Abiotic factor – a nonliving physical or chemical part of an ecosystem
Abrasion – the process of wearing something down by friction
Absolute age – the actual age in years of an event or object
Absorption – the disappearance of a wave into a medium; when a wave is absorbed, the energy transferred by the wave is converted into another form of energy
Acceleration – the rate of change in velocity
Acid – a substance that can donate a proton to another substance and has a pH below 7
Acid rain – rain that has become more acidic than normal due to pollution
Acoustics – the scientific study of sound; the behavior of sound waves inside a space
Active transport – the process of using energy to move materials through a membrane
Adaptation – a characteristic that helps an organism survive in its habitat
Addiction – a physical or psychological need for a habit-forming substance
Aftershock – a smaller earthquake that follows a more powerful earthquake in the same area
Adolescence – the stage of life from the time a human body begins to mature sexually to adulthood
Adulthood – the stage of life that begins once a human body completes its growth and reaches sexual maturity
Air mass – a large body of air that has a uniform temperature and humidity throughout
Air pollution – a large amount of air that has nearly the same temperature and humidity at different locations at the same altitude
Air pressure – the force of air molecules pushing on an area
Air resistance – the fluid friction due to air
Algae – Protists that live mostly in water and use sunlight as a source of energy
Allele – an alternate form of a gene for a specific trait or gene product
Alloy – a solid mixture composed of a metal and one or more other substances
Alluvial fan – a fan-shaped deposit of sediment at the base of a slope, formed as water flows down the slope and spreads at the bottom
Alternating current (AC) – electric current that reverses direction at regular intervals
Altitude – the height above sea level of a place
Ampere (amp) – the unit of measurement of electric current, which is equal to one coulomb per second; the number of amps flowing through a circuit equals the circuit’s amperage
Amphibian – a cold-blooded vertebrate animal that lives in water and breathes with gills when it is young; as an adult, it moves onto land and breathes air with lungs
Amplification – the strengthening of an electrical signal, often used to increase the intensity of a sound wave
Amplitude – the height of the crest or the depth of the trough of a wave measured from the undisturbed surface
Analog – represented by a continuous but varying quantity, such as a wave; in electronics, analog information is represented by a continuous but varying electrical charge
Ancestor – a distant or early form of an organism from which later forms descend
Angiosperm – a plant that has flowers and produces seeds enclosed in fruit
Animalia – part of a classification system that divides all living things into six kingdoms; Kingdom Animalia includes multi-cellular organisms, from humans and lions to insects and microbes, that rely on food for energy
Antibiotic – a medicine that can block the growth and reproduction of bacteria
Antibody – a protein produced by some white blood cells to attack specific foreign materials
Antigen – a marker that a pathogen carries and that stimulates the production of antibodies
Appendicular skeleton – the bones of the skeleton that function to allow movement, such as arm and leg bones
Aquifer – an underground layer of permeable rock that contains water
Archaea – part of a classification system that divides all living things into six kingdoms; Kingdom Archaea includes microscopic organisms with a distinctive cell structure that allows them to live in extreme environments
Artery – a blood vessel with strong walls that carries blood away from the heart
Arthropod – an invertebrate animal with an exoskeleton, a segmented body, and jointed legs
Asexual reproduction – the form of reproduction that involves only one parent producing offspring that are genetically identical to the parent
Asteroid – a small, solid, rocky body that orbits the sun; most orbit in a region between Mars and Jupiter called the asteroid belt
Asthenosphere – the layer in Earth’s upper mantle and directly under the lithosphere in which rock is soft and weak because it is close to melting
Astronomical unit (AU) – Earth’s average distance from the sun, which is approximately 150 million kilometers (93 million miles)
Atmosphere – the outer layer of gases of al large body in space, such as a planet or star; the mixture of gases that surrounds the solid Earth; one of the four parts of the Earth system
Atom – the smallest particle of an element that has the properties of that element
Atomic mass – the average mass of the atoms of an element
Atomic mass number – the total number or protons and neutrons in an atom’s nucleus
Autotroph – an organism that captures energy from sunlight and uses it to produce energy-rich carbon compound, usually through the process of photosynthesis
Axial skeleton – the central part of the skeleton, which includes the cranium, the spinal column, and the ribs
Axis of rotation – an imaginary line about which a turning body rotates
Bacteria – part of a classification system that divides all living things into six kingdoms; Kingdom Bacteria includes microscopic single-celled organisms found in many environments; bacteria can be associated with disease in other organisms
Bacteria of decay – microorganisms that break down dead organisms and return nutrients to the environment
Bar graph – visual tool used to organize, illustrate, and compare observations
Barometer – an instrument that measures air pressure in the atmosphere
Barrier island – a long, narrow island that develops parallel to a coast as a sandbar builds up above the water’s surface
Base – a substance that can accept a proton from another substance and has a pH above 7
Behavior – an organism’s action in response to a stimulus
Bernoulli’s principle – a statement that describes the effects of movement on fluid pressure; an increase in the speed of the motion of a fluid decreases the pressure within the fluid
Big bang – according to scientific theory, the moment in time when the universe started and began to expand
Binary code – a coding system in which information is represented by two figures, such as 1 and 0
Binary fission – a form of asexual reproduction by which some single-celled organisms reproduce; the genetic material is copied, and one cell divides into two independent cells that are each a copy of the original cell; prokaryotes such as bacteria reproduce by binary fission
Binomial nomenclature – the two-part naming system used to identify species; the first part of the name is the genus, and the second part of the name is the species
Biodiversity – describes the great variety of species on earth or within a habitat
Biology – the scientific study of life and all living things
Bioluminescence – the production of light by living organisms
Biomass – organic matter that contains stored energy from sunlight and that can be burned as fuel
Biome – a region of Earth that has a particular climate and certain types of plants
Biosphere – all living organisms on Earth in the air, on the land, and in the waters; one of the four parts of the Earth system
Biotic factor – a living thing in an ecosystem
Black hole – the final stage of an extremely massive star, which is invisible because its gravity prevents any form of radiation from escaping
Blizzard – a blinding snowstorm with winds of at least 56 kilometers per hour (35 miles/hour), usually with temperatures below -7 degrees Celsius (20 degrees Fahrenheit)
Blood – a fluid in the body that delivers oxygen and other materials to cells and removes carbon dioxide and other wastes
Blubber – a layer of fat in some sea mammals that lies beneath the skin; it insulates the animal from cold and stores reserve energy
Boiling – the rapid change in phase from liquid to gas
Boiling point – the temperature at which a substance changes rapidly from a liquid to gas
Bond energy – the amount of energy in a chemical bond between atoms
Budding – a process of asexual reproduction in which an organism develops an outgrowth of the parent; each bud can grow into a new organism, breaking free and becoming separate and independent
Buoyancy – the tenancy of an object to float
Buoyant force – the upward force on objects in a fluid
Calorie – the amount of energy needed to increase the temperature of one gram of water by one degree Celsius
Calories – a unit used to measure and compare the amount of heart energy in a substance
Capillary – a narrow blood vessel that connects arteries with veins
Carbohydrate – a type of carbon-based molecule in living things; carbohydrates include sugars and starches used for energy or as structural materials; carbohydrate molecules contain carbon, hydrogen, and oxygen atoms
Carbon cycle – the continuous movement of carbon through Earth, its atmosphere, and the living things on Earth
Cardiac muscle – the muscle that makes up the heart
Carnivore – a meat eating animal
Carrying capacity – the maximum size that a population can reach in an ecosystem
Catalyst – a substance that increases the rate of a chemical reaction, but is not consumed in the reaction
Cell – the basic unit of structure and function of all living things
Cell membrane – the outer covering which regulates the flow of materials into and out of the cell
Cellular respiration – a process in which cells use oxygen to release energy stored in sugars
Chemical bonds – the link the joins one atom to another in a molecule
Chemical changes – a change that results in the formation of one or more new substance
Chemical energy – the energy stored in certain substances because of their chemical makeup
Chemical formula – an expression that shows the number and types of atoms joined in a compound
Chemical properties – a characteristic of a substance that describes how it can form a new substance
Chemical reaction – the process by which chemical changes occur; in a chemical reaction, atoms are rearranged and chemical bonds are broken and formed
Chemical weathering – the breakdown or decomposition of rock that takes place when minerals change through chemical processes
Central nervous system – the brain and spinal cord; communicates with the rest of the nervous system through electrical signals sent to and from neurons
Centripetal force – any force that keeps an object moving in a circle
