Using the GlossaryThe Glossary is like a small dictionary. It lists important science terms from your book. The words and terms are listed in alphabetical order. Each word is followed by its meaning. Some words have more than one meaning. This glossary gives the scientifi c meaning. That is how the word is used in this book. After the meaning is a page number that tells on what page the word is fi rst used.

Aabiotic The nonliving parts of an ecosystem. (L4 p. 84)

abyssal plain The fl at area in the deep part of the ocean. (L2 p. 223)

acceleration A change in the speed or direction of an object. (L3 p. 348)

acid rain A mixture of rain water and acid caused by pollution. (L2 p. 96)

active Could erupt at any time, when referring to a volcano. (L4 p. 235)

adaptation A feature (physical or behavioral) that improves a living organism’s ability to survive. (L4 p. 60)

addiction Occurs when someone becomes dependent on a drug or some other substance. (L4 p. 171)

adult The stage when an animal is fully grown. (L1 p. 56)

aerobic With air. (L3 p. 194)

air mass A large body of air with almost the same temperature and moisture. (L3 p. 254)

air pollution Occurs when smoke, dust, and poison gases mix with air. (L3 p. 116)

air pressure The force of the air pressing against everything. (L3 p. 244)

air resistance A special kind of friction. (L3 p. 362)

alcohol A liquid that is produced when yeasts are added to foods that contain sugar or starch. (L3 p. 135, L4 p. 166)

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anabolic steroids Drugs that are made to act like certain hormones. (L4 p. 165)

anaerobic Without air. (L3 p. 194)

anemometer A device that measures the wind’s speed. (L2 p. 263)

angiosperm A plant that has fl owers. (L4 p. 36)

animal Living things that feed off other things. Most are able to move. (L3 p. 28)

anther A sac-like structure that sits on top of the fi lament of a plant. It contains the pollen. (L3 p. 61)

antibiotic Medicine that kills or slows down some germs. (L2 p. 182)

aorta The main artery of the heart. It carries the blood to all the arteries. (L3 p. 162)

aquatic Of, or relating to, water. (L4 p. 106)

artery A blood vessel that carries blood away from the heart. (L3 p. 162)

asteroid A very large chunk of irregularly shaped rock fl oating in space. (L3 p. 277, L4 pp. 256, 303)

alcoholism A disease in which people have strong urges to drink, lose control once they start, need to drink more and more to “feel good,” and feel sick when they try to stop. (L4 p. 175)

allergen A substance that causes an allergic reaction. (L3 p. 152)

allergy A response by the immune system to overreact to something that is often considered harmless. (L3 p. 152)

alloy A solution made of two or more metals. (L4 p. 355)

alveoli Tiny air sacs in the lungs where the gas exchange from carbon dioxide to oxygen is made. (L3 p. 186, L4 p. 130)

amber Hardened resin that sometimes contain the preserved bodies of insects and similar creatures. (L4 p. 275)

amphibian Animal that lives in water and on land. They lay their eggs in water. Some have smooth, wet skin. (L1 p. 51)

amyloplasts Organelles, or starch grains, found in fruits and in specialized underground food storage cells that turn simple sugars into starch. (L4 p. 24)

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autumn The season between summer and winter. Autumn is also called fall. (L2 p. 279)

axis The imaginary line that runs through the North and South Poles. (L3 p. 282)

axle A bar that goes through a wheel. It allows two wheels to work together. (L1 p. 291)

BB cell White blood cells that produce antibodies. (L3 p. 150)

backbone A chain of bones in an animal’s back that helps the animal move. (L1 p. 41) Protects the spinal cord. (L1 p. 172)

bacteria Tiny, single-cell living things that can cause illness. (L3 p. 34)

barometer A tool that measures air pressure. (L3 p.244)

basic need What a living thing must have to stay alive. (L2 p. 22)

battery An object that stores energy. (L2 p. 358)

bedrock Rock found beneath the soil. (L3 p. 230)

asteroid belt A band of asteroids. (L4 p. 303)

asthma A condition that causes the inside of the airways to swell. (L3 p. 200)

astronaut A person who goes into space or has trained to go into space in a spacecraft. (L2 p. 308)

astronomer A person who studies stars, planets, and other things in space. (L2 p. 306, L3 p. 274)

astronomical unit (AU) The average distance from the Sun to Earth. 1 AU is about 150,000,000 kilometers (93 million miles). (L4 p. 302)

astronomy The scientifi c study of space. (L3 p. 274)

atmosphere The blanket of gases that surrounds some planets. (L3 p. 242)

atom A tiny particle that is too small to see that makes up all matter. (L2 p. 320, L3 p. 306, L4 p. 348)

atrium One of the two upper chambers of the heart. (L3 p. 161)

attract To pull toward one another. (L4 p. 370)

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breathing rate The number of times in a minute the lungs inhale and exhale. (L3 p. 194)

bronchioles The small branches of the airways that deliver and take away gases to and from the alveoli. (L4 p. 130)

bulb Food-storage organ in plants formed from stems and leaves. (L3 p. 54)

buoyancy Describes the ability to fl oat in water or air or some other fl uid. (L4 p. 335)

burrow A hole or tunnel dug by an animal. (L3 p. 102)

Ccaffeine An addictive natural plant chemical that makes people feel awake and more alert. (L3 p. 134, L4 p. 176)

calcium A mineral that makes your bones and teeth strong. (L1 p. 170)

calorie A unit that describes how much energy is stored in food. (L2 p. 354)

camoufl age Adaptation that allows some animals to blend into their surroundings. (L4 p. 70)

behavior The way a living thing responds to its environment. (L2 p. 60, L4 p. 61)

behavioral adaptation A specifi c type of behavior or set of behaviors that improves an organism’s ability to survive. (L4 p. 73)

biome An ecosystem defi ned by its climate and its most common plants and animals. (L3 p. 83, L4 p. 104)

biotic The living parts of an ecosystem. (L4 p. 84)

bird Animal that has feathers and wings. (L1 p. 52)

blood Carries food and oxygen to your body and takes away waste. (L1 p. 104, L3 p. 168)

boiling point The temperature at which a liquid boils and changes to gas. (L4 p. 343)

bone A hard structure inside your body. Bones are strong. They make up the skeleton. (L1 p. 160)

bone marrow The center of a bone responsible for producing blood cells. (L4 p. 128)

brain The part of the nervous system that controls all the other body systems. (L1 p. 100, L2 p. 142)

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cave An area that can form when slightly acidic water fl ows into cracks in limestone formations and dissolves the rock. (L4 p. 248)

cavity A hole that germs make in a tooth. (L2 p. 189)

cell The building blocks that make up all living things. (L2 p. 112, L3 p. 19, L4 p. 18)

cell membrane The barrier between all cells and the world outside them. (L3 p. 21, L4 p. 19)

cell wall A strong layer that surrounds and supports the cell membrane of plants. (L4 p. 20)

character What you are really like on the inside. (L4 p. 196)

characteristic Features of living and nonliving things. (L3 p. 18)

checkup A visit with a doctor to check on your health. (L2 p. 178)

chemical change A change in which one or more new substances are formed. (L2 p. 343, L4 p. 361)

chemical reaction A change that occurs when two or more molecules combine and the molecules are changed. (L4 p. 361)

cancer A group of diseases characterized by rapid cell growth. (L3 p. 143)

canines The sharp teeth next to the incisors that help tear food. (L2 p. 114)

canyon A long, narrow valley with steep sides. (L2 p. 219)

capillary A small, thin-walled blood vessel that branches out all through the body. (L3 p. 162)

carbon dioxide A gas in the air. Plants take in this gas through openings in their leaves. (L3 p. 72)

cardiovascular exercise Physical activities that raise your heart rate and exercise your heart. (L3 p. 174)

cardiovascular system The system that contains the heart, blood vessels, and blood. It carries important materials throughout the body. (L4 p.131)

carnivore An animal that eats meat. (L3 p. 85, L4 p. 277)

cast 1. An object made by shaping material in a mold. (L4 p. 274) 2. A cover that keeps a broken bone in place while it heals. (L1 p. 180)

