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281 Cards in this Set

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Aa a type of lava that has a jagged surface covered with rough volcanic fragments
abdomenthe distinct, usually elongated posterior region of an arthropod's body
abdominal cavity the hollow part of the body that is between the thorax and the pelvis; contains organs of digestion, excretion, and reproduction
abdominal cavity
abiotic describes the nonliving part of the environment, including water, rocks, light, and temperature
abiotic factor an environmental factor that is not associated with the activities of living organisms
abiotic factor
ABO blood group system a system used to classify human blood by antigens found on the surface of red blood cells
ABO blood group system
aboral surface a surface that is opposite or away from the mouth
aboral surface
abrasion the grinding and wearing away of rock surfaces through the mechanical action of other rock or sand particles
abscisic acid a hormone in plants that helps regulate the growth of buds and the germination of seeds (abbreviation, ABA)
abscisic acid
abscission the separation of leaves or other plant structures by the formation of a layer of cells that develops on the base of the plant structure when the structure is ready to fall
absolute age he numeric age of an object or event, often stated in years before the present, as established by an absolute-dating process, such as radiometric dating
absolute age
absolute dating any method that measures the age of an object or event in years rather than measuring the age relative to another object or event; one such method is radiometric dating
absolute dating
absolute humiditythe mass of water vapor per unit volume of air that contains the water vapor; usually expressed as grams of water vapor per cubic meter of air
absolute humidity
absolute magnitude the brightness that a starwould have at a distance of 32.6 light-years from Earth
absolute magnitude
absolute zero the temperature at which molecular energy is at a minimum (0 K on the Kelvin scale or –273.16ºC on the Celsius scale)
absolute zero
absorption indigestion, the process by which the end products of digestion are absorbed by the organism's fluids and cells
absorption in digestion
absorption in optics, the transfer of light energy to particles of matter
absorption in optics
a diagram or graph that indicates the wavelengths of radiant energy that a substance absorbs
absorption spectrum
absolute age he numeric age of an object or event, often stated in years before the present, as established by an absolute-dating process, such as radiometric dating
absolute age
absolute dating any method that measures the age of an object or event in years rather than measuring the age relative to another object or event; one such method is radiometric dating
absolute dating
absolute humiditythe mass of water vapor per unit volume of air that contains the water vapor; usually expressed as grams of water vapor per cubic meter of air
absolute humidity
absolute magnitude the brightness that a starwould have at a distance of 32.6 light-years from Earth
absolute magnitude
absolute zero the temperature at which molecular energy is at a minimum (0 K on the Kelvin scale or –273.16ºC on the Celsius scale)
absolute zero
absorption indigestion, the process by which the end products of digestion are absorbed by the organism's fluids and cells
absorption in digestion
absorption in optics, the transfer of light energy to particles of matter
absorption in optics
a diagram or graph that indicates the wavelengths of radiant energy that a substance absorbs
absorption spectrum
abyssal plain a large, flat, almost level area of the deep-ocean basin
abyssal plain
abyssal zone the benthic environment that extends from beneath the bathyal zone to a depth of up to 6,000 m
abyssal zone
acanthodian an early fish; the earliest known vertebrate to have jaws
acceleration the rate at which velocity changes over time; an object accelerates if its speed, direction, or both change
a pigment that absorbs light energy and transfers it to chlorophyll in photosynthesis
accessory pigment
acclimation an organism's change in response to a change in the organism's environment
accuracy a description of how close a measurement is to the true value of the quantity measured
acetyl-CoA acetyl coenzyme A, a compound that is synthesized by cells and that plays a major role in metabolism
acid any compound that increases the number of hydronium ions when dissolved in water; acids turn blue litmus paper red and react with bases and some metals to form salts
acid-base indicator a substance that changes in color depending on the pH of the solution that the substance is in
acid-base indicator
acid-ionization constant the term Ka
acid-ionization constant
acid precipitation such as rain, sleet, or snow, that contains a high concentration of acids, often because of the pollution of the atmosphere
acid precipitation
acid rain precipitation that has a pH below normal and has an unusually high concentration of sulfuric or nitric acids, often as a result of chemical pollution of the air from sources such as automobile exhausts and the burning of fossil fuels
acid rain