Childhood – the stage of life after infancy and before the beginning of sexual maturity
Chloroplast – the organelle in plant cells that contains chlorophyll and in which photosynthesis takes place
Circulatory system – the group of organs, consisting of the heart and blood vessels, that circulates blood through the body
Circuit – a closed path through which charge can flow
Classification – the systematic grouping of different types of organisms by their shared characteristics
Cleavage – the property of a mineral that describes its tendency to break along flat surfaces
Climate – the average condition of the atmosphere in an area over many years
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 – the final community that emerges and is not replaced after ecological succession
Cnidarian – an invertebrate animal such as a jellyfish that has a body with radial symmetry, tentacles with stinging cells, and a central internal cavity
Coefficient – the number before a chemical formula that indicates how many molecules are involved in a chemical reaction
Cold front – the boundary formed when a cool air mass pushes into and under a warm air mass
Collision – a situation in which two objects in close contact exchange energy and momentum
Comet – a body that produces a coma of gas and dust; a small, icy body that orbits the sun
Commensalism – an interaction between two species in which one species benefits without harming the other; a type of symbiosis
Community – all the different population of species that live within a habitat
Compact bone – the tough, hard outer layer of a bone
Competition – the interaction between organisms that require the same food and resources
Competitor – a species characterized by a relatively longer life span, with relatively few offspring, when compared with an opportunist species
Compound – a substance that is formed when two or more different elements combine chemically
Compound machine – a machine that is made up of two or more simple machines
Compound microscope – a microscope that used two lenses
Computer – an electronic device that processes digital information
Concave – curved inward toward the center, like the inside of a spoon
Concentration – the amount of solute dissolved in a solvent at a given temperature
Condensation – the process by which a gas becomes a liquid
Conduction – the transfer of heat by direct molecular contact
Conductor – (1) a material that transfers energy easily (2) a material that transfers electric charge easily
Coniferous – a term used to describe cone-bearing trees and shrubs that usually keep their leaves or needles during all the seasons of the year
Conservation – the saving of natural resource through wise use
Constellation – a group of stars that form a pattern in the sky
Consumer – a living thing that gets its energy by eating other living things in a food chain; consumers are also called heterotrophs
Continental climate – a climate that occurs in the interior of a continent, with large temperature differences between seasons
Continental-continental collision – a boundary along which two plates carrying continental crust push together
Continental drift – the hypothesis that Earth’s continents move on Earth’s surface
Continental shelf – the flat or gently sloping land that lies submerged around the edges of a continent and that extends from the shoreline out to the continental slope
Contour interval – on a topographic map, the difference in elevation from one contour line to the next
Contour line – a line on a topographic map that joins points of equal elevation
Convection – the transfer of energy from place to place by the motion of heated gas or liquid; in Earth’s mantle, convection is thought to transfer energy by the motion of solid rock which when under great heat and pressure can move like a liquid
Convection current – a circulation pattern in which material is heated and rises in one area, then cools and sinks in another area, flowing in a continuous loop
Convergent boundary – a boundary along which two tectonic plates push together, characterized either by subduction or a continental collision
Convex – curved outward, like the underside of a spoon
Cooperation – a term used to describe an interaction between two or more living things in which they are said to work together
Coral reef – a built-up limestone deposit formed by small ant-size organisms called coral
Core – Earths center which is made up of an outer zone and an inner zone
Coriolis Effect – the influence of Earth’s rotation on objects that move over Earth
Cornea – a transparent membrane that covers the eye
Corona – the outer layer of the sun’s atmosphere
Corrosion – the chemical wearing away of metal
Covalent bond – a pair of electrons shared by two atoms
Crest – the highest point, or peak, of a wave
Crust – the outer most solid rock layer of earth contains all the surface features
Crystal – a solid substance in which the atoms are arranged in an orderly, repeating, three-dimensional pattern
Cycle – a series of events or actions that repeat themselves regularly; a physical and/or chemical process in which one material continually changes locations and/or forms
Cytokinesis – the division of a parent cell’s cytoplasm following mitosis
Cytoplasm – the fluid that fills a cell in which most life processes occur
Dam – a structure that holds back and controls the flow of water in a river or other body of water
Data – information gathered by observation or experimentation that can be used in calculating or reasoning
Decibel – the unit used to measure the intensity of a sound wave
Deciduous – a term used to describe trees and shrubs that drop their leaves when winter comes
Decomposer – an organism that breaks down dead organism and returns their nutrients to the environment
Degree – evenly divided units of a temperature scale
Delta – an area of land at the end or mouth, of a river that is formed by the buildup of sediment
Density – the quantity that compares of mass of an object to its volume.
Dependent variable – the variable you measure which depends on the value of the independent variable
Deposition – the process in which transported sediment is laid down
Dermis – the inner layer of skin
Desalination – the process of removing salt from ocean water; used to obtain fresh water
Desertification – the expansion of dessert conditions in areas where the natural plant cover has been destroyed
Dew point – the temperature at which air with a given amount of water vapor will reach saturation
Dichotomous key – a series of questions, each with only two answers, that can be used to help identify an organism’s genus and species
Diffraction – the spreading out of waves as they pass through an opening or around the edges of an obstacle
Diffuse reflection – the reflection of parallel light rays in many different directions
Diffusion – the tendency of a substance to move from an area of higher concentration to an area of lower concentration
Digestion – the breaking down of nutrients into a useable form
Digestive system – the structures in the body that work together to transform the energy and materials in food into forms the body can use
Digital – represented by numbers
Dilute – having a low concentration of solute
Direct current (DC) – electric current that flows in one direction only
Diversity – a term used to describe the quality of having many differences
Divide – a continuous high line of land – or ridge – from which water drains to one side or the other
DNA – the genetic material found in all living cells that contains the information needed for an organism to grow, maintain itself, and reproduce; deoxyribonucleic acid
Domain – one of three divisions in a classification system based on different types of cells; the six kingdoms of living things are grouped into three domains: Archaea, Bacteria, and Eukarya
Dominant – a term that describes the allele that determines the phenotype of an individual organism when two different copies are present in the genotype
Doppler Effect – the apparent change in the frequency of a sound wave that occurs when the source and/or the observe are in motion relative to another
Downwelling – the movement of water from the surface to greater depths
Drainage basin – an area of land in which water drains into a stream system; the borders of a drainage basin are called divides
Drought – a long period of abnormally low amounts of rainfall
Dune – a mound of sand built up by wind
Earthquake – a shaking of earths crust caused by the sudden movement of rocks sliding along a fault in the crust
Echinoderm – an invertebrate sea animal with a spiny skeleton, a water vascular system, and tube feet
Echolocation – the sending out of high-pitched sound waves and the interpretation of the returning echoes
Eclipse – an event during which one object in space casts a shadow onto another; a lunar eclipse occurs when the moon moves through Earth’s shadow, and a solar eclipse occurs when the Moon’s shadow crosses Earth
Ecological succession – the natural process by which one community of living things is replaced by another in an orderly predictable sequence until a stable community appears
Ecology – the study of the interaction between organism and their environment
Ecosystem – the living members of a community along with the nonliving element of their environment
Ectotherm – an animal whose body temperature changes with environmental conditions
Efficiency – the percentage of the input work done on a machine that the machine can return in output work; a machines output work divided by its input work and multiplied by 100
Egg – a female reproductive cell (gamete) that forms in the reproductive organs of a female and has just a single copy of the genetic material of the parent
Electric cell – a device that produces electric current using the chemical or physical properties of different materials
Electric charge – a property that allows one object to exert a force on another object without touching it; can be positive or negative
Electric current – a continuous flow of electric charge, which is measured in amperes
Electrical energy – the energy produced by the flow of electrons from one point to another through a conductor
Electric field – an area surrounding a charged object, within which the object can exert a force on another object without touching it
Electric potential – the amount of potential energy per unit charge that a static charge or electric current has; measured in volts and is often called voltage
