Biology Dictionary O

Meanings of biological terminology

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O Symbol for: (1) oxygen; (2) Ordovician Period.

O₃ Chemical formula for: Ozone.

obese /ō-BEESE/ Extremely fat.

obesity /ō-BEESE-ə-tee/ The condition of being obese.

obligate aerobes /AWB-lə-gət AIR-obes/ Organisms that must have oxygen to live.

obligate anaerobes /AWB-lə-gət AN-ər-obes/ Organisms that not only cannot use oxygen, but that are also poisoned by it.

occiput /AWK-sih-pət/ n. The occipital bone.

occipital /awk-SIP-ə-təl/ (1) n. the bone forming the posterior portion of the skull and surrounding the foramen magnum. PICTURE OF BONES OF HUMAN SKULL; (2) adj. of or pertaining to the posterior portion of the skull.

Online Biology Dictionary (OCCLU-)

occlude /awk-LOOD/ (1) to block or obstruct; (2) to close together, as in the case of teeth.

occlusal surface /awk-LOO-səl/ That surface of a tooth that comes into contact with the opposing teeth when chewing takes place.

occlusion /awk-LOO-shən/ (1) closure; (2) the position of the teeth when the jaws are closed.

Online Biology Dictionary (OCT-)

octoploid /AWK-tə-ploid/ (1) exhibiting octoploidy; (2) an organism, cell, or type exhibiting octoploidy.

octoploidy /AWK-tə-ploid-ee/ A condition in which a cell has, or the individual cells of an organism have, eight complete sets of chromosomes. See also: polyploidy.

octipara /awk-TIP-er-ə/ A woman who has given birth to eight children.

Online Biology Dictionary (OCUL-)

ocular /AWK-yə-ler/ Pertaining to the eye.

oculomotorius /AWK-yə-low-mō-TORE-ee-əs/ The oculomotor (or 3rd cranial) nerve; governs five of the seven eye muscles.

oculomycosis /AWK-yə-low-my-KŌ-səs, -sis/ Any fungal disease of the eye.

oculonasal /AWK-yə-low-NAY-səl/ Pertaining to the nose and eyes.

oculozygomatic /AWK-yə-low-zigh-go-MAT-ik/ Pertaining to the zygoma and eyes.

Online Biology Dictionary (ODONT-)

odontogenesis /ō-DAWN-tə-JEN-ə-səs, -sis/ The origin and growth of teeth.

odontology /ō-dawn-TAWL-ə-jee/ Dentistry.

odontopathy /ō-DAWN-tə-path-ee/ Disease of the teeth.

Online Biology Dictionary (ODYN-)

odynacusis /ō-din-ə-KOO-səs/ A condition in which pain in the ears is caused by noises.

odynometer /ō-din-AWM-ə-ter/ An apparatus for measuring pain.

oedema See: edema.

oenology See: enology.

oestrus See: estrus.

oleaginous /awl-ee-AWJ-jin-nəs/ Oily, greasy.

olecranon /ō-LECK-rə-non, Ō-lə-KRAN-on/ The process of the ulna extending behind the elbow and forming the prominence of the elbow. PICTURE

Online Biology Dictionary (OLFAC-)

olfaction /awl-FACK-shən/ The sense of smell.

olfactive /awl-FACT-tiv/ Pertaining to the sense of smell.

olfactology /awl-fact-TAWL-ə-jee/ The study of the sense of smell.

olfactory /awl-FACT-er-ee/ Pertaining to smell.

Online Biology Dictionary (OLIGO-)

oligo Short for oligonucleotide.

Oligocene /ō-LIG-ə-seen/ An epoch of the Paleogene. It lasted from 33.9 to 23.03 mya. GEOLOGIC TIME SCALE MORE INFORMATION

oligogenic trait A phenotypic trait produced by two or more genes working together.

oligomer /aw-LIG-ə-mer/ (often shortened to oligo /Ō-lig-ō AW-/) A chain composed of a few monomers.

oligonucleotide /aw-lig-ō-N(Y)OOK-lee-ō-tide/ (often shortened to oligo /Ō-lig-ō AW-/) A short segment of RNA or DNA. An oligonucleotide of a given length is indicated by adding the suffix -mer To a number indicating the number of nucleotides present. For example, an oligonucleotide containing 12 nucleotides is a 12-mer.

oligosaccharide A saccharide chain composed of several (usually 10 or fewer), simple sugars.

omasum /ō-MAY-səm/ (pl omasa /ō-MAY-sə/)The third stomach chamber of a ruminant. MORE INFORMATION

Online Biology Dictionary (OMBRO-)

ombrology /awm-BRAWL-ə-jee/ The scientific study of rainfall.

ombrophile /AWM-brə-file/ A plant that thrives in regions having high levels of rainfall.

ombrophilous /awm-BRAWF-ə-ləs/ Thriving in regions having high levels of rainfall.