acid shock the sudden runoff of large amounts of highly acidic water into lakes and streams when snow melts in the spring or when heavy rains follow a drought
acid shock
acne an inflammatory disorder of the sebaceous glands that is characterized by skin lesions in the form of pimples, blackheads, and sometimes cysts
acoelomate an animal that lacks a coelom, or body cavity
acquired trait a change in an individual organism's structure or function that occurs during the lifetime of the organism, caused by injury, disease, or environmental factors, and that is not inherited by future generations
acquired trait
ACTH adrenocorticotropic hormone, a hormone that stimulates the adrenal cortex
actin a protein responsible for the contraction and relaxation of muscle
actinide any of the elements of the actinide series, which have atomic numbers from 89 (actinium, Ac) through 103 (lawrencium, Lr)
actinomycete a member of a class of bacteria that form branched filaments and that can be found in soil, in water, or as pathogens in animals and plants
action potential a sudden change in the polarity of the membrane of a neuron, gland cell, or muscle fiber that facilitates the transmission of electrical impulses
action potential
activated complex a molecule in an unstable state intermediate to the reactants and the products in the chemical reaction
activated complex
activationin genetics, the initiation of transcription of a particular gene
activation energy the minimum amount of energy required to start a chemical reaction
activation energy
active site the site on an enzyme that attaches to a substrate
active site
active solar heating the gathering of solar energy by collectors that are used to heat water or heat a building
active solar heating
active transport the movement of chemical substances, usually across the cell membrane, against a concentration gradient; requires cells to use energy
active transport
activity series a series of elements that have similar properties and that are arranged in descending order of chemical activity; examples of activity series include metals and halogens
activity series
actual yield the measured amount of a product of a reaction
actual yield
acyclovir an antiviral drug
adapt in populations, to change genetically over generations in response to the natural environment such that the population has an increased ability to survive and reproduce
adaptation the process of becoming adapted to an environment; an anatomical, physiological, or behavioral change that improves a population's ability to survive
adaptive radiation an evolutionary pattern in which many species evolve from a single ancestral species
adaptive radiation
addiction a physiological or psychological dependence on a substance, such as alcohol or drugs
addition polymer a polymer in which the formula of the repeating structural unit is identical to the molecular formula of the monomer
addition polymer
addition reaction a reaction in which an atom or molecule is added to an unsaturated molecule
addition reaction
adductor muscle the thick muscle that joins the two valves in mollusks and that causes the shell to open
adductor muscle
adenine one of the four bases that combine with sugar and phosphate to form a nucleotide subunit of DNA; adenine pairs with thymine
ADH antidiuretic hormone, a hormone that regulates the resorption of water from the kidney
adhesion the attractive force between two bodies of different substances that are in contact with each other
adiabatic the process that occurs when an air mass rises and expands without exchanging heat with its surroundings
adiabatic coolingthe process by which the temperature of an air mass decreases as the air mass rises and expands
adiabatic cooling
adiabatic process a thermodynamic process in which no heat transfer between the system and its environment takes place
adiabatic process
ADP adenosine diphosphate, an organic molecule that is involved in energy metabolism; composed of a nitrogenous base, a sugar, and two phosphate groups
adrenal gland one of the two endocrine glands located above each kidney
adrenal gland
advection fogcondensation of water vapor that results from the cooling of warm, moist air as the air moves across a cold surface
advection fog
advective cooling the process by which the temperature of an air mass decreases as the air mass moves over a cold surface
advective cooling
adventitious root a root that occurs in an unusual position, such as on stems or leaves
adventitious root
aerial photograph a photograph of the Earth's surface that is taken from the air
aerial photograph
aerobic describes a process that requires oxygen
aerobic exercise physical exercise intended to increase the activity of the heart and lungs to promote the body's use of oxygen
aerobic exercise
a neuron that conducts impulses toward the central nervous system
afferent neuron
aflatoxin a toxic fungal poison that causes liver cancer; found as contaminants in peanuts and corn; produced by a species of Aspergillus
afterbirth the remains of the placenta and the membranes, which are expelled from the mother's body following birth
aftershock an earthquake that follows the main shock of a large earthquake
agar a gel-like base for culturing microbes; extracted from certain red algae
Agent Orange a toxic substance used to case plants to lose their leaves
Agent Orange
