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362 Cards in this Set

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  • Back
a measure of the amount of dissolved salts in a given amount of liquid
the accumulation of salts in soil
the watery fluid that is secreted by the salivary glands of the mouth, that softens and moistens food, and that begins digestion
one of the glands that produce saliva; located under the tongue and near the lower jawbone, cheeks, lips, and palate
salivary gland
an ionic compound that forms when a metal atom or a positive radical replaces the hydrogen of an acid
the movement of sand or other sediments by short jumps and bounces that is caused by wind or water
a maritime habitat characterized by grasses, sedges, and other plants that have adapted to continual, periodic flooding; salt marshes are found primarily throughout the temperate and subarctic regions
salt marsh
the group of individuals or events selected to represent a statistical population
a low ridge of sand deposited along the shore of a lake or sea
a chemical reaction in which esters of fatty acids react with a strong base to produce glycerol and a fatty acid salt; the process that is used to make soap
an organism that feeds on dead organic material
the tissue of the secondary xylem that is distributed around the outside of a tree trunk and is active in transporting sap
a malignant tumor that grows in bone or muscle tissue
the basic unit of contraction in skeletal and cardiac muscle
a natural or artificial body that revolves around a planet
describes air that contains the maximum amount of water vapor that the air can hold at a specific temperature
saturated air
an organic compound formed only by carbon and hydrogen linked by single bonds
saturated hydrocarbon
a solution that cannot dissolve any more solute under the given conditions
saturated solution
a plain full of grasses and scattered trees and shrubs; found in tropical and subtropical habitats and mainly in regions with a dry climate, such as East Africa
a physical quantity that has magnitude but no direction
the relationship between the distance shown on a map and the actual distance
bony structures that cover and protect a fish's body
a microscope that produces an enlarged, three-dimensional image of an object by using a beam of electrons rather than light
scanning electron microscope
a process in which a particle (such as an electron, photon, or neutron) collides with a material and changes energy and direction
an animal that feeds on the bodies of dead animals
a graphical representation of a circuit that uses lines to represent wires and different symbols to represent components
schematic diagram
a disease that is caused by a parasitic blood fluke of the genus Schistosoma and that affects the skin, intestines, liver, vascular system, or other organs
the method of coelom formation in protosomes in which the embryonic mesoderm splits into two layers
the type of cell that wraps around the axons of peripheral neurons
Schwann cell
the knowledge obtained by observing natural events and conditions in order to discover facts and formulate laws or principles that can be verified or tested
a series of steps followed to solve problems, including collecting data, formulating a hypothesis, testing the hypothesis, and stating conclusions
scientific methods
a method of expressing a quantity as a number multiplied by 10 to the appropriate power
scientific notation
an instrument that converts scintillating light into an electrical signal for detecting and measuring radiation
scintillation counter
a type of plant tissue composed of cells that have thickened secondary cell walls that function in plant support
the head of a tapeworm, which has hooks and suckers to adhere to the host tissues
a simple machine that consists of an inclined plane wrapped around a cylinder
the sac that contains the testes in most male mammals
a large, commonly saline body of water that is smaller than an ocean and that may be partially or completely surrounded by land; also a subdivision of an ocean
the process by which new oceanic lithosphere (sea floor) forms as magma rises to Earth's surface and solidifies at a mid-ocean ridge
sea-floor spreading
a submerged mountain on the ocean floor that is at least 1,000 m high and that has a volcanic origin
the oily secretion of the sebaceous glands
an organic compound in which two hydrogen atoms of an ammonia molecule have been replaced by either identical or different groups of atoms
secondary amine
plant growth that results from cell division in the cambia, or lateral meristems, and that causes the stems and roots to thicken
secondary growth
the response to a subsequent infection by a given pathogen or antigen
secondary immune response
a pollutant that forms in the atmosphere by chemical reaction with primary air pollutants, natural components in the air, or both
secondary pollutant
the process by which one community replaces another community that has been partially or totally destroyed
secondary succession
a molecule that is generated when a specific substance attaches to a receptor on the outside of a cell membrane, which produces a change in cellular function