Online Biology Dictionary (OM-)

omitis /ō-MY-tis/ Inflammation of the shoulder.

omnivore An omnivorous organism.

omnivorous Feeding on both plant and animal substances.

omodynia /ō-mō-DIN-ee-ə/ Shoulder pain.

Online Biology Dictionary (OMPHAL-)

omphalitis /awm-fawl-LIGHT-əs/ Inflammation of the navel.

omphalos /AWM-fawl-ləs/ Umbilicus.

Online Biology Dictionary (ONC-)

onchium (pl onchia) /AWNK-ee-əm, AWNK-ee-ə/ A hook found in or on the margin of the oral cavity of certain nematodes.

oncogene /AWNK-ə-jeen, -ō-/ A gene, one or more forms of which is associated with cancer. Many oncogenes are involved, directly or indirectly, in controlling the rate of cell growth.

oncology /awn-CALL-ə-jee/ The medical study and treatment of cancer.

oncospheres /AWNK-ə-sfeer/ Embryonic larvae of a tapeworm, which are armed with hooks serving as anchors.

one gene/one enzyme hypothesis A hypothesis, first proposed by the English physician Archibald Garrod in 1909, which asserts that each gene codes for a single, specific enzyme. MORE INFORMATION

ontogeny /on-TAWJ-ə-nee/ The course of an embryo's development.

Online Biology Dictionary (ONYCH-)

onycholysis /awn-ə-KAWL-ə-sus/ Loosening or detachment of a nail.

onychoma /awn-ə-KOE-mə/ Tumor of the nailbed.

onychosis /awn-ə-KOE-səs/ Any disease of the nails.

onyxis /awn-NIX-səs/ Ingrowth of the nails.

Online Biology Dictionary (OO-)

oocyte /Ō-ə-site/ The cell undergoing meiosis in females; often called "primary oocyte."

oogamous /ō-awe-GAM-əs/ Having a small mobile male gamete and a large immobile female gameteembryo."

oogenesis (also ovogenesis) /ō-ə-JEN-ə-səs, ō-və-JEN-ə-səs/ The process producing female gametes.

oophorectomy /ō-ə-fore-EK-tə-mee/ Surgical removal of an ovary.

oophorocystosis /ō-ə-fore-ə-sist-TŌ-səs/ Condition of having an ovarian cyst.

ootheca /ō-ə-THEK-ə/ A sturdy protein case containing multiple, usually many, eggs; produced by certain insects and mollusks.

open reading frame (ORF) The sequence of DNA or RNA located between the start-code sequence (initiation codon) and the stop-code sequence (termination codon).

operon /AWP-er-on/ A set of adjacent genes with related functions. They are transcribed under the control of an operator gene.

orad /Ō-rad, ORE-ad/ Toward the mouth.

oral /ORE-əl/ Of, pertaining to, or by way of the mouth.

oral cavity /ORE-əl/ The mouth.

orally /ORE-əl-ee/ By way of the mouth.

orbit /ORE-bət, -bit/ The bony cavity that holds the eyeball.

orbital /ORE-bət-əl/ Of or pertaining to the orbit.

Online Biology Dictionary (ORCHI-)

orchidectomy /ORE-kə-DECK-tə-mee/ Surgical removal of a testis.

orchidocele /ORK-id-ə-seel/ Scrotal hernia.

orchiodynia /ork-yō-DIN-ee-yə/ Testicular pain.

orchis /ORE-kiss/ A testicle.

order In taxonomy, a division of a class that itself contains one or more families. CHART OF RELATIVE TAXONOMIC RANKS

ordinal /ORD-(ə)-nəl/ Of or pertaining to an order.

