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abiotic factors  nonliving parts of an organism's environment
absolute humidity  a measure of the actual amount of water vapor in the air at a given time—for example, in grams per cubic meter
absolute magnitude  a classification scheme to compensate for the distance differences to stars; calculations of the brightness that stars would appear to have if they were all at a defined, standard distance
absolute scale  temperature scale set so that zero is at the theoretical lowest temperature possible, which would occur when all random motion of molecules has ceased
absolute zero  the theoretical lowest temperature possible, which occurs when all random motion of molecules has ceased
abyssal plain  the practically level plain of the ocean floor
acceleration  a change in velocity per change in time; by definition, this change in velocity can result from a change in speed, a change in direction, or a combination of changes in speed and direction
accretion disk  fat bulging disk of gas and dust from the remains of the gas cloud that forms around a protostar
acetylcholine  a neurotransmitter secreted into the synapse by many axons and received by dendrites
acetylcholinesterase  an enzyme present in the synapse that destroys acetylcholine
achondrites  homogeneously textured stony meteorites
acid  any substance that is a proton donor when dissolved in water; generally considered a solution of hydronium ions in water that can neutralize a base, forming a salt and water
acid-base indicator  a vegetable dye used to distinguish acid and base solutions by a color change
acquired characteristics  characteristics an organism gains during its lifetime that are not genetically determined and therefore cannot be passed on to future generations
active transport  use of a carrier molecule to move molecules through a cell membrane in a direction opposite that of the concentration gradient; the carrier requires an input of energy other than the kinetic energy of the molecules
adenine  a double-ring nitrogenous-base molecule in DNA and RNA; the complementary base of thymine or uracil
adenosine triphosphate (ATP)  a molecule formed from the building blocks of adenine, ribose, and phosphates; it functions as the primary energy carrier in the cell
aerobic cellular respiration  the biochemical pathway that requires oxygen and converts food, such as carbohydrates, to carbon dioxide and water; during this conversion, it releases the chemical-bond energy as ATP molecules
air mass  a large, more or less uniform body of air with nearly the same temperature and moisture conditions throughout
air mass weather  the weather experienced within a given air mass; characterized by slow, gradual changes from day to day
alcohol  an organic compound with a general formula of ROH, where R is one of the hydrocarbon groups—for example, methyl or ethyl
aldehyde  an organic molecule with the general formula RCHO, where R is one of the hydrocarbon groups—for example, methyl or ethyl
alkali metals  members of family IA of the periodic table, having common properties of shiny, low-density metals that can be cut with a knife and that react violently with water to form an alkaline solution
alkaline earth metals  members of family IIA of the periodic table, having common properties of soft, reactive metals that are less reactive than alkali metals
alkanes  hydrocarbons with single covalent bonds between the carbon atoms
alkenes  hydrocarbons with a double covalent carbon-carbon bond
alkyne  hydrocarbon with a carbon-carbon triple bond
alleles  alternative forms of a gene for a particular characteristic (e.g., attachedearlobe and free-earlobe are alternative alleles for ear shape)
alpha particle  the nucleus of a helium atom (two protons and two neutrons) emitted as radiation from a decaying heavy nucleus; also known as an alpha ray
alpine glaciers  glaciers that form at high elevations in mountainous regions
alternating current  an electric current that first moves one direction, then the opposite direction with a regular frequency
alternation of generations  a term used to describe that aspect of the life cycle in which there are two distinctly different forms of an organism; each form is involved in the production of the other and only one form is involved in producing gametes
alveoli  tiny sacs that are part of the structure of the lungs where gas exchange takes place
amino acids  organic molecules that join to form polypeptides and proteins
amp  unit of electric current; equivalent to C/s
ampere  full name of the unit amp
amplitude  the extent of displacement from the equilibrium condition; the size of a wave from the rest (equilibrium) position
anaphase  the third stage of mitosis, characterized by dividing of the centromeres and movement of the chromosomes to the poles
androgens  male sex hormones produced by the testes that cause the differentiation of typical internal and external genital male anatomy
angle of incidence  angle of an incident (arriving) ray or particle to a surface; measured from a line perpendicular to the surface (the normal)
angle of reflection  angle of a reflected ray or particle from a surface; measured from a line perpendicular to the surface (the normal)
angular momentum quantum number  in the quantum mechanics model of the atom, one of four descriptions of the energy state of an electron wave; this quantum number describes the energy sublevels of electrons within the main energy levels of an atom
anorexia nervosa  a nutritional deficiency disease characterized by severe, prolonged weight loss for fear of becoming obese
anther  the sex organ in plants that produces the pollen that contains the sperm
anticline  an arch-shaped fold in layered bed rock
anticodon  a sequence of three nitrogenous bases on a tRNA molecule capable of forming hydrogen bonds with three complementary bases on an mRNA codon during translation
anticyclone  a high-pressure center with winds flowing away from the center; associated with clear, fair weather
antinode  region of maximum amplitude between adjacent nodes in a standing wave
aorta  the large blood vessel that carries blood from the left ventricle to the majority of the body
apoptosis  also known as "programmed cell death"; death of specific cells that has a genetic basis and is not the result of injury
apparent magnitude  a classification scheme for different levels of brightness of stars that you see; brightness values range from one to six with the number one (first magnitude) assigned to the brightest star and the number six (sixth magnitude) assigned to the faintest star that can be seen
aquifer  a layer of sand, gravel, or other highly permeable material beneath the surface that is saturated with water and is capable of producing water in a well or spring
Archaea  the domain in which are found prokaryotic organisms that live in extreme habitats
archaeology  the study of past human life and culture from material evidence
area  the extent of a surface; the surface bounded by three or more lines
arid  dry climate classification; receives less than 25 cm (10 in) precipitation per year
aromatic hydrocarbon  organic compound with at least one benzene ring structure; cyclic hydrocarbons and their derivatives
arteries  the blood vessels that carry blood away from the heart
arterioles  small arteries located just before capillaries that can expand and contract to regulate the flow of blood to parts of the body
artesian  term describing the condition where confining pressure forces groundwater from a well to rise above the aquifer
asbestos  the common name for any one of several incombustible fibrous minerals that will not melt or ignite and can be woven into a fireproof cloth or used directly in fireproof insulation; about six different commercial varieties of asbestos are used, one of which has been linked to cancer under heavy exposure
assimilation  the physiological process that takes place in a living cell as it converts nutrients in food into specific molecules required by the organism
asteroids  small rocky bodies left over from the formation of the solar system; most are accumulated in a zone between the orbits of Mars and Jupiter
asthenosphere  a plastic, mobile layer of the earth's structure that extends around the earth below the lithosphere
astronomical unit  the radius of the earth's orbit is defined as one astronomical unit (AU)
atom  the smallest unit of an element that can exist alone or in combination with other elements
atomic mass unit  relative mass unit (u) of an isotope based on the standard of the carbon-12 isotope, which is defined as a mass of exactly 12.00 u; one atomic mass unit (1 u) is 1/12 the mass of a carbon-12 atom
atomic number  the number of protons in the nucleus of an atom
atomic weight  weighted average of the masses of stable isotopes of an element as they occur in nature, based on the abundance of each isotope of the element and the atomic mass of the isotope compared to carbon-12
atria  thin-walled sacs of the heart that receive blood from the veins of the body and empty into the ventricles; singular, atrium
atrioventricular valves  located between the atria and ventricles of the heart preventing blood from flowing backward from the ventricles into the atria
autosomes  chromosomes that typically carry genetic information used by the organism for characteristics other than the primary determination of sex
autotroph  an organism that is able to make its food molecules from inorganic raw materials by using basic energy sources such as sunlight
axis  the imaginary line about which a planet or other object rotates
axon  a neuronal fiber that carries information away from the nerve cell body
background radiation  ionizing radiation (alpha, beta, gamma, etc.) from natural sources; between 100 and 500 millirems/yr of exposure to natural radioactivity from the environment
Balmer series  a set of four line spectra, narrow lines of color emitted by hydrogen atom electrons as they drop from excited states to the ground state
band of stability  a region of a graph of the number of neutrons versus the number of protons in nuclei; nuclei that have the neutron to proton ratios located in this band do not undergo radioactive decay
barometer  an instrument that measures atmospheric pressure, used in weather forecasting and in determining elevation above sea level
basal metabolic rate (BMR)  the amount of energy required to maintain normal body activity while at rest
base  any substance that is a proton acceptor when dissolved in water; generally considered a solution that forms hydroxide ions in water that can neutralize an acid, forming a salt and water
basilar membrane  a membrane in the cochlea containing sensory cells that are stimulated by the vibrations caused by sound waves
basin  a large, bowl-shaped fold in the land into which streams drain; also a small enclosed or partly enclosed body of water
beat  rhythmic increases and decreases of volume from constructive and destructive interference between two sound waves of slightly different frequencies
benthic  aquatic organisms that live on the bottom
beta particle  high-energy electron emitted as ionizing radiation from a decaying nucleus; also known as a beta ray
big bang theory  current model of galactic evolution in which the universe was created from an intense and brilliant explosion from a primeval fireball
bile  a product of the liver, stored in the gallbladder, which is responsible for the emulsification of fats
binding energy  the energy required to break a nucleus into its constituent protons and neutrons; also the energy equivalent released when a nucleus is formed
binomial system of nomenclature  a naming system that uses two Latin names, genus and specific epithet, for each type of organism
biodiversity  the number of different kinds of organisms found in an area
bioengineering  also referred to as genetic engineering; the process of purposely altering the genetic makeup of organisms
biogenesis  the concept that life originates only from preexisting life
biological species concept  the concept that species can be distinguished from one another by their inability to interbreed
biology  the science that deals with the study of living things and how living things interact with things around them
biomes  large regional communities primarily determined by climate
biotechnology  the science of gene manipulation
biotic factors  living parts of an organism's environment
blackbody radiation  electromagnetic radiation emitted by an ideal material (the blackbody) that perfectly absorbs and perfectly emits radiation
black hole  the theoretical remaining core of a supernova with an intense gravitational field
blood  the fluid medium consisting of cells and plasma that assists in the transport of materials and heat
Bohr model  model of the structure of the atom that attempted to correct the deficiencies of the solar system model and account for the Balmer series
boiling point  the temperature at which a phase change of liquid to gas takes place through boiling; the same temperature as the condensation point
boundary  the division between two regions of differing physical properties
breaker  a wave whose front has become so steep that the top part has broken forward of the wave, breaking into foam, especially against a shoreline
British thermal unit  the amount of energy or heat needed to increase the temperature of 1 pound of water 1 degree Fahrenheit (abbreviated Btu)
bronchi  major branches of the trachea that ultimately deliver air to bronchioles in the lungs
bronchioles  small tubes that deliver air to the alveoli in the lung; they are capable of contracting
bulimia  a nutritional deficiency disease characterized by a binge-and-purge cycle of eating
calorie  the amount of energy (or heat) needed to increase the temperature of 1 gram of water 1 degree Celsius
Calorie  the nutritionist's "calorie"; equivalent to 1 kilocalorie
cancer  any abnormal growth of cells that has a malignant potential
capillaries  tiny blood vessels through the walls of which exchange between cells and the blood takes place
carbohydrates  organic compounds that include sugars, starches, and cellulose; carbohydrates are used by plants and animals for structure, protection, and food
carbonation  in chemical weathering, a reaction that occurs naturally between carbonic acid (H2CO3) and rock minerals
carbon cycle  the series of processes and organisms through which carbon atoms pass in ecological systems
carbon film  a type of fossil formed when the volatile and gaseous constituents of a buried organic structure are distilled away, leaving a carbon film as a record
carcinogens  agents responsible for causing cancer
carnivores  animals that eat other animals
carrier (genetic)  any individual having a hidden, recessive allele
carrier protein  proteins that pick up and deliver molecules from one place in a cell or multicellular organism and transport them to another; for example, certain blood proteins
carrying capacity (ecosystem)  the optimum population size an area can support over an extended period of time
cast  sediments deposited by groundwater in a mold, taking the shape and external features of the organism that was removed to form the mold, then gradually changing to sedimentary rock
cathode rays  negatively charged particles (electrons) that are emitted from a negative terminal in an evacuated glass tube
cell  the basic structural unit that makes up all living things
cell membrane  the outer-boundary membrane of the cell; also known as the plasma membrane
cell plate  a plant-cell structure that begins to form in the center of the cell and proceeds to the cell membrane, resulting in cytokinesis
cellulose  a polysaccharide abundant in plants that forms the fibers in cell walls that provide structure for plant materials
cell wall  an outer covering on some cells; may be composed of cellulose, chitin, or peptidoglycan depending on the kind of organism
Celsius scale  referent scale that defines numerical values for measuring hotness or coldness, defined as degrees of temperature; based on the reference points of the freezing point of water and the boiling point of water at sea-level pressure, with 100 degrees between the two points
cementation  process by which spaces between buried sediment particles under compaction are filled with binding chemical deposits, binding the particles into a rigid, cohesive mass of a sedimentary rock
Cenozoic  the most recent geologic era; the time of recent life, meaning the fossils of this era are identical to the life found on the earth today
central nervous system  the portion of the nervous system consisting of the brain and spinal cord
centrifugal force  an apparent outward force on an object following a circular path that is a consequence of the third law of motion
centrioles  organelles composed of microtubules located just outside the nucleus
centripetal force  the force required to pull an object out of its natural straight-line path and into a circular path; centripetal means "center seeking"
centromere  the unreplicated region where two chromatids are joined
Cepheid variables  a bright variable star that can be used to measure distance
