A glossary of all key terms from the complete
McDougal Littell Science program
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McDougal Littell
McDougal Littell Science
Multi-Language
Glossary
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ENGLISH GLOSSARY
A
abiotic factor A nonliving physical or chemical part
of an ecosystem.
abrasion The process of wearing something down
by friction.
absolute age The actual age in years of an event
or object.
absorption The disappearance of a wave into
a medium. When a wave is absorbed, the energy
transferred by the wave is converted into another
form of energy, usually thermal energy.
acceleration The rate at which velocity changes
over time.
acid A substance that can donate a proton to another
substance and has a pH below 7.
acid rain Rain that has become more acidic than
normal due to pollution.
active transport The process of using energy to
move materials through a membrane.
acoustics The scientific study of sound; the behavior
of sound waves inside a space.
adaptation A characteristic, a behavior, or any
inherited trait that makes a species able to survive and
reproduce in a particular environment.
addiction A physical or psychological need for a
habit-forming substance, such as alcohol or drugs.
adolescence The stage of life from the time a human
body begins to mature sexually to adulthood.
adulthood The stage of life that begins once a human
body completes its growth and reaches sexual maturity.
aftershock A smaller earthquake that follows a more
powerful earthquake in the same area.
air mass A large volume of air that has nearly the
same temperature and humidity at different locations at
the same altitude.
air pollution Harmful materials added to the air that
can cause damage to living things and the environment.
air pressure The force of air molecules pushing on
an area.
air resistance The fluid friction due to air.
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MCDOUGAL LITTELL SCIENCE
algae Protists that live mostly in water and use sunlight
as a source of energy. Algae is a plural word; the
singular is alga.
allele An alternate form of a gene for a specific trait or
gene product.
alloy A solid mixture composed of a metal and one or
more other substances.
alluvial fan A fan-shaped deposit of sediment at the
base of a slope, formed as water flows down the slope
and spreads at the bottom.
alternating current AC Electric current that
reverses direction at regular intervals.
altitude The distance above sea level.
ampere amp The unit of measurement of electric
current, which is equal to one coulomb per second. The
number of amps flowing through a circuit equals the
circuit’s amperage.
amphibian A cold-blooded vertebrate animal that
lives in water and breathes with gills when it is young; as
an adult, it moves onto land and breathes air with lungs.
amplification The strengthening of an electrical
signal, often used to increase the intensity of a sound
wave.
amplitude The maximum distance that a disturbance
causes a medium to move from its rest position; the
distance between a crest or trough of a wave and line
through the center of a wave.
analog Represented by a continuous but varying
quantity, such as a wave. In electronics, analog
information is represented by a continuous but varying
electrical signal.
ancestor A distant or early form of an organism from
which later forms descend.
angiosperm A plant that has flowers and produces
seeds enclosed in fruit.
Animalia Part of a classification system that divides
all living things into six kingdoms. Kingdom Animalia
includes multicellular organisms, from humans and lions
to insects and microbes, that rely on food for energy.
antibiotic A medicine that can block the growth and
reproduction of bacteria.
antibody A protein produced by some white blood
cells to attack specific foreign materials.
Copyright © by McDougal Littell, a division of Houghton Mifflin Company
ENGLISH
The glossary is an alphabetical listing of the key terms from the complete
McDougal Littell Science program, along with their meanings. The definitions
listed in the glossary are the ones that apply to the way the words are used in
this program.
Copyright © by McDougal Littell, a division of Houghton Mifflin Company
B
bacteria A large group of one-celled organisms that
sometimes cause disease. Bacteria is a plural word; the
singular is bacterium.
Bacteria Part of a classification system that divides
all living things into six kingdoms. Kingdom Bacteria
includes microscopic single-celled organisms found in
many environments. Bacteria can be associated with
disease in other organisms.
barometer An instrument that measures air pressure
in the atmosphere.
barrier island A long, narrow island that develops
parallel to a coast as a sandbar builds up above the
water’s surface.
base A substance that can accept a proton from another
substance and has a pH above 7.
behavior An organism’s action in response to a
stimulus.
Bernoulli’s principle A statement that describes
the effects of movement on fluid pressure. According to
this principle, an increase in the speed of the motion of a
fluid decreases the pressure within the fluid.
big bang The moment in time when the universe
started to expand out of an extremely hot, dense state,
according to scientific theory.
binary code A coding system in which information is
represented by two figures, such as 1 and 0.
binary fission A form of asexual reproduction by
which some single-celled organisms reproduce. The
genetic material is copied, and one cell divides into two
independent cells that are each a copy of the original
cell. Prokaryotes such as bacteria reproduce by binary
fission.
binomial nomenclature The two-part naming
system used to identify species. The first part of the name
is the genus, and the second part of the name is the species.
biodiversity The number and variety of living things
found on Earth or within an ecosystem.
biology The scientific study of life and all living
things; ecology, zoology, and botany are examples of
biological sciences.
bioluminescence The production of light by living
organisms.
biomass Organic matter that contains stored energy
from sunlight and that can be burned as fuel.
biome A region of Earth that has a particular climate
and certain types of plants. Examples are tundra, taiga,
desert, grassland, temperate and tropical forests.
biosphere All living organisms on Earth in the air, on
the land, and in the waters; one of the four parts of the
Earth system.
MULTI-LANGUAGE GLOSSARY
ENGLISH
antigen A marker that a pathogen carries and that
stimulates the production of antibodies.
appendicular skeleton The bones of the skeleton
that function to allow movement, such as arm and
leg bones.
aquaculture The science and business of raising and
harvesting fish in a controlled situation.
aquifer An underground layer of permeable rock that
contains water.
Archaea Part of a classification system that divides
all living things into six kingdoms. Kingdom Archaea
includes microscopic single-celled organisms with a
distinctive cell structure that allows them to live in
extreme environments.
artery A blood vessel with strong walls that carries
blood away from the heart.
artesian well A well in which pressurized water
flows upward to the surface.
arthropod An invertebrate animal with an
exoskeleton, a segmented body, and jointed legs.
asexual reproduction The process by which a
single organism produces offspring that have the same
genetic material.
asteroid A small, solid, rocky body that orbits the
Sun. Most asteroids orbit in a region between Mars and
Jupiter called the asteroid belt.
asthenosphere The layer in Earth’s upper mantle
and directly under the lithosphere in which rock is soft
and weak because it is close to melting.
astronomical unit AU Earth’s average distance
from the Sun, which is approximately 150 million
kilometers (93 million mi).
atmosphere The outer layer of gases of a large body
in space, such as a planet or star; the mixture of gases
that surrounds the solid Earth; one of the four parts of
the Earth system.
atom The smallest particle of an element that has the
chemical properties of that element.
atomic mass The average mass of the atoms of
an element.
atomic mass number The total number of protons
and neutrons in an atom’s nucleus.
atomic number The number of protons in the
nucleus of an atom.
autotroph An organism that captures energy from
sunlight and uses it to produce energy-rich carbon
compounds, usually through the process of
photosynthesis.
axial skeleton The central part of the skeleton, which
includes the cranium, the spinal column, and the ribs.
axis of rotation An imaginary line about which a
turning body such as Earth rotates.
3
C
calorie The amount of energy needed to increase the
temperature of one gram of water by one degree Celsius.
capillary A narrow blood vessel that connects arteries
with veins.
carbohydrate A type of carbon-based molecule in
living things. Carbohydrates include sugars and starches
used for energy or as structural materials. Carbohydrate
molecules contain carbon, hydrogen, and oxygen atoms.
carbon cycle The continuous movement of carbon
through Earth, its atmosphere, and the living things on
Earth.
cardiac muscle The muscle that makes up the heart.
carrying capacity The maximum size that a
population can reach in an ecosystem.
catalyst A substance that increases the rate of a
chemical reaction but is not consumed in the reaction.
cell The smallest unit that is able to perform the basic
functions of life.
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MCDOUGAL LITTELL SCIENCE
cell cycle The normal sequence of growth,
maintenance, and division in a cell.
cell membrane The outer boundary of the
cytoplasm, a layer that controls what enters or leaves the
cell; a protective covering enclosing an entire cell.
cellular respiration A process in which cells use
oxygen to release energy stored in sugars.
cell wall A protective outer covering that lies just
outside the cell membrane of plant cells.
central nervous system The brain and spinal
cord. The central nervous system communicates with the
rest of the nervous system through electrical signals sent
to and from neurons.
centripetal force Any force that keeps an object
moving in a circle.
chemical change A change of one substance into
another substance.
chemical energy Energy that is stored in the
chemical composition of matter. The amount of
chemical energy in a substance depends on the types and
arrangement of its atoms. When wood or gasoline burns,
chemical energy produces heat. The energy used by the
cells in your body comes from chemical energy in the
foods you eat.
chemical formula An expression that shows the
number and type of atoms joined in a compound.
chemical property A characteristic of a substance
that describes how it can form a new substance.
chemical reaction The process by which chemical
changes occur. In a chemical reaction, atoms are
rearranged, and chemical bonds are broken and formed.
chemical weathering The breakdown or
decomposition of rock that takes place when minerals
change through chemical processes.
childhood The stage of life after infancy and before
the beginning of sexual maturity.
chlorophyll A light-absorbing chemical, a pigment,
that traps the energy in sunlight and converts it to
chemical energy. Found in chloroplasts of plant cells
and the cells of other photosynthetic organisms.
chloroplast An organelle in a plant cell that contains
chlorophyll, a chemical that uses the energy from
sunlight to make sugar.
chromosome A structure formed when the DNA in
the nucleus of a eukaryotic cell condenses before the cell
divides.
circuit A closed path through which charge can flow.
circulatory system The group of organs,
consisting of the heart and blood vessels, that circulates
blood through the body.
classification The systematic grouping of different
types of organisms by their shared characteristics.
