10Th Chem S

Front 1

a measure of the amount of dissolved salts in a given amount of liquid

Back 1

salinity

Front 2

the accumulation of salts in soil

Back 2

salinization

Front 3

the watery fluid that is secreted by the salivary glands of the mouth, that softens and moistens food, and that begins digestion

Back 3

saliva

Front 4

one of the glands that produce saliva; located under the tongue and near the lower jawbone, cheeks, lips, and palate

Back 4

salivary gland

Front 5

an ionic compound that forms when a metal atom or a positive radical replaces the hydrogen of an acid

Back 5

salt

Front 6

the movement of sand or other sediments by short jumps and bounces that is caused by wind or water

Back 6

saltation

Front 7

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

Back 7

salt marsh

Front 8

the group of individuals or events selected to represent a statistical population

Back 8

sample

Front 9

a low ridge of sand deposited along the shore of a lake or sea

Back 9

sandbar

Front 10

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

Back 10

saponification

Front 11

an organism that feeds on dead organic material

Back 11

saprophyte

Front 12

the tissue of the secondary xylem that is distributed around the outside of a tree trunk and is active in transporting sap

Back 12

sapwood

Front 13

a malignant tumor that grows in bone or muscle tissue

Back 13

sarcoma

Front 14

the basic unit of contraction in skeletal and cardiac muscle

Back 14

sarcomere

Front 15

a natural or artificial body that revolves around a planet

Back 15

satellite

Front 16

describes air that contains the maximum amount of water vapor that the air can hold at a specific temperature

Back 16

saturated air

Front 17

an organic compound formed only by carbon and hydrogen linked by single bonds

Back 17

saturated hydrocarbon

Front 18

a solution that cannot dissolve any more solute under the given conditions

Back 18

saturated solution

Front 19

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

Back 19

savanna

Front 20

a physical quantity that has magnitude but no direction

Back 20

scalar

Front 21

the relationship between the distance shown on a map and the actual distance

Back 21

scale

Front 22

bony structures that cover and protect a fish's body

Back 22

scales

Front 23

a microscope that produces an enlarged, three-dimensional image of an object by using a beam of electrons rather than light

Back 23

scanning electron microscope

Front 24

a process in which a particle (such as an electron, photon, or neutron) collides with a material and changes energy and direction

Back 24

scattering

Front 25

an animal that feeds on the bodies of dead animals

Back 25

scavenger

Front 26

a graphical representation of a circuit that uses lines to represent wires and different symbols to represent components

Back 26

schematic diagram

Front 27

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

Back 27

schistosomiasis

Front 28

the method of coelom formation in protosomes in which the embryonic mesoderm splits into two layers

Back 28

schizocoely

Front 29

the type of cell that wraps around the axons of peripheral neurons

Back 29

Schwann cell

Front 30

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

Back 30

science

Front 31

a series of steps followed to solve problems, including collecting data, formulating a hypothesis, testing the hypothesis, and stating conclusions

Back 31

scientific methods

Front 32

a method of expressing a quantity as a number multiplied by 10 to the appropriate power

Back 32

scientific notation

Front 33

an instrument that converts scintillating light into an electrical signal for detecting and measuring radiation

Back 33

scintillation counter

Front 34

a type of plant tissue composed of cells that have thickened secondary cell walls that function in plant support

Back 34

sclerenchyma

Front 35

the head of a tapeworm, which has hooks and suckers to adhere to the host tissues

Back 35

scolex

Front 36

a simple machine that consists of an inclined plane wrapped around a cylinder

Back 36

screw

Front 37

the sac that contains the testes in most male mammals

Back 37

scrotum

Front 38

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

Back 38

sea

Front 39

the process by which new oceanic lithosphere (sea floor) forms as magma rises to Earth's surface and solidifies at a mid-ocean ridge

Back 39

sea-floor spreading

Front 40

a submerged mountain on the ocean floor that is at least 1,000 m high and that has a volcanic origin

Back 40

seamount

Front 41

the oily secretion of the sebaceous glands

Back 41

sebum

Front 42

an organic compound in which two hydrogen atoms of an ammonia molecule have been replaced by either identical or different groups of atoms

Back 42

secondary amine

Front 43

plant growth that results from cell division in the cambia, or lateral meristems, and that causes the stems and roots to thicken