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coal One type of fossil fuel that began forming thousands of years ago from large amounts of plant material that was quickly buried. (L4 p. 284)

coast Where an ocean or a sea meets the land. (L2 p. 220)

cold front Occurs when cold air replaces warm air at Earth’s surface. (L3 p. 255)

comet Balls of ice and rock moving through our Solar System. (L3 p. 277, L4 p. 304)

communication The sharing of ideas, thoughts, feelings, and information. (L2 p. 152)

community All the populations of living things in an ecosystem. (L4 p. 88)

complete metamorphosis When an animal goes through stages of change from one form into a completely different form as it matures. (L3 p. 38)

compound Substances that are made of atoms of two or more elements. (L4 p. 350)

condensation Occurs when moist air rises and cools and tiny water droplets form in the air. (L3 p. 251)

chlorophyll A pigment, or coloring, found in the chloroplasts of leaves that allows plants to use energy from sunlight. (L3 p. 73, L4 p. 23)

chloroplast The part of a leaf cell where photosynthesis takes place. (L3 p. 72, L4 p. 20)

cholesterol A waxy fat that your body needs, in small amounts, to build healthy cells. (L3 p. 176)

circular motion When an object moves in a continuously turning motion. (L3 p. 344)

circulatory system A closed system in the human body made up of the heart, blood, and blood vessels. (L3 p. 160, L4 p.131)

clay A type of soil that has the smallest particles. (L3 p. 231)

climate The weather that happens in an area over many years. (L1 p. 220, L3 p. 260)

closed circuit A circuit that is complete with no breaks. (L4 p. 382)

cloud When water vapor and cooler air mix, they change into tiny water droplets that form a cloud. (L1 p. 203)

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convection The fl ow of energy that occurs when a warm liquid or gas rises and sinks when it cools. (L3 p. 316)

coral reef An underwater community found in shallow tropical seas. (L3 p. 120)

core The Earth’s center layer. (L2 p. 241, L4 p. 222)

corm An underground food storage organ in plants that forms from the base of the stem. (L3 p. 54)

counselor A person trained to help you sort out problems and make positive life choices. (L4 p. 204)

crater Cavity formed when a space object impacts the surface of another space object. (L1 p. 233, L3 p. 274, L4 p. 306)

crescent Moon Is seen before and after the new Moon. (L3 p. 293)

crest The high point in a wave. (L3 p. 331)

crosswalk A marked place on a road so that people can get from one side to the other safely. (L2 p. 202)

crust Earth’s rocky outer layer. (L2 p. 241, L4 p. 223)

condense Part of the water cycle. The process when water vapor changes into liquid. (L1 p. 203, L2 p. 271, L4 p. 343)

conduction The transfer of energy through matter when the particles of two objects touch. (L3 p. 315)

conductor A material through which current and heat can fl ow easily. (L4 p. 380)

cone Makes seeds that are not inside a fruit. (L1 p. 30)

confl ict A situation that arises from a disagreement. (L4 p. 203)

conservation The preservation, protection, or restoration of the natural world. (L4 pp. 114, 286)

constellation A group of stars that forms a recognizable pattern. (L2 p. 301, L4 p. 314)

consumer A living thing that does not make its own food and must get its food by eating another living thing. (L3 p. 71)

continent Large landmasses that cover about 25% of Earth’s surface. (L3 p. 214)

continental air mass An air mass that forms over land and usually has dry air. (L3 p. 263)

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dentist A person whose job is to take care of people’s teeth. (L2 p. 189)

deposition The process by which eroded particles from one place are dropped, or deposited, in a new place. (L4 p. 243)

depression Feeling sad for a very long time, to the point that it affects daily life. (L4 p. 202)

desert A very dry place. Many deserts are hot, but some are cold. (L1 p. 70, L2 p. 76, L3 p. 100)

develop To go through changes during growth. (L3 p. 23)

diabetes A disease in which the sugar level in the blood is too high. (L2 p. 131)

diaphragm A large muscle below the lungs that moves air into the lungs when it contracts. (L3 p. 187)

diet The type of food and drink a person takes in. (L2 p. 122)

digestive system All the parts of the body that break down food and absorb nutrients. (L2 p. 112)

dinosaur A large reptile that lived on Earth long ago and is now extinct. (L2 p. 250)

crystal structure Repeating patterns formed by atoms and molecules in minerals. (L3 p. 222)

current electricity A fl ow of electric charges, or electrons, along a path. (L4 p. 380)

curve A bend along a path. (L1 p. 275)

cutting Part of a plant used to grow a new plant. (L3 p. 66)

cytoplasm A jelly-like substance that fi lls the cell. (L3 p. 21, L4 p. 19)

Ddecibel A unit that measures how loud a sound is. (L3 p. 325)

deciduous A plant that loses all of its leaves every year. (L4 p. 39)

decomposer An organism that causes matter to decay. (L4 p. 94)

deforestation The cutting, clearing, and removal of forests for human use. (L3 p. 115)

delta An area where a river has deposited sand and other small particles as it enters another body of water. (L4 p. 244)

density The amount of mass in a certain volume of matter. (L4 p. 334)

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DWI Abbreviation for driving while intoxicated. (L4 p. 174)

Eeardrum A thin piece of skin in the middle ear that picks up sound waves. (L3 p. 323)

ears The part of the body that is used to hear. (L1 p. 114)

Earth The third planet from the Sun and the home God created for us. (L2 p. 292)

earthquake A sudden break in the rock that creates vibrations that cause the land to shake. (L2 p. 241, L4 p. 232)

echo A sound bouncing back from a surface. (L3 p. 323)

eclipse When one object passes through the shadow of another object. (L3 p. 286)

ecosystem Made up of all the living things that live in a particular place and the nonliving things that they interact with. (L1 p. 69, L3 p. 82, L4 p. 84)

edible Able to be eaten. (L2 pp. 38, 123)

dip tip A pointed leaf tip, common in tropical plants, that allows water to run off quickly. (L3 p. 55)

direction Tells which way an object moves. (L1 p. 274)

disease Any change that upsets the function of the body. (L3 p. 142)

distance How far an object moves. (L3 p. 345)

diversity The variety among living things. (L4 p. 102)

doctor A person who treats sick people and helps them get well. (L2 p. 177)

dormant Something that is currently inactive but may become active again in the future. (L4 p. 235)

drought A very long time without rain. (L2 p. 24)

drug A substance that changes the body’s functions and affects the body, mind, or behavior. (L4 p. 160)

dwarf planet Round bodies that orbit the Sun. Dwarf planets share their orbits with other space objects. (L4 p. 304)