Copyright © by McDougal Littell, a division of Houghton Mifflin Company
ENGLISH
biotic factor A living thing in an ecosystem.
black hole The final stage of an extremely massive
star, which is invisible because its gravity prevents any
form of radiation from escaping.
blizzard A blinding snowstorm with winds of at
least 56 kilometers per hour (35 mi/h), usually with
temperatures below –7°C (20°F).
blood A fluid in the body that delivers oxygen and
other materials to cells and removes carbon dioxide and
other wastes.
blubber A layer of fat in some sea mammals that lies
beneath the skin. It insulates the animal from cold and
stores reserve energy.
boiling A process by which a substance changes from
its liquid state to its gas state. The liquid is heated to a
specific temperature at which bubbles of vapor form
within the liquid.
boiling point The temperature at which a substance
changes from its liquid state to its gas state through
boiling.
bond energy The amount of energy in a chemical
bond between atoms.
budding A process of asexual reproduction in which
an organism develops as an outgrowth of the parent.
Each bud can grow into a new organism, breaking free
and becoming separate and independent.
buoyant force The upward force on objects in a
fluid; often called buoyancy.
by-catch The portion of animals that are caught in a
net and then thrown away as unwanted.
Copyright © by McDougal Littell, a division of Houghton Mifflin Company
conductor 1. A material that transfers energy easily.
2. A material that transfers electric charge easily.
coniferous A term used to describe cone-bearing
trees and shrubs that usually keep their leaves or needles
during all the seasons of the year; examples are pine, fir,
and spruce trees.
conservation The process of saving or protecting a
natural resource.
constellation A group of stars that form a pattern in
the sky.
consumer A living thing that gets its energy by eating
other living things in a food chain; consumers are also
called heterotrophs.
continental climate A climate that occurs in
the interior of a continent, with large temperature
differences between seasons.
continental-continental collision A boundary
along which two plates carrying continental crust
push together.
continental drift The hypothesis that Earth’s
continents move on Earth’s surface.
continental shelf The flat or gently sloping land
that lies submerged around the edges of a continent and
that extends from the shoreline out to the continental
slope.
contour interval On a topographic map, the
difference in elevation from one contour line to the next.
contour line A line on a topographic map that joins
points of equal elevation.
convection A process by which energy is transferred
in gases and liquids, occurring when a warmer, less
dense area of gas or liquid is pushed up by a cooler,
more dense area of the gas or liquid.
convection current A circulation pattern in which
material is heated and rises in one area, then cools and
sinks in another area, flowing in a continuous loop.
convergent boundary A boundary along which
two tectonic plates push together, characterized either by
subduction or a continental collision.
convex Curved outward, like the underside of a spoon.
cooperation A term used to describe an interaction
between two or more living things in which they are said
to work together.
coral reef A built-up limestone deposit formed by
small ant-sized organisms called corals.
Coriolis effect The influence of Earth’s rotation on
objects that move over Earth.
cornea A transparent membrane that covers the eye.
corona The outer layer of the Sun’s atmosphere.
covalent bond A pair of electrons shared by
two atoms.
MULTI-LANGUAGE GLOSSARY
ENGLISH
cleavage The property of a mineral that describes its
tendency to break along flat surfaces.
climate The characteristic weather conditions in an
area over a long period of time.
climate zone One of the major divisions in a system
for classifying the climates of different regions based on
characteristics they have in common.
cloning The process of using DNA technology to
produce an offspring that is genetically identical to its
one parent.
cnidarian An invertebrate animal such as a jellyfish
that has a body with radial symmetry, tentacles with
stinging cells, and a central internal cavity.
coefficient The number before a chemical formula
that indicates how many molecules are involved in a
chemical reaction.
collision A situation in which two objects in close
contact exchange energy and momentum.
comet A body that produces a coma of gas and dust;
a small, icy body that orbits the Sun.
commensalism An interaction between two species
in which one species benefits without harming the other;
a type of symbiosis.
community All the populations that live and interact
with each other in a particular place. The community
can live in a place as small as a pond or a park, or it can
live in a place as large as a rain forest or the ocean.
compact bone The tough, hard outer layer of
a bone.
competition The struggle between two or more
living things that depend on the same limited resource.
competitor A species characterized by a relatively
longer life span, with relatively few offspring, when
compared with an opportunist species.
compound A substance made up of two or more
different types of atoms bonded together.
compound machine A machine that is made up of
two or more simple machines.
computer An electronic device that processes digital
information.
concave Curved inward toward the center, like the
inside of a spoon.
concentration The amount of a substance (the
solute) that is contained in another substance (the
solvent) at a given temperature. An example is sugar
dissolved in water—often expressed as parts per million
or parts per billion.
condensation The process by which a gas changes
into a liquid.
conduction The process by which energy is
transferred from a warmer object to a cooler object
by means of physical contact.
5
cytoplasm A thick, gelatin-like material contained
within the cell membrane. Most of the work of the cell is
carried out in the cytoplasm.
D
dam A structure that holds back and controls the flow
of water in a river or other body of water.
data Information gathered by observation or
experimentation that can be used in calculating or
reasoning. Data is a plural word; the singular is datum.
decibel dB The unit used to measure the intensity of a
sound wave.
deciduous A term used to describe trees and shrubs
that drop their leaves when winter comes; examples are
maple, oak, and birch trees.
decomposer An organism that feeds on and breaks
down dead plant or animal matter.
degree Evenly divided units of a temperature scale.
delta An area of land at the end, or mouth, of a river
that is formed by the buildup of sediment.
density A property of matter representing the mass
per unit volume.
deposition The process in which transported
sediment is laid down.
dermis The inner layer of the skin.
desalination The process of removing salt from
ocean water. Desalination is used to obtain fresh water.
desertification The expansion of desert conditions
in areas where the natural plant cover has been destroyed.
dew point The temperature at which air with a given
amount of water vapor will reach saturation.
dichotomous key A series of questions, each with
only two answers, that can be used to help identify an
organism’s genus and species.
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MCDOUGAL LITTELL SCIENCE
diffraction The spreading out of waves as they pass
through an opening or around the edges of an obstacle.
diffuse reflection The reflection of parallel light
rays in many different directions.
diffusion The tendency of a substance to move from
an area of higher concentration to an area of lower
concentration.
digestion The process of breaking down food into
usable materials.
digestive system The structures in the body that
work together to transform the energy and materials in
food into forms the body can use.
digital Represented by numbers. In electronics, digital
information is represented by the numbers 1 and 0,
signaled by a circuit that is either on or off.
dilute adj. Having a low concentration of solute.
v. To add solvent in order to decrease the concentration
of a solution.
direct current DC Electric current that flows in one
direction only.
divergent boundary A boundary along which two
tectonic plates move apart, characterized by either a
mid-ocean ridge or a continental rift valley.
diversity A term used to describe the quality of
having many differences; biodiversity describes the great
variety and many differences found among living things.
divide A continuous high line of land—or ridge—from
which water drains to one side or the other.
DNA The genetic material found in all living cells that
contains the information needed for an organism to grow,
maintain itself, and reproduce (Deoxyribonucleic acid).
domain One of three divisions in a classification
system based on different types of cells. The six
kingdoms of living things are grouped into three
domains: Archaea, Bacteria, and Eukarya.
dominant A term that describes the allele that
determines the phenotype of an individual organism
when two different copies are present in the genotype.
Doppler effect A change in the observed frequency
of a wave, occurring when the source of the wave or the
observer is moving. Changes in the frequency of light
are often measured by observing changes in wavelength,
whereas changes in the frequency of sound are often
detected as changes in pitch.
downwelling The movement of water from the
surface to greater depths.
drainage basin An area of land in which water
drains into a stream system. The borders of a drainage
basin are called divides.
drought A long period of abnormally low amounts
of rainfall.
dune A mound of sand built up by wind.
Copyright © by McDougal Littell, a division of Houghton Mifflin Company
ENGLISH
crest The highest point, or peak, of a wave.
crust A thin outer layer of rock above a planet’s
mantle, including all dry land and ocean basins. Earth’s
continental crust is 40 kilometers thick on average and
oceanic crust is 7 kilometers thick on average.
crystal A solid substance in which the atoms are
arranged in an orderly, repeating, three-dimensional
pattern.
cycle n. A series of events or actions that repeat
themselves regularly; a physical and/or chemical
process in which one material continually changes
locations and/or forms. Examples include the
water cycle, the carbon cycle, and the rock cycle.
v. To move through a repeating series of events or actions.
cytokinesis The division of a parent cell’s cytoplasm
following mitosis.