age structure the classification of members of a population into groups according to age or the distribution of members of a population in terms of age groups
age structure
aggregation a grouping of cells or other organisms
agnathan a member of a class of primitive, jawless fishes
agriculture the change from a hunting and gathering society to an agricultural society that began about 10,000 years ago
agriculture the raising of crops and livestock for food or for other products that are useful to humans
AIDS acquired immune deficiency syndrome, a disease caused by HIV, an infection that results in an ineffective immune system
air mass a large body of air throughout which temperature and moisture content are similar
air mass
air pollution the contamination of the atmosphere by the introduction of pollutants from human and natural sources
air pollution
air pressure the measure of the force with which air molecules push on a surface
air pressure
albedo the fraction of solar radiation that is reflected off the surface of an object
albumen the white of an egg, composed primarily of the protein albumin
alcohol an organic compound that contains one or more hydroxyl groups attached to carbon atoms
alcoholic fermentation the anaerobic process by which yeasts and other microorganisms break down sugars to form carbon dioxide and ethanol
alcoholic fermentation
alcoholic hepatitis liver inflammation resulting from alcoholism
alcoholism a chronic disorder in which a person repeatedly drinks alcoholic beverages in an amount that interferes with the person's health and activities; the term implies a certain degree of addiction or dependence
aldehyde an organic compound that contains the carbonyl group, —CHO
aldosterone a hormone that helps maintain water and salt balance
algae eukaryotic organisms that convert the sun’s energy into food through photosynthesis but that do not have roots, stems, or leaves (singular, alga)
alginate a salt of alginic acid
alkali metal one of the elements of Group 1 of the periodic table (lithium, sodium, potassium, rubidium, cesium, and francium)
alkali metal
alkaline a solution that has a pH greater than 7 because of the dissociation of a base in water to produce hydroxide ions
alkaline-earth metal one of the elements of Group 2 of the periodic table (beryllium, magnesium, calcium, strontium, barium, and radium)
alkaline-earth metal
alkane a hydrocarbon characterized by a straight or branched carbon chain that contains only single bonds
alkene a hydrocarbon that contains one or more double bonds
alkyl group a group of atoms that forms when one hydrogen atom is removed from an alkane molecule
alkyl group
alkyl halide a compound formed from an alkyl group and a halogen (fluorine, chlorine, bromine, or iodine)
alkyl halide
alkyne a hydrocarbon that contains one or more triple bonds
allantois a membranous sac that acts as an organ of respiration and nutrition for the embryo; in humans, its blood vessels become the blood vessels of the umbilical cord
allele one of the alternative forms of a gene that governs a characteristic, such as hair color
allele frequency the proportion of gene copies in a population that are a given allele, expressed as a percentage
allele frequency
allergy a physical response to an antigen, which can be a common substance that produces little or no response in the general population
alloy a solid or liquid mixture of two or more metals
alluvial fan a fan-shaped mass of rock material deposited by a stream when the slope of the land decreases sharply; for example, alluvial fans form when streams flow from mountains to flat land
alluvial fan
alluvium rock and soil carried and deposited by streams
alpha decay the release of an alpha particle from a nucleus
alpha decay
alpha particle a positively charged atom that is released in the disintegration of radioactive elements and that consists of two protons and two neutrons
alpha particle
alpine glaciera narrow, wedge-shaped mass of ice that forms in a mountainous region and that is confined to a small area by surrounding topography; examples include valley glaciers, cirque glaciers, and piedmont glaciers
alpine glacier
alternating current an electric current that changes direction at regular intervals (abbreviation, AC)
alternating current
alternation of generations the alternation of sexual reproduction and asexual reproduction in certain plants and animals
alternation of generations
alternative energy from fossil fuels and that is still in development
alternative energy
altitude in astronomy, the angle between an object in the sky and the horizon
altitude in astronomy
altitude the height of an object above a reference point, such as sea level or the Earth's surface
altricial describes organisms that are not very developed when born and that require care or nursing
altruistic behavior self-sacrificing behavior that benefits another individual
altruistic behavior
alveolus any of the tiny air cells of the lungs where oxygen and carbon dioxide are exchanged
amber a hardened tree resin (a thick, saplike substance) in which fossils may be trapped and preserved
amine an organic compound that can be considered to be a derivative of ammonia
amino acid any one of 20 different organic molecules that contain a carboxyl and an amino group and that combine to form proteins
amino acid–based hormone
