when the water droplets that form clouds become large enough, the water droplets fall to the earth (rain, sleet, snow)

liquid water returns to the atmosphere (vaporizes)

evaporation of water from plants

water vapor in the air condenses to form clouds, in a process called

surface water found on land that is eventually carried back to an ocean or lake. 

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 (NO3). Bacteria are responsible for nitrification. Plants can use nitrates and nitrites to make proteins. 

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.