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Science Vocabulary

front 1 Acceleration	back 1 Any change in the speed or direction of motion of an object.
front 2 Acid	back 2 A substance with a pH less than 7.0 that releases hydrogen ions in a water solution; for example, vinegar.
front 3 Acid Rain	back 3 Rain that is highly acidic because of sulfur oxides, nitrogen oxides, and other air pollutants dissolved into it; can damage plant and animal life.
front 4 Activation Energy	back 4 The energy needed to enable a chemical reaction to take place.

front 5 Adaptation	back 5 A process that helps an organism survive and function in its environment.
front 6 Adequacy	back 6 Being satisfactory; being sufficient for a job.
front 7 Aging	back 7 The changes that bring about the decline of an organism.
front 8 Air Mass	back 8 A large body of air that has the same moisture and temperature throughout.

front 9 Air Pressure	back 9 The weight of the atmosphere.
front 10 Air Resistance	back 10 Friction caused by air.
front 11 Alimentary Canal	back 11 The tube that makes up the digestive canal.
front 12 Allele	back 12 A different form of a gene.

front 13 Alpha Particle	back 13 A radioactive particle made up of two protons and two neutrons bound tightly together.
front 14 Alternating Current	back 14 A current in which the electrons flow first in one direction and then in the opposite direction.
front 15 Alveoli	back 15 Small air sacs in the lungs at the end of the bronchioles where oxygen passes in the blood and carbon dioxide is released from the blood.
front 16 Amino Acids	back 16 The building blocks of proteins.

front 17 Amniocentesis	back 17 A procedure that is used to examine fetal cells to identify certain types of genetic disorders present in a fetus.
front 18 Amniotic Egg	back 18 A covering that protects and nourishes a developing embryo.
front 19 Amplitude	back 19 The distance between the rest position and crest of a wave.
front 20 Antibodies	back 20 Substances produced by the body's immune system that fight diseases.

front 21 Antigen	back 21 A protein on the surface of a pathogen.
front 22 Aorta	back 22 A large artery that carries oxygen-rich blood from the heart to other parts of the body.
front 23 Applying ideas	back 23 Taking information learned one set of circumstances and using it in another situation.
front 24 Artery	back 24 A blood vessel that carries blood away from the heart.

front 25 Asexual Reproduction	back 25 A method of reproduction in which an organism is produced from a single cell.
front 26 Assess	back 26 To determine the importance, adequacy, or significance of something.
front 27 Assumption	back 27 A belief that something is true without checking its validity.
front 28 Asteroid	back 28 A small celestial body, sometimes called a minor planet, that revolves around the sun.

front 29 Astronomy	back 29 The study of all celestial bodies in the universe.
front 30 Atmosphere	back 30 The layers of gases that surround the Earth.
front 31 Atom	back 31 The smallest particle of an element that can exist alone.
front 32 Atomic Mass	back 32 The sum of protons and neutrons in the nuclease of an atom.

front 33 Atomic Number	back 33 The number of protons in the atom.
front 34 ATP	back 34 A compound in which energy is stored for later use in a cell.
front 35 Atrium	back 35 One of the upper chambers of the heart (plural, atria)
front 36 Axis	back 36 The imaginary line running through Earth's center from the North Pole from the South Pole on which the planet rotates.

front 37 Backbone	back 37 A segmented column of bones.
front 38 Bacteria	back 38 A one-celled organism that has DNA.
front 39 Balanced Equation	back 39 A chemical equation in which the same number of each type of atom appears on both sides.
front 40 Base	back 40 A substance with a pH greater than 7.0 that releases hydroxide ions in a water solution; for example, milk of magnesia.

front 41 Behavior	back 41 An organism's actions or reactions to its environment.
front 42 Beta Particle	back 42 An electron emitted from the nuclease of a radioactive atom.
front 43 Bias	back 43 Anything that sways an experiment's results in a way that makes them inaccurate.
front 44 Big Bang Theory	back 44 The idea that the universe began with an explosion of a dense, hot, compact mass under extreme pressure.

front 45 Binary Fission	back 45 A method of reproduction in which a cell divides into two new cells.
front 46 Biodegradable	back 46 Organic materials that naturally decompose.
front 47 Biodiversity	back 47 A healthy variety of plant and animal species coexisting in an environment and making the environment more stable.
front 48 Biogenesis	back 48 The principle that living things only come from living things.

front 49 Biological Clock	back 49 An internal control of natural behavioral cycles.
front 50 Biological Process	back 50 A fundamental property that is common to all living organisms.
front 51 Biology	back 51 The study of all living things.
front 52 Biomass	back 52 The total mass of the living organisms in a particular place.

front 53 Black Hole	back 53 The collapsed leftovers of a supernova.
front 54 Blue Star	back 54 A massive, hot star that uses up its hydrogen quickly, expands, and turs into a giant or supergiant
front 55 Boiling Point	back 55 The temperature at which a liquid turns into a gas.
front 56 Bosons	back 56 Force-carrying subatomic particles.

front 57 Botany	back 57 The study of plants.
front 58 Brain Stem	back 58 The part of the human brain that controls automatic functions such as breathing and heartbeat.
front 59 Bronchi	back 59 The two tubes that lead from the trachea into each of the lungs.
front 60 Bronchioles	back 60 Tubes branching off the bronchi in the lungs and ending in alveoli.

front 61 Bud	back 61 The part of a plant where the new growth takes place.
front 62 Calorie	back 62 A measure of energy.
front 63 Camouflage	back 63 A coloring pattern that enables an animal to blend into their surroundings and not be seen by predators.
front 64 Capillaries	back 64 Very small blood vessels.

front 65 Carbohydrate	back 65 The main source of food energy.
front 66 Carbon Cycle	back 66 A process that keeps the carbon on Earth in balance.
front 67 Carbon-oxygen Cycle	back 67 The continuous circulation of carbon and oxygen through the biosphere primarily through the processes of photosynthesis, respiration, and decomposition.
front 68 Carnivore	back 68 An animal that eats other animals.

front 69 Carrying Capacity	back 69 The maximum population an ecosystem can support without losing resources.
front 70 Cartilage	back 70 A tough, flexible material that covers bones and joints.
front 71 Catalyst	back 71 A substance that provides a faster mechanism by which a reaction may take place.
front 72 Cause	back 72 Something that makes something else (an effect) happen.

front 73 Cause-and-Effect Relationship	back 73 Something that can make something else (a cause) happen results in another (an effect).
front 74 Cell	back 74 The smallest unit of life that can exist independently and that makes up all living organisms.
front 75 Cell Cycle	back 75 The process of division of a cell into new identical cells.
front 76 Cell Membrane	back 76 The soft, flexible covering that holds a cell together and separates it from other cells.

