APES Vocab Unit 1- Section: Cycles

The Carbon Cycle

The process through which carbon compounds are moved throughout the environment, involves various processes such as photosynthesis, decomposition, respiration, and combustion.

The Nitrogen Cycle

The nitrogen cycle is the movement of atoms and molecules that contain the element nitrogen between sources and sinks. The reservoirs that hold the nitrogen compounds hold them for relatively short periods of time and the atmosphere is the main reservoir of nitrogen as around 78% of the air on earth is nitrogen. There are 5 relative steps in the nitrogen cycle. First, there is nitrogen fixation, the phase when gaseous nitrogen (N2) is converted to ammonia (NH3 or NH4+) via biological fixation due to bacteria such as cyanobacteria. Next, there's nitrification, where NH3 or NH4+ is converted into NO3- via bacteria. Then assimilation occurs, as organisms incorporate NO3- or ammonia formed versions, plants take it in by their roots and animals take it in via plants. Denitrification is the reduction of NO3- to gaseous N2 by anaerobic bacteria. This process only occurs when there is little to no oxygen such as deep in the soil near the wettable. Finally, there is ammonification, when organically bound nitrogen plants and animals are recycled after their death.

The Phosphorus Cycle

The process of how phosphorus moves through the earth's systems, primarily through rocks, soil, water, and living organisms, without a significant atmospheric component. Typically the limiting factor in an environment

The Hydrologic Cycle

is the continuous movement of water within the Earth and atmosphere, involving processes such as evaporation, sublimation, condensation, precipitation, transpiration, runoff, and infiltration.