Carbon Cycle

Note: As you begin here, you should add information to the notes page that you started back in the water cycle and add them to your Travel Log notes page.

Carbon is essential to the biotic world. Carbon (chemical symbol C) is the most abundant element in living things. In the environment, carbon is found in many forms. One of the most common and most important forms is carbon dioxide gas (CO₂). This gas makes up about 3 – 4% of the atmosphere (air), and it is found dissolved in the waters of oceans. In addition, carbon is a major component in energy supplying nutrients called carbohydrates. When an animal eats a plant, they get the energy stored in the plant as carbohydrates.

Take a look at this diagram. This cycle is a bit more complex than the water cycle, but no less important. There are two major pathways for carbon coming from the air to the land and sea.

Start with the carbon dioxide in the air; follow it through the sea pathway.
Then comeback and follow it through the land pathway.

Notice that there are three main ways that carbon, in the form of carbon dioxide, is returned to the air:

respiration in plants and animals
decomposition of dead organisms
burning of wood and fossil fuels (coal, gasoline, oil, and natural gas)

All of these pathways, except the burning of fossil fuels, is natural. As you’ll see later, burning fossil fuels adds additional carbon dioxide to the atmosphere, and this extra carbon dioxide is causing problems.

But for now, that’s the cycle.

Take a few minutes and explore this carbon cycle interactivity. You may want to get the Notes Page you used for the water cycle and add information about the sources and pathways of carbon in the environment.

EPA Carbon Cycle

Before we leave the topic of the carbon cycle, there is one more thing on this part of the trail that you should understand.

The role of living things in both the water and carbon cycle can’t be over stressed. So we want you to see how two very important biological processes play a part in each of these cycles. You will study these two processes in depth later, but for now we want you to see that they are “complimentary” processes; that is, the products of one process are used in the other process.

First, photosynthesis - Producers (plants) take in light energy from the sun, water from the ground, and carbon dioxide from the air and make the carbon rich food (carbohydrates) that consumers eat.
Next, cellular respiration - Organisms here on land and in water give off carbon dioxide as their bodies process and use the energy in the carbon rich food.

Remember the glass experiment? When you exhaled, the water vapor in your breath condensed on the glass and formed the frost. That water was the product of cellular respiration! See, even humans play a role in the carbon cycle. Check this out in the diagram below:

Do you see the cycle here? A very important one too; the producers bring the energy into the ecosystem and they also produce oxygen. Without producers what might happen?

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