front 77 Cell Specialization	back 77 The process in which the cells of an organism develop in different shapes, structures, and functions.
front 78 Cell Wall	back 78 A tough, flexible covering that surrounds the cell membrane of a plant cell.
front 79 Cellular Respiration	back 79 The chemical process requiring oxygen by which living things convert food to energy.
front 80 Cerebellum	back 80 The part of the brain , which controls movement, coordination, and balance; located below the cerebrum at the base of the skull.

front 81 Cerebrum	back 81 The largest part of the human brain, which coordinates all higher functions such as perception, thinking, and conscious actually.
front 82 Chain Reaction	back 82 A reaction in which nuclei are split apart in a controlled way, resulting in a great quantity of nuclear energy.
front 83 Chemical Formula	back 83 A shorthand way of showing which elements are contained in a molecule.
front 84 Chart	back 84 A visual representation of data.

front 85 Chemical Bonding	back 85 The process though which atoms are combined.
front 86 Chemical Change	back 86 A change that produces a new substance.
front 87 Chemical Equation	back 87 A shorthand way of describing what happens in a chemical reaction.
front 88 Chemical Reaction	back 88 The process in which two or more substances combine to form one or more substances.

front 89 Chemical Weathering	back 89 Process that changes the composition of the rocks and occurs through chemical reactions.
front 90 Chlorophyll	back 90 The green substance in a plant cell that is used to capture light energy.
front 91 Chloroplast	back 91 An organelle in a plant cell that contains chlorophyll.
front 92 Chromatin	back 92 The part of a cell's nucleus that contains genetic information.

front 93 Chromosome	back 93 A structure in a cell that contains DNA.
front 94 Circadian Clock	back 94 A biological clock that controls daily activity.
front 95 Circular Argument	back 95 A form of faulty logic which a conclusion is supported by reasons that simply restate the conclusion.
front 96 Circulatory System	back 96 the system, consisting of the heart, blood vessels, and the blood, that carries nutrients and oxygen to the body's tissues removes carbon dioxide and waste products.

front 97 Climate	back 97 Average weather conditions in a particular region over a long period of time.
front 98 Cloning	back 98 The process of creating a genetically identical replica of an organism.
front 99 Closed Universe	back 99 The theory that the universe at some future time will begin to contract and collapse into its original state as a solar nebula.
front 100 Coal	back 100 A solid fossil fuel.

front 101 Codon	back 101 A combination of three bases.
front 102 Coefficient	back 102 A number added to the reactants and the products to balance a chemical equation.
front 103 Cold-Blooded	back 103 A classification of an organism that cannot control its own body temperature.
front 104 Colloid	back 104 A mixture in which fine particles are spread out throughout a second substance; for example, foam.

front 105 Collusion	back 105 When two or more moving objects run into one another.
front 106 Comet	back 106 A small object made of dust and frozen gas that orbits in a predictable path around the sun.
front 107 Commensalism	back 107 A relationship that benefits organism, while the other is neither harmed nor helped.
front 108 Common Ancestor	back 108 An individual in a species history to which all individuals in that species can be traced.

front 109 Compare	back 109 To identify how things are alike.
front 110 Complete Metamorphosis	back 110 a type of metamorphosis that takes place in four stages.
front 111 Complex Machine	back 111 Two or more simple machines put together.
front 112 Composting	back 112 The use of natural biological processes to aid in the decomposition of organic materials.

front 113 Compound	back 113 A group of molecules that each contain the atoms of two or more elements.
front 114 Concentrated	back 114 When a solution contains a large amount of solute.
front 115 Conclusion	back 115 A logical result or generalization.
front 116 Condensation	back 116 The change of a of a gas into a liquid.

front 117 Condense	back 117 To change from gas to a liquid; for example, from steam to water.
front 118 Conduction	back 118 Transfer of heat through direct contact.
front 119 Conductor	back 119 A substance through which electric current flows easily.
front 120 Conservation	back 120 The controlled use and preservation of natural resources.

front 121 Constancy	back 121 The tendency for things to remain unchanged.
front 122 Constellation	back 122 A pattern of stars in the sky that humans have observed and named.
front 123 Consumer	back 123 An organism that must eat other organisms to obtain energy.
front 124 Contaminants	back 124 Substances that harm the environment.

front 125 Context	back 125 The situation within which something is said or done.
front 126 Continental Drift	back 126 The movements of continents.
front 127 Contraction	back 127 A decrease in size of a substance due to its atoms moving closer together, often caused by a decrease in temperature.
front 128 Contrast	back 128 To identify how things are different.

front 129 Control Variable	back 129 A factor that is kept the same or constant during an experiment.
front 130 Convection	back 130 The movement of heat through a liquid or gas.
front 131 Convection Currents	back 131 Currents of molten rock the mantle that carry much of the heat to Earth's surface.
front 132 Copernican Theory	back 132 The idea that the Sun is at the center of the solar system

front 133 Core	back 133 The center of the Earth.
front 134 Coriolis Effect	back 134 The apparent change in motion of wind and water on Earth's surface due to rotation.
front 135 Covalent Bond	back 135 A bond in which electrons are shared by the bonded atoms of the molecule.
front 136 Crest	back 136 The high point of a wave.

front 137 Crust	back 137 The outermost layer of Earth.
front 138 Crustal Plates	back 138 The exterior layer of Earth's crust (surface); also called tectonic plates
front 139 Current	back 139 A large movement of water.
front 140 Cytoplasm	back 140 In a cell, the jellylike matter that surrounds the nucleus and contains cell structures (called organelles) that carry out the cell's activities.

front 141 Data	back 141 Information gathered during an experiment or investigation.
front 142 Daughter Cells	back 142 The cells produced as a result of cell division, each identical to the parent cell.
front 143 Decomposer	back 143 An organism that feed off the dead bodies of a once-living organism.
front 144 Dendrite	back 144 A branching fiber on a nerve cell the receives messages from another nerve cell.

front 145 Denitrification	back 145 The process by which certain bacteria in the soil change nitrates into gaseous nitrogen, returning it to the air.
front 146 Density	back 146 A measure of mass in relation to volume.
front 147 Dependent Variable	back 147 A factor is changed in response to the independent variable during an experiment.
front 148 Diagram	back 148 A picture or an illustration that shows information.

front 149 Diffraction	back 149 The process in which a waves spread out into a region behind or around a barrier.
front 150 Diffusion	back 150 Movement of a substance from a region of higher concentration to a region of lower concentration.
front 151 Digestion	back 151 The breaking down of food into nutrients that the body's cells can use.
front 152 Digestive System	back 152 The system of the body that breaks down food into nutrients the body can use and expels leftover wastes.

front 153 Dilute	back 153 A solution with the small amount of solute.
front 154 Direct Current	back 154 Electric current that moves in one direction only.
front 155 Dissolve	back 155 To become part of a solution.
front 156 Distillation	back 156 A process for separating liquids that have different boiling points.

