Science makes sense when every idea has a reason.

All 171 science terms and definitions

Every flashcard above, written out as a list. Use it to revise without clicking through the cards, to search the page for a term, or to print the whole set.

Acid

a substance that donates hydrogen ions (H^+); in a typical aqueous solution near room temperature, an acid has a pH below 7. Never taste an unknown substance to identify it.

Acidemia

An arterial blood pH below the usual physiologic reference range.

Acidosis

A physiologic process that tends to lower blood pH.

Activation energy

the minimum energy a collision needs to start a reaction.

Adaptation

an inherited feature that has been shaped by natural selection because it improved survival and reproduction in a particular environment.

Alkalemia

An arterial blood pH above the usual physiologic reference range.

Alkalosis

A physiologic process that tends to raise blood pH.

Alpha decay

A nuclear change that emits a helium-4 nucleus, lowering mass number by 4 and atomic number by 2.

Amino acid

a small organic molecule that serves as a building block of proteins.

Anion

A negatively charged ion.

Atom

the smallest unit that still has the identity of an element.

Atomic number

the number of protons in an atom, which identifies the element.

Base

a substance that accepts hydrogen ions; in a typical aqueous solution near room temperature, a base has a pH above 7.

Beta-minus decay

A nuclear change in which a neutron becomes a proton while an electron and an antineutrino are emitted; mass number stays constant and the daughter’s atomic number increases by 1.

Black hole

a region where gravity is so strong that beyond its event horizon nothing, including light, can escape.

Blinding

keeping participants, researchers, or both from knowing treatment assignments when that knowledge could influence reports or measurements.

Buffer

a substance or mixture that resists a sudden change in pH by accepting or releasing hydrogen ions.

Caption

text beside or below a figure that explains what the image shows and may provide essential evidence.

Carrying capacity

the largest population size an environment can sustain over time with its available resources.

Cation

A positively charged ion.

Cell

the smallest unit of life.

Chemical change

A change that produces substances with new chemical compositions.

Chemical reaction

a change that rearranges atoms into new substances.

Chromosome

a DNA, protein structure that carries many genes; after DNA replication, one chromosome consists of two sister chromatids until they separate.

Claim

a statement that something is true.

Climate

the long-term average weather of a region.

Codon

a three-base sequence in messenger RNA that specifies an amino acid or a stop signal during translation.

Coefficient

A number placed before a formula to show relative amount in an equation.

Column

a vertical set of cells in a table; read its heading before using a value.

Community

all the populations of different species that live and interact in one area.

Compound

A pure substance containing two or more elements chemically combined in fixed proportions.

Conclusion

a judgment that summarizes what the data show, and no more.

Condensation

gas turning into liquid.

Conservation of mass

the rule that total mass stays constant in a closed system, including during a chemical reaction.

Consumer

an organism that obtains energy by eating other organisms rather than by making its own food.

Control group

a group that receives a comparison condition, such as no treatment, a placebo, or a standard treatment.

Controlled variable

a factor kept the same to keep a test fair (also called a constant).

Convenience sample

a sample selected because its members are easy to reach; it may not represent the population.

Covalent bond

a bond in which atoms share one or more pairs of electrons.

Crust

Earth’s thin, solid outer layer.

Decomposer

an organism, such as many bacteria and fungi, that breaks down dead material and returns nutrients to the environment.

Density

Mass per unit volume.

Dependent variable

the factor you measure in an experiment.

Displacement

Vector change from initial position to final position.

Dissociation

Separation of existing ions when an ionic substance dissolves.

DNA

the molecule that stores a cell’s genetic instructions.

Double helix

the twisted-ladder shape formed by two strands of DNA.

Ecosystem

a community of organisms together with the nonliving conditions they interact with.

Effector

the tissue, organ, or cell that carries out the response directed by a control center.

Efficiency

Useful output energy divided by input energy, usually written as a percentage.

Electric potential

Electric potential energy per unit charge at a point, measured in volts.

Electrolyte

A substance that produces mobile ions and enables a solution to conduct electricity.

Electron

A negatively charged subatomic particle found in the electron cloud.

Element

A substance whose atoms all have the same proton count.

Empirical formula

The lowest whole-number ratio of elements in a compound.

Endothermic

Absorbing heat into the system; Delta H is positive under the stated convention.

Enzyme

a biological catalyst, usually a protein, that speeds up a chemical reaction.

Equipotential line

Line whose points share the same electric potential. Electric-field lines cross it at right angles.

Erosion

the carrying away of rock and sediment by water, wind, or ice.

Evaporation

liquid turning into gas.

Evidence

observations or measurements offered to support a claim.

Exothermic

Releasing heat from the system; Delta H is negative under the stated convention.

