The Nitrogen Cycle Vocabulary

A collection of vocabulary flashcards keying in on terms, chemical formulas, and biological processes described in the lecture transcript on the nitrogen cycle.

Nutrient cycle

The process by which matter is reused and recycled over and over again between living organisms and the environment.

Nitrogen cycle

The process by which the element nitrogen moves around through ecosystems.

Nitrogen gas ($N_2$)

A form of nitrogen that makes up about 78 percent of the atmosphere, containing a triple bond between nitrogen atoms that makes it difficult to break apart.

Nitrogen fixing bacteria

Bacteria found in the soil and root nodules of legumes that break the triple bond of nitrogen gas to form usable nitrogen compounds.

Legumes

A group of plants that host nitrogen fixing bacteria in their root nodules.

Nitrogen fixation

The process of moving nitrogen from the air to the soil by converting nitrogen gas ($N_2$) into ammonia ($NH_3$) or ammonium ($NH_4^+$).

Ammonia ($NH_3$)

A nitrogen compound produced by nitrogen fixation or ammonification that can be taken up by plants or converted into nitrates.

Ammonium ($NH_4^+$)

The ionized form of ammonia produced during nitrogen fixation when an extra hydrogen atom is added.

Assimilation

The process where plants take up nitrogen compounds, such as ammonia or nitrates, and use them to construct biological molecules like DNA, RNA, and proteins.

Nitrification

The two-step chemical process carried out by nitrifying bacteria that oxidizes ammonia first into nitrite ($NO_2^-$) and then into nitrate ($NO_3^-$).

Nitrifying bacteria

Bacteria in well-aerated soils that add oxygen to ammonia to convert it into nitrite ($NO_2^-$) and subsequently into nitrate ($NO_3^-$).

Nitrite ($NO_2^-$)

An intermediate nitrogen compound produced during nitrification when nitrifying bacteria oxidize ammonia before converting it into nitrate.

Nitrate ($NO_3^-$)

A primary plant fertilizer compound produced during nitrification that can be assimilated by plants or converted back into nitrogen gas by denitrification.

Ammonification

The process in which decomposers break down dead organisms and returned nitrogen back to the soil as ammonia.

Denitrification

The process in low-oxygen environments where denitrifying bacteria convert nitrates ($NO_3^-$) back into atmospheric nitrogen gas ($N_2$).

Denitrifying bacteria

Bacteria that convert nitrates ($NO_3^-$) into nitrogen gas ($N_2$) in waterlogged or low-oxygen soils, reducing soil fertility.