Why is the cycling of matter essential to the continuance of life?

Biogeochemical cycles move matter from one organism to another and from living organisms to the abiotic environment and back again. The cycles of matter- carbon, nitrogen, phosphorus, sulfur and hydrologic- involve biological, geologic and chemical interactions. These five cycles are particularly important to organisms, because these materials make up the chemical compounds of cells.

Explanation: In the carbon cycle organisms fix, or incorporate, carbon from the atmosphere into chemical compounds through photosynthesis. Organisms also release carbon during cellular respiration. Other biological molecules that are not released during cellular respiration can be stored as fossil fuels for millions of years. Aquatic organisms incorporate Ca2+ and HCO3-  into their shells. When these organisms die, their shells sink to the ocean floor and become part of the sedimentary rock layer. The CO2 in these rock layers will later be released due to weathering or subduction. Atmospheric nitrogen is very stable and must be broken apart in order to combine with other elements. Bacteria are exclusively involved in all five steps of the nitrogen cycle, except assimilation. Nitrogen-fixing bacteria carry out biological nitrogen fixation in soil and aquatic environments. Soil bacteria perform nitrification, a two step process. First soil bacteria convert ammonia or ammonia to nitrite. Then other soil bacteria oxidize nitrite to nitrate. The process of nitrification furnishes these bacteria with energy. Ammonification begins when organisms produce nitrogen-containing waste products such as urea and uric acid. These substances, as well as the nitrogen compounds that occur in dead organisms, are decomposed, releasing nitrogen into the abiotic environment. Finally, denitrifying bacteria reverse the action of nitrogen-fixing and nitrifying bacteria by returning nitrogen to the atmosphere.

In the phosphorus cycle, plants roots absorb inorganic phosphates. Animals obtain most of their required phosphate from the foods they eat. Phosphorus is then released back into the soil when organisms die and decompose. In aquatic environments, phosphorus is

absorbed and assimilated by algae and plants, which are then consumed by plankton and larger organisms. A small portion of phosphate in the aquatic food web finds its way back to the land in the manure of sea birds.

A tiny fraction of the global sulfur is present in living organisms. Plant roots absorb sulfate and assimilate it by incorporating the sulfur into plant proteins. Animals assimilate sulfur when they consume plant proteins and convert them to animal proteins. Sulfur is returned to the atmosphere by bacteria which converts sulfates to hydrogen sulfide gas.