front 157 DNA	back 157 The molecules that contains hereditary information and controls the activities of each cell; found in the chromosomes.
front 158 Dominant	back 158 An allele for which the phenotype will always be present.
front 159 Dominant Gene	back 159 One gene in a pair that determines the effect of the gene pair.
front 160 Dominant Trait	back 160 A trait that will appear in an offspring if one parent contributes it; dominant traits suppress recessive traits.

front 161 Double Blind	back 161 An investigation in which neither the researchers nor the patients know who is receiving placebos.
front 162 Drag	back 162 The force slowing or stopping the movement of an object through a gas or liquid.
front 163 Drawing Conclusions	back 163 Expressing unstated ideas that are logically connected to give information.
front 164 Earthquake	back 164 A sudden vibration in the Earth in which plates slip past one another.

front 165 Ecology	back 165 The study of the relationship of organisms to their environment.
front 166 Ecosystem	back 166 A community of populations of organisms and the habits and natural resources that affect the community.
front 167 Effect	back 167 A result of an action or condition.
front 168 Effort	back 168 A force applied to an object.

front 169 Egg Cell	back 169 The female reproductive cell; also called the ovum.
front 170 Either-or Error	back 170 A form of faulty logic in which only two choices are presented although other options exist.
front 171 El Niño	back 171 An uncommon condition caused by unusually warm temperatures in the tropical Pacific Ocean.
front 172 Electric Circuit	back 172 A continuous pathway over which electric current can flow.

front 173 Electric Current	back 173 The flow that holds electrons in orbit around the nucleus of an atom.
front 174 Electric Field	back 174 The area of force that surrounds a charged particle.
front 175 Electromagnetic Spectrum	back 175 The entire spectrum of radiation, ranging from radio waves to gamma rays.
front 176 Electron	back 176 A particle with a negative electron that orbits the nucleus of an atom.

front 177 Electromagnet	back 177 The wide range of wavelengths that is made by coiling a wire around a piece of iron and running an electric current through the wire.
front 178 Electromagnetic Radiation	back 178 The wave motion of alternating electric and magnetic fields.
front 179 Electromagnetic Spectrum	back 179 The wide range of wavelengths over which electromagnetic waves exist.
front 180 Electromagnetic Wave	back 180 A wave that can travel through a vacuum.

front 181 Electromagnetism	back 181 The relationship between electricity and magnetism.
front 182 Electron	back 182 A negatively charged particle that revolves around the nucleus of an atom.
front 183 Element	back 183 A substance that cannot be broken down into simpler substances by chemical means; for example, carbon.
front 184 Elliptical Galaxy	back 184 A galaxy that looks like a sphere or an elongated sphere of stars.

front 185 Embryo	back 185 An organism in its early stage of development.
front 186 Endocrine System	back 186 The body system made up of endocrine glands; these glands secrete hormones into the bloodstream to regulate body processes.
front 187 Endoplasmic Reticulum	back 187 A cell organelle that produces lipids, breaks down chemicals, and transports proteins for delivery to all of a cell
front 188 Endothermic Reaction	back 188 A reaction in which more energy is absorbed than is released.

front 189 Energy	back 189 The ability to do work.
front 190 Energy Pyramid	back 190 A model of the energy flow in an ecosystem.
front 191 Energy Shells	back 191 The energy levels at which electrons orbit the nucleus of an atom.
front 192 Entropy	back 192 The tendency of a system to become randomly disorganized.

front 193 Environment	back 193 All the living and nonliving things that affect an organism's life in some way.
front 194 Environmental Science	back 194 The study of how human beings interact with their environment.
front 195 Enzyme	back 195 A specialized protein that breaks down organic molecules.
front 196 Epicenter	back 196 The point on Earth's surface directly above the focus of an earthquake.

front 197 Epidemic	back 197 The rapid spread of an infectious disease through an entire population.
front 198 Epigenome	back 198 Chemical tag covering the genome.
front 199 Equilibrium	back 199 A condition in which change takes place in equal and opposite ways.
front 200 Erosion	back 200 The gradual wearing away and moving of rock, soil, and sand along Earth's surface.

front 201 Error	back 201 Mistake in an investigation, including inaccuracy of measuring instruments and sampling.
front 202 Eukaryote	back 202 An organism composed of one or more cells containing a nucleus and organelles.
front 203 Evaluate	back 203 To examine something in order to judge its significance.
front 204 Evaporation	back 204 The change of a liquid to a gas.

front 205 Evidence	back 205 Observations and data from experiments that support or oppose a stated point of view.
front 206 Evolution	back 206 A series of changes that occur over time.
front 207 Excretion	back 207 The process in which waste products are removed from the body.
front 208 Exothermic Reaction	back 208 A reaction in which more energy is released than absorbed.

front 209 Expansion	back 209 An increase in size of a substance due to its atoms moving farther apart, often caused by an increase in temperature.
front 210 Experiment	back 210 A procedure that is designed to test a hypothesis
front 211 Explanation	back 211 The addition of newly acquired evidence to facts that are already known.
front 212 Extinction	back 212 The dying off of an entire plant or animal species.

front 213 Fact	back 213 Something that can be proven true.
front 214 Famine	back 214 Widespread starvation.
front 215 Fat	back 215 An energy source derived from primarily animal products.
front 216 Fault	back 216 A break in the Earth's crust.

front 217 Faulty Logic	back 217 Errors in reasoning.
front 218 Fermentation	back 218 A type of cellular respiration not requiring oxygen, in which food is broken down into carbon dioxide and alcohol, with the release of energy.
front 219 Fetus	back 219 The developing stage of a baby.
front 220 Filter	back 220 A tool to separate a mixture.

front 221 Filtration	back 221 A process for separating a mixture.
front 222 Fission	back 222 The splitting of the nucleus of an atom.
front 223 Flat Universe	back 223 The theory that the universe will at some future time reach a size and stay at that size.
front 224 Flower	back 224 The part of the plant in which reproduction occurs.

front 225 Focus	back 225 In Earth science, the point beneath Earth's surface where the rocks break and move to start an earthquake.
front 226 Food Chain	back 226 The transfer of energy from one organism to the next, each organism consuming the previous one.
front 227 Food Web	back 227 The complex pattern of energy transfer in a ecosystem; consisted of many interrelated food chain.
front 228 Force	back 228 Any push or pull that can affect an object either in motion or at rest.

front 229 Fossil	back 229 A trace remain of an organism of a past geological age.
front 230 Fossil Fuels	back 230 Fuel, such as petroleum, coal, and natural gas, that are used to produce energy for industrialized societies.
front 231 Fraternal Twins	back 231 Two children who develop from two eggs fertilized by two sperm during the reproductive cycle.
front 232 Freezing Point	back 232 The temperature at which a liquid changes into a solid.

front 233 Frequency	back 233 The number of waves that pass a given point in a given amount of time.
front 234 Friction	back 234 A force that slows a moving object.
front 235 Front	back 235 The boundary between two air masses.
front 236 Fusion	back 236 The combining of two atomic nuclei to form one nucleus.

