Nephrons
The tubular excretory unit of the vertebrate kidney.
Neritic zone
The shallow regions of the ocean overlying the continental shelves.
Nerve
A ropelike bundle of neuron fibers (axons and dendrites) tightly wrapped in connective
tissue.
Nervechord
Nerve chord is also called a spinal cord; a hollow structure that extends the length of the
animal just above the notochord.
Nerve fiber
A filamentous process extending from the cell body of a neuron and conducting the nerve
impulse; an axon.
Nerve impulse
A rapid, transient, self-propagating change in electric potential across the membrane of an
axon.
Nervous system
All the nerve cells of an animal; the receptor-conductor-effector system; in humans, the
nervous system consists of the central nervous system (brain and spinal cord) and the
peripheral nervous system.
Net primary production
In a community or an ecosystem, the increase in the amount of plant or algal material
between the beginning and end of a specified time period, such as a growing season.
Net primary productivity (NPP)
The gross primary productivity minus the energy used by the producers for cellular
respiration; represents the storage of chemical energy in an ecosystem available to
consumers.
Net productivity
In a trophic level, a community, or an ecosystem, the amount of energy (in calories) stored
in chemical compounds or the increase in biomass (in grams or metric tons) in a particular
period of time; it is the difference between gross productivity and the energy used by the
organisms in respiration.
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