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electron Negatively charged particle that moves around the nucleus of an atom. (L4 p. 348)

element Matter that is made of only one kind of atom. (L4 p. 349)

embryo The part of the seed that develops into a plant. (L4 p. 46)

emotion A mental state or a feeling you get inside. (L2 p. 163, L4 p. 202)

emotional health Deals with emotions, or how you feel about certain situations. (L4 p. 149)

enamel The hard outer layer of a tooth. (L2 p. 188)

endangered At risk of dying out. (L2 p. 100)

endangered species Species whose populations are so low that they may die out and no longer exist. (L4 p. 112)

endocrine system The system that makes hormones and adds them to blood. They control many body processes and functions. (L4 p. 133)

energy 1. The ability to do work or cause change. (L1 p. 302, L2 p. 352) 2. What living things use to do work. (L1 p. 76, L3 pp. 21, 306)

electric circuit The loop, or path, along which an electric current travels. (L4 p. 381)

electric fi eld An invisible fi eld around any object with an electric charge. (L4 p. 378)

electric motor Uses an electromagnet to cause motion. (L4 p. 390)

electrical discharge A sudden jump of a spark between two objects. (L4 p. 379)

electrical energy Energy due to the electrical charge found on atoms. (L3 p. 310)

electrical force The force produced by the motion of the charged particles in an atom. (L3 p. 364)

electricity The fl ow of electrical power or charges. (L1 p. 294, L4 p. 376)

electromagnet A temporary magnet that works only when electricity runs through it. (L4 p. 387)

electromagnetism The interaction of electrical charges and electric and magnetic fi elds. (L4 p. 386)

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excrete To get rid of. (L4 p. 134)

excretory system The system that gets rid of waste products in the body. (L4 p. 134)

exercise Any activity that develops or maintains physical fi tness. (L1 p. 148, L4 p. 140)

exhale To release air from the body through the mouth or nose. (L3 p. 184)

exosphere The outer layer of the atmosphere. (L3 p. 246)

extinct 1. When all of one kind of living thing dies. (L1 p. 85, L2 p. 252)2. No longer erupting, when referring to a volcano. (L4 p. 235)

eyes The part of the body that is used to see. (L1 p. 112)

Ffall The season after summer. The daylight hours are shorter. Many trees change color and lose their leaves. (L1 p. 214)

family health The well-being of the members of the family as a group. (L4 p. 151)

fault A crack or break in Earth’s crust. (L4 p. 232)

environment An organism’s local surroundings, including living and nonliving things. There can be many environments in an ecosystem. (L4 p. 90)

epicenter The location on Earth’s surface directly above the focus of an earthquake. (L4 p. 232)

epidermal Tissue that makes up the outermost layer in a plant leaf. (L4 p. 28)

equator An imaginary line that runs around the middle of Earth. It divides Earth into a northern half and a southern half. (L2 p. 278)

erosion The movement of rocks and soil caused by wind, water, ice, and gravity. (L2 p. 238, L4 p. 241)

esophagus The tube that food passes through from your mouth to your stomach. (L2 p. 116)

evaporate Part of the water cycle. The process when water changes into water vapor. (L1 p. 203, L2 p. 270, L3 p. 251, L4 p. 343)

evergreen A tree that does not lose all its leaves in winter. (L4 p. 41)

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fl uid A liquid or gas. (L3 p. 316)

focus The location underground where the break or shift in the crust creates the earthquake. (L4 p. 232)

fog A cloud that is close to the ground. (L1 p. 206)

food ad A notice from a company that tries to get people to buy its food. (L2 p. 131)

food chain A diagram of how food energy goes from one living thing to another (L2 p. 86, L3 p. 86)

food group Different kinds of food that have similar properties. (L2 p. 124)

food guide An eating plan designed to help people have a balanced diet. (L2 p. 124)

food label A notice on food packaging that lists information about a type of food. (L2 p. 132)

food web A food web is made up of two or more connected food chains. It shows the relationships between plants and animals in an ecosystem. (L2 p. 88, L3 p. 88)

force A push or pull on an object. (L1 p. 280, L3 p. 352)

fern A non-fl owering plant that has xylem and phloem tissues. Ferns also have stems and leaves. They reproduce by spores. (L4 p. 42)

fi brous root A type of root found in plants where no root grows larger than another. (L3 p. 52)

fi lament The stalk that makes up part of the stamen. (L3 p. 61)

fi rst aid Fast help for someone who is sick or hurt. (L2 p. 200)

fi rst-quarter Moon Occurs when the Moon is illuminated on the right side. (L3 p. 292)

fi sh Animals that have fi ns and live only in water. (L1 p. 50)

fi ssure A large crack in Earth’s surface, usually caused by an earthquake. (L2 p. 242)

fi tness A condition of being healthy. (L1 p. 148)

fl exible Something that moves freely. (L1 p. 141)

fl oss A thread that helps you clean between teeth and around the gums. (L1 p. 121, L2 p. 189)

fl ower Part of a plant that has petals and produces seeds. (L1 p. 29, L2 p. 32)

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full Moon Occurs when the surface of the Moon that faces Earth is fully lit. (L1 p. 234, L3 p. 292)

fungus Living thing that does not move and feeds on dead or living matter. (L3 p. 33)

Ggalaxy A very large group of stars, planets, their moons, asteroids, comets, dust, and gases. The Solar System is part of the Milky Way galaxy. (L2 p. 300, L4 p. 316)

gas A kind of matter that fi lls its container. It does not have a defi nite volume or shape. (L2 p. 334, L4 p. 340)

generator A machine that uses a magnet to produce electricity. (L4 p. 388)

genetic Passing along from parent to child. (L3 p. 143)

geologist Scientist who studies the structure of Earth. (L4 p. 254)

geothermal energy Thermal energy that is made and kept in the Earth. (L4 p. 283)

forest Ecosystem where many trees and other plants grow. (L1 p. 70, L2 p. 79)

fossil The remains of a living thing that died long ago. (L2 p. 248)

fossil fuel Nonrenewable energy resources that come from the remains of living organisms that died and were buried. (L4 p. 284)

freeze To change from a liquid to a solid. (L2 p. 336)

frequency The number of vibrations, per second, of an energy wave. (L3 p. 324)

friction A force that acts between two objects that are in contact with each other. Friction slows motion. (L1 p. 282, L3 p. 357)

front The boundary that separates two different air masses. (L3 p. 254)

frostbite Injury that occurs when bare skin freezes. (L3 p. 132)

fruit The fl eshy part of a plant that protects the seeds. (L1 p. 29, L3 p. 62)

fulcrum The point where a lever rests. (L2 p. 385)

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gravity The force that pulls or attracts objects toward each other. (L1 p. 282, L3 p. 355)

grief An overwhelming feeling of sadness or suffering. (L4 p. 202)

grooming Caring for your body and the way you look. (L2 p. 190)

groundwater Water that has settled in places in the soil and rock. (L3 p. 217)

gums The pink fl esh that supports your teeth. (L1 p. 120)

gymnosperm A seed-bearing plant that produces seeds. (L3 p. 63, L4 p. 40)

