Science glossary 6th grade




Science glossary 6th grade


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Science glossary 6th grade


abiotic factor - nonliving physical or chemical part of an ecosystem; describes the nonliving part of the environment, including water, rocks, light, and temperature.  
abrasion - grinding and wearing away of rock surfaces through the mechanical action of other rock or sand particles driven by water, wind, or gravity.
absolute dating - any method of measuring the age of an event or object in years.
absolute magnitude - amount of light a star actually gives off; a measure of how bright a star would be if it were seen from a standard distance.
absolute zero - temperature at which molecular energy is at a minimum (0 K on the Kelvin scale or -273.16oC on the Celsius scale)
absorption (absorb) - process of taking in; soaking up; or making a part of something.
abyssal plain - large, flat, almost level area of the deep-ocean basin.
abyssal zone - open-ocean zone that extends from about 2 000 meters down to about 6 000 meters down.
acceleration - rate at which speed or direction changes; can be found by dividing the change in speed by the given time, usually expressed in meters per second. 
accuracy - extent to which a measurement is in proximity to the standard or expected value. 
acid - substance that increases the H+ concentration when added to a water solution. 
acid precipitation - rain, sleet, or snow that contains a high concentration of acids.    
acid rain - rain that has become more acidic than normal due to pollution.
activation energy - least amount of energy required to start a particular chemical reaction. 
active transport - movement of molecules from where they are less crowded to where they are more crowded; the process of using energy to move materials through a membrane.
adaptation - any structure or behavior that helps an organism survive in its environment; a characteristic of an organism that
increases its chance of survival in its environment;  a particular development, behavior, or physiological change in a population of organisms, in response to changes in the populations. 
adenosine triphosphate (ATP) - molecule that acts as the main energy source for cell processes.
adoptive family - legal addition of children to the family of non-biological parents.
air mass - large body of air that has nearly the same temperature and humidity as the Earth’s surface over which it formed.
air pollution - contamination of the atmosphere by the introduction of pollutants from human and natural sources.
air pressure - measure of the force of air molecules pushing on a surface.
air quality - measure of the pollutants in the air that is used to express how clean or polluted the air is.
air resistance - force of air on moving objects. 
alga (plural-algae) - protists that live mostly in water and use sunlight as a source of energy.   
allele - any of two or more alternate forms of a gene that an organism may have for a particular trait. 
alloy - solid metal dissolved in another solid metal.
alluvial fan - fan-shaped deposit of sediment at the base of a slope, formed as water flows down the slope and spreads at the bottom.
altitude - distance above sea level.
alveolus (plural-alveoli) - grape-like cluster of tiny “balloons” in the lungs.
ameba (amoeba) - microscopic, unicellular Protist that moves using pseudopod.
amino acid - building block of protein; an organic molecule containing an amino (-NH2) and a carboxyl(-COOH) group from which proteins are synthesized.
ammonia - poisonous gas made of nitrogen and hydrogen.
amorphous solid - solid that does not keep a definite shape.
amphibian - cold-blooded vertebrate animal that lives in water when it is young and as an adult, it moves onto land.
amplitude - measure of the energy a wave carries; the maximum distance that the particles of a wave’s medium vibrate from their rest position;  in any periodic function, the maximum absolute variation of the function. 
anabolic (anabolism) - building up process.
anal pore - tiny opening through which a paramecium and other unicellular organisms eliminates waste.
analyze (analysis/plural-analyses) - to separate into parts in order to determine what something is or how it works; to examine in detail.
anatomy - study of the structure of the body.
anemometer - instrument used to measure wind speed.
angiosperm - plant that has flowers and produces seeds enclosed in fruit.                                                                       
Animalia (Animal) - kingdom made up of complex, multicellular organisms that lack cell walls, can usually move around, and
quickly respond to their environment. 
anion - atom that has gained electrons; a negative ion.  
anther - part of the stamen that produces pollen.                                                                                                                                          1
anthracite - hard, brittle coal that is almost pure carbon.
antibiotic - substance produced by helpful bacteria that destroys or weakens disease-causing bacteria.
antibody - substance produced in and by the body that protects against specific disease infections.                               
anticline - upward fold in a rock layer.
anticyclone - rotation of air around a high-pressure center in the direction opposite to Earth’s rotation.    
antigen - any foreign substance that causes an immune response.
aorta - largest artery in the body.
aphelion - in the orbit of a planet or other body in the solar system, the point that is farthest from the sun.
apogee - point of the moon’s orbit farthest from the Earth.
apparent magnitude - brightness of a star as it appears from Earth.
aqueous - solution containing water.
aquifer - body of rock or sediment that stores groundwater and allows the flow of groundwater.
Archaean (plural-Archaea) - kingdom made up of unicellular prokaryotic cells that can survive in extreme environments.
archeology (archaeology) -  study of the cultural remains of ancient people.
archipelago - group or chain of islands clustered together in a sea or ocean.
area - a measure of the size of a surface or a region.
artery - blood vessel that carries blood away from the heart.
artesian spring - spring whose water flows from a crack in the cap rock over the aquifer.
artificial satellite - any human-made object placed in orbit around a body in space.
arthropod - invertebrate animal with an exoskeleton, a segmented body, and jointed legs.
asexual reproduction - formation of an organism from a single cell; form of reproduction in which new individuals             are formed
without the involvement of gametes. 
assumption (assume) - is something taken for granted or accepted as true without proof.
asteroid - tiny chunks of rock of varying sizes that orbit the sun.
asteroid belt - area in space where hundreds of thousands of asteroids orbit the sun between Mars and Jupiter.
asthenosphere - solid, plastic layer of the mantle beneath the lithosphere; layer made of rock that flows very slowly,
which allows tectonic plates to move on top of it.
astronomical unit (AU) - average distance from Earth to the sun, which is used to measure vast distances in space.             (approximately 150 million kilometers)   
astronomy - study of planets, stars and other objects beyond the Earth.
atmosphere - mixture  of gases that surround Earth, other planets, moons or stars.
atoll - ring of coral reefs that surrounds an island that has sunk beneath the waves.
atom - tiny particle of matter consisting of a nucleus that contains protons and neutrons and an electron cloud that contains
electrons; the smallest unit of a chemical element that can still retain the properties of that element; building block of
atomic mass - average of the masses of all the existing isotopes of an element.
atomic mass unit (amu) - unit used to measure the masses of subatomic particles; a proton has a mass of one amu.
atomic number - number of protons in the nucleus of an atom; number that identifies the kind of atom; the number determines an
element’s placement on the periodic table. 
ATP - see adenosine triphosphate.
atrium (plural-atria) - upper heart chamber.
aurora - bands of light given off by collisions of particles in the Earth’s upper atmosphere.
autotroph  - organism that makes its own food from simple substances; producer; an organism that captures energy           from sunlight
and uses it to produce energy-rich carbon compounds, usually through the process of photosynthesis.
autumnal equinox - first day of autumn. (September 20 or 21)
average speed - distance traveled divided by the time it takes to travel this distance.
axis (plural-axes) - imaginary line drawn through the center of a body around which the body rotates or spins; a reference to the
line in a coordinate system or graph. 
bacillus (plural-bacilli) - rod-shaped bacterium.
background radiation - energy left from the big bang that is spread evenly throughout the universe.
Bacteria - kingdom made up of unicellular prokaryotic cells that usually have a cell wall and reproduce by binary fission. 
bacteriophage - virus that infects bacterial cells.
bacterium (plural-bacteria) - unicellular, heterotrophic microorganism containing no nuclear membrane.
balanced forces - describes forces acting on an object that cancel each other.
bar graph - tool that uses bars to show the relationships between variables; can be horizontal or vertical and can display any
numerical data.                                                                                                                                               
barometer - instrument that measures air pressure in the atmosphere.
barrier island - long ridge of sand or narrow island that develops parallel to a coast as a sandbar builds up above the water’s
barrier reef - type of coral reef that is separated from the shore by a lagoon.
base - substance that increases the OH­- concentration of a solution; a proton acceptor.­ 
batholith - huge, irregularly shaped intrusion that extends deep in the Earth’s crust.                                                                          2
bathyal zone - open-ocean zone that extends from a continental slope down about 2 000 meters.
bay - body of water that is partly enclosed by land.
beach - area of the shoreline that is made up of deposited sediment.
bedrock - layer of rock beneath soil.
behavior - organism’s action in response to a stimulus.
benthic - region near the bottom of a pond, lake, or ocean.
benthos - organisms that live at the bottom of oceans or bodies of fresh water.
bias - preference for a person or thing that interferes with impartial judgment; a prejudice.
big bang theory - states the universe was formed by the explosion of a small amount of very dense and hot matter.
bile - substance produced by the liver that aids in digestion.
binary fission - form of asexual reproduction for prokaryotic cells such as bacteria.
binary star - double star system in which two stars revolve around each other.                                                                   
binomial nomenclature - naming system in which organisms are given two names:  a genus and species.
biodiversity - existence of a wide range of different species in a given area or specific period of time.
biology - study of life and all living things; ecology, zoology, and botany are examples of biological sciences.
biomass - plant material, manure, or any other organic matter that is used as an energy source.
biomes - large geographic areas with similar climates and ecosystems; the six most common are tundra, taiga, temperate forest,
tropical rain forest, grassland, and desert; a complex biotic community characterized by the interaction of living
organisms and climatic factors. 
biosphere -  all living organisms on Earth in the air, on the land, and in the waters; the part of Earth where life exists.
biotic factor - living thing in an ecosystem; describes the living part of the environment relating to, caused by, or
produced by living organisms. 
bituminous - dark brown or black coal found deep within the Earth and called soft coal.
black hole - core of a very massive star that remains after a supernova explosion.
blizzard - blinding snow storm with winds of at least 56 km/hr, usually with temperatures below -7 oC.
blue shift - shift toward the blue end of the spectrum of a star moving toward the Earth.
boiling - process in which particles of a liquid change to gas, travel to the surface of the liquid and then into the air.
boiling point - temperature at which a liquid boils.
bone - hard stiff material containing the minerals calcium and phosphorus.
botany - study of plants.
Boyle’s Law - law stating that the volume of a fixed amount of gas varies indirectly with the pressure of the gas.
bronchus (plural-bronchi) - tube that branches off from the trachea.
budding - reproductive process in yeast, in which a new yeast cell is formed from a tiny bud.
butte - flat-topped rock or hill formation with steep sides.
caldera - large, circular depression that forms when the magma chamber below a volcano partially empties and causes the ground
above to sink.
calorie - unit of energy; the amount of heat needed to raise one gram of water one degree Celsius at standard atmospheric pressure.
canyon - deep valley with very steep sides—often carved from the Earth by a river.
cape - pointed piece of land that sticks out into a sea, ocean, lake or river. 
capillary - tiny thin-walled blood vessel.
carbohydrate - organic compound made up of the elements carbon, hydrogen and oxygen, and a main source of energy for living
things; include sugars and starches used for energy or as structural materials.
carbonation - process in which carbonic acid reacts chemically with another substance.
carbon cycle - continuous movement of carbon through Earth, its atmosphere, and the living things on Earth.
cardiac muscle - muscle found only in the heart.
carnivore - animal or plant that consumes or obtains nutrients from animals. 
carrying capacity - maximum size that a population can reach in an ecosystem.
cartilage - strong, flexible connective tissue that supports such structures as the nose and ears.
catabolic (catabolism) - breaking down process.
cast - type of fossil that forms when sediments fill in the cavity left by a decomposed organism.
catalyst - substance that speeds up or slows down chemical reactions, but is not itself changed by the reaction; a substance that
speeds up or slows down the rate of a reaction without being consumed or altered. 
cation - atom that has lost electrons; a positive ion.  
cause - reason for an action or a condition.
cavern - cave.                                                                                                                                                                                                
cell - smallest, basic unit of structure and function in a living thing; building block of life.
cell membrane - thin, flexible envelope of protoplasm that forms the outer covering of an animal cell and that is inside the cell
wall of a plant cell; controls movement of materials into and out of the cell.
cell theory - major theory based on observations and conclusions by many scientists that states that the cell is the basic unit of life,
organisms are composed of one or more cells, and all cells come from other cells.
cellular respiration (respiration) - process in which cells use oxygen to release energy stored in sugars.
cellulose - forms the rigid cells walls of plants; organic compound made of long chains of glucose molecules.                               3
cell wall - outermost boundary of plant and bacterial cells.
Celsius (oC) - temperature scale used in the metric system at which water freezes at 0o and boils at 100o.
cementation - process by which sediments are cemented together by minerals dissolved in water to form sedimentary rock.
centrifugal - motion away from the center of axis. 
centrioles - one of the two tiny parts found in the centrosome composed of microtubules.
centripetal force - inward  force on a particle or object moving in a circular path.
centrosome - small organelle just outside the nucleus that contains the centrioles and is involved with mitosis.
cepheid variable - pulsating variable star; star that varies in brightness and size.
chain of infection - series of infections that is directly or immediately connected to a particular source.
change of state - physical change that occurs when matter changes to another state. 
channel - path that a stream follows.
characteristic - property, feature, quality or trait that describes an object.
Charles’s Law (Charles’) - law stating that the volume of a fixed amount of gas varies directly with the temperature of the gas.
chemical change - change a substance undergoes when it turns into another substance.                                                     
chemical digestion - breaking down of food by enzymes.
chemical energy - energy that is stored in the chemical composition of matter; the energy released when a chemical compound
reacts to produce new compounds. 
chemical equation - description of a chemical reaction using symbols and formulas.
chemical formula - combination of chemical symbols used as a shorthand for the names of chemical substances.
chemical property - property that describes a substances ability to change into another substance.
chemical reaction - process by which a substance is changed into another substance through a rearrangement or new combination
of its atoms.
chemical rock - sedimentary rock formed from large amounts of minerals when a body of water dries up.
chemical symbol - shorthand way of representing the elements; usually consists of one or two letters, the first of which is always
capitalized, but the second is never capitalized.
chemical weathering - breakdown and alteration of rocks at or near Earth’s surface as a result of chemical           processes. 
chemistry - study of what substances are made of and how they change and combine.
chlorofluorocarbons (CFCs) - group of chemical compounds used in refrigerators, aerosol sprays, and foam packaging that
destroy ozone molecules.
chlorophyll - green substance needed for photosynthesis.
chloroplast - large, irregularly shaped organelle that contains the green pigment needed for photosynthesis.
chordate - animal with a notochord, a dorsal hollow nerve cord, and gill slits.
chromatin - material that makes up the chromosomes found in the nucleus.