second messenger
a hormone that is released in the intestines in response to a high concentration of acid and that stimulates the secretion of water and bicarbonate from the pancreas
the process by which the glands of the body release their substances; a substance produced by a gland
fragments of organic or inorganic material that are transported and deposited by wind, water, or ice and that accumulate in layers on the Earth's surface
a rock that forms from compressed or cemented layers of sediment
sedimentary rock
a plant embryo that is enclosed in a protective coat
the protective, outer covering of a seed
seed coat
a young plant grown from a seed
a plant that produces seeds
seed plant
any part of a larger structure, such as the body of an organism, that is set off by natural or arbitrary boundaries
the division of the body of an organism into a series of similar parts
an area along a fault where relatively few earthquakes have occurred recently but where strong earthquakes are known to have occurred in the past
seismic gap
a method that is used to help predict major earthquakes and that is based on the assumption that a major earthquake is more likely to occur along the part of an active fault where no earthquakes have occurred for a certain period of time
seismic gap method
a vibration in rock that travels out from the focus of an earthquake in all directions; seismic waves can also be caused by explosions
seismic wave
a tracing of earthquake motion that is recorded by a seismograph
an instrument that records vibrations in the ground
the study of earthquakes, including their origin, propagation, energy, and prediction
the human practice of breeding animals or plants that have certain desired traits
selective breeding
a method of harvesting only middle-aged or mature trees individually or in small groups
selective cutting
the process by which a changing current in a circuit generates a voltage in that same circuit
the transfer of pollen grains from an anther to the stigma of the same flower or to the stigma of another flower on the same plant
the fluid that contains sperm and various secretions produced by the male reproductive organs
the fluid-filled canal in the inner ear that helps maintain balance and coordinate movements
semicircular canal
an element or compound that conducts electric current better than an insulator does but not as well as a conductor does
in each new DNA double helix, one strand is from the original molecule, and one strand is new
semi-conservative replication
the type of valve that separates the right ventricle in the heart from the pulmonary artery and that separates the left ventricle from the aorta (abbreviation, SL valve)
semilunar valve
a saclike organ of female or hermaphroditic invertebrates that stores sperm
seminal receptacle
one of two glandular structures in male vertebrates that hold and secrete seminal fluid
seminal vesicle
one of the many tubules in the testis where sperm are produced
seminiferous tubule
a membrane that permits the passage of only certain molecules
semipermeable membrane
an organ that receives stimuli and gives rise to the senses such as sight, smell, hearing, and pain
sense organ
a division of the peripheral nervous system that acquires information from the external and internal environments of the body
sensory division
a neuron that carries stimuli from a sense organ to the central nervous system
sensory neuron
a specialized structure that contains the ends of sensory neurons and that responds to specific types of stimuli
sensory receptor
in a flower, one of the outermost rings of modified leaves that protect the flower bud
a tank that separates solid waste from liquids and that digests organic matter in the process
sept septum ic tank
a dividing wall, or partition, such as the wall between adjacent cells in a fungal hypha, the internal wall between adjacent segments of an annelid, and the thick wall between the right and left chambers of the heart
describes two or more components of a circuit that provide a single path for current
a circuit in which the parts are joined one after another such that the current in each part is the same
series circuit
describes an organism that remains attached to a surface for its entire life and does not move
one of the external bristles or spines that project from the body of an annelid
a facility where sewage is processed to reduce the organic and bacterial content
sewage treatment plant
a gamete or haploid reproductive cell that unites with another haploid reproductive cell to form a zygote
sex cell
one of the pair of chromosomes that determine the sex of an individual
sex chromosome
a hormone that is required for the sexual development and function of an organism
sex hormone
an autosomal trait that is influenced by the presence of male or female sex hormones
sex-influenced trait
the type of inheritance in which a gene is located on a sex chromosome
sex linkage
a trait that is determined by a gene found on one of the sex chromosomes, such as the X chromosome or the Y chromosome in humans