Hhabitat The place where a plant or an animal fi nds the things it needs to live. (L2 p. 74, L3 p. 82)

hail Precipitation that falls as large pellets of ice. Hail forms inside a cloud. (L2 p. 274)

handicap A disability that makes activities and tasks especially diffi cult. (L4 p. 144)

hardness The ability of one material to be scratched or to scratch another material. (L3 p. 224)

germ A tiny living thing that can make people sick. (L2 p. 176)

germinate The process of a seed growing into a new plant. (L2 p. 31, L3 p. 62)

germination The process in which an embryo plant emerges from its resting stage and begins to sprout. (L4 p. 46)

geyser A fountain of hot water and steam. (L3 p. 217)

gill A body part that fi sh use to obtain oxygen from the water. (L1 p. 50, L2 p. 50)

glacier A long-lasting body of ice that develops over land. (L3 p. 216, L4 p. 246)

global warming The belief of scientists that Earth’s climate is heating up, causing the temperature to rise. (L3 p. 118)

grafting Combining the branch of one tree with the branch of another in order to form a new plant. (L3 p. 66)

grain The particles that make up a rock. (L4 p. 265)

grassland Ecosystem that is covered with grass. (L1 p. 70, L2 p. 78, L3 p. 104)

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hurricane A very large storm that forms over warm waters; brings damaging winds, heavy rains, and large waves. (L2 p. 266)

hydroelectric power Power generated by water turbines. (L4 p. 389)

hygiene Keeping yourself and the things around you clean and healthy. (L2 p. 186)

hypothermia A lowered body temperature, caused by exposure to extreme cold temperatures. (L3 p. 132)

Iice age A period of time when large parts of Earth were covered with ice sheets. (L4 p. 254)

igneous rock Rock that is formed when magma or lava cools and hardens, to form new rock. (L2 p. 230, L4 p. 265)

illegal drugs Drugs that are against the law. (L4 p. 161)

immune system Protects the body from disease and infection. (L4 p. 132)

hatch To break out from eggs. (L1 p. 56)

head lice Tiny insects that live in hair and make a person’s head itch. (L2 p. 191)

heart A fi st-sized muscle that constantly pumps blood through the body. (L1 p. 104, L3 p. 160)

heart attack Death of the heart muscle. (L3 p. 176)

heart rate The number of heart beats per minute. (L3 p. 164)

heat The movement of thermal energy from warmer places to cooler places. (L1 p. 302, L2 p. 364, L3 p. 314)

helmet Covers the head to protect the skull from injury. (L1 p. 181)

herbivore An animal that eats only plants. (L3 p. 85, L4 p. 277)

hormone A chemical that causes something to happen in the body. (L4 p. 133)

hot spot volcano A volcano that is formed when magma pushes up through thin areas of crust. (L4 p. 231)

humus Dark, moist soil that is full of nutrients that plants need. (L1 p. 249, L3 p. 232)

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inner planet A small, rocky planet, like Earth. (L4 p. 303)

insect Animals with three body parts, three pairs of legs, and two antennae. (L1 p. 44, L3 p. 31)

instinct Behaviors that animals are born knowing how to do. (L4 p. 73)

instrument An object that makes special sounds we call music. (L1 p. 314)

insulator A material that will not carry electric current or heat easily. (L3 p. 315, L4 p. 380)

integumentary system Body system that includes the skin, hair, and nails. (L4 p. 127)

intertidal zone The zone in the ocean covered by the high tide and uncovered by the low tide. (L3 p. 110)

intestine A long tube in the body through which food passes after it is broken down in the stomach. It is divided into the small intestine and the large intestine. (L2 p. 116)

invertebrate An animal that does not have a backbone. (L2 p. 58)

immunity The body’s natural ability to fi ght off disease or infection. (L3 p. 148)

incisors The teeth in the front of the mouth that are used for biting and cutting through food. (L2 p. 114)

inclined plane A simple machine, such as a ramp, that makes work easier. (L1 p. 292, L2 p. 383)

incomplete metamorphosis When insects do not go through a major set of changes as they mature. The three stages of incomplete metamorphosis are egg, nymph, and adult. (L3 p. 38)

inertia The tendency of objects to resist changes in their motion. (L3 p. 352)

inhale Bringing air into the body through the mouth or nose. (L3 p. 184)

inhaler A plastic tube full of medicine. The medicine helps relax the airways, so it is easier to breathe. (L3 p. 200)

inherit To pass a trait along from parents to their young. (L4 p. 61)

injury A place in the body that is hurt. (L1 p. 178)

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larynx The voice box, located in the neck. (L4 p. 209)

lava Melted rock that fl ows from a volcano. (L1 p. 248, L2 p. 244, L4 p. 235)

leaf The part of a plant that makes food. Most leaves are green. (L1 p. 20, L3 p. 55)

learned behavior A behavior that is learned, usually from an adult. (L4 p. 76)

lever A simple machine made of a bar that is pushed against a fulcrum to lift heavy objects. (L1 p. 290, L2 p. 385)

life cycle All the stages a living thing goes through during its lifetime. (L1 p. 56, L2 p. 30, L3 p. 38)

life decision A very important decision. It matters for as long as you live. (L4 p. 184)

life span The length of a life. (L3 p. 24)

light A form of energy you can see. (L2 p. 355)

light wave Energy waves that can be seen by the eyes. (L3 p. 330)

Jjet stream A high-speed wind that circles around Earth at both polar areas. (L3 p. 252)

joint Where two bones meet. (L1 p. 164)

Kkinetic energy The energy of motion. (L3 p. 307)

Llake A large body of water that has land all around it. (L2 p. 224, L3 p. 108)

landform A natural shape, or feature, of Earth’s surface. Landforms include mountains, plains, canyons, rivers, and lakes. (L2 p. 214)

landslide When large amounts of rock and dirt slide quickly down mountains and hills. (L2 p. 240, L4 p. 233)

larva A young animal that does not look like the adult. A caterpillar is a larva. (L2 p. 64)

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loudness The quality of how loud or soft a sound is. (L2 p. 375, L3 p. 325)

lunar eclipse Occurs when Earth is between the Sun and the Moon, blocking most of the light from the Sun. Earth’s shadow falls on the Moon. (L3 p. 286)

lungs The body part that brings air into the body. The lungs take oxygen from the air so that blood can deliver it throughout the body. (L1 p. 102, L3 p. 185)

lymphatic system The system that cleans the fl uid that surrounds cells in the body and also removes waste products and bacteria. (L4 p. 132)

Mmachine A tool that helps you do work. (L1 p. 288)

magma Molten rock found below Earth’s surface. (L1 p. 248, L4 p. 224)

magnet An object that has a force that can pull and push metal objects. (L1 p. 284)

light year The distance light travels in one Earth year. A light year equals about 10 trillon km (6 trillion miles). (L4 p. 314)

linear motion An object moving in a straight path. (L3 p. 344)

liquid A form of matter that does not have its own shape and takes the shape of its container. (L2 p. 333, L4 p. 340)

litter Trash that is not recycled or disposed of properly. (L2 p. 98, L3 p. 234)

living Living things are made of cells, are highly organized, respond to their environment, grow and develop, and reproduce. (L1 p. 18, L3 p. 18)

living thing Things that grow and change, make more living things like themselves, and respond to things around them. (L2 p. 18)

loam A mix of sand, silt, and clay that is good for growing plants. (L3 p. 231)

Local Group The cluster of galaxies that the Milky Way belongs to. (L4 p. 317)

location Describes where a place is. (L1 p. 220)

