AP Environmental Science: The Nitrogen Cycle

Vocabulary flashcards focusing on key terms, chemical transformations, reservoirs, and human impacts described in the nitrogen cycle lecture.

Sources (Nitrogen Cycle)

Things or processes that release nitrogen into the atmosphere.

Sinks (Nitrogen Cycle)

Reservoirs or processes that take in increasing amounts of nitrogen.

Atmospheric Nitrogen ($N_2$)

The largest reservoir of nitrogen, making up about $78\%$ of the atmosphere in a gaseous form that is not biologically usable by plants or animals.

Nitrogen Fixation

The critical process of converting atmospheric nitrogen gas ($N_2$) into biologically usable forms such as ammonia ($NH_3$) or nitrate ($NO_3$).

Legumes

Plant species such as peas and beans that host nitrogen-fixing bacteria in root nodules in a mutualistic symbiotic relationship.

Synthetic Nitrogen Fixation

An energy-intensive industrial process where humans combust fossil fuels to fix atmospheric nitrogen gas into nitrates ($NO_3$) to manufacture synthetic fertilizers.

Assimilation

The process where plants take up nitrates or ammonia through their roots, and animals consume plants or other animals, incorporating nitrogen into their DNA and proteins.

Ammonification

The process where soil bacteria, microbes, and decomposers convert waste and dead organic biomass back into ammonia ($NH_3$) in the soil.

Nitrification

A multi-step soil process performed by bacteria that converts ammonium ($NH_4$) into nitrite ($NO_2$) and then into nitrate ($NO_3$).

Denitrification

The conversion of soil nitrate ($NO_3$) back into gaseous nitrous oxide ($N_2O$) by soil bacteria, which ultimately breaks down into atmospheric nitrogen gas.

Nitrous Oxide ($N_2O$)

A greenhouse gas produced by soil bacteria during denitrification—especially in waterlogged or tilled agricultural soils—that traps heat in Earth's atmosphere.

Ammonia Volatilization

The process where excess fertilizer leads to ammonia gas entering the atmosphere, causing acid precipitation, human respiratory tract irritation, and lost crop nutrients.

Leaching

The process where rainwater or irrigation water carries excess nitrates directly out of the soil into local bodies of water.