CO2 accounted for about 80 percent of all greenhouse gas emissions from human activities. Carbon dioxide is naturally present in the atmosphere as part of the Earth's carbon cycle (the natural circulation of carbon among the atmosphere, oceans, soil, plants, and animals). the atmosphere as part of the Earth's carbon cycle (the natural circulation of carbon among the atmosphere, oceans, soil, plants, and animals).
They are naturally present in the atmosphere in the form of carbon dioxide and gaseous oxygen. Because they're always circulating between the soil, the air, and the water, living matter's constantly renewed. Atmospheric oxygen comes mainly from green plants.
The ultimate goal of the ETC is to produce the high-energy molecule adenosine triphosphate (ATP) to catalyze biochemical reactions. The precursors of ATP, adenosine diphosphate (ADP) and inorganic phosphate (Pi) are readily imported into the mitochondrial matrix.
