In the nitrogen cycle, nitrogen continually moves in and out of organisms and the atmosphere.
Plants cannot utilize nitrogen in its atmospheric form (N2). All plant life, and ultimately all animal life too, depends on bacteria to convert atmospheric nitrogen into usable forms.
In a process called nitrogen fixation, N2 is converted by bacteria into ammonia (NH3) which plants take up through their roots. The NH3 acts as a fertilizer.
Consumers take in nitrogen through their diet. The nitrogen from plants and animals ultimately returns to the soil in organic matter. Microbes decompose the organic matter, breaking it down and releasing nitrogen in the form of ammonium (NH4).
A small amount of N2 is fixed by lightning, producing nitrate (NO3).
Some of the soil's nitrogen is lost through soil erosion, transferring the nitrogen to streams and rivers, and eventually bringing it to the ocean.
In other steps of the nitrogen cycle, called nitrification and denitrification, various types of bacteria feed on nitrogen compounds in organic matter or the soil, eventually returning it as N2 to the atmosphere, completing the cycle.
Humans play a significant role in the nitrogen cycle. For instance, we manufacture nitrogen fertilizers and apply them to fields. Although nitrogen fertilizers promote plant growth, they also deplete the soil of other nutrients. Also, nitrogen fertilizers can leach out of soils and pollute aquatic ecosystems.
When we burn fossil fuels, we create nitrogen pollution such as smog and acid rain.
Identify the main events of the nitrogen cycle by dragging the terms to their correct locations.