540 to 610 Fossil Fuel Deposits 4000 Ecosystems gain most of their carbon dioxide from the atmosphere . A number of autotrophic organisms have specialized mechanisms that allow for absorption of this gas into their cells. With the addition of water and energy from solar radiation , these organisms use photosynthesis to chemically convert the carbon dioxide to carbon-based sugar molecules. These molecules can then be chemically modified by these organisms through the metabolic addition of other elements to produce more complex compounds like proteins , cellulose , and amino acids . Some of the organic matter produced in plants is passed down to heterotrophic animals through consumption.
Carbon dioxide enters the waters of the ocean by simple diffusion .
This substance is used to produce shells and other body parts by organisms such as coral, clams, oysters, some protozoa, and some algae. When these organisms die, their shells and body parts sink to the ocean floor where they accumulate as carbonate-rich deposits. After long periods of time, these deposits are physically and chemically altered into sedimentary rocks . Carbon is released from ecosystems as carbon dioxide gas by the process of respiration . Respiration takes place in both plants and animals and involves the breakdown of carbon-based organic molecules into carbon dioxide gas and some other compound by products.