cerebellum  a region of the brain connected to the medulla oblongata that receives many kinds of sensory stimuli and coordinates muscle movement
cerebrum  a region of the brain that surrounds most of the other parts of the brain and is involved in consciousness and thought
chain reaction  a self-sustaining reaction where some of the products are able to produce more reactions of the same kind; in a nuclear chain reaction neutrons are the products that produce more nuclear reactions in a self-sustaining series
chemical bond  an attractive force that holds atoms together in a compound
chemical change  a change in which the identity of matter is altered and new substances are formed
chemical energy  a form of energy involved in chemical reactions associated with changes in internal potential energy; a kind of potential energy that is stored and later released during a chemical reaction
chemical equation  concise way of describing what happens in a chemical reaction
chemical reaction  a change in matter where different chemical substances are created by forming or breaking chemical bonds
chemical weathering  the breakdown of minerals in rocks by chemical reactions with water, gases of the atmosphere, or solutions
chemistry  the science concerned with the study of the composition, structure, and properties of substances and the transformations they undergo
Chinook  a warm wind that has been warmed by compression; also called Santa Ana
chloroplast  an energy-converting, membranous, saclike organelle in plant cells containing the green pigment chlorophyll
chondrites  subdivision of stony meteorites containing small spherical lumps of silicate minerals or glass
chondrules  small spherical lumps of silicate minerals or glass found in some meteorites
chromatid  one of two component parts of a chromosome formed by replication and attached at the centromere
chromatin  areas or structures within the nucleus of a cell composed of long, loosely arranged molecules of deoxyribonucleic acid (DNA) in association with proteins
chromatin fibers  see nucleoproteins
chromosomal aberrations  changes in the gene arrangement in chromosomes; for example, translocation and duplication mutations
chromosomes  complex tightly coiled structures within the nucleus composed of various kinds of histone proteins and DNA that contains the cell's genetic information
class  a group of closely related orders found within a phylum
cleavage furrow  an indentation of the cell membrane of an animal cell that pinches the cytoplasm into two parts
climate  the general pattern of weather that occurs in a region over a number of years
coalescence process (meteorology)  the process by which large raindrops form from the merging and uniting of millions of tiny water droplets til67002_glo.qxd 5/8/03 11:08 AM Page 617
cochlea  the part of the ear that converts sound into nerve impulses
coding strand  one of two DNA strands that serves as a template, or pattern, for the synthesis of RNA
codominance  when an organism has two different alleles for a trait and they both express themselves
codon  a sequence of three nucleotides of an mRNA molecule that directs the placement of a particular amino acid during translation
coitus  see sexual intercourse
cold front  the front that is formed as a cold air mass moves into warmer air
combination chemical reaction  a synthesis reaction in which two or more substances combine to form a single compound
comets  celestial objects originating from the outer edges of the solar system that move about the sun in highly elliptical orbits; solar heating and pressure from the solar wind form a tail on the comet that points away from the sun
commensalism  a relationship between two organisms in which one organism is helped and the other is not affected
community  all of the kinds of interacting organisms within an ecosystem
compaction  the process of pressure from a depth of overlying sediments squeezing together the deeper sediments and squeezing out water
competition  a kind of interaction between organisms in which both organisms are harmed to some extent
complementary base  a nitrogenous base in nucleic acids that can form hydrogen bonds with another base of a specific nucleotide
complex carbohydrates  macromolecules formed as a result of the chemical combining of simple sugars (monomers) to form polysaccharides; for example, starch
compound  a pure chemical substance that can be decomposed by a chemical change into simpler substances with a fixed mass ratio
compressive stress  a force that tends to compress the surface as the earth's plates move into each other
concentration  an arbitrary description of the relative amounts of solute and solvent in a solution; a larger amount of solute makes a concentrated solution, and a small amount of solute makes a dilute concentration
conception  fertilization
condensation (sound)  a compression of gas molecules; a pulse of increased density and pressure that moves through the air at the speed of sound
condensation (water vapor)  when more vapor or gas molecules are returning to the liquid state than are evaporating
condensation nuclei  tiny particles such as tiny dust, smoke, soot, and salt crystals that are suspended in the air on which water condenses
condensation point  the temperature at which a gas or vapor changes back to a liquid
conduction  the transfer of heat from a region of higher temperature to a region of lower temperature by increased kinetic energy moving from molecule to molecule
cones  light-sensitive cells in the retina of the eye that respond to different colors of light
constructive interference  the condition in which two waves arriving at the same place, at the same time and in phase, add amplitudes to create a new wave
consumers  organisms that must obtain energy in the form of organic matter
continental air mass  dry air masses that form over large land areas
continental climate  a climate influenced by air masses from large land areas; hot summers and cold winters
continental drift  a concept that continents shift positions on the earth's surface, moving across the surface rather than being fixed, stationary landmasses
continental glaciers  glaciers that cover a large area of a continent; for example, Greenland and the Antarctic
continental shelf  a feature of the ocean floor; the flooded margins of the continents that form a zone of relatively shallow water adjacent to the continents
continental slope  a feature of the ocean floor; a steep slope forming the transition between the continental shelf and the deep ocean basin
control group  the situation used as the basis for comparison in a controlled experiment
controlled experiment  an experiment that allows for a comparison of two events that are identical in all but one respect
control processes  mechanisms that ensure that an organism will carry out all metabolic activities in the proper sequence (coordination) and at the proper rate (regulation)
control rods  rods inserted between fuel rods in a nuclear reactor to absorb neutrons and thus control the rate of the nuclear chain reaction
convection  transfer of heat from a region of higher temperature to a region of lower temperature by the displacement of highenergy molecules—for example, the displacement of warmer, less dense air (higher kinetic energy) by cooler, more dense air (lower kinetic energy)
convection cell  complete convective circulation pattern; also, slowly turning regions in the plastic asthenosphere that might drive the motion of plate tectonics
convection zone (of a star)  part of the interior of a star according to a model; the region directly above the radiation zone where gases are heated by the radiation zone below and move upward by convection to the surface, where they emit energy in the form of visible light, ultraviolet radiation, and infrared radiation
convergent boundaries  boundaries that occur between two plates moving toward each other
copulation  see sexual intercourse
core (of a star)  dense, very hot region of a star where nuclear fusion reactions release gamma and X-ray radiation
core (of the earth)  the center part of the earth, which consists of a solid inner part and liquid outer part; makes up about 15 percent of the earth's total volume and about onethird of its mass
Coriolis effect  the apparent deflection due to the rotation of the earth; it is to the right in the Northern Hemisphere
corpus luteum  a glandlike structure produced in the ovary that produces hormones (progesterone and estrogen) that prevent the release of other eggs
correlation  the determination of the equivalence in geologic age by comparing the rocks in two separate locations
coulomb  unit used to measure quantity of electric charge; equivalent to the charge resulting from the transfer of 6.24 billion particles such as the electron
Coulomb's law  relationship between charge, distance, and magnitude of the electrical force between two bodies
covalent bond  a chemical bond formed by the sharing of a pair of electrons
covalent compound  chemical compound held together by a covalent bond or bonds
creep  the slow downhill movement of soil down a steep slope
crest  the high mound of water that is part of a wave; also refers to the condensation, or high-pressure part, of a sound wave
critical angle  limit to the angle of incidence when all light rays are reflected internally
critical mass  mass of fissionable material needed to sustain a chain reaction
crossing-over  the process that occurs when homologous chromosomes exchange equivalent sections of DNA during meiosis
crude oil  petroleum pumped from the ground that has not yet been refined into usable products
crust  the outermost part of the earth's interior structure; the thin, solid layer of rock that rests on top of the Mohorovicic discontinuity
curie  unit of nuclear activity defined as 3.70 x 1010 nuclear disintegrations per second
cycle  a complete vibration
cyclone  a low-pressure center where the winds move into the low-pressure center and are forced upward; a low-pressure center with clouds, precipitation, and stormy conditions
cytokinesis  division of the cytoplasm of one cell into two new cells
cytoplasm  the more fluid portion of the protoplasm that surrounds the nucleus
cytosine  a single-ring nitrogenous-base molecule in DNA and RNA; complementary to guanine
dark energy  a recently discovered mystery force that is apparently accelerating the expanding universe
dark matter  missing matter of the universe that is believed to exist, but is invisible and unseen
data  measurement information used to describe something
data points  points that may be plotted on a graph to represent simultaneous measurements of two related variables
daughter cells  two cells formed by cell division
daughter chromosomes  chromosomes produced by DNA replication that contain identical genetic information; formed after chromosome division in anaphase
daughter nuclei  two nuclei formed by mitosis
decibel scale  a nonlinear scale of loudness based on the ratio of the intensity level of a sound to the intensity at the threshold of hearing
decomposers  organisms that use dead organic matter as a source of energy
decomposition chemical reaction  a chemical reaction in which a compound is broken down into the elements that make up the compound, into simpler compounds, or into elements and simpler compounds
deflation  the widespread removal of base materials from the surface by the wind
delta  a somewhat triangular deposit at the mouth of a river formed where a stream flowing into a body of water slowed and lost its sediment-carrying ability
denature  a change in the chemical and physical properties of a molecule as a result of the breaking of chemical bonds within the molecule; for example, the change in egg white as a result of cooking
dendrites  neuronal fibers that receive information from axons and carry it toward the nerve-cell body
denitrifying bacteria  bacteria capable of converting nitrite (NO2-) to nitrogen gas (N2), which is released into the atmosphere
density  the compactness of matter described by a ratio of mass per unit volume
deoxyribonucleic acid (DNA)  a polymer of nucleotides that serves as genetic information; in prokaryotic cells, it is a double-stranded DNA loop and contains attached HU proteins and in eukaryotic cells, it is found in strands with attached histone proteins—when tightly coiled, it is known as a chromosome
deoxyribose  a 5-carbon sugar molecule; a component of DNA
depolarized  having lost the electrical difference existing between two points or objects
destructive interference  the condition in which two waves arriving at the same point at the same time out of phase add amplitudes to create zero total disturbance
dew  condensation of water vapor into droplets of liquid on surfaces
dew point temperature  the temperature at which condensation begins
diaphragm  a muscle separating the lung cavity from the abdominal cavity that is involved in exchanging the air in the lungs
diastolic blood pressure  the blood pressure recorded while the heart is relaxing
diastrophism  all-inclusive term that means any and all possible movements of the earth's plates, including drift, isostatic adjustment, and any other process that deforms or changes the earth's surface by movement
diet  the food and drink consumed by a person from day to day
differentiation  the process of forming specialized cells within a multicellular organism
diffuse reflection  light rays reflected in many random directions, as opposed to the parallel rays reflected from a perfectly smooth surface such as a mirror
diffusion  net movement of a kind of molecule from an area of higher concentration to an area of lesser concentration
diploid  having two sets of chromosomes: one set from the maternal parent and one set from the paternal parent
direct current  an electrical current that always moves in one direction
direct proportion  when two variables increase or decrease together in the same ratio (at the same rate)
disaccharides  two monosaccharides joined together with the loss of a water molecule; examples of disaccharides are sucrose (table sugar), lactose, and maltose
dispersion  the effect of spreading colors of light into a spectrum with a material that has an index of refraction that varies with wavelength
divergent boundaries  boundaries that occur between two plates moving away from each other
divide  line separating two adjacent watersheds
DNA code  a sequence of three nucleotides of a DNA molecule
DNA polymerase  an enzyme that bonds DNA nucleotides together when they base pair with an existing DNA strand
DNA replication  the process by which the genetic material (DNA) of the cell reproduces itself prior to its distribution to the next generation of cells
domain  a classification group above that of kingdoms
dome  a large, upwardly bulging, symmetrical fold that resembles a dome
dominant allele  an allele that expresses itself and masks the effects of other alleles for the trait
Doppler effect  an apparent shift in the frequency of sound or light due to relative motion between the source of the sound or light and the observer
double bond  covalent bond formed when two pairs of electrons are shared by two atoms
dune  a hill, low mound, or ridge of windblown sand or other sediments
duodenum  the first part of the small intestine, which receives food from the stomach and secretions from the liver and pancreas
earthquake  a quaking, shaking, vibrating, or upheaval of the earth's surface
earthquake epicenter  point on the earth's surface directly above an earthquake focus
earthquake focus  place where seismic waves originate beneath the surface of the earth
echo  a reflected sound that can be distinguished from the original sound, which usually arrives 0.1 s or more after the original sound
eclipse  when the shadow of a celestial body falls on the surface of another celestial body
ecology  the branch of biology that studies the relationships between organisms and their environment
ecosystem  an interacting unit consisting of a collection of organisms and abiotic factors
egg  the haploid sex cell produced by sexually mature females
ejaculation  the release of sperm cells and seminal fluid through the penis
elastic rebound  the sudden snap of stressed rock into new positions; the recovery from elastic strain that results in an earthquake
elastic strain  an adjustment to stress in which materials recover their original shape after a stress is released
electrical energy  a form of energy from electromagnetic interactions; one of five forms of energy—mechanical, chemical, radiant, electrical, and nuclear
electrical force  a fundamental force that results from the interaction of electrical charge and is billions and billions of times stronger than the gravitational force; sometimes called the "electromagnetic force" because of the strong association between electricity and magnetism
electrical insulators  electrical nonconductors, or materials that obstruct the flow of electric current
electrical nonconductors  materials that have electrons that are not moved easily within the material—for example, rubber; electrical nonconductors are also called electrical insulators
electric charge  a fundamental property of electrons and protons; electrons have a negative electric charge and protons have a positive electric charge