Electric power – the rate at which electrical energy is generated from, or converted into, another source of energy, such as kinetic energy
Electromagnet – a magnet that consists of a piece of iron or steel inside a coil of current-carrying wire
Electromagnetic radiation – energy that travels across distances as certain types of waves; types of electromagnetic radiation are radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, x-rays, and gamma rays
Electromagnetic spectrum – the continuous band of wave formed by all the electromagnetic wave together
Electromagnetic wave (EM wave) – a type of wave, such as light wave or radio wave, that does not require a medium to travel; a disturbance that transfers energy through a field
Electromagnetism – magnetism that results from the flow of electric charge
Electron – a negatively charged particle located outside an atom’s nucleus; an electron is about 2000 times smaller than either a proton or neutron
Electronic – (adj) operating by means of an electrical signal (n) an electronic device or system
Element – a pure substance that cannot be broken down into a simpler substance by ordinary chemical changes; an element consisting of one type of atom
Elevation – a measure of how high something is above a reference point, such as sea level
Elimination – the removal of undigested materials from the body
Ellipse – an oval or flattened circle
El Nino – a disturbance of wind patterns and ocean currents in the Pacific Ocean that causes temporary climate change in many parts of the world
Embryo – a multi-cellular organism, plant or animal, in its earliest stages of development
Emigration – in population studies, the movement of individuals out of an ecosystem
Endangered species – a group of organisms that is in danger of extinction
Endocrine system – a group of organs called glands and the hormones they produce that help regulate conditions inside the body
Endoskeleton – an internal support system; such a skeleton made of bone tissue is a distinguishing characteristic of vertebrate animals
Endotherm – an animal that maintains a constant body temperature
Endothermic reaction – a chemical reaction that absorbs energy
Energy – the ability to do work or to cause change
Energy efficiency – a measurement of usable energy after an energy conversion
Energy pyramid – a model used to show the amount of energy available to living things in an ecosystem
Environment – everything that surrounds a living thing; an environment is made up of both living and nonliving factors
Enzyme – a type of protein that is a catalyst for chemical reactions in living things
Epicenter – the point on Earth’s surface directly above the focus of an earthquake
Epidermis – the outer layer of the skin
Equator – an imaginary east-west line around the center of Earth that divides the planet into the Northern Hemisphere and the Southern Hemisphere; a line set at 0o latitude
Equinox – in an orbit, a position and time in which sunlight shines equally on the Northern Hemisphere and the Southern Hemisphere; a time of year when daylight and darkness are nearly equal for most of the Earth
Erosion – the process in which sediment is picked up and moved from one place to another
Estuary – a shoreline area where fresh water from a rive mixes with salt water from the ocean
Eukaryotic cell – a cell in which the genetic material is enclosed within a nucleus, surrounded by its own membrane
Eutrophication – an increase in nutrients in a lake or pond; can occur naturally or as a result of pollution, and causes increased growth of algae and plants
Evaporation – the process by with liquid changes into gas
Evolution – the process through which species change over time; can refer to the changes in a particular population or to the formation and extinction of species over the course of Earth’s history
Exfoliation – in geology, the process in which layers of sheets of rock gradually break off
Exoskeleton – the strong, flexible outer covering of some invertebrate animals, such as arthropods
Exothermic reaction – a chemical reaction that releases energy
Experiment – an organized procedure to study something under controlled conditions
Extinction – species that no longer exist
Extrusive igneous rock – igneous rock that forms as lava and cools on Earth’s surface
False-color image – a computer image in which the colors are not what the human eye would see; can assign different colors to different types of radiation coming from an object to highlight its features
Fault – a fracture in Earth’s lithosphere along which blocks of rock move past each other
Fault-block mountain – a mountain that forms as blocks of rock move up or down along normal faults in areas where the lithosphere is being pulled apart
Faulting – the process by which internal forces cause earth’s crust break and slide along fractures called faults
Fermentation – a chemical process by which cells release energy from sugar when no oxygen is present
Fertilization – the joining together of an egg and sperm cells during sexual reproduction to produce a new individual
Fiber optics – technology based on the use of laser light to send signals through transparent wires called optical fibers; often used in communications
Field – an area around an object where the object can apply a force on another object without touching it
First law of motion – an object at rest remains at rest and an object in motion will remain in motion unless an outside force acts on the object
Floodplain – a flat area of land on either side of a stream that becomes flooded when a river overflows its banks
Flower – the reproductive structure of an angiosperm, containing male and female parts
Fluid – a substance that can flow easily, such as a gas or liquid
Fluorescence – a phenomenon in which a material absorbs electromagnetic radiation of one wavelength and gives off electromagnetic radiation of a different wavelength
Focal length – the distance from the center of a convex lens to its focal point
Focal point – the point at which parallel light rays reflected from a concave mirror come together; the point at which parallel light rays refracted by a convex lens come together
Focus – in an earthquake, the point underground where the rocks first began to move
Folding – the process by which rock layers in Earth’s crust are squeezed into wavelike patterns called folds
Folded mountain – a mountain that forms as continental crust is compressed and rocks bend into large folds
Foliation – the arrangement of minerals within rocks into flat or wavy parallel bands; a characteristic of most metamorphic rocks
Food chain – a sequence of organisms through which nutrients are passed along in an ecosystem
Food web – a number of interconnected food chains
Force – a push or pull; something that changes the motion of an object
Fossil – the remains or trace of an ancient organism usually found in sediment rocks
Fossil fuels – fuels formed from the remains of prehistoric organisms that are burned for energy
Fracture – the tendency of a mineral to break into irregular pieces
Freezing – the process by which a substance changes from its liquid state into its solid state
Freezing point – the temperature at which a substance changes from liquid to a solid
Freezing rain – rain that freezes when it hits the ground or another surface and coats the surface with ice
Frequency – the number of waves that pass by a fixed point in a given amount of time
Fresh water – water that is not salty and has little or no taste, color, or smell; most lakes and rivers are made up of fresh water
Friction – a force that resists motion and must be overcome to start and/or keep an object moving
Front –the boundary between air masses
Fruit – the ripened ovary of a flowering plant that contains the seeds
Fulcrum – a fixed point around which a lever rotates
Full moon – the phase of the moon that occurs when earth is between the sun and the moon so that the entire moon’s lighted side can be seen from earth
Fungi – Part of a classification system that divides all living things into six kingdoms; Kingdom Fungi includes multi-cellular mushrooms and molds and single-celled yeasts
Fusion – a process in which particles of an element collide and combine to form a heavier element, such as the fusion of hydrogen and into helium that occurs in the sun’s core
Galaxy – millions or billions of stars held together in a group by their own gravity
Gamete – a sperm or egg cell, containing half the usual number of chromosomes of an organism (one chromosome from each pair), which is found only in the reproductive organs of a plant or animal
Gamma rays – part of the electromagnetic spectrum that consists of waves with the highest frequencies; electromagnetic waves with frequencies ranging from more than 1019 hertz to more than 1024 hertz
Gas – matter with no definite volume and no definite shape; molecules are very far apart, and the amount of space between them can change easily
Gas giant – a large planet that consists mostly of gases in a dense form; the four large planets in the outer solar system – Jupiter, Saturn, Uranus, and Neptune – are gas giants
Gene – a piece of genetic information that influences
Generator – a device that converts kinetic energy, or the energy of motion, into electrical energy
Genetic engineering – the scientific process in which DNA is separated from an organism, changed, and then reinserted into the same or a different organism
Genetic material – the nucleic acid DNA that is present in all living cells and contains the information needed for a cell’s growth, maintenance, and reproduction
Genome – all the DNA or an organism, including its genes; the genetic material of an organism
Genotype – the genetic makeup of an organism; all the genes that an organism has
Genus – the first part of a binomial name that groups together closely related species
Geographic information systems – computer systems that can store, arrange, and display geographic data in different types of maps
Geologic time scale – the summary of Earth’s history, divide into intervals of time defined by major events or changes on Earth
Geosphere – all the features on Earth’s surface – continents, islands, and seafloor – and everything below the surface – the inner and out core and the mantle; one of the four parts of the Earth system
Geothermal energy – heat energy that originates from within Earth and drives the movement of Earth’s tectonic plates; can be used to generate electricity
Germination – the beginning of growth of a new plant from a spore or a seed