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maritime air mass An air mass that forms over an ocean that usually has wet air. (L3 p. 263)

marrow The spongy part of the bone where red and white blood cells are produced. (L3 p. 150)

mass The amount of matter in an object. (L1 p. 284, L2 p. 322, L3 p. 354)

matter Anything that has mass and takes up space. (L2 p. 320, L3 p. 306)

mature To reach full growth. (L3 p. 38)

mechanical force A force created by the movement of an object over a distance. (L3 p. 362)

medicine A drug that can help protect people from sickness, or treat or cure a sickness. (L4 p. 160)

melt To change from a solid to a liquid. (L2 p. 336)

melting point The temperature at which a substance melts. (L4 p. 342)

mental health The fi tness and well-being of your mind. (L4 p. 149)

mesosphere The third layer of the atmosphere. (L3 p. 246)

magnetic domain A tiny magnetic fi eld caused by electrons in some materials. (L4 p. 373)

magnetic fi eld An invisible area in which magnetic forces are present. (L4 p. 371)

magnetic force The force that pulls certain metals toward a magnet. (L3 p. 363)

magnetic pole A place on a magnet where its magnetic fi eld is strongest. (L4 p. 370)

magnetism A physical property that describes how an object reacts to a magnetic fi eld. (L4 p. 331)

malleability A measure of how easily the shape of a solid substance can be changed when it is hammered or bent. (L4 p. 331)

mammal An animal that has hair or fur and nurses its young with milk. (L1 p. 49)

mantle The middle layer of Earth made up of molten rock. (L2 p. 241, L4 p. 223)

maria A feature of the Moon’s surface; maria are smooth, dark areas. Also called seas. (L3 p. 291)

marine Having to do with the ocean. (L4 p. 106)

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Milky Way The galaxy that our Solar System is part of. It contains over 100 billion stars. (L4 p. 316)

mimicry The action of an animal imitating another animal or object to avoid predators. (L4 p. 71)

mineral A natural solid that comes from Earth instead of living things. All minerals are solids, occur in nature, have a defi nite make-up, and have a crystalline shape. (L2 pp. 123, 228, L3 p. 222, L4 p. 264)

mineral resource Useful material mined or dug out of the ground. (L1 p. 252)

mitochondria Cell parts that break down food to obtain energy. (L4 p. 19)

mixture Two or more substances that are added together but can be separated. (L4 p. 354)

molars The wide, fl at-surfaced, strong teeth in the back of the mouth that crush food. (L2 p. 115)

mold 1. A type of fungus. (L3 p. 33)2. A formation around an object that leaves an imprint of the object. (L4 p. 274)

molecule A group of atoms joined together. (L4 p. 350)

metamorphic rock Rock that forms as a result of heat and pressure. These rocks can form from sedimentary, igneous, and other metamorphic rock. (L2 p. 232, L4 p. 265)

meteor A meteoroid that passes through Earth’s atmosphere and burns up. (L3 p. 278, L4 p. 305)

meteorite A meteor that strikes the surface of a planet or a moon.(L3 p. 278, L4 p. 256)

meteoroids Small chunks of rock that do not orbit the sun. (L3 p. 278, L4 p. 256)

meteorologist A person who works in the science of weather and the atmosphere. (L2 p. 258, L3 p. 250)

meteorology The study of the atmosphere. (L3 p. 250)

mid-ocean ridge A long, underwater mountain range. (L2 p. 222)

migrate To travel back and forth between two places. Some animals migrate to fi nd food or to lay eggs or have their young. (L2 p. 60)

migration The act of traveling from one place to another and back again. (L4 p. 74)

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Nnatural gas A fossil fuel used to heat water and homes. (L4 p. 284)

natural resource Materials supplied by nature. (L3 p. 114)

nectar A sweet liquid stored at the base of fl ower petals that animals use for food. (L3 p. 60, L4 p. 66)

nerve A long fi ber that carries messages between the brain and other body parts. (L2 p. 145, L4 p. 127)

nerve ending The tip of a nerve that reacts to temperature and pressure, and senses smell, light, sound, and taste. (L2 p. 145)

nervous system The body system that controls the body and senses what is happening inside and outside the body. (L2 p. 142)

neutron A neutrally charged particle that makes up the center part of an atom. (L4 p. 348)

new Moon Occurs when the Moon is between the Sun and Earth and is illuminated on the side we cannot see. (L1 p. 234, L3 p. 292)

moon A large object that revolves around a planet. (L1 p. 233, L2 p. 293)

moraine An area of disorganized rocks, soil, and other debris left behind by a retreating or melting glacier. (L4 p. 247)

moss A tiny, green, non-fl owering plant that grows in damp places. (L4 p. 42)

motion Refers to the change in position of an object from one place to another. (L1 p. 266, L3 p. 342)

mountain A landform that is much higher than the land around it. (L2 p. 216)

mucus A sticky substance made in the nose, throat, and windpipe. It traps pathogens before they get into your lungs. (L3 p. 148)

mudfl ow An event where wet soil may fl ow downhill. Volcanoes can cause mudfl ows. (L4 p. 245)

muscle A body part that works with your bones to help you move. Muscles help you stand straight. Muscles also help your bones stay in place. (L1 p. 132)

muscular system The system made up of the muscles in the body. (L4 p. 129)

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nymph a smaller version of an adult animal. (L3 p. 42)

Oobese Over a healthy weight. (L2 p. 131)

obesity A medical condition that occurs when a person is signifi cantly above a normal, healthy weight. (L4 p. 143)

observatory A special building used by scientists to study space using large telescopes. (L2 p. 306)

ocean Large body of saltwater. (L1 p. 72, L2 p. 220, L3 p. 110)

oil A fossil fuel that is used to produce gasoline, diesel, tar, and asphalt. (L4 p. 284)

omnivore An animal that eats both plants and animals. (L3 p. 85)

opaque A material that does not let any light pass through it. (L3 p. 334)

open circuit A circuit with a break in it. (L4 p. 382)

orbit The path an object takes as it moves around another object. (L1 p. 233, L2 pp. 280, 293, L3 p. 282)

newton The SI unit of force. (L3 p. 353)

niche The function, or role, that one type of organism has in its habitat. (L4 p. 103)

nicotine A dangerous poison found in tobacco. (L4 p. 166)

nonedible Something that is not fi t to be eaten. (L2 p. 123)

nonrenewable resources Resources that exist in fi xed amounts. (L4 p. 283)

nonverbal communication Using communication other than words, such as gestures, eye contact, body language, and facial expressions, to communicate. (L2 p. 156, L4 p. 208)

nose The part of the body that is used to smell and breathe. (L1 p. 115)

nucleus A body inside a cell that controls various cell activities. (L3 p. 21, L4 p. 19)

nutrient Substance that a living thing needs to grow. (L2 pp. 23, 112)

nutrition The study of food and the nourishment it gives to your body. (L4 p. 138)

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oxygen A gas found in air that animals need to live. (L1 p. 102, L2 p. 49)

ozone A gas that can do good or bad things. In the stratosphere it is good and protects Earth against harmful rays of the Sun. In the troposphere, it is pollution and is bad. (L3 p. 246)