electric circuit  consists of a voltage source that maintains an electrical potential, a continuous conducting path for a current to follow, and a device where work is done by the electrical potential; a switch in the circuit is used to complete or interrupt the conducting path
electric current  the flow of electric charge
electric field  force field produced by an electrical charge
electric field lines  a map of an electric field representing the direction of the force that a test charge would experience; the direction of an electric field shown by lines of force
electric generator  a mechanical device that uses wire loops rotating in a magnetic field to produce electromagnetic induction in order to generate electricity
electrolyte  water solution of ionic substances that conducts an electric current
electromagnet  a magnet formed by a solenoid that can be turned on and off by turning the current on and off
electromagnetic force  one of four fundamental forces; the force of attraction or repulsion between two charged particles
electromagnetic induction  process in which current is induced by moving a loop of wire in a magnetic field or by changing the magnetic field
electron  subatomic particle that has the smallest negative charge possible and usually found in an orbital of an atom, but gained or lost when atoms become ions
electron configuration  the arrangement of electrons in orbitals and suborbitals about the nucleus of an atom
electron dot notation  notation made by writing the chemical symbol of an element with dots around the symbol to indicate the number of outer orbital electrons
electron pair  a pair of electrons with different spin quantum numbers that may occupy an orbital
electrostatic charge  an accumulated electric charge on an object from a surplus or deficiency of electrons; also called "static electricity"
element  a pure chemical substance that cannot be broken down into anything simpler by chemical or physical means; there are over 100 known elements, the fundamental materials of which all matter is made
El Niño  changes in the atmospheric pressure systems, ocean currents, water temperatures, and wind patterns that seem to be linked to worldwide changes in the weather
endocrine glands  secrete chemical messengers into the circulatory system
endocrine system  a number of glands that communicate with one another and other tissues through chemical messengers transported throughout the body by the circulatory system
endoplasmic reticulum (ER)  folded membranes and tubes throughout the eukaryotic cell that provide a large surface upon which chemical activities take place
endosymbiotic theory  a theory suggesting that some organelles found in eukaryotic cells may have originated as free-living prokaryotes
energy  the ability to do work
English system  a system of measurement that originally used sizes of parts of the human body as referents
entropy  the measure of disorder in thermodynamics
environment  the surroundings; anything that affects an organism during its lifetime
environmental resistance  the collective set of factors that limit population growth
enzymes  protein molecules, produced by organisms, that are able to control the rate at which chemical reactions occur
eon  the largest blocks of time in the earth's geologic history—the Hadean, Archean, Proterozoic, and Phanerozoic eons
epinephrine  a hormone produced by the adrenal medulla that increases heart rate, blood pressure, and breathing rate
epiphyte  a plant that lives on the surface of another plant without doing harm
epochs  subdivisions of geologic periods
equation  a statement that describes a relationship in which quantities on one side of the equal sign are identical to quantities on the other side
eras  the major blocks of time in the earth's geologic history; the Cenozoic,Mesozoic, Paleozoic, and Precambrian
erosion  the process of physically removing weathered materials, for example, rock fragments are physically picked up by an erosion agent such as a stream or a glacier
essential amino acids  those amino acids that cannot be synthesized by the human body and must be part of the diet (e.g., lysine, tryptophan, and valine)
esters  class of organic compounds with the general structure of RCOOR', where R is one of the hydrocarbon groups—for example, methyl or ethyl; esters make up fats, oils, and waxes and some give fruit and flowers their taste and odor
estrogen  one of the female sex hormones that cause the differentiation of typical female internal and external genital anatomy; responsible for the changes in breasts, vagina, uterus, clitoris, and pelvic bone structure at puberty
estuary  a special category of aquatic ecosystem that consists of shallow, partially enclosed areas where freshwater enters the ocean
ether  class of organic compounds with the general formula ROR', where R is one of the hydrocarbon groups—for example, methyl or ethyl; mostly used as industrial and laboratory solvents
Eubacteria  the domain in which are found organisms commonly known as bacteria
Eucarya  the domain in which are found all eukaryotic organisms
eukaryote  an organism composed of cells possessing a nuclear membrane and other membranous organelles
eukaryotic cells  one of the two major types of cells; characterized by cells that have a true nucleus, as in plants, fungi, protists, and animals
euphotic zone  the upper layer of the ocean, where the sun's rays penetrate
evaporation  process of more molecules leaving a liquid for the gaseous state than returning from the gas to the liquid; can occur at any given temperature from the surface of a liquid
evolution  the continuous genetic adaptation of a population of organisms to its environment over time
excited states  as applied to an atom, describes the energy state of an atom that has electrons in a state above the minimum energy state for that atom; as applied to a nucleus, describes the energy state of a nucleus that has particles in a state above the minimum energy state for that nuclear configuration
exfoliation  the fracturing and breaking away of curved, sheet-like plates from bare rock surfaces via physical or chemical weathering, resulting in dome-shaped hills and rounded boulders
exocrine glands  use ducts to secrete to the surface of the body or into hollow organs of the body, for example, sweat glands or pancreas
exosphere  the outermost layer of the atmosphere, where gas molecules merge with the diffuse vacuum of space
experiment  a re-creation of an event in a way that enables a scientist to gain valid and reliable empirical evidence
experimental group  the group in a controlled experiment that is identical to the control group in all respects but one
exponential growth phase  a period of time during population growth when the population increases at an accelerating rate
external energy  the total potential and kinetic energy of an everyday-sized object
external parasite  a parasite that lives on the outside of its host
facilitated diffusion  diffusion assisted by carrier molecules
Fahrenheit scale  referent scale that defines numerical values for measuring hotness or coldness, defined as degrees of temperature; based on the reference points of the freezing point of water and the boiling point of water at sea-level pressure, with 180 degrees between the two points
family (elements)  vertical columns of the periodic table consisting of elements that have similar properties
family (organisms)  a group of closely related genera within an order
fats  organic compounds of esters formed from glycerol and three long-chain carboxylic acids that are also called triglycerides; called fats in animals and oils in plants
fatty acid  one of the building blocks of true fats and phospholipids; composed of a longchain carbon skeleton with a carboxylic acid functional group at one end; for example, linoleic acid
fault  a break in the continuity of a rock formation along which relative movement has occurred between the rocks on either side
fault plane  the surface along which relative movement has occurred between the rocks on either side; the surface of the break in continuity of a rock formation
ferromagnesian silicates  silicates that contain iron and magnesium; examples include the dark-colored minerals olivine, augite, hornblende, and biotite
fertilization  the joining of haploid nuclei, usually from an egg and a sperm cell, resulting in a diploid cell called the zygote
fiber  natural (plant) or industrially produced polysaccharides that are resistant to hydrolysis by human digestive enzymes
first law of motion  every object remains at rest or in a state of uniform straight-line motion unless acted on by an unbalanced force
first law of thermodynamics  a statement of the law of conservation of energy in the relationship between internal energy, work, and heat
floodplain  the wide, level floor of a valley built by a stream; the river valley where a stream floods when it spills out of its channel
fluids  matter that has the ability to flow or be poured; the individual molecules of a fluid are able to move, rolling over or by one another
folds  bends in layered bed rock as a result of stress or stresses that occurred when the rock layers were in a ductile condition, probably under considerable confining pressure from deep burial
foliation  the alignment of flat crystal flakes of a rock into parallel sheets
follicle  the saclike structure near the surface of the ovary that encases the soon-to-bereleased secondary oocyte
follicle-stimulating hormone (FSH)  the pituitary secretion that causes the ovaries to begin to produce larger quantities of estrogen and to develop the follicle and prepare the egg for ovulation
food chain  a sequence of organisms that feed on one another, resulting in a flow of energy from a producer through a series of consumers
Food Guide Pyramid  a tool developed by the U.S. Department of Agriculture to help the general public plan for good nutrition; guidelines for required daily intake from each of five food groups
food web  a system of interlocking food chains
force  a push or pull capable of changing the state of motion of an object; since a force has magnitude (strength) as well as direction, it is a vector quantity
formula  describes what elements are in a compound and in what proportions
formula weight  the sum of the atomic weights of all the atoms in a chemical formula
fossil  any evidence of former life
fossil fuels  organic fuels that contain the stored radiant energy of the sun converted to chemical energy by plants or animals that lived millions of years ago; coal, petroleum, and natural gas are the common fossil fuels
Foucault pendulum  a heavy mass swinging from a long wire that can be used to provide evidence about the rotation of the earth
fovea centralis  the area of sharpest vision on the retina, containing only cones, where light is sharply focused
fracture strain  an adjustment to stress in which materials crack or break as a result of the stress
free fall  when objects fall toward the earth with no forces acting upward; air resistance is neglected when considering an object to be in free fall
free-living nitrogen-fixing bacteria  soil bacteria that provide nitrogen compounds that can be taken up by plants through their roots
freezing point  the temperature at which a phase change of liquid to solid takes place; the same temperature as the melting point for a given substance
frequency  the number of cycles of a vibration or of a wave occurring in one second, measured in units of cycles per second (hertz)
freshwater  water that is not saline and is fit for human consumption
freshwater communities  aquatic communities that have low salt concentrations
front  the boundary, or thin transition zone, between air masses of different temperatures
frost  ice crystals formed by water vapor condensing directly from the vapor phase; frozen water vapor that forms on objects
frost wedging  the process of freezing and thawing water in small rock pores and cracks that become larger and larger, eventually forcing pieces of rock to break off
fuel rod  long zirconium alloy tubes containing fissionable material for use in a nuclear reactor
full moon  the moon phase when the earth is between the sun and the moon and the entire side of the moon facing the earth is illuminated by sunlight
functional group  the atom or group of atoms in an organic molecule that is responsible for the chemical properties of a particular class or group of organic chemicals
fundamental charge  smallest common charge known; the magnitude of the charge of an electron and a proton
fundamental frequency  the lowest frequency (longest wavelength) that can set up standing waves in an air column or on a string
fundamental properties  a property that cannot be defined in simpler terms other than to describe how it is measured; the fundamental properties are length, mass, time, and charge
fungus  the common name for the kingdom Fungi; examples, yeast and mold
g  symbol representing the acceleration of an object in free fall due to the force of gravity
galactic clusters  gravitationally bound subgroups of as many as 1,000 stars that move together within the Milky Way galaxy
galaxy  group of billions and billions of stars that form the basic unit of the universe, for example, the earth is part of the solar system, which is located in the Milky Way galaxy
gallbladder  an organ attached to the liver that stores bile
galvanometer  a device that measures the size of an electric current from the size of the magnetic field produced by the current
gamete  a haploid sex cell
gametogenesis  the generating of gametes; the meiotic cell-division process that produces sex cells; oogenesis and spermatogenesis
gametophyte stage  a life-cycle stage in plants in which a haploid sex cell is produced by mitosis
gamma ray  very short wavelength electromagnetic radiation emitted by decaying nuclei
gases  a phase of matter composed of molecules that are relatively far apart moving freely in a constant, random motion and have weak cohesive forces acting between them, resulting in the characteristic indefinite shape and indefinite volume of a gas
gasohol  solution of ethanol and gasoline
gastric juice  the secretions of the stomach that contain enzymes and hydrochloric acid
Geiger counter  a device that indirectly measures ionizing radiation (beta and/or gamma) by detecting "avalanches" of electrons that are able to move because of the ions produced by the passage of ionizing radiation
gene  a unit of heredity located on a chromosome and composed of a sequence of DNA nucleotides
gene flow  the movement of genes from one generation to another or from one place to another
gene frequency  a measure of how often a specific gene for a characteristic shows up in the individuals of a population
generative processes  actions that increase the size of an individual organism (growth) or increase the number of individuals in a population (reproduction)
genetic recombination  the gene mixing that occurs as a result of sexual reproduction
genetics  the study of genes, how genes produce characteristics, and how the characteristics are inherited
genome  a set of all the genes necessary to specify an organism's complete list of characteristics
genotype  the catalog of genes of an organism, whether or not these genes are expressed
genus  (plural, genera) a group of closely related species within a family
geographic barriers  geographic features that keep different portions of a species from exchanging genes
geographic isolation  a condition in which part of the gene pool is separated by geographic barriers from the rest of the population
geologic time scale  a "calendar" of geologic history based on the appearance and disappearance of particular fossils in the sedimentary rock record
geomagnetic time scale  time scale established from the number and duration of magnetic field reversals during the past 6 million years
giant planets  the large outer planets of Jupiter, Saturn, Uranus, and Neptune that all have similar densities and compositions
glacier  a large mass of ice on land that formed from compacted snow and slowly moves under its own weight
gland  an organ that manufactures and secretes a material either through ducts or directly into the circulatory system
globular clusters  symmetrical and tightly packed clusters of as many as a million stars that move together as subgroups within the Milky Way galaxy
glycerol  an alcohol with three hydroxyl groups per molecule; for example, glycerin (1,2,3-propanetriol)
glycogen  a highly branched polysaccharide synthesized by the human body and stored in the muscles and liver; serves as a direct reserve source of energy
glycol  an alcohol with two hydroxyl groups per molecule; for example, ethylene glycol that is used as an antifreeze
Golgi apparatus  a stack of flattened, smooth, membranous sacs; the site of synthesis and packaging of certain molecules in eukaryotic cells
gonad  a generalized term for organs in which meiosis occurs to produce gametes; ovary or testis
granite  light-colored, coarse-grained igneous rock common on continents; igneous rocks formed by blends of quartz and feldspars, with small amounts of micas, hornblende, and other minerals