Gestation – in mammals, the period of time spent by a developing offspring inside the mother’s body
Geyser – a type of hot spring that shoots water into the air
Gill – a respiratory organ that filters oxygen dissolved in water
Glacier – a large mass of ice that exists year-round and moves over land
Gland – an organ in the body that produces a specific substance
Global winds – winds that travel long distances in steady patterns over several weeks
Glucose – a sugar molecule that is a major energy source for most cells, produced by the process of photosynthesis
Gravity – the force that objects exert on each other because of their mass
Greenhouse Effect – the trapping of heat in earth’s atmosphere by carbon dioxide
Greenhouse gases – gases, such as carbon dioxide and methane that absorb and give off infrared radiation as part of the greenhouse effect
Grounding – the creation of a harmless, low-resistance path – a ground – for electricity to follow
Groundwater – water that collects and is stored underground
Group – a vertical column in the Periodic Table of Elements; elements in the same group have similar properties
Growth – the increase in size of an organism
Gymnosperm – a plant that produces seeds that are not enclosed in flowers or fruits
Habitat – the particular environment in which an organism lives
Hail – layered lumps or balls of ice that fall from cumulonimbus clouds
Half-life – the amount of time it takes for half of the nuclei of a radioactive isotope to decay into atoms of another element
Hardness – the resistance of a mineral or other material to being scratched
Heat – (1) the flow of energy from an object at a higher temperature to an object at a lower temperature (2) energy that is transferred from a warmer object to a cooler object
Herbivore – a plant eating animal
Heredity – the passing of genes from parents to offspring; the genes are expressed in the traits of the offspring
Hertz (Hz) – the unit used to measure frequency; equal to one complete wavelength per second
Heterotroph – an organism that consumes other organisms to get energy
Hibernate – to enter a sleeplike state of reduced body activity how some animals survive the winter
Hibernation – a sleeplike state in which certain animals spend the winter; reduces the animal’s need for food and helps protect it from cold
High-pressure system – a generally calm and clear weather system that occurs when air sinks down in a high-pressure center and spreads out toward areas of lower pressure as it nears the ground
Homeostasis – the process by which an organism or cell maintains the internal conditions needed for health and functioning, regardless of outside conditions
Horizontal – parallel to the horizon; level
Hormone – a chemical that is made in one organ and travels through the blood to another organ
Horsepower (hp) – the unit of measurement of power for engines and motors; one horsepower equals 745 watts
Host cell – a cell that a virus infects and uses to make copies of itself
Hot spot – an area where a column of hot material rises from deep within a planet’s mantle and heats the lithosphere above it, often causing volcanic activity at the surface
Humidity – the amount of water vapor in air
Humus – a decayed organic matter in soil
Hurricane – a large rotating storm that forms over the ocean in the tropics has strong winds and heavy rain
Hydrocarbon – a compound that contains only carbon and hydrogen
Hydroelectric energy – electricity that is generated by the conversion of the energy of moving water
Hydrogen fuel cell – a device that used hydrogen and oxygen to produce electricity; the byproducts are heat and water
Hydrosphere – all water on Earth – in the atmosphere and in the oceans, lakes, glaciers, rivers, streams, and underground reservoirs; one of the four parts of the Earth system
Hydrothermal vent – an opening in the sea floor from which heated water rises and mixes with the ocean water above
Hyphae – threadlike tubes that form the structural parts of the body of a fungus
Hypothesis – a possible answered to a scientific problem based on observation and/or prior knowledge
Ice age – a period of time during which surface temperatures drop significantly and huge ice sheets spread out beyond the polar regions
Iceberg – a mass of floating ice that broke away from a glacier
Ice core – a tubular sample that shows the layers of snow and ice that have built up over the years
Igneous rock – rock that forms as molten rock, cools and becomes solid
Image – a picture of an object formed by rays of light
Immigration – in population studies, the movement of an organism into a range inhabited by individuals of the same species
Immune system – a group of organs that provides protection against disease-causing agents
Immunity – resistance to a disease; can result from antibodies formed in the body during a previous attack of the same illness
Impact crater – a round pit left behind on the surface of a planet or other body in space after a smaller object strikes the surface
Impermeable – resistant to the passage of water
Incandescence – (1) the production of light by materials having high temperatures (2) light produced by an incandescent object
Inclined plane – a simple machine that is a sloping surface
Incubation – the process of keeping eggs warm by bodily heat until they hatch
Independent variable – the variable that you control in an experiment
Index fossil – a fossil of an organism that was common, lived in many areas, and existed only during a certain span of time; used to help determine the age of rock layers
Induction – the build-up of a static charge in an object when the object is close to, but not touching, a charged object
Inertia – the tendency of an object at rest to remain at rest or an object in motion to remain in motion
Infancy – the stage of life that begins at birth and ends when a baby begins to walk
Infrared light – part of the electromagnetic spectrum that consists of waves with frequencies between those of microwaves and visible light
Infrared radiation – radiation of lower frequencies than visible light
Inner core – a solid sphere of metal, mainly nickel and iron, at Earth’s center
Inorganic compound – a compound that is not considered organic; all compounds that do not contain carbon are inorganic, as are some types of carbon-containing compounds
Insect – an arthropod with three body segments, six legs, two antennae, and compound eyes
Insoluble – not able to dissolve in a given solvent
Insulator – (1) a material that does not transfer energy easily (2) a material that does not transfer electric charge easily
Integumentary system – the body system that includes the skin and its associated structures
Intensity – the amount of energy of a wave, per wavelength; associated with the amplitude of a sound wave and with the quality of loudness produced by the sound wave
Interaction – the condition of acting or having an influence upon something; living things in an ecosystem interact with both living and nonliving parts of their environment
Interference – the meeting and combining of waves; the adding or subtracting of wave amplitudes that occurs as waves overlap
Interphase – the period in the cell cycle in which a cell grows, maintains itself, and prepares for division
Intertidal zone – the narrow ocean margin between the high-tide mark and the low-tide mark
Intrusive igneous rock – igneous rock that forms as magma cools below Earth’s surface
Invertebrate – an animal that has no backbone
Involuntary muscle – a muscle that moves without conscious control
Ion – an atom or group of atoms that has a positive or negative electric charge
Ionic bond – the electrical attraction between a negative ion and a positive ion
Irrigation – the process of supplying water to land to grow crops
Isobar – a line on a weather map connecting places that have the same air pressure
Isomer – any of two or more compounds that contain the same atoms but that have a different structure
Isotope – an atom of one element that has a different number of neutrons than another atom of the same element
Jet stream – a wind that flows in the upper troposphere from west to east over vast distances at great speed
Joule – a unit used to measure energy and work; one calorie is equal to 4.18 joules of energy; one joule of work is done when a force of one Newton moves an object one meter
Kelp forest – a large community of kelp, a type of seaweed that can attach to the ocean floor
Kettle lake – a bowl-shaped lake that was formed as sediment built up around a block of ice left behind by a glacier
Kilowatt (kW) – a unit of measurement for power equal to 1000 watts
Kilowatt-hour (kWh) – the unit of measurement for electrical energy equal to one kilowatt of power over a one-hour period
Kinetic energy – the energy of motion
Kinetic theory of matter – a theory stating that all matter is made of particles in motion
Kingdom – one of the six large groupings of living things that have common characteristics; the kingdoms are Plantae, Animalia, Fungi, Protista, Archaea, and Bacteria
Lander – a craft designed to land on a planet’s surface
Larva – a free-living early form of a developing organism that is very different from its adult form
Laser – a device that produces an intense, concentrated beam of light that can be brighter than sunlight; often used in medicine and communications
Latitude – the distance measure in degrees north or south of the equator
Lava – molten rock that reaches a planet’s surface through a volcano
Law – in science, a rule or principle describing a physical relationship that always works in the same way under the same conditions
Law of conservation energy – energy can be neither created nor destroyed
Law of conservation of mass – atoms/matter are not created or destroyed in a chemical reaction
Law of conservation of momentum – a law stating that the amount of momentum a system of objects has does not change as long as there are no outside forces acting on that system
Law of reflection – a law of physics stating that the angle at which light strikes a surface (the angle of incidence) equals the angle at which it reflects off the surface (the angle of reflection)
Lens – a piece of transparent glass or plastic with curved surfaces that bend light rays
Lever – a solid bar that rotates, or turns, around a fixed point (fulcrum); one of the six simple machines
Lichen – an organism that results from a close association between single-celled algae and fungi