Copyright © by McDougal Littell, a division of Houghton Mifflin Company
earthquake A shaking of the ground caused by the
sudden movement of large blocks of rocks along a fault.
echinoderm An invertebrate sea animal with a spiny
skeleton, a water vascular system, and tube feet.
echolocation The sending out of high-pitched sound
waves and the interpretation of the returning echoes.
eclipse An event during which one object in space
casts a shadow onto another. On Earth, a lunar eclipse
occurs when the Moon moves through Earth’s shadow,
and a solar eclipse occurs when the Moon’s shadow
crosses Earth.
ecology The scientific study of how living things
interact with each other and their environment.
ecosystem All the living and nonliving things that
interact in a particular environment. An ecosystem can
be as small as a meadow or a swamp, or as large as a
forest or a desert.
ectotherm An animal whose body temperature
changes with environmental conditions.
efficiency The percentage of the input work done on
a machine that the machine can return in output work.
A machine’s output work divided by its input work and
multiplied by 100.
egg A female reproductive cell (gamete) that forms in
the reproductive organs of a female and has just a single
copy of the genetic material of the parent.
electric cell A device that produces electric current
using the chemical or physical properties of different
materials. A battery consists of two or more cells linked
together.
electric charge A property that allows one object
to exert a force on another object without touching it.
Electric charge can be positive or negative: positive
charge is a property of the proton, while negative charge
is a property of the electron.
electric current A continuous flow of electric
charge, which is measured in amperes.
electric field An area surrounding a charged object,
within which the object can exert a force on another
object without touching it.
electric potential The amount of potential energy
per unit charge that a static charge or electric current
has. Electric potential is measured in volts and is often
called voltage.
electric power The rate at which electrical energy
is generated from, or converted into, another source of
energy, such as kinetic energy.
electromagnet A magnet that consists of a piece of
iron or steel inside a coil of current-carrying wire.
electromagnetic radiation Energy that travels
across distances as certain types of waves. Types of
electromagnetic radiation are radio waves, microwaves,
infrared radiation, visible light, ultraviolet radiation,
x-rays, and gamma rays.
electromagnetic spectrum The range of all
electromagnetic frequencies, including the following
types (from lowest to highest frequency): radio waves,
microwaves, infrared light, visible light, ultraviolet light,
x-rays, and gamma rays.
electromagnetic wave A type of wave, such as a
light wave or radio wave, that does not require a medium
to travel; a disturbance that transfers energy through
a field.
electromagnetism Magnetism that results from the
flow of electric charge.
ENGLISH
E
electron A negatively charged particle located outside
an atom’s nucleus. An electron is about 2000 times
smaller than either a proton or neutron.
electronic adj. Operating by means of an
electrical signal. An electronic device is a device
that uses electric current to represent coded information.
n. An electronic device or system, such as a computer,
calculator, CD player, or game system.
element A substance that cannot be broken down into
a simpler substance by ordinary chemical changes. An
element consists of atoms of only one type.
elevation A measure of how high something is above
a reference point, such as sea level.
ellipse An oval or flattened circle.
El Niño A disturbance of wind patterns and ocean
currents in the Pacific Ocean that causes temporary
climate changes in many parts of the world.
embryo A multicellular organism, plant or animal, in
its earliest stages of development.
emigration In population studies, the movement of
individuals out of an ecosystem.
endocrine system A group of organs called glands
and the hormones they produce that help regulate
conditions inside the body.
endoskeleton An internal support system; such a
skeleton made of bone tissue is a distinguishing
characteristic of vertebrate animals.
endotherm An animal that maintains a constant
body temperature.
endothermic reaction A chemical reaction that
absorbs energy.
energy The ability to do work or to cause a change. For
example, the energy of a moving bowling ball knocks
over pins; energy from food allows animals to move and
to grow; and energy from the Sun heats Earth’s surface
and atmosphere, which causes air to move.
MULTI-LANGUAGE GLOSSARY
7
8
MCDOUGAL LITTELL SCIENCE
F
false-color image A computer image in which the
colors are not what the human eye would see. A falsecolor image can assign different colors to different types
of radiation coming from an object to highlight its
features.
fault A fracture in Earth’s lithosphere along which
blocks of rock move past each other.
fault-block mountain A mountain that forms as
blocks of rock move up or down along normal faults in
areas where the lithosphere is being pulled apart.
fermentation A chemical process by which cells
release energy from sugar when no oxygen is present.
fertilization Part of the process of sexual
reproduction in which a male reproductive cell and a
female reproductive cell combine to make a new cell
that can develop into a new organism.
fiber optics Technology based on the use of laser
light to send signals through transparent wires called
optical fibers. This technology is often used in
communications.
field An area around an object where the object can
apply a force—such as gravitational force, magnetic
force, or electrical force—on another object without
touching it.
floodplain A flat area of land on either side of a
stream that becomes flooded when a river overflows its
banks.
flower The reproductive structure of an angiosperm,
containing male and female parts.
fluid A substance that can flow easily, such as a gas
or a liquid.
fluorescence A phenomenon in which a material
absorbs electromagnetic radiation of one wavelength
and gives off electromagnetic radiation of a different
wavelength.
focal length The distance from the center of a
convex lens to its focal point.
focal point The point at which parallel light rays
reflected from a concave mirror come together; the point
at which parallel light rays refracted by a convex lens
come together.
focus In an earthquake, the point underground where
the rocks first begin to move.
folded mountain A mountain that forms as
continental crust is compressed and rocks bend into
large folds.
foliation The arrangement of minerals within rocks
into flat or wavy parallel bands; a characteristic of most
metamorphic rocks.
Copyright © by McDougal Littell, a division of Houghton Mifflin Company
ENGLISH
energy efficiency A measurement of usable energy
after an energy conversion.
energy pyramid A model used to show the amount
of energy available to living things in an ecosystem.
environment Everything that surrounds a living
thing. An environment is made up of both living and
nonliving factors.
enzyme A type of protein that is a catalyst for
chemical reactions in living things.
epicenter The point on Earth’s surface directly above
the focus of an earthquake.
epidermis The outer layer of the skin.
equator An imaginary east-west line around the
center of Earth that divides the planet into the Northern
Hemisphere and the Southern Hemisphere; a line set at
0° latitude.
equinox In an orbit, a position and time in which
sunlight shines equally on the Northern Hemisphere and
the Southern Hemisphere; a time of year when daylight
and darkness are nearly equal for most of Earth.
erosion The process in which sediment is picked up
and moved from one place to another.
estuary A shoreline area where fresh water from the
lower end of a river mixes with salt water from the
ocean.
eukaryotic cell A cell in which the genetic
material is enclosed within a nucleus, surrounded by
its own membrane.
eutrophication An increase in nutrients in a lake
or pond. Eutrophication can occur naturally or as a
result of pollution, and causes increased growth of
algae and plants.
evaporation A process by which a substance changes
from its liquid state to its gas state by random particle
movement. Evaporation usually occurs at the surface of
a liquid over a wide range of temperatures.
evolution The process through which species change
over time; can refer to the changes in a particular
population or to the formation and extinction of species
over the course of Earth’s history.
exfoliation In geology, the process in which layers or
sheets of rock gradually break off.
exoskeleton The strong, flexible outer covering of
some invertebrate animals, such as arthropods.
exothermic reaction A chemical reaction that
releases energy.
experiment An organized procedure to study
something under controlled conditions.
extinction The permanent disappearance of a species.
extrusive igneous rock Igneous rock that forms
as lava cools on Earth’s surface.
Copyright © by McDougal Littell, a division of Houghton Mifflin Company
G
galaxy Millions or billions of stars held together in a
group by their own gravity.
gamete A sperm or egg cell, containing half the
usual number of chromosomes of an organism
(one chromosome from each pair), which is found
only in the reproductive organs of a plant or animal.
gamma rays Part of the electromagnetic spectrum
that consists of waves with the highest frequencies;
electromagnetic waves with frequencies ranging from
more than 1019 hertz to more than 1024 hertz.
gas Matter with no definite volume and no definite
shape. The molecules in a gas are very far apart, and the
amount of space between them can change easily.
gas giant A large planet that consists mostly of gases
in a dense form. The four large planets in the outer solar
system—Jupiter, Saturn, Uranus, and Neptune—are gas
giants.
gene The basic unit of heredity that consists of a
segment of DNA on a chromosome.
generator A device that converts kinetic energy, or
the energy of motion, into electrical energy. Generators
produce electric current by rotating a magnet within a
coil of wire or rotating a coil of wire within a magnetic
field.
genetic engineering The scientific process in
which DNA is separated from an organism, changed, and
then reinserted into the same or a different organism.
genetic material The nucleic acid DNA that is
present in all living cells and contains the information
needed for a cell’s growth, maintenance, and reproduction.
genome All the DNA of an organism, including its
genes; the genetic material of an organism.
genotype The genetic makeup of an organism; all the
genes that an organism has.
genus The first part of a binomial name that groups
together closely related species. The genus Felis
includes all species of small cats.
geographic information systems Computer
systems that can store, arrange, and display geographic
data in different types of maps.
geologic time scale The summary of Earth’s
history, divided into intervals of time defined by major
events or changes on Earth.
geosphere All the features on Earth’s surface—
continents, islands, and seafloor—and everything below
the surface—the inner and outer core and the mantle;
one of the four parts of the Earth system.
geothermal energy Heat energy that originates
from within Earth and drives the movement of Earth’s
tectonic plates. Geothermal energy can be used to
generate electricity.
germination The beginning of growth of a new plant
from a spore or a seed.
gestation In mammals, the period of time spent by a
developing offspring inside the mother’s body.
geyser A type of hot spring that shoots water into
the air.