greenhouse effect  the process of increasing the temperature of the lower parts of the atmosphere through redirecting energy back toward the surface; the absorption and reemission of infrared radiation by carbon dioxide, water vapor, and a few other gases in the atmosphere
ground state  energy state of an atom with electrons at the lowest energy state possible for that atom
groundwater  water from a saturated zone beneath the surface; water from beneath the surface that supplies wells and springs
growth-stimulating hormone (GSH)  a hormone produced by the anterior pituitary gland that stimulates tissues to grow
guanine  a double-ring nitrogenous-base molecule in DNA and RNA. It is the complementary base of cytosine
gyre  the great circular systems of moving water in each ocean
habitat  the place or part of an ecosystem occupied by an organism
hail  a frozen form of precipitation, sometimes with alternating layers of clear and opaque, cloudy ice
hair hygrometer  a device that measures relative humidity from changes in the length of hair
half-life  the time required for one-half of the unstable nuclei in a radioactive substance to decay into a new element
halogen  member of family VIIA of the periodic table, having common properties of very reactive nonmetallic elements common in salt compounds
haploid  having a single set of chromosomes resulting from the reduction division of meiosis
hard water  water that contains relatively high concentrations of dissolved salts of calcium and magnesium
heart  the muscular pump that forces the blood through the blood vessels of the body
heat  total internal energy of molecules, which is increased by gaining energy from a temperature difference (conduction, convection, radiation) or by gaining energy from a form conversion (mechanical, chemical, radiant, electrical, nuclear)
heat of formation  energy released in a chemical reaction
Heisenberg uncertainty principle  you cannot measure both the exact momentum and the exact position of a subatomic particle at the same time—when the more exact of the two is known, the less certain you are of the value of the other
hemoglobin  an iron-containing molecule found in red blood cells, to which oxygen molecules bind
herbivores  animals that feed directly on plants
hertz  unit of frequency; equivalent to one cycle per second
Hertzsprung-Russell diagram  diagram to classify stars with a temperature-luminosity graph
heterotroph  an organism that requires a source of organic material from its environment; it cannot produce its own food
heterozygous  describes a diploid organism that has two different alleles for a particular characteristic
high  short for high-pressure center (anticyclone), which is associated with clear, fair weather
high latitudes  latitudes close to the poles; those that for a period of time during the winter months receive no solar radiation at noon
high-pressure center  another term for anticyclone
homeostasis  the process of maintaining a constant internal environment as a result of constant monitoring and modification of the functioning of various systems
homologous chromosomes  a pair of chromosomes in a diploid cell that contain similar genes at corresponding loci throughout their length
homozygous  describes a diploid organism that has two identical alleles for a particular characteristic
hormones  chemical messengers secreted by endocrine glands to regulate other parts of the body
horsepower  measurement of power defined as a power rating of 550 ft•lb/s
host  an organism that a parasite lives in or on
hot spots  sites on the earth's surface where plumes of hot rock materials rise from deep within the mantle
humid  moist climate classification; receives more than 50 cm (20 in) precipitation per year
humidity  the amount of water vapor in the air; see relative humidity
hurricane  a tropical cyclone with heavy rains and winds exceeding 120 km/h
hydration  the attraction of water molecules for ions; a reaction that occurs between water and minerals that make up rocks
hydrocarbon  an organic compound consisting of only the two elements hydrogen and carbon
hydrocarbon derivatives  organic compounds that can be thought of as forming when one or more hydrogen atoms on a hydrocarbon have been replaced by an element or a group of elements other than hydrogen
hydrogen bonding  a strong bond that occurs between the hydrogen end of one molecule and the fluorine, oxygen, or nitrogen end of another molecule
hydrologic cycle  water vapor cycling into and out of the atmosphere through continuous evaporation of liquid water from the surface and precipitation of water back to the surface
hydronium ion  a molecule of water with an attached hydrogen ion, H3O+
hypothalamus  a region of the brain located in the floor of the thalamus and connected to the pituitary gland that is involved in sleep and arousal; emotions such as anger, fear, pleasure, hunger, sexual response, and pain; and automatic functions such as temperature, blood pressure, and water balance
hypothesis  a tentative explanation of a phenomenon that is compatible with the data and provides a framework for understanding and describing that phenomenon
ice-crystal process  a precipitation-forming process that brings water droplets of a cloud together through the formation of ice crystals
ice-forming nuclei  small, solid particles suspended in air; ice can form on the suspended particles
igneous rocks  rocks that formed from magma, which is a hot, molten mass of melted rock materials
immune system  a system of white blood cells specialized to provide the body with resistance to disease; there are two types, antibody-mediated immunity and cellmediated immunity
impulse  a change of motion is brought about by an impulse; the product of the size of an applied force and the time the force is applied
incandescent  matter emitting visible light as a result of high temperature; for example, a lightbulb, a flame from any burning source, and the sun are all incandescent sources because of high temperature
incident ray  line representing the direction of motion of incoming light approaching a boundary
incus  the ear bone that is located between the malleus and the stapes
independent assortment  the segregation, or assortment, of one pair of homologous chromosomes independently of the segregation, or assortment, of any other pair of chromosomes
index fossils  distinctive fossils of organisms that lived only a brief time; used to compare the age of rocks exposed in two different locations
index of refraction  the ratio of the speed of light in a vacuum to the speed of light in a material
inertia  a property of matter describing the tendency of an object to resist a change in its state of motion; an object will remain in unchanging motion or at rest in the absence of an unbalanced force
inferior vena cava  a major vein that returns blood to the heart from the lower body
infrasonic  sound waves having too low a frequency to be heard by the human ear; sound having a frequency of less than 20 Hz
initiation code  the code on DNA with the base sequence TAC that begins the process of transcription
inorganic chemistry  the study of all compounds and elements in which carbon is not the principal element
insulators  materials that are poor conductors of heat—for example, heat flows slowly through materials with air pockets because the molecules making up air are far apart; also, materials that are poor conductors of electricity, for example, glass or wood
intensity  a measure of the energy carried by a wave
interference  phenomenon of light where the relative phase difference between two light waves produces light or dark spots, a result of light's wavelike nature
intermediate-focus earthquakes  earthquakes that occur in the upper part of the mantle, between 70 to 350 km below the surface of the earth
intermolecular forces  forces of interaction between molecules
internal energy  sum of all the potential energy and all the kinetic energy of all the molecules of an object
internal parasite  a parasite that lives inside its host
interphase  the stage between cell divisions in which the cell is engaged in metabolic activities
interstitial cell-stimulating hormone(ICSH)  the chemical messenger molecule released from the pituitary that causes the testes to produce testosterone, the primary male sex hormone; same as follicle-stimulating hormone in females
intertropical convergence zone  a part of the lower troposphere in a belt from 10°N to 10°S of the equator where air is heated, expands, and becomes less dense and rises around the belt
intrusive igneous rocks  coarse-grained igneous rocks formed as magma cools slowly deep below the surface
inverse proportion  the relationship in which the value of one variable increases while the value of the second variable decreases at the same rate (in the same ratio)
inversion  a condition of the troposphere when temperature increases with height rather than decreasing with height; a cap of cold air over warmer air that results in trapped air pollution
ion  an atom or a particle that has a net charge because of the gain or loss of electrons; polyatomic ions are groups of bonded atoms that have a net charge
ion exchange reaction  a reaction that takes place when the ions of one compound interact with the ions of another, forming a solid that comes out of solution, a gas, or water
ionic bond  chemical bond of electrostatic attraction between negative and positive ions
ionic compounds  chemical compounds that are held together by ionic bonds—that is, bonds of electrostatic attraction between negative and positive ions
ionization  process of forming ions from molecules
ionization counter  a device that measures ionizing radiation (alpha, beta, gamma, etc.) by indirectly counting the ions produced by the radiation
ionized  an atom or a particle that has a net charge because it has gained or lost electrons
ionosphere  refers to that part of the atmosphere—parts of the thermosphere and upper mesosphere—where free electrons til67002_glo.qxd 5/8/03 11:08 AM Page 623 and ions reflect radio waves around the earth and where the northern lights occur
iron meteorites  meteorite classification group whose members are composed mainly of iron
island arcs  curving chains of volcanic islands that occur over belts of deep-seated earthquakes; for example, the Japanese and Indonesian islands
isomers  chemical compounds with the same molecular formula but different molecular structure; compounds that are made from the same numbers of the same elements but have different molecular arrangements
isotope  atoms of an element with identical chemical properties but with different masses; isotopes are atoms of the same element with different numbers of neutrons
jet stream  a powerful, winding belt of wind near the top of the troposphere that tends to extend all the way around the earth, moving generally from the west in both hemispheres at speeds of 160 km/h or more
joint  a break in the continuity of a rock formation without a relative movement of the rock on either side of the break
joule  metric unit used to measure work and energy; can also be used to measure heat; equivalent to newton-meter
Kelvin scale  a temperature scale that does not have arbitrarily assigned referent points, and zero means nothing; the zero point on the Kelvin scale (also called absolute scale) is the lowest limit of temperature, where all random kinetic energy of molecules ceases
ketone  an organic compound with the general formula RCOR', where R is one of the hydrocarbon groups; for example, methyl or ethyl
keystone species  species in an ecosystem that affects many aspects of the ecosystem and whose removal causes significant alteration of the ecosystem
kidneys  the primary organs involved in regulating blood levels of water, hydrogen ions, salts, and urea
kilocalorie  the amount of energy required to increase the temperature of 1 kilogram of water 1 degree Celsius; equivalent to 1,000 calories
kilogram  the fundamental unit of mass in the metric system of measurement
kinetic energy  the energy of motion; can be measured from the work done to put an object in motion, from the mass and velocity of the object while in motion, or from the amount of work the object can do because of its motion
kinetic molecular theory  the collection of assumptions that all matter is made up of tiny atoms and molecules that interact physically, that explain the various states of matter, and that have an average kinetic energy that defines the temperature of a substance
kingdom  a category within a domain used in the classification of organisms
Kuiper Belt  a disk-shaped region of small icy bodies some 30 to 100 AU from the sun; the source of short-period comets
kwashiorkor  a protein-deficiency disease common in malnourished children caused by prolonged protein starvation leading to reduced body size, lethargy, and low mental ability
lack of dominance  the condition of two unlike alleles both expressing themselves, neither being dominant
lag phase  a stage of a population growth curve during which both natality and mortality are low
lake  a large inland body of standing water
large intestine  the last portion of the food tube; primarily involved in reabsorbing water
last quarter  the moon phase between the full phase and the new phase when the moon is perpendicular to a line drawn through the earth and the sun; one half of the lighted moon can be seen from the earth, so this phase is called the last quarter
latent heat  refers to the heat "hidden" in phase changes
latent heat of fusion  the heat absorbed when 1 gram of a substance changes from the solid to the liquid phase, or the heat released by 1 gram of a substance when changing from the liquid phase to the solid phase
latent heat of vaporization  the heat absorbed when 1 gram of a substance changes from the liquid phase to the gaseous phase, or the heat released when 1 gram of gas changes from the gaseous phase to the liquid phase
lava  magma, or molten rock, that is forced to the surface from a volcano or a crack in the earth's surface
law of conservation of energy  energy is never created or destroyed; it can only be converted from one form to another as the total energy remains constant
law of conservation of mass  same as law of conservation of matter; mass, including single atoms, is neither created nor destroyed in a chemical reaction
law of conservation of momentum  the total momentum of a group of interacting objects remains constant in the absence of external forces
law of dominance  when an organism has two different alleles for a trait, the allele that is expressed and overshadows the expression of the other allele is said to be dominant; the allele whose expression is overshadowed is said to be recessive
law of independent assortment  members of one allelic pair will separate from each other independently of the members of other allele pairs
law of segregation  when gametes are formed by a diploid organism, the alleles that control a trait separate from one another into different gametes, retaining their individuality
light ray  model using lines to show the direction of motion of light to describe the travels of light
light-year  the distance that light travels through empty space in one year, approximately 9.5 x 1012 km
limiting factors  the identifiable factors that prevent unlimited population growth
limnetic zone  the region in a lake that does not have rooted vegetation
linear scale  a scale, generally on a graph, where equal intervals represent equal changes in the value of a variable
lines of force  lines drawn to make an electric field strength map, with each line originating on a positive charge and ending on a negative charge; each line represents a path on which a charge would experience a constant force and lines closer together mean a stronger electric field
line spectrum  narrow lines of color in an otherwise dark spectrum; these lines can be used as "fingerprints" to identify gases
linkage group  genes located on the same chromosome that tend to be inherited together
lipid  large, nonpolar, organic molecules that do not easily dissolve in polar solvents such as water; there are three different types of lipids: true fats (pork chop fat or olive oil), phospholipids (the primary component of cell membranes), and steroids (most hormones)
liquids  a phase of matter composed of molecules that have interactions stronger than those found in a gas but not strong enough to keep the molecules near the equilibrium positions of a solid, resulting in the characteristic definite volume but indefinite shape of a liquid
liter  a metric system unit of volume usually used for liquids
lithosphere  solid layer of the earth's structure that is above the asthenosphere and includes the entire crust, the Moho, and the upper part of the mantle
littoral zone  the region in a lake with rooted vegetation
liver  an organ of the body responsible for secreting bile, filtering the blood, detoxifying molecules, and modifying molecules absorbed from the gut
locus  the spot on a chromosome where an allele is located
loess  very fine dust or silt that has been deposited by the wind over a large area
longitude  angular distance of a point east or west from the prime meridian on a parallel