sex-linked trait
reproduction in which gametes from two parents unite
sexual reproduction
an evolutionary mechanism by which traits that increase the ability of individuals to attract or acquire mates appear with increasing frequency in a population; selection in which a mate is chosen on the basis of a particular trait or traits
sexual selection
an area on Earth's surface where no direct seismic waves from a particular earthquake can be detected
shadow zone
a feature that evolved in the common ancestor of a group of related organisms
shared derived character
the process by which water flows over a layer of soil and removes the topsoil
sheet erosion
a radiation-absorbing material that is used to decrease radiation leakage from nuclear reactors
a large, gently sloped volcano that forms by eruptions of basaltic lava flows
shield volcano
the portion of a plant that grows mostly above the ground; includes the stems and leaves
shield volcano
the boundary between land and a body of water
a plant that produces flowers or changes in some other way when exposed to periods of daylight that are shorter than a critical length of time
short-day plant
a comet whose orbital period is less than 200 years
short-period comet
Le Système International d’Unités, or the International System of Units, which is the measurement system that is accepted worldwide
a set of symptoms, such as headache, fatigue, eye irritation, and dizziness, that may affect workers in modern, airtight office buildings; believed to be caused by indoor pollutants
sick-building syndrome
a region that connects two sieve cells and that has one or more sieve areas, which consist of clusters of pores through which the cytoplasm of the cells is connected and through which materials are transported
sieve plate
in the phloem of a flowering plant, a conducting tube that is made up of a series of sieve-tube members stacked end to end
sieve tube
one of the component cells of a sieve tube, which is found mainly in flowering plants
sieve-tube member
anything that serves to direct, guide, or warn
a prescribed decimal place that determines the amount of rounding off to be done based on the precision of the measurement
significant figure
a mineral that contains a combination of silicon and oxygen and that may also contain one or more metals
silicate mineral
a type of ooze that contains silica and that is composed of the skeletal remains of organisms
siliceous ooze
the basic unit of the structure of silicate minerals; a silicon ion chemically bonded to and surrounded by four oxygen ions
silicon-oxygen tetrahedron
a sheet of hardened magma that forms between two layers of rock and that is parallel to them
a periodic motion whose path is formed by one or more vibrations that are symmetric about an equilibrium position
simple harmonic motion
a leaf that has an undivided blade
simple leaf
one of the six basic types of machines, which are the basis for all other forms of machines
simple leaf
a covalent bond in which two atoms share one pair of electrons
single bond
a reaction in which one element or radical takes the place of another element or radical in a compound
single-displacement reaction
any place where a plant stores or uses organic nutrients, such as sugar or starches
a circular depression that forms when rock dissolves, when overlying sediment fills an existing cavity, or when the roof of an underground cavern or mine collapses
a mass of cardiac muscle cells that lies at the junction of the superior vena cava with the right atrium and that initiates and regulates contraction of the heart (abbreviation, SA node)
sinoatrial node
in fishes, amphibians, and reptiles, a chamber that collects blood from the veins and transmits it to the right atrium
sinus venosus
a hollow tube of bivalves used for sucking in and expelling sea water
a voluntary muscle that is attached to the bones and that moves parts of the body
skeletal muscle
the bones, cartilage, ligaments, and tendons whose primary function is to support and protect the body and to allow the body to move
skeletal system
the bones of a human or animal body that form the framework of the body, support the muscles and organs, and protect the inner organs
a transparent structure that projects from the surface of a sea star and that enables respiration
skin gill
a type of precipitation made up of ice pellets
a landslide characterized by the downward movement of one or more masses of rock or debris along curved surfaces
the region of the digestive tube between the stomach and the colon (large intestine) where food's acidity is neutralized and most of the nutrients are absorbed
small intestine
the melting or fusing of ore in order to separate impurities from pure metal
urban air pollution composed of a mixture of smoke and fog produced from industrial pollutants and burning fuels
the portion of the endoplasmic reticulum that lacks attached ribosomes
smooth endoplasmic reticulum
the elongated muscle that is not under voluntary control and that is found in the digestive tract, blood vessels, glands, and hair follicles, but not in the heart
smooth muscle
a region that is permanently covered by snow