amino acid–based hormone a hormone that is made up of simple amino acids, peptides, or proteins
amino acid–based hormone
ammonia a colorless gas that has an alkaline reaction in water; forms in nature as an end product of animal metabolism (formula, NH3)
ammonification the formation of ammonia compounds in the soil by the action of bacteria on decaying matter
amniocentesis a procedure used in fetal diagnosis in which amniotic fluid is removed from the uterus of the pregnant woman
amnion the membrane that contains a developing embryo and its surrounding fluid
amniotic egg a type of egg that is produced by reptiles, birds, and egg-laying mammals and that contains a large amount of yolk; usually surrounded by a leathery or hard shell within which the embryo and its embryonic membranes develop
amniotic egg
amniotic sac the sac formed by the amnion
amniotic sac
a disease that is caused by an amoeba and that causes inflammation of the intestine
amoebic dysentery
amoebocyte in sponges and other invertebrates, an amoeba-like cell that moves through the body fluids, removes wastes, and participates in other processes
amoeboid movementamoeba-like movement; the movement of a cell by the formation of pseudopods
amoeboid movement
amorphous solid a solid in which the particles are not arranged with periodicity or order
amorphous solid
Amphoteric describes a substance, such as water, that has the properties of an acid and the properties of a base
amplexus the copulatory embrace of amphibians
the maximum distance that the particles of a wave’s medium vibrate from their rest position
amygdala a structure or body in the form of an almond; an almond-shaped structure located in the brain
amylase an enzyme that breaks down starches into sugars
anaerobic describes a process that does not require oxygen
anal fin a single fin usually located behind the anus of a fish
anal fin
analogous in comparisons of different organisms, describes features that are similar in function and appearance but not in structure or origin
analog signal a signal whose properties, such as amplitude and frequency, can change continuously in a given range
analog signal
anal pore in protozoans, an opening from which wastes are eliminated
anal pore
anaphase a phase of mitosis and meiosis in which the chromosomes separate
androgen a hormone that is secreted by the testes and that controls secondary male characteristics
anemia a condition in which the oxygen-carrying ability of red blood cells is reduced and the production of red blood cells decreases
an instrument used to measure wind speed
angiosperm a flowering plant that produces seeds within a fruit
angle of incidence the angle between a ray that strikes a surface and the perpendicular to that surface at the point of contact
angle of incidence
angle of reflection the angle formed by the line perpendicular to a surface and the direction in which a reflected ray moves
angle of reflection
angular acceleration the time rate of change of angular velocity expressed in radians per second per second
angular acceleration
angular displacement a change in angular position, described by a rotation around an axis
angular displacement a
angular momentum for a rotating object, the product of the object’s position and linear momentum at the moment the object passes a given point
angular momentum
quantum number the quantum number that indicates the shape of an orbital
quantum number
angular speed the rate at which a body rotates about an axis, usually expressed in radians per second
angular speed
angular unconformity an unconformity, or break in the geologic record, created when younger sediment is deposited on top of the eroded surface of older rocks that have been tilted or folded
angular unconformity
Animalia the classification kingdom containing complex, multicellular organisms that lack cell walls, are usually able to move around, and possess specialized sense organs that help them quickly respond to their environment
anion an ion that has a negative charge
annelid a worm that has ringlike segments, a true coelom, and a closed vascular system, such as an earthworm or a leech
annual ring in secondary xylem (wood), the growth ring formed in one season
annual ring
anode the electrode on whose surface oxidation takes place; anions migrate toward the anode, and electrons leave the system from the anode
antacid a weak base that neutralizes stomach acid
antagonistic hormone a hormone that counteracts the effect of another hormone
antagonistic hormone
antenna a feeler that is on the head of an invertebrate, such as a crustacean or an insect, and that senses touch, taste, or smell
antennule in crustaceans, a second pair of antennae, usually smaller than the first
anterior the front part of a body or structure
anther in flowering plants, the tip of a stamen, which contains the pollen sacs where grains form
anthracite one of the hardest forms of coal
anthropoid primate one of a subgroup of primates that includes monkeys, apes, and humans
antibiotic a substance that can inhibit the growth of or kill some microorganisms
antibody a protein that reacts to a specific antigen or that inactivates or destroys toxins
anticline an arch-shaped fold in rock layers in which the oldest layer is in the center of the fold
