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Term Term description

A reduced form of nicotinamide adenine dinucleotide phosphate (NADP - a coenzyme occurring in most living cells), used in a number of reductive synthesis such as fatty acids and steroids.

native elements

Some 20 elements occur in nature in a pure (i.e., uncombined) or nearly pure form. They are partitioned into three families: metals, semimetals, and nonmetals. Examples include gold, carbon, aluminum, lead, tin, and zinc.

natural resources

Something, such as a forest, a mineral deposit, or fresh water, that is found in nature and is necessary or useful to humans.

natural selection

The mechanism for evolutionary change in which environmental pressures cause certain genetic combinations in a population to become more abundant; genetic combinations best adapted for present environmental conditions tend to be selected for, and non-adaptive traits are selected against.

natural world

The world and its naturally occurring phenomena, together with all of the physical laws that govern them. 


A person who studies and appreciates nature.


The phenomena of the physical world collectively, including plants, animals, the landscape, and other features and products of the earth.


A large cloud of particles and gases in space that is visible either as a hazy patch of light (either an emission or a reflection nebula) or an irregular dark region against a brighter background (dark nebula).


Hebrew term meaning 'living being'; commonly rendered as 'soul' in English translations.


Any of several slender cylindrical worms, usually of tiny size, that live in great numbers in water, soil, plants, and animals. They have a simple structure, with a long hollow gut separated from the body wall by a fluid-filled space. Several nematodes are parasites on animals and humans and cause disease.


Any of a class of synthetic compounds having a chemical structure similar to that of nicotine and related alkaloids, used as systemic insecticides on plants and as topical or systemic insecticides on animals.


The functional position or role of an organism in its ecosystem.

night soil

The term used for human excrement removed at night from sewage tanks and used as fertilizer.


A compound containing the group NO3. Nitrates dissolve extremely easily in water and are an important component of the nitrogen cycle. They are easily used by plants and algae.


The oxidation of an ammonia (NH3) compound into nitric acid (HNO3), nitrous acid (HNO2), or any nitrate (NO3-) or nitrite (NO2-), usually through the action of bacteria.

nitrifying bacteria

Bacteria that change ammonium (NH3) compounds into nitrites (NO2) or change nitrites into nitrates (NO3) as part of the nitrogen cycle.


A compound containing the group NO2. Nitrites are an important component of the nitrogen cycle and are used as food preservatives.


A nonmetallic element that makes up about 78 percent of the atmosphere by volume, occurring as a colorless, odorless N2 gas. It is a component of all plant and animal proteins, making it essential for life.

nitrogen cycle

The continuous process by which nitrogen is exchanged between organisms and the environment. Some of the atmosphere's free nitrogen combines with other elements to form compounds that are deposited in the soil. These are then converted by bacteria, in a process called nitrification, into nutrients that are absorbed by the roots of green plants. Nitrogen is then passed into the food chain and returned to the soil by the metabolism and decay of plants and animals.

nitrogen cycle

Cyclic movement of nitrogen in different chemical forms from the environment to organisms and then back to the environment.

nitrogen fixation

The process by which nitrogen in the atmosphere is converted into ammonium.

nitrogen fixers

Microorganisms involved in the process of converting relatively inert atmospheric nitrogen (N2) into biologically available forms, ammonia (NH3) or nitrous oxide (NO2).


An enzyme complex that catalyzes the reduction of molecular nitrogen in the nitrogen-fixation process of bacteria.

nitrous oxide

A potent greenhouse gas. In 2012, nitrous oxide (N2O) accounted for about 6% of all U.S. greenhouse gas emissions from human activities. Activities such as agriculture, fossil fuel combustion, wastewater management, and industrial processes are increasing the amount of N2O in the atmosphere.


A swelling on a root of a leguminous plant, containing nitrogen-fixing bacteria.

nomadic lifestyle

A nomadic lifestyle is one of wandering. A nomad is a person with no fixed home who moves according to the seasons from place to place in search of food, water, and grazing land.


A substance that cannot be decomposed to a harmless natural state by the action of bacteria, and may therefore damage the environment.

nonrenewable energy

Energy that comes from sources that will run out or will not be replenished in our lifetimes—or even in many, many lifetimes. Most non-renewable energy sources are fossil fuels: coal, petroleum, and natural gas.

Northwestern Glacier

A glacier found at the head of Northwestern Fjord in Kenai Fjords National Park in Alaska which has been steadily receding over the past century.

notrogen fixers

Microorganisms involved in the process of converting relatively inert atmospheric nitrogen (N2) into biologically available forms, ammonia (NH3) or nitrous oxide (NO2).

nuclear energy

The energy released during a nuclear reaction, a process in which the structure and energy content of an atomic nucleus are changed by interaction with another nucleus or particle.

nuclear fission

The splitting of an atomic nucleus into approximately equal parts, either spontaneously or as a result of the impact of a particle usually with an associated release of energy. Sometimes shortened to: fission

nuclear fusion

A reaction in which two nuclei combine to form a nucleus with the release of energy. Sometimes shortened to: fusion.

nuclear power

Power, especially electricity, the source of which is nuclear fission and produced by a nuclear reactor.

nucleic acids

Large organic molecules made of nucleotides that contribute to DNA and that function in the transmission of hereditary traits, in protein synthesis, and in control of cellular activities.


A chemical component in foods required by organisms to survive and grow. Macronutrients (proteins, carbohydrates and lipids) provide the bulk energy an organism's metabolic system needs to function while micronutrients (including C, H, P, K, N, S, Ca, Fe, Mg) provide the necessary cofactors for metabolism and building blocks for macronutrient synthesis.

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