Life cycle – the changes that an organism undergoes as it develops and produces offspring
Light – a visible form of radiant energy that moves in waves outward in all directions from its source
Lightning – a discharge of electricity from one part of a cloud to another or between a cloud and the ground, causing a bright flash of light
Light-year – the distance light travels in one year, which is about 9.5 trillion kilometers (6 trillion miles)
Limiting factor – a factor or condition that prevents the continuing growth of a population in an ecosystem
Lipid – a type of carbon-based molecule in living things; includes fats and oils used for energy or as structural materials
Liquefaction – a process in which the shaking of ground causes loose, wet soil to act like a liquid
Liquid – matter that has a definite volume but does not have a definite shape; molecules are close together but not bound to one another
Lithosphere – the layer of Earth made up of the crust and the rigid rock of the upper mantle, averaging about 40 kilometers thick and broken into tectonic plates
Lock – a section of waterway, closed off by gates, in which the water level is raised or lowered to move ships through
Loess – deposits of fine-grained, wind-blown sediment
Longitude – the distance measured in degrees east and west of the prime meridian
Longitudinal wave – a type of wave in which the disturbance moves in the same direction that the wave travels
Longshore current – the overall direction and movement of the waves that strike the shore at an angle
Longshore drift – the zigzag movement of sand along a beach, cause by the action of waves
Low-pressure system – a large and often stormy weather system that occurs when air moves around and into a low-pressure center, then moves up to higher altitudes
Luminescence – the production of light without the high temperatures needed for incandescence
Lung – a respiratory organ that absorbs oxygen from the air
Luster – the property of a mineral that describes the way in which light reflects from its surface; major types are metallic and non-metallic
Machine – any device that makes doing work easier
Magma – molten rock beneath Earth’s surface
Magnet – an object that attracts certain other materials
Magnetic domain – a group of atoms whose magnetic fields align, or point in the same direction
Magnetic field – an area surrounding a magnet within which the magnet can exert a force; are concentrated into a pattern of lines that extend from the magnet’s north pole to its south pole
Magnetic reversal – a switch in the direction of Earth’s magnetic field so that the magnetic north pole becomes the magnetic south pole and the magnetic south pole becomes the magnetic north
Magnetism – the force exerted by a magnet; opposite poles of two magnets attract, or pull together, whereas like poles of two magnets repel, or push apart
Main sequence – the stage in which stars produce energy through the fusion of hydrogen into helium
Mammal – a warm-blooded vertebrate animal whose your feed on milk produced by the mother’s mammary glands
Mantle – the layer of rock between Earth’s outer core and crust, in which most rock is hot enough to flow in convection currents; Earth’s thickest layer
Map legend – a chart that explains the meaning of each symbol used on a map; also called a key
Map scale – the comparison of distance on a map with actual distance on what the map represents, such as Earth’s surface; may be expressed as a ratio, a bar scale, or equivalent units
Mare – a large, dark plain of solidified lave on the Moon; the plural form of mare is maria
Marine climate – a climate influenced by a nearby ocean, with generally mild temperatures and steady precipitation
Mass – the amount of matter in an object
Mass extinction – one of several periods in Earth’s history when large numbers of species became extinct at nearly the same time
Mass wasting – the downhill movement of loose rock or soil
Matter – anything that has mass and takes up space
Mechanical advantage – the number of times a machine multiplies the input force; output force divided by input force
Mechanical energy – the form of energy with which moving objects perform work
Mechanical wave – a wave, such as a sound wave or a seismic wave that transfers kinetic energy through matter
Mechanical weathering – the breakdown of rock into smaller pieces of the same material without any change in its composition
Medium – a substance through which a wave moves
Meiosis – a part of sexual reproduction in which cells divide to form sperm cells in a male and egg cells in a female; occurs only in reproductive cells
Melting – the process by which a substance changes from its solid state to its liquid state
Melting point – the temperature at which a substance changes from a solid to a liquid
Menstruation – a period of about five days during which blood and tissue exit the body through the vagina
Metabolism – the sum of all the chemical reactions that take place in the body
Metal – describes shinny solids that conduct electricity found at the left on the Periodic Table
Metallic bond – a certain type of bond in which nuclei float in a sea of electrons
Metalloid – an element that has properties of both metals and non-metals
Metamorphic rock – rock formed as heat or pressure causes existing rock to change in structure, texture, or mineral composition
Metamorphism – the process by which a rock’s structure or mineral composition is changed by pressure or heat
Metamorphosis – the process of a complete change in body form during development from juvenile to an adult stage
Meteor – a brief streak of light produced by a small particle entering Earth’s atmosphere at a high speed
Meteorite – a small object from outer space that passes through Earth’s atmosphere and reaches the surface
Meteorologist – a scientist who studies weather
Meter (m) – the standard SI unit for length
Microclimate – the climate of a smaller area within a sub-climate
Microorganism – a very small organism that usually cannot be seen without a microscope
Microscope – an instrument that used glass lenses to magnify an object
Microwaves – part of the electromagnetic spectrum that consists of waves with higher frequencies than radio waves, but lower frequencies than infrared waves
Mid-ocean ridge – a long line of sea-floor mountains where new ocean crust is formed by volcanic activity along a divergent boundary
Migrate – to move from one environment to another, where conditions are more favorable; how some animals survive the change in seasons
Migration – the movement of animals from one region to another in response to changes in the seasons or the environment
Mineral – a naturally occurring solid substance made of inorganic (nonliving) material
Mitochondria – organelles that release energy by using oxygen to break down sugars
Mitosis – the phases in the cell cycle during which the nucleus divides
Mixture – forms when two or more materials are put together without forming a new substance
Mobile – able to move from place to place
Molecule – the smallest particle of a compound
Mollusk – an invertebrate animal with a soft body, a muscular foot, and a mantle; have a hard outer shell
Molting – the process of an arthropod shedding its exoskeleton to allow for growth
Momentum – a measure of mass in motion; the product of an object’s mass and velocity
Monomer – one of many small, repeating units linked together to form a polymer
Monsoon – a wind that changes direction with the seasons
Moraine – a deposit of till left behind by a retreating glacier; can form along a glacier’s sides or at its end
Motion – a change in the position of an object relative to another object, which is assumed to be at rest
Mountain – a feature on Earth’s surface that rises high above the surrounding landscape; produced by folding, faulting, or volcanic activity
Multi-cellular – described a living thing that is composed of more than one cell
Muscular system – the muscles of the body that, together with the skeletal system, function to produce movement
Mutation – a change in the genetic material of an organism
Mutualism – an interaction between two species in which both benefit; a type of symbiosis
Nanotechnology – the science and technology of building electronic circuits and devices from single atoms and molecules
Natural resource – any type of matter or energy from Earth’s environment that humans use to meet their needs
Natural selection – the process that favors those organisms that are best able to survive and reproduce
Neap tide – a tide of small range occurring during the first – and third – quarter phases of the Moon
Nebula – a cloud of gas and dust in space; stars form in nebulae
Net force – the overall force acting on an object when all of the forces acting on it are combined
Neuron – a nerve cell
Neutral – describing a solution that is neither an acid nor a base; a neutral solution has a pH of 7
Neutron – a particle that has no electric charge and is located in an atom’s nucleus
Neutron star – a dense core that may be left behind after a higher-mass star explodes in a supernova
New moon– the phase of the moon that occurs when the moon is between Earth and the sun, so that the moon cannot be seen from Earth
Newton’s first law – a scientific law stating that objects at rest remain at rest, and objects in motion remain in motion with the same velocity, unless acted on by an unbalanced force
Newton’s second law – a scientific law stating that the acceleration of an object increases with increased force and decreases with increased mass
Newton’s third law – a scientific law stating that every time one object exerts a force on another object, the second object exerts a force that is equal in size and opposite in direction back on the first object
Niche – the role a living thing plays in its habitat
Nitrogen cycle – the continuous movement of nitrogen through Earth, its atmosphere, and the living things on Earth
Noble Gases – a group of gaseous elements that seldom react with other elements; found in the extreme right column on the Periodic Table of the Elements
Nonmetal – describes solids and gases that are poor conductors of electricity; found at the right on the Periodic Table of the Elements
Nonpoint-source pollution – pollution with a source that is hard to find or scattered
Nonrenewable Resource – a resource, such as a mineral, that cannot be replaced by nature within a relatively shot time span (i.e., within human history)
Nuclear Energy – the energy stored within the nucleus of an atom; used by nuclear power plants to produce electricity