Ppaleontology Scientists who study fossils. (L4 p. 274)

pathogen A germ that causes infections and disease. (L3 p. 142)

peak The top of a mountain. (L2 p. 216)

peer pressure When friends, or other people your age, try to infl uence you. (L3 p. 202, L4 p. 181)

permanent magnet A magnet that holds its magnetic force forever. (L4 p. 374)

personality The sum of all the qualities you have that make you a unique individual. (L2 p. 162, L4 p. 196)

ore Deposits of mineral compounds that contain minerals valuable enough to mine. (L4 p. 285)

organ Formed when different tissues work together. (L4 p. 31)

organ system A group of organs that work together to accomplish a major task. (L4 p. 126)

organelle Tiny parts that make up a cell. (L4 p. 18)

organic matter The decaying remains of living things. (L3 p. 232)

outer planet Large planets located outside the asteroid belt, mostly made of gases. (L4 p. 303)

outwash plain A formation left behind by a melting glacier. (L4 p. 247)

ovary Structure in the plant where seeds are formed. (L3 p. 61, L4 p. 48)

overfi shing Taking more fi sh than can be replaced by natural reproduction. (L4 p. 113)

over-the-counter medicine A drug that does not need a prescription. (L4 p. 163)

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pistil The central part of the fl ower that includes the ovary, style, and stigma. (L3 p. 61)

pitch The high or low quality of a sound. (L2 p. 374, L3 p. 324)

plain A large, fl at area of land. (L2 p. 217)

planet A large ball of gas or rock that travels around a star. (L1 p. 236, L2 p. 292, L3 p. 276)

plant Producer. A living thing that makes its own food. (L2 p. 21, L3 p. 32)

plasma The liquid part of blood. (L3 p. 169)

plate tectonics The study of the movement of Earth’s tectonic plates. (L4 p. 230)

platelet Part of the blood that clumps together to help stop bleeding and to form scabs. (L3 p. 169)

poison A substance that can make you sick if you eat it, drink it, or breathe it. Many poisons are deadly. (L2 p. 198)

polar Cold climate zones that surround Earth’s poles. (L3 p. 262)

polar climate Climate that can be wet or dry but is always cold. (L1 p. 221)

petrifi cation The process in which minerals replace the hard parts of dead organisms, including bones, teeth, shells, and wood. (L4 p. 274)

phases The monthly cycle of the Moon in which it appears to have different shapes due to the way light hits its surface. (L1 p. 234)

phloem A type of plant transport tissue that carries sugars and other nutrients from the leaves to the rest of the plant. (L4 p. 29)

photosynthesis The process plants use to manufacture food. (L3 p. 72, L4 p. 22)

physical change A change in an object’s appearance, but not in what it is made of. (L2 p. 340, L4 p. 360)

physical health The fi tness and well-being of your body. (L4 p. 148)

physical property Something that can be measured or observed about matter without changing its identity. (L4 p. 330)

pigment A chemical that absorbs some light energy while refl ecting other light energy. (L4 p. 233)

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prescription medicine A drug that must be prescribed, or ordered, by a doctor or other health-care professional. (L4 p. 163)

prey Animals that are hunted and eaten by predators. (L4 p. 95)

producer A living thing that is able to make its own food. (L3 p. 70)

prop root A root that grows from the lower stem of a plant into the soil to help support the plant stem. (L3 p. 52)

property A quality you can use to describe things. Color, shape, and size are properties. (L2 p. 321)

proton A positive-charged particle that is located in the center part of an atom. (L4 p. 348)

pull A kind of force that causes things to move toward the force. (L1 p. 280)

pulley A simple machine made from a rope or string that fi ts in a groove on a wheel. Used to raise or lower things. (L1 p. 293, L2 p. 388)

pulp The soft tissue that reaches from the top of each tooth to the root. (L2 p. 188)

pole A location on the “top” or “bottom” of Earth. The top location is called the North Pole, and the bottom location is called the South Pole. (L2 p. 278)

pollen A powder made by the male parts of a fl ower. (L2 p. 32)

pollination The transfer of pollen from the male to the female parts of a plant. (L4 p. 47)

pollution Harmful substances that are added to the air, water, or ground. (L2 p. 95)

population A group of the same kind of living thing in an ecosystem. (L4 p. 87)

position An object’s location. (L1 p. 264, L3 p. 342)

potential energy Stored energy; the energy an object has because of its position. (L3 p. 307)

precipitation Water that falls to Earth as rain, snow, sleet, or hail. (L2 p. 273)

predator An animal that hunts and kills other animals for food. (L4 p. 95)

premolars The teeth next to the canines that help grind food. (L2 p. 114)

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reference point A way to explain where you are, such as a landmark. (L1 p. 265)

refl ect The bouncing of a wave off a surface. (L3 p. 332)

refl ex A body’s response to something that the brain does not need to think about. (L2 p. 146)

refract The bending of an energy wave as it passes from one material through another. (L3 p. 333)

relationship How you get along with another person. (L2 p. 162)

renewable resources Resources that can be replaced over time by natural processes or can be used over and over without being used up. (L4 p. 283)

repel To push away. (L4 p. 370)

reproduce To make new living things. (L1 p. 58, L3 p. 24)

reproductive system The system that contains the organs that enable living things to produce young. (L4 p. 133)

reptile Animal that has dry scaly skin and is born on land. (L1 p. 51)

resistance skills Things that can help you avoid making wrong decisions. (L4 p. 185)

pupa One of the stages in development right before adulthood. (L2 p. 64, L3 p. 40)

push A kind of force that causes things to move away from the force. (L1 p. 280)

Rradiation The transfer of energy that travels as waves. (L3 p. 318)

rain gauge A tool that collects rain as it falls. It shows how much rain has fallen. (L1 p. 197)

rain shadow An area protected from precipitation by a mountain. (L3 p. 266)

receiver In communication, the person who gets a message. (L2 p. 152)

recycle To collect things so new things can be made from them. (L1 p. 87)

red blood cell Part of blood that picks up oxygen in the lungs and transports it to all the cells. It gives blood its red color. (L3 p. 169)

reduce To use less of something. (L1 p. 86)

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ribs The bones in the chest. They form a cage. The ribs protect your lungs and heart. (L1 p. 162)

river A natural stream of fl owing freshwater. (L3 p. 108)

river system A system of smaller streams draining into larger rivers. (L3 p. 217)

rock A natural solid made from minerals. (L1 p. 246, L2 p. 229, L4 p. 265)

rock cycle The series of natural processes that changes one kind of rock into another kind. (L4 p. 268)

rocket A spacecraft that uses burning fuel to push it forward. (L2 p. 308)

root The part of a plant that takes in water from the soil. Roots also hold the plant in the ground. (L1 p. 20, L3 p. 52)

rotation The movement of a planet or other object as it turns on its axis. (L3 p. 282)

rusting A chemical change between iron and oxygen in the air. (L4 p. 361)

resource A material found in nature that people use. (L1 p. 251, L2 p. 40)

respect Appreciating someone and treating that person with dignity. (L4 p. 195)

respiration The opposite of photosynthesis, when oxygen is used to break down sugar and release carbon dioxide and water as by-products. (L3 p. 73)

respiratory system The system that obtains oxygen for the body and gets rid of carbon dioxide. (L4 p. 130)

response In communication, how the receiver reacts to a message. (L2 p. 152)

responsible Being dependable. (L4 p. 195)

responsible decision A decision that is made by thinking about your choices and picking the one that helps you become a better friend with Jesus. (L4 p. 184)

reuse To use the same thing again. (L1 p. 86)

revolve To move around another object. (L2 p. 293, L3 p. 282)

