Washington Comprehensive Assessment of Science (WCAS) Grade 8 key terms

Anything that has mass and takes up space. Matter is made of particles called atoms and can exist as a solid, liquid, or gas depending on how those particles are arranged and moving.

The smallest unit of an element that keeps the properties of that element. Atoms combine in fixed ways to form molecules and all the substances around us.

Two or more atoms joined together by chemical bonds. A molecule can be made of the same kind of atom, like oxygen gas, or different kinds, like water.

A pure substance made of only one kind of atom that cannot be broken into simpler substances by ordinary chemical means. Each element has a unique set of properties.

An organized chart that arranges all known elements by increasing atomic number and by repeating patterns in their properties. It helps predict how elements will behave and combine.

A process in which substances break apart and recombine to form new substances with different properties. Atoms are rearranged but never created or destroyed.

The principle that the total mass of matter stays the same during a chemical reaction because atoms are only rearranged, not lost or gained.

The physical form a substance takes, such as solid, liquid, or gas. Changes between states happen when particles gain or lose energy, without forming a new substance.

How much mass a substance has in a given volume, often written as mass divided by volume. Denser materials sink below less dense ones when placed together.

A measure of how much matter an object contains, usually measured in grams or kilograms. Mass stays the same regardless of where the object is located.

The amount of space an object or substance takes up, often measured in liters or cubic centimeters. Volume can be found by measuring dimensions or by displacement.

The energy an object has because of its motion. Faster-moving objects and particles have more kinetic energy, which affects temperature and state of matter.

Stored energy an object has because of its position or arrangement, such as a ball held above the ground or a stretched spring. It can change into kinetic energy.

The movement of energy from one object or system to another, such as heat flowing from a warm object to a cooler one. Energy is never created or destroyed.

A push or pull that can change an object's motion, direction, or shape. Forces are described by their strength and direction and are measured in newtons.

Three rules describing how forces affect motion: objects resist changes in motion, force equals mass times acceleration, and every action has an equal and opposite reaction.

A force that resists motion when two surfaces rub against each other. Friction changes kinetic energy into heat and can slow or stop moving objects.

A force of attraction between any two objects that have mass. Its strength increases with greater mass and decreases with greater distance between objects.

A disturbance that carries energy from one place to another without carrying matter along with it. Waves can travel through matter or, in some cases, through empty space.

The distance between two matching points on a repeating wave, such as from one crest to the next. Longer wavelengths carry less energy for light waves.

The number of wave cycles that pass a point each second, measured in hertz. Higher frequency means more cycles per second and more energy for light waves.

The smallest unit of life that can carry out all the basic activities of living things. Some organisms are a single cell, while others are made of many cells.

The thin outer covering of a cell that controls what enters and leaves. It allows useful materials in and lets waste products out.

A specialized structure inside a cell that performs a particular job, such as making energy or building proteins. Different organelles work together to keep the cell alive.

The process plants and some other organisms use to make food, using sunlight, water, and carbon dioxide to produce sugar and release oxygen.

The process cells use to release energy from food molecules, usually by combining sugar with oxygen to produce carbon dioxide, water, and usable energy.

A green organelle found in plant cells where photosynthesis takes place. It contains a pigment that captures light energy to help make food.

A community of living organisms interacting with one another and with the nonliving parts of their environment, such as water, air, and soil.

A model showing how energy and matter move through an ecosystem as organisms eat and are eaten. It links multiple food chains into one network.

All the individuals of the same species living in the same area at the same time. Population size can change due to births, deaths, and movement.

The process by which organisms with traits better suited to their environment tend to survive and reproduce more, so those traits become more common over generations.

A feature or behavior that helps an organism survive and reproduce in its environment. Adaptations develop over many generations through natural selection.

Sections of DNA that carry instructions for traits and are passed from parents to offspring. Genes help determine features such as eye color or plant height.

A characteristic of an organism, such as size, color, or behavior. Traits can be influenced by genes, by the environment, or by a combination of both.

The ongoing processes that change rock from one type to another through melting, cooling, weathering, erosion, and pressure. It recycles Earth's rocky material over long periods.

The breakdown of rocks and other materials into smaller pieces by processes such as water, wind, ice, and chemical reactions. It happens in place without moving the pieces.

The movement of weathered rock, soil, and other materials from one place to another by forces such as water, wind, or ice. It shapes landforms over time.

The theory that Earth's outer shell is broken into large plates that slowly move over time, causing earthquakes, mountain building, and volcanic activity at their boundaries.

A sudden shaking of the ground caused by the release of built-up energy along faults where Earth's plates move against each other.

An opening in Earth's surface where melted rock, ash, and gases escape from below. Volcanoes often form where tectonic plates meet or pull apart.

The continuous movement of water between Earth's surface and the atmosphere through evaporation, condensation, precipitation, and collection. It recycles Earth's water supply.

The condition of the atmosphere at a particular place and time, including temperature, precipitation, wind, and cloud cover. Weather changes from day to day.

The typical pattern of weather in a region over many years, including average temperature and precipitation. Climate is different from short-term daily weather.

The Sun and all the objects that orbit it, including planets, moons, asteroids, and comets. Gravity keeps these objects moving in their paths around the Sun.

The curved path an object follows as it travels around another object in space. Orbits are shaped and maintained by the pull of gravity.

A recurring period of the year with a characteristic pattern of temperature and daylight. Seasons on Earth are caused mainly by the tilt of Earth's axis as it orbits the Sun.