Back 43

secondary growth

Front 44

the response to a subsequent infection by a given pathogen or antigen

Back 44

secondary immune response

Front 45

a pollutant that forms in the atmosphere by chemical reaction with primary air pollutants, natural components in the air, or both

Back 45

secondary pollutant

Front 46

the process by which one community replaces another community that has been partially or totally destroyed

Back 46

secondary succession

Front 47

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

Back 47

second messenger

Front 48

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

Back 48

secretin

Front 49

the process by which the glands of the body release their substances; a substance produced by a gland

Back 49

secretion

Front 50

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

Back 50

sediment

Front 51

a rock that forms from compressed or cemented layers of sediment

Back 51

sedimentary rock

Front 52

a plant embryo that is enclosed in a protective coat

Back 52

seed

Front 53

the protective, outer covering of a seed

Back 53

seed coat

Front 54

a young plant grown from a seed

Back 54

seedling

Front 55

a plant that produces seeds

Back 55

seed plant

Front 56

any part of a larger structure, such as the body of an organism, that is set off by natural or arbitrary boundaries

Back 56

segment

Front 57

the division of the body of an organism into a series of similar parts

Back 57

segmentation

Front 58

an area along a fault where relatively few earthquakes have occurred recently but where strong earthquakes are known to have occurred in the past

Back 58

seismic gap

Front 59

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

Back 59

seismic gap method

Front 60

a vibration in rock that travels out from the focus of an earthquake in all directions; seismic waves can also be caused by explosions

Back 60

seismic wave

Front 61

a tracing of earthquake motion that is recorded by a seismograph

Back 61

seismogram

Front 62

an instrument that records vibrations in the ground

Back 62

seismograph

Front 63

the study of earthquakes, including their origin, propagation, energy, and prediction

Back 63

seismology

Front 64

the human practice of breeding animals or plants that have certain desired traits

Back 64

selective breeding

Front 65

a method of harvesting only middle-aged or mature trees individually or in small groups

Back 65

selective cutting

Front 66

the process by which a changing current in a circuit generates a voltage in that same circuit

Back 66

self-induction

Front 67

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

Back 67

self-pollination

Front 68

the fluid that contains sperm and various secretions produced by the male reproductive organs

Back 68

semen

Front 69

the fluid-filled canal in the inner ear that helps maintain balance and coordinate movements

Back 69

semicircular canal

Front 70

an element or compound that conducts electric current better than an insulator does but not as well as a conductor does

Back 70

semiconductor

Front 71

in each new DNA double helix, one strand is from the original molecule, and one strand is new

Back 71

semi-conservative replication

Front 72

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)

Back 72

semilunar valve

Front 73

a saclike organ of female or hermaphroditic invertebrates that stores sperm

Back 73

seminal receptacle

Front 74

one of two glandular structures in male vertebrates that hold and secrete seminal fluid

Back 74

seminal vesicle

Front 75

one of the many tubules in the testis where sperm are produced

Back 75

seminiferous tubule

Front 76

a membrane that permits the passage of only certain molecules

Back 76

semipermeable membrane

Front 77

an organ that receives stimuli and gives rise to the senses such as sight, smell, hearing, and pain

Back 77

sense organ

Front 78

a division of the peripheral nervous system that acquires information from the external and internal environments of the body

Back 78

sensory division

Front 79

a neuron that carries stimuli from a sense organ to the central nervous system

Back 79

sensory neuron

Front 80

a specialized structure that contains the ends of sensory neurons and that responds to specific types of stimuli

Back 80

sensory receptor

Front 81

in a flower, one of the outermost rings of modified leaves that protect the flower bud

Back 81

sepal

Front 82

a tank that separates solid waste from liquids and that digests organic matter in the process

Back 82

sept septum ic tank

Front 83

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

Back 83

septum

Front 84

describes two or more components of a circuit that provide a single path for current

Back 84

series

Front 85

a circuit in which the parts are joined one after another such that the current in each part is the same

Back 85

series circuit

Front 86

describes an organism that remains attached to a surface for its entire life and does not move

Back 86

sessile

Front 87

one of the external bristles or spines that project from the body of an annelid

Back 87

seta

Front 88

a facility where sewage is processed to reduce the organic and bacterial content

Back 88

sewage treatment plant

Front 89

a gamete or haploid reproductive cell that unites with another haploid reproductive cell to form a zygote