chromosome - thick, rod-like object found in the nucleus that directs the activities of the cell and passes on the traits of the cell to
new cells.
chromosphere - middle layer of the sun’s atmosphere.
cilium (plural-cilia) - small, hair-like projection on the outside of a cell used for movement.
cinder - small volcanic bomb about the size of a golf ball.
cinder cone - volcano made mostly of cinders and other rock particles that have been blown into the air.
circle graph - tool used to show the parts of a whole.
circuit - interconnection of electrical elements forming a complete path for the flow of current. 
circulatory system - body system that transports materials.
cirrus cloud - feathery, fibrous cloud that forms at a very high altitude.
class - classification group between phylum  and order.
classification - is the grouping of living things according to similar characteristics.
classification key - system for identifying organisms by using pairs of descriptions.
classify - to group information, objects, or ideas based on their similarities.
clastic rock - sedimentary rocks made up of rock fragments mixed with sand, clay and mud.
cleavage - breakage of a mineral along definite lines or smooth, flat surfaces.
cliff - steep face of rock and soil.                                                                 
climate - pattern of weather that occurs in a particular 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.
climax community - community that has reached the final stage of ecological succession.
cloud - collection of small water droplets or ice crystals suspended in the air, which forms when the air is cooled and condensation
cnidarian - invertebrate animal that has a body with radial symmetry, tentacles with stinging cells, and a central internal cavity.
coal - fossil fuel that forms underground from partially decomposed plant material.
coastal plain - low, flat area along the coast.
coastline - location where land and ocean surface meet.
coccus (plural-cocci) - sphere-shaped bacterium.
coefficient - number placed in front of a chemical formula in a chemical equation so that the equation is balanced.                               4
cold - is the absence of heat.
cold-blooded - having a body temperature that can change somewhat with changes in the temperature of the environment.
cold front - type of front that forms when a mass of cold air meets and replaces a mass of warm air.
colonial - unicellular organisms that live independently but clustered side by side.
coma - cloud of gas and dust surrounding the nucleus of a comet.
comet - object made of ice, gas and dust that orbits the sun.
commensalism - interaction between two species in which one species benefits without harming the other.
communicable - capable of spreading from one diseased person or animal to another person or animal, either directly or   indirectly.
communications satellite - artificial satellite that beams television programs, radio messages, telephone conversations, and other                 information all over the world.
community - all the populations of organisms belonging to different species and sharing the same geographical area.
compaction - process by which layers of sediments are pressed together to form sedimentary rock.
competition - struggle among living things to get the proper amount of food, water and energy from the environment.
composite volcano - volcano built up of alternating layers of rock particles and lava
composition - chemical makeup of a rock; describes either the minerals or other materials in the rock.           
compound - substance made up of molecules that contain more than one kind of atom; two or more elements chemically
combined; a substance made up of at least two different elements held together by chemical bonds          that can only be
broken down into elements by chemical processes. 
compound light microscope - microscope containing more than one lens that uses light to make an object look larger.
compound machine - combination of two or more simple machines.
compression - stress that occurs when forces act to squeeze an object.
compressional wave - wave in which matter in the medium moves forward and backward in the same direction the wave travels.
concentration - relative amount of a particular substance, a solute, or mixture.   
conclusion - summary of the results of the experiment where data is analyzed to determine the meaning of what
happened in the experiment.
condensation - process in which a gas loses heat energy and changes into a liquid; the act of making more dense or compact. 
conditioning - process in which behavior is modified so that a response associated with one stimulus becomes associated with
another stimulus.
conduction - transfer of energy that occurs when molecules bump into each other; the transmission of heat through a medium and
without the motion of the medium;  the process by which energy is transferred from a warmer object to a cooler object by
means of physical contact.
conifer - cone-bearing trees and shrubs that usually keep their leaves or needles during all the seasons of the year.
conjugation - type of sexual reproduction in unicellular organisms in which hereditary material is exchanged.
conservation - controlled use and/or maintenance of natural resources; the wise use of and preservation of natural resources.
conservation of energy - states that energy cannot be created nor destroyed but only changed from one form to another. 
conservation of mass (conservation of matter) - states that mass cannot be created or destroyed. 
constant - factor in an experiment that does not change.
constellation - group of stars in which people thought they saw imaginary figures of animals or people; a star pattern identified
and named as a definite group. 
constructive boundary - type of plate boundary where new material is added to the plates.
consumer - organism that feeds on other organisms for food.  (heterotroph)
contact metamorphism - type of metamorphism that occurs when rocks are heated by contact with magma or lava. 
continental climate - climate that occurs in the interior of a continent, with large temperature differences between seasons.
continental crust - section of the Earth’s crust that makes up the Earth’s landmasses.
continental drift (theory of continental drift) - states that the continents once formed a single land mass, broke up, and drifted to
their present locations.
continental glacier - large, slowly moving sheets of ice that can cover an entire continent.
continental polar - cold, dry air mass that forms over northern Canada.
continental rise - gently sloping section of the continental margin located between the continental slope and the abyssal plain.
continental shelf - gently sloping section of the continental margin located between the shoreline and the continental slope.
continental slope - steeply inclined section of the continental margin located between the continental rise and the continental           shelf.
continental tropical - dry, hot air mass that forms over Mexico in the summer.
contractile vacuole - cell organelle that pumps excess water out of the cell.
control (controlled variable) - standard used for comparison in an experiment; experiment run exactly the same way as the
experiment with the variable, but the variable is left out.
convection - transfer of heat energy by the circulation or movement of gases or liquids; the movement of matter due to
differences in density that are caused by temperature variations. 
convection current - any movement of mater that results from differences in density; may be vertical, circular, or cyclical.
convergent boundary - area where two tectonic plates collide. 
cooperation - interaction between two or more living things in which they work together.                                                                                5
coral reef - limestone structure built from the shells of coral animals in war, shallow ocean waters.
core - central part of the Earth below the mantle.
Coriolis effect - curving of the path of a moving object from an otherwise straight path due to the Earth’s rotation.
corona - outermost layer of the sun’s atmosphere.
cosmology - study of the origin, properties, processes, and evolution of the universe.
covalent bond - chemical bond between two atoms of the same or different elements in which each atom shares an electron.   
crater - bowl-shaped depression that forms on the surface of an object when a falling body strikes the object’s surface or when an
explosion occurs.
creep - slow downhill movement of weathered rock material.
crest - highest point of a wave. 
crevasse - crack on the surface of a glacier.
crust - thin, solid, outermost layer of the Earth covering the mantle. 
cryosphere - frozen part of the Earth’s surface; includes the polar ice caps, continental ice sheets, glaciers, sea ice, and permafrost. 
crystal - natural solid substance that has a definite geometric shape.
crystalline solid - solid made up of crystals.
cumulonimbus cloud - large cloud that produces thunderstorms.         
cumulus cloud - puffy cloud with a flat bottom that forms at an altitude of 2.4 to 13.5 kilometers.                          
cycle - series of events or actions that repeat themselves regularly; a physical and/or chemical process in which one material
continuously changes locations and/or forms.
cyclic behaviors - innate behaviors, such as migration or hibernation that occur in a repeated pattern, often in response to changes
in the environment.
cyclone - area in the atmosphere that has lower pressure than the surrounding areas and has winds that spiral toward the center.
cytology - study of cells.
cytoplasm - thick, gelatin-like substance outside the nucleus; holds the organelles.
data table - tool used to display information in rows and columns so that it is easier to read and understand.
datum (plural-data) - recorded observations and measurements; information gathered by observation or experimentation that can
be used in calculating or reasoning.
day - time required for Earth to rotate once on its axis.
deciduous - trees and shrubs that drop their leaves when winter comes.
decomposer - any organism that feeds or obtains nutrients by breaking down organic matter from dead organisms. 
deep current - stream-like movement of ocean water far below the surface caused by differences in density.
deep-water zone - zone of a lake or pond below the open-water zone, where no light reaches.
deflation - form of wind erosion in which fine, dry soil particles are blown away.
deforestation - removal of trees and other vegetation from an area.
deformation - bending, tilting, and breaking of Earth’s crust; the change in the shape of rock in response to stress.
dehydration - excessive loss of water.
delta - buildup of sediment deposited in a triangular or fan shape at the mouth of a river or stream.
density - mass per unit volume, or how much mass is contained in a given volume of an object; number of individuals in the same
species that live in a given area.                                                                                                                   
deoxyribonucleic acid (DNA) - nucleic acid that stores the information needed to build proteins and carries genetic             information
about an organism; present in all cellular organisms. 
dependent variable - factor being measured or observed in an experiment;  a factor that responds to, or depends on, other factors;
factor that changes as a result of manipulation of one or more independent variable.  (outcome variable)
deposition - natural process by which sediments are laid down in new locations.   
dermis  - lower layer of skin.
desalination - process of removing salt from ocean water.
desert - driest biome on Earth; receives less than 25 cm of rain each year and supports little plant life.
desertification - process by which human activities or climatic changes make areas more desertlike.
desert pavement - is a layer of gravel and larger stones left behind when dry winds blow away fine grained sediments.
desert soil - soil found in dry regions that contains a large quantity of minerals.
destructive boundary - type of plate boundary where plate material is subducted.
development - act, process or result of maturing.
dew point - at constant pressure and water vapor content, the temperature at which the rate of condensation equals the rate of
diaphragm - muscle at the bottom of the chest that aids in breathing.
dichotomous key - series of questions, each with only two answers, that can be used to help identify an organisms genus and
differential weathering - process by which softer, less weather resistant rocks wear away at a faster rate than harder, more
weather resistant rocks do.
diffraction - bending of waves around a barrier (or obstruction) or traveling through an opening.  
diffusion - process by which food, oxygen, water and other materials enter and leave a cell through openings in the cell
membrane; the movement of molecules from where they are crowded to where they are less crowded.                        6
digestion - process by which food is broken down into simpler substances.
digestive system - body system that breaks down the food into simple substances.
dike - narrow, flat formation of igneous rock formed in vertical cracks in the existing rocks.
direct transmission - transmitting disease organisms in which the agent moves immediately from the infected person to the
susceptible person, as in person-to-person contact.
disease - illness of the body or mind that interferes with a person’s ability to function normally.
dislocation - forcing a bone out of joint.
divergent boundary - type of plate boundary where the plates move apart, such as a midocean ridge.
diversity - quality of having many differences.
divide - boundary between drainage areas that have streams that flow in opposite directions.
division - in the taxonomy of plants, the group smaller than a kingdom but larger than a class.
division of labor - division of the work that keeps an organism alive among the different parts of its body.
doldrums - is the windless zone of the equator.
domain - one of three divisions in a classification system based on different types of cells:  archaea, bacteria, and eukarya.
dome - raised area shaped roughly like the top half of a sphere created by rising magma.
dome mountain - dome that has been worn away in places to form many separate peaks.
dominance - tendency of certain (dominant) alleles to make the expression of their corresponding (recessive) alleles.
Doppler effect - apparent change in the wavelengths of light that occurs when an object is moving toward or away from the Earth.
drainage basin - area drained by a main river and its channels.
drainage system - network of rills, gullies, and streams that forms a river.
drumlin - oval-shaped mound of till.
ductility (ductile) - ability of a substance to be pulled into thin strands without breaking.
dune - mound of sand built up by wind.
dwarf planet - celestial body that orbits the sun, is round because of its own gravity, but has not cleared its orbital path; celestial
body similar to a planet but orbiting in a zone that has many other objects in it.
earthquake - shaking of the ground caused by a sudden release of energy in the Earth’s crust along a fault.
Earth system - all of the nonliving things, living things, and processes that make up the planet Earth, including the solid Earth, the
hydrosphere, the atmosphere, and the biosphere.
echinoderm - invertebrate sea animal with a spiny skeleton, a water vascular system, and tube feet.
eclipse - total or partial blocking out of the sun or moon by a shadow.
ecological succession - process of gradual change from one community of organisms to another.
ecology - study of how living things interact with each other and their environment.
ecosystem - integrated unit of a biological community, its physical environment, and interactions. 
ectotherm - animal whose body temperature changes with environmental conditions.
edema - too much water.                                                                                                                                                                   
efficiency - ability of a machine to convert work input to work output; always less than 100 percent in real machines due to some
loss to friction or heat;  a machine’s output work divided by its input work and multiplied by 100.
effort force (Fe) - force applied to a machine.
elastic rebound - sudden return of elastically deformed rock to its undeformed shape.
electromagnet - magnet consisting of a coil of wire wrapped around a core that becomes strongly magnetized when            current flows
through the coil producing a magnetic field. 
electromagnetic radiation - emission and propagation of the entire range of electromagnetic spectrum including:  gamma rays,
x-ray, ultraviolet radiation, visible light, microwaves, and radio waves. 
electromagnetic spectrum - arrangement of different forms of light in order of increasing frequency and decreasing           wavelength.
electromagnetic wave - transverse wave that does not need a medium to travel; whose speed in a vacuum is 300 000 km per
second and has varying wavelengths and frequencies; waves generated by the oscillation of a charged particle and
characterized by periodic variations of electric and magnetic fields. 
electron - negatively charged particle that moves around the nucleus of an atom in a region called the electron cloud.
electron cloud - space in which electrons are most likely to be found.
electron microscope - microscope that uses a beam of electrons to magnify the image of an object.
element - pure substance made up of only one kind of atom that cannot be broken down into simpler substances by ordinary
chemical changes. 
elevation - height of an object above sea level.                                                                                                            
ellipse - oval orbit.
elliptical galaxy - oval-shaped galaxy.
elliptical orbit - oval or egg-shaped orbit.
El Nino - disturbance of wind patterns and ocean currents in the Pacific Ocean that causes temporary climate changes in many
parts of the world.
embryo - multicellular organism in its earliest stages of development.
emotion - strong feeling.                                                                                                                                                                                   7