Exposure

Contact with a chemical or physical agent by a particular route, frequency, and duration. Radiation exposure does not necessarily mean radioactive material is present on the person or object.

Fact

a statement supported by reliable observation or evidence.

Fission

A nuclear process in which a heavy nucleus splits into smaller nuclei and other particles.

Fitness

an individual’s relative contribution of heritable information to later generations in a particular environment.

Force

Push or pull that can change motion. Force is a vector measured in newtons.

Fossil

preserved remains, impressions, or traces of past life.

Fusion

A nuclear process in which light nuclei combine to form a heavier nucleus.

Gamma radiation

High-energy electromagnetic radiation emitted by a nucleus; it carries no mass number or atomic number.

Gene

a DNA sequence used to make a functional RNA or protein product and thereby influence cell function or traits.

Glucagon

a pancreatic hormone that raises blood glucose, especially by promoting the release of stored fuel.

Greenhouse gas

a gas, such as carbon dioxide, that absorbs and re-emits infrared radiation, slowing energy loss to space.

Grounding

Connecting an object to Earth or another large charge reservoir so charge can flow.

Half-life

The time required for half of a specified radioactive sample to decay.

Hemoglobin

the iron-containing protein in red blood cells that carries most oxygen in the blood.

Homeostasis

dynamic regulation of internal variables within workable ranges despite internal or external disturbances.

Hydrogen bond

an attraction between a partly positive hydrogen atom in one region and a partly negative atom, often oxygen or nitrogen, nearby.

Hypothesis

a testable proposed explanation that can be used to make predictions.

Independent variable

the factor you change on purpose in an experiment.

Indicator

a substance whose visible change, often a color change, gives information about pH or another chemical condition.

Inertia

Tendency of an object to resist a change in velocity. Mass measures inertia.

Insulator

a material with high electrical resistance, such as rubber, plastic, or glass.

Insulin

a pancreatic hormone that lowers blood glucose by promoting glucose uptake and storage.

Ion

an atom or bonded group of atoms with a net electric charge.

Ionic bond

Electrostatic attraction between oppositely charged ions.

Ionization

Formation of ions, often by reaction of a molecular substance with water.

Isotopes

atoms of one element that have different numbers of neutrons.

Kinetic energy

Energy associated with motion.

Light-year

the distance light travels in one year.

Main idea

the central point of a passage.

Mantle

Earth’s thick layer of hot, mostly solid rock below the crust; over long time scales, parts of it deform and flow.

Mass number

The total number of protons and neutrons in a particular nucleus.

Mean

the sum of the values divided by how many there are (the average).

Median

the middle value when the numbers are put in order.

Mixture

A physical combination of substances with variable composition.

Mode

the value that appears most often in a data set.

Molecular formula

The actual number of each type of atom in a molecule.

Molecule

A discrete, electrically neutral group of covalently bonded atoms.

Mutation

a change in a DNA sequence; its effect may be harmful, neutral, or beneficial depending on the change and context.

Natural hazard

a natural event or process that can harm people, infrastructure, or ecosystems.

Negative feedback

a response that counteracts a change and moves a regulated condition back toward its usual range.

Net force

Vector sum of all external forces acting on the chosen system.

Net ionic equation

An equation showing the species that undergo the chemical change, with spectators removed.

Neutron

An electrically neutral subatomic particle in the nucleus.

Normal force

Contact force exerted perpendicular to a surface.

Nuclear reaction

A change in the composition or energy state of a nucleus.

Observational study

a study that records existing conditions without assigning a treatment; it can reveal associations but may not isolate a cause.

Octet rule

a useful main-group pattern in which many atoms gain, lose, or share electrons to reach eight valence electrons; important exceptions exist.

Opinion

a personal judgment or preference.

Organ

two or more tissues working together as one structure, such as the heart or stomach.

Organ system

a group of organs that work together in major body functions, such as circulation.

Outlier

an unusually large or small value in a data set.

Period

Time required for one complete cycle.

pH

a logarithmic measure of acidity, commonly shown from 0 to 14 in introductory aqueous examples; each one-unit change represents a tenfold change in hydrogen-ion activity.

Phase

Position within a repeating cycle.

Phylogenetic tree

a branching diagram that shows hypothesized evolutionary relationships among groups.

Physical change

A change in form or state without a change in chemical identity.

Placebo

a comparison treatment designed to resemble an experimental treatment without containing its active component.

Plasma membrane

the boundary that controls what enters and leaves the cell.

Polarization

In electrostatics, a separation of positive and negative charge within matter. For a transverse wave, the term describes the orientation of the oscillations.

Population

the whole group being studied.

Precipitate

A solid formed from species in solution during a reaction.

Precipitation

water falling from clouds as rain, snow, or hail.

Prediction

the specific result you expect if a hypothesis holds.