Back 89

sex cell

Front 90

one of the pair of chromosomes that determine the sex of an individual

Back 90

sex chromosome

Front 91

a hormone that is required for the sexual development and function of an organism

Back 91

sex hormone

Front 92

an autosomal trait that is influenced by the presence of male or female sex hormones

Back 92

sex-influenced trait

Front 93

the type of inheritance in which a gene is located on a sex chromosome

Back 93

sex linkage

Front 94

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

Back 94

sex-linked trait

Front 95

reproduction in which gametes from two parents unite

Back 95

sexual reproduction

Front 96

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

Back 96

sexual selection

Front 97

an area on Earth's surface where no direct seismic waves from a particular earthquake can be detected

Back 97

shadow zone

Front 98

a feature that evolved in the common ancestor of a group of related organisms

Back 98

shared derived character

Front 99

the process by which water flows over a layer of soil and removes the topsoil

Back 99

sheet erosion

Front 100

a radiation-absorbing material that is used to decrease radiation leakage from nuclear reactors

Back 100

shielding

Front 101

a large, gently sloped volcano that forms by eruptions of basaltic lava flows

Back 101

shield volcano

Front 102

the portion of a plant that grows mostly above the ground; includes the stems and leaves

Back 102

shield volcano

Front 103

the boundary between land and a body of water

Back 103

shoreline

Front 104

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

Back 104

short-day plant

Front 105

a comet whose orbital period is less than 200 years

Back 105

short-period comet

Front 106

Le Système International d’Unités, or the International System of Units, which is the measurement system that is accepted worldwide

Back 106

SI

Front 107

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

Back 107

sick-building syndrome

Front 108

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

Back 108

sieve plate

Front 109

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

Back 109

sieve tube

Front 110

one of the component cells of a sieve tube, which is found mainly in flowering plants

Back 110

sieve-tube member

Front 111

anything that serves to direct, guide, or warn

Back 111

signal

Front 112

a prescribed decimal place that determines the amount of rounding off to be done based on the precision of the measurement

Back 112

significant figure

Front 113

a mineral that contains a combination of silicon and oxygen and that may also contain one or more metals

Back 113

silicate mineral

Front 114

a type of ooze that contains silica and that is composed of the skeletal remains of organisms

Back 114

siliceous ooze

Front 115

the basic unit of the structure of silicate minerals; a silicon ion chemically bonded to and surrounded by four oxygen ions

Back 115

silicon-oxygen tetrahedron

Front 116

a sheet of hardened magma that forms between two layers of rock and that is parallel to them

Back 116

sill

Front 117

a periodic motion whose path is formed by one or more vibrations that are symmetric about an equilibrium position

Back 117

simple harmonic motion

Front 118

a leaf that has an undivided blade

Back 118

simple leaf

Front 119

one of the six basic types of machines, which are the basis for all other forms of machines

Back 119

simple leaf

Front 120

a covalent bond in which two atoms share one pair of electrons

Back 120

single bond

Front 121

a reaction in which one element or radical takes the place of another element or radical in a compound

Back 121

single-displacement reaction

Front 122

any place where a plant stores or uses organic nutrients, such as sugar or starches

Back 122

sink

Front 123

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

Back 123

sinkhole

Front 124

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)

Back 124

sinoatrial node

Front 125

in fishes, amphibians, and reptiles, a chamber that collects blood from the veins and transmits it to the right atrium

Back 125

sinus venosus

Front 126

a hollow tube of bivalves used for sucking in and expelling sea water

Back 126

siphon

Front 127

a voluntary muscle that is attached to the bones and that moves parts of the body

Back 127

skeletal muscle

Front 128

the bones, cartilage, ligaments, and tendons whose primary function is to support and protect the body and to allow the body to move

Back 128

skeletal system

Front 129

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

Back 129

skeleton

Front 130

a transparent structure that projects from the surface of a sea star and that enables respiration

Back 130

skin gill

Front 131

a type of precipitation made up of ice pellets

Back 131

sleet

Front 132

a landslide characterized by the downward movement of one or more masses of rock or debris along curved surfaces

Back 132

slump

Front 133

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

Back 133

small intestine

Front 134

the melting or fusing of ore in order to separate impurities from pure metal

Back 134

smelting

Front 135

urban air pollution composed of a mixture of smoke and fog produced from industrial pollutants and burning fuels