empirical evidence - observations, measurement  and other types of data that people gather and test to support and evaluate
scientific explanations.
endocytosis - into the cell.
endoplasmic reticulum (ER) - maze of clear tubular passageways that leads out from the nuclear membrane; involved in the
manufacture and transport of proteins.
endoskeleton - internal system of bones that protects and supports an animal’s internal organs and also provides a place for muscle
attachment; skeleton inside the body.
endospore - oval-shaped structure that protects a bacterium.
endotherm - animal that maintains a constant body temperature.
endothermic reaction - chemical reaction that absorbs energy.
energy - capacity for work; a source of usable power. 
energy conversion - change from one form of energy to another.
energy efficiency - measurement of useable energy after an energy conversion; the ratio of useable energy to the total energy after
an energy conversion.
energy level - most likely location in the electron cloud in which an electron can be found.
energy pyramid - pyramidal diagram that compares the amount of energy available at each position, or level, in the          feeding order; 
                a model used to show the amount of energy available to living things in an ecosystem.
energy resource - natural resource that humans use to generate energy.
energy transfer - change of energy from one form to another. 
engineering - application of science and mathematics to solve real-life problems.
entropy - measure of randomness or disorder of a closed system. 
environment - sum of conditions affecting an organism, including all living and nonliving things in an area, such as plants,
animals, water, soil, weather, landforms, and air. 
enzyme - special type of protein that regulates chemical activities within the body.
epicenter - place on the Earth’s surface directly above the focus of an earthquake.
epidermis - outermost layer of the skin.
epiglottis - small flap of tissue that closes over the windpipe.
equator - imaginary line at 0o latitude that circles the Earth halfway between the north and south geographical poles           and divides
the Earth into two equal halves. 
equinox - occurs twice yearly when the sun appears to cross the celestial equator, with the result that day and night are the same
length all over the world; the vernal equinox occurs March 20 or 21 and the autumnal equinox occurs September 20 or 21.
erosion - process of wearing away of the Earth’s surface by breaking down and carrying away soil, rock, or sediment by wind,
water, ice or gravity. 
esophagus - pipe-shaped tube that transports food to the stomach.                                                                                   
esteem - favorable regard; respect.
estimation - method of making a rough measurement.
estivation - behavioral adaptation for survival during hot, dry summer months, during which an animal becomes inactive; in
amphibians, involves hiding in cooler, more humid ground.
estrogen - hormone produced by ovaries; responsible for the development and growth of secondary sex characteristics in females.
estuary - shoreline area where fresh water from a river mixes with salt water from the ocean.
euglena - microscopic, unicellular Protist that is usually green and moves using a flagellum (pl-flagella.)
Eukarya - domain made up of all eukaryotes.
eukaryotic cell (eukaryotes) - more complex type of cell with a true nucleus.  (kingdoms:  Protista, Fungi, Plantae, and Animalia)
eutrophication - increase in the amount of nutrients, such a nitrates, in a marine or aquatic ecosystem.
evaporation - process in which a liquid changes into a gas by absorbing heat energy, usually at the surface. 
evaporite - sedimentary rock formed when water evaporates and leaves behind mineral deposits.
evidence - thing or things helpful in forming a conclusion or judgment. 
excretion - process of getting rid of waste materials.
excretory system - body system that removes body wastes.
exfoliation - breaking off of pieces of rocks that are parallel to the rock’s surface.
exhale - to breathe out.
exocytosis - out of the cell.
exoskeleton - lightweight body covering that protects and supports an arthropod’s body, prevents it from drying out, and is shed
by molting; a hard outer covering.
exosphere - upper atmosphere.
exothermic reaction - chemical reaction that releases energy.
experiment - organized procedure that is carried out and repeated under controlled conditions in order to discover, demonstrate, or
test a hypothesis; includes all components of the scientific method. 
experimental bias - error that distorts results in a particular way; something that causes certain outcomes to be favored over
extended family - parents, children, and other relatives such as grandparents, aunts, uncles, and so forth.
extensor - muscle that straightens a joint.                                                                                                                                                    8
extinction (extinct) - permanent disappearance of a species.
extrusion - igneous rock formation that forms on the Earth’s surface.
extrusive rock - igneous rock formed from melted rock or lava that cools and hardens at or near the Earth’s surface.
eyespot - light-sensitive organelle in lower organisms.
fact - quality of being real or actual.
family - classification group between order and genus; the oldest and most basic social unit.
fat - energy-rich organic compound made up of carbon, hydrogen and oxygen, that is solid at room temperature.
fault - crack or break in the Earth’s crust along which one block moves relative to another.
fault-block mountain - mountain formed by a block of rock uplifted by a normal fault.
fermentation - energy-releasing, chemical process in which sugars and starches are changed into alcohol and carbon dioxide when
no oxygen is present.
fern - seedless, vascular, fringe-leafed plant that grow in cool, wooded environments.
fertilization - joining of egg and sperm to make a new cell.
fiber - structure that resembles a thread; it can be a strand of nerve tissue or a cell that is threadlike.
fibrin - substance that traps blood cells and plasma, forming a scab.
first aid - emergency medical care for someone who has been hurt or who is sick.
first law of thermodynamics - states the internal energy in a system remains constant and the change in thermal energy of a
system is equal to the work done on the system.
fjord - long, narrow sea inlet that is bordered by steep cliffs.
flagellum (plural-flagella) - whip-like structure that propels some one-celled organisms.
flammability - ability to burn.
flexor - muscle that bends a joint when it contracts.
floodplain - area along a river that forms from sediments deposited when the river overflows its banks.
flower - reproductive structure of an angiosperm, containing male and female parts.
focus (plural-foci or focuses) - point beneath the Earth’s surface where rocks first break and move during an earthquake.
folding (fold) - bending of rock layers due to stress; (bend in a rock.)
foliated rock - texture of some metamorphic rocks in which mineral crystals are arranged in parallel bands along which the rocks
tend to break.
food chain - transfer of energy through various stages as a result of feeding patterns of a series of organisms.              
food vacuole - spherical part that forms from pseudopods that engulf and digest captured food.                                
food web (food cycle) - interconnected feeding relationships in a food chain found in a particular place and time.
foot wall - block of rock below a fault.
force - quality that tends to produce movement or acceleration of a body in the direction of its application; push or a         pull; can be
measured by the amount of acceleration it can give a mass;  has size and direction.
forest soil - soil that forms under a cover of leaves and other plant remains and contains very little humus.
fossil - remains or traces (whole or part) of past plant and animal life that has been preserved in sedimentary rock. 
fossil fuel - nonrenewable energy resource that began to form millions of years ago from remains of once-living plants and
animals; provides energy and includes coal, oil, and natural gas. 
fossil record - historical sequence of life indicated by fossils found in layers of Earth’s crust.
foster family - child care provided in a family setting by non-biological parents.
fracture - mineral breakage that forms an irregular surface that may be rough or jagged; a bone break.
freezing - change of a liquid to a solid.
freezing point - temperature at which a liquid changes to a solid.
freezing rain - rain that freezes when it hits the ground or another surface and coats the surface with ice.
frequency - number of waves that pass a given point in one second; measured in waves per second, or hertz (Hz). 
friction - force that resists motion between two objects in contact and that always acts opposite to the direction of motion.
fringing reef - type of coral reef that touches the shoreline of a volcanic island. 
front - boundary between air masses of different densities and usually different temperatures.
frost action - mechanical weathering process caused by the repeated freezing and melting of water.
fruit - ripened ovary of a flowering plant that contains the seeds.
fulcrum - pivot point of a lever. 
full moon - phase of the moon when the entire lighted side of the moon is visible.
function - special, normal, or proper activity of an organ or part. ( job; what it does; physiology)
Fungus (plural-Fungi) - kingdom made up of multicellular eukaryotic cells that have no movement, reproduce by              spores, and
get food by breaking down substances to absorb the nutrients.             
galaxy - large collection of stars, gases, and dust that are part of the universe bound together by gravitational forces.
(EX - Milky Way) 
gall bladder - organ in the digestive system that stores bile.
gamete - sex cell:  the egg or the sperm.
gamma ray - electromagnetic radiation with wavelengths shorter than those of x-rays and having greater energy and penetrating
gas - phase in which matter has no definite shape or volume.                                                                                                              9
gas giant - planet that has a deep, massive atmosphere, such as Jupiter, Saturn, Uranus, or Neptune. 
gasohol - mixture of gasoline and alcohol that is used as a fuel.
gem - rare, very valuable and beautiful mineral.
gene - specific part of a chromosome or sequence of DNA that determines a particular feature or characteristic in an organism. 
genetic material - nucleic acid (DNA) that is present in all living cells and contains the information needed for a cell’s growth,
maintenance, and reproduction.
genotype - sum total of the genetic information contained in an organism. 
genus (plural-genera) - group of organisms that are closely related; classification group between family and species.
geocentric - Earth-centered.
geologic column - ordered arrangement of rock layers that is based on the relative ages of the rocks and in which the oldest rocks
are at the bottom.
geology - study of the Earth’s origin, history, and structure.
geologist - scientist that studies the Earth’s origin, history, and structure.
geosphere - all the features on Earth’s surface and everything below the surface; the mostly solid, rocky part of the Earth; extends
from the center of the core to the surface of the crust.
geostationary (geosynchronous) orbit - orbit that is about 36 000 km above Earth’s surface and in which a satellite is above a
fixed spot on the equator; orbit in which a satellite moves at a speed that exactly matches the Earth’s rate of rotation.
geothermal energy - energy produced from the heat energy within the Earth that can be used to generate electricity.
germ - microorganism, especially one that causes disease.
germination - 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 - natural hot spring that occasionally sprays water and steam above the ground.
giant star - star with a diameter 10 to 100 times as large as the sun.
gill - respiratory organ that filters oxygen dissolved in water.
glacial drift - rock material carried and deposited by glaciers.
glacier - large mass of moving ice and snow that exists year round.                                                                                  
Global Positioning System (GPS) - determines the position, speed, and direction of a person anywhere on Earth.
global warming - rise in global temperatures because of the increase of greenhouse gases in the atmosphere.
global wind - wind that travels long distances in steady patterns over several weeks.
globular cluster - stars grouped in huge spherical clusters.
Glossopteris - extinct seed fern that grew about 250 million years ago.
glucose - simple sugar into which all carbohydrates are broken down in the body to produce energy.
Golgi apparatus (body) - secretory structure consisting of a stack of flat sacs that store and convert or modify proteins.
gram (g) - basic unit of mass in the metric system.  (kilogram is commonly used instead of gram)
graph - diagram that shows the relationship; tool used to collect, organize, and summarize data in a visual way so that it is easy to
use and understand.
grasslands - temperate and tropical regions that receive between 25 cm and 75 cm of precipitation each year and are dominated by
climax communities of grasses.
grassland soil - very rich, fertile soil that is excellent for growing crops.
gravity - force of attraction between objects that is due to their masses. 
greenhouse effect - heat-trapping process in which heat becomes trapped by cloud layers and cannot escape back into space; 
warming of the surface and lower atmosphere of Earth that occurs when water vapor, carbon dioxide, and other gases
absorb and reradiate thermal energy;  prevents Earth from being too cold to support life.
greenhouse gases - gases, such as carbon dioxide and methane, that absorb and give off infrared radiation as part of         the
greenhouse effect.
groundwater - water that soaks into the ground and collects in the small spaces between bits of rock and soil.
growth - stage in the process of growing; a measure of progressive development.
gulf - part of the ocean that is partly surrounded by water.  (larger than a bay)
gullet - funnel-shaped structure in the paramecium and other unicellular organisms.
guyot - flat-topped seamount.
gymnosperm - plant that produces seeds that are not enclosed in flowers or fruit.
habitat - place in an ecosystem where an organism normally lives;  the natural environment in which a living thing gets all that it
needs to live.
hail - layered lumps or balls of ice that fall from cumulonimbus clouds.
half-life - amount of time required for half of an original sample of radioactive material to decay or undergo radioactive
halophile - Archaea that tolerate salty surroundings.
hanging wall - block of rock above a fault.
harbor - sheltered area of water where ships may anchor safely.
hardness - ability of a mineral to resist being scratched.
hard water - water containing large amounts of dissolved minerals.
Haversian canal - passageway running through the thick bone, containing blood vessels and nerves.                                       10
heat - transfer of energy from an object with a higher temperature to an object with a lower temperature. 
heat of fusion - amount of heat energy required to convert a unit mass of substance from a solid to a liquid           through melting at a
constant temperature and pressure. 
heat of vaporization - amount of heat energy needed to change a unit mass of substance from a liquid to a gas at its boiling point.   
heliocentric -  sun-centered.
hemisphere - northern or southern half of the Earth.
hemoglobin - iron-containing substances in red blood cells.
herbivore - animal that eats only plants. 
heredity - passing of genetic traits from parent to offspring.
Hertzsprung-Russell diagram (H-R diagram) - chart of the relationship between the absolute magnitude and the surface
temperature of stars.
heterotroph - organism that is not able to make its own food and thus feeds on other organisms; consumer.
heterozygous - cell or organism that has two different alleles for a particular trait. 
hibernation - behavioral adaptation for survival during cold, winter months, where an animal becomes inactive and           its metabolic
needs are lowered; in amphibians, involves burying themselves in mud or leaves until temperatures become warmer.
high-pressure system - usually calm and clear weather system that forms when air sinks down and spreads out toward areas of
lower pressure as it nears the ground.
high tide - bulge in the ocean on the side of the Earth facing the moon and on the opposite side.
hill - raised area or mound of land.
homeostasis - ability of an organism to keep conditions inside its body the same even though conditions in its external        environment change.
homozygous - cell or organism that has identical rather than different alleles for a particular trait.                            
horizon - line where the sky and the Earth appear to meet.
hormone - chemical substance made in the body that triggers a specific response, such as growth.
host - organism in which a parasite lives; a person or organism in whom an infectious pathogen can live and multiply.
host cell - cell that a virus infects and uses to make copies of itself.
hot spot - volcanically active area of Earth’s surface, commonly far from a tectonic plate boundary.
humidity - amount of water vapor in the air.
humus - dark, organic material formed in soil from the decayed remains of plants and animals.
hurricane - large, swirling, low-pressure system that forms over tropical oceans and has winds of at least 120 km per hour.
hydroelectric energy (power) - production of electricity by the flow of water.
hydrosphere - all of the water on the Earth; 97 percent is salt water and only 3 percent is fresh water.
hypha (plural-hyphae) - threadlike tubes that form the structural parts of the body of a fungus.
hypothesis (plural-hypotheses) - suggested solution or prediction to a scientific problem; “educated” guess; testable idea or
explanation that leads to scientific investigation.
ice age - period of time during which surface temperatures drop significantly and huge ice sheets spread out beyond the polar
ice core - long cylinder of ice obtained from drilling through ice caps or ice sheets; used to study past climates.
igneous rock - type of rock formed from cooled and hardened magma or lava. 
immune system - human body’s network of cells and organs that produce disease-fighting antibodies.
immunity - body’s ability to resist infection.


