Science terms starting with P

1,062 terms

pleiotropic (adj.) See: pleiotropy.
Pleiotropy The simultaneous effect of a given gene on more than one apparently unrelated trait.
Pleistocene The oldest epoch of the Quaternary period, ranging from 2.6 million to 10,000 years ago.
Pleistocene epoch An interval of the Quaternary period, from 1.8 million to about 11,500 years before present.
Plenum The space between a hanging ceiling and the floor above or roof; usually contains HVAC ducts, electrical wiring, fire suppression system piping, etc.
ploidy (PLOY-dee) The number of sets of chromosomes in a cell or an organism. For example, haploid means one set and diploid means two sets.
Plot A forest area defined by its condition.
Plow Wind A term used in the midwestern United States to describe strong, straight-line winds associated with the downdrafts spreading out in advance of squall…
Plug Flow Digester A type of anaerobic digester that has a horizontal tank in which a constant volume of material is added and forces material in the tank to move through…
Plumb Exactly vertical; at right angles to the horizontal.
Plumb Bob A pointed weight hung from a string. Used for vertical alignment.
Plume A visible or measurable discharge of a contaminant from a given point of origin.
Plume Blight Visibility impairment caused by air pollution plumes aggregated from individual sources.
Plume downwash Downward movement of plumes immediately to the lee of flow obstacles such as buildings, bluffs, or smokestacks, caused by wake turbulence or lee cavity…
Plume Impingement The collision of a plume with topography that rises above the plume altitude; often a temporary condition that occurs as the plume sweeps by the face of a…
Plume model A computer model used to calculate air pollutant concentrations at receptor locations.
Plume-dominated Fire A fire whose behavior is governed primarily by the local wind circulation produced in response to the strong convection above the fire rather than by the…
plumule The first bud of an embryo, or that portion of the young shoot above the cotyledon s.
Plunge pool A natural or artifically created pool that dissipates the energy of free-falling water.
Pluripotency The potential of a cell to develop into more than one type of mature cell, depending on environment.
Pluripotent (ploo-RIH-poh-tent) Able to mature or develop in any of several ways.
Pluripotent stem cell (PSC) A single stem cell that has the capability of developing cells of all germ layers (endoderm, ectoderm, and mesoderm).
Pluripotent stem cells Stem cells that can become all the cell types that are found in an implanted embryo, fetus, or developed organism, but not embryonic components of the…
plus tree See: elite tree.
Pluton A body of igneous rock that solidified below the Earth's surface.
Plutonic Pertaining to a class of igneous rocks that have solidified far below the Earth's surface.
Pluvial In hydrology, anything that is brought about directly by precipitation.
Pluvial lake A lake formed during episodes of heavy precipitation or glacial melting, such as during the Pleistocene, and may either be extinct or remain as a remnant…
Ply One of several layers of fabric or of other strength-contributing material.
PM10 Particulate that is less than 10 microns in diameter. These particulates are present in the smoke created by burning wood.
PM2.5 Particulate that is less than 2.5 microns in diameter.
PMD Prognostic Discussion
PMO Program Management Office
PNA Abbreviation for peptide nucleic acid.
Pneumatic Powered or inflated by compressed air.
Pneumatic Gate (Rubber Gate or Bladder Gate) A tubular flexible gate anchored to a foundation or inside a pipe that is operated by filling with air under pressure.
pneumatic reactor See: airlift fermenter.
PNHDL Panhandle
PNS Public Information Statement - a narrative statement issued by a National Weather Service Forecast Office that can be used for: 1) A current or expected…
POH Probability of Hail - a product from the NEXRAD hail detection algorithm that estimates the likelihood that hail is present in a storm.
Point Discharge Instantaneous rate of discharge, in contrast to the mean rate for an interval of time.
Point light source A light source that has no visible surface area, and appears as a point, such as a star.
Point mutation A change in a single base pair of a DNA sequence in a gene. (See Mutation.)
Point of diversion A specifically named place where water is removed from a body of water. The location of a surface water or groundwater extraction associated with a water…
Point Precipitation Precipitation at a particular site, in contrast to the mean precipitation over an area.
Point source Any discernible, confined, or discrete conveyance from which pollutants are or may be discharged, including, but not limited to, any pipe, ditch, channel…
Point source (emissions) A stationary location or fixed facility from which pollutants are discharged; any single identifiable source of pollution; e.g.
Point-Contact Cell A high efficiency silicon photovoltaic concentrator cell that employs light trapping techniques and point-diffused contacts on the rear surface for…
polar bodies In female animals, the products of a meiotic division that do not develop into a functional ovum.
Polar Body A polar body is a structure produced when an early egg cell, or oogonium, undergoes meiosis.
Polar Cap Absorption (PCA) In solar-terrestrial terms, an anomalous condition of the polar ionosphere whereby HF and VHF (3 - 300 MHz) radiowaves are absorbed, and LF and VLF (3 -…
Polar day Polar day In polar regions, the portion of the year when the Sun is continuously in the sky.
Polar explorer Polar explorer A person working for a long time at one of the polar observing stations. Russian word is "polyarnik."
Polar Front A semipermanent, semicontinuous front that separates tropical air masses from polar air masses.
Polar Jet Marked by a concentration of isotherms and strong vertical shear, this jet is the boundary between the polar air and the subtropical air.