Back 135

smog

Front 136

the portion of the endoplasmic reticulum that lacks attached ribosomes

Back 136

smooth endoplasmic reticulum

Front 137

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

Back 137

smooth muscle

Front 138

a region that is permanently covered by snow

Back 138

snowfield

Front 139

the line above which ice and snow remain throughout the year

Back 139

snowline

Front 140

a substance that is used as a cleaner and that dissolves in water

Back 140

soap

Front 141

the interaction between animals of the same species that are not related or are only distant relatives

Back 141

social behavior

Front 142

an insect that lives in a large community, such as an ant or a bee

Back 142

social insect

Front 143

a carrier protein that uses ATP to actively transport sodium ions out of a cell and potassium ions into the cell

Back 143

sodium-potassium pump

Front 144

a muscular portion of the palate that separates the mouth cavity from the nasal cavity and the pharynx

Back 144

soft palate

Front 145

software a set of instructions or commands that tells a computer what to do; a computer program

Back 145

software

Front 146

soft water that contains a very low concentration of calcium and magnesium compounds

Back 146

soft water

Front 147

soil a loose mixture of rock fragments and organic material that can support the growth of vegetation

Back 147

soil

Front 148

soil conservation a method to maintain the fertility of the soil by protecting the soil from erosion and chemical decay

Back 148

soil conservation

Front 149

soil profile a vertical section of soil that shows the layers of horizons

Back 149

soil profile

Front 150

soil structurethe arrangement of soil particles

Back 150

soil structure

Front 151

soil texturethe soil quality that is based on the proportions of soil particles

Back 151

soil texture

Front 152

solar cell a device that when exposed to a source of light, such as the sun, converts the light into electricity

Back 152

solar cell

Front 153

solar collector a device that absorbs solar radiation and stores it as usable energy

Back 153

solar collector

Front 154

solar eclipse the passing of the moon between Earth and the sun; during a solar eclipse, the shadow of the moon falls on Earth

Back 154

solar eclipse

Front 155

solar energy the energy received by Earth from the sun in the form of radiation

Back 155

solar energy

Front 156

solar flare an explosive release of energy that comes from the sun and that is associated with magnetic disturbances on the sun's surface

Back 156

solar flare

Front 157

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

Back 157

solar nebula

Front 158

solar system the sun and all of the planets and other bodies that travel around it

Back 158

solar system

Front 159

solar tracking the movement of leaves or flowers in response to the sun's movement across the sky

Back 159

solar tracking

Front 160

solar water heating a system that uses solar energy to heat water for household use

Back 160

solar water heating

Front 161

solar wind the movement of electrically charged atomic particles, mostly helium and hydrogen, from the sun through the solar system

Back 161

solar wind

Front 162

solar year the time required for the Earth to make one revolution around the sun; approximately 365.24 days

Back 162

solar year

Front 163

solenoid a coil of wire with an electric current in it

Back 163

solenoid

Front 164

solid the state of matter in which the volume and shape of a substance are fixed

Back 164

solid

Front 165

solid waste a discarded solid material, such as garbage, refuse, or sludges

Back 165

solid waste

Front 166

solifluction the slow, downslope flow of soil saturated with water in areas surrounding glaciers at high elevations

Back 166

solifluction

Front 167

solstice the point at which the sun is as far north or as far south of the equator as possible

Back 167

solstice

Front 168

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

Back 168

solubility

Front 169

solubility equilibrium the physical state in which the opposing processes of dissolution and crystallization of a solute occur at equal rates

Back 169

solubility equilibrium

Front 170

solubility product constant the equilibrium constant for a solid that is in equilibrium with the solid's dissolved ions

Back 170

solubility product constant

Front 171

soluble capable of dissolving in a particular solvent

Back 171

soluble

Front 172

solute in a solution, the substance that dissolves in the solvent

Back 172

solute

Front 173

solution a homogeneous mixture throughout which two or more substances are uniformly dispersed

Back 173

solution

Front 174

solvated describes a solute molecule that is surrounded by solvent molecules

Back 174

solvated

Front 175

solvent in a solution, the substance in which the solute dissolves

Back 175

solvent

Front 176

somatic mutation a mutation that occurs in a body cell

Back 176

somatic mutation

Front 177

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

Back 177

somatic nervous system

Front 178

sonar sound navigation and ranging, a system that uses acoustic signals and returned echoes to determine the location of objects or to communicate