front 237 Galaxy	back 237 A collection of dust, gas, and stars held together by gravity.
front 238 Gamma Ray	back 238 A high-energy electromagnetic wave.
front 239 Gas	back 239 The state of matter that has no definite shape or volume; for example, the air.
front 240 Gas Cloud	back 240 A vast cloud of gas and dust out of which a star may form.

front 241 Gene	back 241 A strand of DNA that carries information for a specific trait.
front 242 Generator	back 242 A device that converts mechanical energy to electrical energy.
front 243 Genetic Disorder	back 243 A disease, disability, or difference caused by an abnormal gene.
front 244 Genetics	back 244 The study of how characteristics are passed from one organism to another.

front 245 Genome	back 245 All the genetic information about a single individual or species as coded by the DNA that make up its chromosomes.
front 246 Genotype	back 246 The genetic makeup of an organism.
front 247 Geochemical Cycle	back 247 The movement of elements from one chemical storehouse to another.
front 248 Geochemistry	back 248 The study of distribution of chemical elements in Earth's crust.

front 249 Geology	back 249 The study of the composition and structure of Earth.
front 250 Geothermal Energy	back 250 Energy that comes from Earth's hot interior.
front 251 Giant	back 251 A star that is not as massive as a blue star, but has run out of hydrogen, resulting in the inner core chrinking and the outer core expanding.
front 252 Gills	back 252 Special organs to take oxygen out of water.

front 253 Glacier	back 253 A large mass of moving ice.
front 254 Gland	back 254 An organ that secretes chemicals to be used by the body.
front 255 Global Warming	back 255 The trend toward higher average temperatures on Earth's surface.
front 256 Globular Cluster	back 256 A group of older stars that looks like a ball of stars.

front 257 Glucose	back 257 A simple sugar that is used to produce energy in plants.
front 258 Golgi Complex	back 258 A cell organelle that receives proteins from the endoplasmic reticulum and modifies them for different functions.
front 259 Graph	back 259 A physical representation of data.
front 260 Gravitational Potential Energy	back 260 The energy an object possessbecause of its gravity.

front 261 Gravity	back 261 A force of attraction between two objects that is due to their mass.
front 262 Greenhouse Effect	back 262 The natural heating of a planet by the process of atmospheric gases trapping heat energy.
front 263 Greenhouse Gas	back 263 A gas that prevents the greengouse effect by absorbing infrared reflection.
front 264 Group	back 264 A column of the Periodic Table that lists elements that have the same number of electrons in their outermost energy shell.

front 265 Habitat	back 265 The place in which an organism lives.
front 266 Half-life	back 266 The time needed for half of the nuclei in a sample of radioactive material to decay into another substance by giving off nuclear particles or energy.
front 267 Hardness	back 267 The measure of force needed to break a substace.
front 268 Hasty Generalization	back 268 A form of faulty logic in which a conclusion is based on insufficent evidence.

front 269 Heat	back 269 Energy of moving atoms.
front 270 Hemisphere	back 270 The left or right half of the human brain.
front 271 Herbicide	back 271 A chemical that kills plants.
front 272 Herbivore	back 272 An animal that eats plants.

front 273 Heteorogeneous	back 273 A non-unifom mixture, such as oil and vifegar.
front 274 Homeostasis	back 274 The tendency of a system to achieve a relatively stable equilibrium.
front 275 Homogeneous	back 275 A uniform mixture, such as salt and water; also called a solution.
front 276 Homologous Structures	back 276 Body parts from different organisms with a common genetic heritage that have similar structure but perform different functions; for example a bird's wing and a human's arm.

front 277 Hormone	back 277 A chemical prodyced within the body that regulates body function.
front 278 Host	back 278 An organism on which a parasite lives.
front 279 Humidity	back 279 The measure of water vapor in the air.
front 280 Hurricane	back 280 A large tropical storm with average wind speeds of at leaset 74 miles per hour.

front 281 Hybrid	back 281 An organism that carries both the dominant and recessive versions of a particular trait.
front 282 Hydrocarbon	back 282 A compound composed of only carbon and hydrogen.
front 283 Hydroelectric Power	back 283 Electrical power produced from the mechanical energy found in moving water.
front 284 Hypothesis	back 284 A reasonable explanation of evidence or a prediction based on evidence.

front 285 Identical Twins	back 285 Two children who were formed from the same fertilized egg.
front 286 Igneous Rock	back 286 A type of rock formed when hot liquid rock cools; for example, granite.
front 287 Immune System	back 287 Molecules, cells, and organs that work together to defend the body against pathogens.
front 288 Immunization	back 288 A process in which the body receives a vaccine.

front 289 Implication	back 289 A fact or idea that is suggested by stated information.
front 290 Imply	back 290 To suggest something without actually stating it.
front 291 Incineration	back 291 The burning of solid wastes.
front 292 Inclined Plane	back 292 A simple machine consisting of a flat, slanted surface.

front 293 Incomplete Dominance	back 293 A pattern of inheritance in which a trait appears as a blend when dominant and recessive versions of it are inherited.
front 294 Incomplete Metamorphosis	back 294 A type of metamorphosis that that takes place in three stages.
front 295 Independent Variable	back 295 A factor that is changed by a scientist during an experiment.
front 296 Inertia	back 296 The tendency of an object to stay at rest or in motion unless acted upon by an outside force.

front 297 Infection	back 297 The presence of a pathogen inside the body.
front 298 Infer	back 298 To figure out something that is suggested by stated information.
front 299 Inference	back 299 A fact or idea that you figure out based on stated information.
front 300 Infrared Radiation	back 300 Energy in the electromagnetic radiation spectrum with wavelengths longer than those of visible light and shorter than those of radio waves.

front 301 Inner Core	back 301 The solid iron and nickel center of the Earth.
front 302 Insulation	back 302 Material that protects against electric shock.
front 303 Invasive Species	back 303 A plant or animal that is not native to an area and has a negative effect on that area.
front 304 Invertebrate	back 304 An animal with no backbone or skull.

front 305 Involuntary Muscle	back 305 A muscle over which a person has limited control.
front 306 Ion	back 306 An atom that has taken on a negative or positive charge by gaining or losing electrons.
front 307 Ionic Bond	back 307 The bond between two or more ions (atoms in which one or more electrons have been gained or lost).
front 308 Ionosphere	back 308 The region of Earth's atmosphere that reflet radio waves toward the ground.

front 309 Irregular Galaxy	back 309 A galaxy that differs from the two basic shapes of galaxies.
front 310 Irrelevant Information	back 310 Information that includes any facts that do not directly a person's decision.
front 311 Isomers	back 311 Compounds that have the same number and types of atoms (and thus the same chemical formula) but a different arrangement of atoms and different properties.
front 312 Joint	back 312 The place where one bone meets another.

front 313 Joule	back 313 A unit of work.
front 314 Kinetic Energy	back 314 The energy an object has because of its motion.
front 315 Kingdom	back 315 The most general classification of an organism.
front 316 Landfill	back 316 A place where solid wastes are buried.

