HiSET Science key terms

A testable, educated prediction about what will happen in an experiment, usually stating a relationship between variables; it must be possible to support or reject it using evidence.

The factor in an experiment that the researcher deliberately changes or manipulates to see whether it affects another factor; it is the presumed cause being tested.

The factor in an experiment that is measured or observed; it may change in response to the independent variable and is the presumed effect being studied.

In a controlled experiment, the group that does not receive the experimental treatment and is used as a standard for comparison against the group that does.

Information gathered directly through the senses or with instruments, such as a measurement, color change, or sound; observations are the raw evidence scientists use to draw conclusions.

A logical explanation or interpretation based on observations and prior knowledge rather than on direct sensing; inferences go beyond what was actually observed.

A well-tested, broad explanation for a set of related observations, supported by much evidence and accepted by most scientists; it is not a guess.

A systematic error or slant that pushes results or interpretations in a particular direction, often caused by how a study is designed, measured, or reported.

Recorded observations or measurements that scientists collect and analyze; data can be numbers or descriptions and are used as evidence to support or reject a hypothesis.

The smallest unit of an element that still has the properties of that element; it consists of protons and neutrons in a nucleus with electrons around it.

A pure substance made of only one kind of atom, which cannot be broken down into simpler substances by ordinary chemical means; examples include oxygen and iron.

A pure substance formed when two or more different elements are chemically bonded in fixed proportions, such as water or carbon dioxide; its properties differ from its elements.

The amount of mass in a given volume of a substance, often calculated as mass divided by volume; denser materials pack more matter into the same space.

A push or pull on an object that can change its motion, direction, or shape; force is measured in newtons and has both size and direction.

The tendency of an object to resist changes in its motion; an object at rest stays at rest, and a moving object keeps moving in a straight line, unless a net force acts.

The energy an object has because of its motion; faster-moving and more massive objects have more kinetic energy. It increases with both mass and speed.

Stored energy that an object has because of its position, condition, or arrangement, such as a book held above the floor or a stretched spring; it can be converted to kinetic energy.

A process in which substances are changed into new substances with different properties by breaking and forming chemical bonds; evidence can include color change, gas, heat, or precipitate.

The transfer of heat through direct contact between particles, as when a metal spoon warms in hot soup; energy moves from warmer areas to cooler areas without the material flowing.

The smallest living unit of an organism; cells have a membrane, contain genetic material, and carry out life processes such as obtaining energy and making proteins.

The process by which plants, algae, and some bacteria use sunlight, water, and carbon dioxide to make sugars and release oxygen; it stores light energy in chemical bonds.

The process cells use to release energy from food molecules, usually by combining oxygen with glucose to produce carbon dioxide, water, and usable energy; it occurs in most living cells.

The molecule that carries genetic instructions in living things; DNA is made of two strands twisted together and its sequence of bases encodes information for building proteins and traits.

A section of DNA that provides instructions for making a protein or for controlling a trait; genes are passed from parents to offspring and can exist in different versions.

The process by which individuals with traits better suited to their environment tend to survive and reproduce more, so those helpful traits become more common in later generations.

All the living organisms in a particular area together with the nonliving parts of their environment, such as water, soil, air, and sunlight; organisms interact with each other and with these parts.

A diagram or model showing many interconnected food chains in an ecosystem, illustrating how energy and matter move from producers to various consumers and decomposers.

The ability of a living thing to keep its internal conditions, such as temperature or water balance, within a stable range even when the outside environment changes.

The ongoing set of processes that change rocks among igneous, sedimentary, and metamorphic forms through melting, cooling, weathering, erosion, deposition, compaction, and heat and pressure.

The scientific model that Earth's outer shell is broken into large moving plates; their interactions cause earthquakes, volcanoes, mountain building, and the shifting of continents over time.

The breakdown of rocks and other materials at or near Earth's surface by physical, chemical, or biological processes; it does not involve transporting the broken pieces away.

The movement or carrying away of weathered rock, soil, and other materials by agents such as water, wind, ice, or gravity; it often follows weathering and can reshape landscapes.

The continuous movement of water through evaporation, condensation, precipitation, and collection on Earth; it transfers water between the oceans, atmosphere, land, and living things.

The warming of Earth's surface and lower atmosphere when certain gases trap heat that would otherwise escape to space; this natural process helps keep Earth warm enough for life.

The Sun and all the objects that orbit it, including planets, moons, asteroids, and comets; gravity holds the system together and keeps objects in orbit.

A force of attraction between any two objects that have mass; on Earth it pulls objects toward the planet's center and keeps the Moon and satellites in orbit.

The typical weather conditions of a region over many years, including average temperature and precipitation patterns; climate differs from day-to-day weather and can be affected by the greenhouse effect.

The changing appearance of the Moon as seen from Earth, caused by the relative positions of the Sun, Earth, and Moon; the Moon does not actually change shape.

The motion of an object around another object, such as Earth orbiting the Sun once each year; revolution is different from rotation, which is spinning on an axis.