Back 178

sonar

Front 179

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

Back 179

sonic boom

Front 180

sonic boomthe process by which natural agents, such as running water, separate the particles of a sediment according to size, shape, or gravity

Back 180

sonic boom

Front 181

sorus a cluster of spores or sporangia

Back 181

sorus

Front 182

sound quality the result of the blending of several pitches through interference

Back 182

sound quality

Front 183

sound wave a longitudinal wave that is caused by vibrations and that travels through a material medium

Back 183

sound wave

Front 184

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

Back 184

source

Front 185

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

Back 185

source reduction

Front 186

space probe an uncrewed vehicle that carries scientific instruments into space to collect scientific data

Back 186

space probe

Front 187

space shuttle a reusable space vehicle that takes off like a rocket and lands like an airplane

Back 187

space shuttle

Front 188

space station a long-term orbiting platform from which other vehicles can be launched or scientific research can be carried out

Back 188

space station

Front 189

spawn to deposit eggs or sperm directly into the water; spawning is observed in certain fishes, amphibians, mollusks, and crustaceans

Back 189

spawn

Front 190

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

Back 190

specialist

Front 191

specialization the evolutionary adaptation of a cell, organ, organism, or population for a particular function or environment

Back 191

specialization

Front 192

speciation the formation of new species as a result of evolution

Back 192

speciation

Front 193

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

Back 193

speciation

Front 194

species-area effect a pattern in which the number of species in an area increases as the area increases

Back 194

species-area effect

Front 195

species diversity an index that combines the number and relative abundance of different species in a community

Back 195

species diversity

Front 196

species richness the number of different species in an area or community

Back 196

species richness

Front 197

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

Back 197

specific heat

Front 198

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

Back 198

specific humidity

Front 199

spectator ions ions that are present in a solution in which a reaction is taking place but that do not participate in the reaction

Back 199

spectator ions

Front 200

spectroscope an instrument that splits white light into a band of colors

Back 200

spectroscope

Front 201

the band of colors produced when white light passes through a prism

Back 201

spectrum

Front 202

speed the distance traveled divided by the time interval during which the motion occurred

Back 202

speed

Front 203

sperm the male gamete (sex cell)

Back 203

sperm

Front 204

spermatid an immature sperm cell that has almost completed its development

Back 204

spermatid

Front 205

spermatogenesis the process by which male gametes form

Back 205

spermatogenesis

Front 206

the part of the eukaryotic cell cycle during which replication of DNA occurs

Back 206

S phase

Front 207

spice a seasoning that is usually made from the root, stem, or seeds of certain plants

Back 207

spice

Front 208

spicule a needle of silica or calcium carbonate in the skeleton of some sponges

Back 208

spicule

Front 209

spinal cord a column of nerve tissue running from the base of the brain through the vertebral column

Back 209

spinal cord

Front 210

spinal nerve a nerve that arises from the spinal cord and extends between the vertebrae

Back 210

spinal nerve

Front 211

spinal reflex a reflex whose pathway is connected to a center in the spinal cord

Back 211

spinal reflex

Front 212

spindle a network of microtubules that forms during mitosis and moves chromatids to the poles

Back 212

spindle

Front 213

spindle fiber one of the microtubules that extend across a dividing eukaryotic cell; assists in the movement of chromosomes

Back 213

spindle fiber

Front 214

spinneret an organ that spiders and certain insect larvae use to produce silky threads for webs and cocoons

Back 214

spinneret

Front 215

spin quantum number the quantum number that describes the intrinsic angular movement of a particle

Back 215

spin quantum number

Front 216

spiracle an external opening in an insect or arthropod, used in respiration

Back 216

spiracle

Front 217

spiral cleavage the division of cells in an oblique or alternating pattern

Back 217

spiral cleavage

Front 218

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

Back 218

spiral galaxy

Front 219

a spiral-shaped bacterium

Back 219

spirillum

Front 220

a narrow point of land that extends into the water

Back 220

spit

Front 221

spleen the largest lymphatic organ in the body; serves as a blood reservoir, disintegrates old red blood cells, and produces lymphocytes and plasmids

Back 221

spleen

Front 222

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

Back 222

sponge

Front 223

spongin a fibrous protein that contains sulfur and composes the fibers of the skeleton of some sponges