front 317 Landform	back 317 Natural formations that occur on Earth.
front 318 Larva	back 318 A wormlike creature that begins the process of complete metamorphosis.
front 319 Lava	back 319 Magma, or molten rock, that breaks through Earth's surface in a volcanic eruption.
front 320 Law of Chance	back 320 A description of the probability of something happening.

front 321 Law of Conservation of Energy	back 321 Law states that energy can be transferred but cannot be created or destroyed.
front 322 Law of Conservation of Matter	back 322 Law that states that matter cannot be created or destroyed.
front 323 Law of Nature	back 323 A property of nature that does not change.
front 324 Leaves	back 324 The site of food production in a plant.

front 325 Lever	back 325 A simple machine in which a small force times a large distance at one end becomes a larger times a small distance at the other end.
front 326 Life Cycle	back 326 The stages of life that all living things go through: beginning, growth, maturity, decline, and death.
front 327 Life Science	back 327 See biology.
front 328 Ligament	back 328 A tough strand of connective tissue.

front 329 Light	back 329 The range of electromagnetic wavelengths that humans can visibly see.
front 330 Light-year	back 330 The distance that light travels in one year: about 6 million miles.
front 331 Limiting Factors	back 331 A factor that limits the size of a population.
front 332 Limiting Reactants	back 332 The reactant that is used up first in a chemical reaction.

front 333 Lipid	back 333 An energy-storing fat.
front 334 Liquid	back 334 The state of matter that has a definite volume but has a definite shape; for example, water at room temperature.
front 335 Load	back 335 An object to which force is being applied.
front 336 Longitudinal Wave	back 336 A wave that pushes and pulls molecules back and forth parallel to its direction of travel; for example, sound waves.

front 337 Lunar Eclipse	back 337 An event in which Earth moves between the sun and the moon and casts a shadow on the moon.
front 338 Lysosome	back 338 A special organelle in an animal cell that gets rid of waste materials, protects the cell from foreign invaders, and destroys worn-out or damaged organelles.
front 339 Machine	back 339 A device that is designed to make work easier.
front 340 Magma	back 340 Hot liquid rock beneath Earth's surface.

front 341 Magnetism	back 341 A trait in which an object attracts and repels another object.
front 342 Main Idea	back 342 The central topic of a paragraph, passage, or diagram.
front 343 Mantle	back 343 Semi-solid layer of rock found under the crust.
front 344 Mass	back 344 The amount of matter an object contains.

front 345 Matter	back 345 Anything that has weight and takes up space.
front 346 Mechanical Energy	back 346 The sum of an object's kinetic and potential energy.
front 347 Meiosis	back 347 A form of cell division by which a single cell divides into four daughter cells.
front 348 Melting	back 348 The process by which a solid turns into a liquid.

front 349 Melting Point	back 349 The temperature at which a solid changes into a liquid.
front 350 Menstrual Cycle	back 350 The growth and release of a mature egg.
front 351 Mesosphere	back 351 The layer of Earth's atmosphere in which air temperature drops with increasing altitude.
front 352 Metabolism	back 352 All the chemical processes taking place in a living organism.

front 353 Metamorphic Rock	back 353 A type of rock formed when rock is subject to extreme heat or pressure; for example, marble.
front 354 Metamorphosis	back 354 The process in which insects and amphibians go through the stages of life.
front 355 Meteor	back 355 A bright streak of light in the night shy caused by a meteoroid burning as it enters Earth's atmosphere.
front 356 Meteorite	back 356 A fragment of a meteor that is found on the surface of Earth.

front 357 Meteorology	back 357 The study of the atmosphere.
front 358 Migrate	back 358 To move from one place to another.
front 359 Milestone	back 359 A turning point or points at which everything changes.
front 360 Milky Way	back 360 The spiral galaxy in which our sun is located.

front 361 Mineral	back 361 See Vitamin.
front 362 Minerals	back 362 Inorganic substances needed in trace amounts for growth and health.
front 363 Mitochondria	back 363 A bean-shaped organelle that breaks down the chemical bonds of food molecules.
front 364 Mitosis	back 364 A form of cell division by which a single cell divides into two identical cells.

front 365 Mixture	back 365 A mechanical combination of substances in which each substance keeps its own properties; for example, gravel, air, mayonnaise.
front 366 Model	back 366 A representation of facts or information.
front 367 Molecule	back 367 A substance made of two atoms bonded together.
front 368 Molting	back 368 The process through which an organism sheds its exoskeleton.

front 369 Momentum	back 369 An object's mass multiplied by its velocity, or its speed in a straight line.
front 370 Moon	back 370 A solid, spherical object that orbits a planet.
front 371 Multicellular Organism	back 371 An organism that consists of more than one cell.
front 372 Muscle	back 372 A contracting tissue that is responsible for bone movement.

front 373 Mutation	back 373 A change in an organism's DNA that causes a change in an inherited characteristic.
front 374 Mutualism	back 374 A relationship between two organisms in which both organisms benefit.
front 375 Natural Gas	back 375 A gaseous fossil fuel.
front 376 Natural Resources	back 376 Materials formed in nature that are useful to humans.

front 377 Natural Selection	back 377 The idea that individuals with favorable traits are the most likely members of a species to survive, reproduce, and pass on those traits.
front 378 Negative Feedback	back 378 A reaction to change in a way that brings it back to its original state.
front 379 Nerve Impulse	back 379 Electrical signals that travel to and from nerve cells throughout the body.
front 380 Nerves	back 380 A bundle of nerves that transmits information in the body.

front 381 Nervous System	back 381 The communications and control system of an organism consisting of interconnected nerves.
front 382 Neuron	back 382 A nerve cell that makes up brain tissue.
front 383 Neutral	back 383 When a solution has a pH of 7.
front 384 Neutron	back 384 A particle in the nucleus of an atom that has no electrical change.

front 385 Neutron Star	back 385 A very dense small star made up entirely of neutrons from the leftover materials near the center of a supernova.
front 386 Newton's First Law of Motion	back 386 States that an object will tend to stay at rest or in motion unless acted by an outside force; also known as inertia.
front 387 Newton's Second Law of Motion	back 387 States that the greater the mass of an object, the greater the force needed to move that object.
front 388 Newton's Third Law of Motion	back 388 States that for every force applied to an object, an equal force acts in the opposite direction.

front 389 Nitrification	back 389 The process by which bacteria covert nitrogen in the soil to ammonia, nitrite, and nitrate, a form of nitrogen that plants can use.
front 390 Nitrogen Cycle	back 390 The continuous circulation of nitrogen through the biosphere primarily through the action of bacteria, precipitation, and decomposition.
front 391 Nitrogen Fixation	back 391 A process by which certain bacteria take nitrogen from the atmosphere and combine it with other substances into a form that other plants can use.
front 392 Nonconductor	back 392 A material in which electrons cannot be made to flow.