Probability

a number from 0 to 1 that describes how likely an event is; for equally likely outcomes, it equals favorable outcomes divided by total outcomes.

Product

a new substance that forms in a chemical reaction, written to the right of the arrow.

Protein

a polymer of amino acids folded into a shape that supports a specific structural, transport, signaling, or catalytic function.

Proton

A positively charged subatomic particle in the nucleus.

Protostar

a contracting, heating mass of gas and dust that has not yet begun stable hydrogen fusion.

Radiometric dating

estimating numerical age by measuring radioactive parent and daughter isotopes.

Random assignment

using chance to place subjects into treatment groups, helping balance preexisting differences.

Random sample

a sample selected by a chance-based method so members of the population have a known opportunity to be chosen.

Range

the largest value in a data set minus the smallest.

Reactant

a starting substance in a chemical reaction, written to the left of the arrow.

Receptor

a structure that detects a signal or change, such as a protein a hormone binds to.

Renewable resource

a resource replenished on a time scale useful to people; it can still be depleted if use exceeds replenishment.

Ribosome

the cell structure that builds proteins.

RNA

a nucleic acid that is usually single-stranded; different RNAs help carry, interpret, regulate, or use genetic information.

Row

a horizontal set of cells in a table; use the row label to identify what the values describe.

Salt

an ionic compound; a salt is one product of many acid, base neutralization reactions.

Sample

a smaller group chosen to represent a whole population.

Scientific notation

a number written as a value at least 1 but less than 10, multiplied by a power of 10.

Set point

the reference value or range around which a regulated condition is controlled.

Solar system

the Sun and the objects gravitationally bound to it.

Speciation

the origin of a new species, often after populations become reproductively isolated.

Species

a group of organisms that can interbreed and produce fertile offspring; other criteria are used where interbreeding cannot be observed.

Spectator ion

An ion that appears unchanged on both sides of an ionic equation.

Star

a self-gravitating sphere of hot plasma powered by nuclear fusion.

Stratosphere

the atmospheric layer above the troposphere; it contains the ozone-rich region.

Strong acid

An acid that ionizes extensively in water under the stated conditions.

Subscript

A small number in a formula that shows relative atom or ion count.

Supernova

the explosive death of a massive star or a thermonuclear stellar explosion.

Supporting detail

a fact, example, or reason that backs up a main idea.

System

Object or collection of objects chosen for analysis.

Table

data arranged in labeled rows and columns for organized comparison.

Tectonic plates

large moving sections of Earth’s rigid lithosphere.

Tissue

an organized group of cells and, in many tissues, extracellular material that work together in related functions.

Transcription

making an RNA copy from a DNA template.

Translation

using the codons in messenger RNA to assemble amino acids into a polypeptide.

Trend

the overall direction of a set of data: up, down, or steady.

Trophic level

a feeding position in a food chain, such as producer, primary consumer, or secondary consumer.

Troposphere

the lowest atmospheric layer, containing most air and almost all weather.

Valence electron

An outer electron that strongly influences bonding and chemical behavior.

Validity

how well a method measures or tests what it claims to measure or test.

Water cycle

the constant movement of water through evaporation, condensation, precipitation, and collection.

Weather

the short-term state of the atmosphere.

Weathering

the breaking down of rock into smaller pieces.

Weight

Gravitational force on an object.

White dwarf

the dense stellar remnant left after a Sun-like star sheds its outer layers.

Work

Energy transferred by the component of force along a displacement. A force perpendicular to the displacement does no work.

Science vocabulary by grade: 316 more terms

The terms from the grade-level science flashcard decks, written out and grouped by the grade band they are introduced in. These are in addition to the general science glossary above, with duplicates removed.

Grades K-1

Alarm

A loud sound that warns people. A smoke alarm beeps to tell you to get out.

Beak

The hard mouth part of a bird, used to pick up food. A woodpecker taps trees with its beak.

Code

An agreed plan where each flash or beep means something. Two knocks can be a code for come in.

Communicate

To send a message to someone. You communicate by waving, talking, or flashing a light.

Constellation

A group of stars that makes a picture in the sky. The Big Dipper looks like a spoon.

Crescent moon

A thin, curved sliver of moon that looks like a smile. You see a crescent moon a few days after a dark new moon.

Cub

A baby bear, lion, or tiger. A bear cub stays close to its mother.

Daylight

The time when the sun is up and the sky is bright. You play outside after school in daylight.

Ear

The body part that takes in sounds so you can hear. You cover your ears at a loud parade.

Echo

A sound that bounces off something far away and comes back. You hear an echo in a tunnel.

Egg

A round or oval case that a baby animal grows inside. A chick hatches out of an egg.

Fins

Flat body parts fish use to swim and steer. A goldfish moves its fins to turn.