impermeable membrane - when materials will not pass through a membrane.
imprinting - type of learning in which an animal forms a social attachment to another organism soon after birth or hatching.
inclined plane - simple machine that uses a slanted surface that makes it easier to move a mass from a lower point to a higher
                point; allows heavy loads to be lifted by using less force over a greater distance. 
incubation - process of keeping eggs warm by bodily heat until they hatch.
incubation period - time between contact with a source of infection and the outbreak of symptoms.
independent variable - one factor changed by the person doing the experiment in order to study changes in the dependent
                variable; factor that is deliberately manipulated.  (test variable) 
index fossil - fossil that is used to establish the age of a rock layer because the fossil is distinct, abundant, and widespread and the
                species that formed the fossil existed for only a short span of geologic time.
indicator - chemical compound that changes color depending on the pH of the solution or other chemical change. 
indirect transmission - transmitting disease organisms in which the agents do not pass directly from an infected person to a
                susceptible person but by means of an intermediate host.
inertia - property of a mass to resist changes in motion; measure of an object’s ability to remain at rest or to keep moving unless
                overcome by a force. 
infection - invasion of the body by organisms.
infectious disease - disease caused by microorganisms living in or on the body.
inference (infer) - conclusion based on an observation.
infiltration - process in which water soaks into the soil.
infrared radiation - invisible heat energy from the sun.
ingestion - eating.                                                                                                                                                                                           11
inhale - to breathe in.
inlet - small part of a body of water that reaches into a coast.
innate behavior - behavior that an animal is born with and does not have to learn.
inner core - solid, innermost layer of the Earth.
inorganic - composed of material that is not and never was living.
inorganic compound - compound that does not usually contain the element carbon.
insect - arthropod with three body segments, six legs, two antennae, and compound eyes.
instinct - complex pattern of innate behavior.
insulation - substance that reduces the transfer of electricity, heat, or sound.
interaction - condition of acting or having an influence upon something.
interference - ability of two or more waves to combine and form a new wave when they overlap; can be constructive, forming a
                larger wave, or destructive, forming a smaller wave.
International Date Line - transition line for calendar days, located at the 180­o meridian (longitude).
International System of Units (SI) - system of units used in science; metric system.
intertidal zone - portion of the shoreline that is covered with water at high tide and exposed to the air at low tide.
intrusion - igneous rock formed when magma forces its way into sedimentary rock and hardens below or on the Earth’s surface.
intrusive rock - rock that forms from melted rock or magma that cools and hardens deep below the Earth’s surface.
invertebrate - animal without a backbone; about 97 percent of animals are invertebrates.
investigation - procedure that is carried out in order to observe a response caused by a stimulus; not a complete experiment. 
ion - atom that loses or gains electrons; charged atom.                                                                                                                         
ionosphere - layer of electrically charged particles in the thermosphere.
island - piece of land that is surrounded by water.
isobar - line on a weather map connecting places that have the same air pressure.
isotherm - line on a weather map connecting locations that have the same temperature.
isostasy - balance between the downward force of the crust and the upward force of the mantle.
isotope - atom of a substance that has the same number of protons but a different number of neutrons as another atom of the same
isthmus - narrow strip of land connecting two larger landmasses. (has water on two sides) 
jet stream - narrow belt of strong winds that flows from west to east at great speeds near the top of the troposphere.
joint - crack in the crustal rock; a place where bones meet.
Kelvin (K) - temperature scale (SI unit) that has its zero at absolute zero where matter stops moving; water freezes at 273.15o  and
                boils at 373.15o. 
kettle lake - bowl-shaped lake that was formed as sediment built up around a block of ice left behind by a glacier.
kidney - major excretory organ.
kilogram - see gram.
kinetic energy - energy possessed by a body because of its motion.   
kingdom - largest classification grouping.
Kuiper Belt - region of the solar system that is just beyond the orbit of Neptune and that contains small bodies made mostly of ice.
Kuiper Belt object - one of the hundreds or thousands of minor planet-sized objects that orbit the sun in a flat belt beyond
                Neptune’s orbit.
laccolith - dome-like intrusion that pushes overlying rocks into an arch and has a flat floor.
lake - filled or partially filled basin of fresh or salt water surrounded by land.
land breezes - nightly movements of air created when cold air over the land forces up the warmer air above the sea.
land degradation - process by which human activity and natural processes damage land to the point that it can no longer support
                the local ecosystem.
landform - physical features on Earth’s surface.
landslide - sudden movement of rock and soil down a slope.
La Nina - change in the eastern Pacific Ocean in which the surface water temperature becomes unusually cool. 
large intestine - organ in the digestive system in which water is absorbed and undigested food is stored.
larva (plural-larvae) - free-living early form of a developing organism that is very different from its adult form.
larynx - voice box.
lateral fault - crack along which the blocks of rock move horizontally past one another.
lateral moraine - till deposited along the sides of a glacier.
latitude - measure of distance in degrees north or south of the equator.
launch - process of setting a rocket or spacecraft in motion.
lava - hot, molten rock that has reached the Earth’s surface.
lava plateau - layers of lava that build up on a flat area on the Earth’s surface.
law - rule or principle describing a physical relationship that always works in the same way under the same conditions; descriptive
                statement or equation that reliably predicts events under certain conditions.
law of conservation of energy - states that no matter how energy is transferred or transformed, all of the energy is still present in
                one form or another.
law of conservation of matter - states that matter is neither created nor destroyed, only changed in form.                                              12
law of definite proportions - states that a given compound is always made of the same elements in the same proportion by mass.
law of electric charges - states that like charges repel and opposite charges attract.
law of inertia -  states that an object’s motion will not change unless that object is acted on by an outside force.
law of superposition - states that in layers of sedimentary rocks, younger rocks normally lie on top of older rocks if the layers
                have not been disturbed.
leaching - removal of substances that can be dissolved from rock, ore, or layers of soil due to the passing of water.
legend - key that explains what symbols on a map represent.
lens - curved pieces of glass that bend light rays as they pass through it.
levee - ridgelike deposit of sediments on a flood plain.
lever - simple machine made from a rod or plank that pivots about a point (fulcrum); used to transmit and enhance power or
lichen - organism made up of a fungus and a green alga.
life cycle - entire sequence of events in an organism’s growth and development. 
life span - maximum length of time a particular organism can be expected to live.
life zone - narrow region of space around a star in which a planet that contains life can exist.
ligament - strong, stringy connective tissue that fastens the bones together in a moveable joint.
light - electromagnetic radiation that lies within the visible range. 
lightning - electric discharge that takes place between two oppositely charged surfaces, such as between a cloud and the ground,
                between two clouds, or between two parts of the same cloud.
light-year - distance light travels in one year.  (about 9.46 trillion km)
lignite - soft, brown coal with a woody texture.
limiting factor - factor or condition that prevents the continuing growth of a population in an ecosystem.
line graph - tool used to show the relationship between two variables.
lipids - include fats, oils, or waxes used for energy or as structural materials that do not dissolve in water.
liquid - phase in which matter has no definite shape but does have a definite volume. 
liter (L) - basic unit of volume in the metric system.                                                                                                              
lithosphere - topmost, solid part of the Earth.
littoral zone - shallow zone of a lake or pond where light reaches the bottom and nurtures plants.
liver - organ that produces bile.
load - materials carried by a stream.
local wind - movement of air over short distances; occurs in specific areas as a rest of certain geographical features.
loess - many layers of fine sand and silt deposited by wind in the same area.
longitude - measure of distance east and west of the prime meridian.
longitudinal wave - particles of the medium vibrate in the direction of the moving energy; the type of wave made by sound
                energy; L wave.
longshore current - overall direction and movement of water as waves strike the shore at an angle.
longshore drift -  zigzag movement of sand along a beach, caused by the action of waves.
love - deep, tender feeling of affection and emotional attachment.
low Earth orbit - orbit that is less than 1 500 km above Earth’s surface.
low-pressure system - large and often stormy weather system that forms when air circles, then moves up to higher altitudes.
low tide - lowest level of the ocean that occurs between the two high tides.
luminosity - actual brightness of an object such  as a star.
lunar eclipse - eclipse that occurs when the Earth comes directly between the sun and the full moon.
lunar phases - different appearances of the moon from Earth throughout the month.
lung - respiratory organ that absorbs oxygen from the air.
luster - way a mineral reflects light.
L wave - surface wave.
lysosome - small, round structure involved with the digestive activities of a cell.
machine - any device that makes doing work easier.
magma - hot, molten rock deep inside the Earth.
magma chamber - body of molten rock that feeds a volcano.
magnet - any material that attracts iron or materials containing iron.
magnetic - having the property of attracting iron and certain other materials by virtue of a surrounding field of force.
magnetic field - region where magnetic force exists around magnets or electric currents.
magnetic pole - one of two points, such as the ends of a magnet, that have opposing magnetic qualities.
magnetosphere - magnetic field of a planet.
magnitude - measure of a star’s brightness.
main-sequence star - star located in an area that runs from the upper left to the lower right of the Hertzsprung-Russell diagram.
malleability (malleable) - ability of a substance to be hammered into thin sheets without breaking.                           
mammal - warm-blooded vertebrate animal whose young feed on milk produced by the mother’s mammary glands.
mantle - layer of rock between the Earth’s crust and core.
maria - dark, broad, smooth, lowland area on the moon.                                                                                                                     13
marine climate - climate influenced by a nearby ocean, with generally mild temperatures and steady precipitation.
maritime polar - air mass that forms over the Pacific Ocean and brings cool air in the summer and heavy snow in the winter.
maritime tropical - warm, moist air mass that forms over the ocean near the equator.
marrow - soft tissue filling the ends and inner spaces of bones.
mass - measure of the amount of matter in an object. 
mass number - sum of the protons and the neutrons in the nucleus of an atom.
material resource - natural resource that humans use to make objects or to consume as food and drink.
mass wasting - downhill movement of loose rock or soil.
matter - anything that has mass and volume.  (gas, liquid, or solid) 
maturation - emergence of personal and behavioral characteristics through growth processes.
mature river - river that has been developing for thousands of years.
meanders - loop in a river.
measurement - way to describe the world with numbers; can describe objects and events with length, volume, mass,            temperature, and rates.
mechanical advantage (M.A.) - comparison of the effort force to the resistance for a machine; output force divided by input           force.
mechanical digestion - physical action of breaking foods into smaller parts.
mechanical energy - amount of work an object can do because of the object’s kinetic and potential energies.
mechanical wave - wave that can travel only through matter; can be either a transverse or a compressional wave.
mechanical weathering - process by which rocks break down by natural processes and do not change the chemical
                composition of the rock material. (physical weathering)
medium - material through which a wave travels.  (gas, liquid, or solid)
meiosis - form of cell division that halves the number of chromosomes in a male and female sex cell as they form. 
melting - change of a solid to a liquid.
melting point - temperature at which a solid changes to a liquid.
meltwater - stream of water formed by the melting of ice as a valley glacier moves.                                                     
membrane - thin layer of tissue that surrounds or lines a cell, a group of cells, or a cavity; any barrier separating two fluids.   
meniscus - surface of a liquid.
Mercator projection - map projection that has correct shapes of continents, but their areas are distorted; has lines of longitude
                drawn parallel to each other.
meridian - imaginary line used to measure longitude that runs north and south between the Earth’s geographic poles.
Mesosaurus - extinct reptile that swam in freshwater ponds, lakes, and rivers.
mesosphere - layer of the atmosphere between the stratosphere and the thermosphere and in which temperature decreases as
                altitude increases; strong, lower part of the mantle between the asthenosphere and the outer core.
mesa - land formation with a flat area on top and steep walls.  (usually in dry areas)
metabolism - all chemical activities in an organism essential to life.
metal - element that is a good conductor of heat and electricity, is shiny, has a high melting point, is ductile and malleable and
                forms positive ions.
metalloids - elements that have characteristics of both metals and nonmetals, generally are brittle and dull, and are poor
                conductors of heat and electricity.
metamorphic rock - type of rock changed by intense heat, pressure or chemical processes. 
metamorphism - changing of one type of rock into another as a result of tremendous heat, great pressure or chemical reactions.
metamorphosis - developmental process in which an animal changes drastically in body form between the juvenile            and the adult;
                can be complete (egg, larva, pupa, and adult) or incomplete (egg, nymph, and adult).
metazoan - multicellular animals that cause scabies and pubic lice.
meteor - bright streak of light produced by a burning meteoroid in Earth’s atmosphere.
meteorite - chunks of rock that strike the Earth’s surface.
meteoroid - relatively small, rocky body that travels through space.
meteorologist - scientist who studies weather.
meteorology  - study of the Earth’s atmosphere, weather, and climate.
meter (m) - basic unit of length in the metric system.
methanogen - Archaea that produce methane as a waste product of metabolism.
metric system - universal system of measurement.
microbiology - study of microorganisms.
microclimate - climate of a smaller area within a subclimate.
microorganism - very small organism that can be seen only with a microscope.
microscope - instrument that produces an enlarged image of an object.
microscopic - relating to an object too small to be visible without the use of a microscope. 
microwave - high frequency electromagnetic wave used to cook or heat food.
mid-ocean ridge - continuous, seismic mountain range extending across the floor of the world’s major oceans; area            where two
                oceanic plates are moving away from each other; area where new crustal material may be released.
migration - instinctive seasonal movement of animals, usually to find food or to reproduce in a better environment.                           14
Milky Way - galaxy in which the Earth’s solar system is located.                                                                                                         
mineral - naturally occurring, inorganic solid that has a definite chemical composition and crystal shape.
mitochondrion (plural-mitochondria) - oval-shaped organelle that is referred to as the powerhouse of a cell.
mitosis - duplication and division of the nucleus and of the chromosomes during cell reproduction; a process of nuclear division in
                cells during which the number of chromosomes is reduced by half. 
mixture - two or more pure substances that are mixed but not chemically combined. 
mobile - able to move from place to place.
model - pattern, plan, representation, or description designed to show the structure or workings of an object, system, or concept.
Moho - boundary between the Earth’s outermost layer and the mantle.
Mohs hardness scale - scale used to determine the hardness of a mineral.
mold - fossil formed in a rock by a dissolved organism that leaves an empty space, showing its outward shape.
molecule - smallest particle of a substance that has all the physical and chemical properties of that substance; made up of two or
                more atoms that are chemically bonded. 
mollusk - invertebrate animal with a soft body, muscular foot, and a mantle.
molting - process of an arthropod shedding its exoskeleton to allow for growth.
momentum - vector quantity that is the product of an object’s mass and velocity; the general effect of ongoing motion.
month - division of the year that is based on the orbit of the moon around the Earth.
monsoon - major seasonal land and sea breeze; a wind that changes direction with the seasons.
moon - natural satellite that revolves around a planet. 
moon phase - fraction of the moon’s disc that is illuminated as seen from Earth; (the eight moon phases:  new moon,         waxing-crescent, first quarter, waxing-gibbous, full moon, waning-gibbous, last quarter, waning-crescent.) 
moraine - deposit of till left behind by a retreating glacier.                                                                                                   
moss - seedless, nonvascular, small, grass-like plant that live in moist, cool environments.
motion - change of position over time.
mountain - area of significantly increased elevation on Earth’s surface, usually rising to a summit.
mountain soil - soil found on the slopes of mountain ranges that contains very small amounts of clay and sand and often no
muck fire - fire that burns organic material in the soil.
mudflow - flow of a mass of mud or rock and soil mixed with a large amount of water.
multicellular - having many cells.
muscle - tissue that has the ability to contract or shorten; a special tissue that causes movement.
muscle strain - problem that occurs when a muscle is overused after it has not been exercised for several weeks.
muscle tear - separating of the fibers of a muscle by sudden force or stretching.
mutation - process by which a gene undergoes a change in DNA sequence or a structural change. 
mutualism - interaction between two species in which both benefit.
nanotechnology - study of the science and technology of building electronic circuits and devices from single atoms and
NASA - National Aeronautics and Space Administration.
natural gas - mixture of gaseous hydrocarbons located under the surface of the earth, often near petroleum deposits; used as a
natural resource - any type of matter or energy from Earth’s environment that humans use to meet their needs; includes water,
                petroleum, minerals, forests, and animals.
natural selection - theory stating every organism displays slight variations from other organisms of its kind, and the struggle for
                limited natural resources results in individuals with certain natural variations adapted to their specific environments. 
neap tide - high tide lower than usual during first and third quarter moons; a twice-monthly tide of minimal range that occurs
                when the sun, moon, and Earth are at right angles to each other, thus decreasing the total tidal force exerted on Earth. 
nebula - massive cloud of dust and gas in which stars are probably born.
nebular theory - idea that the solar system began in a vast gas cloud.
nekton - all organisms that swim actively in open water, independent of currents.
nephron - microscopic chemical filtering factory in the kidneys.
neritic zone - ocean area that extends from the low tide line to the end of a continental shelf.
net force - combination of all of the forces acting on an object.
neutral -  particle, object, or system that lacks a net charge. 
neutron - electrically neutral particle found in the nucleus of an atom. 
neutron star - rapidly spinning core of a massive star that remains after a supernova explosion.
new moon - phase of the moon when it is not visible in the sky.
Newton (N)  - SI unit for force.
Newton’s laws of motion - three rules describing how things move—an object will move with constant motion if no net force is
                acting on it; an object that has an unbalanced force acting on it will accelerate in the direction of the force; and forces
                occur in equal but opposite pairs.
niche - unique position occupied by a particular species in terms of the area it inhabits and the function it performs within the
                community.                                                                                                                                                                                      15
nitrate - nitrogen (N) compound.
nitrogen cycle - continuous movement of nitrogen through Earth, its atmosphere, and the living things on Earth.
nodule - potato-sized lump of mineral on the ocean floor.
non-communicable - illness that is not caused by a disease-causing organism; a non-infectious disease.
nonmetal - element that is a poor conductor of heat and electricity, has a dull surface, low melting point, is brittle, breaks easily
                and forms negative ions.
non-point source - pollution that comes from many different sources, such as industries, homes, and farms.            
nonrenewable resource - any resource that cannot be replaced by nature, such as fossil fuels and minerals; resource that forms at a rate that is much slower than the rate at which the resource is consumed.
nonvascular plant - plant lacking vascular tissue and that absorbs water and other dissolved substances directly through its cell walls.
normal fault - crack formed when the hanging wall moves down relative to the foot wall.
normal force - upward force of the ground, perpendicular to the surface.
nostril - opening in the nose.
nova - star that suddenly increases in brightness.
nuclear energy - energy locked within the atomic nucleus; the energy released by a fission or fusion reaction.
nuclear family - parents and their children.
nuclear fission - splitting of an atomic nucleus into two smaller nuclei during which vast amounts of energy is released. 
nuclear fusion - combining two lighter atomic nuclei to form heavier elements which produce large amounts of energy.  
nuclear membrane - thin membrane that separates the nucleus from the protoplasm of the cell.
nucleic acid - large organic compound that stores information that helps the body make the proteins it needs.
nucleolus (plural-nucleoli) - cell structure located in the nucleus and made up of RNA and protein; may play important role in
                making proteins for the cell.
nucleotide - building blocks of DNA.
nucleus (plural-nuclei) - spherical organelle in eukaryotic cells that contains the genetic material and directs all the              activities of
                the cell; positively charged center of an atom containing most of the mass. 
nutrient - useable portion of food; a substance that an organism needs to live.
objective - not influenced by emotions or personal prejudices, nor particular to one person.
observation - process of obtaining information by using the senses.
occluded front - type of front that occurs when a cold front overtakes a warm front, pushes it upward, and meets cool air.
ocean - large body of salt water that  surrounds a continent.
ocean basin - depression of the surface of Earth occupied by water.
ocean crust - section of the Earth’s crust under the ocean floor. 
ocean current - movement of ocean water that follows a regular pattern.
ocean-floor spreading - process in which the ocean floor on either side of a rift valley is pushed away by lava erupting from the
                rift valley that forms new ocean floor.
oceanographer - scientist who studies the ocean.
oceanography - study of the Earth’s oceans, including their physical features, life forms, and natural resources.
oil - energy-rich organic compound made up of carbon, hydrogen and oxygen that is liquid at room temperature.
omnivore - animals that eat both plants and animals.
Oort cloud - spherical region that surrounds the solar system, that extends from the Kuiper Belt to almost halfway to the nearest
                star and that contains billions of comets.
open cluster - group of stars that are close together relative to surrounding stars.
open-water zone - zone of a pond or lake that extends from the littoral zone and that is only as deep as light can reach.
oral groove - mouth-like indentation in a paramecium and other unicellular organisms.
orbit - path one object takes when moving around another object in space.
order - classification group between class and family.
ore - rock from which metals and other minerals can be removed in usable amounts.
organ - group of different tissues working together. 
organelle - parts that make up a cell.
organic - composed of material that is or was living.
organic compound - compound that contains the element carbon.
organic rock - sedimentary rock built up from the remains of living things.
organism - entire living thing made up of one or more cells that carries out all the basic life functions. 
organ system (system) - organs that work together to perform certain functions.
osmosis - movement of water through a cell membrane.
outcome variable - factor being measured or observed in an experiment;  a factor that responds to, or depends on, other factors. 
                (dependent variable)
outer core - liquid layer of the Earth surrounding the inner core.
outwash plain - sediments deposited by rivers of glacial meltwater in a fan-shaped area in front of a terminal moraine.
ovary - enlarged base of the pistil that holds the ovule.
ovule - organ that produces and holds the eggs in a flower.                                                                                                                   16
oxbow lake - small lake formed when a bend in a river is cut off from the river.
oxidation - process in which oxygen chemically combines with another substance.
ozone (O3) - gas molecule that consists of three oxygen atoms.
ozone layer - stratospheric layer with a high concentration of ozone; protects Earth by absorbing harmful ultraviolet  radiation.
pacemaker - controls the pace at which the heart beats.
paleontologist - scientist who uses the remains or traces of long-dead organisms to form a picture of the Earth’s past.
pancreas - gland that produces pancreatic juice and insulin.
Pangaea - one large landmass of which all the continents were once a part according to the theory of continental drift.
parallax - apparent change in the position of an object when viewed from different locations.
parallel - imaginary line used to measure latitude that runs east and west around the Earth.
paramecium (pl-paramecia) - microscopic, unicellular Protist that move by means of cilium (pl-cilia.)
parasite - organism that feeds on other living organisms often harming them in the process.
parasitism - relationship between two species in which one species is harmed while the other benefits.
parent rock - rock formation that is the source of soil.
particle - very small piece of matter such as an atom, molecule, or ion.
particulate - tiny particle or droplet, such as dust, dirt, or pollen that are mixed in with air.                                          
pathogen - specific cause of disease.  (EX-bacteria or virus)                                    
passive transport - movement of materials through a membrane without any input of energy.
peat - soft substance made of decayed plant fiber; softest type of coal.
peer pressure - process by which a person feels forced to do what others want them to do.
pelagic environment - in the ocean, the zone near the surface or at middle depths, beyond the sublittoral zone and above the
                abyssal zone.
peninsula - body of land that is surrounded by water on three sides.
penumbra - outer area of a shadow cast by an object in space onto another object in space in which the light is only           partly                 blocked.
pepsin - enzyme produced by the stomach that digests protein.
percolation - movement of water through rock or soil.
perigee - point of the moon’s orbit closest to the Earth.
perihelion - point in the orbit of a planet at which the planet is closest to the sun.
periodic - describes something that occurs or repeats at regular intervals.
periosteum - tough membrane surrounding a long bone.
peristalsis - powerful waves of muscle contractions that push the food through the digestive system.
permeability - capability of a porous substance or membrane to allow a fluid or gas to enter it; the measure or degree to which a
                substance can be penetrated by a liquid or gas. 
permeable membrane - when materials will pass through a membrane.
petal - colorful blades that surround the inner parts of a flower.
petrified - having turned to stone.
petroleum - liquid mixture of complex hydrocarbon compounds; used widely as a fuel source.
petrologist - scientist who studies rocks and their mineral composition.
pH - symbol for the measure of the acidity or alkalinity of a solution. 
phagocytosis - cellular eating.
phase - state in which matter can exist; solid, liquid, gas and plasma are the states of matter; the change in the sunlit           area of one
                celestial body as seen from another celestial body.
phenotype - appearance or other observable characteristic of an organism resulting from the interaction of its genetic makeup and
                its environment. 
pheromone - powerful chemical produced by an animal to influence the behavior of another animal of the same species.
phloem - vascular tissue that carries dissolved food from the leaves to the rest of the plant.
phospholipids - lipid that contains phosphorus and that is a structural component in cell membranes.
photoelectric effect - production of an electric current when photons of certain frequencies of light have enough energy to knock
                electrons out of atoms of a metal plate.
photon -tiny packet of energy released by an electron.
photosphere - lowest layer of the sun’s atmosphere.
photosynthesis - process by which green plants make glucose for food by combining carbon dioxide and water by using the sun’s
photovoltaic cell - device that converts sunlight directly into electricity; solar cell.
phylogeny - evolutionary history of an organism.
phylum (plural-phyla)  - second largest classification group; between kingdom and class.
physical change - change in which physical properties of a substance are altered, but the substance remains the same kind of
physical property - characteristic that distinguishes one type of matter from another and can be observed without changing the
                identity of the substance.                                                                                                                                                              17

