O antigens
(Boivin antigens) The heat-stable,
alcohol-resistant lipopolysaccharide–protein somatic antigens of Gram-negative bacteria
(particularly members of the Enterobacteriaceae); O antigens are important in
the serological characterization of enterobacteria. Antigenic specificity is
determined by the polysaccharide O-specific chains.O antigens may be modified
e.g. by bacteriophage conversion or by mutation (e.g. in salmonellae a mutation
may give rise to T1 side-chains, consisting of ribose and galactose residues,
instead of normal O-specific chains.
O side chain
see lipopolysaccharide.
O-specific chain
see
lipopolysaccharide.
O-type starter
see lactic acid starters.
O1 strains (of Vibrio
cholerae)
seevibrio.
O/129
2,4-Diamino-6,7-diisopropylpteridine: a
water-soluble agent bacteriostatic for
e.g. many members of the Vibrionaceae (e.g. most Vibrio strains).
Sensitivity to O/129 may be determined using O/129-impregnated discs on
nutrient agar containing 0.5% w/v NaCl. Some strains of Vibrio cholerae produce
a trimethoprimresistant dihydrofolate reductase (DHFR) and are resistant to both
trimethoprim and O/129; the gene encoding the DHFR may be borne on a plasmid or
on a transposon.
O139 Bengal (Vibrio cholerae)
See cholera.
oak butt rot
See BUTT ROT.
oak-moss
Evernia prunastri.
oak wilt
A disease of oak trees (Quercus spp)
caused by Ceratocystis fagacearum. Infection occurs via wounds (made e.g.
by man or woodpeckers). The fungus forms pressure cushions (sclerotia)
between the infected xylem and phloem, bursting open the overlying bark and
allowing entry of insects, particularly sap-feeding beetles of the Nitidulidae,
which act as vectors of the disease.
Oakley–Fulthorpe test
see double diffusion.
oar weed
Any species of Laminaria
which has an oar-shaped thallus, e.g. L. digitata and L.
hyperborea.
Oat diseases
See CEREAL DISEASES.
Oat mosaic virus
see potyviruses.
Oat necrotic mottle
virus
see potyviruses.
Oat sterile dwarf
virus
see fijivirus.
Oat Striate Virus
see rhabdoviridae.
obligate
aerobe
(ob-lig-it air-obe)
An organism that requires oxygen for cellular respiration and cannot live without it.
An organism that requires oxygen for cellular respiration and cannot live without it.
obligate
anaerobe
(an-ur-obe)
An organism that cannot use oxygen and is poisoned by it.
An organism that cannot use oxygen and is poisoned by it.
oceanic
zone
The
region of water lying over deep areas beyond the continental shelf.
oligotrophic
lake
A
nutrient-poor, clear, deep lake with minimum phytoplankton.
omnivore
[L. omnis, all
+ vorare, to devour]
A heterotrophic animal that consumes both meat and plant material.
A heterotrophic animal that consumes both meat and plant material.
oncogene
(on-koh-jeen)
[Gk. onkos, tumor + genos, birth, race]
A gene found in viruses or as part of the normal genome that is involved in triggering cancerous characteristics.
A gene found in viruses or as part of the normal genome that is involved in triggering cancerous characteristics.
ontogeny
(on-toj-en-ee)
The embryonic development of an organism.
The embryonic development of an organism.
oocyte
(o-uh-sight)
[Gk. oion, egg + kytos, vessel]
A cell that gives rise by meiosis to an ovum.
A cell that gives rise by meiosis to an ovum.
oogamy
(oh-og-um-ee)
A condition in which male and female gametes differ, such that a small, flagellated sperm fertilizes a large, nonmotile egg.
A condition in which male and female gametes differ, such that a small, flagellated sperm fertilizes a large, nonmotile egg.
oogenesis
(oo-oh-jen-eh-sis)
The process in the ovary that results in the production of female gametes.
The process in the ovary that results in the production of female gametes.
open
circulatory system
An
arrangement of internal transport in which blood bathes the organs directly and
there is no distinction between blood and interstitial fluid.
operant
conditioning
A type of
associative learning that directly affects behavior in a natural context; also
called trial-and-error learning.
operator
A segment
of DNA that interacts with a repressor protein to regulate the transcription of
the structural genes of an operon.
operon
(op-ur-on)
[L. opus, operis, work]
A unit of genetic function common in bacteria and phages, consisting of coordinately regulated clusters of genes with related functions.
A unit of genetic function common in bacteria and phages, consisting of coordinately regulated clusters of genes with related functions.
opportunistic
species
Species
characterized by high reproduction rates, rapid development, early
reproduction, small body size, and uncertain adult survival.
opsonization
An immune
response in which the binding of antibodies to the surface of a microbe
facilitates phagocytosis of the microbe by a
macrophage.
orbital
[L. orbis, circle,
disk]
In the current model of atomic structure, the volume of space surrounding the atomic nucleus in which an electron will be found 90 percent of the time.
In the current model of atomic structure, the volume of space surrounding the atomic nucleus in which an electron will be found 90 percent of the time.
order
A
taxonomic grouping of related, similar families; the category below class and
above family.
organ
[Gk. organon, tool]
A specialized center of body function composed of several different types of tissues.
A specialized center of body function composed of several different types of tissues.
organ-identity
gene
A plant
gene in which a mutation causes a floral organ to develop in the wrong
location.
organ of
Corti
The
actual hearing organ of the vertebrate ear, located in the floor of the
cochlear canal in the inner ear; contains the receptor cells (hair cells) of
the ear.
organelle
(or-guh-nel)
[Gk. organon, instrument, tool]
One of several formed bodies with a specialized function, suspended in the cytoplasm and found in eukaryotic cells.