MULTI-LANGUAGE GLOSSARY
ENGLISH
food chain A model used to show the feeding
relationship between a single producer and a chain of
consumers in an ecosystem. In a typical food chain, a
plant is the producer that is eaten by a consumer, such as
an insect; then the insect is eaten by a second consumer,
such as a bird.
food web A model used to show a feeding relationship
in which many food chains overlap in an ecosystem.
force A push or a pull; something that changes the
motion of an object.
fossil A trace or the remains of a once-living thing
from long ago.
fossil fuels Fuels formed from the remains of
prehistoric organisms that are burned for energy.
fracture The tendency of a mineral to break into
irregular pieces.
freezing The process by which a substance changes
from its liquid state into its solid state.
freezing point The temperature at which a
substance changes from its liquid state to its solid state
through freezing.
freezing rain Rain that freezes when it hits the
ground or another surface and coats the surface with ice.
frequency The number of wavelengths (or wave
crests) that pass a fixed point in a given amount of time,
usually one second.
fresh water Water that is not salty and has little or no
taste, color, or smell. Most lakes and rivers are made up
of fresh water.
friction A force that resists the motion between two
surfaces in contact.
front The boundary between air masses.
fruit The ripened ovary of a flowering plant that
contains the seeds.
fulcrum A fixed point around which a lever rotates.
Fungi Part of a classification system that divides all
living things into six kingdoms. Kingdom Fungi
includes multicellular mushrooms and molds and
single-celled yeasts.
fusion A process in which particles of an element
collide and combine to form a heavier element, such as
the fusion of hydrogen into helium that occurs in the
Sun’s core.
9
H
habitat The natural environment in which a living
thing gets all that it needs to live; examples include a
desert, a coral reef, and a freshwater lake.
hail Layered lumps or balls of ice that fall from
cumulonimbus clouds.
half-life The length of time it takes for half of the
atoms in a sample of a radioactive element to decay into
atoms of another element.
hardness The resistance of a mineral or other material
to being scratched.
heat 1. The flow of energy from an object at a higher
temperature to an object at a lower temperature. 2.
Energy that is transferred from a warmer object to a
cooler object.
heredity The passing of genes from parents to
offspring; the genes are expressed in the traits of the
offspring.
hertz Hz The unit used to measure frequency. One
hertz is equal to one complete wavelength per second.
10 MCDOUGAL LITTELL SCIENCE
heterotroph An organism that consumes other
organisms to get energy.
hibernation A sleeplike state in which certain
animals spend the winter. Hibernation reduces an
animal’s need for food and helps protect it from cold.
high-pressure system A generally calm and clear
weather system that occurs when air sinks down in a
high-pressure center and spreads out toward areas of
lower pressure as it nears the ground.
homeostasis The process by which an organism or
cell maintains the internal conditions needed for health
and functioning, regardless of outside conditions.
horizontal Parallel to the horizon; level.
hormone A chemical that is made in one organ and
travels through the blood to another organ.
horsepower hp The unit of measurement of power for
engines and motors. One horsepower equals 745 watts.
host cell A cell that a virus infects and uses to make
copies of itself.
hot spot An area where a column of hot material
rises from deep within a planet’s mantle and heats the
lithosphere above it, often causing volcanic activity at
the surface.
humidity The amount of water vapor in air.
humus The decayed organic matter in soil.
hurricane A tropical low-pressure system with
sustained winds of 120 kilometers per hour (74 mi/h)
or more.
hydrocarbon A compound that contains only carbon
and hydrogen.
hydroelectric energy Electricity that is generated
by the conversion of the energy of moving water.
hydrogen fuel cell A device that uses hydrogen
and oxygen to produce electricity. The byproducts are
heat and water.
hydrosphere All water on Earth—in the atmosphere
and in the oceans, lakes, glaciers, rivers, streams, and
underground reservoirs; one of the four parts of the
Earth system.
hydrothermal vent An opening in the sea floor
from which heated water rises and mixes with the ocean
water above.
hyphae Threadlike tubes that form the structural parts
of the body of a fungus. Hyphae is a plural word; the
singular is hypha.
hypothesis A tentative explanation for an observation
or phenomenon. A hypothesis is used to make testable
predictions.
Copyright © by McDougal Littell, a division of Houghton Mifflin Company
ENGLISH
gill A respiratory organ that filters oxygen dissolved
in water.
glacier A large mass of ice that exists year-round and
moves over land.
gland An organ in the body that produces a specific
substance, such as a hormone.
global winds Winds that travel long distances in
steady patterns over several weeks.
glucose A sugar molecule that is a major energy
source for most cells, produced by the process of
photosynthesis.
gravity The force that objects exert on each other
because of their mass.
greenhouse effect The process by which certain
gases in a planet’s atmosphere absorb and emit infrared
radiation, resulting in an increase in surface temperature.
greenhouse gases Gases, such as carbon dioxide
and methane, that absorb and give off infrared radiation
as part of the greenhouse effect.
grounding The creation of a harmless, low-resistance
path—a ground—for electricity to follow. Grounding is
an important electrical safety procedure.
groundwater Water that collects and is stored
underground.
group A vertical column in the periodic table of the
elements. Elements in a group have similar properties.
gymnosperm A plant that produces seeds that are
not enclosed in flowers or fruit.
Copyright © by McDougal Littell, a division of Houghton Mifflin Company
ice age A period of time during which surface
temperatures drop significantly and huge ice sheets
spread out beyond the polar regions.
iceberg A mass of floating ice that broke away from
a glacier.
ice core A tubular sample that shows the layers of
snow and ice that have built up over the years.
igneous rock Rock that forms as molten rock cools
and becomes solid.
image A picture of an object formed by rays of light.
immigration In population studies, the movement of
an organism into a range inhabited by individuals of the
same species.
immune system A group of organs that provides
protection against disease-causing agents.
immunity Resistance to a disease. Immunity can
result from antibodies formed in the body during a
previous attack of the same illness.
impact crater A round pit left behind on the surface
of a planet or other body in space after a smaller object
strikes the surface.
impermeable Resistant to the passage of water.
incandescence 1. The production of light by
materials having high temperatures. 2. Light produced
by an incandescent object.
inclined plane A simple machine that is a sloping
surface, such as a ramp.
incubation The process of keeping eggs warm by
bodily heat until they hatch.
index fossil A fossil of an organism that was
common, lived in many areas, and existed only during
a certain span of time. Index fossils are used to help
determine the age of rock layers.
induction The build-up of a static charge in an
object when the object is close to, but not touching, a
charged object.
inertia The resistance of an object to a change in the
speed or the direction of its motion.
infancy The stage of life that begins at birth and ends
when a baby begins to walk.
infrared light Part of the electromagnetic spectrum
that consists of waves with frequencies between those of
microwaves and visible light.
infrared radiation Radiation of lower frequencies
than visible light.
inner core A solid sphere of metal, mainly nickel and
iron, at Earth’s center.
inorganic compound A compound that is not
considered organic. All compounds that do not contain
carbon are inorganic, as are some types of carboncontaining compounds.
insect An arthropod with three body segments, six
legs, two antennae, and compound eyes.
insulator 1. A material that does not transfer energy
easily. 2. A material that does not transfer electric
charge easily.
integumentary system The body system that
includes the skin and its associated structures.
intensity The amount of energy of a wave, per
wavelength. Intensity is associated with the amplitude of
a sound wave and with the quality of loudness produced
by the sound wave.
interaction The condition of acting or having
an influence upon something. Living things in an
ecosystem interact with both the living and nonliving
parts of their environment.
interference The meeting and combining of waves;
the adding or subtracting of wave amplitudes that occurs
as waves overlap.
interphase The period in the cell cycle in which a
cell grows, maintains itself, and prepares for division.
intertidal zone The narrow ocean margin between
the high-tide mark and the low-tide mark.
intrusive igneous rock Igneous rock that forms as
magma cools below Earth’s surface.
invertebrate An animal that has no backbone.
involuntary muscle A muscle that moves without
conscious control.
ion An atom or group of atoms that has a positive or
negative electric charge.
ionic bond The electric attraction between a negative
ion and a positive ion.
irrigation The process of supplying water to land to
grow crops.
isobar A line on a weather map connecting places that
have the same air pressure.
isomer Any of two or more compounds that contain
the same atoms but that have different structures.
isotope An atom of one element that has a
different number of neutrons than another atom
of the same element.
ENGLISH
I
J
jet stream A wind that flows in the upper
troposphere from west to east over vast distances
at great speeds.
MULTI-LANGUAGE GLOSSARY
11
K
kelp forest A large community of kelp, a type of
seaweed that can attach to the ocean floor.
kettle lake A bowl-shaped lake that was formed as
sediment built up around a block of ice left behind by
a glacier.
kilowatt kW A unit of measurement for power equal
to 1000 watts.
kilowatt-hour kWh The unit of measurement for
electrical energy equal to one kilowatt of power over a
one-hour period.
kinetic energy The energy of motion. A moving
object has the most kinetic energy at the point where it
moves the fastest.
kinetic theory of matter A theory stating that all
matter is made of particles in motion.
