1. Water Cycle-the cycle of processes by which water circulates between the earth's oceans, atmosphere, and land, involving precipitation and returns to the atmosphere by evaporation and transpiration
Evaporation-  substance in a liquid state changing to a gaseous state
Transpiration- process where plants absorb water through the roots and then give off water vapor through pores in their leaves
Precipitation- rain, snow, sleet, or hail that falls to the ground
Runoff- surface water found on land that is eventually carried back to an ocean or lake

2. Carbon Cycle-the series of processes by which carbon compounds are interconverted in the environment Respiration- intake of oxygen and the release of carbon dioxide from the oxidation of complex organic substances Erosion- the process of eroding or being eroded by wind, water, or other natural agents Combustion- when carbon returns to the atmosphere through combustion or burning of fossil fuels Nitrogen Cycle-nitrogen and its compounds are interconverted in the environment and in living organisms

3. Nitrogen fixation- bacteria combine nitrogen from the atmosphere with hydrogen to make ammonia (NH3) in the soil Ammonification- production of ammonia by bacteria during the decay of organic matter Nitrification- production of nitrates and nitrites from ammonia Assimilation- absorption of nitrogen into organic compounds by plants (absorbed through roots). Denitrification- conversion of nitrate to nitrogen gas, which is released back into the atmosphere Phosphorus Cycle- the movement of phosphorus through the