Back 223

spongin

Front 224

spongy bone less-dense bone tissue that has many open spaces

Back 224

spongy bone

Front 225

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

Back 225

spongy mesophyll

Front 226

an early and now disproved theory that living organisms come to life spontaneously from nonliving material

Back 226

spontaneous generation

Front 227

sporangiophore a plant or fungal structure that bears a sporangium or spores

Back 227

sporangiophore

Front 228

sporangium a specialized sac, case, capsule, or other structure that produces spores

Back 228

sporangium

Front 229

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

Back 229

spore

Front 230

sporophyte in plants and algae that have alternation of generations, the diploid individual or generation that produces haploid spores

Back 230

sporophyte

Front 231

a sporozoan that has been released from the oocyst and is ready to penetrate a new host cell

Back 231

sporozoite

Front 232

spring a flow of water above ground level that occurs where the water table intersects the ground surface

Back 232

spring

Front 233

spring constant an expression of the ratio of force to displacement for a spring or other elastic material

Back 233

spring constant

Front 234

spring tide a tide of increased range that occurs two times a month, at the new and full moons

Back 234

spring tide

Front 235

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

Back 235

springwood

Front 236

squall line a narrow band of heavy thunderstorms

Back 236

squall line

Front 237

stabilizing selection a type of natural selection in which the average form of a trait is favored and becomes more common

Back 237

stabilizing selection

Front 238

stalactite a cone-shaped calcite deposit suspended from the ceiling of a cave

Back 238

stalactite

Front 239

stalagmite an upward-pointing, cone-shaped calcite deposit built up from the floor of a cave

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stalagmite

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stamen the male reproductive structure of a flower that produces pollen and consists of an anther at the tip of a filament

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stamen

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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

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standard atmospheric pressure

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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

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standard electrode potential

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standard solution a solution of known concentration, expressed in terms of the amount of solute in a given amount of solvent or solution

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standard solution

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standard temperature and pressure for a gas, the temperature of 0ºC and the pressure 1.00 atm

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standard temperature and pressure

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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

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standard time zone

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a pattern of vibration that simulates a wave that is standing still

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standing wave

Front 247

staphylococcus a usually pathogenic bacterium that occurs in grapelike clusters of cocci

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staphylococcus

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star a large celestial body that is composed of gas and that emits light; the sun is a typical star

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star

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start codon a specific sequence of bases in mRNA to which a molecule of tRNA binds in the first step of protein synthesis

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start codon

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states of matter the physical forms of matter, which are solid, liquid, gas, and plasma

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states of matter

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electric charge at rest; generally produced by friction or induction

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static electricity

Front 252

static friction the force that resists the initiation of sliding motion between two surfaces that are in contact and at rest

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static friction

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stationary front a front of air masses that moves either very slowly or not at all

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stationary front

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station model a pattern of meteorological symbols that represents the weather at a particular observing station and that is recorded on a weather map

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station model

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statistics the collection and classification of data that are in the form of numbers

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statistics

Front 256

steam fog condensation of water vapor that results when cool air moves over warm water

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steam fog

Front 257

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

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steroid

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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

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steroid hormone

Front 259

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

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sticky end

Front 260

stigma the expanded apex of a pistil, supported by the style; the part of the pistil that receives the pollen

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stigma

Front 261

stimulant a drug that increases the activity of the body or the activity of some part of the body

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stimulant

Front 262

stimulus anything that causes a reaction or change in an organism or any part of an organism

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stimulus

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stock an igneous intrusion that has an area less than 100 km2

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stock

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stoichiometry the proportional relationships between two or more substances during a chemical reaction

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stoichiometry

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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

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stolon

Front 266

stoma one of many openings in a leaf or a stem of a plant that enable gas exchange to occur (plural, stomata)

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stoma

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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

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stomach

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stone canal in echinoderms, a short canal that connects the madreporite to the ring canal around the mouth

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stone canal

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stony-iron meteorite a rare type of meteorite that contains both iron and silicate minerals

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stony-iron meteorite

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stony meteorite a very common kind of meteorite that is composed primarily of silicate minerals

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stony meteorite

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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

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stop codon

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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

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storm surge

Front 273

strain any change in a rock’s shape or volume caused by stress; deformation

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strain

Front 274

strata layers of rock (singular, stratum)