L
lander A craft designed to land on a planet’s surface.
larva A free-living early form of a developing
organism that is very different from its adult form.
laser A device that produces an intense, concentrated
beam of light that can be brighter than sunlight. Lasers
are often used in medicine and communications.
latitude The distance in degrees north or south from
the equator.
lava Molten rock that reaches a planet’s surface through
a volcano.
law In science, a rule or principle describing a physical
relationship that always works in the same way under the
same conditions. The law of conservation of energy is an
example.
law of conservation of energy A law stating
that no matter how energy is transferred or transformed,
it continues to exist in one form or another.
law of conservation of mass A law stating that
atoms are not created or destroyed in a chemical reaction.
law of conservation of momentum A law
stating that the amount of momentum a system of
objects has does not change as long as there are no
outside forces acting on that system.
law of reflection A law of physics stating that the
angle at which light strikes a surface (the angle of
incidence) equals the angle at which it reflects off the
surface (the angle of reflection).
12 MCDOUGAL LITTELL SCIENCE
lens A transparent optical tool that refracts light.
lever A solid bar that rotates, or turns, around a fixed
point (fulcrum); one of the six simple machines.
lichen An organism that results from a close
association between single-celled algae and fungi.
lightning A discharge of electricity from one part of a
cloud to another or between a cloud and the ground,
causing a bright flash of light.
light-year The distance light travels in one year,
which is about 9.5 trillion kilometers (6 trillion mi).
limiting factor A factor or condition that prevents
the continuing growth of a population in an ecosystem.
lipid A type of carbon-based molecule in living things.
Lipids include fats, oils, and waxes used for energy or as
structural materials. Lipids are made up of subunits of
fatty acids.
liquefaction A process in which the shaking of
ground causes loose, wet soil to act like a liquid.
liquid Matter that has a definite volume but does not
have a definite shape. The molecules in a liquid are
close together but not bound to one another.
lithosphere The layer of Earth made up of the crust
and the rigid rock of the upper mantle, averaging about
40 kilometers thick and broken into tectonic plates.
lock A section of a waterway, closed off by gates, in
which the water level is rasied or lowered to move
ships through.
loess Deposits of fine-grained, wind-blown sediment.
longitude The distance in degrees east or west of the
prime meridian. Longitude lines are numbered from
0° to 180°.
longitudinal wave A type of wave in which the
disturbance moves in the same direction that the
wave travels.
longshore current The overall direction and
movement of water as waves strike the shore at an angle.
longshore drift The zigzag movement of sand along
a beach, caused by the action of waves.
low-pressure system A large and often stormy
weather system that occurs when air moves around
and into a low-pressure center, then moves up to
higher altitudes.
luminescence The production of light without the
high temperatures needed for incandescence.
lung A respiratory organ that absorbs oxygen from
the air.
luster The property of a mineral that describes the way
in which light reflects from its surface. Major types of
luster are metallic and nonmetallic.
Copyright © by McDougal Littell, a division of Houghton Mifflin Company
ENGLISH
joule J A unit used to measure energy and work. One
calorie is equal to 4.18 joules of energy; one joule of
work is done when a force of one newton moves an
object one meter.
Copyright © by McDougal Littell, a division of Houghton Mifflin Company
machine Any device that makes doing work easier.
magma Molten rock beneath Earth’s surface.
magnet An object that attracts certain other materials,
particularly iron and steel.
magnetic domain A group of atoms whose
magnetic fields align, or point in the same direction.
Magnetic materials have magnetic domains, whereas
nonmagnetic materials do not.
magnetic field An area surrounding a magnet
within which the magnet can exert a force. Magnetic
fields are concentrated into a pattern of lines that extend
from the magnet’s north pole to its south pole.
magnetic reversal A switch in the direction of
Earth’s magnetic field so that the magnetic north pole
becomes the magnetic south pole and the magnetic south
pole becomes the magnetic north pole.
magnetism The force exerted by a magnet. Opposite
poles of two magnets attract, or pull together, whereas
like poles of two magnets repel, or push apart.
main sequence The stage in which stars produce
energy through the fusion of hydrogen into helium.
mammal A warm-blooded vertebrate animal
whose young feed on milk produced by the mother’s
mammary glands.
mantle The layer of rock between Earth’s outer core
and crust, in which most rock is hot enough to flow in
convection currents; Earth’s thickest layer.
map legend A chart that explains the meaning of
each symbol used on a map; also called a key.
map scale The comparison of distance on a map
with actual distance on what the map represents, such as
Earth’s surface. Map scale may be expressed as a ratio,
a bar scale, or equivalent units.
mare A large, dark plain of solidified lava on the
Moon. The plural form of mare is maria.
marine climate A climate influenced by a nearby
ocean, with generally mild temperatures and steady
precipitation.
mass A measure of how much matter an object is
made of.
mass extinction One of several periods in Earth’s
history when large numbers of species became extinct at
nearly the same time.
mass wasting The downhill movement of loose rock
or soil.
matter Anything that has mass and volume. Matter
exists ordinarily as a solid, a liquid, or a gas.
mechanical advantage The number of times a
machine multiplies the input force; output force divided
by input force.
mechanical energy A combination of the kinetic
energy and potential energy an object has.
mechanical wave A wave, such as a sound wave
or a seismic wave, that transfers kinetic energy
through matter.
ENGLISH
M
mechanical weathering The breakdown of rock
into smaller pieces of the same material without any
change in its composition.
medium A substance through which a wave moves.
meiosis A part of sexual reproduction in which cells
divide to form sperm cells in a male and egg cells in a
female. Meiosis occurs only in reproductive cells.
melting The process by which a substance changes
from its solid state to its liquid state.
melting point The temperature at which a substance
changes from its solid state to its liquid state through
melting.
menstruation A period of about five days during
which blood and tissue exit the body through the vagina.
metal An element that tends to be shiny, easily shaped,
and a good conductor of electricity and heat.
metallic bond A certain type of bond in which
nuclei float in a sea of electrons.
metalloid An element that has properties of both
metals and nonmetals.
metamorphic rock Rock formed as heat or
pressure causes existing rock to change in structure,
texture, or mineral composition.
metamorphism The process by which a rock’s
structure or mineral composition is changed by pressure
or heat.
metamorphosis The transformation of an animal
from its larval form into its adult form.
meteor A brief streak of light produced by a small
particle entering Earth’s atmosphere at a high speed.
meteorite A small object from outer space that
passes through Earth’s atmosphere and reaches
the surface.
meteorologist A scientist who studies weather.
meter m The international standard unit of length,
about 39.37 inches.
microclimate The climate of a smaller area within
a subclimate.
microorganism A very small organism that can be
seen only with a microscope. Bacteria are examples of
microorganisms.
microscope An instrument that uses glass lenses to
magnify an object.
microwaves Part of the electromagnetic spectrum
that consists of waves with higher frequencies than radio
waves, but lower frequencies than infrared waves.
MULTI-LANGUAGE GLOSSARY
13
N
nanotechnology The science and technology of
building electronic circuits and devices from single
atoms and molecules.
14 MCDOUGAL LITTELL SCIENCE
natural resource Any type of matter or energy
from Earth’s environment that humans use to meet
their needs.
natural selection The process through which
members of a species that are best suited to their
environment survive and reproduce at a higher rate
than other members of the species.
neap tide A tide of small range occurring during the
first- and third-quarter phases of the Moon.
nebula A cloud of gas and dust in space. Stars form
in nebulae.
net force The overall force acting on an object when
all of the forces acting on it are combined.
neuron A nerve cell.
neutral Describing a solution that is neither an acid
nor a base. A neutral solution has a pH of 7.
neutron A particle that has no electric charge and is
located in an atom’s nucleus.
neutron star A dense core that may be left behind
after a higher-mass star explodes in a supernova.
Newton’s first law A scientific law stating that
objects at rest remain at rest, and objects in motion
remain in motion with the same velocity, unless acted
on by an unbalanced force.
Newton’s second law A scientific law stating that
the acceleration of an object increases with increased
force and decreases with increased mass.
Newton’s third law A scientific law stating that
every time one object exerts a force on another object,
the second object exerts a force that is equal in size and
opposite in direction back on the first object.
niche The role a living thing plays in its habitat. A plant
is a food producer, whereas an insect both consumes food
as well as provides food for other consumers.
nitrogen cycle The continuous movement of
nitrogen through Earth, its atmosphere, and the living
things on Earth.
nonmetal An element that is not a metal and has
properties generally opposite to those of a metal.
nonpoint-source pollution Pollution with a
source that is hard to find or scattered.
nonrenewable resource A resource that exists in
a fixed amount or is used up more quickly than it can be
replaced in nature.
nuclear fission The process of splitting the nuclei
of radioactive atoms, which releases huge amounts of
energy mainly in the form of radiation and heat energy.
nucleic acid One of several carbon-based molecules
that carry an organism’s genetic code. One of the nucleic
acids—DNA—contains the information needed to make
proteins. RNA, a second type of nucleic acid, translates
the information into proteins.