the line above which ice and snow remain throughout the year
a substance that is used as a cleaner and that dissolves in water
the interaction between animals of the same species that are not related or are only distant relatives
social behavior
an insect that lives in a large community, such as an ant or a bee
social insect
a carrier protein that uses ATP to actively transport sodium ions out of a cell and potassium ions into the cell
sodium-potassium pump
a muscular portion of the palate that separates the mouth cavity from the nasal cavity and the pharynx
soft palate
software a set of instructions or commands that tells a computer what to do; a computer program
soft water that contains a very low concentration of calcium and magnesium compounds
soft water
soil a loose mixture of rock fragments and organic material that can support the growth of vegetation
soil conservation a method to maintain the fertility of the soil by protecting the soil from erosion and chemical decay
soil conservation
soil profile a vertical section of soil that shows the layers of horizons
soil profile
soil structurethe arrangement of soil particles
soil structure
soil texturethe soil quality that is based on the proportions of soil particles
soil texture
solar cell a device that when exposed to a source of light, such as the sun, converts the light into electricity
solar cell
solar collector a device that absorbs solar radiation and stores it as usable energy
solar collector
solar eclipse the passing of the moon between Earth and the sun; during a solar eclipse, the shadow of the moon falls on Earth
solar eclipse
solar energy the energy received by Earth from the sun in the form of radiation
solar energy
solar flare an explosive release of energy that comes from the sun and that is associated with magnetic disturbances on the sun's surface
solar flare
solar nebula a rotating cloud of gas and dust from which the sun and planets formed; also any nebula from which stars and planets may form
solar nebula
solar system the sun and all of the planets and other bodies that travel around it
solar system
solar tracking the movement of leaves or flowers in response to the sun's movement across the sky
solar tracking
solar water heating a system that uses solar energy to heat water for household use
solar water heating
solar wind the movement of electrically charged atomic particles, mostly helium and hydrogen, from the sun through the solar system
solar wind
solar year the time required for the Earth to make one revolution around the sun; approximately 365.24 days
solar year
solenoid a coil of wire with an electric current in it
solid the state of matter in which the volume and shape of a substance are fixed
solid waste a discarded solid material, such as garbage, refuse, or sludges
solid waste
solifluction the slow, downslope flow of soil saturated with water in areas surrounding glaciers at high elevations
solstice the point at which the sun is as far north or as far south of the equator as possible
solubility the ability of one substance to dissolve in another at a given temperature and pressure; expressed in terms of the amount of solute that will dissolve in a given amount of solvent to produce a saturated solution
solubility equilibrium the physical state in which the opposing processes of dissolution and crystallization of a solute occur at equal rates
solubility equilibrium
solubility product constant the equilibrium constant for a solid that is in equilibrium with the solid's dissolved ions
solubility product constant
soluble capable of dissolving in a particular solvent
solute in a solution, the substance that dissolves in the solvent
solution a homogeneous mixture throughout which two or more substances are uniformly dispersed
solvated describes a solute molecule that is surrounded by solvent molecules
solvent in a solution, the substance in which the solute dissolves
somatic mutation a mutation that occurs in a body cell
somatic mutation
the portion of the neural structure that provides nerve connections to the skin, skeleton, and muscles of the body, but not to the viscera, blood vessels, and glands
somatic nervous system
sonar sound navigation and ranging, a system that uses acoustic signals and returned echoes to determine the location of objects or to communicate
sonic boom the explosive sound heard when a shock wave from an object traveling faster than the speed of sound reaches a person’s ears
sonic boom
sonic boomthe process by which natural agents, such as running water, separate the particles of a sediment according to size, shape, or gravity
sonic boom
sorus a cluster of spores or sporangia
sound quality the result of the blending of several pitches through interference
sound quality
sound wave a longitudinal wave that is caused by vibrations and that travels through a material medium
sound wave
source a part of a plant that makes sugars and other organic compounds and from which these compounds are transported to other parts of the plant
source reduction any change in the design, manufacture, purchase, or use of materials or products to reduce their amount or toxicity before they become municipal solid waste; also the reuse of products or materials