longitudinal wave  a mechanical disturbance that causes particles to move closer together and farther apart in the same direction that the wave is traveling
longshore current  a current that moves parallel to the shore, pushed along by waves that move accumulated water from breakers
loudness  a subjective interpretation of a sound that is related to the energy of the vibrating source, related to the condition of the transmitting medium, and related to the distance involved
low latitudes  latitudes close to the equator; those that receive vertical solar radiation at noon during some part of the year
luminous  an object or objects that produce visible light; for example, the sun, stars, lightbulbs, and burning materials are all luminous
lunar highlands  light-colored mountainous regions of the moon
lung  a respiratory organ in which air and blood are brought close to one another and gas exchange occurs
L-wave  seismic waves that move on the solid surface of the earth much as water waves move across the surface of a body of water
lymph  liquid material that leaves the circulatory system to surround cells
lymphatic system  a collection of thin-walled tubes that collects, filters, and returns lymph from the body to the circulatory system
lysosome  a specialized, submicroscopic organelle that holds a mixture of hydrolytic enzymes
macromolecule  very large molecule, with a molecular weight of thousands or millions of atomic mass units, that is made up of a combination of many smaller, similar molecules
magma  a mass of molten rock material either below or on the earth's crust from which igneous rock is formed by cooling and hardening
magnetic field  model used to describe how magnetic forces on moving charges act at a distance
magnetic poles  the ends, or sides, of a magnet about which the force of magnetic attraction seems to be concentrated
magnetic quantum number  from the quantum mechanics model of the atom, one of four descriptions of the energy state of an electron wave; this quantum number describes the energy of an electron orbital as the orbital is oriented in space by an external magnetic field, a kind of energy sub-sublevel
magnetic reversal  the flipping of polarity of the earth's magnetic field as the north magnetic pole and the south magnetic pole exchange positions
main sequence stars  normal, mature stars that use their nuclear fuel at a steady rate; stars on the Hertzsprung-Russell diagram in a narrow band that runs from the top left to the lower right
malleus  the ear bone that is attached to the tympanum
manipulated variable  in an experiment, a quantity that can be controlled or manipulated; also known as the independent variable
mantle  middle part of the earth's interior; a 2,870 km (about 1,780 mile) thick shell between the core and the crust
maria  smooth dark areas on the moon
marine climate  a climate influenced by air masses from over an ocean, with mild winters and cool summers compared to areas farther inland
marine communities  aquatic communities that have a high salt content
maritime air mass  a moist air mass that forms over the ocean
mass  a measure of inertia, which means a resistance to a change of motion
mass defect  the difference between the sum of the masses of the individual nucleons forming a nucleus and the actual mass of that nucleus
mass movement  erosion caused by the direct action of gravity
mass number  the sum of the number of protons and neutrons in a nucleus defines the mass number of an atom; used to identify isotopes; for example, uranium 238
masturbation  stimulation of one's own sex organs
matter  anything that occupies space and has mass
meanders  winding, circuitous turns or bends of a stream
measurement  the process of comparing a property of an object to a well-defined and agreed-upon referent
mechanical energy  the form of energy associated with machines, objects in motion, and objects having potential energy that results from gravity
mechanical weathering  the physical breaking up of rocks without any changes in their chemical composition
medulla oblongata  a region of the more primitive portion of the brain connected to the spinal cord that controls such automatic functions as blood pressure, breathing, and heart rate
meiosis  the specialized pair of cell divisions that reduces the chromosome number from diploid (2n) to haploid (n)
melting point  the temperature at which a phase change of solid to liquid takes place; the same temperature as the freezing point for a given substance
Mendelian genetics  the pattern of inheriting characteristics that follows the laws formulated by Gregor Mendel
menstrual cycle  (menses, menstrual flow, period) the repeated building up and shedding of the lining of the uterus
Mesozoic  a geologic era; the time of middle life, meaning some of the fossils for this time period are similar to the life found on the earth today, but many are different from anything living today
messenger RNA (mRNA)  a molecule composed of ribonucleotides that functions as a copy of the gene and is used in the cytoplasm of the cell during protein synthesis
metabolic processes  the total of all chemical reactions within an organism; for example, nutrient uptake and processing, and waste elimination
metal  matter having the physical properties of conductivity, malleability, ductility, and luster
metamorphic rocks  previously existing rocks that have been changed into a distinctly different rock by heat, pressure, or hot solutions
metaphase  the second stage in mitosis, characterized by alignment of the chromosomes at the equatorial plane
meteor  the streak of light and smoke that appears in the sky when a meteoroid is made incandescent by friction with the earth's atmosphere
meteorite  the solid iron or stony material of a meteoroid that survives passage through the earth's atmosphere and reaches the surface
meteoroids  remnants of comets and asteroids in space
meteorology  the science of understanding and predicting weather
meteor shower  event when many meteorites fall in a short period of time
meter  the fundamental metric unit of length
metric system  a system of referent units based on invariable referents of nature that have been defined as standards
microclimate  a local, small-scale pattern of climate; for example, the north side of a house has a different microclimate than the south side
microvilli  tiny projections from the surfaces of cells that line the intestine
middle latitudes  latitudes equally far from the poles and equator; between the high and low latitudes
mineral (geology)  a naturally occurring, inorganic solid element or chemical compound with a crystalline structure
minerals (biology)  inorganic elements that cannot be manufactured by the body but are required in low concentrations; essential to metabolism
miscible fluids  two or more kinds of fluids that can mix in any proportion
mitochondrion  a membranous organelle resembling a small bag with a larger bag inside that is folded back on itself; serves as the site of aerobic cellular respiration
mitosis  a process that results in equal and identical distribution of replicated chromosomes into two newly formed nuclei
mixture  matter composed of two or more kinds of matter that has a variable composition and can be separated into its component parts by physical means
model  a mental or physical representation of something that cannot be observed directly that is usually used as an aid to understanding
moderator  a substance in a nuclear reactor that slows fast neutrons so the neutrons can participate in nuclear reactions
mold  the preservation of the shape of an organism by the dissolution of the remains of a buried organism, leaving an empty space where the remains were
mole  an amount of a substance that contains Avogadro's number of atoms, ions, molecules, or any other chemical unit; a mole is thus 6.02 _ 1023 atoms, ions, or other chemical units
molecule  from the chemical point of view: a particle composed of two or more atoms held together by an attractive force called a chemical bond; from the kinetic theory point of view: smallest particle of a compound or gaseous element that can exist and still retain the characteristic properties of a substance
momentum  the product of the mass of an object times its velocity
monomer  individual, repeating units or segments of complex molecules that chemically combine to form long chainlike molecules called polymers; for example, monosaccharides link to form polysaccharides
monosaccharides  simple sugars containing 3 to 6 carbon atoms; the most common kinds are 6-carbon molecules such as glucose and fructose
moraines  deposits of rocks and other mounded materials bulldozed into position by a glacier and left behind when the glacier melted
morphological species concept  the concept that species can be distinguished from one another by structural characteristics
mortality  the number of individuals leaving the population by death per thousand individuals in the population
motor neurons  those neurons that carry information from the central nervous system to muscles or glands
motor unit  all of the muscle cells stimulated by a single neuron
mountain  a natural elevation of the earth's crust that rises above the surrounding surface
multiple alleles  a term used to refer to conditions in which there are several different alleles for a particular characteristic, not just two
multiregional hypothesis  states that Homo erectus evolved into Homo sapiens
mutagenic agent  anything that causes permanent change in DNA
mutation  any change in the genetic information of a cell
mutualism  a relationship between two organisms in which both organisms benefit
natality  the number of individuals entering the population by reproduction per thousand individuals in the population
natural frequency  the frequency of vibration of an elastic object that depends on the size, composition, and shape of the object
natural selection  the processes that encourage the passage of beneficial genes and discourage the passage of harmful or unfavorable genes from one generation to the next
nebulae  a diffuse mass of interstellar clouds of hydrogen gas or dust that may develop into a star
negative electric charge  one of the two types of electric charge; repels other negative charges and attracts positive charges
negative ion  atom or particle that has a surplus, or imbalance, of electrons and, thus, a negative charge
nephrons  millions of tiny tubular units that make up the kidneys, which are responsible for filtering the blood
nerve cell  see neuron
nerve impulse  a series of changes that take place in the neuron, resulting in a wave of depolarization that passes from one end of the neuron to the other
nerves  bundles of neuronal fibers
nervous system  a network of neurons that carry information from sense organs to the central nervous system and from the central nervous system to muscles and glands
net force  the resulting force after all forces have been added; if a net force is zero, all the forces have canceled each other and there is not an unbalanced force
neuron  the cellular unit consisting of a cell body and fibers that makes up the nervous system; also called nerve cell
neurotransmitter  a molecule released by the axons of neurons that stimulates other cells
neutralized  acid or base properties have been lost through a chemical reaction
neutron  neutral subatomic particle usually found in the nucleus of an atom
neutron star  very small superdense remains of a supernova with a center core of pure neutrons
new crust zone  zone of a divergent boundary where new crust is formed by magma upwelling at the boundary
newton  a unit of force defined as kg=m/s2; that is, a 1 newton force is needed to accelerate a 1 kg mass 1 m/s2
niche  the functional role of an organism
nitrifying bacteria  bacteria that can convert ammonia (NH3) into nitrite-containing (NO2-) compounds, which in turn can be converted into nitrate-containing (NO3-) compounds
nitrogenous base  a category of organic molecules found as components of the nucleic acids. There are five common types: thymine, guanine, cytosine, adenine, and uracil
noble gas  members of family VIII of the periodic table, having common properties of colorless, odorless, chemically inert gases; also known as rare gases or inert gases
node  regions on a standing wave that do not oscillate
noise  sounds made up of groups of waves of random frequency and intensity
nonelectrolytes  water solutions that do not conduct an electric current; covalent compounds that form molecular solutions and cannot conduct an electric current
nonferromagnesian silicates  silicates that do not contain iron or magnesium ions; examples include the minerals of muscovite (white mica), the feldspars, and quartz
nonmetal  an element that is brittle (when a solid), does not have a metallic luster, is a poor conductor of heat and electricity, and is not malleable or ductile
nonsilicates  minerals that do not have the silicon-oxygen tetrahedra in their crystal structure
norepinephrine  a hormone produced by the adrenal medulla that increases heart rate, blood pressure, and breathing rate
normal  a line perpendicular to the surface of a boundary
normal fault  a fault where the hanging wall has moved downward with respect to the foot wall
north pole (of a magnet)  short for "north seeking"; the pole of a magnet that points northward when it is free to turn
nova  a star that explodes or suddenly erupts and increases in brightness
nuclear energy  the form of energy from reactions involving the nucleus, the innermost part of an atom
nuclear fission  nuclear reaction of splitting a massive nucleus into more stable, less massive nuclei with an accompanying release of energy
nuclear force  one of four fundamental forces, a strong force of attraction that operates over very short distances between subatomic particles; this force overcomes the electric repulsion of protons in a nucleus and binds the nucleus together
nuclear fusion  nuclear reaction of low-mass nuclei fusing together to form more stable and more massive nuclei with an accompanying release of energy
nuclear membrane  the structure surrounding the nucleus that separates the nucleoplasm from the cytoplasm
nuclear reactor  steel vessel in which a controlled chain reaction of fissionable materials releases energy
nucleic acids  complex molecules that store and transfer genetic information within a cell; constructed of fundamental monomers known as nucleotides; the two common forms are DNA and RNA
nucleoli  (singular, nucleolus) nuclear structures composed of completed or partially completed ribosomes and the specific parts of chromosomes that contain the information for their construction
nucleons  name used to refer to both the protons and neutrons in the nucleus of an atom
nucleoproteins  the double-stranded DNA with attached proteins; also called chromatin fibers
nucleosomes  histone clusters with their encircling DNA
nucleotide  the building block of the nucleic acids, composed of a 5-carbon sugar, a phosphate, and a nitrogenous base
nucleus (atom)  tiny, relatively massive and positively charged center of an atom containing protons and neutrons; the small, dense center of an atom
nucleus (cell)  the central part of a cell that contains the genetic material
numerical constant  a constant without units; a number
nutrients  molecules required by the body for growth, reproduction, or repair
nutrition  collectively, the processes involved in taking in, assimilating, and utilizing nutrients
obese  a term describing a person who gains a great deal of unnecessary weight and is 15% to 20% above his or her ideal weight
obligate intracellular parasites  infectious particles (viruses) that can function only when inside a living cell
observed lapse rate  the rate of change in temperature compared to change in altitude
occluded front  a front that has been lifted completely off the ground into the atmosphere, forming a cyclonic storm
ocean  the single, continuous body of salt water on the surface of the earth
ocean basin  the deep bottom of the ocean floor, which starts beyond the continental slope
ocean currents  streams of water within the ocean that stay in about the same path as they move over large distances; steady and continuous onward movement of a channel of water in the ocean
oceanic ridges  long, high, continuous, suboceanic mountain chains; for example, the Mid-Atlantic Ridge in the center of the Atlantic Ocean Basin
oceanic trenches  long, narrow, deep troughs with steep sides that run parallel to the edge of continents
ocean wave  a moving disturbance that travels across the surface of the ocean
octet rule  a generalization that helps keep track of the valence electrons in most representative elements; atoms of the representative elements (A families) attempt to acquire an outer orbital with eight electrons through chemical reactions
offspring  descendants of a set of parents
ohm  unit of resistance; equivalent to volts/amps
Ohm's law  the electric potential difference is directly proportional to the product of the current times the resistance
oil field  petroleum accumulated and trapped in extensive porous rock structure or structures
