Science terms starting with A

1,045 terms

allelomorph See: allele.
Allelopathy The secretion of chemicals, such as phenolic and terpenoid compounds, by a plant's roots, which inhibit the growth or reproduction of competitor plants.
allergen (AL-er-jen) A substance that causes an allergic response. Examples include pollen, molds, and certain foods.
Alliance of Small Island States (AOSIS) The group of Pacific and Caribbean nations who call for relatively fast action by developed nations to reduce greenhouse gas emissions.
Allochthonous Exotic species of a given area. Also refers to deposits of material that originated elsewhere, e.g., drifted plant material on the bottom of a lake.
allogamy Cross fertilization in plants. See: fertilization.
Allogeneic (A-loh-jeh-NAY-ik) Taken from different individuals of the same species. Also called allogenic.
Allogeneic cell transplantation Transplantation of cells from one individual to another of the same species.
Allogeneic Stem Cell Transplant A transplant involving the infusion of a donor's genetically matched bone marrow or stem cells to produce new, healthy marrow.
Allogeneic transplantation Cell, tissue or organ transplants from one member of a species to a genetically different member of the same species.
allogenic Taken from different individuals of the same species. Also called allogeneic.
allometric When the growth rate of one part of an organism differs from that of another part or of the rest of the body.
Allopatric In the context of natural populations of animals or plants, inhabiting distinct and separate areas.
allopatric speciation Speciation occurring at least in part because of geographic isolation.
allopolyploid A polyploid organism with sets of chromosomes derived from different species. Opposite: autopolyploid.
allosome Synonym for sex chromosome.
allosteric control See: allosteric regulation.
allosteric enzyme An enzyme that has two structurally distinct forms, one of which is active and the other inactive.
allosteric regulation A catalysis-regulating process in which the binding of a small effector molecule to one site on an enzyme affects the activity at another site.
allosteric site That part of an enzyme molecule where the non-covalent binding of an effector molecule can affect the enzyme's catalytic activity.
allosteric transition A reversible interaction of a small molecule with a protein molecule, resulting in a change in the shape of the protein and consequent alteration of the…
allotetraploid An allopolyploid having two different progenitor genomes.
Allotment An area of land where one or more livestock operators graze their livestock. Allotments generally consist of BLM lands but may also include other…
allotype A classification of antibody molecules according to the antigenicity of the constant regions; a variation that is determined by a single allele.
Allowable bearing capacity The maximum pressure that can be permitted on foundation soil, giving consideration to all pertinent factors, with adequate safety against rupture of the…
Allowable pile bearing load The maximum load that can be permitted on a pile with adequate safety against movement of such magnitude that the structure is endangered.
allozygote A individual that is heterozygous for two different mutant allele s.
allozyme See: allosteric enzyme.
Alluvial Formed by the action of running water; of or related to river and stream deposits.
Alluvial fan A fan-shaped depositional landform consisting of alluvial deposits that formed where a flowing stream slows and spreads out (depositing its load)…
Alluvial flats Small flat areas or plains (with slopes of less than 5 or 10 feet per mile) built of fine sediments deposited during flooding events.
Alluvial plains Small flat areas or plains (with slopes of less than 5 or 10 feet per mile) built of fine sediments deposited during flooding events.
Alluvial valley An alluvium-filled basin, usually occurring between mountain ranges.
Alluvian fan terrace A relict landform consisting of thick gravel, sand, and boulder deposits occurring along mountain fronts.
Alluvium Deposits of clay, silt, sand, gravel, or other particulate materials that have been deposited by a stream or other body of running water in a streambed…
Along-slope Wind System A closed, thermally driven diurnal mountain wind circulation whose lower branch blows up or down the sloping sidewalls of a valley or mountain.
ALP Animas-La Plata Project.
alpha globulin See: haptoglobin.
Alpha Particle A positively charged particle, indistinguishable from a helium atom nucleus and consisting of two protons and two neutrons.
Alpha particle (alpha radiation, alpha ray) A positively charged particle (a Helium-4 nucleus) made up of two neutrons and two protons.
alpha radiation Same as alpha particle.
Alpine Refers to high mountain areas above the timberline (where trees cease to inhabit extremely cold environments).
Alpine tundra Vegetation in montane habitats above the tree line. Vegetation consists of perennial forbs, grasses, sedges, and short woody shrubs.
ALQDS All Quadrants
Alquist-Priolo Earthquake Fault Zoning Act California seismic zoning act passed in 1972, in response to the 1971 San Fernando earthquake, to prevent building across the traces of active faults.
Alternating Current A type of electrical current, the direction of which is reversed at regular intervals or cycles; in the U.S.
Alternating current (AC) An electric current that reverses its direction at regularly recurring intervals.
Alternative Under the National Environmental Policy Act, a comprehensive management strategy.
Alternative Energy Energy derived from nontraditional sources (e.g., compressed natural gas, solar, hydroelectric, wind).