front 393 Nonrenewable Resources	back 393 Resources that cannot be replaced or that take hundreds or thousands of years to replace.
front 394 Nonvascular Plant	back 394 A plant that has no specialized tissue to transport water and nutrients to parts of the plant.
front 395 Nuclear Energy	back 395 The energy released during nuclear fission or fusion reactions, generally used to produce electricity.
front 396 Nuclear Fission	back 396 The splitting of atomic nucleus into two smaller nuclei and two or three neutrons, releasing large amounts of energy.

front 397 Nuclear Force	back 397 The force that holds neutrons and protons together in the nucleus of an atom.
front 398 Nuclear Membrane	back 398 In a cell, the layer of matter that separates the nucleus from the cytoplasm.
front 399 Nuclear Power Plant	back 399 A facility that generates electricity by using radioactive fuel, which explodes in a nuclear chain reaction.
front 400 Nuclear Reactor	back 400 A device in which controlled chain reactions are carried out.

front 401 Nucleolus	back 401 A body within the nucleus of a cell that is responsible for making protein.
front 402 Nucleus	back 402 In life science, the part of a cell that controls the cell's activities; in physical science, an atom's small, dense core, which consists of protons and neutrons.
front 403 Neuron	back 403 A nerve cell, the basic unit of the nervous system.
front 404 Neurotransmitter	back 404 A chemical involved in communication between neurons or a neuron and a muscle.

front 405 Nutrient	back 405 A substance, found in food, that is necessary for growth and health of an organism; for example, proteins, carbohydrates, fats, minerals, and vitamins.
front 406 Nutrition	back 406 The study of the health value of food.
front 407 Nymph	back 407 A smaller version of an adult insect.
front 408 Oceanography	back 408 The study of Earth's oceans.

front 409 Omnivore	back 409 An animal that eats both plants and animals.
front 410 Open Cluster	back 410 A small group of stars that is located along the spiral disk of a spiral galaxy.
front 411 Open Universe	back 411 The theory that the universe will continue to slowly expand forever.
front 412 Opinion	back 412 A personal belief that is often on a person's own value system.

front 413 Orbit	back 413 The path in which a planet travels around the Sun.
front 414 Order	back 414 The tendency of properties and behavior to be predictable.
front 415 Organ	back 415 A group of different tissues that perform together to perform a specific function or functions.
front 416 Organ System	back 416 A group of organs that work together.

front 417 Organelle	back 417 A specialized structure within the cytoplasm of a cell that performs a special life activity.
front 418 Organic	back 418 A carbon-containing compound.
front 419 Organic Chemistry	back 419 The study of carbon.
front 420 Organic Molecule	back 420 A molecule that contains carbon combined with nitrogen, hydrogen, or oxygen; the building blocks of all living organisms.

front 421 Organism	back 421 A living thing.
front 422 Orbit	back 422 The path taken by a planet or moon around the focus of the system to which it belongs; for example, Earth's orbit around the Sun.
front 423 Osmosis	back 423 Diffusion of a solvent, often water, through a semipermeable membrane until its concentration is equal on both sides of the membrane.
front 424 Outer Core	back 424 The liquid outer layer of Earth's core.

front 425 Oversimplification	back 425 A form of faulty logic in which something is so simplified so much that it becomes incorrect.
front 426 Oxidation	back 426 A reaction in which an element loses electrons; often in oxidation, the element reacts with oxygen; for example, iron reacts with oxygen to form iron oxide (rust).
front 427 Ozone	back 427 A type of oxygen gas that surrounds Earth and absorbs ultraviolet rays.
front 428 Paleontology	back 428 The study of prehistoric animal and plant life through the analysis of fossil remains.

front 429 Pangaea	back 429 The massive supercontinent that split into the seven continents.
front 430 Parallel Circuit	back 430 A circuit in which there is more than one path for electric current to take.
front 431 Parasitism	back 431 A relationship that helps one organism while causes harm to the other.
front 432 Parent Cell	back 432 The cell undergoing mitosis and cell division.

front 433 Particle Accelerator	back 433 A long, narrow tunnel, charged with electric and magnetic fields, used to accelerate and collide particles in order to release energy and create new particles.
front 434 Pathogen	back 434 A harmful bacterium, virus, or fungus that invades the human body.
front 435 Period	back 435 A row of the Periodic Table that contains elements that have the same number of energy shells.
front 436 Periodic Table	back 436 An arrangement of the elements according to their properties and atomic number.

front 437 Petroleum	back 437 A liquid fossil fuel; also called oil.
front 438 pH Scale	back 438 Range of numbers from 0 to 14 that indicates the relative acidic or basic character of a solution: 7 indicates a neutral solution; numbers lower than 7 indicate an acid; numbers higher than 7 is a base.
front 439 Phase	back 439 Matter in the form of a solid, liquid, or gas.
front 440 Phase Change	back 440 A physical change to the shape of a substance.

front 441 Phases of Matter	back 441 The three forms of substance: solid, liquid, and gas.
front 442 Phenotype	back 442 In genetics, the observable physical characteristics of an individual organism.
front 443 Photosynthesis	back 443 The chemical process by which green plants convert water and carbon dioxide into food and oxygen using energy absorbed from sunlight or other light.
front 444 Physical Change	back 444 A change to a substance that does not change its chemical identity.

front 445 Physical Properties	back 445 Properties that can be observed without changing the chemical identity of the substance.
front 446 Physical Weathering	back 446 A process that breaks down rocks but does not change the composition of the rock.
front 447 Pistil	back 447 The female reproductive structure in a flowering plant.
front 448 Placenta	back 448 A special tissue through which a developing placental embryo receives nourishment from its mother.

front 449 Planet	back 449 A large celestial body that revolves around a star; for example, Earth and Jupiter.
front 450 Plate Tectonics	back 450 A theory that explains how Earth's crust is formed, changes over time, and is destroyed.
front 451 Pollen	back 451 A grain that contains the male sex cell of a flowering plant.
front 452 Pollination	back 452 The process by which flowering plants reproduce.

front 453 Pollution	back 453 Any form of contamination that affects the quality of life.
front 454 Polymer	back 454 A hydrocarbon that contains a large of carbon atoms.
front 455 Population	back 455 A group of organisms of the same species that live in the same area.
front 456 Population Density	back 456 The number of people who live in a specific area.

front 457 Potential Energy	back 457 Energy stored in the position of an object at rest.
front 458 Power	back 458 The rate at which work is done.
front 459 Precipitate	back 459 When a solute begins to come out of a solution.
front 460 Predator	back 460 An animal that gets its food by hunting and killing for it.

front 461 Prediction	back 461 A guess based on facts.
front 462 Prism	back 462 A triangular piece of glass that breaks light into a spectrum of colors.
front 463 Producer	back 463 An organism that capture the sun's energy and make their own food.
front 464 Product	back 464 A substance formed as a result of a chemical reaction.

