Neutral variation
Genetic diversity that confers no apparent selective advantage.
Neutron
An electrically neutral particle (a particle having no electrical charge), found in the atom.
Niche
The position or function of an organism in a community of plants and animals.
Nematocyst
A capsule within specialized cells of certain coelenterates, such as jellyfish, containing a
barbed, threadlike tube that delivers a paralyzing sting when propelled into attackers and
prey. Also called stining cell.
Nictitating membrane
A protective fold of skin in the eyes of reptiles and birds and some mammals
Nitrification
The oxidation of ammonia or ammonium to nitrites and nitrates, as by nitrifying bacteria.
Nitrogen cycle
Worldwide circulation and reutilization of nitrogen atoms, chiefly due to metabolic
processes of living organisms; plants take up inorganic nitrogen and convert it into organic
compounds (chiefly proteins), which are assimilated into the bodies of one or more animals;
bacterial and fungal action on nitrogenous waste products and dead organisms return
nitrogen atoms to the inorganic state.
Nitrogen fixation
The assimilation of atmospheric nitrogen by certain prokaryotes into nitrogenous
compounds that can be directly used by plants.
Nitrogenase
An enzyme, unique to certain prokaryotes, that reduces N 2 to NH 3.
Nitrogenous base
An organic base that contains the element nitrogen.
Nitrogenous compounds
Nitrogen a chemical element, at no.7. it forms about 78 percent of the atmosphere and is a
constituent of all proteins and nucleic acids.
Nocturnal
Applied to organisms that are active during the hours of darkness.
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