Ordovician Period (O) /ord-ə-VISH-ən/ The geologic period between the Cambrian and the Silurian. It lasted from about 488 to 444 mya. Historically, the Ordovician was recognized later than the Cambrian and Silurian, with which it was at first confused. During the Ordovician, especially late in the period, sea levels were high. The Panthalassic Ocean covered much of the northern hemisphere. WORLD MAP DURING ORDOVICIAN

Online Biology Dictionary (OREXI-)

orexigenic /ō-REKS-ə-JEN-ik/ Stimulating or increasing appetite.

oreximania /ō-REKS-ə-MANE-ee-yə/ Abnormal, extreme hunger.

Online Biology Dictionary (ORGAN-)

organ /OR-gən/ A discreet portion of an organism serving a particular function or set of functions.

organelle /OR-gə-NELL/ One of the tiny, membrane-bounded organs with various specialized functions found in eukaryotic cells.

organic /ore-GAN-ik/ (1) of or relating to organisms or the chemical compounds made by them; (2) referring to a chemical compound containing carbon.

organism /ORE-gə-niz-əm/ Either of two types of entities: (1) one that engages in binary fission (a prokaryote), or (2) one that engages in mitosis (a eukaryote). Controversy exists over whether or not viruses are living things; they do not engage in binary fission or mitosis.

Origin of Species The shortened name usually used to refer to Charles Darwin's most famous book, On the Origin of Species by means of Natural Selection, or the Preservation of Favored Races in the Struggle for Life. ABOUT THE DEFINITION OF SPECIES

Online Biology Dictionary (ORNITH-)

ornithine cycle (or urea cycle) /ORN-ə-theen/ A cycle of chemical reactions in which the toxic nitrogenous products of protein catabolism are converted to urea, which is nontoxic. In the cycle, ornithine is first converted to citrulline, which is then converted to argino-succinic acid, which is converted to arginine. Urea then splits off of arginine, which produces ornithine again. CHART OF UREA CYCLE

ornithology /ORE-nə-THAWL-ə-jee/ The scientific study of birds — ornithology /ORE-nə-THAWL-ə-jəst, -jist/

ornithophily /ORE-nə-THAWF-ə-lee/ Pollination by birds.

orogeny /ore-AWJ-ə-nee/ Process of mountain building.

oropharynx /ORE-ō-FAIR-inx/ The portion of the pharynx below the soft palate.

ortet /ORE-tet/ The ancestral individual that founds a clone. Compare: ramet.

Online Biology Dictionary (ORTHO-)

orthopedic /ORE-thō-PEED-ik/ Correcting deformity.

orthopnea /ORE-thawp-NEE-ə, ore-THAWP-nee-ə/ An inability to breath easily when the torso is not in an upright position.

Orthoptera /ore-THAWP-ter-ə/ The order of insects including the grasshoppers, locusts, and crickets.

Oryza sativa /ore-EYE-zə sə-TIE-və/ The scientific name for rice.

osculum /OSS-kyə-ləm/ In sponges, the main opening through which water is discharged.

Online Biology Dictionary (OSMO-)

osmoregulation /AWZ-mō-reg-yə-LAY-shən/ Regulation of water balance.

osmosis /awz-MŌ-səs/ The movement of a solvent, usually water, due to osmotic pressure.

osmotic pressure /awz-MAWT-ick/ Pressure caused by a difference in concentration between solutions on the two sides of a selectively permeable membrane. The result is movement of the solvent in the direction of higher solute concentration.

osphresiology /aws-free-zee-AWL-ə-jee/ The scientific study of the sense of smell.

osseous /AW-see-əs/ adj. Bony, composed of bone.

ossicle /AW-sick-əl/ A small bone, particularly the three small bones in the human ear.

ossification /aw-sə-fə-KAY-shən/ The process of bone formation. See: osteoblasts

osteoblast /AW-stee-ə-blasts/ Any of the special cells that secrete the mineral that combine with collagen fibers to form bone.

osteology /AW-stee-AWL-ə-jee/ The scientific study of bones — osteologist /OSS-tee-AWL-ə-jist/

osteoporosis /AW-stee-ō-pə-RŌ-səs, -sis/ The loss of bone tissue and density over time, so that, ultimately, the bones thin and become fragile.

osteosarcoma (also osteogenic sarcoma) /AW-stee-ō-sar-KŌ-mə/ A sarcoma of the bone; usually affects the large bones of the arm or leg; more common in young people and affects more males than females.

ostreophagous /AW-stree-AW-fə-gəs/ Having a diet of oysters.