physical weathering - process by which rocks break down by natural processes and do not change the chemical composition of
the rock material. (mechanical weathering)
physics - study of different forms of energy.
physiology - study of the functions and activities of the body.
pinocytosis - cellular drinking.
pioneer community - first community of organisms to move into a new environment.
pioneer species - first plants to grow in new or disturbed environments and that change environmental conditions so that other
plant species can grow there.
pistil - female reproductive part of a flower.
placenta - organ that transports materials between a pregnant female mammal and the offspring developing inside her body.
plain - flat land area not far above sea level.
planet - large, spherical body in space that orbits a star and does not produce light of its own.
planetary ring - disk of matter that encircles a planet and consists of numerous particles in orbit, ranging in size from dust grains
up to objects tens of meters across.
planetesimal - small body from which a planet originated in the early stages of development of the solar system.
plankton - microscopic organisms that float or drift in large numbers in salt or fresh water; zooplankton—animal-like and
phytoplankton—plant-like.   (planet comes from the word plankton)
Plantae (Plant) - kingdom that is made up of multicellular eukaryotic cells that are usually green, have cell walls made of
cellulose, and use the sun’s energy to make sugar by photosynthesis.                                                 
plasma - phase in which matter is very high in energy and cannot be contained by the walls of ordinary matter, very           rare on Earth;
yellowish liquid portion of the blood.