Nuclear fission – the process of splitting the nuclei of radioactive atoms, which releases huge amounts of energy mainly in the form of radiation and heat energy
Nucleic acid – one of several carbon-based molecules that carry an organism’s genetic code; one of the nucleic acids – DNA – contains the information needed to construct proteins
Nucleus – (1) The structure within a cell that controls cell activity and contains genetic material. (2) The center of an atom
Nutrients – Food substances that an organism uses for producing energy as well as for its growth and repair
Nutrition – The process that includes ingestion, digestion, and elimination
Observation – anything we perceive through use of one or more of our five senses
Ocean current – a mass of moving ocean water
Oceanic-continental subduction – a boundary along which a plate carrying oceanic crust sinks beneath a plate with continental crust
Oceanic-oceanic subduction – a boundary along which a plate carrying oceanic crust sinks beneath another plate with oceanic crust
Offspring – the new organisms produced by one or two parent organisms
Ohm () – the unit of measurement for electrical resistance
Ohm’s law – the mathematical relationship among current, voltage, and resistance, expressed in the formula I = V/R (current = voltage/resistance)
Omnivore – a consumer that can eat both plants and other animals
Opportunist – a species characterized by a relatively short life span, with relatively large quantities of offspring, as compared with a competitor species
Optics – the study of light, vision, and related technology
Orbit – (n.) the path of an object in space as it moves around another object due to gravity (v.) to revolve around, or move in an orbit
Ore – a rock that contains enough of a valuable mineral to be mined for profit
Organ – a group of tissues that act together to perform a function
Organelle – a structure in a cell that is enclosed by a membrane and that performs a particular function
Organic compound – a compound that is based on carbon
Organism – an individual living thing, made up of one or many cells, that is capable of growing and reproducing
Organ System – a group of organs that act together to carry out a life process
Original remains – a fossil that is the actual body or body parts of an organism
Osmosis – the movement of water through a membrane from an area of higher concentration to an area of lower concentration
Outer Core – the layer that surrounds Earth’s inner core, it is about 2,300 kilometers thick; thought to be liquid because S-waves cannot travel through it
Overfishing – the catching of at a faster rate than they can reproduce
Ozone – a gas molecule that consists of three oxygen atoms
Pangaea – a hypothetical super-continent that included all of the landmasses on Earth; it began breaking apart about 200 million years ago
Parallax – the apparent shift in the position of an object when viewed from different locations
Parallel circuit – a circuit in which current follows more than one path
Parasite – an organism that absorbs nutrients from the body of another organism, often harming it in the process
Parasitism – a relationship between two species in which one species is harmed while the other benefits; a type of symbiosis
Parent – an organism that produces a new organism or organisms similar to or related to itself
Particulates – tiny particles or droplets, such as dust, dirt, and pollen that are mixed in with air
Pascal (Pa) – the unit used to measure pressure; one Pascal is the pressure exerted by one Newton of force on an area of one square meter, or one N/m2
Pascal’s principle – a statement that says when an outside pressure is applied at any point to a fluid in a container, that pressure is transmitted throughout the liquid with equal strength
Passive transport – the movement of materials through a membrane without any input of energy
Pathogen – an agent that causes disease
Pedigree – a chart that shows family relationships, including two or more generations
Penumbra – a region of lighter shadow that may surround an umbra
Percentage – a ration that states the number of times an outcome is likely to occur out of a possible 100 times
Period – a horizontal row in the Periodic Table of Elements; elements in a period have varying properties
Periodic Table of Elements – a table of the elements, arranged by atomic numbers, that shows the patterns in their properties
Peripheral nervous system – the part of the nervous system that lies outside the brain and spinal cord
Peristalsis – wavelike contractions of smooth muscles in the organs of the digestive tract; moves food through the digestive system
Permeable – allowing the passage of water
pH – the concentration of hydrogen ions in a solution ; a measurement of acidity
Phases – (1) the changing apparent shape of the moon, as seen from Earth; (2) the three forms, or state, of matter—solid, liquid, and gas
Phenotype – the observable characteristics or traits of an organism
Photosynthesis – the process by which green plants and other producers use simple compounds and energy from light to make sugar, an energy-rich compound; this is an endothermic process in which light is absorbed and used to change carbon dioxide and water into glucose and oxygen
Physical change – a change in the appearance of a substance that does not alter the chemical makeup of the substance
Physical property – a characteristic of a substance that can be determined without changing the identity of the substance
Phytoplankton – microscopic floating organisms that live in water and, like plants, convert sunlight, carbon dioxide, and water, into food
Pioneer species – the first species to move into a lifeless environment
Pitch – the quality of highness or lowness of a sound; associated with frequency of a sound wave
Placenta – an organ that transports materials between a pregnant female mammal and the offspring developing inside her body
Plain – a broad, flat landscape region at a low elevation, made up of layered sedimentary rock
Planet – a spherical body, larger than a comet or asteroid, that orbits the sun, or a similar body that orbits a different star
Plankton – mostly microscopic organisms that drift in great numbers through bodies of water
Plantae – Part of a classification system that divides all living things into six kingdoms; Kingdom Plantae includes multi-cellular organisms, such as tree, grass, and moss, that are capable of photosynthesis, capturing energy from the sun
Plastic – a polymer that can be molded or shaped
Plateau – a large area of earth’s surface made up of horizontally layered rocks, found at relatively high elevation
Plate tectonics – the theory that Earth’s crust is broken up into a number of large pieces, or plates, that move and interact, producing many of Earth’s surface features
Point-source pollution – pollution that enters water from a known source
Polar covalent bond – the unequal sharing of electrons between two atoms that gives rise to negative and positive regions of electric charge
Polarization – a way of filtering light so that all of the waves vibrate in the same direction
Pollen – tiny multi-cellular grains that contain the undeveloped sperm cells of a plant
Pollutants – harmful substance that contaminate the environment, offer produced by human activates
Pollution – the release of harmful substances into the air, water, or land
Polymer – a very large carbon-based molecule made of smaller, repeating units
Population – all the members of a particular species that live within a habitat
Population density – a measure of the number of organisms that live in a given area
Population dynamics – the study of the changes in the number of individuals in a population and the factors that affect those changes
Position – an object’s location
Potential energy – stored energy; the energy an object has due to its position, molecular arrangement, or chemical composition
Power – the rate at which work is done
Precipitate – a solid substance that forms as a result of a reaction between chemicals in two liquids
Precipitation – any type of liquid or solid water that falls to Earth’s surface, such as rain, snow, or hail
Predator – an animal that hunts and kills (another animal) for its food
Pressure – a measure of how much force is acting on a certain area; how concentrated a force is; equal to force divided by area
Prevailing winds – the winds that commonly blow in the same direction at given latitude
Prey – the animal hunted by a predator (to be its food)
Primary colors – three colors of light – red, green, and blue – that can be mixed to produce all possible colors
Primary pigments – three colors of substances – cyan, yellow, and magenta – that can be mixed to produce all possible colors
Primary wave – an earthquake wave that can travel through liquids and solids; a P-wave
Prime meridian – an imaginary north-south line that divides the planet into the Eastern Hemisphere and the Western Hemisphere
Prism – an optical tool that uses refraction to separate the different wavelengths that make up white light
Probability – the likelihood or chance that a specific outcome will occur out of a total number of outcomes
Probe – a spacecraft that is sent into a planet’s atmosphere or onto a solid surface
Problem – a scientific query, always stated in the form of a question
Producer – an organism that makes its own food; algae and plants
Product – a substance formed by a chemical reaction; a product is made by the rearrangement of atoms and bonds in reactants
Projection – a representation of Earth’s curved surface on a flat map
Prokaryotic cell – a cell that lacks a nucleus and other organelles, with DNA that is not organized into chromosomes
Protein – a macromolecule in living things that is made of smaller molecules called amino acids
Protista – Part of a classification system that divides all living things into six kingdoms; Kingdom Protista includes mostly single-celled organisms with cells similar to those of the Plantae, Animalia, and Fungi kingdoms
Proton – a positively charged particle located in an atom’s nucleus
Protozoa – animal-like protists that eat other organisms or decaying parts of other organisms
Pulley– a wheel with a grooved rim that turns on an axle; one of the six simple machines
Punnett square – a chart used to show all the ways genes from two parents can combine and be passed to offspring; used to predict all genotypes that are possible