Copyright © by McDougal Littell, a division of Houghton Mifflin Company
ENGLISH
mid-ocean ridge A long line of sea-floor mountains
where new ocean crust is formed by volcanic activity
along a divergent boundary.
migration The movement of animals from one region
to another in response to changes in the seasons or
the environment.
mineral A substance that forms in nature, is a solid, has
a definite chemical makeup, and has a crystal structure.
mitochondria Organelles that release energy by
using oxygen to break down sugars.
mitosis The phase in the cell cycle during which the
nucleus divides.
mixture A combination of two or more substances
that do not combine chemically but remain the same
individual substances. Mixtures can be separated by
physical means.
mobile Able to move from place to place.
molecule A group of atoms that are held together by
covalent bonds so that they move as a single unit.
mollusk An invertebrate animal with a soft body, a
muscular foot, and a mantle. Many mollusks have a hard
outer shell.
molting The process of an arthropod shedding its
exoskeleton to allow for growth.
momentum A measure of mass in motion. The
momentum of an object is the product of its mass
and velocity.
monomer One of many small, repeating units linked
together to form a polymer.
monsoon A wind that changes direction with
the seasons.
moraine A deposit of till left behind by a retreating
glacier. Moraines can form along a glacier’s sides and at
its end.
motion A change of position over time.
multicellular A term used to describe an organism
that is made up of many cells.
multicellular organism An organism that is made
up of many cells.
muscular system The muscles of the body that,
together with the skeletal system, function to produce
movement.
mutation Any change made to DNA.
mutualism An interaction between two species in
which both benefit; a type of symbiosis.
Copyright © by McDougal Littell, a division of Houghton Mifflin Company
O
ocean current A mass of moving ocean water.
oceanic-continental subduction A boundary
along which a plate carrying oceanic crust sinks beneath
a plate with continental crust.
oceanic-oceanic subduction A boundary along
which a plate carrying oceanic crust sinks beneath
another plate with oceanic crust.
offspring The new organisms produced by one or two
parent organisms.
ohm Ω The unit of measurement for electrical
resistance.
Ohm’s law The mathematical relationship among
current, voltage, and resistance, expressed in the formula
I = V/R (current = voltage/resistance).
opportunist A species characterized by a relatively
short life span, with relatively large quantities of
offspring, as compared with a competitor species.
optics The study of light, vision, and related
technology.
orbit n. The elliptical path of an object in space
as it moves around another object due to gravity; for
example, the Moon moves in an orbit around Earth.
v. To revolve around, or move in an orbit; for example,
the Moon orbits Earth.
ore A rock that contains enough of a valuable mineral
to be mined for a profit.
organ A structure in a plant or an animal that is made
up of different tissues working together to perform a
particular function.
organelle A structure in a cell that is enclosed by a
membrane and that performs a particular function.
organic compound A compound that is based
on carbon.
organism An individual living thing, made up of one
or many cells, that is capable of growing and
reproducing.
organ system A group of organs that together
perform a function that helps the body meet its needs for
energy and materials.
osmosis The movement of water through a membrane
from an area of higher concentration to an area of lower
concentration.
outer core A layer of molten metal, mainly nickel
and iron, that surrounds Earth’s inner core.
overfishing The catching of fish at a faster rate than
they can reproduce.
ozone A gas molecule that consists of three
oxygen atoms.
ENGLISH
nucleus The structure in a eukaryotic cell that
contains the genetic material a cell needs to reproduce
and function.
nutrient A substance that an organism needs to live.
Examples include water, minerals, and materials that
come from the breakdown of food particles.
nutrition The study of the materials that nourish
the body.
P
Pangaea A hypothetical supercontinent that included
all of the landmasses on Earth. It began breaking apart
about 200 million years ago.
parallax The apparent shift in the position of an object
when viewed from different locations.
parallel circuit A circuit in which current follows
more than one path. Each device that is wired in
a parallel circuit has its own path to and from the
voltage source.
parasite An organism that absorbs nutrients from
the body of another organism, often harming it in
the process.
parasitism A relationship between two species in
which one species is harmed while the other benefits; a
type of symbiosis.
parent An organism that produces a new organism or
organisms similar to or related to itself.
particle A very small piece of matter, such as an
atom, molecule, or ion.
particulates Tiny particles or droplets, such as dust,
dirt, and pollen, that are mixed in with air.
pascal Pa The unit used to measure pressure. One
pascal is the pressure exerted by one newton of force on
an area of one square meter, or one N/m2.
Pascal’s principle A statement that says when an
outside pressure is applied at any point to a fluid in a
container, that pressure is transmitted throughout the
fluid with equal strength.
passive transport The movement of materials
through a membrane without any input of energy.
pathogen An agent that causes disease.
pedigree A chart that shows family relationships,
including two or more generations.
penumbra A region of lighter shadow that may
surround an umbra; for example, the spreading cone of
lighter shadow cast by a space object.
percentage A ratio that states the number of times an
outcome is likely to occur out of a possible 100 times.
original remains A fossil that is the actual body or
body parts of an organism.
MULTI-LANGUAGE GLOSSARY
15
point-source pollution Pollution that enters water
from a known source.
16 MCDOUGAL LITTELL SCIENCE
polar covalent bond The unequal sharing of
electrons between two atoms that gives rise to negative
and positive regions of electric charge.
polarization A way of filtering light so that all of the
waves vibrate in the same direction.
pollen Tiny multicellular grains that contain the
undeveloped sperm cells of a plant.
pollution The release of harmful substances into the
air, water, or land.
polymer A very large carbon-based molecule made of
smaller, repeating units.
population A group of organisms of the same species
that live in the same area. For example, a desert will
have populations of different species of lizards and
cactus plants.
population density A measure of the number of
organisms that live in a given area. The population
density of a city may be given as the number of people
living in a square kilometer.
population dynamics The study of the changes in
the number of individuals in a population and the factors
that affect those changes.
position An object’s location.
potential energy Stored energy; the energy an
object has due to its position, molecular arrangement,
or chemical composition.
power The rate at which work is done.
precipitate n. A solid substance that forms as a
result of a reaction between chemicals in two liquids.
v. To come out of solution.
precipitation Any type of liquid or solid water that
falls to Earth’s surface, such as rain, snow, or hail.
predator An animal that hunts other animals and
eats them.
pressure A measure of how much force is acting on a
certain area; how concentrated a force is. Pressure is
equal to the force divided by area.
prey An animal that other animals hunt and eat.
primary colors Three colors of light—red,
green, and blue—that can be mixed to produce all
possible colors.
primary pigments Three colors of substances—
cyan, yellow, and magenta—that can be mixed to
produce all possible colors.
prime meridian An imaginary north-south line that
divides the planet into the Eastern Hemisphere and the
Western Hemisphere. The prime meridian passes
through Greenwich, England.
prism An optical tool that uses refraction to separate
the different wavelengths that make up white light.
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ENGLISH
period A horizontal row in the periodic table of the
elements. Elements in a period have varying properties.
periodic table A table of the elements, arranged
by atomic number, that shows the patterns in their
properties.
peripheral nervous system The part of the
nervous system that lies outside the brain and spinal cord.
peristalsis Wavelike contractions of smooth muscles
in the organs of the digestive tract. The contractions
move food through the digestive system.
permeable Allowing the passage of water.
pH The concentration of hydrogen ions in a solution; a
measurement of acidity.
phenotype The observable characteristics or traits of
an organism.
photosynthesis The process by which green plants
and other producers use simple compounds and energy
from light to make sugar, an energy-rich compound.
This is an endothermic process in which light is
absorbed and used to change carbon dioxide and
water into glucose and oxygen.
physical change A change in a substance that does
not change the substance into a different one.
physical property A characteristic of a substance
that can be observed without changing the identity of
the substance.
phytoplankton Microscopic floating organisms that
live in water and, like plants, convert sunlight and carbon
dioxide into food.
pioneer species The first species to move into a
lifeless environment. Plants like mosses are typical
pioneer species on land.
pitch The quality of highness or lowness of a sound.
Pitch is associated with the frequency of a sound wave—
the higher the frequency, the higher the pitch.
placenta An organ that transports materials between a
pregnant female mammal and the offspring developing
inside her body.
planet A spherical body, larger than a comet or
asteroid, that orbits the Sun, or a similar body that orbits
a different star.
plankton Mostly microscopic organisms that drift in
great numbers through bodies of water.
Plantae Part of a classification system that divides
all living things into six kingdoms. Kingdom Plantae
includes multicellular organisms, such as trees, grass,
and moss, that are capable of photosynthesis, capturing
energy from the Sun.
plastic A polymer that can be molded or shaped.
Copyright © by McDougal Littell, a division of Houghton Mifflin Company
Q
quasar The very bright center of a distant galaxy.