plate - broken sections of the Earth’s crust that are in constant motion.

plateau - broad, flat area of land that rises more than 600 meters above sea level.

plasticity - ability of a solid to flow.                                                                                             

platelet - part of a cell in the blood that aids in clotting.

plate tectonics - theory for the movement of the continents suggesting that the solid plates of the lithosphere are moved slowly by

                convection currents originating deep inside the Earth whose movements cause seismic activity along their borders.   

platform - area of a continent that is composed of flat-lying layers of sedimentary rock.
point-source - single, identifiable pollution source.
polar easterlies  - prevailing winds that blow from east to west between 60o and 90o latitude in both hemispheres.
polar zone - climate zone in each hemisphere that extends from the pole to about 60o latitude.
Polaris - north star.
pollen - tiny multicellular grains that contain the undeveloped sperm cells of a plant.
pollination - transfer of pollen to an egg-producing organ.
pollution - introduction of harmful waste products, chemicals, and substances into the environment; may occur naturally or as a
result of human activities. 
population - group of organisms of the same species living in a specific geographical area. 
population density - measure of the number of organisms that live in a given area.
pore space - space between soil particles.
porosity - percentage of the total volume of a rock or sediment that consists of open spaces.
porphyry - igneous rock whose cooling rate changed and thus has two or more different-sized crystals.
port - man-made place along the coastline where ships can load and unload cargo; not a natural harbor.
potable - suitable for drinking.
potential energy - energy an object has because of its position, shape or condition; stored  energy. 
power - measures the rate at which work is done in a certain period of time; unit is the watt (W).
prairie soil - very rich, fertile soil that is excellent for growing crops.
precipitation - water falling from clouds, including rain, snow, sleet, and hail.
precision - degree of accuracy or exactness of a measurement or tool.
predator - organism that preys on and consumes animals; usually an animal. 
pressure - force exerted per unit area. 
prevailing winds - winds that blow mainly from one direction during a given period.
prey - organism caught or hunted for food by another organism. 
primary succession - ecological succession that begins in a place that does not have soil.
primary wave - fastest type of seismic wave, which can travel through solids, liquids, and gases; P wave.
prime meridian - imaginary line at 0o longitude that runs north and south through Greenwich, England.
principle of uniformitarianism - idea that geologic processes that occurred in the past can be explained by current geologic
prism - piece of glass with polished plane surfaces that disperses a beam of white light into its component colors.
probe - uncrewed vehicle that carries scientific instruments into space to collect scientific data. 
producer - organism that makes its own food from the environment; usually a green plant.  (autotroph) 
product - substance or compound resulting from a chemical reaction.                                                                                               18

prograde rotation - counterclockwise spin of a planet or moon as seen from above the planet’s North Pole; rotation in the same
direction as the sun’s rotation.
projectile motion - curved path that an object follows when thrown, launched, or otherwise projected near the surface of Earth.
prokaryotic cell (prokaryotes) - simplest type of cell with no true nucleus to surround the genetic materials.  (kingdoms:
Archaea and Bacteria)
prominence - solar storm in the form of huge bright arches or loops of gas from the sun; loop of relatively cool, incandescent gas
that extends above the photosphere and above the sun’s edge as seen from Earth.
property – quality, characteristic, feature or trait that describes an object.
protein - organic compound made up of carbon, hydrogen, oxygen, nitrogen and sometimes sulfur and phosphorus,           necessary for
the growth and repair of body structures; a biological macromolecule composed of one or more chains of amino acids. 
Protista (Protist) - kingdom made up of unicellular eukaryotic cells. 
proton - positively charged particle found in the nucleus of an atom. 
protoplanet - early stage of a planet.
protoplasm - all the living material found in both plant and animal cells.
protostar - new star.                                                                                                                                                                                     
protozoan (plural-protozoa) - unicellular animal-like protists.
pseudopod - “false foot” in amoeba.
ptyalin - enzyme in saliva that breaks down some starches into sugars.
puberty - period during which the physical and emotional changes which lead to adulthood take place; time frame in which the
reproductive organs become functional.
pulley - surface, such as a wheel, that redirects force using a rope; a simple machine that allows you to pull down to            lift a weight. 
pulsar - neutron star emitting radio waves.
Punnett square - graphic checkerboard used to determine results from a particular genetic cross. 
pure substance - substance that contains only one kind of molecule.
purification - process by which water is cleaned so that it is usable.
P wave - seismic wave that causes particles of rock to move in a back-and-forth direction.
qualitative - description that does not use measurement or numbers.
quantitative - description that uses measurement or numbers.
quark - particle that makes up all subatomic nuclear particles.                                                                                                              
quasar - quasi-stellar radio source that is probably an early stage in the formation of a galaxy.
radar - is an electronic system used to locate and identify distant objects.
radiant energy - visible and invisible energy from the sun that moves in waves, such as light and heat.
radiation - transfer of energy as electromagnetic waves or rays.
radioactive decay - process in which a radioactive isotope tends to break down into a stable isotope of the same element or
another element.
radioactivity - process by which an unstable nucleus gives off nuclear radiation.
radiometric dating - method of determining the absolute age of an object by comparing the relative percentages of a radioactive
parent isotope and a stable daughter isotope. 
radius - is a line segment connecting the center of the circle to a point on the circumference.
rain shadow - area on the downwind side of a mountain that gets less precipitation than the side that faces the wind.
rarefaction - place where particles are spaced far apart.
rate - ratio of two measurements with different units—for example, speed, measured in kilometers per hour (km/h);            fraction in
which the numerator and denominator have different units.
rate of reaction - speed at which reactants are consumed and products are produced in a given reaction. 
reactant - any substance or molecule that participates in a chemical reaction. 
recessive - allele for a trait that will be masked unless the organism is homozygous for this trait. 
recycling - process of recovering valuable or useful materials from waste or scrap.
red blood cell - cell that carries oxygen through the body.
red giant  - large, reddish star late in its life cycle.
red shift - shift of light from moving stars toward the red end of the spectrum.
reflection (reflect) - occurs when a wave (light, sound, or heat) strikes an object or surface and bounces off.
reflecting telescope - optical telescope in which a series of mirrors gather light from the stars.
refracting telescope - optical telescope in which a series of lenses are used to focus and magnify light from the stars. 
refraction - bending of a wave as it moves from one medium into another of different density.
regional metamorphism - type of metamorphism that occurs over large areas when rocks buried deep within the Earth are
changed by increases in temperature and pressure.
relative dating - any method of determining whether an event or object is older or younger than other events or objects.
relative humidity - ratio of the amount of water vapor in the air to the amount of water vapor needed to reach saturation at a given
relief - difference in elevations within a landscape region.
remote sensing - way of collecting information about Earth from a distance–for example, by satellites and sonar.                               19

