Understandings:

• Autotrophs convert carbon dioxide into carbohydrates and other carbon compounds.
• In aquatic ecosystems carbon is present as dissolved carbon dioxide and hydrogencarbonate ions.
• Carbon dioxide diffuses from the atmosphere or water into autotrophs.
• Carbon dioxide is produced by respiration and diffuses out of organisms into water or the atmosphere.
• Methane is produced from organic matter in anaerobic conditions by methanogenic archaeans and some diffuses into the atmosphere or accumulates in the ground.
• Methane is oxidized to carbon dioxide and water in the atmosphere.
• Peat forms when organic matter is not fully decomposed because of acidic and/or anaerobic conditions in waterlogged soils.
• Partially decomposed organic matter from past geological eras was converted either into coal or into oil and gas that accumulate in porous rocks.
• Carbon dioxide is produced by the combustion of biomass and fossilized organic matter.
• Animals such as reef-building corals and mollusca have hard parts that are composed of calcium carbonate and can become fossilized in limestone.