Alternative fuel As defined in the Energy Policy Act of 1992 (EPACT): Methanol, denatured ethanol and other alcohols, separately or in blends of at least 10 percent by…
Alternative Fuel Vehicles A dedicated, flexible fuel, or dual-fuel vehicle designed to operate on at least one alternative fuel.
Alternative Fuels A popular term for "non-conventional" transportation fuels derived from natural gas (propane, compressed natural gas, methanol, etc.
Alternative mRNA splicing The inclusion or exclusion of different exons to form different mRNA transcripts. (See RNA.)
Alternative splicing Different ways of combining a gene's exons to make variants of the complete protein
Alternatives Courses of action that may meet the objectives of a proposal at varying levels of accomplishment, including the most likely future conditions without the…
Alternator A belt-driven device mounted on the front of the engine that recharges the battery while the engine is running.
ALTHO although
Altimeter An instrument that indicates the altitude of an object above a fixed level. Pressure altimeters use an aneroid barometer with a scale graduated in…
Altimeter Setting A correction of the station pressure to sea level used by aviation. This correction takes into account the standard variation of pressure with height and…
Altocumulus A cloud of a class characterized by globular masses or rolls in layers or patches, the individual elements being larger and darker than those of…
Altostratus A cloud of a class characterized by a generally uniform gray sheet or layer, lighter in color than nimbostratus and darker than cirrostratus.
Alu sequences A highly repeated family of 300-bp long sequences dispersed throughout the human genome, so named because they are released by the digestion of genomic…
Alum A type of immune adjuvant (a substance used to help boost the immune response to a vaccine). Also called aluminum sulfate.
AM area manager.
AMA adaptive management area.
amber stop codon See: stop codon.
Ambient Surrounding natural conditions or environment at a given place and time. Environmental or surrounding conditions.
Ambient Air The air external to a building or device.
Ambient air quality The condition of the air in the surrounding environment.
Ambient Air Quality Standards Regulations prescribing the levels of airborne pollutants that may not be exceeded during a specified time in a defined area.
Ambient lighting Provides general illumination indoors for daily activities, and outdoors for safety and security.
Ambient Temperature The temperature of a medium, such as gas or liquid, which comes into contact with or surrounds an apparatus or building element.
Ambursen dam A buttress dam in which the upstream part is a relatively thin flat slab usually made of reinforced concrete.
AMCR alternative management control review.
AMD Amend
American Indian Religious Freedom Act of 1978 (AIRFA) Act requiring federal agencies to consult with tribal officials to ensure protection of religious cultural rights and practices.
American Society for Testing and Materials (ASTM) International A nonprofit organization that develops and delivers international standards. ASTM standards, test methods, specifications, and procedures are recognized…
Amino acid (uh-MEE-noh A-sid) One of several molecules that join together to form proteins. There are 20 common amino acids found in proteins.
amino acids A group of 20 different kinds of small molecules that link together in long chains to form proteins.
aminoacyl site (Abbreviation: A-site). One of two sites on ribosomes to which the aminoacyl tRNA molecules can bind.
aminoacyl tRNA synthetase An enzyme that catalyses the attachment of an amino acid to its specific tRNA molecule.
amitosis A cell division (including nuclear division through constriction of the nucleus) that occurs without chromosome differentiation as in mitosis.
Ammonia A colorless, pungent, gas (NH3) that is extremely soluble in water, may be used as a refrigerant; a fixed nitrogen form suitable as fertilizer.
Ammonium One form of nitrogen that is usable by plants.
amniocentesis A procedure for obtaining foetal cells for prenatal diagnosis by sampling the amniotic fluid from a pregnant mammal.
Amnion The thin membrane that lines the fluid-filled sac in which the embryo develops in higher vertebrates, reptiles and birds.
Amniotic fluid Liquid contents of the amniotic sac of higher vertebrates, containing foetal, but not maternal cells.
amorph A mutation that abolishes gene function. Synonym: null mutation.
Amorphous Semiconductor A non-crystalline semiconductor material that has no long-range order.
AMOS Automatic Meteorological Observing System
AMP Abbreviation for adenosine monophosphate.
Amp-Hours A measure of the flow of current (in amperes) over one hour.
Amperage The strength of an electric current measured in amperes. The amount of electric current flow, similar to the flow of water in gallons per minute (gpm).
Ampere A unit of measure for an electrical current; the amount of current that flows in a circuit at an electromotive force of one Volt and at a resistance of…
Ampere (amp) A unit of electric current or rate of flow of electrons. One volt across 1 ohm of resistance causes a current flow of 1 ampere.
Amperometric Based on the electric current that flows between two electrodes in a solution.
Amphibian A cold-blooded, smooth-skinned vertebrate of the class Amphibia, such as a frog, toad, or salamander, that characteristically hatches as an aquatic larva…
amphidiploid A plant derived from doubling the chromosome number of an interspecific F1 hybrid. Naturally found hybrids of this sort are referred to as allopolyploid.
amphimixis True sexual reproduction involving the fusion of male and female gametes and the formation of a zygote.
ampicillin A penicillin-type antibiotic that prevents bacterial growth by interfering with synthesis of the cell wall.