front 465 Prokaryote	back 465 An organism whose cells do not contain a nucleus and other specialized cell structure.
front 466 Protein	back 466 A molecule that is necessary for cell growth and repair and sometimes energy.
front 467 Proton	back 467 A particle in the nucleus of an atom that has a positive electric change.
front 468 Pulley	back 468 A simple machine consisting of a rope that fits into a wheel that can be moved.

front 469 Pulsar	back 469 A neutron star that spins, sending out beams of pulsing radiation.
front 470 Punctuated Equilibrium	back 470 A fore of rapid evolution in which species suddenly appear or disappear on Earth.
front 471 Punnett Square	back 471 A diagram that shows the possible combinations of genotypes two parent organisms can produce.
front 472 Pupa	back 472 A resting insect in the third stage of complete metamorphosis.

front 473 Pure Substance	back 473 A substance made of identical atoms or molecule.
front 474 Quarks	back 474 A subatomic particle that make up the protons and neutrons.
front 475 Radiation	back 475 The movement of heat without particles.
front 476 Radioactivity	back 476 A property of some elements that involves giving off particles or energy from the nucleus until a more stable element is produced.

front 477 Radio metrics	back 477 Methods of using the decay rate of materials and soil to learn how long they have been there.
front 478 Reactant	back 478 A substance that is an ingredient of a chemical reaction.
front 479 Reaction Rate	back 479 The speed at which a chemical reaction takes place.
front 480 Recessive Gene	back 480 A gene that has no effect if a dominant gene is present.

front 481 Recycling	back 481 The breaking down of trash into its component substances and reusing them in new products.
front 482 Red Dwarf Star	back 482 The smallest and coolest of stars, having the longest lifetime of all star.
front 483 Red Giant	back 483 A giant star that glows a cool, red color.
front 484 Reflection	back 484 The process in which a wave bounces off a smooth surface.

front 485 Reflex	back 485 A rapid, automatic response to a condition in an organism's environment; for example, squinting in strong light.
front 486 Refraction	back 486 The process in which a wave crosses a boundary and begins to move in a slightly different direction.
front 487 Relevant Information	back 487 Information that includes facts that directly affect a person's decision.
front 488 Renewable Resources	back 488 Resources that can be used and then replaced over a relatively short period of time.

front 489 Reproduction	back 489 The process by which an organism produces future generation of its own kind.
front 490 Reservoir	back 490 A lake created by a dam.
front 491 Resistance	back 491 A force that opposes, or slows motion; in reference to electricity, the opposition a material offers to the free flow of electric current.
front 492 Resource	back 492 A material that people need from Earth.

front 493 Resource Recovery	back 493 The process of burning trash to create electricity.
front 494 Respiration	back 494 The process by which living things take in oxygen and release carbon dioxide to obtain energy.
front 495 Respiratory System	back 495 The system of the body involved in exchanging oxygen for carbon dioxide.
front 496 Response	back 496 The reaction of an organism to stimulus.

front 497 Restate	back 497 To use different words and phrases to express the same idea.
front 498 Revolution	back 498 A planet's complete trip around the Sun.
front 499 Revolve	back 499 To move in a circular or elliptical path around a central object; for example, Earth revolves around the Sun.
front 500 Rhinovirus	back 500 A virus that causes certain types of colds.

front 501 Ribosome	back 501 A cell organelle on which the amino acids combine to make protein.
front 502 Richter Scale	back 502 A measure of the amount of energy released by an earthquake; the Richter scale starts at 0 and although it has no upper limit, no earthquake recorded has measured stronger than a 9.
front 503 Root	back 503 The part of a plant that anchors it in the ground and absorbs water and minerals from the soil.
front 504 Root Hairs	back 504 The long extensions of the root that serve as the main point of entrance for water into the root.

front 505 Rotate	back 505 To turn on its own central axis.
front 506 Salt	back 506 A neutral compound with a pH of 7.0 that results from the chemical combination of an acid and a base; for example, sodium chloride (table salt).
front 507 Saturated Fat	back 507 A type of fat that is solid at room temperature.
front 508 Scientific Fact	back 508 A conclusion, based on evidence, that scientists agree on.

front 509 Scientific Methods	back 509 Organized ways of solving problems; the processes scientists use for getting information and testing ideas.
front 510 Sea Floor Spreading	back 510 The movement of the sea floor crust away from the mid-ocean ridges, where new crust is pushing up from the mantle.
front 511 Sedimentary Rock	back 511 A type of rock formed by the hardening of particles of sand, mud, clay, or sediments; for example, sandstone.
front 512 Seismic Waves	back 512 Vibrations caused by movement of rock during an earthquake.

front 513 Semiconductor	back 513 A material in which only a small amount of electric current can be made to flow.
front 514 Senses	back 514 The means by which animals get information about their environment: sight, hearing, taste, touch, and smell.
front 515 Sequence	back 515 The order in which things happen.
front 516 Series Conductor	back 516 A circuit in which there is only one path for electric current to take.

front 517 Sexual Reproduction	back 517 A form of reproduction in which genetic material from two parents is combined in the offspring.
front 518 Silicon	back 518 An element common in Earth's crust.
front 519 Simple Machine	back 519 a device to do work (example: lever).
front 520 Skeleton	back 520 The frame of the human body.

front 521 Skull	back 521 A bone that protects the brain and other organs in the head.
front 522 Social Behavior	back 522 The behavior of animals of the same species as they live together.
front 523 Software	back 523 Instructions that tell a computer how to perform a task.
front 524 Soil	back 524 A mixture of tiny rock fragments and organic materials produced by living things.

front 525 Solar Cell	back 525 A device that produces electricity when sunlight strikes it.
front 526 Solar Energy	back 526 Energy from the sunlight.
front 527 Solar Nebula	back 527 A cloud of interstellar gas and dust from which the solar system is formed.
front 528 Solar System	back 528 The sun and the objects that revolve around it, such as the planets and their moons.

front 529 Solid	back 529 A state of matter that has a definite shape and takes up a definite amount of space.
front 530 Solubility	back 530 Related to the amount of a solute that will dissolve in a given amount of solvent at a given temperature and pressure.
front 531 Solute	back 531 The substance in a solution that is dissolved in a solution.
front 532 Solute	back 532 The substance being dissolved in a solution; for example, salt in salt water.

front 533 Solution	back 533 A type of mixture in which the ingredients are distributed evenly throughout.
front 534 Solvent	back 534 The substance doing the dissolving in a solution; for example, water in salt water.
front 535 Sound	back 535 A sensation caused by vibrations and perceived by hearing.
front 536 Sound Waves	back 536 Vibrations transmitted through substances in waves with frequencies that can be heard.

front 537 Space Probe	back 537 Unmanned spacecraft used for the exploration of space.
front 538 Species	back 538 A group of organisms with similar characteristics that can interbreed to produce fertile offspring.
front 539 Spectrometer	back 539 A device used to analyze what things are made of.
front 540 Sperm	back 540 The male sex cell.