R
radiation Energy that travels across distances in the
form of electromagnetic waves.
radioactivity The process by which the nucleus of an
atom of an element releases energy and particles.
radio waves The part of the electromagnetic
spectrum that consists of waves with the lowest
frequencies.
rain shadow An area on the downwind side of a
mountain that gets less precipitation than the side that
faces the wind.
ratio A comparison between two quantities, often
written with a colon, as 3 : 4.
reactant A substance that is present at the
beginning of a chemical reaction and is changed
into a new substance.
reactive Likely to undergo a chemical change.
recessive A term that describes an allele that is not
expressed when combined with a dominant form of
the gene.
recrystallization The process by which bonds
between atoms in minerals break and re-form in new
ways during metamorphism.
recycling The reusing of materials that people would
otherwise throw away, such as paper, glass, plastics, and
certain metals.
red blood cell A type of blood cell that picks up
oxygen in the lungs and delivers it to cells throughout
the body.
reference point A location to which another
location is compared.
reflection The bouncing back of a wave after it
strikes a barrier.
refraction The bending of a wave as it crosses the
boundary between two mediums at an angle other than
90 degrees.
regeneration In some organisms, the process by
which certain cells produce new tissue growth at the site
of a wound or lost limb; also a form of asexual
reproduction.
regular reflection The reflection of parallel light
rays in the same direction.
relative age The age of an event or object in relation
to other events or objects.
relative humidity The comparison of the amount of
water vapor in air with the maximum amount of water
vapor that can be present in air at that temperature.
relative motion The idea that the observation of
motion depends on the observer.
relief In geology, the difference in elevation between
an area’s high and low points.
relief map A map that shows the differences in
elevation in an area. Relief maps can show elevations
through the use of contour lines, shading, colors, and,
in some cases, three-dimensional materials.
MULTI-LANGUAGE GLOSSARY
ENGLISH
probability The likelihood or chance that a specific
outcome will occur out of a total number of outcomes.
probe A spacecraft that is sent into a planet’s
atmosphere or onto a solid surface.
producer An organism that captures energy from
sunlight and transforms it into chemical energy that is
stored in energy-rich carbon compounds. Producers are
a source of food for other organisms.
product A substance formed by a chemical reaction.
A product is made by the rearrangement of atoms and
bonds in reactants.
projection A representation of Earth’s curved surface
on a flat map.
prokaryotic cell A cell that lacks a nucleus and
other organelles, with DNA that is not organized into
chromosomes.
protein A macromolecule in living things that is made
up of chains of amino acid subunits. Proteins control the
chemical activity of a cell and support growth and repair.
Protista Part of a classification system that divides
all living things into six kingdoms. Kingdom Protista
includes mostly single-celled organisms with cells
similar to those of the Plantae, Animalia, and Fungi
kingdoms.
proton A positively charged particle located in an
atom’s nucleus.
protozoa Animal-like protists that eat other organisms
or decaying parts of other organisms. Protozoa is a
plural word; the singular is protozoan.
pulley A wheel with a grooved rim that turns on an
axle; one of the six simple machines.
Punnett square A chart used to show all the ways
genes from two parents can combine and be passed to
offspring; used to predict all genotypes that are possible.
pupil The circular opening in the iris of the eye that
controls how much light enters the eye.
pyroclastic flow A dense cloud of superheated
gases and rock fragments that moves quickly downhill
from an erupting volcano.
17
resistor An electrical device that slows the flow of
charge in a circuit.
resonance The strengthening of a sound wave when
it combines with an object’s natural vibration.
respiration The exothermic process by which living
things release energy from glucose and oxygen and
produce carbon dioxide and water.
respiratory system A system that interacts with
the environment and with other body systems to bring
oxygen to the body and remove carbon dioxide.
retina A light-sensitive membrane at the back of the
inside of the eye.
revolution The motion of one body around another,
such as Earth in its orbit around the Sun; the time it
takes an object to go around once.
rift valley A deep valley formed as tectonic plates
move apart, such as along a mid-ocean ridge.
ring In astronomy, a wide, flat zone of small particles
that orbit around a planet’s equator.
rip current A narrow stream of water that breaks
through sandbars and drains rapidly back into deeper water.
RNA A molecule that carries genetic information from
DNA to a ribosome, where the genetic information is
used to bring together amino acids to form a protein
(Ribonucleic acid).
robot A machine that works automatically or by
remote control.
rock A naturally formed solid that is usually made up
of one or more types of minerals.
rock cycle The set of natural, repeating processes that
form, change, break down, and re-form rocks.
S
salinity The measure of the amount of dissolved salt
contained in water.
18 MCDOUGAL LITTELL SCIENCE
salt water Water that contains dissolved salts and
other minerals. Oceans consist of salt water.
sandbar A ridge of sand built up by the action of
waves and currents.
satellite An object that orbits a more massive object.
saturated Containing the maximum amount of a
solute that can be dissolved in a particular solvent at a
given temperature and pressure.
saturation A condition of the atmosphere in which
the rates of evaporation and condensation are equal.
scale One of the thin, small, overlapping plates that
cover most fish and reptiles and some other animals.
scattering The spreading out of light rays in all
directions as particles reflect and absorb the light.
screw A simple machine that is an inclined plane
wrapped around a cylinder. A screw can be used to raise
and lower weights as well as to fasten objects.
season One part of a pattern of temperature changes
and other weather trends over the course of a year.
Astronomical seasons are defined and caused by
the position of Earth’s axis relative to the direction
of sunlight.
second s A unit of time equal to one-sixtieth of a
minute.
sediment Solid materials such as rock fragments,
plant and animal remains, or minerals that are carried by
water or by air and that settle on the bottom of a body of
water or on the ground.
sedimentary rock Rock formed as pieces of older
rocks and other loose materials get pressed or cemented
together or as dissolved minerals re-form and build up
in layers.
seed A plant embryo that is enclosed in a protective
coating and has its own source of nutrients.
seismic wave The vibrations caused by an
earthquake.
seismograph An instrument that constantly records
ground movements.
selective breeding The process of breeding plants
and animals with specific traits to produce offspring that
have these traits.
sensor A mechanical or electronic device that receives
and responds to a signal, such as light.
septic system A small sewage system, often for
one home or business, that uses an underground tank to
treat wastewater.
series circuit A circuit in which current follows a
single path. Each device that is wired in a series circuit
shares a path to and from the voltage source.
sessile The quality of being attached to one spot; not
free-moving.
Copyright © by McDougal Littell, a division of Houghton Mifflin Company
ENGLISH
remote-sensing A method of using scientific
equipment to gather information about something from
a distance. Most remote-sensing methods make use of
different types of electromagnetic radiation.
renewable resource A natural resource that can be
replaced in nature at about the same rate as it is used.
replication The process by which DNA is copied
before it condenses into chromosomes. Replication takes
place before a cell divides.
reptile A cold-blooded vertebrate that has skin covered
with scales or horny plates and has lungs.
resistance 1. The ability of an organism to protect
itself from a disease or the effects of a substance. 2.
The property of a material that determines how easily a
charge can move through it. Resistance is measured in
ohms.
Copyright © by McDougal Littell, a division of Houghton Mifflin Company
solubility The amount of solute that dissolves in a
certain amount of a solvent at a given temperature and
pressure to produce a saturated solution.
solute In a solution, a substance that is dissolved in
a solvent.
solution A mixture of two or more substances that is
identical throughout; a homogeneous mixture.
solvent In a solution, the substance that dissolves a
solute and makes up the largest percentage of a solution.
sonar Instruments that use echolocation to measure
distance and to locate objects underwater; acronym for
“sound navigation and ranging.”
sound A type of wave that is produced by a vibrating
object and that travels through matter.
space station A satellite in which people can live
and work for long periods.
specialization The specific organization of a
cell and its structure that allows it to perform a
specific function.
speciation The evolution of a new species from an
existing species.
species A group of living things that are so closely
related that they can breed with one another and produce
offspring that can breed as well.
specific heat The amount of energy required to raise
the temperature of one gram of a substance by one
degree Celsius.
spectrum 1. Radiation from a source separated into
a range of wavelengths. 2. The range of colors that
appears in a beam of visible light when it passes through
a prism. See also electromagnetic radiation.
speed A measure of how fast something moves
through a particular distance over a definite time period.
Speed is distance divided by time.
sperm A male reproductive cell (gamete) that forms in
the reproductive organs of a male and has just a single
copy of the genetic material of the parent.
sponge A simple multicellular invertebrate animal that
lives attached to one place and filters food from water.
spongy bone Strong, lightweight tissue inside
a bone.
spore A single reproductive cell that can grow into a
multicellular organism.
spring A flow of water from the ground at a place
where the surface of the land dips below the water table.
spring tide A tide of large range occurring during the
new and full moons, resulting in an extra-high tidal
bulge and an extra-low tidal dip.
states of matter The different forms in which
matter can exist. Three familiar states are solid, liquid,
and gas.
MULTI-LANGUAGE GLOSSARY
ENGLISH
sewage system A system that collects and treats
wastewater from a city or a town.
sexual reproduction A type of reproduction in
which male and female reproductive cells combine to
form offspring with genetic material from both cells.
short circuit An unintended and undesired path
connecting one part of a circuit with another.
simple machine One of the basic machines on
which all other mechanical machines are based. The six
simple machines are the lever, inclined plane, wheel and
axle, pulley, wedge, and screw.
sinkhole An open basin that forms when the roof of a
cavern becomes so thin that it falls in.
skeletal muscle A muscle that attaches to
the skeleton.
skeletal system The framework of bones that
supports the body, protects internal organs, and anchors
all the body’s movement.
sleet Small pellets of ice that form when rain passes
through a layer of cold air and freezes before hitting
the ground.
slope A measure of how steep a landform is. Slope is
calculated as the change in elevation divided by the
distance covered.
smog The combination of smoke and fog; a type of air
pollution that occurs when sunlight causes unburnt fuels,
fumes, and other gases to react chemically, often seen as
a brownish haze.
smooth muscle Muscle that performs involuntary
movement and is found inside certain organs, such as
the stomach.
soil horizon A soil layer with physical and chemical
properties that differ from those of soil layers above or
below it.
soil profile The soil horizons in a specific location; a
cross section of soil layers that displays all soil horizons.
solar cell A type of technology in which lightsensitive materials convert the energy of sunlight into
electrical energy.
solar system The Sun and its family of orbiting
planets, moons, and other objects.
solar wind A stream of electrically charged particles
that flows out in all directions from the Sun’s corona.
solid Matter that has a definite shape and a definite
volume. The molecules in a solid are in fixed positions
and are close together.
solstice In an orbit, a position and time during which
one hemisphere gets its maximum area of sunlight,
while the other hemisphere gets its minimum amount;
the time of year when days are either longest or
shortest, and the angle of sunlight reaches its maximum
or minimum.
