Combustion occurs when any organic material is reacted (burned) in
the presence of oxygen to give off the products of carbon dioxide and water
and ENERGY. The organic material can be any fossil fuel such as natural
gas (methane), oil, or coal. Other organic materials that combust are wood,
paper, plastics, and cloth. Organic materials contain at least carbon and
hydrogen and may include oxygen. If other elements are present they also
ultimately combine with oxygen to form a variety of pollutant molecules
such as sulfur oxides and nitrogen oxides.
Metabolism occurs in animals and humans after the ingestion of organic
plant or animal foods. In the cells a series of complex reactions occurs
with oxygen to convert for example glucose sugar into the products of carbon
dioxide and water and ENERGY. This reaction is also carried out by bacteria
in the decomposition/decay of waste materials on land and in the water.
An important summary statement is that during combustion/metabolism
oxygen is used and carbon
dioxide is a product. The whole
purpose of both processes is to convert chemical energy into other forms
of energy such as heat.