front 541 Spiral Galaxy	back 541 A galaxy that has a huge core of stars surrounded by spiral arms.
front 542 Spore	back 542 A tiny reproductive cell.
front 543 Sprain	back 543 A joint injury in which the ligaments are stretched or torn.
front 544 Squamous Cell Skin Caner	back 544 A type of cancer that looks raised, pink spots or growths that may be open at the center.

front 545 Stamen	back 545 The male reproductive structure in a flowering plant.
front 546 Static Electricity	back 546 Electricity in which electrons are transferred from one object to another.
front 547 Stationary Front	back 547 The zone between two air masses, caused when the masses stop moving.
front 548 Stem	back 548 The part of a plant that holds the leaves up towards the sunlight and transports water and minerals from the roots to the leaves.

front 549 Stimulus	back 549 Anything in the environment that influences the nervous system; for example, the sight of a snake or the smell of coffee.
front 550 Stomata	back 550 Tiny openings in a leaf that allows gases to enter and exit the leaf.
front 551 Stratosphere	back 551 The second layer of Earth's atmosphere; contains ozone gas.
front 552 Structural Formula	back 552 A diagram using symbols representing the arrangement of atoms in a molecule.

front 553 Style	back 553 A long tube through which pollen moves from the stigma to the ovary in a flowering plant.
front 554 Subatomic Particles	back 554 Particles smaller than protons, neutrons, and electrons; also called elementary particles.
front 555 Substance	back 555 Matter of one particular type.
front 556 Summarize	back 556 To condense or shorten a larger amount of information into a few sentences.

front 557 Superconductor	back 557 A conductor in which there is no electrical resistance.
front 558 Supergiant	back 558 A very large star.
front 559 Supernova	back 559 A flash of light caused by the explosion of a massive blue star that has become too hot.
front 560 Supporting Details	back 560 Observations, measurements, and other facts that back up a conclusion.

front 561 Synapse	back 561 The space between two neurons and a muscle across which nerve impulses are transmitted.
front 562 Table	back 562 A type of list that organizes information in rows and columns.
front 563 Technology	back 563 The use of knowledge, materials, and tools to solve human problems and to provide for human needs and wishes.
front 564 Tectonic Plates	back 564 Large fragments of Earth's crust and an upper mantle that fit together like a puzzle piece.

front 565 Temperature	back 565 The measure of heat energy; the measure of the warmth of the air in Earth's atmosphere.
front 566 Tendon	back 566 A strong, fibrous connective tissue that connects bones and muscles.
front 567 Thermosphere	back 567 The outermost layer of Earth's atmosphere in which the temperature rises with the altitude.
front 568 Timeline	back 568 An illustration that shows when a series of events took place and the order in which they occurred.

front 569 Tissue	back 569 A group of similar cells that have a similar function; for example, muscle tissue.
front 570 Topic Sentence	back 570 The sentence that contains the main idea in a paragraph.
front 571 Trachea	back 571 The tube through which air passes from the back of the mouth to the lungs; also called the windpipe.
front 572 Trait	back 572 An inherited characteristic such as hair color or blood type.

front 573 Transistor	back 573 An electric device used to amplify, detect, or switch electric current.
front 574 Transverse Wave	back 574 A wave in which the disturbance is at right angles to the direction of the wave's travel; for example, light waves.
front 575 Trophic Level	back 575 In a food chain, the position occupied by each species.
front 576 Tropical Rain Forest	back 576 Dense forest found near the equator where the climate is hot and wet.

front 577 Troposphere	back 577 The layer of Earth's atmosphere that is closest to the ground.
front 578 Trough	back 578 The low point of a wave.
front 579 Ultraviolet Light	back 579 A type of light with wavelengths too short to be visible to the human eye; also known as black light.
front 580 Ultraviolet Rays	back 580 A type of harmful energy in the sunlight.

front 581 Unicellular Organism	back 581 An organism that consists of a single cell.
front 582 Unstated Assumption	back 582 A fact or idea that is taken for granted and not actually stated.
front 583 Uterus	back 583 A woman's womb, in which her unborn baby develops.
front 584 Vaccination	back 584 An injected dose of dead or weakened disease-causing agent. The body reacts to a vaccination by forming antibodies to fight the disease.

front 585 Vacuole	back 585 A large compartment in a plant cell that stores water and other liquids.
front 586 Vacuum	back 586 A space that contains no matter.
front 587 Value	back 587 A principle or a quality that a person believes is important.
front 588 Vaporization	back 588 The change of a liquid to a gas.

front 589 Vascular Plant	back 589 A plant that has specialized tissue for transporting water and nutrients to parts of the plant.
front 590 Vein	back 590 A blood vessel that carries blood toward the heart.
front 591 Velocity	back 591 The rate of motion of an object in a certain direction.
front 592 Ventricle	back 592 One of the lower chambers of the heart.

front 593 Vertebrate	back 593 An animal with a backbone and a skull.
front 594 Vesicle	back 594 A membrane-covered compartment near the cell membrane that stores proteins and other organic substances.
front 595 Virus	back 595 A tiny particle of genetic material with a protein covering.
front 596 Visible Light	back 596 See Light.

front 597 Vitamin	back 597 A chemical that is necessary for proper body growth, body activity, and the prevention of certain diseases.
front 598 Volcano	back 598 A place where magma breaks through Earth's surface.
front 599 Volt	back 599 Unit of measurement for the voltage of electricity.
front 600 Voltage	back 600 The energy needed to move an electron or other charged particle, measured in volts.

front 601 Volume	back 601 The amount of space taken up by a substance or object.
front 602 Voluntary Muscles	back 602 A muscle that a person can consciously control.
front 603 Warm-blooded	back 603 A classification of animals who can control their own internal body temperatures.
front 604 Water Cycle	back 604 The circulation of water on Earth through evaporation from the surface into the atmosphere and back to the surface through precipitation.

front 605 Wave	back 605 A disturbance that travels through space or matter; for example radio waves.
front 606 Wavelength	back 606 The distance from the top of one wave to the top to the next wave.
front 607 Weather	back 607 The state of the atmosphere at any given time with respect to temperature, moisture, wind direction and velocity, and air pressure.
front 608 Weather Map	back 608 A map showing where cold, warm, and stationary front are, as well as areas of high and low pressure.

front 609 Weathering	back 609 The process by which large rocks are broken down in place into smaller rocks; may be chemical or mechanical.
front 610 Wheel and Axel	back 610 A simple machine composed of two objects that turn in a circular motion on the same center, multiplying both force and speed.
front 611 White Dwarf Star	back 611 A small, hot star that is the leftover core of a giant or supergiant.
front 612 Wind	back 612 Moving air.

front 613 Work	back 613 The process in which an object moves in response to an applied force.
front 614 Zoology	back 614 The study of animals.
front 615 Zygote	back 615 A fertilized egg resulting when the sperm from the father joins with the egg produced by the mother.