Pupil – the circular opening in the iris of the eye that controls how much light enters the eye
Pyroclastic flow – a dense cloud of superheated gases and rock fragments that moves quickly downhill from an erupting volcano
Quasar – the very bright center of a distant galaxy
Radiation – the transfer of heat through space in the form of waves
Radioactivity – the process by which the nucleus of an atom of an element releases energy and particles
Radio waves – the part of the electromagnetic spectrum that consists of waves with the lowest frequencies
Rain shadow – an area on the downwind side of a mountain that gets less precipitation than the other side that faces the wind
Ratio – a comparison between two quantities, often written with a colon, as 3:4
Reactant – a substance that is present at the beginning of a chemical reaction and is changed into a new substance
Reactive – likely to undergo a chemical change
Recessive – a term that describes an allele that is not expressed when combined with a dominant form of a gene
Recrystallization – the process by which bonds between atoms in minerals break and re-form in new ways during metamorphism
Recycling – the reusing of materials that people would otherwise throw away, such as paper, glass, plastics, and certain materials
Red blood cell – a type of blood cell that picks up oxygen in the lungs and delivers it to cells throughout the body
Reference point – a location to which another location is compared
Reflection – the bouncing back of a wave after it strikes a barrier
Refraction – the bending of a wave as it crosses the boundary between two mediums at an angle other than 90 degrees
Regeneration – in some organisms, the process by which certain cells produce new tissue growth at the site of a wound or lost limb; also a form of asexual reproduction
Regular reflection – the reflection of parallel light rays in the same direction
Regulation – the process that helps an organism maintains a constant internal environment
Relative age – the age of an event or object in relation to other events or objects
Relative humidity – the comparison of the amount of water vapor in the air with the maximum amount of water vapor that can be present in the air at that temperature
Relative motion – the idea that the observation of motion depends on the observer
Relief – in geology, the difference in elevation between an area’s high and low points
Relief map – a map that shows the differences in elevation in an area; can show elevations through the use of contour lines, shading, colors, and in some cases, three-dimensional materials
Remote sensing – a method of using scientific equipment to gather information about something from a distance
Renewable resource – a resource that can be replenished by nature within a relatively short time span (i.e., within human history)
Replication – the process by which DNA is copied before it condenses into chromosomes; takes place before a cell divides
Reproduction – the process by which an organism produce s new individuals, or offspring
Reptile – a cold-blooded vertebrate that has skin covered with scales or horny plates and has lungs
Research – the gathering of facts, data, and opinion on a scientific topic
Resistance – (1) the ability of an organism to protect itself from a disease or the effects of a substance (2) the property of a material that determines how easily a charge can move through it; measured in ohms
Resistor – an electrical device that slows the flow of charge in a circuit
Resonance – the strengthening of a sound wave when it combines with an object’s natural vibration
Respiration – the process by which organism use energy stored in food—nutrients combine with oxygen, releasing energy (and carbon dioxide and water as waste products
Respiratory system – a system that interacts with the environment and with other body systems to bring oxygen to the body and remove carbon dioxide
Retina – a light-sensitive membrane at the back of the inside of the eye
Revolution – the motion of one body around another; the time it takes an object to go around once
Rift valley – a deep valley formed as tectonic plates move apart, such as a long a mid-ocean ridge
Ring – in astronomy, a wide, flat zone of small particles that orbit around a planet’s equator
Rip current – a narrow stream of water that breaks through sandbars and drains rapidly back into deeper water
RNA – a molecule that carries genetic information from DNA to a ribosome, where the genetic information is used to bring together amino acids to form a protein; ribonucleic acid
Robot – a machine that works automatically or by remote control
Rock – a naturally formed solid that is usually made up of one or more types of minerals
Rock cycle – the set of natural, repeating processes that form, change, break down, and re-form rocks
Salinity – the measure of the amount of dissolved salt contained in water
Salt water – water that contains dissolved salts and other minerals
Sandbar – a ridge of sand built up by the action of waves and currents
Satellite – solid object in solar system the revolve around planets; also called moon
Saturated – containing the maximum amount of a solute that can be dissolved in a particular solvent at a given temperature and pressure
Saturation – a condition of the atmosphere in which the rate of evaporation and condensation are equal
Scale – one of the thin, small, overlapping plates that cover most fish and reptiles and some other animals
Scattering – the spreading out of light rays in all directions as particles reflect and absorb light
Science – the study of the natural world
Scientific method – an organized STEP-BY-STEP Approach to problem solving in science
Screw – a simple machine that is an inclined plane wrapped around a cylinder
Season – one part of a pattern of temperature changes and other weather trends over the course of a year; astronomical seasons are defined and caused by the position of Earth’s axis relative to the direction of sunlight
Second (s) – a unit of time equal to one-sixtieth of a minute
Secondary wave – an earthquake wave that can travel only through solids; an S-wave
Second law of motion – the relationship among force, mass, and acceleration; F = (m)(a)
Sediment – solid materials such as rock fragments, plant and animal remains, or minerals that are carried by water or by air and that settle on the bottom of a body of water or on the ground
Sedimentary rock – rock formed as pieces of older rocks and other loose materials get pressed or cemented together or as dissolved minerals re-form and build up in layers
Seed – a plant embryo that is enclosed in a protective coating and has its own source of nutrients
Seismic wave – the vibrations caused by an earthquake
Seismograph – an instrument that constantly records ground movements
Selective breeding – the process of breeding plants and animals with specific traits to produce offspring that have these traits
Sensor – a mechanical or electronic device that receives and responds to a signal, such as light
Septic system – a small sewage system, often for one home or business, that uses an underground tank to treat wastewater
Series circuit – a circuit in which current follows a single path
Sessile – the quality of being attached to one spot; not free-moving
Sewage system – a system that collects and treats wastewater from a city or a town
Sexual reproduction – the form of reproduction that involves two parents, producing offspring that are not identical to either parent
Short circuit – an unintended and undesired path connecting one part of a circuit with another
Simple machine – one of the basic machines on which all other mechanical machines are based; the six simple machines are the lever, inclined plane, wheel and axle, pulley, wedge, and screw
Sinkhole – an open basin that forms when the roof of a cavern becomes so thin that it falls in
SI units – System of International Units, used by all scientists to express measurements
Skeletal muscle – a muscle that attaches to the skeleton
Sleet – small pellets of ice that form when rain passes through a layer of cold air and freezes before hitting the ground
Slope – a measure of how steep a landform is; calculated as the change in elevation divided by the distance covered
Smog – the combination of smoke and fog; a type of air pollution that occurs when sunlight causes unburnt fuels, fumes, and other gases to react chemically, often seen as a brownish haze
Smooth muscle – muscle that performs involuntary movement and is fond inside certain organs, such as the stomach
Soil horizon – a soil layer with physical and chemical properties that differ from those of soil layers above or below it
Soil profile – the soil horizons in a specific location; a cross section of soil layers that displays all soil horizons
Solar cell – a device that converts the energy of sunlight into electrical energy
Solar System – the sun and all objects that revolve around it, including the planets and their moons, asteroids, comet, and their meteors
Solar wind – a stream of electrically charged particles that flows out in all directions from the sun’s corona
Solid – matter that has a definite shape and definite volume; molecules in a solid are in fixed positions and are close together
Solstice – in an orbit, a position and time during which one hemisphere gets its maximum area of sunlight, while the other hemisphere gets its minimum amount; the time of year when days are either longest or shortest, and the angle of the sunlight reaches its maximum or minimum
Solubility – the maximum amount of solute that can dissolve in a given amount of solvent at a given temperature
Soluble – the ability of a substance to dissolve in a given solvent
Solute – the substance that dissolves in the solvent
Solution – a mixture in which the components remain evenly distributed
Solvent – the substance (e.g., water) that dissolves the solute
Sonar – a system that uses underwater sound waves to measure distance and locate objects
Sound – the form of energy produced by a vibrating object; moves in waves
Space station – a satellite in which people can live and work for long periods
Specialization – the specific organization of a cell and its structure that allows it to perform a specific function
Speciation – the evolution of a new species from an existing species
Species – a group of organisms of the same kind that can produce fertile offspring
Specific heat – the amount of energy required to raise the temperature of one gram of a substance by one degree Celsius