Flashlight

A small light you carry and switch on and off. You can flash it to send a message at night.

Flower

The plant part that makes seeds so new plants can grow. An apple tree flower becomes an apple.

Full moon

A moon that looks like a whole bright circle. A full moon lights up the yard at night.

Fur

Soft hair that covers many animals and keeps them warm. A rabbit has thick fur in winter.

Inherit

To get looks or traits from your parents. Kittens inherit fur color from their mother and father.

Leaf

The flat plant part that uses sunlight to make food for the plant. A maple tree has green leaves.

Light

What lets you see things. The sun, a lamp, and a flashlight all give light.

Lighthouse

A tall tower with a bright light by the sea. Its light warns boats about rocks.

Longest day

The summer day with the most daylight of the whole year. It happens in June where we live.

Loud

A big, strong sound that is easy to hear. A fire truck siren is loud.

Message

The news or idea you send to someone. Saying dinner is ready is a message.

Milk

Food that mother mammals make for their babies. A calf drinks milk from its mother.

Mirror

A smooth, shiny surface that bounces light back. You see your face in the bathroom mirror.

Moon

The big round object that circles Earth and shines in the night sky. You can sometimes see the moon in daytime too.

Nest

A safe home a bird builds for its eggs and chicks. A robin builds a nest from twigs and grass.

Noon

The middle of the day, when the sun looks highest in the sky. Shadows are shortest at noon.

Offspring

The young that come from parents. A puppy is the offspring of two dogs.

Opaque

Lets no light through, so it makes a shadow. A wooden door is opaque.

Parent

A grown-up animal or plant that has young. A mother cat is a parent to her kittens.

Pattern

Something that happens the same way again and again. Day and night repeat, so they make a pattern.

Pitch

How high or low a sound is. A tiny bird chirps high, and a big truck rumbles low.

Pluck

To pull a string and let it go so it vibrates. You pluck a guitar string to hear a note.

Quiet

A small, soft sound that is hard to hear. A whisper in your ear is quiet.

Reflect

When light bounces off something. Light reflects off a puddle and makes it look shiny.

Roots

Plant parts that grow down and soak up water from the soil. Carrots we eat are roots.

Season

One of four parts of the year with its own weather. Spring, summer, fall, and winter are the seasons.

Seedling

A tiny new plant that has just grown from a seed. A bean seedling has two small leaves.

Seeing

Light bounces off a thing and goes into your eyes. That is how you see your shoes.

Shadow

A dark spot made where something blocks the light. Your body blocks sunlight and makes a shadow on the sidewalk.

Shortest day

The winter day with the least daylight of the whole year. It happens in December where we live.

Signal

A light or sound that tells people something. A red traffic light is a signal to stop.

Sound

What your ears hear when something vibrates. A drum makes a sound when the top shakes.

Stem

The plant part that holds up the plant and carries water to the leaves. A sunflower has a thick stem.

Summer

The warmest season, with the most daylight. In summer it is still light after dinner.

Sunrise

When the sun first shows in the morning and the sky gets light. Sunrise happens in the east.

Sunset

When the sun goes down at the end of the day and the sky gets dark. Sunset happens in the west.

Translucent

Lets some light through, but you cannot see clearly. Wax paper is translucent.

Transparent

Lets almost all light pass through, so you see right through it. A clean window is transparent.

Vibrate

To shake back and forth very fast. Pluck a rubber band and it vibrates, so you hear a buzz.

Whistle

A sharp, loud sound you blow. A coach blows a whistle to tell players to stop.

Wings

Body parts that help an animal fly. A robin flaps its wings to leave the ground.

Winter

The coldest season, with the least daylight. In winter it is dark when you eat dinner.

Year

The time it takes for all four seasons to happen once. Your birthday comes once a year.

Grade 2

Absorb

To soak up a liquid like water. A paper towel absorbs juice that spills on the table.

Air

The invisible gas all around us. Plants take in a gas from the air and use light to make their own food.

Bake

To heat food in an oven until it changes for good. Batter bakes into a cake, and the cake cannot turn back into batter.

Canyon

A deep valley with steep rock walls, carved slowly by a river. The Grand Canyon took millions of years to form.

Desert

A very dry place where little rain falls. Cactus plants and lizards live in the desert.

Earthquake

A sudden shaking of the ground. An earthquake can rattle dishes off a shelf in less than a minute.

Evaporate

When a liquid warms up and turns into a gas in the air. A wet sidewalk evaporates dry in the sun.

Flexible

Able to bend without breaking. A garden hose is flexible, so you can curl it up.

Flood

When water quickly covers land that is usually dry. A river can flood a street after a big storm.

Freeze

When cooling turns a liquid into a solid. Water in a tray freezes into ice cubes in the freezer.