oils  organic compounds of esters formed from glycerol and three long-chain carboxylic acids that are also called triglycerides; called fats in animals and oils in plants
olfactory epithelium  the cells of the nasal cavity that respond to chemicals
omnivores  animals that are carnivores at some times and herbivores at others
oogenesis  the specific name given to the gametogenesis process that leads to the formation of eggs
Oort cloud  a spherical "cloud" of small, icy bodies from 30,000 AU out to a light-year from the sun; the source of long-period comets
opaque  materials that do not allow the transmission of any light
orbital  the region of space around the nucleus of an atom where an electron is likely to be found
order  a group of closely related families within a class
ore mineral  mineral deposits with an economic value
organ  a structure composed of two or more kinds of tissues that perform a particular function
organelles  cellular structures that perform specific functions in the cell; the function of an organelle is directly related to its structure
organic acids  organic compounds with a general formula of RCOOH, where R is one of the hydrocarbon groups; for example, methyl or ethyl
organic chemistry  the study of compounds in which carbon is the principal element
organism  an independent living unit
organ system  a group of organs that performs a particular function
orgasm  a complex series of responses to sexual stimulation that results in intense frenzy of sexual excitement
osmosis  the net movement of water molecules through a selectively permeable membrane
osteoporosis  a disease condition resulting from the demineralization of the bone, resulting in pain, deformities, and fractures; related to a loss of calcium
out-of-Africa hypothesis  states that modern humans (Homo sapiens) originated in Africa, as had several other hominid species, and migrated from Africa to Asia and Europe and displaced species such as H. erectus and H. heidelbergensis that had migrated into these areas previously
oval window  the membrane-covered opening of the cochlea, to which the stapes is attached
ovaries  the female sex organs that produce haploid sex cells—the eggs or ova
overtones  higher resonant frequencies that occur at the same time as the fundamental frequency, giving a musical instrument its characteristic sound quality
oviduct  the tube (fallopian tube) that carries the oocyte to the uterus
ovulation  the release of a secondary oocyte from the surface of the ovary
oxbow lake  a small body of water, or lake, that formed when two bends of a stream came together and cut off a meander
oxidation  the process of a substance losing electrons during a chemical reaction; a reaction between oxygen and the minerals making up rocks
oxidation-reduction reaction  a chemical reaction in which electrons are transferred from one atom to another; sometimes called "redox" for short
oxidizing agents  substances that take electrons from other substances
oxidizing atmosphere  an atmosphere that contains molecular oxygen
oxytocin  a hormone released from the posterior pituitary that causes contraction of the uterus
ozone shield  concentration of ozone in the lower portions of the stratosphere that absorbs potentially damaging ultraviolet radiation, preventing it from reaching the surface of the earth
paleontology  the science of discovering fossils, studying the fossil record, and deciphering the history of life
Paleozoic  a geologic era; time of ancient life, meaning the fossils from this time period are very different from anything living on the earth today
pancreas  an organ of the body that secretes many kinds of digestive enzymes into the duodenum
parasite  an organism that lives in or on another organism and derives nourishment from it
parasitism  a relationship which involves one organism living in or on another living organism from which it derives nourishment
parts per billion  concentration ratio of parts of solute in every one billion parts of solution (ppb); could be expressed as ppb by volume or as ppb by weight
parts per million  concentration ratio of parts of solute in every one million parts of solution (ppm); could be expressed as ppm by volume or as ppm by weight
Pauli exclusion principle  no two electrons in an atom can have the same four quantum numbers; thus, a maximum of two electrons can occupy a given orbital
pelagic  describes aquatic organisms that float or swim actively
penis  the portion of the male reproductive system that deposits sperm in the female reproductive tract
pepsin  an enzyme produced by the stomach that is responsible for beginning the digestion of proteins
percent by volume  the volume of solute in 100 volumes of solution
percent by weight  the weight of solute in 100 weight units of solution
perception  recognition by the brain that a stimulus has been received
perigee  when the moon's elliptical orbit brings the moon closest to the earth
perihelion  the point at which an orbit comes closest to the sun
period (geologic time)  subdivisions of geologic eras
period (periodic table)  horizontal rows of elements with increasing atomic numbers; runs from left to right on the element table
period (wave)  the time required for one complete cycle of a wave
periodic law  similar physical and chemical properties recur periodically when the elements are listed in order of increasing atomic number
peripheral nervous system  the fibers that communicate between the central nervous system and other parts of the body
permeability  the ability to transmit fluids through openings, small passageways, or gaps
permineralization  the process that forms a fossil by alteration of an organism's buried remains by circulating groundwater depositing calcium carbonate, silica, or pyrite
petroleum  oil that comes from oil-bearing rock, a mixture of hydrocarbons that is believed to have formed from ancient accumulations of buried organic materials such as remains of algae
phagocytosis  the process by which the cell wraps around a particle and engulfs it
pharynx  the region at the back of the mouth cavity; the throat
phase change  the action of a substance changing from one state of matter to another; a phase change always absorbs or releases internal potential energy without a temperature change
phases of matter  the different physical forms that matter can take as a result of different molecular arrangements, resulting in characteristics of the common phases of a solid, liquid, or gas
phenotype  the physical, chemical, and behavioral expression of the genes possessed by an organism
phospholipids  a class of complex waterinsoluble organic molecules that resemble fats but contain a phosphate group (PO4) in their structure; a component of cellular membranes
photoelectric effect  the movement of electrons in some materials as a result of energy acquired from absorbed light
photon  a quantum of energy in a light wave; the particle associated with light
pH scale  scale that measures the acidity of a solution with numbers below 7 representing acids, 7 representing neutral, and numbers above 7 representing bases
phylogeny  the science that explores the evolutionary relationships among organisms and seeks to reconstruct evolutionary history
phylum  a subdivision of a kingdom
physical change  a change of the state of a substance but not the identity of the substance
phytoplankton  planktonic organisms that carry on photosynthesis
pistil  the sex organ in plants that produces eggs or ova
pitch  the frequency of a sound wave
pituitary gland  the gland at the base of the brain that controls the functioning of other glands throughout the organism
placenta  an organ made up of tissues from the embryo and the uterus of the mother that allows for the exchange of materials between the mother's bloodstream and the embryo's bloodstream; it also produces hormones
Planck's constant  proportionality constant in the relationship between the energy of vibrating molecules and their frequency of vibration; a value of 6.63 x 10-34 Js
plankton  aquatic organisms that are so small and weakly swimming that they are simply carried by currents.
plasma (biology)  the watery matrix that contains the molecules and cells of the blood
plasma (physics)  a phase of matter; a very hot gas consisting of electrons and atoms that have been stripped of their electrons because of high kinetic energies
plasma membrane  the outer-boundary membrane of the cell; see cell membrane.
plastic strain  an adjustment to stress in which materials become molded or bent out of shape under stress and do not return to their original shape after the stress is released
plate tectonics  the theory that the earth's crust is made of rigid plates that float on the asthenosphere
pleiotropy  the multiple effects that a gene may have on the phenotype of an organism
point mutation  a change in the DNA of a cell as a result of a loss or change in a single nitrogenous-base
polar air mass  cold air mass that forms in cold regions
polar body  the smaller of two cells formed by unequal meiotic division during oogenesis
polar climate zone  climate zone of the high latitudes; average monthly temperatures stay below 10°C (50°F), even during the warmest month of the year
polarized  light whose constituent transverse waves are all vibrating in the same plane; also known as plane-polarized light
Polaroid  a film that transmits only polarized light
polyatomic ion  ion made up of many atoms
polygenic inheritance  the concept that a number of different pairs of alleles may combine their efforts to determine a characteristic
polymers  huge, chainlike molecules made of hundreds or thousands of smaller repeating molecular units called monomers
polypeptide chain  polymers of amino acids; sometimes called proteins
polysaccharides  polymers consisting of monosaccharide units joined together in straight or branched chains; starches, glycogen, or cellulose
pond  a small body of standing water, smaller than a lake
pons  a region of the brain immediately anterior to the medulla oblongata that connects to the cerebellum and higher regions of the brain and controls several sensory and motor functions of the head and face
population  a group of organisms of the same species located in an area
population growth curve  a graph of the change in population size over time
porosity  the ratio of pore space to the total volume of a rock or soil sample, expressed as a percentage; freely admitting the passage of fluids through pores or small spaces between parts of the rock or soil
positive electric charge  one of the two types of electric charge; repels other positive charges and attracts negative charges
positive ion  atom or particle that has a net positive charge due to an electron or electrons being torn away
potential energy  energy due to position; energy associated with changes in position (e.g., gravitational potential energy) or changes in shape (e.g., compressed or stretched spring)
power  the rate at which energy is transferred or the rate at which work is performed; defined as work per unit of time
Precambrian  the time before the time of ancient life, meaning the rocks for this time period contain very few fossils
precipitation  water that falls to the surface of the earth in the solid or liquid form
predation  a relationship between two organisms that involves the capturing, killing, and eating of one by the other
predator  an organism that captures, kills, and eats another animal
pressure  defined as force per unit area; for example, pounds per square inch (lb/in2)
prey  an organism captured, killed, and eaten by a predator
primary carnivores  carnivores that eat herbivores and are therefore on the third trophic level
primary coil  part of a transformer; a coil of wire that is connected to a source of alternating current
primary consumers  organisms that feed directly on plants—herbivores
primary loop  part of the energy-converting system of a nuclear power plant; the closed pipe system that carries heated water from the nuclear reactor to a steam generator
primary oocyte  the diploid cell of the ovary that begins to undergo the first meiotic division in the process of oogenesis
primary spermatocyte  the diploid cell in the testes that undergoes the first meiotic division in the process of spermatogenesis
prime meridian  the referent meridian (0°) that passes through the Greenwich Observatory in England
principal quantum number  from the quantum mechanics model of the atom, one of four descriptions of the energy state of an electron wave; this quantum number describes the main energy level of an electron in terms of its most probable distance from the nucleus
principle of uniformity  a frame of reference that the same processes that changed the landscape in the past are the same processes you see changing the landscape today
prions  proteins that can be passed from one individual to another and cause disease
probability  the chance that an event will happen, expressed as a percent or fraction
producers  organisms that produce new organic material from inorganic material with the aid of sunlight
prokaryote  an organism composed of cells that lack a nuclear membrane and other membranous organelles
prokaryotic cells  one of the two major types of cells; they do not have a typical nucleus bound by a nuclear membrane and lack many of the other membranous cellular organelles; for example, members of the Eubacteria and Archaea
promoter  a region of DNA at the beginning of each gene, just ahead of an initiator code
proof  a measure of ethanol concentration of an alcoholic beverage; proof is double the concentration by volume; for example, 50 percent by volume is 100 proof
properties  qualities or attributes that, taken together, are usually unique to an object; for example, color, texture, and size
prophase  the first phase of mitosis during which individual chromosomes become visible
proportionality constant  a constant applied to a proportionality statement that transforms the statement into an equation
proteins  macromolecular polymers made of smaller molecules of amino acids, with molecular weight from about six thousand to fifty million; proteins are amino acid polymers with roles in biological structures or functions; without such a function, they are known as polypeptides
protein synthesis  the process whereby the tRNA utilizes the mRNA as a guide to arrange the amino acids in their proper sequence according to the genetic information in the chemical code of DNA
proton  subatomic particle that has the smallest possible positive charge, usually found in the nucleus of an atom
protoplanet nebular model  a model of the formation of the solar system that states that the planets formed from gas and dust left over from the formation of the sun
protoplasm  the living portion of a cell as distinguished from the nonliving cell wall
protostar  an accumulation of gases that will become a star
pseudoscience  use of the appearance of science to mislead; the assertions made are not valid or reliable
psychrometer  a two-thermometer device used to measure the relative humidity
puberty  a time in the life of a developing individual characterized by the increasing production of sex hormones, which cause it to reach sexual maturity
pulmonary artery  the major blood vessel that carries blood from the right ventricle to the lungs
pulmonary circulation  the flow of blood through certain chambers of the heart and blood vessels to the lungs and back to the heart
pulsars  the source of regular, equally spaced pulsating radio signals believed to be the result of the magnetic field of a rotating neutron star
Punnett square  a method used to determine the probabilities of allele combinations in an offspring
pure substance  materials that are the same throughout and have a fixed definite composition
pure tone  sound made by very regular intensities and very regular frequencies from regular repeating vibrations
P-wave  a pressure, or compressional, wave in which a disturbance vibrates materials back and forth in the same direction as the direction of wave movement
P-wave shadow zone  a region on the earth between 103° and 142° of arc from an earthquake where no P-waves are received; believed to be explained by P-waves being refracted by the core
pyloric sphincter  a valve located at the end of the stomach that regulates the flow of food from the stomach to the duodenum
quad  one quadrillion Btu (1015 Btu); used to describe very large amounts of energy
quanta  fixed amounts; usually referring to fixed amounts of energy absorbed or emitted by matter ("quanta" is plural and "quantum" is singular)
quantities  measured properties; includes the numerical value of the measurement and the unit used in the measurement
quantum mechanics  model of the atom based on the wave nature of subatomic particles, the mechanics of electron waves; also called wave mechanics
quantum numbers  numbers that describe energy states of an electron; in the Bohr model of the atom, the orbit quantum numbers could be any whole number 1, 2, 3, and so on out from the nucleus; in the quantum mechanics model of the atom, four quantum numbers are used to describe the energy state of an electron wave
rad  a measure of radiation received by a material (radiation absorbed dose)
