Ulna Elbow.
ultimate causation (factors) Those aspects of behavior
that are concerned with why the behavior evolved and its functional
significance in an ecological context.
ultimate cause The
evolutionary factors responsible for the origin, state of being,
or purpose of a biological system.
ultimobranchial gland In jawed fishes, primitive
tetrapods, and birds, the small gland(s) that forms ventral to
the esophagus; produces the hormone calcitonin that helps regulate
calcium concentrations.
Ultimobranchial The last embryonic gill slit [often a pouch].
ultradian rhythm A cyclical rhythm of less than
24 hours.
ultraplankton phytoplankton with cells between 2 and 5 micrometers in width
ultrastructure Structure of an organism or cell
at the electron microscopic level.
ultraviolet That portion of the sun's total range
of radiation having wavelengths immediately shorter than the shortest
of the visible spectrum (purple); between approximately 380 and
100 nm.
umbel An inflorescence in which the individual
pedicels all arise from the apex of the peduncle.
umbilical cord Cordlike structure that connects
the fetus to the placenta.
umbilical Refers to the
navel, or umbilical cord.
umbo pl. umbones. One of
the prominences on either side of the hinge region in a bivalve
mollusc shell. Also, the "beak" of a brachiopod shell.
Umwelt The sensory and perceptual world of the
animal, dependent upon the types of sensory receptors that it
possesses and the internal nervous system processes for receiving
and interpreting those stimuli.
unconditioned response (UCR) In classical conditioning,
the animal's response that is initially given to the unconditioned
stimulus.
unconditioned stimulus (US) In classical conditioning,
the stimulus that produces what is initially the unconditioned
response.
unconventional air pollutants Toxic or hazardous
substances, such as asbestos, benzene, beryllium, mercury, polychlorinated
biphenyls, and vinyl chloride, not listed in the original Clean
Air Act because they were not released in large quantities; also
called noncriteria pollutants.
unconventional oil Resources such as shale oil
and tar sands that can be liquefied and used like oil.
undernourished Those who receive less than 90 percent
of the minimum dietary intake over a long-term time period;
they lack energy for an active, productive life and are more susceptible
to infectious diseases.
understory That vegetation which characterizes
the lower level of plants in a forest; the vegetation below the
canopy.
undiscovered resources Potential supplies of a
mineral or other useful material believed to exist based on history,
scientific theory, or general knowledge of geology, biology, or
geography of an unexplored area.
undulating membrane Name applied to two quite different
structures in protozoa. In some Mastigophora it is a finlike ridge
across the surface of a cell, with the axoneme of a flagellum
near its surface. In some ciliates it is a line of cilia that
are fused at their bases, usually beating to force food particles
toward the gullet.
undulating ridges Undulatory waves in the surface
of some protozoa, probably aided by subpellicular microtubules;
the means of locomotion in some species.
ungulate Hooved. Noun, any hooved
mammal.
unicellular (cytoplasmic) organization The life-form
in which all functions are carried out within the confines of
a single plasma membrane; members of the kingdom Protista display
unicellular organization; also called cytoplasmic organization.
uniformitarianism Methodological assumptions that
the laws of chemistry and physics have remained constant throughout
the history of the earth, and that past geological events occurred
by processes that can be observed today.
Uniramia The subphylum of arthropods whose members
are characterized by a head with one pair of antennae and one
pair of mandibles. All appendages are uniramous.
uniramous appendage Arthropod appendage that is
unbranched, characteristic of living arthropods other than Crustacea,
although some crustacean appendages are uniramous.
unisexual The condition of having either stamens
or pistil, not both; an imperfect flower.
unit membrane The transmission electron microscopic
interpretation of a biological membrane, consisting of two electron-dense
lines separated by a translucent space.
universal veil A membrane that totally encloses
some young mushrooms; after it breaks, its remnants appear as
a volva at the base and scales on the cap.
universalists Those who believe that some fundamental
ethical principles are universal and unchanging. In this vision,
these principles are valid regardless of the context or situation.
unsaturated fat A fat containing one or more double
bonds between carbon atoms.
upwelling Convection currents within a body of
water that carry nutrients from bottom sediments toward the surface.
uracil A nitrogen base found in RNA.
urban Peculiar to the human environment, as contrasted
with that found normally around wild animals.
urban area An area in which a majority of the people
are not directly dependent on natural resource-based occupations.
urbanization An increasing concentration of the
population in cities and a transformation of land use to an urban
pattern of organization.
urban renewal Programs to revitalize old, blighted
sections of inner cities.
urea A nitrogen-containing waste product excreted
in the urine of many vertebrates
uredium (pl. uredia)The structure that produces
uredospores in rust fungi; sometimes called a uredinium.
uredospore A reddish, binucleate spore formed by
rust fungi; often forms the repeating stage of the rust; also
called a urediniospore.
ureotelic excretion Having urea as the chief excretory
product of nitrogen metabolism; occurs in mammals.
ureter The tube which conveys urine from the kidney
to the bladder.
urethra The tube from
the urinary bladder to the exterior in both sexes.
uric acid the main nitrogenous excretory product
in birds, reptiles, some invertebrates, and insects
uricotelic excretion Having uric acid as the chief
excretory product of nitrogen metabolism; occurs in reptiles and
birds.
urinary bladder The storage organ for urine.
urn Region near the center of an infusoriform larva
of a dicyemid mesozoan.
Urochordata The subphylum of chordates whose members
have all four chordate characteristics as larvae. Adults are sessile
or planktonic and enclosed in tunic that usually contains cellulose.
Sea squirts or tunicates.
urogenital opening The common opening for urine
and gametes in bony fishes and other animals.
urophysis A discrete structure in the spinal cord
of the fish tail that produces neuropeptides that help control
water and ion balance, blood pressure, and smooth muscle contractions.
586
uropod
Posteriormost appendage of many crustaceans.
uropolar cells Somatoderm cells at the posterior
end of the trunk of a dicyemid mesozoan.
urosome Portion of the body posterior to the major
point of body flexion in many copepods; usually includes one or
more free thoracic segments and abdomen.
urstigmata Sense organs between the coxae of the
first and second pairs of legs on some mites. Apparently they
are humidity receptors. Also called Claparedé organs.
uterine bell Structure in female acanthocephalans
that allows fully developed, shelled embryos to pass out of the
body and that retains undeveloped ones.
uterine tube The tube that leads from the ovary
to the uterus; also called fallopian tube.
uterus (womb)The portion of female mammals' reproductive tract in which the embryo develops.
utilitarian conservation A philosophy that resources
should be used for the greatest good for the greatest number for
the longest time.
utilitarianism See utilitarian conservation.
utricle That part of
the inner ear containing the receptors for dynamic body balance;
the semicircular canals lead from and to the utricle.
Utriculus A bottle.