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Nanometer: A unit of measurement that is equal to 1*10^-9 meters, or 0.000000001 meters.

Neutron: In chemistry, the part of the atomic nucleus that provides mass, but has no charge. Compare with electron and proton.

Nitrogenous: A substance that contains nitrogen.

Nitrogenous base: A nitrogenous molecule that has the same chemical properties as a base.

Node: In plants, a joint in the stem where one or more leaves can grow.

Nucleoid: A region in the bacterial cell where the chromosomes are kept, but not in a membrane, and generally not very distinct from other parts of the bacterium.

Nucleoside: A molecule composed of either a purine or a pyrimidine that is bound to a sugar with five carbon atoms.

Nucleotide: An organic compound made up of a nitrogenous base (adenine, cytosine, guanine and thyminein DNA, adenine, cytosine, guanine and uracil in RNA), a sugar (deoxyribose in DNA and ribose in RNA) and a phosphate group. Nucleotides form the basic physical structure of both DNA and RNA.

Nucleus: In biology, its the organelle that houses the DNA and keeps it distinct from the rest of the eukaryotic cell. In chemistry, it is the center of an atom, which contains at least one proton, and in elements other than hydrogen, at least one neutron.

Nutrient: Any substance taken from its environment and used for a metabolic reaction.