Spectrum – (1) radiation from a source separated into a range of wavelengths (2) the range of colors that appears in a beam of visible light when it passes through a prism
Speed – the distance traveled per unit of time; e.g., meters per second
Sperm – a male reproductive cell (gamete) that forms in the reproductive organs of a male and has just a single copy of the genetic material of the parent
Sponge – a simple multi-cellular invertebrate animal that lives attached to one place and filters food from water
Spongy bone – strong, lightweight tissue inside a bone
Spore – a single reproductive cell that can grow into a multi-cellular organism
Spring – a flow of water from the ground at a place where the surface of the land dips below the water table
Spring tide – a tide of large range occurring during the new and full moons, resulting in an extra-high tidal bulge and an extra-low tidal dip
States of matter – the different forms in which matter can exist
Static charge – the buildup of electric charge in an object caused by the uneven distribution of charged particles
Statistical analysis – a rigorous mathematical method of examining experimental data; also called statistics
Stimulus – something that causes a response in an organism or a part of the body
Storm surge – a rapid rise in water level in a coastal area that occurs when a hurricane pushes a huge mass of ocean water, often leading to flooding and widespread destruction
Streak – the color of a mineral powder left behind when a mineral is scraped across a surface; a method for classifying minerals
Stress – the force applied by an object pressing on, pulling on, or pushing against another object
Subduction – the process by which an oceanic tectonic plate sinks under another plate into Earth’s mantle
Sublimation – the process by which a substance changes directly from its solid state to its gas state without becoming a liquid first
Subscript – a number written slightly below and to the right of a chemical symbol that shows how many atoms of an element are in a compound
Substance – matter of a particular type – elements, compounds, mixtures
Succession – a natural process that involves a gradual change in the plant and animal communities that live in an area
Sunspot – a darker spot on the photosphere of the sun; appears dark because it is cooler than the surrounding area
Suspension – a mixture in which the different parts are identifiable as separate substances; a heterogeneous mixture
Sustainable – a term that describes the managing of certain natural resources so that they are not harmed or used up
Symbiosis – the interaction between individuals from two different species that live closely together
System – a group of components, or parts that work together for a common purpose
Taxonomy – the science of classifying and naming organisms
Technology – the application of scientific knowledge and other resources to develop new products for a common purpose
Tectonic plates – one of the large moving pieces into which Earth’s lithosphere is broken and which commonly carries both oceanic and continental crust
Tectonics – the processes in which the motion of hot material under a crust changes the crust of a space body
Telescope – a device that gathers visible light or another form of electromagnetic radiation
Temperature – a measure of the average molecular motion of a substance
Tentacle – a long, slender, flexible extension of the body of certain animals, such as jellyfish; used to touch, move, or hold
Terminal velocity – the final, maximum velocity of a falling object
Terrestrial planet – Earth or a planet similar to Earth that has a rocky surface; the four planets in the inner solar system – Mercury, Venus, Earth, Mars
Theory – in science, a set of widely accepted explanations of observations and phenomena; a theory is a well-tested explanation that is consistent with all available evidence
Theory of plate tectonics – a theory stating that Earth’s lithosphere is broken into huge plates that move and change in size over time
Thermal energy – the energy an object has due to the motion of its particles; the total amount of kinetic energy of particles in an object
Thermometer – a device for measuring temperature
Third law of motion – for every action there is an equal and opposite reaction
Thunder – the sound wave created by intensely heated air around a lightening bolt
Thunderstorm – a brief intense rainstorm that affects a small area and is accompanied by lighting and thunder
Tidal range – the difference in height between high tide and low tide
Tides – the rise and fall in the level of the oceans water that take place each day
Till – sediment of different sizes left directly on the ground by a melting, or retreating glacier
Tissue – a group of similar cells that act together to form a function
Topography – all natural and human-made surface features of a particular area
Tornado – a violent whirling wind, sometimes visible as a funnel-shaped cloud
Trait – any type of feature that can be used to tell two species apart
Transform boundary – a boundary along which two tectonic plates scrape past each other, and crust is neither formed nor destroyed
Transformer – a device uses electromagnetism to increase or decrease voltage
Transmission – the passage of a wave through a medium
Transpiration – the movement of water vapor out of a plant and into the air
Transport – the process of moving materials throughout an organism
Transverse wave – a type of wave in which the disturbance moves at right angles, or perpendicular, to the direction in which the wave travels
Tropical storm – a low-pressure system that starts in the tropics with winds of a least 65 kilometers per hour (40 miles per hour) but less than 120 kilometers per hour (74 miles per hour)
Trough – the lowest point, or valley, of a wave
Tsunami – a water wave caused by an earthquake, volcanic eruption, or landslide
Turnover – the yearly rising and sinking of cold and warm water layers in a lake
Ultrasound – sound waves with frequencies about 20,000 hertz, the upper limit of typical hearing levels in humans; used for medical purposes, among other things
Ultraviolet light – the part of the electromagnetic spectrum that consists of waves with frequencies higher than those of visible light and lower than those of x-rays
Ultraviolet radiation – radiation of higher frequencies than visible light, which can cause sunburn and other types of damage
Umbra – the dark, central region of a shadow, such as the cone of a complete shadow cast by an object
Unicellular – describes a living thing composed of a single cell; e.g., an ameba
Unicellular organism – an organism that is made up of a single cell
Uniformitarianism – a theory stating that processes shaping Earth today, such as erosion and deposition, also shaped Earth in the past, and that these processes cause large changes over geologic time
Universe – space and all the matter and energy in it
Upwelling – the vertical movement of deep water up to the surface
Urban – a term that describes a city environment
Urban heat island – the warmer body of air over a city
Urine – liquid waste that is secreted by the kidneys
Vaccine – a small amount of a weakened pathogen that is introduced into the body to stimulate the production of antibodies
Vacuum – a space containing few or no particles of matter
Variable – the changeable condition that can affect the outcome of an experiment
Vascular system – long tube-like tissues in plants through which water and nutrients move from one part of the plant to another
Vector – a quantity that has both size and directions
Vein – a blood vessel that carries blood back to the heart
Velocity – the speed of an object in a certain direction
Vertebrate – an animal with an internal backbone
Vertical – going straight up or down from a level surface
Vestigial organ – a physical structure that was fully developed and functional in an earlier group of organisms but is reduced and unused in later species
Vibration – a rapid, back-and-forth motion
Virus – a nonliving disease-causing particle that uses the materials inside cells to make copies of itself; consists of genetic material enclosed in a protein coat
Visible light – the part of the electromagnetic spectrum that consists of waves detectable by the human eye
Volcanism – the process of molten material moving from a space body’s hot interior onto its surface
Volcano – (1) an opening in Earth’s surface through which hot, liquid rock flows from deep underground (2) a mountain formed by a series of volcanic eruptions
Volt (V) – the unit of measurement for electric potential, which is equal to one joule per coulomb; the number of volts of an electric charge equals the charge’s voltage
Volume – the amount of space an object occupies
Voluntary muscle – a muscle that can be moved at will
Warm front – the boundary formed when a warm air slides up and over a cool air mass
Water cycle – the continuous movement of water between Earth’s surface and the atmosphere by means of evaporation, condensation, and precipitation
Water table – the highest part in the ground that is saturated, or completely filled with water
Watt (W) – the unit of measurement for power, which is equal to one joule of work done or energy transferred in one second
Wave – a disturbance that transfers energy from one place to another without requiring matter to move the entire distance
Wavelength – the distance from one point on a wave to the corresponding point on the next wave
Weather – the changing conditions of the atmosphere with respect to heat, cold, sunshine, rain, snow, clouds, and wind
Weather forecasting – an attempt to make accurate predications of future weather
Weathering – the breaking down of rocks into smaller pieces; mostly caused by movements of water, wind, and ice
Wedge – a simple machine that has a thick end and a thin end
Weight – the force of gravity on an object
Wetland – a wet, swampy area that is often flooded with water
Wheel and axle – a simple machine that is a wheel attached to a shaft, or axle
Wind – the movement of air over Earth’s surface; blows from areas off higher air pressure to areas of lower pressure
Wind direction – the direction from which the wind is blowing
Winter storm – blizzards and ice storms
Work – the moving of an object over a distance by force
X-rays – the part of the electromagnetic spectrum that consists of waves with high frequencies and high energies; electromagnetic waves with frequencies ranging from more than 1016 hertz to more than 1021 hertz