renewable resource - any natural  resource that can be replaced or restored by natural processes, such as wind, water, soil and
living resources, at the same rate that it is consumed .
repeat (repetition) - produce again but not necessarily getting the same answer.
replicate (replication) - continually get the same answer.
reproducible - result that is the same no matter who produces it or where or when it is produced.
reproduction - process by which living things give rise to the same type of living thing.
reptile - cold-blooded vertebrate that has skin covered with scales or horny plates and lungs.
reservoir - artificial body of water that usually forms behind a dam.
residual soil - soil that rains on top of its parent rock.
resistance force (Fr) - force a machine must overcome.
resource - any material that can be used to satisfy a need. 
respiration (cellular respiration) - process by which living things take in oxygen and use it to produce energy.
respiratory system - body system responsible for getting oxygen into the body.
response - some action or movement of the organism brought on by a signal.                                                                
responsibility - duty or obligation.
retrograde motion - rotation of a planet on its axis from east to west (clockwise), which is the reverse motion of most planets.
retrovirus - microscopic organism that can cause tumors and diseases in animals and people;  they contain RNA and use it to
make DNA which is the opposite of most viruses.
reverse fault - crack formed when the hanging wall moves up relative to the foot wall.
revolution -  motion of a body that travels around another body in space.
ribonucleic acid (RNA) - nucleic acid that “reads” the genetic information carried by DNA and guides the protein-making
process; a single-stranded nucleic acid consisting of a phosphate group and one of four nitrogenous bases that encodes
information needed to synthesize proteins. 
ribosome - grain-like body made up of RNA and attached to the inner surface of an endoplasmic passageway; a
protein-making site of the cell.
Richter scale - measure of the amount of energy an earthquake releases.
rift valley - formed when the block of land between two normal faults slides downward; a long, narrow valley in Earth’s crust
where two continental plates are separating between two faults. 
rift zone - area of deep cracks that forms between two tectonic plates that are pulling away from each other.
rille - valley on the moon.
Ring of Fire - major earthquake and volcano zone that extends nearly all the way around the edge of the Pacific Ocean.
risky behavior - behavior that is more likely to allow exposure to infectious agents.
river - large, body of water that flows across land surfaces within a channel and usually empties into a sea or ocean.
Robinson projection - map projection that has accurate continent shapes and accurate land areas; has parallel latitude lines and
curved longitude lines.
robot - machine that works automatically or by remote control.
rock - is a naturally occurring, solid material made of one or more minerals or organic matter.
rock cycle - continuous changing of rocks from one kind to another.
Rock fall - rapid mass movement of rock down a steep slope or cliff.
root-pry - mechanical weathering process caused by plant roots growing in a crack in a rock.
rotation - spin of a body on its axis.
salinity - measure of the amount of dissolved salts in a given amount of liquid.                                                                               
salinization -  accumulation of salts in soil.
saltation - movement of sand or other sediments by short jumps and bounces that is caused by wind or water.
sandbar - low ridge of sand deposited along the shore of a lake or sea by the action of waves and currents.
saprophyte - organism that feeds on dead things.
satellite - natural or artificial object in space orbiting another object in space.
saturation - condition of the atmosphere in which the rates of evaporation and condensation are equal.
savanna - grassland that often has scattered trees and that is found in tropical and subtropical areas where seasonal rains, fires, and
drought happen.
scale - one of the thin, small, overlapping plates that cover most fish and reptiles and some other animals.
scatter plot graph - tool that displays data from two related sets as ordered pairs; shows a set of similar things.
science - process of trying to understand the world around us; the knowledge obtained by observing natural events and conditions
in order to discover facts and formulate laws or principals that can be verified or tested.
scientific inquiry - may include one or more experiments or investigations.
scientific literacy - understanding of the methods of scientific inquiry, the scope of scientific knowledge, and the role of science in
scientific method - basic steps that scientists follow in uncovering facts and solving scientific problems; a plan of inquiry that uses
science process skills as tools to gather, organize, analyze, and communicate information. 
scientific name - combination of the genus name and the species name of a living thing.
screw - type of simple machine that consists of an inclined plane wrapped around a cylinder.                                                     20
sea breezes - daily movements of air created when cooler, denser air moving inland from the ocean forces warm air            over the land                 to rise.
sea cliff - steep face of rock produced by wave erosion.
sea-floor spreading - process by which new oceanic lithosphere sea floor forms when magma rises to Earth’s surface and
solidifies at a mid-ocean ridge, as older, existing sea floor moves away from the ridge.
seamount - submerged mountain on the ocean floor that is at least 1 000 m high and that has a volcanic origin.
season - division of the year associated with specific weather conditions; determined by both Earth’s tilt relative to the sun and
Earth’s position in its orbit around the sun.
sea stack - column of resistant rock left standing after waves eroded a sea cliff.                                                                            
secondary succession - ecological succession that begins in a place that already has soil and was               once the home of               living
secondary wave - type of seismic wave that can travel through solids but not through liquids and gases.
second law of thermodynamics - law that states all natural processes proceed in a preferred direction. (EX - heat flows from high
temperature regions to low temperature regions) 
sediment - small pieces of rocks, shells or the remains of plants and animals that have been carried along and deposited by wind,
water or ice.
sedimentary rock - type of rock formed in layers of sediment that are compressed and cemented. 
seed - plant embryo that is enclosed in a protective coating and has its own source of nutrients.
seismic wave - wave of energy that travels through the Earth and away from an earthquake in all directions.
seismograph - instrument used to detect and measure shock waves from an earthquake.
seismogram - seismograph’s record of seismic waves.
seismologist - scientist who studies earthquakes.
seismology - study of earthquakes.
self-esteem - pride in oneself; self-respect.
semi-permeable membrane - when selected or only some materials will pass through a membrane.
sepal - leaf-like structures at the base of a flower.
septum - thick wall of tissue that separates the heart into right and left sides.
serendipity - knack for making fortunate discoveries by accident.  (Mark Twain quotation)
sessile - quality of being attached to one spot; not free-moving.
sexual reproduction - formation of an organism from the uniting of two different sex cells; reproduction involving              the union of
gametes producing an offspring with traits from both parents. 
shearing - type of stress that cause a rock to twist or tear apart by pushing on the rock in two opposite directions.
shear stress - stress that occurs when forces act in parallel but opposite directions, pushing parts of a solid in opposite directions.
shield - large area of very old rock exposed at the surface.
shield volcano - gently sloping, dome-shaped volcano composed almost entirely of quiet lava flows.
shoreline - boundary between land and a body of water.
sill - sheet-like mass of igneous rock.
simple machine - machine that works with only one motion; (an inclined plane, lever, wheel and axle, pulley, wedge, and screw.)
single-parent family - single mother or father and their children.
sinkhole - open basin that forms when the roof of a cavern becomes so thin that it collapses.
skeletal muscle - voluntary tissue made up of striped fibers; responsible for voluntary movement.
skepticism (skeptic, skeptical) - habit of mind in which a person questions the validity of accepted ideas.
skin - outer covering of the body.
sleet - small pellets of ice that form when rain passes through a layer of cold air and freezes before hitting the ground.
slip face - side of a sand dune with a steep slope.
small intestine - organ in the digestive system in which food is absorbed.
smog - combination of smoke and fog; air pollution that forms when ozone and vehicle exhaust react with sunlight.
smooth muscle - nonstriped muscle tissue that is not voluntary; responsible for involuntary movement.                  
social behaviors - interactions among organisms of the same species, including courtship and mating, caring for the young, and
getting food.
society - group of animals of the same species that live and work together in the same way and in which each member has a certain
soft water - water that does not contain many minerals.
soil - loose mixture of rock fragments, organic material, water, and air that can support the growth of vegetation.
soil conservation - method to maintain the fertility of the soil by protecting the soil from erosion and nutrient loss.
soil horizon - soil layer with physical and chemical properties that differ from those of soil layers above or below it.
soil profile - cross section of soil horizons.
soil structure - arrangement of soil particles.
soil texture - soil quality that is based on the proportions of soil particles.
solar cell - device that converts the energy of sunlight into electrical energy.
solar eclipse - eclipse that occurs when the new moon comes directly between the sun and Earth.
solar energy - energy from the sun that is nonpolluting, renewable, and abundant but is available only when the sun is shining.  21
solar flare - explosive increase in brightness near sunspots on the sun’s surface that releases great amounts of energy into space.
solar mass - quantity equal to the mass of the sun.
solar nebula - rotating cloud of gas and dust from which the sun and planets formed.                        
solar system - star/sun—planets and all the other objects that orbit it. 
solar wind - continuous stream of high-energy particles released into space in all directions from the sun’s corona.
solid - phase in which matter has a definite shape and volume. 
solstice - occurs twice yearly when the sun is directly over the northernmost or southernmost edges of the tropics; in the Northern
Hemisphere, the winter solstice (December 21 or 22) has the fewest daylight hours and the summer solstice (June 21 or
22) has the most daylight hours; point at which the sun is as far north or south of the equator as possible.
soluble - able to be dissolved in water.
solubility - ability or tendency of one substance to dissolve in another at a given temperature and pressure.
solute - substance that is being dissolved by another substance. 
solution - mixture of two or more substances uniformly dispersed throughout a single phase.
solvent - substance in which another substance dissolves.
sonar - sound navigation and ranging; echo-sounding instrument used to measure depth underwater.
sound - wide inlet of the ocean that is parallel to the coastline.
source - place where a river or stream begins.
space probe - uncrewed vehicle that carries scientific instruments into space to collect scientific data.
space shuttle - reusable space vehicle that takes off like a rocket and lands like an airplane.
space station - long-term orbiting platform from which other vehicles can be launched or scientific research can be carried out.
specialization - specific organization of a cell and its structure that allows it to perform a specific function.
species - group of organisms that are able to interbreed or produce young; a group of organisms of common ancestry able to
reproduce only among themselves and usually geographically distinct.
specific gravity - ratio of the mass of a substance to the mass of an equal volume of water. 
spectroscope - instrument that separates light into its various colors and wavelengths. 
spectrum - range of electromagnetic radiation that is ordered by wavelength or frequency; band of colors produced by the
breaking up of white light.
speed - amount of distance traveled divided by time taken; the time-rate at which any physical process takes place.
spinoff - commercialized product incorporating NASA technology or “know how” that benefits the public. 
spiral galaxy - pinwheel-shaped galaxy that has huge spiral arms.
spirillum (plural-spirilla) - spiral-shaped bacterium.
spit - long, underwater pile of sand connected to a curving shoreline.
sponge - simple multicellular invertebrate animal that lives attached to one place and filters food from water.
spontaneous generation - theory that states that life can spring from nonliving matter.
spore - single reproductive cell that can grow into a multicellular organism.
sprain - tearing or twisting of a ligament or muscle.
spring tide - high tide that is higher than usual; occurs twice monthly at the new and full phases of the moon.
stable rock - rock that has the ability to resist chemical weathering.
stalactite - icicle-like deposit hanging from the ceiling of a cavern, usually made of limestone.
stalagmite - icicle-like deposit built up on the floor or a cavern, usually made of limestone. 
stamen - male reproductive part of a flower.
star - large, gaseous, self-luminous body held together by gravity and powered by thermonuclear reactions. 
state (of matter) - phase in which matter can exist; solid, liquid, gas and plasma are the states of matter.
static electricity - electric charge at rest; generally produced by friction or induction.
stationary front - type of front that forms when a mass of warm air meets a mass of cold air and no movement occurs.
step family - formed when parents remarry.
stewardship - behavior that leads to the protection, conservation and reclamation of natural resources.
stigma - sticky top part of a pistil.
stimulus (plural-stimuli) - signal to which an organism reacts; a condition that produces a reaction. 
stock - intrusion similar to a batholith that has an exposed area of less than 100 square km.
stoma (pl-stomata) - tiny opening in plant leaves through which water vapor, oxygen and carbon dioxide pass.
stomach - organ in which foods are physically and chemically digested.
storm surge - rapid rise in water level in a coastal area that is caused by strong winds from a hurricane.
strait – narrow body of water that connects two larger bodies of water-
strata - layers of sedimentary rocks.
stratified drift - glacial deposit that has been sorted and layered by the action of streams or melt water.
stratosphere - layer of the atmosphere that is above the troposphere and in which temperature increases as altitude increases.
stratus cloud - gray, smooth cloud that forms at an altitude of about 2.5 kilometers.
streak - color of a mineral in powder form.
stress - force that pushes or pulls rocks.
structure - arrangement of parts in an organism.  (part; what it is; anatomy)
subatomic particle - particle that is smaller than an atom.                                                                                                        22
subduction - process in which the ocean floor plunges back into the interior of the Earth through a trench.
subjective - opinions and experiences particular to one person.
sublimation - process in which a solid changes directly into a gas.                                            
subscript - number placed to the lower right of a chemical symbol to indicate the number of atoms of the element in the
subsidence - sinking of regions of the Earth’s crust to lower elevations.
subsoil - soil in the B horizon made mostly of clay and some humus.
substance - matter of a particular type; (elements, compounds, and mixtures.)
succession - progressive replacement, on a single site, of one type of community by another.
summer solstice - time of year when the Northern Hemisphere has its longest day and the Southern hemisphere has its shortest. 
(June 20 or 21) 
sun - closest star to Earth and the center of our solar system. 
sunspot - solar storm that appears as dark patches on the sun’s face because it is cooler than the surrounding regions and has a
strong magnetic field.
supergiant star - star with a diameter up to 1 000 times the diameter of the sun.
supernova - exploding star.
superposition - states that in layers of sedimentary rocks, younger rocks normally lie on top of older rocks if the layers have not
been disturbed.  (law of superposition)
surface current - horizontal movement of ocean water that is caused by wind and that occurs at or near the ocean’s surface.
surface runoff - water entering a river or stream after a heavy rain or during a spring thaw of snow or ice.
surface wave - slowest type of seismic wave.
surface zone - area in the ocean where water is mixed by waves and currents; S wave.
sustainable - managing of certain natural resources so that they are not harmed or used up.
swamp - type of freshwater wetland that has spongy, muddy land and lots of water.
S wave - seismic wave that causes particles of rock to move in a side-to-side direction.
swell - one of a group of long ocean waves that have steadily traveled a great distance from their point of generation.
symbiosis - positive interaction between individuals from two different species that live closely together.
symptoms - signs that indicate that a disease is present.
syncline - downward fold in a rock layer.
syndrome - group of signs and symptoms that occur together and characterize a particular abnormality.
systematic observations - observations obtained by following a preplanned method of observation.
system (organ system) - group of organs that work together to perform certain functions; a set of objects, organisms, or different
parts acting to form a whole. 
taiga - cold region of cone-bearing evergreen trees that lies just below the tundra and is the Earth’s largest terrestrial biome.
talus slope - pile or rock fragments at the base of a mountain or on a mountain slope.
taxonomy - science of classification.
technology - use of knowledge gained through scientific thinking and problem solving to make products or tools people can use.
tectonic plate - block of lithosphere that consists of the crust and the rigid, outermost part of the mantle.
tectonic plate boundary - edge between two or more plates classified a divergent, convergent, or transform by the movement
taking place between the plates.
tectonics - branch of Earth science that deals with the movements that shape the Earth’s crust.
telescope - instrument that collects electromagnetic radiation from the sky and concentrates it for better observation.
temperate deciduous forest  - biome that lies at latitudes below about 50o in both the northern and southern hemispheres, usually
has four distinct seasons, and supports a wide variety of plants and animals.
temperate zone - climate zone in each hemisphere that extends from about 30o to 60o latitude.
temperature - measure of how hot or cold something is; measure of the average kinetic energy of the particles in an object.
temperature inversion - atmospheric condition in which a layer of cool air containing pollutants is trapped under a layer of warm
tendon - tough, elastic connective tissue attaching a muscle to a bone.
tension - stress that occurs when forces act to stretch an object.
tentacle - long, slender, flexible extension of the body of certain animals that are used to touch, move, and hold.
terminal moraine - ridge or rounded hill of till deposited at the front end of a glacier.
terrace - flat platform formed at the base of a sea cliff as the sea cliff erodes.
terrestrial planet - one of the highly dense planets nearest to the sun; Mercury, Venus, Mars and Earth
territory - area that an animal defends from other members of the same species and that contains food, shelter, and         potential
test variable - one factor changed by the person doing the experiment in order to study changes in the outcome variable.
(independent variable)  
testosterone - hormone produced by testes; responsible for the development and growth of secondary sex characteristics in males.
texture - quality of a rock that is based on the sizes, shapes, and position of the rock’s grains.
theory - set of ideas that explains related observations and is supported by a large body of evidence acquired through scientific
investigation.                                                                                                                                                                         23
theory of continental drift - idea that says that all of the present-day continents were joined together in one large landmass that
split apart and the continents drifted to their present positions.
theory of plate tectonics - idea that combines the ideas of continental drift and ocean-floor spreading to explain the           formation of
the Earth’s crust and its movements.
thermal conduction - transfer of energy as heat through a material.
thermal energy - total kinetic energy of a substance’s atoms.
thermal expansion - increase in the size of a substance in response to an increase in the temperature of the substance.
thermal pollution - temperature increase in a body of water that is caused by human activity and that has a harmful effect on
water quality and on the ability of that body of water to support life.
thermocline - area of rapid temperature change in the ocean. 
thermometer - instrument that measures and indicates temperature.
thermophile - Archaea that survive in high heat and acid.
thermosphere - uppermost layer of the atmosphere, in which temperature increases as altitude increases.
thrust fault - crack formed when compression causes the hanging wall to slide over the foot wall.
thunder - sound caused by the rapid expansion of air along an electrical strike.
thunderstorm - usually brief, heavy storm that consists of rain, strong winds, lightning and thunder.
tidal energy - energy produced by the rise and fall of the tides.
tidal range - difference in levels of ocean water at high tide and low tide.
tide - periodic rise and fall of the water level of the oceans caused by the moon’s gravitational pull on the Earth.
till - unsorted rock material deposited by a glacier as it melts.
time zone - north-south section of the earth in which all clocks show the same time.
tissue - group of cells similar in structure and joined together to perform a common function; four basic types of tissue are muscle,
connective, nerve, and epidermal. 
topographic map - flat map showing contour lines that represent the height and depth of features on the Earth’s surface.
topography - surface, shape, size and composition of a land area.
topsoil - soil in the A horizon that is made mostly of humus and other organic materials.                                   
tornado - destructive, rotating column of air that has very high wind speeds and that may be visible as a funnel-shaped cloud.
total eclipse - total blocking out of the moon when the moon passes through the umbra of the Earth’s shadow.
toxic - poisonous.
toxin - poison.
trace fossil - fossilized mark that formed in sedimentary rock by the movement of an animal on or within soft sediment.
trachea - windpipe.
trade winds - prevailing winds that blow from east to west from 30o latitude to the equator in both hemispheres.
trait - is a characteristic or behavior that can be used to tell two species apart.
transform boundary - boundary where two plates grind and slide past each other horizontally.
transfusion - process of transferring blood from one body to another.
transmitted - in the context of disease, passed from one individual to another.
transpiration - loss of water vapor through the stomata of a leaf.
transported soil - soil that is moved from its place of origin.
transverse wave - wave in which the wave energy is at right angles to the electric and magnetic fields generated by   moving
photons of energy.
trench - deep V-shaped valley along the ocean floor.
trial - one repetition of a procedure.
tributary - stream that flows into a lake or into a larger stream.
tropical rain forest - hot, wet, equatorial biome that contains the largest number of species.
tropical soil - soil in warm, humid climates formed from the rapid decay of plants and animals.
tropical storm - low-pressure system that starts in the tropics with winds of at least 65 km/hr but less than 120 km/hr.
tropical zone - climate zone in each hemisphere that extends from about 30o latitude to the equator.
tropism - response of a plant to an outside stimulus such as gravity or light; the motion of an organism or part of an           organism
toward or away from an external stimulus. 
troposphere - layer of the atmosphere closest to the ground where temperature decreases as altitude increases; contains 75% of the
atmospheric gases, dust, ice, and liquid water and is where weather, smog, and clouds occur.
trough - lowest point of a wave. 
tsunami - giant sea wave caused by an underwater earthquake.
tundra - cold, dry, treeless biome located at latitudes surrounding the north pole and that has winters six to nine months long.
tundra soil - soil found in the polar regions that has peat on the surface and very limited subsoil.
turbidity current - flow of water down the continental slope that is very dense because of the sediments it carries.
ultraviolet radiation (UV) - type of energy that comes to Earth from the sun and is mostly absorbed by the ozone layer; can cause
cancer and other health problems in many types of plants and animals.
umbra - inner area of a shadow cast by one object in space onto another object in space in which the light is completely blocked  
out.                                                                                                                                                                                          24