19
system A group of objects or phenomena that interact.
A system can be as simple as a rope, a pulley, and a
mass. It also can be as complex as the interaction of
energy and matter in the four parts of the Earth system.
T
taxonomy The science of classifying and naming
organisms.
technology The use of scientific knowledge to solve
problems or engineer new products, tools, or processes.
20 MCDOUGAL LITTELL SCIENCE
tectonic plate One of the large, moving pieces
into which Earth’s lithosphere is broken and which
commonly carries both oceanic and continental crust.
tectonics The processes in which the motion of hot
material under a crust changes the crust of a space body.
Earth has a specific type of tectonics called plate tectonics.
telescope A device that gathers visible light or
another form of electromagnetic radiation.
temperature A measure of the average amount of
kinetic energy of the particles in an object.
tentacle A long, slender, flexible extension of the
body of certain animals, such as jellyfish. Tentacles are
used to touch, move, or hold.
terminal velocity The final, maximum velocity of a
falling object.
terrestrial planet Earth or a planet similar to Earth
that has a rocky surface. The four planets in the inner
solar system—Mercury, Venus, Earth, and Mars—are
terrestrial planets.
theory In science, a set of widely accepted
explanations of observations and phenomena. A theory
is a well-tested explanation that is consistent with all
available evidence.
theory of plate tectonics A theory stating that
Earth’s lithosphere is broken into huge plates that move
and change in size over time.
thermal energy The energy an object has due to the
motion of its particles; the total amount of kinetic
energy of particles in an object.
thermometer A device for measuring temperature.
thunder The sound wave created by intensely heated
air around a lightning bolt.
thunderstorm A storm with lightning and thunder.
tidal range The difference in height between high
tide and low tide.
tide The periodic rising and falling of the water level of
the ocean due to the gravitational pulls of the Moon and
the Sun.
till Sediment of different sizes left directly on the
ground by a melting, or retreating, glacier.
tissue A group of similar cells that are organized to do
a specific job.
topography All natural and human-made surface
features of a particular area.
tornado A violently rotating column of air stretching
from a cloud to the ground.
trait Any type of feature that can be used to tell two
species apart, such as size or bone structure.
transform boundary A boundary along which two
tectonic plates scrape past each other, and crust is
neither formed nor destroyed.
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ENGLISH
static charge The buildup of electric charge in
an object caused by the uneven distribution of
charged particles.
stimulus Something that causes a response in an
organism or a part of the body.
storm surge A rapid rise in water level in a coastal
area that occurs when a hurricane pushes a huge mass of
ocean water, often leading to flooding and widespread
destruction.
streak The color of a mineral powder left behind when
a mineral is scraped across a surface; a method for
classifying minerals.
stress The force applied by an object pressing on,
pulling on, or pushing against another object.
subduction The process by which an oceanic
tectonic plate sinks under another plate into
Earth’s mantle.
sublimation The process by which a substance
changes directly from its solid state to its gas state
without becoming a liquid first.
subscript A number written slightly below and to the
right of a chemical symbol that shows how many atoms
of an element are in a compound.
substance Matter of a particular type. Elements,
compounds, and mixtures are all substances.
succession A natural process that involves a gradual
change in the plant and animal communities that live in
an area.
sunspot A darker spot on the photosphere of the Sun.
A sunspot appears dark because it is cooler than the
surrounding area.
suspension A mixture in which the different parts
are identifiable as separate substances; a heterogeneous
mixture.
sustainable A term that describes the managing of
certain natural resources so that they are not harmed
or used up. Examples include maintaining clean
groundwater and protecting top soil from erosion.
symbiosis The interaction between individuals from
two different species that live closely together.
Copyright © by McDougal Littell, a division of Houghton Mifflin Company
U
ultrasound Sound waves with frequencies above
20,000 hertz, the upper limit of typical hearing levels in
humans, used for medical purposes, among other things.
ultraviolet light The part of the electromagnetic
spectrum that consists of waves with frequencies higher
than those of visible light and lower than those of x-rays.
ultraviolet radiation Radiation of higher
frequencies than visible light, which can cause sunburn
and other types of damage.
umbra The dark, central region of a shadow, such as
the cone of complete shadow cast by an object.
unicellular A term used to describe an organism that
is made up of a single cell.
unicellular organism An organism that is made up
of a single cell.
uniformitarianism A theory stating that processes
shaping Earth today, such as erosion and deposition, also
shaped Earth in the past, and that these processes cause
large changes over geologic time.
universe Space and all the matter and energy in it.
upwelling The vertical movement of deep water up to
the surface.
urban A term that describes a city environment.
urban heat island The warmer body of air over
a city.
urinary system A group of organs that filter waste
from an organism’s blood and excrete it in a liquid
called urine.
urine Liquid waste that is secreted by the kidneys.
V
vaccine A small amount of a weakened pathogen that
is introduced into the body to stimulate the production
of antibodies.
vacuum A space containing few or no particles
of matter.
variable Any factor that can change in a controlled
experiment, observation, or model.
vascular system Long tubelike tissues in plants
through which water and nutrients move from one part
of the plant to another.
vector A quantity that has both size and direction.
vein A blood vessel that carries blood back to the heart.
velocity A speed in a specific direction.
vertebrate An animal with an internal backbone.
vertical Going straight up or down from a
level surface.
vestigial organ A physical structure that was
fully developed and functional in an earlier group of
organisms but is reduced and unused in later species.
vibration A rapid, back-and-forth motion.
virus A nonliving disease-causing particle that uses the
materials inside cells to make copies of itself. A virus
consists of genetic material enclosed in a protein coat.
visible light The part of the electromagnetic
spectrum that consists of waves detectable by the
human eye.
volcanism The process of molten material moving
from a space body’s hot interior onto its surface.
volcano An opening in the crust through which
molten rock, rock fragments, and hot gases erupt; a
mountain built up from erupted materials.
volt V The unit of measurement for electric potential,
which is equal to one joule per coulomb. The number of
volts of an electric charge equals the charge’s voltage.
volume An amount of three-dimensional space, often
used to describe the space that an object takes up.
voluntary muscle A muscle that can be moved
at will.
ENGLISH
transformer A device that uses electromagnetism to
increase or decrease voltage. A transformer is often used
in the distribution of current from power plants.
transmission The passage of a wave through
a medium.
transpiration The movement of water vapor out of a
plant and into the air.
transverse wave A type of wave in which the
disturbance moves at right angles, or perpendicular, to
the direction in which the wave travels.
tropical storm A low-pressure system that starts in
the tropics with winds of at least 65 kilometers per hour
(40 mi/h) but less than 120 kilometers per hour (74 mi/h).
trough The lowest point, or valley, of a wave.
tsunami A water wave caused by an earthquake,
volcanic eruption, or landslide.
turnover The yearly rising and sinking of cold and
warm water layers in a lake.
W
water cycle The continuous movement of water on
Earth, through its atmosphere, and in the living things
on Earth.
water table The highest part in the ground that is
saturated, or completely filled with water.
MULTI-LANGUAGE GLOSSARY
21
wedge A simple machine that has a thick end and a
thin end. A wedge is used to cut, split, or pierce objects,
or to hold objects together.
weight The force of gravity on an object.
wetland A wet, swampy area that is often flooded
with water.
wheel and axle A simple machine that is a wheel
attached to a shaft, or axle.
wind The horizontal movement of air caused by
differences in air pressure.
work The use of force to move an object over a
distance.
X, Y, Z
x-rays The part of the electromagnetic spectrum that
consists of waves with high frequencies and high
energies; electromagnetic waves with frequencies
ranging from more than 1016 hertz to more than
1021 hertz.
22 MCDOUGAL LITTELL SCIENCE
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ENGLISH
watt W The unit of measurement for power, which is
equal to one joule of work done or energy transferred in
one second. For example, a 75 W light bulb converts
electrical energy into heat and light at a rate of 75 joules
per second.
wave A disturbance that transfers energy from one
place to another without requiring matter to move the
entire distance.
wavelength The distance from one wave peak or
crest to the next peak or crest. Wavelength can be
measured as the distance from any part of one wave
to the identical part of the next wave.
weather The condition of Earth’s atmosphere at a
particular time and place.
weathering The process by which natural forces
break down rocks.
MULTI-LANGUAGE GLOSSARY
23
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ENGLISH
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