8th Grade Science Study Notes: The Nitrogen Cycle

Vocabulary flashcards covering key terms, chemical compounds, and processes involved in the Nitrogen Cycle.

Nitrogen Cycle

The constant movement of nitrogen between living (biotic) and non-living (abiotic) parts of an ecosystem.

Atmospheric Nitrogen ($N_2$)

Nitrogen gas that makes up $78\text{\%}$ of the air around us, which plants and animals cannot absorb or use directly from the air.

Nitrate ($NO_3$)

A compound formed in the soil during nitrification or directly from lightning fixation carried down by precipitation; it is the specific nitrogen compound assimilated by plants to create protein needed to live, grow, and build tissue.

Ammonia ($NH_3$)

A compound produced by nitrogen-fixing bacteria in soil/roots, by lightning fixation, or when decomposers break down waste and dead matter.

Nitrite ($NO_2$)

A compound formed in the soil during nitrification when bacteria convert ammonia ($NH_3$) into nitrites ($NO_2$).

Order of Nitrogen through the Cycle

Air $\rightarrow$ Bacteria $\rightarrow$ Plants $\rightarrow$ Animals.

Human Nitrogen Acquisition

The process by which humans get nitrogen by eating meat and vegetables, as it cannot be obtained by breathing it in.

Nitrogen Fixation

The process of combining atmospheric nitrogen gas ($N_2$) with other elements to turn it into usable compounds, performed by bacteria in soil and root nodules of legumes (like beans/peas) as well as lightning.

Nitrification

The process occurring in the soil of converting ammonia ($NH_3$) into nitrites ($NO_2$) and then into nitrates ($NO_3$).

Assimilation

The process of how plants take in and absorb nitrogen compounds (nitrates) from the soil through their roots.

Decomposition (Ammonification)

Part of the decaying process where dead organisms and animal wastes are broken down by bacteria and fungi, turning nitrogen back into ammonia ($NH_3$).

Denitrification

The process where extra nitrogen in the soil is converted back into nitrogen gas ($N_2$) and released back into the air, carried out by soil bacteria.