One of several formed bodies with a specialized function, suspended in the cytoplasm and found in eukaryotic cells.
organic
[Gk. organon, instrument,
tool]
Pertaining to (1) organisms or living things generally, or (2) compounds formed by living organisms, or (3) the chemistry of compounds containing carbon.
Pertaining to (1) organisms or living things generally, or (2) compounds formed by living organisms, or (3) the chemistry of compounds containing carbon.
organic
chemistry
The study
of carbon compounds (organic compounds).
organic
compound
A
chemical comound containing the element carbon and usually synthesized by
cells.
organism
An
individual living thing, such as a bacterium, fungus, protist, plant or animal.
organogenesis
(or-gan-oh-jen-eh-sis)
[Gk. organon, instrument, tool + genos, origin,
descent]
An early period of rapid embryonic development in which the organs take form from the primary germ layers.
An early period of rapid embryonic development in which the organs take form from the primary germ layers.
orgasm
Rhythmic,
involuntary contractions of certain reproductive structures in both sexes
during the human sexual response cycle.
origin of
replication
A
specific sequence of bases in a nucleic acid molecule to which the enzymes
responsible for replicating the nucleic acid bind to initiate the copying
process.
osmoconformer
An animal
that does not actively adjust its internal osmolarity because it is isotonic
with its environment.
osmolarity
(oz-moh-lar-eh-tee)
Solute concentration expressed as molarity.
Solute concentration expressed as molarity.
osmoregulation
Adaptations
to control the water balance in organisms living in hypertonic, hypotonic, or
terrestrial environments.
osmoregulator
An animal
whose body fluids have a different osmolarity than the environment, and that
must either discharge excess water if it lives in a hypotonic environment or take in water
if it inhabits a hypertonic environment.
osmosis
(oz-moh-sis)
[Gk. osmos, impulse, thrust]
The diffusion of water across a selectively permeable membrane.
The diffusion of water across a selectively permeable membrane.
osmotic
potential
(oz-mot-ik)
[Gk. osmos, impulse, thrust]
The tendency of water to move across a selectively permeable membrane into a solution; it is determined by measuring the pressure required to stop the osmotic movement of water into the solution.
The tendency of water to move across a selectively permeable membrane into a solution; it is determined by measuring the pressure required to stop the osmotic movement of water into the solution.
osmotic
pressure
A measure
of the tendency of a solution to take up water when separated from pure water
by a selectively permeable membrane.
Osteichthyes
The
vertebrate class of bony fishes, characterized by a skeleton reinforced by
calcium phosphate; the most abundant and diverse vertebrates.
ostracoderm
(os-trak-uh-durm)
An extinct agnathan; a fishlike creature encased in an armor of bony plates.
An extinct agnathan; a fishlike creature encased in an armor of bony plates.
outgroup
A species
or group of species that is closely related to the group of species being
studied, but clearly not as closely related as any study-group members are to
each other.
ovarian
cycle
(oh-vair-ee-un)
The cyclic recurrence of the follicular phase, ovulation, and the luteal phase in the mammalian ovary, regulated by hormones.
The cyclic recurrence of the follicular phase, ovulation, and the luteal phase in the mammalian ovary, regulated by hormones.
ovarian
follicle
[L. ovum, egg
+ folliculus, small ball]
A developing oocyte and the specialized cells surrounding it; located near the surface of the ovary; following ovulation, forms the corpus luteum.
A developing oocyte and the specialized cells surrounding it; located near the surface of the ovary; following ovulation, forms the corpus luteum.
ovary
(oh-vur-ee)
[L. ovum, egg]
1) In flowers, the portion of a carpel in which the egg-containing ovules develop. (2) In animals, the structure that produces female gametes and reproductive hormones.
1) In flowers, the portion of a carpel in which the egg-containing ovules develop. (2) In animals, the structure that produces female gametes and reproductive hormones.
oviduct
[L. ovum, egg
+ ductus, duct]
A tube passing from the ovary to the vagina in invertebrates or to the uterus in vertebrates.
A tube passing from the ovary to the vagina in invertebrates or to the uterus in vertebrates.
oviparous
(oh-vip-ur-us)
Referring to a type of development in which young hatch from eggs laid outside the mother's body.
Referring to a type of development in which young hatch from eggs laid outside the mother's body.
ovoviviparous
(oh-voh-vy-vip-ur-us)
Referring to a type of development in which young hatch from eggs that are retained in the mother's uterus.
Referring to a type of development in which young hatch from eggs that are retained in the mother's uterus.
ovulation
The
release of an egg from ovaries. In humans, an ovarian follicle releases an egg
during each menstrual cycle.
ovule
(ov-yool)
[L. dim. of ovum, egg]
A structure that develops in the plant ovary and contains the female gametophyte.
A structure that develops in the plant ovary and contains the female gametophyte.
ovum pl. ova
(oh-vum)
[L. egg]
The female gamete; the haploid, unfertilized egg, which is usually a relatively large, nonmotile cell.
The female gamete; the haploid, unfertilized egg, which is usually a relatively large, nonmotile cell.
oxidation
The loss of
electrons from a substance involved in a redox reaction.
oxidative
phosphorylation
(fos-for-eh-lay-shun)
The production of ATP using energy derived from the redox reactions of an electron transport chain.
The production of ATP using energy derived from the redox reactions of an electron transport chain.
oxidizing
agent
The
electron acceptor in a redox reaction.
oxygen
debt
In
muscle, the cumulative deficit of oxygen that develops during strenuous
exercise when the supply of oxygen is inadequate for the demand; ATP is
produced anaerobically by glycolysis, and the resulting pyruvic acid is
converted to lactic acid, which is subsequently metabolized when adequate
oxygen is available.
