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Carbon Cycle

Teacher/Instructor Patrick Roisen
Patrick Roisen

M.Ed., Stanford University
Winner of multiple teaching awards

Patrick has been teaching AP Biology for 14 years and is the winner of multiple teaching awards.

The carbon cycle is a cycle where carbon is exchanged throughout the Earth's atmosphere, the terrestrial biosphere, the oceans and sediments. Carbon in living organisms turns to soil when they die, entering the sediment. Then, it might return to the biosphere in the form of a plant growing out of that soil which is eaten by an animal. That animal emits carbon in the form of carbon dioxide as a product of respiration.

The carbon cycle was one of the major ways that materials cycle through the environment and it's one that's directly affecting humans right now if you've paid any attention the news. And there's one that's important for us to understand. So it's how carbon moves to both organisms like you, me, trees, puppy dogs and the environment. So it begins when plants take in carbon dioxide through the process known as photosynthesis and they convert the carbon dioxide using the energy of the sun into organic molecules, such as glucose or whatever. We, animals and the plants themselves and other organisms can release that carbon dioxide by means of respiration which is the burning of organic compounds in our body to release it as CO2. Similarly fires can do that same process only much faster we call it oxidation, by burning organic molecules. As, as you've seen during forest fires or whatever.

Last there's a bunch of geochemical processes that can absorb carbon dioxide such as when fossil fuels are formed over long periods of time and release it such as when heating or cooling of the waters can absorb or release carbon dioxide. Now let's take a closer look at this diagram here, and here we can see a very simple diagram that shows carbon dioxide or carbon from the atmosphere going into trees through photosynthesis it can be released by plants respiring, by other things respiring they're either plants or soil bacteria. Carbon can be absorbed into the ocean and released in the oceans, fossils fuels that were formed over long periods of time could've formed in a geological reservoir that's a storage facility for this particular chemical and it can be released by burning those fuels. So there's lots of ways that carbon dioxide can be cycled.

I kind of like this diagram because it shows you this idea that it's constantly going around. So carbon dioxide in the air can through photosynthesis be taken in and turned into a organic compound, within the soil bacteria and other things in the soil can release that carbon through respiration. The plants can release the carbon as carbon dioxide through respiration, as well as any of the other animals that are consuming the plants. You can have carbon being absorbed by the water, you can also have forest firs releasing the stored up organic compounds as carbon dioxide. So these are some of the ways that carbon can cycled through the environment.