source reduction
space probe an uncrewed vehicle that carries scientific instruments into space to collect scientific data
space probe
space shuttle a reusable space vehicle that takes off like a rocket and lands like an airplane
space shuttle
space station a long-term orbiting platform from which other vehicles can be launched or scientific research can be carried out
space station
spawn to deposit eggs or sperm directly into the water; spawning is observed in certain fishes, amphibians, mollusks, and crustaceans
specialist an individual or a species that is adapted to a particular environmental factor or ecological niche and that can tolerate only a narrow range of conditions
specialization the evolutionary adaptation of a cell, organ, organism, or population for a particular function or environment
speciation the formation of new species as a result of evolution
speciationa group of organisms that are closely related and can mate to produce fertile offspring; also the level of classification below genus and above subspecies
species-area effect a pattern in which the number of species in an area increases as the area increases
species-area effect
species diversity an index that combines the number and relative abundance of different species in a community
species diversity
species richness the number of different species in an area or community
species richness
specific heat the quantity of heat required to raise a unit mass of homogeneous material 1 K or 1ºC in a specified way given constant pressure and volume
specific heat
specific humidity the mass of water vapor per mass of air that contains the water vapor; usually expressed as grams of water vapor per kilograms of humid air
specific humidity
spectator ions ions that are present in a solution in which a reaction is taking place but that do not participate in the reaction
spectator ions
spectroscope an instrument that splits white light into a band of colors
the band of colors produced when white light passes through a prism
speed the distance traveled divided by the time interval during which the motion occurred
sperm the male gamete (sex cell)
spermatid an immature sperm cell that has almost completed its development
spermatogenesis the process by which male gametes form
the part of the eukaryotic cell cycle during which replication of DNA occurs
S phase
spice a seasoning that is usually made from the root, stem, or seeds of certain plants
spicule a needle of silica or calcium carbonate in the skeleton of some sponges
spinal cord a column of nerve tissue running from the base of the brain through the vertebral column
spinal cord
spinal nerve a nerve that arises from the spinal cord and extends between the vertebrae
spinal nerve
spinal reflex a reflex whose pathway is connected to a center in the spinal cord
spinal reflex
spindle a network of microtubules that forms during mitosis and moves chromatids to the poles
spindle fiber one of the microtubules that extend across a dividing eukaryotic cell; assists in the movement of chromosomes
spindle fiber
spinneret an organ that spiders and certain insect larvae use to produce silky threads for webs and cocoons
spin quantum number the quantum number that describes the intrinsic angular movement of a particle
spin quantum number
spiracle an external opening in an insect or arthropod, used in respiration
spiral cleavage the division of cells in an oblique or alternating pattern
spiral cleavage
spiral galaxy a galaxy that consists of a nucleus of older stars and a disk with spiral arms made mainly of dust, gas, and young stars
spiral galaxy
a spiral-shaped bacterium
a narrow point of land that extends into the water
spleen the largest lymphatic organ in the body; serves as a blood reservoir, disintegrates old red blood cells, and produces lymphocytes and plasmids
sponge an aquatic invertebrate of the phylum Porifera that attaches to stones or plants and that has a porous structure and a tough, elastic skeleton
spongin a fibrous protein that contains sulfur and composes the fibers of the skeleton of some sponges
spongy bone less-dense bone tissue that has many open spaces
spongy bone
spongy mesophyll inside a leaf, the tissue that is made up of loosely arranged parenchyma cells that contain chloroplasts and are surrounded by air spaces that promote the diffusion of oxygen, carbon dioxide, and water throughout the leaf
spongy mesophyll
an early and now disproved theory that living organisms come to life spontaneously from nonliving material
spontaneous generation
sporangiophore a plant or fungal structure that bears a sporangium or spores
sporangium a specialized sac, case, capsule, or other structure that produces spores
spore a reproductive cell or multicellular structure that is resistant to environmental conditions and that can develop into an adult without fusion with another cell
sporophyte in plants and algae that have alternation of generations, the diploid individual or generation that produces haploid spores