radiant energy  the form of energy that can travel through space; for example, visible light and other parts of the electromagnetic spectrum
radiation  the transfer of heat from a region of higher temperature to a region of lower temperature by greater emission of radiant energy from the region of higher temperature
radiation zone  part of the interior of a star according to a model; the region directly above the core where gamma and X rays from the core are absorbed and reemitted, with the radiation slowly working its way outward
radioactive decay  the natural spontaneous disintegration or decomposition of a nucleus
radioactive decay constant  a specific constant for a particular isotope that is the ratio of the rate of nuclear disintegration per unit of time to the total number of radioactive nuclei
radioactive decay series  series of decay reactions that begins with one radioactive nucleus that decays to a second nucleus that decays to a third nucleus and so on until a stable nucleus is reached
radioactivity  spontaneous emission of particles or energy from an atomic nucleus as it disintegrates
radiometric age  age of rocks determined by measuring the radioactive decay of unstable elements within the crystals of certain minerals in the rocks
range  the geographical distribution of a species
rarefaction  a thinning or pulse of decreased density and pressure of gas molecules
ratio  a relationship between two numbers, one divided by the other; the ratio of distance per time is speed
real image  an image generated by a lens or mirror that can be projected onto a screen
recessive allele  an allele that, when present with a dominant allele, does not express itself and is masked by the effect of the dominant allele
recombinant DNA  DNA that has been constructed by inserting new pieces of DNA into the DNA of another organism, such as a bacterium
Recommended Dietary Allowances (RDA)  U.S. dietary guidelines for a healthy person that focus on the amounts of foods desired from six classes of nutrients
red giant stars  one of two groups of stars on the Hertzsprung-Russell diagram that have a different set of properties than the main sequence stars; bright, low-temperature giant stars that are enormously bright for their temperature
redox reaction  short name for oxidationreduction reaction
reducing agent  supplies electrons to the substance being reduced in a chemical reaction
reduction division (also meiosis)  a type of cell division in which daughter cells get only half the chromosomes from the parent cell
referent  referring to or thinking of a property in terms of another,more familiar object
reflected ray  a line representing direction of motion of light reflected from a boundary
reflection  the change when light, sound, or other waves bounce backwards off a boundary
refraction  a change in the direction of travel of light, sound, or other waves crossing a boundary
regulator protein  proteins that help determine the activities that will occur in a cell or multicellular organism; for example, enzymes and some hormones
relative dating  dating the age of a rock unit or geological event relative to some other unit or event
relative humidity  ratio (times 100 percent) of how much water vapor is in the air to the maximum amount of water vapor that could be in the air at a given temperature
reliable  a term used to describe results that remain consistent over successive trials
rem  measure of radiation that considers the biological effects of different kinds of ionizing radiation
replacement (chemical reaction)  reaction in which an atom or polyatomic ion is replaced in a compound by a different atom or polyatomic ion
replacement (fossil formation)  process in which an organism's buried remains are altered by circulating groundwaters carrying elements in solution; the removal of original materials by dissolutions and the replacement of new materials an atom or molecule at a time
representative elements  name given to the members of the A-group families of the periodic table; also called the main-group elements
reservoir  a natural or artificial pond or lake used to store water, control floods, or generate electricity; a body of water stored for public use
resonance  when the frequency of an external force matches the natural frequency of a material and standing waves are set up
response  the reaction of an organism to a stimulus
responsive processes  those abilities to react to external and internal changes in the environment; for example, irritability, individual adaptation, and evolution
retina  the light-sensitive region of the eye
reverberation  apparent increase in volume caused by reflections, usually arriving within 0.1 second after the original sound
reverse fault  a fault where the hanging wall has moved upward with respect to the foot wall
revolution  the motion of a planet as it orbits the sun
rhodopsin  a light-sensitive pigment found in the rods of the retina
ribonucleic acid (RNA)  a polymer of nucleotides formed on the template surface of DNA by transcription. Three forms that have been identified are mRNA, rRNA, and tRNA
ribose  a 5-carbon sugar molecule that is a component of RNA
ribosomal RNA (rRNA)  a globular form of RNA; a part of ribosomes
ribosomes  small structures composed of two protein and ribonucleic acid subunits; involved in the assembly of proteins from amino acids
Richter scale  expresses the intensity of an earthquake in terms of a scale with each higher number indicating 10 times more ground movement and about 30 times more energy released than the preceding number
ridges  long, rugged mountain chains rising thousands of meters above the abyssal plains of the ocean basin
rift  a split or fracture in a rock formation, land formation, or in the crust of the earth
rip current  strong, brief current that runs against the surf and out to sea
RNA polymerase  an enzyme that attaches to the DNA at the promoter region of a gene and assists in combining RNA nucleotides when the genetic information is transcribed into RNA
rock  a solid aggregation of minerals or mineral materials that have been brought together into a cohesive solid
rock cycle  understanding of igneous, sedimentary, or metamorphic rock as a temporary state in an ongoing transformation of rocks into new types; the process of rocks continually changing from one type to another
rock flour  rock pulverized by a glacier into powdery, silt-sized sediment
rods  light-sensitive cells in the retina of the eye that respond to low-intensity light but do not respond to different colors of light
rotation  the spinning of a planet on its axis
runoff  water moving across the surface of the earth as opposed to soaking into the ground
salinity  a measure of dissolved salts in seawater, defined as the mass of salts dissolved in 1,000 g of solution
salivary amylase  an enzyme present in saliva that breaks starch molecules into smaller molecules
salivary glands  glands that produce saliva
salt  any ionic compound except one with hydroxide or oxide ions
San Andreas fault  in California, the boundary between the North American Plate and the Pacific Plate that runs north-south for some 1,300 km (800 miles) with the Pacific Plate moving northwest and the North American Plate moving southeast
saturated air  air in which an equilibrium exists between evaporation and condensation; the relative humidity is 100 percent
saturated molecule  an organic molecule that has the maximum number of hydrogen atoms possible
saturated solution  the apparent limit to dissolving a given solid in a specified amount of water at a given temperature; a state of equilibrium that exists between dissolving solute and solute coming out of solution
scientific law  a relationship between quantities, usually described by an equation in the physical sciences; is more important and describes a wider range of phenomena than a scientific principle
scintillation counter  a device that indirectly measures ionizing radiation (alpha, beta, gamma, etc.) by measuring the flashes of light produced when the radiation strikes a phosphor
sea  a smaller part of the ocean with characteristics that distinguish it from the larger ocean
sea breeze  cool, dense air from over water moving over land as part of convective circulation
seafloor spreading  the process by which hot, molten rock moves up from the interior of the earth to emerge along mid-oceanic rifts, flowing out in both directions to create new rocks and spread apart the seafloor
seamounts  steep, submerged volcanic peaks on the abyssal plain
second  the standard unit of time in both the metric and English systems of measurement
secondary carnivores  carnivores that feed on primary carnivores and are therefore at the fourth trophic level
secondary coil  part of a transformer, a coil of wire in which the voltage of the original alternating current in the primary coil is stepped up or down by way of electromagnetic induction
secondary consumers  animals that eat other animals—carnivores
secondary loop  part of a nuclear power plant; the closed pipe system that carries steam from a steam generator to the turbines, then back to the steam generator as feedwater
secondary oocyte  the larger of the two cells resulting from the unequal cytoplasmic division of a primary oocyte in meiosis I of oogenesis
secondary sex characteristics  characteristics of the adult male or female, including the typical shape that develops at puberty: broader shoulders, heavier long-bone muscles, development of facial hair, axillary hair, and chest hair, and changes in the shape of the larynx in the male; rounding of the pelvis and breasts and changes in deposition of fat in the female
secondary spermatocyte  cells in the seminiferous tubules that go through the second meiotic division, resulting in four haploid spermatids
second law of motion  the acceleration of an object is directly proportional to the net force acting on that object and inversely proportional to the mass of the object
second law of thermodynamics  a statement that the natural process proceeds from a state of higher order to a state of greater disorder
sedimentary rocks  rocks formed from particles or dissolved minerals from previously existing rocks that were deposited from air or water
sediments  accumulations of silt, sand, or gravel that settled out of the atmosphere or out of water
segregation  the separation and movement of homologous chromosomes to the opposite poles of the cell
seismic waves  vibrations that move as waves through any part of the earth, usually associated with earthquakes, volcanoes, or large explosions
seismograph  an instrument that measures and records seismic wave data
selecting agents  specific environmental factors that favor the passage of certain characteristics from one generation to the next and discourage others
selectively permeable  the property of a membrane that allows certain molecules to pass through it, but interferes with the passage of others
semen  the sperm-carrying fluid produced by the seminal vesicles, prostate glands, and bulbourethral glands of males
semiarid  climate classification between arid and humid; receives between 25 and 50 cm (10 and 20 in) precipitation per year
semicircular canals  a set of tubular organs associated with the cochlea that sense changes in the movement or position of the head
semiconductors  elements that have properties between those of a metal and those of a nonmetal, sometimes conducting an electric current and sometimes acting like an electrical insulator depending on the conditions and their purity; also called metalloids
semilunar valves  pulmonary artery and aorta valves that prevent the flow of blood backward into the ventricles
seminal vesicle  a part of the male reproductive system that produces a portion of the semen
seminiferous tubules  sperm-producing tubes in the testes
sensory neurons  those neurons that send information from sense organs to the central nervous system
sex chromosomes  a pair of chromosomes that determines the sex of an organism; X and Y chromosomes
sex-determining chromosome  the chromosomes X and Y that are primarily responsible for determining if an individual will develop as a male or female
sexual intercourse  the mating of male and female; the deposition of the male sex cells, or sperm cells, in the reproductive tract of the female; also known as coitus or copulation
sexuality  a term used in reference to the totality of the aspects—physical, psychological, and cultural—of our sexual nature
sexual reproduction  the propagation of organisms involving the union of gametes from two parents
shallow-focus earthquakes  earthquakes that occur from the surface down to 70 km deep
shear stress  produced when two plates slide past one another or by one plate sliding past another plate that is not moving
shell model of the nucleus  model of the nucleus that has protons and neutrons moving in energy levels or shells in the nucleus (similar to the shell structure of electrons in an atom)
shells  the layers that electrons occupy around the nucleus
shield volcano  a broad, gently sloping volcanic cone constructed of solidified lava flows til67002_glo.qxd 5/8/03 11:08 AM Page 631
shock wave  a large, intense wave disturbance of very high pressure; the pressure wave created by an explosion, for example
sickle-cell anemia  a disease caused by a point mutation; this malfunction produces sickle-shaped red blood cells
silicates  minerals that contain siliconoxygen tetrahedra either isolated or joined together in a crystal structure
sill  a tabular-shaped intrusive rock that formed when magma moved into the plane of contact between sedimentary rock layers
simple harmonic motion  the vibratory motion that occurs when there is a restoring force opposite to and proportional to a displacement
single bond  covalent bond in which a single pair of electrons is shared by two atoms
single-factor cross  a genetic study in which one characteristic is followed from the parental generation to the offspring
small intestine  the portion of the digestive system immediately following the stomach; responsible for digestion and absorption
soil  a mixture of unconsolidated weathered earth materials and humus, which is altered, decay-resistant organic matter
solenoid  a cylindrical coil of wire that becomes electromagnetic when a current runs through it
solids  a phase of matter with molecules that remain close to fixed equilibrium positions due to strong interactions between the molecules, resulting in the characteristic definite shape and definite volume of a solid
solstices  time when the sun is at its maximum or minimum altitude in the sky, known as the summer solstice and the winter solstice
solubility  dissolving ability of a given solute in a specified amount of solvent, the concentration that is reached as a saturated solution is achieved at a particular temperature
solute  the component of a solution that dissolves in the other component; the solvent
solution  a homogeneous mixture of ions or molecules of two or more substances
solvent  the component of a solution present in the larger amount; the solute dissolves in the solvent to make a solution
soma  the cell body of a neuron, which contains the nucleus
sonic boom  sound waves that pile up into a shock wave when a source is traveling at or faster than the speed of sound
sound quality  characteristic of the sound produced by a musical instrument; determined by the presence and relative strengths of the overtones produced by the instrument
south pole (of a magnet)  short for "south seeking"; the pole of a magnet that points southward when it is free to turn
speciation  the process of generating new species
species  a group of organisms that can interbreed naturally to produce fertile offspring
specific dynamic action (SDA)  the amount of energy needed to process the food that we eat
specific heat  each substance has its own specific heat, which is defined as the amount of energy (or heat) needed to increase the temperature of 1 gram of a substance 1 degree Celsius
speed  a measure of how fast an object is moving—the rate of change of position per change in time; speed has magnitude only and does not include the direction of change
sperm  the haploid sex cells produced by sexually mature males
spermatids  haploid cells produced by spermatogenesis that change into sperm
spermatogenesis  the specific name given to the gametogenesis process that leads to the formation of sperm
spinal cord  the portion of the central nervous system located within the vertebral column, which carries both sensory and motor information between the brain and the periphery of the body
spindle fibers  an array of microtubules extending from pole to pole; used in the movement of chromosomes
spin quantum number  from the quantum mechanics model of the atom, one of four descriptions of the energy state of an electron wave; this quantum number describes the spin orientation of an electron relative to an external magnetic field
spontaneous generation  the theory that living organisms arose from nonliving material
spontaneous mutation  a change in the DNA of an organism for which there is no known cause
stable equilibrium phase  a stage in a population growth curve following rapid growth in which there is both a decrease in natality and an increase in mortality so that the size of the population is stable