Fruit

The soft part that grows around seeds and keeps them safe. A peach is a fruit with a seed inside.

Glacier

A giant, slow-moving sheet of ice on land. Most of Earth’s fresh water is frozen in glaciers and ice near the poles.

Habitat

The place where an animal or plant lives and finds what it needs. A pond is a frog’s habitat.

Hard

Not easy to press, dent, or scratch. A rock is hard, so your finger cannot squash it.

Irreversible

A change you cannot undo. Burning a piece of paper is irreversible, because the ash can never turn back into paper.

Island

A piece of land with water all the way around it. Hawaii is a group of islands in the ocean.

Lake

Water with land all around it, usually fresh water you could drink if it were clean. People swim and fish in lakes.

Landslide

When rock and dirt slide fast down a steep hill. Heavy rain can start a landslide that covers a road in minutes.

Living Thing

Something that grows, needs food or water, and can make more of its own kind. A cat and an oak tree are living things.

Map

A flat drawing that shows where places are from above. On a map, blue usually shows water and green shows land.

Material

The stuff an object is made of. A window is made of the material glass.

Melt

When heat turns a solid into a liquid. An ice cube melts into water on a warm day.

Model

A small copy you build to show how something real works. A toy bridge made of craft sticks is a model.

Mountain

Land that rises very high above the ground around it. You climb a long way to reach the top of a mountain.

Nonliving Thing

Something that does not grow, eat, or drink. A rock in the garden is nonliving.

Object

One thing that is made out of materials. A spoon, a chair, and a kite are all objects.

Ocean

A huge body of salty water. Most of Earth’s water is ocean water, and it is too salty to drink.

Part

One piece of a bigger object. A wheel is a part of a wagon.

Plan

A drawing or list you make before you build. You draw a plan of your fort before stacking the cushions.

Pollen

Tiny yellow dust made by flowers. Pollen sticks to a bee’s fuzzy legs when it lands on a flower.

Pollination

When pollen moves from one flower to another flower. A bee going from blossom to blossom does pollination, and then seeds can grow.

Pollinator

An animal that carries pollen between flowers. Bees, butterflies, and hummingbirds are pollinators.

Pond

A small body of still fresh water. Ducks, frogs, and water lilies all live at a pond.

Property

Something you can tell about a material, like its color, hardness, or shape. "Bumpy" is a property of a basketball.

Rainforest

A warm, wet place with tall trees and heavy rain. Monkeys, frogs, and parrots live in a rainforest.

Rebuild

To use the same pieces again to make something new. The blocks from a tower can be rebuilt into a bridge.

Reversible

A change you can undo to get the first thing back. Melting is reversible, because the water can freeze into ice again.

River

Fresh water that flows downhill in a long path. A river often flows all the way to the ocean.

Root

The part of a plant that grows down and drinks in water from the ground. Carrots are big roots.

Rough

Bumpy or scratchy when you touch it. Sandpaper feels rough on your fingertips.

Rust

The flaky orange stuff that grows on iron or steel left in wet air. A rusty nail cannot be made shiny new again.

Seed

The small part of a plant that can grow into a new plant. An apple seed can grow into an apple tree.

Seed Dispersal

When seeds get carried away from the plant that made them. Wind blows dandelion seeds far from the parent plant.

Shelter

A safe place where an animal hides from weather and danger. A bird’s nest in a tree is shelter.

Smooth

Flat and even when you touch it, with no bumps. An ice cube feels smooth.

Soft

Easy to press in with your hand. A pillow is soft and sinks down when you push it.

Soil

The dirt that plants grow in. It holds roots in place and holds water, but plants do not eat it.

Sort

To put things into groups that match in some way. You can sort blocks into a wood pile and a plastic pile.

Sprout

A tiny new plant just breaking out of a seed. A bean sprout pushes up days after you plant the bean.

Stiff

Hard to bend. A wooden ruler is stiff, so it stays straight when you hold it.

Stretchy

Able to get longer when you pull it, then go back. A rubber band is stretchy.

Strong

Able to hold a lot of weight or pulling without breaking. A steel chain is strong enough to hold a swing.

Sunlight

Light from the sun. Plants use sunlight to make their own food, so a plant in a dark closet turns pale.

Take Apart

To separate an object into its pieces. You take apart a block tower by lifting off one block at a time.

Test

To try something out to see if it works. You test your paper bridge by setting a toy car on it.

Volcano

A mountain that can burst open and pour out hot melted rock. A volcano can cover the land with lava in one day.

Waterproof

Water cannot soak in or pass through. A rubber rain boot is waterproof, so your sock stays dry.

Grades 3-5

Absorption

A material taking in wave energy instead of reflecting or letting it pass.