a sporozoan that has been released from the oocyst and is ready to penetrate a new host cell
spring a flow of water above ground level that occurs where the water table intersects the ground surface
spring constant an expression of the ratio of force to displacement for a spring or other elastic material
spring constant
spring tide a tide of increased range that occurs two times a month, at the new and full moons
spring tide
springwood a type of wood that forms early in the growing season, usually in the spring, and consists of secondary xylem whose cells have a relatively large diameter
squall line a narrow band of heavy thunderstorms
squall line
stabilizing selection a type of natural selection in which the average form of a trait is favored and becomes more common
stabilizing selection
stalactite a cone-shaped calcite deposit suspended from the ceiling of a cave
stalagmite an upward-pointing, cone-shaped calcite deposit built up from the floor of a cave
stamen the male reproductive structure of a flower that produces pollen and consists of an anther at the tip of a filament
standard atmospheric pressure the Earth's normal air pressure at an altitude of sea level; equal to the pressure of a column of mercury 760 mm high
standard atmospheric pressure
standard electrode potential the potential developed by a metal or other material immersed in an electrolyte solution relative to the potential of the hydrogen electrode, which is set at zero
standard electrode potential
standard solution a solution of known concentration, expressed in terms of the amount of solute in a given amount of solvent or solution
standard solution
standard temperature and pressure for a gas, the temperature of 0ºC and the pressure 1.00 atm
standard temperature and pressure
standard time zone one of 24 regions of the Earth, measured at about 15º longitude, where the time varies by 1 h from one region to the next
standard time zone
a pattern of vibration that simulates a wave that is standing still
standing wave
staphylococcus a usually pathogenic bacterium that occurs in grapelike clusters of cocci
star a large celestial body that is composed of gas and that emits light; the sun is a typical star
start codon a specific sequence of bases in mRNA to which a molecule of tRNA binds in the first step of protein synthesis
start codon
states of matter the physical forms of matter, which are solid, liquid, gas, and plasma
states of matter
electric charge at rest; generally produced by friction or induction
static electricity
static friction the force that resists the initiation of sliding motion between two surfaces that are in contact and at rest
static friction
stationary front a front of air masses that moves either very slowly or not at all
stationary front
station model a pattern of meteorological symbols that represents the weather at a particular observing station and that is recorded on a weather map
station model
statistics the collection and classification of data that are in the form of numbers
steam fog condensation of water vapor that results when cool air moves over warm water
steam fog
steroid a type of lipid that consists of four carbon rings to which various functional groups are attached and that usually has a physiological action
steroid hormone a type of hormone that is derived from the steroid cholesterol; various steroid hormones are secreted by the adrenal cortex, testis, ovary, and placenta
steroid hormone
sticky end the single-stranded end of a DNA molecule that can form base pairs with another single-stranded end that has the complementary nucleotide sequence
sticky end
stigma the expanded apex of a pistil, supported by the style; the part of the pistil that receives the pollen
stimulant a drug that increases the activity of the body or the activity of some part of the body
stimulus anything that causes a reaction or change in an organism or any part of an organism
stock an igneous intrusion that has an area less than 100 km2
stoichiometry the proportional relationships between two or more substances during a chemical reaction
stolon in plants, a creeping stem that can develop roots and shoots at its nodes or at its tip to form new individuals; the creeping hypha of some fungi that gives rise to new individuals
stoma one of many openings in a leaf or a stem of a plant that enable gas exchange to occur (plural, stomata)
stomach the saclike, expandable digestive organ that is located between the esophagus and the small intestine and that breaks down food into a liquid by the action of muscles, enzymes, and acids
stone canal in echinoderms, a short canal that connects the madreporite to the ring canal around the mouth
stone canal
stony-iron meteorite a rare type of meteorite that contains both iron and silicate minerals
stony-iron meteorite
stony meteorite a very common kind of meteorite that is composed primarily of silicate minerals
stony meteorite
stop codon in an mRNA molecule, a sequence of three nucleotides (UUA, UAG, and UGA) that does not encode an amino acid and therefore stops protein synthesis
stop codon
storm surge a local rise in sea level near the shore that is caused by strong winds from a storm, such as those from a hurricane