standard atmospheric pressure  the average atmospheric pressure at sea level, which is also known as normal pressure; the standard pressure is 29.92 inches or 760.0 mm of mercury (1,013.25 millibar)
standard unit  a measurement unit established as the standard upon which the value of the other referent units of the same type are based
standing waves  condition where two waves of equal frequency traveling in opposite directions meet and form stationary regions of maximum displacement due to constructive interference and stationary regions of zero displacement due to destructive interference
stapes  the ear bone that is attached to the oval window
starch  a group of complex carbohydrates (polysaccharides) that plants use as a stored food source and that serves as an important source of food for animals
stationary front  occurs when the edge of a weather front is not advancing
steam generator  part of a nuclear power plant; the heat exchanger that heats feedwater from the secondary loop to steam with the very hot water from the primary loop
step-down transformer  a transformer that decreases the voltage
step-up transformer  a transformer that increases the voltage
steroids  a group of lipid molecules characterized by an arrangement of interlocking rings of carbon; they serve as hormones that aid in regulating body processes
stimulus  any change in the internal or external environment of an organism that it can detect
stony-iron meteorites  meteorites composed of silicate minerals and metallic iron
stony meteorites  meteorites composed mostly of silicate minerals that usually make up rocks on the earth
storm  a rapid and violent weather change with strong winds, heavy rain, snow, or hail
strain  adjustment to stress; a rock unit might respond to stress by changes in volume, changes in shape, or by breaking
stratosphere  the layer of the atmosphere above the troposphere where temperature increases with height
stream  body of running water
stress  a force that tends to compress, pull apart, or deform rock; stress on rocks in the earth's solid outer crust results as the earth's plates move into, away from, or alongside each other
structural protein  protein molecules whose function is to provide support and shape to a cell or multicellular organism; for example, muscle protein fibers
structural similarities  one of the characteristics of living things; describes the fact that all living things are composed of cells, either prokaryotic or eukaryotic
subduction zone  the region of a convergent boundary where the crust of one plate is forced under the crust of another plate into the interior of the earth
sublimation  the phase change of a solid directly into a vapor or gas
submarine canyons  a feature of the ocean basin; deep, steep-sided canyons that cut through the continental slopes
subspecies  regional groups within a species that are significantly different structurally, physiologically, or behaviorally, yet are capable of exchanging genes by interbreeding with other members of the species
superconductors  some materials in which, under certain conditions, the electrical resistance approaches zero
supercooled  water in the liquid phase when the temperature is below the freezing point
superior vena cava  a major vein that returns blood to the heart from the head and upper body
supernova  a rare catastrophic explosion of a star into an extremely bright, but short-lived phenomenon
supersaturated  containing more than the normal saturation amount of a solute at a given temperature
surf  the zone where breakers occur; the water zone between the shoreline and the outermost boundary of the breakers
surface wave  a seismic wave that moves across the earth's surface, spreading across the surface like water waves spread on the surface of a pond from a disturbance
S-wave  a sideways, or shear wave in which a disturbance vibrates materials from side to side, perpendicular to the direction of wave movement
S-wave shadow zone  a region of the earth more than 103° of arc away from the epicenter of an earthquake where S-waves are not recorded; believed to be the result of the core of the earth that is a liquid, or at least acts like a liquid
swell  regular groups of low-profile, longwavelength waves that move continuously
symbiotic nitrogen-fixing bacteria  bacteria that live in the roots of certain kinds of plants, where they convert nitrogen gas molecules into compounds that the plants can use to make amino acids and nucleic acids
synapse  the space between the axon of one neuron and the dendrite of the next, where chemicals are secreted to cause an impulse to be initiated in the second neuron
synapsis  the condition in which the two members of a pair of homologous chromosomes come to lie close to one another
syncline  a trough-shaped fold in layered bedrock
systemic circulation  the flow of blood through certain chambers of the heart and blood vessels to the general body and back to the heart
systolic blood pressure  the blood pressure recorded in a large artery while the heart is contracting
talus  steep, conical or apron-like accumulations of rock fragments at the base of a slope
taxonomy  the science of classifying and naming organisms
telophase  the last phase in mitosis characterized by the formation of daughter nuclei
temperate climate zone  climate zone of the middle latitudes; average monthly temperatures stay between 10°C and 18°C (50°F and 64°F) throughout the year
temperature  how hot or how cold something is; a measure of the average kinetic energy of the molecules making up a substance
tensional stress  the opposite of compressional stress; occurs when one part of a plate moves away from another part that does not move
termination code  the DNA nucleotide sequence at the end of a gene with the code ATT, ATC, or ACT that signals "stop here"
terrestrial planets  planets Mercury,Venus, Earth, and Mars that have similar densities and compositions as compared to the outer giant planets
testes  the male sex organs that produce haploid cells called sperm
testosterone  the male sex hormone produced in the testes that controls male sexual development
thalamus  a region of the brain that relays information between the cerebrum and lower portions of the brain, providing some level of awareness in that it determines pleasant and unpleasant stimuli and is involved in sleep and arousal
theory  a broad, detailed explanation that guides the development of hypotheses and interpretations of experiments in a field of study
theory of natural selection  the idea that some individuals within a population will have favorable combinations of genes that make it very likely that those individuals will survive, reproduce, and pass their genes to the next generation
thermometer  a device used to measure the hotness or coldness of a substance
third law of motion  whenever two objects interact, the force exerted on one object is equal in size and opposite in direction to the force exerted on the other object; forces always occur in matched pairs that are equal and opposite
thrust fault  a reverse fault with a low-angle fault plane
thunderstorm  a brief, intense electrical storm with rain, lightning, thunder, strong winds, and sometimes hail
thymine  a single-ring nitrogenous-base molecule in DNA but not in RNA; it is complementary to adenine
thyroid-stimulating hormone (TSH)  a hormone secreted by the pituitary gland that stimulates the thyroid to secrete thyroxine
thyroxine  a hormone produced by the thyroid gland that speeds up the metabolic rate
tidal bore  a strong tidal current, sometimes resembling a wave, produced in very long, very narrow bays as the tide rises
tidal currents  a steady and continuous onward movement of water produced in narrow bays by the tides
tides  periodic rise and fall of the level of the sea from the gravitational attraction of the moon and sun
tissue  a group of specialized cells that work together to perform a specific function
tornado  a long, narrow, funnel-shaped column of violently whirling air from a thundercloud that moves destructively over a narrow path when it touches the ground
total internal reflection  condition where all light is reflected back from a boundary between materials; occurs when light arrives at a boundary at the critical angle or beyond
trachea  a major tube supported by cartilage that carries air to the bronchi; also known as the windpipe
transcription  the process of manufacturing RNA from the template surface of DNA; three forms of RNA that may be produced are mRNA, rRNA, and tRNA
transfer RNA (tRNA)  a molecule composed of ribonucleic acid. It is responsible for transporting a specific amino acid into a ribosome for assembly into a protein
transform boundaries  in plate tectonics, boundaries that occur between two plates sliding horizontally by each other along a long, vertical fault; sudden jerks along the boundary result in the vibrations of earthquakes
transformer  a device consisting of a primary coil of wire connected to a source of alternating current and a secondary coil of wire in which electromagnetic induction increases or decreases the voltage of the source
transition elements  members of the B-group families of the periodic table
translation  the assembly of individual amino acids into a polypeptide
transparent  term describing materials that allow the transmission of light; for example, glass and clear water are transparent materials
transportation  the movement of eroded materials by agents such as rivers, glaciers, wind, or waves
transverse wave  a mechanical disturbance that causes particles to move perpendicular to the direction that the wave is traveling
triglyceride  organic compound of esters formed from glycerol and three long-chain carboxylic acids; also called fats in animals and oils in plants
triple bond  covalent bond formed when three pairs of electrons are shared by two atoms
trophic level  a step in the flow of energy through an ecosystem
tropical air mass  a warm air mass from warm regions
tropical climate zone  climate zone of the low latitudes; average monthly temperatures stay above 18°C (64°F), even during the coldest month of the year
tropical cyclone  a large, violent circular storm that is born over the warm, tropical ocean near the equator; also called hurricane (Atlantic and eastern Pacific) and typhoon (in western Pacific)
troposphere  layer of the atmosphere from the surface to where the temperature stops decreasing with height
trough  the low mound of water that is part of a wave; also refers to the rarefaction, or low-pressure part of a sound wave
true fats  also known as neutral fats; a category of lipids composed of glycerol and fatty acids; for example, pork chop fat or olive oil
tsunami  very large, fast, and destructive ocean wave created by an undersea earthquake, landslide, or volcanic explosion; a seismic sea wave
tumor  a mass of undifferentiated cells not normally found in a certain portion of the body
turbidity current  a muddy current produced by underwater landslides
tympanum  the eardrum
typhoon  the name for hurricanes in the western Pacific
ultrasonic  sound waves too high in frequency to be heard by the human ear; frequencies above 20,000 Hz
unconformity  a time break in the rock record
undertow  a current beneath the surface of the water produced by the return of water from the shore to the sea
unit  in measurement, a well-defined and agreed-upon referent
universal law of gravitation  every object in the universe is attracted to every other object with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between the centers of the two masses
unpolarized light  light consisting of transverse waves vibrating in all conceivable random directions
unsaturated molecule  an organic molecule that does not contain the maximum number of hydrogen atoms; a molecule that can add more hydrogen atoms because of the presence of double or triple bonds
uracil  a single-ring nitrogenous-base molecule in RNA but not in DNA; it is complementary to adenine
uterus  the organ in female mammals in which the embryo develops
vacuole  a large sac within the cytoplasm of a cell, composed of a single membrane
vagina  the passageway between the uterus and outside of the body; the birth canal
valence  the number of covalent bonds an atom can form
valence electrons  electrons of the outermost shell; the electrons that determine the chemical properties of an atom and the electrons that participate in chemical bonding
valid  a term used to describe meaningful data that fit into the framework of scientific knowledge
Van Allen belts  belts of radiation caused by cosmic-ray particles becoming trapped and following the earth's magnetic field lines between the poles
vapor  the gaseous state of a substance that is normally in the liquid state
variables  changing quantities usually represented by a letter or symbol
veins  the blood vessels that return blood to the heart
velocity  describes both the speed and direction of a moving object; a change in velocity is a change in speed, in direction of travel, or both
ventifacts  rocks sculpted by wind abrasion
ventricles  the powerful muscular chambers of the heart whose contractions force blood to flow through the arteries to all parts of the body
vibration  a back-and-forth motion that repeats itself
villi  tiny fingerlike projections in the lining of the intestine that increase the surface area for absorption
viroids  infectious particles that are composed solely of a small, single strand of RNA
virtual image  an image where light rays appear to originate from a mirror or lens; this image cannot be projected on a screen
virus  a nucleic acid particle coated with protein that functions as an obligate intracellular parasite
vitamin-deficiency disease  poor health caused by the lack of a certain vitamin in the diet; for example, scurvy for lack of vitamin C
vitamins  organic molecules that cannot be manufactured by the body but are required in very low concentrations for good health
volcanism  volcanic activity; the movement of magma
volcano  a hill or mountain formed by the extrusion of lava or rock fragments from a mass of magma below
volt  the ratio of work done to move a quantity of charge
voltage source  a device that does work in moving a quantity of charge
volume  how much space something occupies
vulcanism  volcanic activity; the movement of magma
warm front  the front that forms when a warm air mass advances against a cool air mass
watershed  the region or land area drained by a stream; a stream drainage basin
water table  the boundary below which the ground is saturated with water
watt  metric unit for power; equivalent to J/s
wave  a disturbance or oscillation that moves through a medium
wave equation  the relationship of the velocity of a wave to the product of the wavelength and frequency of the wave
wave front  a region of maximum displacement in a wave; a condensation in a sound wave
wave height  the vertical distance of an ocean wave between the top of the wave crest and the bottom of the next trough
wavelength  the horizontal distance between successive wave crests or other successive parts of the wave
wave mechanics  alternate name for quantum mechanics derived from the wavelike properties of subatomic particles
wave period  the time required for two successive crests or other successive parts of the wave to pass a given point
weak acid  acids that only partially ionize because of an equilibrium reaction with water
weak base  a base only partially ionized because of an equilibrium reaction with water
weathering  slow changes that result in the breaking up, crumbling, and destruction of any kind of solid rock
white dwarf stars  one of two groups of stars on the Hertzsprung-Russell diagram that have a different set of properties than the main sequence stars; faint, white-hot stars that are very small and dense
wind  a horizontal movement of air that moves along or parallel to the ground, sometimes in currents or streams
wind abrasion  the natural sand-blasting process that occurs when wind-driven particles break off small particles of rock and polish the rock they strike
wind chill factor  a factor that compares heat loss from bodies in still air with those in moving air; moving air removes heat more rapidly and causes a person to feel that the air is colder than its actual temperature; the cooling power of wind
work  the magnitude of applied force times the distance through which the force acts; can be thought of as the process by which one form of energy is transformed to another
X chromosome  the chromosome in a human female egg (and in one-half of sperm cells) that is associated with the determination of sexual characteristics
X-linked gene  a gene located on one of the sex-determining X chromosomes
Y chromosome  the sex-determining chromosome in one-half of the sperm cells of human males responsible for determining maleness
zone of saturation  zone of sediments beneath the surface in which water has collected in all available spaces
zooplankton  small, weakly swimming animals of many kinds
zygote  a diploid cell that results from the union of an egg and a sperm; a fertilized egg







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