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sedimentary rock A rock formed when bits of broken rock, soil, and shells are pressed together. (L2 p. 231, L4 p. 265)

seed The fi rst stage of the life cycle for most plants. It has stored food and a tiny plant inside. (L1 p. 26, L2 p. 31)

seedling A young plant that has just started to grow. (L2 p. 31, L4 p. 46)

sender In communication, the person sending a message. (L2 p. 152)

septum A wall separating the right and left sides of the heart. (L3 p. 161)

serving The amount of food in one portion. (L2 p. 133)

sexual reproduction When an egg and a sperm cell from two parents unite and form the fi rst cell of a new life. (L3 p. 24)

shadow A dark or shaded area that appears when light is blocked. (L2 p. 377)

shampoo Used to clean hair. (L1 p. 122)

shell A hard covering that protects an animal’s soft body. (L1 p. 41)

Ssaliva The liquid in your mouth that mixes with food and helps break down food. (L2 p. 113)

sand A type of soil made up of particles big enough to be seen. (L2 p. 231, L3 p. 231)

satellite An object in space that orbits a larger body, such as a planet or a star. A satellite can be natural or human-made. (L2 p. 265, L4 p. 298)

scale Small, hard plate in the skin that helps protect some fi sh from injury. (L1 p. 50)

screw A simple machine that holds objects together. It is an inclined plane wrapped around a rod. (L1 p. 292, L2 p. 383)

seamount An underwater mountain peak. (L2 p. 223)

season A period of the year that is usually marked by changes in weather. (L1 p. 210, L3 p. 284)

secondhand smoke The mix of smoke from a burning cigarette, cigar, or pipe, and the smoke that a smoker exhales. (L4 p. 173)

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sleet Precipitation that forms as rain freezes and becomes tiny pellets of ice. (L2 p. 274)

smoke detector An alarm that sounds when it senses smoke. (L2 p. 197)

smokeless tobacco Made from the leaves of the tobacco plant, but is typically chewed and spit out, not smoked. (L4 p. 173)

smoking The breathing in of smoke from tobacco or other drugs. (L3 p. 198)

snack A small amount of food or drink between meals. (L2 p. 130)

soap Used to clean skin. (L1 p. 122)

soil Made of tiny grains of rocks and dead plants and animals. Soil is nonliving. (L1 p. 69)

soil pollution Contamination that makes soil unsafe for use. (L3 p. 234)

solar eclipse This occurs when the orbit of the Moon travels between Earth and the Sun. (L3 p. 286)

solar energy Light and thermal energy from the Sun. It keeps Earth warm. (L2 p. 368)

shelter A place where an animal can go to be safe or to stay out of the heat, cold, or other bad weather. (L1 p. 68, L2 p. 52)

side effects Reactions that happen when you take medicine. (L4 p. 160)

silt A type of soil with soft particles smaller than sand. (L3 p. 231)

simple machine A tool without many moving parts that makes it easier for people to do work. (L2 p. 382)

sinkhole A large hole in the ground that forms when an underground cave collapses. (L4 p. 248)

skeletal system The system made up of the bones in the body. (L4 p. 128)

skeleton The body’s frame made up of bones. (L1 p. 160)

skin The body’s covering and its biggest organ. It helps keep water and harmful things out of the body. The skin also keeps us from drying out (losing water). (L1 p. 105)

skull The boney skeleton of the head. It protects your brain. (L1 p. 163)

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spin A motion of turning around quickly. (L1 p. 276)

spinal cord A bundle of nerves that runs from your brain down your back, through your vertebrae. It carries messages between your brain and most of your body. (L2 p. 146)

spiritual health The feelings one has toward life; most often based on the relationship with God. (L4 p. 152)

spore A single cell that can grow into a new plant. (L4 p. 42)

spring The season after winter, when plants start to grow and daylight becomes longer. (L1 p. 212)

stalactite A cone-shaped formation that forms when water that drips through a cave ceiling leaves a continual deposit of mineral hanging from the ceiling. (L4 p. 248)

stalagmite A cone-shaped formation that forms when water has dripped from a stalactite and it builds up on the cave fl oor. (L4 p. 248)

stamen The male part of the fl ower. It includes the fi lament and anther. (L3 p. 61)

Solar System The Sun and the group of objects that orbit it. It includes the planets, moons, asteroids, meteors, and comets. (L2 p. 293)

solid Something that has a defi nite volume and a defi nite shape. (L2 p. 330, L4 p. 340)

solution Occurs when one substance dissolves in another, forming a liquid mixture. (L4 p. 355)

sound A form of energy you can hear. (L1 p. 310, L2 p. 355)

sound wave A fast back-and-forth movement of energy. You hear sounds when the energy of a sound wave reaches your ears. (L1 p. 312, L3 p. 322)

space The area beyond Earth’s atmosphere. (L4 p. 294)

space probe A device sent to space that collects and sends information back to Earth. (L2 p. 307, L4 p. 298)

species A kind of living or nonliving thing. (L3 p. 18)

speed The measure of how fast or how slow something moves a given distance. (L1 p. 272, L3 p. 345)

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style A tube-like structure that connects the stigma and the ovary. (L3 p. 61)

subsoil Soil that is rocky and hard and contains broken rock pieces. (L1 p. 249)

succession The process of an ecosystem changing from one type to another. (L4 p. 111)

sugar In photosynthesis, the food a plant makes to obtain energy. (L3 p. 72)

summer The season when days are the warmest and daylight is the longest. (L1 p. 213)

Sun The closest star to Earth. It gives Earth light and heat. (L1 p. 235, L2 p. 291)

sunscreen A product used to block the rays of light that cause sunburn. (L3 p. 132)

surface The surface of Earth includes the land and areas under water. (L1 p. 245)

symbiosis A relationship between two different types of organisms. (L4 p. 98)

symptom A sign of being sick. (L2 p. 176)

star A fi ery ball of gas that gives off large amounts of energy. (L1 p. 235, L2 p. 291, L4 p. 295)

static electricity The buildup of an electric charge on an object or surface. (L4 p. 378)

stem The part of a plant that holds up the leaves. Water and food move through a stem. (L1 p. 20)

stigma The sticky knob at the top of the pistil. (L3 p. 61)

stomach A sac-like body part that produces acid to break down food and absorbs nutrients from food. (L1 p. 101, L2 p. 116)

stratosphere The layer of air above the troposphere. The ozone is found here. (L3 p. 246)

strength Used to describe how much weight a muscle can move. (L1 p. 142)

stress A feeling of being pressured by things happening in your life. (L4 p. 203)

stretch To reach out with your muscles to keep them fl exible. (L1 p. 141)

strip mining The process of stripping away soil and rock from Earth to take minerals. (L3 p. 115)

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temperate forest A woodland found in areas with warm summers and cold winters. (L3 p. 92)

temperate rain forest A type of rain forest found in cooler coastal areas north of the equator. (L3 p. 94)

temperature A measure of how hot or cold something is. (L1 p. 196, L2 p. 362)

temporary magnet A magnet that holds its magnetic force for only a short time. (L4 p. 374)

terrestrial On, or relating to, the Earth. (L4 p. 104)

texture How something feels. (L2 p. 325)

thermal energy The energy of moving particles in matter. (L2 p. 364, L3 p. 308)

thermometer A tool that measures temperature. (L1 p. 196, L2 p. 363)

thermosphere The fourth layer of Earth’s atmosphere. It is between the mesosphere and exosphere layers. (L3 p. 246)

third-quarter Moon Occurs when the Moon is illuminated on the left side. (L3 p. 292)