Polar Jet Stream Used interchangably with Polar Jet; a jet stream marked by a concentration of isotherms and strong vertical shear, this jet is the boundary between the…
Polar low Polar low Small, shallow depression which forms mainly in winter over some high-latitude seas within a polar or arctic air mass.
polar mutation A mutation that influences the functioning of genes that are downstream from the site of mutagenesis but are in the same transcription unit.
Polar night Polar night In polar regions, the portion of the year when the Sun does not rise above the horizon.
polar nuclei Two centrally located nuclei in the embryo sac that unite with a second sperm cell in a triple fusion.
Polar Orbiting Satellite A weather satellite which travels over both poles each time it orbits the Earth. It orbits about 530 miles (850 km) above the Earth's surface.
polar transport A directed movement within plants of compounds (usually endogenous plant growth regulators) mostly in one direction; polar transport overcomes the…
Polar vortex Polar vortex Large-scale cyclonic circulation in the middle and upper troposphere centered generally in the polar regions.
Polarity The observed differentiation of an organism, tissue or cell into parts having opposed or contrasted properties or form.
Polarization Radar A radar which takes advantage of ways in which the transmitted waves' polarization affect the backscattering.
pole cells A group of cells in the posterior of Drosophila embryos that are precursors to the adult germ line.
Polishing treatment The final sewage treatment process to further reduce BOD5, suspended solids, and other pollutants.
pollen Mature microspores of seed plants.
pollen culture The in vitro culture and germination of pollen grains to generate haploid plants. See: anther culture;.
pollen grain The mature microspore, produced in the pollen sac of angiosperms or the microsporangium of gymnosperms.
pollination Transfer of pollen from anther to stigma in the process of fertilization in angiosperms; transfer of pollen from male to female cone in the process of…
Pollutant Any inorganic or organic substance that contaminates air, water or soil. Generally, any substance introduced into the environment that adversely affects…
Pollution A resource that is out of place. Generally, the presence of matter or energy whose nature, location or quantity produces undesired environmental effects.
Poly(A) polymerase Catalyzes the addition of adenine residues to the 3' end of pre-mRNAs to form the poly(A) tail. (See Polymerase.)
poly-(A) tail See: polyadenylation.
polyacrylamide gel Inert electrophoresis matrix, formed by the polymerization of acrylamide monomer in the presence of the cross-linker N,N'-methylene-bis-acrylamide.
Polyacrylamide gel electrophoresis Electrophoresis through a matrix composed of a synthetic polymer, used to separate proteins, small DNA, or RNA molecules of up to 1000 nucleotides.
polyadenylation Post-transcription al addition of multiple adenine residues to the 3' end of eukaryotic mRNA. Also called poly-(A) tailing.
polycistronic A single mRNA that contains the information necessary for the production of more than one polypeptide. Particularly characteristic of prokaryotic mRNA s.
Polyclonal antibodies A mixture of immunoglobulin molecules secreted against a specific antigen, each recognizing a different epitope.
polyclonal antibody A serum sample that contains a mixture of distinct immunoglobulin molecules, each recognizing a different antigenic determinant of a given antigen.
polycloning site See: polylinker.
Polycrystalline A semiconductor (photovoltaic) material composed of variously oriented, small, individual crystals.
polydactyly An abnormality in which a person is born with more than the normal number of fingers or toes. See also
polyembryony The production of more than one embryo from a single egg cell (in animals) or from a range of embryogenic cell types (in plants).
Polyethylene A registered trademark for plastic sheeting material that can be used as a vapor retarder. This plastic is used to make grocery bags.
polyethylene glycol (Abbreviation: PEG). A polymer having the general formula HOCH2(CH2OCH2)nCH2OH and available in a range of molecular weights.
polygalacturonase (Abbreviation: PG). An enzyme which catalyses the breakdown of pectin. A tomato engineered to contain an antisense-PG gene succeeded in delaying the onset…
polygene One of a number of genes, each of small effect, which together act to determine the phenotype of a quantitative trait.
Polygenic Controlled by or associated with more than one gene.
Polygenic disorder Genetic disorder resulting from the combined action of alleles of more than one gene (e.g., heart disease, diabetes, and some cancers).
polyhydroxybutyrate (Abbreviation: PHB). A biopolymer, with physical properties similar to polystyrene, originally discovered in the bacterium Alcaligenes eutropus.
Polylinker A short DNA sequence containing several re- striction enzyme recognition sites that is contained in cloning vectors.
polymer (PAH-lih-mer) A molecule made up of small identical molecules called monomers. The monomers are joined together in a repeating pattern.
polymerase An enzyme that catalyses the formation of polymers from monomers . A DNA polymerase synthesizes DNA from deoxynucleoside triphosphates using a…
Polymerase (DNA) Synthesizes a double-stranded DNA molecule using a primer and DNA as a template.
polymerase chain reaction (puh-LIM-eh-rayz ...) A laboratory method used to make many copies of a specific DNA sequence. Also called PCR.
polymerase chain reaction (PCR) A procedure that en- zymatically amplifies a DNA polymerase. (See Polymerase.)
Polymerase, DNA or RNA Enzyme that catalyzes the synthesis of nucleic acids on preexisting nucleic acid templates, assembling RNA from ribonucleotides or DNA from…
polymerization The chemical fusion of a number of identical or similar monomers to form a polymer.