Acquired trait

A characteristic gained during an organism’s life, such as a scar or a learned skill.

Amplitude

The height of a wave from its rest position. Bigger amplitude means more energy.

Ancestor

An organism from an earlier generation that later organisms descended from.

Apparent brightness

How bright a star looks from Earth, which depends on both its actual brightness and its distance.

Average (mean)

Add the values and divide by how many there are. It smooths out variation between trials.

Axis

The imaginary tilted line Earth spins around.

Balanced forces

Forces that cancel out, so the object’s motion does not change.

Camouflage

Coloring or patterning that helps an organism blend in and avoid being seen.

Cause and effect

A relationship where one event makes another event happen.

Competition

Two organisms needing the same limited resource, such as water or space.

Conductor

A material that lets energy or electric charge pass through easily, such as metal.

Conservation

Using resources carefully so they last longer.

Conservation of matter

The total amount of matter stays the same, even when it changes form or dissolves.

Constraint

A limit on a solution, such as cost, time, size, or available materials.

Contact force

A force that acts only when two objects touch, such as friction or a push.

Correlation

Two things changing together. Correlation alone does not prove one caused the other.

Criteria

The requirements a solution has to meet to count as successful.

Current

The flow of electric charge through a circuit.

Data

The measurements and observations collected during an investigation.

Deposition

The dropping of eroded material in a new place.

Dissolve

To spread evenly through a liquid so the material seems to disappear.

Electric circuit

A complete loop that lets electric current flow.

Energy

The ability to cause change or do work.

Energy transfer

Energy moving from one place or object to another.

Energy transformation

Energy changing from one form to another, such as electrical energy becoming light.

Engineering design

The process of defining a problem, designing solutions, testing them, and improving them.

Environmental change

A change in a habitat that can help some organisms and harm others.

Erosion control

A design solution that slows or redirects moving water and soil, such as plants, terraces, or barriers.

Extinct

No longer existing anywhere on Earth.

Fair test

An investigation where only one variable changes at a time.

Food chain

A single path showing how energy moves from one organism to the next.

Food web

Several connected food chains showing the feeding relationships in an ecosystem.

Freezing

A liquid changing to a solid as it loses thermal energy.

Friction

A force that resists sliding between two surfaces that touch.

Function

The job a structure does for the organism.

Gas

Matter that spreads out to fill whatever container it is in.

Gravity

A force that pulls objects toward each other. Earth’s gravity pulls everything toward its center.

Groundwater

Water stored underground in the spaces in soil and rock.

Heat transfer

Thermal energy moving from a warmer object to a cooler one.

Heredity

The passing of traits from parents to offspring.

Inference

An explanation you reason out from what you observed. You infer that it rained because the ground is wet.

Inherited trait

A trait passed from parents to offspring.

Iteration

Improving a design by testing it, learning from the failure, and trying again.

Landform

A natural feature of Earth’s surface, such as a mountain, valley, canyon, or plain.

Life cycle

The stages an organism passes through from beginning to adult to reproduction.

Liquid

Matter that keeps its volume but takes the shape of its container.

Magnet

An object that attracts iron, nickel, and cobalt and has a north and a south pole.

Magnetic pole

One of the two ends of a magnet. Like poles push apart and opposite poles pull together.

Mass

How much matter is in an object. It does not change if you move the object somewhere else.

Matter

Anything that has mass and takes up space.

Melting

A solid changing to a liquid as it gains thermal energy.

Metamorphosis

A major change in body form during a life cycle, as in a caterpillar becoming a butterfly.

Moon phase

The shape of the lit part of the Moon we see, which repeats about every 29.5 days.

Motion

A change in an object’s position over time.

Natural resource

Something from Earth that people use, such as water, soil, minerals, or fuel.

Non-contact force

A force that acts at a distance, such as gravity or magnetism.

Nonrenewable resource

A resource that takes far longer to form than to use, such as coal or oil.

Observation

Something you notice or measure with your senses or a tool. A thermometer reading is an observation.

Orbit

The curved path one object takes around another in space.

Organism

Any living thing.

Particle

A piece of matter far too small to see, even with a classroom microscope.

Photosynthesis

The process plants use to make food from air, water, and light energy.

Planet

A large object that orbits a star and is not itself a star.

Pollution

Harmful material added to air, water, or land.

Potential energy

Stored energy, such as a raised object or a stretched rubber band.

Predator

An animal that hunts and eats other animals.

Prey

An animal that is hunted and eaten.

Producer

An organism that makes its own food, usually using sunlight.

Prototype

An early version of a design built to be tested.

Reasoning

The explanation of how the evidence supports the claim.

Recycling

Processing used materials so they can become new products.

Reflection

A wave bouncing off a surface, such as light off a mirror.

Refraction

A wave bending as it passes from one material into another.