Online Biology Dictionary (OT-)

otalgia /ō-TAL-zhə/ Ear pain.

otiatrics /ō-dee-AT-riks/ Treatment of diseases of the ear.

otic /Ō-dick, -tick, AWE-/ Of, pertaining to, near, or in the ear.

otitis /ō-TIGHT-əs/ Inflammation of the ear (otitis media: inflammation of the middle ear).

otology /ō-TAWL-ə-jee/ The scientific study of the ear, its diseases, and treatments.

ouabain /waw-BYE-ən/ A compound that blocks the transfer of ions in and out of cells.

outbreeding (also crossbreeding) /OUT-breed-ing/ The mating of unrelated individuals.

outcross /OUT-cross/ (1) mating in which the male and female gametes are derived from different individuals; used in opposition to self-fertilization; (2) the pollination of a stigma with pollen from another plant (used in opposition to self-pollination); (3) outbreed.

outcrosser /OUT-cross-er/ An individual, or a type of organism, that engages in outcrossing.

Online Biology Dictionary (OV-)

ova See: ovum.

ovarian /ō-VARE-ee-ən/ Pertaining to, in, or like the ovary.

ovariectomy /ō-VER-ee-EK-tə-mee/ Excision of an ovary.

ovary /ō-VER-ee/ (1) in animals: a female gonad; (2) in plants: the portion of a carpel containing the ovules.

overlapping clones See: genomic library.

overlapping inversion An inversion that involves a chromosomal region already affected by an inversion.

overwinding Positive coiling of DNA; results in the DNA double helix being wound more tightly.

Online Biology Dictionary (OVI-)

ovicular /ō-VIK-yə-ler/ Pertaining to or like eggs.

oviduct /Ō-və-dəkt/ An egg-carrying tube.

ovine /Ō-vine, -veen/ Pertaining to or resembling sheep.

oviparous /ō-VIP-er-əs/ Egg laying.

ovipositor /ō-və-PAWZ-ə-ter/ An organ for laying eggs.

ovogenesis /ō-vō-JEN-ə-sis/ See: oogenesis.

ovotestis /ō-vō-TEST-əs/ An organ in hermaphrodites that serves both as a testis and an ovary.

ovulation /aw-vyə-LAY-shən/ The production of ova (eggs).

ovule /AW-vyool, Ō-vyool/ The structure that develops into a seed after fertilization.

ovum (pl ova) /Ō-vəm, pl: Ō-və/ An unfertilized egg; a female gamete.

Online Biology Dictionary (OXI-)

oxidant /AWKS-ə-dənt/ An oxidizing agent.

oxidation /AWKS-ə-day-shən/ The gain of oxygen atoms, the loss of hydrogen atoms (or of electrons) by a compound.

oxidation reduction reactions /AWKS-ə-day-shən rə-DƏK-shən/ Chemical reactions involving the transfer of electrons from a reductant to an oxidant (which oxidizes the reductant and reduces the oxidant).

oxidize /AWKS-ə-dize/ (1) to remove electrons from or dehydrogenate; (2) to combine with oxygen.

oxyblepsia /AWKS-ee-BLEP-see-ə/ Acuteness of vision.

oxychromatic /awks-ee-krō-MAT-ik/ Staining with acid dyes.

oxyesthesia /awks-ee-es-THEE-shə/ Abnormally sharp sensation.

oxygen (O) /AWKS-ə-jehn/ A gaseous chemical element; odorless, tasteless, colorless; atomic weight 15.9994, atomic number 8, valence 2⁻. The second most abundant of the biologically important elements. Makes up 75% of an animal's weight, and 80% of a plant's. During respiration oxygen is used to produce ATP. During photosynthesis, plants produce oxygen from carbon dioxide, a fact originally discovered by Jan Ingenhousz. PERIODIC TABLE

oxygenate /AWKS-ə-jə-nate/ To saturate with oxygen.

oxyhemoglobin /AWKS-ee-HEEM-ə-glōb-ən/ Oxygenated hemoglobin.

ozone (O₃) /Ō-zōn/ A molecule, much more unstable than diatomic oxygen, composed of three oxygen atoms. Near the Earth's surface ozone is a pollutant produced by internal combustion engines, but it also serves a beneficial function in that it forms a protective high-altitude atmospheric layer that blocks ultraviolet radiation.

ozostomia /ō-zə-STŌM-ee-yə/ Bad breath.

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