The Carbon Cycle: All living things are composed of organic molecules, which are carbon based compounds. Therefore, the carbon cycle is extremely important. The exchange pool for carbon is the atmosphere where the carbon resides in the form of carbon dioxide. Carbon enters the biotic community through the process of photosynthesis in which CO2 is removed from the air and used to make carbohydrates. Carbon moves through trophic levels and at every level respiration releases CO2 into the atmosphere. The burning of fossil fuels has significantly increased the amount of CO2 in the atmosphere.