anticodon a region of tRNA that consists of three bases complementary to the codon of mRNA
anticyclone the rotation of air around a high-pressure center in the direction opposite to Earth's rotation
antigen a substance that stimulates an immune response
antigen shifting the production of new antigens by a virus as it mutates over time
antigen shifting
antinode a point in a standing wave, halfway between two nodes; it indicates a position of maximum intensity
antiviral drug a drug that destroys viruses or prevents their growth or replication
antiviral drug
anus the posterior opening of the digestive tract
aorta the main artery in the body; it carries blood from the left ventricle to systemic circulation
aortic arch the bend of the aorta between its ascending and descending portions
aortic arch
aortic valve the valve that regulates the flow of blood from the left ventricle to the aorta
aortic valve
aphelion the point in the orbit of a planet at which the planet is farthest from the sun
aphotic zone the deeper parts of the ocean, where there is so little light that plants cannot carry out photosynthesis
aphotic zone
apical dominance the inhibition of lateral bud growth on the stem of a plant by auxin produced in the terminal bud
apical dominance
apical meristem the growing region at the tips of stems and roots in plants
apical meristem
apical organ a ciliated plate located at the back of the larva of an annelid
apogee in the orbit of a satellite, the point at which the satellite is farthest from Earth
the brightness of a star as seen from Earth
apparent magnitude
appendage a structure that extends from the main body, such as a limb, tentacle, fin, or wing
appendicular skeleton the bones of the arms and legs
appendicular skeleton
applied science the use of science to solve practical problems
applied science
aquaculture the raising of aquatic plants and animals for human use or consumption
aqueous solution a solution in which water is the solvent
aqueous solution
aquifer a body of rock or sediment that stores groundwater and allows the flow of groundwater
arable land farmland that can be used to grow crops
arable land
arachnid an arthropod that has eight legs and no wings or antennae; a spider, scorpion, mite, or tick
arachnoid membrane the middle membrane of the three sacs that surround the brain and spinal cord
arachnoid membrane
Archaeain a modern taxonomic system, a domain made up of prokaryotes (most of which are known to live in extreme environments) that are distinguished from other prokaryotes by differences in their genetics and in the makeup of their cell wall; this domain al arachnid igns with the traditional kingdom Archaebacteria
archaeaprokaryotes (most of which are known to live in extreme environments) that are distinguished from other prokaryotes by differences in their genetics and in the makeup of their cell wall; members of the domain Archaea (singular, archaeon)
Archaebacteria a kingdom made up of prokaryotes (most of which are known to live in extreme environments) that are distinguished from other prokaryotes by differences in their genetics and in the makeup of their cell wall; currently, biologists prefer to classify members of this kingdom into the domain Archaea
archegonium a female reproductive structure of small, nonvascular plants that produces a single egg and in which fertilization and development take place
archenteron the primitive gastric cavity of an embryo
Archimedes' principle the principle that states that the buoyant force on an object in a fluid is an upward force equal to the weight of the volume of fluid that the object displaces
Archimedes' principle
area a measure of the size of a surface or a region
arête a sharp, jagged ridge that forms between cirques
Arrhenius base a substance that increases the concentration of hydroxide ions in aqueous solution
Arrhenius base
arteriole a small artery that gives rise to capillaries
artery a blood vessel that carries blood away from the heart to the body's organs
artesian formation a sloping layer of permeable rock sandwiched between two layers of impermeable rock and exposed at the surface
artesian formation
artesian spring a spring whose water flows from a crack in the bed over the artesian aquifer
artesian spring
artesian well a well whose water comes from an artesian aquifer
artesian well
arthropod a member of the phylum Arthropoda, which includes invertebrate animals such as insects, crustaceans, and arachnids; characterized by having segmented bodies and paired appendages
artificial eutrophication a process that increases the amount of nutrients in a body of water through human activities, such as waste disposal and land drainage
artificial satellite any human-made object placed in orbit around a body in space
artificial selection the selective breeding of organisms (by humans) for specific desirable characteristics
artificial selection
artificialtransmutationthe transformation of atoms of one element into atoms of another element as a result of a nuclear reaction, such as bombardment with neutrons
artificial transmutation
asbestos any of six silicate minerals that form bundles of minute fibers that are heat resistant, flexible, and durable
ascocarp the reproductive portion of an ascomycete
ascogonium the female sexual organ or cell in ascomycetes
ascospore a spore produced in an ascus by ascomycetes