unconformity - break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long
period of time.
undertow - subsurface current that is near shore and that pulls objects out to sea.                                                         
unfoliated rock - texture of some metamorphic rocks in which crystals are not arranged in bands and do not break in layers.
unicellular - having one cell.
uniformitarianism - idea that geologic processes that occurred in the past can be explained by current geologic processes.
(principle of uniformitarianism)
universe - space and the total sum of all matter and energy. 
uplift - rising of regions of the Earth’s crust to higher elevations.
upwelling - movement of deep, cold, and nutrient-rich water to the surface.
urban - city environment.
urban heat island - warmer body of air over a city.
urbanization - growth of urban areas caused by people moving into cities.
urea - nitrogenous waste formed in the liver.
ureter - tube that conducts urine to the urinary bladder.
urethra - tube through which urine passes out of the body.
urinary bladder - muscular sac that stores urine.
vaccination - immunization against specific diseases by injection or by mouth so that active immunity is developed.
vaccine - preparation  usually composed of dead or weakened viruses that help the body to develop active immunity         against a
vacuole - large, round sac floating in the cytoplasm of a cell in which water, food, enzymes and other materials are stored.
validate (valid; validity) - others repeat someone else’s experiment with same results.
valley glacier - long, narrow sheets of ice that moves very slowly down a steep mountain valley.
value - that which is desirable or worthy of esteem for its own sake.
Van Allen radiation belt - two doughnut-shaped regions of particles surrounding the Earth that trap radiation from the sun.
vaporization - change of a liquid to a gas.
variable - factor being tested in an experiment; an event, condition, or factor that can be changed or controlled in order to study or
test a hypothesis in a scientific experiment. 
variable star - star that regularly varies in brightness.
vascular plant - plant with specialized tissue that moves water, food, and dissolved substances to cells throughout the plant.
vascular system - long tube-like tissues in plants through which water and nutrients move from one part of the plant to another.
vector - physical quantity with both a magnitude and direction. 
vein - blood vessel that carries blood from the body back to the heart.
vegetative reproduction - growth of new plants from a part of a parent plant.
velocity - time-rate at which a body changes its position vector; displacement divided by the time of travel; quantity whose
magnitude is expressed in units of distance over time; the speed of an object in a particular direction.
vent - opening in a volcano from which lava erupts.
ventricle - lower chamber of the heart.
verify - repeat own experiment.
vernal equinox - first day of spring.  (March 20 or 21)
vertebra (plural-vertebrae) - bone in the vertebral column.
vertebrate - animal with a backbone; only about 3 percent of animals are vertebrates.
vibration - repetitive movement around an equilibrium point. 
villus (plural-villi) - hair-like projection in the small intestine that absorbs digested food in the bloodstream.
virus - microscopic, parasitic particle composed of nucleic acid and protein that can be reproduced only in a living cell; a
noncellular, disease-causing particle that uses the genetic material from its host to reproduce. 
viscosity - is the resistance of a liquid to flow.
visibility -  distance at which a given standard object can be seen and identified with the unaided eye.
vocal cord - tissue in the larynx that vibrates with the passage of air to form sounds.
volcanic ash - rock particles more than 0.25 millimeters but less than 5 millimeters in diameter that are blown into the air during
volcanic eruptions.
volcanic bomb - rock particle from a few centimeters to several meters in diameter that is blown into the air during volcanic
volcanic dust - very fine particles of rock fragments that are blown into the air during volcanic eruptions.
volcano - vent or fissure in the Earth’s surface through which magma and gases are expelled.
volume - amount of space an object takes up; 3-D; the loudness of a sound or signal. 
waning-crescent - phase of the moon between one-half and new moon when the lighted area of the moon appears to grow smaller.
waning-gibbous - phase of the moon between full and one-half when the lighted area of the moon appears to grow smaller.
warm-blooded - able to maintain a constant body temperature.
warm front - type of front that forms when a mass of warm air overtakes a mass of cold air and moves over it.
water cycle - continuous movement of water between the atmosphere, land, oceans, and living things through evaporation,         25
condensation, and precipitation.
waterfall - river that falls off steeply.
water pollution - waste matter or other material that is introduced into water and that is harmful to organisms that live in, drink, or
are exposed to the water. 
watershed - area of land that is drained by a river system.
water table - upper surface of underground water; the upper boundary of the zone of saturation.                             
wave - transfer of energy or movement.
wavelength - distance between a point on one wave and an identical point on the next wave measured from crest to crest or trough
to trough; in compressional waves, is measured from one compression or rarefaction to the next. 
waxing-crescent - phase of the moon between the new moon and one-half moon when the lighted area of the moon          appears to
grow larger.
waxing-gibbous - phase of the moon between one-half and full when the lighted area of the moon appears to grow larger.
weather - short-term condition of Earth’s atmosphere at a particular time and place; includes temperature, humidity, precipitation,
wind and visibility.
weathering - natural process by which atmospheric and environmental agents, such as wind, rain, and temperature changes,
disintegrate and decompose rocks.
wedge - moving inclined plane with one or two sloping sides; a type of simple machine that consists of an inclined plane used to
separate two objects; used to cut, split, or pierce objects or to hold objects together.
weight - measure of the force of attraction between objects due to gravity.
westerlies - prevailing winds that blow from west to east between 30o and 60o latitude in both hemispheres.
wetland - an area of land that is periodically underwater or whose soil contains a great deal of moisture.
wheel and axle - simple machine made from two rigidly attached wheels that rotate together; consists of a rod driven through the
center of a cylinder that is allowed to rotate freely, yielding a mechanical advantage equal to the cylinder’s diameter. 
white blood cell - blood cell that acts as a defense system against disease.
whitecap - bubbles in the crest of a breaking wave.
white dwarf - small, very dense star of carbon that results when a star of low mass, like our sun, collapses.
wildfire - unplanned fire in land that is undeveloped except for roads and power lines and other such structures.
wind - horizontal movement of air caused by different air pressure.
windbreak - rows of trees planted between fields of crops to prevent wind erosion of soil.
wind power - use of a windmill to drive an electric generator.
winter solstice - time of year when the Northern Hemisphere has its shortest day and the Southern Hemisphere has its longest day.
(December 21 or 22)
work - occurs when a force produces movement parallel to the direction in which the force is applied; unit is the joule (J).
xenozoonoses - potentially, deadly viruses that are found in animals and can be transplanted to humans through nonhuman tissue
x-ray (x ray, X-ray, X ray) - electromagnetic radiation having a wavelength shorter than that of ultraviolet light but longer than
that of a gamma ray and having a correspondingly high energy.
xylem - vascular tissue that carries water and dissolved minerals from the soil to the leaves.
year -  time required for the Earth to orbit once around the sun.
zenith - point in the sky directly above an observer on Earth.
zone of aeration - underground region in which the pore spaces are filled mostly with air.
zone of saturation - underground region in which all the pre spaces are filled with water.
zoology - study of animals.



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Science glossary 6th grade



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