(ob-lig-it air-obe)
An organism that requires oxygen for cellular respiration and cannot live without it.

(an-ur-obe)
An organism that cannot use oxygen and is poisoned by it.

The region of water lying over deep areas beyond the continental shelf.

A nutrient-poor, clear, deep lake with minimum phytoplankton.

[L. omnis, all + vorare, to devour]
A heterotrophic animal that consumes both meat and plant material.

(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.

(on-toj-en-ee)
The embryonic development of an organism.

(o-uh-sight) [Gk. oion, egg + kytos, vessel]
A cell that gives rise by meiosis to an ovum.

(oh-og-um-ee)
A condition in which male and female gametes differ, such that a small, flagellated sperm fertilizes a large, nonmotile egg.

(oo-oh-jen-eh-sis)
The process in the ovary that results in the production of female gametes.

An arrangement of internal transport in which blood bathes the organs directly and there is no distinction between blood and interstitial fluid.

A type of associative learning that directly affects behavior in a natural context; also called trial-and-error learning.

A segment of DNA that interacts with a repressor protein to regulate the transcription of the structural genes of an 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.

Species characterized by high reproduction rates, rapid development, early reproduction, small body size, and uncertain adult survival.

An immune response in which the binding of antibodies to the surface of a microbe facilitates phagocytosis of the microbe by a macrophage.

[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.

A taxonomic grouping of related, similar families; the category below class and above family.

[Gk. organon, tool]
A specialized center of body function composed of several different types of tissues.

A plant gene in which a mutation causes a floral organ to develop in the wrong location.

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.

(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.

[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.

The study of carbon compounds (organic compounds).

A chemical comound containing the element carbon and usually synthesized by cells.

An individual living thing, such as a bacterium, fungus, protist, plant or animal.

(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.

Rhythmic, involuntary contractions of certain reproductive structures in both sexes during the human sexual response cycle.

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.

An animal that does not actively adjust its internal osmolarity because it is isotonic with its environment.

(oz-moh-lar-eh-tee)
Solute concentration expressed as molarity.

Adaptations to control the water balance in organisms living in hypertonic, hypotonic, or terrestrial environments.

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.

(oz-moh-sis) [Gk. osmos, impulse, thrust]
The diffusion of water across a selectively permeable membrane.

(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.

A measure of the tendency of a solution to take up water when separated from pure water by a selectively permeable membrane.

The vertebrate class of bony fishes, characterized by a skeleton reinforced by calcium phosphate; the most abundant and diverse vertebrates.

(os-trak-uh-durm)
An extinct agnathan; a fishlike creature encased in an armor of bony plates.

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.

(oh-vair-ee-un)
The cyclic recurrence of the follicular phase, ovulation, and the luteal phase in the mammalian ovary, regulated by hormones.

[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.

(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.

[L. ovum, egg + ductus, duct]
A tube passing from the ovary to the vagina in invertebrates or to the uterus in vertebrates.

(oh-vip-ur-us)
Referring to a type of development in which young hatch from eggs laid outside the mother's body.

(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.

The release of an egg from ovaries. In humans, an ovarian follicle releases an egg during each menstrual cycle.

(ov-yool) [L. dim. of ovum, egg]
A structure that develops in the plant ovary and contains the female gametophyte.

(oh-vum) [L. egg]
The female gamete; the haploid, unfertilized egg, which is usually a relatively large, nonmotile cell.

The loss of electrons from a substance involved in a redox reaction.

(fos-for-eh-lay-shun)
The production of ATP using energy derived from the redox reactions of an electron transport chain.

The electron acceptor in a redox reaction.

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.