ascus the spore sac where ascomycetes produce ascospores
asexualreproductionreproduction that does not involve the union of gametes and in which a single parent produces offspring that are genetically identical to the parent
asexual reproduction
aspirin the common name of acetylsalicylic acid, a pain reliever
assortative mating sexual reproduction in which males and females do not breed randomly
assortative mating
asteroid a small, rocky object that orbits the sun; most asteroids are located in a band between the orbits of Mars and Jupiter
asteroid belt the region of the solar system that is between the orbits of Mars and Jupiter and in which most asteroids orbit
asteroid belt
asthenosphere the solid, plastic layer of the mantle beneath the lithosphere; made of mantle rock that flows very slowly, which allows tectonic plates to move on top of it
astronomical unit the average distance between the Earth and the sun; approximately 150 million kilometers (symbol, AU)
astronomical unit
astronomy the scientific study of the universe
asymmetrical irregular in shape; without symmetry
atherosclerosis a disease characterized by the buildup of fatty materials on the interior walls of the arteries
atmosphere a mixture of gases that surrounds a planet or moon
atmosphere of pressure the pressure of the Earth's atmosphere at sea level; exactly equivalent to 760 mm Hg
atmosphere of pressure
atmospheric pressure the force per unit area that is exerted on a surface by the weight of the atmosphere
the passage of an electromagnetic wave signal through the atmosphere between a transmitter and a receiver
atmospheric transmission
atoll a nearly circular coral reef surrounding a lagoon
atom the smallest unit of an element that maintains the chemical properties of that element
atomic mass the mass of an atom expressed in atomic mass units units units
atomic mass
atomic mass unit a unit of mass that describes the mass of an atom or molecule; it is exactly 1/12 of the mass of a carbon atom with mass number 12 (symbol, amu)
atomic mass unit
atomic number the number of protons in the nucleus of an atom; the atomic number is the same for all atoms of an element
atomic number
atomic radius one-half of the distance between the center of identical atoms that are not bonded together
ATP adenosine triphosphate, an organic molecule that acts as the main energy source for cell processes; composed of a nitrogenous base, a sugar, and three phosphate groups
ATP synthetase an enzyme that catalyzes the synthesis of ATP
ATP synthetase
atriopore an opening from the atrial cavity to the exterior in certain fish
atrioventricular node heart tissues that generate the activity that produces heartbeat (abbreviation, AV node)
atrioventricular node
atrioventricular valve a one-way valve that separates each atrium from the ventricle beneath it (abbreviation, AV valve)
atrioventricular valve
atrium a chamber that receives blood that is returning to the heart
attenuated strain a virus strain that has less potency and that is used in vaccines to produce an immune response
attenuated strain
auditory canal the tube through which air enters the ear
auditory canal
Aufbau principle the principle that states that the structure of each successive element is obtained by adding one proton to the nucleus of the atom and one electron to the lowest-energy orbital that is available
Aufbau principle
aurora colored light produced by charged particles from the solar wind and from the magnetosphere that react with and excite the oxygen and nitrogen of Earth’s upper atmosphere; usually seen in the sky near Earth’s magnetic poles
an early hominid that may have lived more than 3.6 million years ago
autoimmune disease a disease in which the immune system attacks the organism's own cells
autoimmune disease
autonomic nervous system the part of the nervous system that controls involuntary actions
autonomic nervous system
autooxidation a spontaneous, self-catalyzed oxidation that occurs in the presence of air and that is initiated by factors such as heat or light
autosome any chromosome that is not a sex chromosome
autotrophythe ability of an organism to drop a body part and, usually, to regenerate a new one
autonomic nervous system
autumnal equinox the moment when the sun passes directly above the equator from north to south; day and night are of equal length on the day that the autumnal equinox occurs
auxin a plant hormone that regulates cell elongation
auxinthe weighted average of the masses of all naturally occurring isotopes of an element
average velocity the total displacement divided by the time interval during which the displacement occurred
autumnal equinox
Avogadro's law the law that states that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules
Avogadro's law
Avogadro's number 6.02 ¥ 1023, the number of atoms or molecules in 1 mol
axial skeleton the bones of the skull and vertebral column
average velocity
axis an imaginary straight line running through the Earth from pole to pole
axon an elongated extension of a neuron that carries impulses away from the cell body
azimuthal projection a map projection that is made by moving the surface features of the globe onto a plane
azimuthal projection
AZT azidothymidine, a drug that blocks DNA replication and is useful in the treatment of AIDS