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strata

Front 275

stratification the process in which sedimentary rocks are arranged in layers

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stratification

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stratified drift a glacial deposit that has been sorted and layered by the action of streams or meltwater

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stratified drift

Front 277

stratopause a high-temperature zone that marks the upper boundary of the stratosphere

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stratopause

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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

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stratosphere

Front 279

stratovolcano a large volcanic cone composed of alternating layers of lava and pyroclastic material; also called composite volcano

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stratovolcano

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stratus cloud a gray cloud that has a flat, uniform base and that commonly forms at very low altitudes

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stratus cloud

Front 281

streak the color of a mineral in powdered form

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streak

Front 282

stream load the materials other than the water that are carried by a stream

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stream load

Front 283

stream piracy the capture of a stream in one watershed by a stream in another watershed

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stream piracy

Front 284

streptococcus a pathogenic bacterium that occurs in pairs or chains of cocci

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streptococcus

Front 285

stress in geology, the amount of force per unit area that acts on a rock

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stress in geology

Front 286

stress a physical or mental response to an unusual environmental condition

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stress a physical or mental

Front 287

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

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striated muscle

Front 288

strike-slip fault a fault in which the two fault blocks move past each other horizontally

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strike-slip fault

Front 289

strip mining the process by which rock and soil are stripped from the surface to expose the underlying material to be mined

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strip mining

Front 290

strobilus a conelike structure of sporangia-bearing leaves

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strobilus

Front 291

stroke a sudden loss of consciousness or paralysis that occurs when the blood flow to the brain is interrupted

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stroke

Front 292

stroma in plants, the solution that surrounds the thylakoids in a chloroplast

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stroma

Front 293

strong electrolyte a compound that completely or largely dissociates in an aqueous solution, such as soluble mineral salts

Back 293

strong electrolyte

Front 294

strong force the interaction that binds nucleons together in a nucleus

Front 295

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

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structural formula

Front 296

structural gene a gene that codes for a product, such as an enzyme, protein, or RNA, rather than serving as a regulator

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structural gene

Front 297

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

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structural isomers

Front 298

structure the arrangement of parts in an organism

Back 298

structure

Front 299

style in plants, the slender, upper part of the pistil

Back 299

style

Front 300

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

Back 300

subarctic climate

Front 301

subcutaneous tissue the layer of cells that lies beneath the skin

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subcutaneous tissue

Front 302

subduction the process by which one lithospheric plate moves beneath another as a result of tectonic forces

Back 302

subduction

Front 303

subduction zone the region where one lithospheric plate moves under another one into the asthenosphere

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subduction zone

Front 304

sublimation the process in which a solid changes directly into a gas (the term is sometimes also used for the reverse process)

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sublimation

Front 305

sublittoral zone the benthic environment from the extreme low-water level to about 200 m deep

Back 305

sublittoral zone

Front 306

submarine canyon a deep valley in the continental slope or in the continental shelf

Back 306

submarine canyon

Front 307

submergent coastline a coast along which the land sinks or sea level rises

Back 307

submergent coastline

Front 308

submersible an underwater research vessel

Back 308

submersible

Front 309

subsidence the sinking of regions of the ground surface with little or no horizontal movement

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subsidence

Front 310

farmers who grow food for their own use rather than for sale

Back 310

subsistence farmers

Front 311

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

Back 311

subspecies

Front 312

substitution a mutation in which a nucleotide or a codon in DNA is replaced with a different nucleotide

Back 312

substitution

Front 313

substitution reaction a reaction in which one or more atoms replace another atom or group of atoms in a molecule

Back 313

substitution reaction

Front 314

substrate a part, substance, or element that lies beneath and supports another part, substance, or element; the reactant in reactions catalyzed by enzymes

Back 314

substrate

Front 315

subsurface mining a mining method in which ore is extracted from beneath the ground surface

Back 315

subsurface mining

Front 316

suburban sprawl low-density development that spreads out around cities

Back 316

suburban sprawl

Front 317

succession the replacement of one type of community by another at a single location over a period of time

Back 317

succession

Front 318

summer solstice the first day of summer

Back 318

summer solstice

Front 319

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

Back 319

summerwood

Front 320

sunspot a dark area of the photosphere of the sun that is cooler than the surrounding areas and that has a strong magnetic field

Back 320

sunspot

Front 321

sunspot cycle a periodic variation, occurring approximately every 11 years, in the number of sunspots