storm surge
strain any change in a rock’s shape or volume caused by stress; deformation
strata layers of rock (singular, stratum)
stratification the process in which sedimentary rocks are arranged in layers
stratified drift a glacial deposit that has been sorted and layered by the action of streams or meltwater
stratified drift
stratopause a high-temperature zone that marks the upper boundary of the stratosphere
stratosphere the layer of the atmosphere that lies between the troposphere and the mesosphere and in which temperature increases as altitude increases; contains the ozone layer
stratovolcano a large volcanic cone composed of alternating layers of lava and pyroclastic material; also called composite volcano
stratus cloud a gray cloud that has a flat, uniform base and that commonly forms at very low altitudes
stratus cloud
streak the color of a mineral in powdered form
stream load the materials other than the water that are carried by a stream
stream load
stream piracy the capture of a stream in one watershed by a stream in another watershed
stream piracy
streptococcus a pathogenic bacterium that occurs in pairs or chains of cocci
stress in geology, the amount of force per unit area that acts on a rock
stress in geology
stress a physical or mental response to an unusual environmental condition
stress a physical or mental
striated musclethe type of muscle that has a striped appearance because of the arrangement of the contractile fibers in the muscle cells; skeletal muscle and cardiac muscle are the two kinds of skeletal muscle
striated muscle
strike-slip fault a fault in which the two fault blocks move past each other horizontally
strike-slip fault
strip mining the process by which rock and soil are stripped from the surface to expose the underlying material to be mined
strip mining
strobilus a conelike structure of sporangia-bearing leaves
stroke a sudden loss of consciousness or paralysis that occurs when the blood flow to the brain is interrupted
stroma in plants, the solution that surrounds the thylakoids in a chloroplast
strong electrolyte a compound that completely or largely dissociates in an aqueous solution, such as soluble mineral salts
strong electrolyte
strong force the interaction that binds nucleons together in a nucleus
structural formula a formula that indicates the location of the atoms, groups, or ions relative to one another in a molecule and that indicates the number and location of chemical bonds
structural formula
structural gene a gene that codes for a product, such as an enzyme, protein, or RNA, rather than serving as a regulator
structural gene
structural isomers two or more compounds that have the same number and kinds of atoms and the same molecular weight but that differ in the order in which the atoms are attached to one another
structural isomers
structure the arrangement of parts in an organism
style in plants, the slender, upper part of the pistil
subarctic climate the climate characterized by taiga vegetation, located at the south borders of the tundra; it is moist enough to support considerable vegetation, but the trees are low and spaced far apart
subarctic climate
subcutaneous tissue the layer of cells that lies beneath the skin
subcutaneous tissue
subduction the process by which one lithospheric plate moves beneath another as a result of tectonic forces
subduction zone the region where one lithospheric plate moves under another one into the asthenosphere
subduction zone
sublimation the process in which a solid changes directly into a gas (the term is sometimes also used for the reverse process)
sublittoral zone the benthic environment from the extreme low-water level to about 200 m deep
sublittoral zone
submarine canyon a deep valley in the continental slope or in the continental shelf
submarine canyon
submergent coastline a coast along which the land sinks or sea level rises
submergent coastline
submersible an underwater research vessel
subsidence the sinking of regions of the ground surface with little or no horizontal movement
farmers who grow food for their own use rather than for sale
subsistence farmers
subspecies a taxonomic classification below species that groups organisms that live in different geographical areas, differ morphologically from other populations of the species, but can interbreed with other populations of the species
substitution a mutation in which a nucleotide or a codon in DNA is replaced with a different nucleotide
substitution reaction a reaction in which one or more atoms replace another atom or group of atoms in a molecule
substitution reaction
substrate a part, substance, or element that lies beneath and supports another part, substance, or element; the reactant in reactions catalyzed by enzymes
subsurface mining a mining method in which ore is extracted from beneath the ground surface
subsurface mining
suburban sprawl low-density development that spreads out around cities
suburban sprawl
succession the replacement of one type of community by another at a single location over a period of time
summer solstice the first day of summer
summer solstice
