Objective 8: TSWBAT describe the cycling of chemical elements in ecosystems.

Life on earth depends on the recycling of essential chemical elements Atoms present in the complex molecules of an organism at its time of death are returned as simpler compounds to the atmosphere, water, or soil by the actions of decomposers This decomposition replenished the pools of inorganic nutrients that plants and other autotrophs use to build new organic matter These circuits are also called biogeochemical cycles. The cycling of chemical elements in ecosystems

There are two general categories of biogeochemical cycles Carbon, oxygen, sulfur and nitrogen occur in the atmosphere and cycles of these elements is essentially global The carbon and oxygen atoms a plant acquires from the air as CO 2 may have been released into the atmosphere by the respiration of a plant or animal in some distant place. Phosphorus, potassium, calcium and the traces element generally cycle on a more localized scale, at least over the short term Soil is the main abiotic reservoir of these elements and recycled in the same general vicinity usually.

Most nutrients accumulate in four reservoirs, defined by 2 characteristics. Does it contain organic or inorganic material? Are the material directly available for use by organisms? One compartment of organic material is composed of the living organism themselves and detritus These nutrients are available to other organisms when consumers feed and detritivores consume nonliving organic matter

The other organic compartment includes “fossilized” deposits of once-living organisms from which nutrients cannot be assimilated directly In one compartment of inorganic material nutrients are available for use by organisms This would include matter that is dissolved in water or present in soil or air Organisms assimilate these materials and return them through the fairly rapid processes of cellular respiration, excretion and decomposition

In the other compartment of inorganic material, nutrients are not available The nutrients are tied up in rocks Although organisms cannot directly use these, they slowly become available through weathering and erosion. Similarly, the unavailable organic nutrients move into the compartment of available inorganic nutrients through erosion or when fossil fuels are burned

The Water Cycle The Nitrogen Cycle The Phosphorus Cycle The Carbon Cycle

Biogeochemical Cycles