Repeated trial

Doing the same test more than once so a single odd result does not mislead you.

Resource

Something an organism needs to survive, such as food, water, shelter, or space.

Response

What an organism does when it senses a stimulus.

Revolution

Earth orbiting the Sun, which takes about one year.

Rotation

Earth spinning on its axis, which takes about 24 hours and causes day and night.

Scale

How big or small something is compared with something familiar.

Simple machine

A device such as a lever, pulley, or ramp that changes the size or direction of a force.

Solid

Matter with a fixed shape and volume. Its particles are packed tightly and vibrate in place.

Solution

A mixture where one substance dissolves evenly in another, like salt in water.

Speed

How far something travels in a certain amount of time.

Stimulus

A change in the environment that an organism responds to.

Structure

A body part of an organism, such as a root, a wing, or a stomach.

Survival advantage

A trait that makes an organism more likely to live long enough to reproduce.

Temperature

A measure of how fast the particles in a material are moving on average.

Thermal energy

The energy of moving particles inside a material. More motion means a higher temperature.

Trade-off

Giving up some of one desirable quality to gain more of another.

Trait

A characteristic of an organism, such as eye color, leaf shape, or height.

Unbalanced forces

Forces that do not cancel out, so the object speeds up, slows down, or changes direction.

Variable

Anything in an investigation that can change, such as temperature, amount of light, or time.

Variation

Differences among individuals of the same kind of organism.

Vibration

A fast back-and-forth motion, which is how sound is produced.

Volume

The amount of space an object takes up.

Volume (loudness)

How loud a sound is. Larger amplitude makes a louder sound.

Watershed

All the land that drains into one river, lake, or bay.

Wave

A disturbance that carries energy from place to place without carrying the material with it.

Wavelength

The distance from one wave crest to the next.

Grades 6-8

Abiotic factor

A nonliving part of an ecosystem, such as sunlight, soil, or temperature.

Acceleration

A change in speed or direction over time.

Air mass

A large body of air with fairly uniform temperature and humidity.

Analog signal

A signal that varies smoothly and continuously.

Artificial selection

People choosing which organisms reproduce to increase a desired trait.

Asexual reproduction

Reproduction from one parent, producing offspring genetically identical to it.

Biodiversity

The variety of living things in an ecosystem. Higher biodiversity usually means more stability.

Biotic factor

A living part of an ecosystem.

Carbon cycle

The movement of carbon among the atmosphere, living things, oceans, and rock.

Cell membrane

The boundary that controls what enters and leaves a cell.

Cell theory

All living things are made of cells, and new cells come from existing cells.

Cell wall

A rigid outer layer in plant cells that provides support and shape.

Cellular respiration

The process that releases energy from food molecules, usually using oxygen.

Chemical energy

Energy stored in the bonds between atoms.

Chemical formula

A shorthand that shows which elements are in a compound and how many atoms of each.

Chemical property

How a substance reacts with other substances, such as flammability.

Chloroplast

The organelle where photosynthesis takes place in plant cells.

Climate change

A long-term shift in global temperature and weather patterns.

Commensalism

A relationship where one species benefits and the other is unaffected.

Common ancestor

A species that two or more later species both descended from.

Conduction

Thermal energy transfer through direct contact between particles.

Convection

Thermal energy transfer by the movement of a heated fluid, such as air or water.

Convection current

A circular flow in the mantle, driven by heat, that helps move tectonic plates.

Convergent boundary

Where two plates push together, building mountains or forming trenches.

Cost-benefit analysis

Weighing what a solution costs against what it achieves.

Crest

The highest point of a wave.

Digital signal

A signal encoded as discrete values, which resists noise and copies without losing quality.

Divergent boundary

Where two plates pull apart and new crust forms.

Dominant trait

A version of a trait that shows up whenever its allele is present.

Eclipse

An event where one body blocks light from reaching another, such as the Moon shadowing Earth.

Electric charge

A property of matter that causes attraction or repulsion. Like charges repel, opposites attract.

Electromagnet

A magnet made by running electric current through a coil of wire.

Electromagnetic spectrum

The full range of light, from radio waves through visible light to gamma rays.

Embryological evidence

Similarities in early development that point to shared ancestry.

Energy efficiency

The fraction of input energy that ends up doing the useful job rather than escaping as waste heat.

Energy pyramid

A diagram showing that only a small fraction of energy passes to each higher feeding level.

Extended structure

A repeating network of atoms, like a salt crystal, rather than separate molecules.

Field

The region around an object where it can exert a non-contact force, such as a magnetic field.

Forecasting

Using current data and past patterns to predict a natural hazard before it happens.

Fossil fuel

Coal, oil, or natural gas, formed from the buried remains of ancient organisms.