TT cell White blood cells that provide a defense against pathogens or cancers that have invaded other living cells. (L3 p. 151)

taiga A type of forest found in cool mountain regions. It is Earth’s largest biome. (L3 p. 93)

taproot Found in plants that have a main root. (L3 p. 52)

tectonic plate Large slabs of rock comprising Earth’s crust. (L4 p. 225)

teeth The part of the body that is used to chew and bite. (L1 p. 120)

telescope A tool that uses lenses and mirrors to collect and focus light so that objects in space can be seen more clearly. (L1 p. 232, L2 p. 306, L4 p. 296)

temperate Climate zones located between the poles and the equator that are not as cold as polar zones or as warm as tropical zones. (L3 p. 263)

temperate climate Climate that has a mix of warm, cold, wet, and dry weather. (L1 p. 221)

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tornado A powerful windstorm that may form within a thunderstorm; its winds form a funnel shape. (L2 p. 266)

total eclipse Occurs when the Moon and Sun line up perfectly, so that the Sun is completely blocked by the Moon, and the Moon’s shadow falls on Earth. (L3 p. 286)

touch A sense that is used to fi nd out how something feels. (L1 p. 111)

trace fossil A track, trail, or burrow made in soft material by an animal that lived long ago. (L4 p. 275)

trachea A tube in the throat that transports air from the larynx to the bronchi. (L3 p. 186, L4 p. 130)

translucent A material that absorbs some light and lets some light pass through it. (L3 p. 334)

transparent A material that lets almost all light pass through it. (L3 p. 334)

tree ring The ring seen in cut wood, showing a new layer of growth for every year of life. (L3 p. 53)

thorn A small, sharp pointed growth along the stem of some plants that protects the plant from animals. (L3 p. 53)

thunderstorm A type of weather with heavy rains, lightning, and thunder. (L2 p. 266)

tissue A group of similar cells that work together to perform certain jobs for living things. (L4 p. 28)

tobacco A plant with leaves that people smoke or chew. (L3 p. 135, L4 p. 166)

tone The quality of the sound and the style or manner of expression you use as you speak. (L4 p. 208)

tongue The part of the body that is used to taste and speak. (L1 p. 116)

toothpaste A cream or gel that is used to clean the teeth. (L1 p. 120)

top predators A predatory animal that no other predator animal will eat. (L4 p. 96)

topsoil Top layer of soil in which plants grow. (L1 p. 249, L3 p. 232)

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turbine A wheel shaped like a fan that spins when acted on by a force, usually steam or water. (L4 p. 389)

turn When an object changes directions. (L1 p. 275)

UUniverse Everything that exists, including all the galaxies, stars, solar systems, planets, and moons. (L2 p. 302, L4 p. 318)

Vvaccine A weakened or killed form of the same pathogens that cause diseases that is introduced to the body to form antibodies. (L2 p. 181, L3 p. 151)

vacuole The part of a cell that stores food and water. (L4 p. 20)

valley The low area between two mountains. (L2 p. 216)

values Standards, ideas, beliefs, and goals you believe are important. (L2 p. 165, L4 p. 194)

vegetative reproduction When a new plant grows from part of an already-growing plant. (L3 p. 66)

trench A long, v-shaped cut in the ground. Ocean trenches are the deepest parts of the ocean. (L3 p. 215)

tropical Climate zones found along the equator that have warm climates with high temperatures throughout the year. Tropical rain forests have heavy precipitation with high humidity. (L3 p. 262)

tropical climate Climate that is hot and wet. (L1 p. 221)

tropical rain forest A type of rain forest found near the equator that has only rainy and dry seasons. (L3 p. 94)

troposphere The layer of air we live in. Weather takes place here. (L3 p. 246)

trough The low points of a wave. (L3 p. 331)

tsunami A wave caused by an underwater earthquake that travels quickly over long distances. (L4 p. 233)

tuber An underground stem that stores water and food to help keep the plant alive. (L3 p. 54)

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Wwaning The phases between the third-quarter Moon, full Moon, and new Moon. (L3 p. 293)

waning crescent The part of the Moon we see between the third-quarter and the new Moon. (L3 p. 293)

warm front Occurs when warm air replaces cooler air at Earth’s surface. (L3 p. 255)

waste Any food not used by the body. (L2 p. 117)

water cycle Water moving from the surface of the Earth to the atmosphere and back again. (L1 p. 202, L2 p. 272, L3 p. 243)

water resistance A special kind of friction. (L3 p. 362)

water vapor Water in the form of a gas. (L1 p. 203, L2 p. 270)

wave The way that energy travels from one place to another. (L2 p. 372)

wavelength The distance between two crests (high points) or two troughs (low points) of a wave. (L3 p. 331)

vein A blood vessel that carries blood back to the heart. (L3 p. 163)

ventricle A heart chamber that collects blood from the atria and pumps it out of the heart. (L3 p. 161)

verbal communication Spoken or written words that give information, ideas, thoughts, or feelings. (L2 p. 155, L4 p. 208)

vertebrate An animal that has a backbone (L2 p. 58)

vibrate To move back and forth. (L1 p. 310)

vibrating motion A back-and-forth movement. (L3 p. 344)

vitamin A substance that is needed in small amounts for growth, activity, and good health. Living things make vitamins. (L2 p. 123)

vocal folds Two folds of tissue in the larynx with a gap between them that vibrate and produce sounds. (L4 p. 209)

volcano An opening in Earth’s surface from which gas, volcanic ash, and lava fl ow. (L2 p. 244, L4 p. 235)

volume How much space something takes up. (L2 p. 323)

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wetland An area of land that is usually wet. Swamps, marshes, and bogs are types of wetlands. (L2 p. 80, L3 p. 109)

wheel Something round that turns and usually has an axle. (L1 p. 291)

wheel and axle A simple machine with a rod, or axle, through the center of a wheel. (L2 p. 386)

white blood cell The part of blood that helps fi ght off bacteria and viruses. (L3 p. 169)

wind Air in motion. (L1 p. 194)

wind vane A tool that points in the direction the wind is coming from. (L1 p. 197)

winter The coldest season. The daylight is shortest during winter. (L1 p. 215)

work Happens when a force acts on an object and causes motion. (L1 p. 288)

wrinkle ridge Feature on the Moon’s surface formed when parts of the surface are pushed together. Eventually the rock buckles, forming wrinkles. (L3 p. 291)

waxing The phases between the new Moon, fi rst-quarter Moon, and full Moon. (L3 p. 293)

waxing crescent The part of the moon we see after the new Moon and before the fi rst-quarter Moon. (L3 p. 293)

weather The conditions of the air around you. (L1 p. 194, L2 p. 260)

weather map A map that shows weather information for a large area during a certain time. (L2 p. 263)

weather satellite A human-made object that travels around Earth and gives information used by weather forecasters. (L2 p. 265)

weathering The breaking up of large rocks into smaller pieces by wind, water, and ice. (L2 p. 238, L4 p. 240)

wedge A simple machine with slanted sides that pushes or cuts things apart. It is made up of two inclined planes. (L1 p. 293, L2 p. 384)

weight The measure of the force of gravity. (L1 p. 283, L3 p. 356)

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XX-ray A picture of the bones in your body. (L1 p. 179)

xylem A type of plant transport tissue that carries water and nutrients from a plant’s roots to its leaves. (L4 p. 28)

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