summerwood a type of wood that forms late in the growing season, usually in the summer, and consists of secondary xylem whose cells have a relatively small diameter
sunspot a dark area of the photosphere of the sun that is cooler than the surrounding areas and that has a strong magnetic field
sunspot cycle a periodic variation, occurring approximately every 11 years, in the number of sunspots
sunspot cycle
superconductor a material whose resistance is zero at a certain critical temperature, which varies with each material
supercontinent cyclethe process by which supercontinents form and break apart over millions of years
supercontinent cycle
supercooled liquidfreezing point without solidifying
supercooled liquid
supercooling a condition in which a substance is cooled below its freezing point, condensation point, or sublimation point without going through a change of state
supergiant one of the largest stars known; it has a huge atmosphere and is extremely bright
superior vena cava the large vein that carries blood from the upper part of the body to the right atrium of the heart
superior vena cava
supernova a gigantic explosion in which a massive star collapses and throws its outer layers into space
superposition a principle that states that younger rocks lie above older rocks if the layers have not been disturbed
supersaturated solution a solution that holds more dissolved solute than is required to reach equilibrium at a given temperature
supersaturated solution
surf the area between the breaker zone and the shore
surface current a horizontal movement of ocean water that is caused by wind and that occurs at or near the ocean's surface
surface current
surface impoundment a natural depression or a human-made excavation that serves as a disposal facility that holds an accumulation of wastes
surface impoundment
surface mining a mining method in which soil and rocks are removed to reach underlying coal or minerals
surface mining
surface tension the force that acts on the surface of a liquid and that tends to minimize the area of the surface
surface tension
surface water all the bodies of fresh water, salt water, ice, and snow that are found above the ground
surface water
surface wave in geology, a seismic wave that travels along the surface of a medium and that has a stronger effect near the surface of the medium than it has in the interior
surface wave
survivorship the percentage of newborn individuals in a population that can be expected to survive to a given age
suspension a mixture in which particles of a material are more or less evenly dispersed throughout a liquid or gas
sustainabilitythe condition in which human needs are met in such a way that a human population can survive indefinitely
swamp a wetland ecosystem in which shrubs and trees grow
S wave a secondary wave, or shear wave; a seismic wave that causes particles of rock to move in a side-to-side direction perpendicular to the direction in which the wave is traveling; S waves are the second-fastest seismic waves and can travel only through solids
S wave
sweat gland one of the many organs in the skin that release sweat
Swell one of a group of long ocean waves that have steadily traveled a great distance from their point of generation
swim bladder in bony fishes, a gas-filled sac that is used to control buoyancy
swim bladder
swimmeret in some crustaceans, an abdominal appendage modified to allow movement, respiration, or the carrying of eggs
symbiosis a relationship in which two different organisms live in close association with each other
symmetry a body arrangement in which parts that lie on opposite sides of a central line are identical
sympathetic division the part of the autonomic nervous system that controls internal organs during conditions of high stress or increased activity
sympathetic division
synapse the junction at which the end of the axon of a neuron meets the end of a dendrite or the cell body of another neuron or meets another cell
synapsid a now extinct mammal-like reptile
synapsis the pairing of homologous chromosomes during meiosis
syncline a downward fold of stratified rocks in which the sides slope downward toward each other
synovial fluid the transparent fluid that lubricates joints
synovial fluid
synthesis reaction a reaction in which two or more substances combine to form a new compound
synthesis reaction
syphilis a sexually transmitted disease caused by the bacterium Treponema pallidum
syrinx the sound-producing organ of birds
system a set of particles or interacting components considered to be a distinct physical entity for the purpose of study
systematics the classification of living organisms in terms of their natural relationships; it includes describing, naming, and classifying the organisms
systemic circulation the movement of blood from the heart to all parts of the body and back to the heart
systemic circulation
systole the phase of the heartbeat in which the heart muscle contracts and forces blood into the aorta and pulmonary artery
systolic pressure the pressure or force that blood exerts against the arterial wall when the heart muscle contracts
systolic pressure