Nitrogen Cycle

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Nitrogen Noun

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[ny-truh-jen]

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Nitrogen

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A chemical element essential for all living things, serving as a fundamental component for building proteins and DNA molecules.

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Example: This diagram shows the nitrogen cycle: bacteria fix nitrogen in the soil, plants absorb it, and decomposers return it to the soil after organisms die.

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Protein Noun

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[proh-teen]

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Protein

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Large, complex molecules made from amino acids that are essential for cell structure, function, and various biological processes.

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Example: This diagram shows that proteins are large molecules made by linking many smaller units, called amino acids, together into a long chain.

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DNA Noun

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[dee-en-ey]

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DNA

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Deoxyribonucleic acid, the molecule carrying genetic instructions for the development, functioning, growth, and reproduction of all known organisms.

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Example: This image shows that DNA is built from units called nucleotides, which contain a phosphate, a sugar, and a nitrogenous base, linking DNA to the nitrogen cycle.

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Amino Acid Noun

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[uh-mee-noh as-id]

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Amino Acid

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Organic compounds containing both carboxyl and amino functional groups, which serve as the fundamental molecular building blocks of proteins.

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Example: This diagram shows a protein breaking down into its building blocks, which are amino acids, releasing them to be recycled in the nitrogen cycle.

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Nitrate Noun

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[ny-treyt]

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Nitrate

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A water-soluble, nitrogen-containing compound that is readily absorbed by plants and is essential for synthesizing proteins and other molecules.

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Example: This image shows a model of a nitrate molecule, which is made of one nitrogen atom (N) and three oxygen atoms (O).

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Atmospheric Nitrogen Noun

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[at-muh-sfer-ik ny-truh-jen]

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Atmospheric Nitrogen

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The gaseous form of nitrogen (N2) that constitutes about 80% of Earth's atmosphere but is unusable by most organisms.

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Example: This diagram shows that Earth's atmosphere is mostly (78%) nitrogen gas, which is the largest reservoir of nitrogen for the nitrogen cycle.

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Nitrogen Fixation Noun

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[ny-truh-jen fik-sey-shuhn]

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Nitrogen Fixation

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The chemical process by which atmospheric nitrogen is converted into ammonia or other molecules available to living organisms for use.

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Example: This image shows root nodules on a legume plant, which house special bacteria that perform nitrogen fixation by converting atmospheric nitrogen into a usable form.

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Denitrification Noun

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[dee-ny-truh-fi-key-shuhn]

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Denitrification

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A microbial process where nitrate is reduced and ultimately produces molecular nitrogen (N2), returning it to the atmosphere.

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Example: This diagram shows denitrification as the process where bacteria convert nitrates (NO3-) in the soil back into nitrogen gas (N2), which returns to the atmosphere.

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Runoff Noun

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[ruhn-of]

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Runoff

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The flow of water over land that occurs when excess rainwater cannot be absorbed, often transporting pollutants into waterways.

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Example: This diagram shows how water carries nutrients from farm fertilizers, manure, and livestock waste off the land and into a river, a process called runoff.

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Algal Bloom Noun

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[al-guhl bloom]

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Algal Bloom

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A rapid increase or accumulation in the population of algae in freshwater or marine water systems, often due to nutrient enrichment.

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Example: Excess nutrients, like nitrogen, in water from sources like fertilizer runoff can cause a rapid, dense growth of algae called an algal bloom.