter
This was buried under thick sediment and with the absence of O2 , decomposers could not break down the material
This caused large amounts of carbon to be locked in the ground
Over millions of years, this plant matter and carbon compressed, and converted to coal and oil (fossil fuels)
Now that we’re using all of these fossil fuels today, what do you think could happen to the cycle?