Back 321

sunspot cycle

Front 322

superconductor a material whose resistance is zero at a certain critical temperature, which varies with each material

Back 322

superconductor

Front 323

supercontinent cyclethe process by which supercontinents form and break apart over millions of years

Back 323

supercontinent cycle

Front 324

supercooled liquidfreezing point without solidifying

Back 324

supercooled liquid

Front 325

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

Back 325

supercooling

Front 326

supergiant one of the largest stars known; it has a huge atmosphere and is extremely bright

Back 326

supergiant

Front 327

superior vena cava the large vein that carries blood from the upper part of the body to the right atrium of the heart

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superior vena cava

Front 328

supernova a gigantic explosion in which a massive star collapses and throws its outer layers into space

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supernova

Front 329

superposition a principle that states that younger rocks lie above older rocks if the layers have not been disturbed

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superposition

Front 330

supersaturated solution a solution that holds more dissolved solute than is required to reach equilibrium at a given temperature

Back 330

supersaturated solution

Front 331

surf the area between the breaker zone and the shore

Back 331

surf

Front 332

surface current a horizontal movement of ocean water that is caused by wind and that occurs at or near the ocean's surface

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surface current

Front 333

surface impoundment a natural depression or a human-made excavation that serves as a disposal facility that holds an accumulation of wastes

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surface impoundment

Front 334

surface mining a mining method in which soil and rocks are removed to reach underlying coal or minerals

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surface mining

Front 335

surface tension the force that acts on the surface of a liquid and that tends to minimize the area of the surface

Back 335

surface tension

Front 336

surface water all the bodies of fresh water, salt water, ice, and snow that are found above the ground

Back 336

surface water

Front 337

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

Back 337

surface wave

Front 338

survivorship the percentage of newborn individuals in a population that can be expected to survive to a given age

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survivorship

Front 339

suspension a mixture in which particles of a material are more or less evenly dispersed throughout a liquid or gas

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suspension

Front 340

sustainabilitythe condition in which human needs are met in such a way that a human population can survive indefinitely

Back 340

sustainability

Front 341

swamp a wetland ecosystem in which shrubs and trees grow

Back 341

swamp

Front 342

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

Back 342

S wave

Front 343

sweat gland one of the many organs in the skin that release sweat

Front 344

Swell one of a group of long ocean waves that have steadily traveled a great distance from their point of generation

Back 344

swell

Front 345

swim bladder in bony fishes, a gas-filled sac that is used to control buoyancy

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swim bladder

Front 346

swimmeret in some crustaceans, an abdominal appendage modified to allow movement, respiration, or the carrying of eggs

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swimmeret

Front 347

symbiosis a relationship in which two different organisms live in close association with each other

Back 347

symbiosis

Front 348

symmetry a body arrangement in which parts that lie on opposite sides of a central line are identical

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symmetry

Front 349

sympathetic division the part of the autonomic nervous system that controls internal organs during conditions of high stress or increased activity

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sympathetic division

Front 350

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

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synapse

Front 351

synapsid a now extinct mammal-like reptile

Back 351

synapsid

Front 352

synapsis the pairing of homologous chromosomes during meiosis

Back 352

synapsis

Front 353

syncline a downward fold of stratified rocks in which the sides slope downward toward each other

Back 353

syncline

Front 354

synovial fluid the transparent fluid that lubricates joints

Back 354

synovial fluid

Front 355

synthesis reaction a reaction in which two or more substances combine to form a new compound

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synthesis reaction

Front 356

syphilis a sexually transmitted disease caused by the bacterium Treponema pallidum

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syphilis

Front 357

syrinx the sound-producing organ of birds

Back 357

syrinx

Front 358

system a set of particles or interacting components considered to be a distinct physical entity for the purpose of study

Back 358

system

Front 359

systematics the classification of living organisms in terms of their natural relationships; it includes describing, naming, and classifying the organisms

Back 359

systematics

Front 360

systemic circulation the movement of blood from the heart to all parts of the body and back to the heart

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systemic circulation

Front 361

systole the phase of the heartbeat in which the heart muscle contracts and forces blood into the aorta and pulmonary artery

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systole

Front 362

systolic pressure the pressure or force that blood exerts against the arterial wall when the heart muscle contracts

Back 362

systolic pressure