Fossil record

The full collection of fossils, which shows how life has changed over Earth’s history.

Frequency

How many wave cycles pass a point each second. Higher frequency means higher pitch or bluer light.

Front

The boundary where two air masses meet, often bringing a change in weather.

Galaxy

An enormous collection of stars, gas, and dust bound together by gravity.

Genetic variation

Differences in genes among individuals, which natural selection acts on.

Geologic time scale

The timeline of Earth’s history, divided by major changes in rock and fossil records.

Global temperature rise

The measured increase in Earth’s average surface temperature over the past century.

Glucose

A sugar made in photosynthesis and used as a fuel by cells.

Gravitational force

An attraction between any two objects with mass. It grows with mass and shrinks with distance.

Homologous structure

A body part shared by different species because they inherited it from a common ancestor.

Humidity

The amount of water vapor in the air.

Igneous rock

Rock formed when melted rock cools and hardens.

Law of conservation of energy

Energy is not created or destroyed. It changes form or moves from place to place.

Law of conservation of mass

Atoms are rearranged in a reaction but never created or destroyed, so total mass stays the same.

Limiting factor

A resource in short supply that keeps a population from growing further.

Longitudinal wave

A wave whose particles move back and forth along the direction of travel, like sound.

Medium

The material a mechanical wave travels through.

Metamorphic rock

Rock changed by heat and pressure without melting.

Mitigation

Reducing the severity of a hazard or impact before it occurs.

Mitochondria

The organelles where cellular respiration releases energy from food molecules.

Multicellular

Made of many cells that are organized into tissues and organs.

Mutualism

A relationship where both species benefit.

Natural selection

Individuals with helpful traits survive and reproduce more, so those traits become more common.

Newton’s first law

An object keeps doing what it is doing unless an unbalanced force acts on it.

Newton’s second law

Acceleration depends on the net force and the mass: more force means more acceleration, more mass means less.

Newton’s third law

For every force there is an equal force in the opposite direction on the other object.

Nitrogen cycle

The movement of nitrogen from the air into soil and living things and back again.

Nucleus (atom)

The dense center of an atom containing protons and neutrons.

Nucleus (cell)

The organelle that holds DNA and directs the cell’s activities.

Ocean current

A steady flow of ocean water that moves thermal energy around the globe.

Organelle

A structure inside a cell that carries out a specific job.

Parasitism

A relationship where one species benefits and the other is harmed.

Per capita consumption

The average amount of a resource used per person, a key driver of total human impact.

Periodic table

A chart of the elements arranged by atomic number so elements with similar properties line up.

Physical property

A characteristic you can measure without changing the substance, like density or boiling point.

Plate tectonics

The theory that Earth’s outer shell is broken into moving plates.

Power

How quickly energy is transferred or work is done.

Pure substance

Matter with a fixed composition throughout, either an element or a compound.

Radiation

Energy transfer by electromagnetic waves, which needs no material to travel through.

Recessive trait

A version of a trait that shows up only when the dominant version is absent.

Reference point

A fixed object used to judge whether something is moving.

Relative dating

Determining that lower rock layers are older than the layers above them.

Rock cycle

The continuous change of rock among igneous, sedimentary, and metamorphic forms.

Scale of the solar system

The Sun holds over 99% of the mass, and the distances between planets are vastly larger than the planets.

Sedimentary rock

Rock formed when layers of sediment are pressed and cemented together.

Seismic wave

An energy wave from an earthquake, used to map Earth’s interior.

Sensory receptor

A cell or structure that detects a stimulus and sends a signal to the brain.

Sexual reproduction

Reproduction from two parents, producing offspring with a new combination of genes.

Specific heat

How much energy it takes to raise the temperature of a material. Water’s is unusually high.

Static electricity

A buildup of electric charge on a surface.

Sustainability

Meeting present needs without using up what future generations will need.

Symbiosis

A close, long-term relationship between two different species.

Synthetic material

A material people make from natural resources, such as plastic from petroleum.

System and surroundings

The part you are studying, and everything outside it that energy can move to or from.

Thermal equilibrium

The state reached when two objects in contact have the same temperature and net heat flow stops.

Transform boundary

Where two plates slide past each other, often producing earthquakes.

Transmission

Wave energy passing through a material rather than bouncing off or being absorbed.

Transverse wave

A wave whose particles move at right angles to the direction the wave travels, like light.

Trough

The lowest point of a wave.

Unequal heating

The Sun heating Earth’s surface unevenly, which drives wind and ocean circulation.

Uneven resource distribution

Resources such as oil, fresh water, and minerals are concentrated where past geologic processes put them.

Unicellular

Made of a single cell.

Velocity

Speed together with direction.

Wave speed

How fast a wave travels, set mainly by the medium it moves through.