Praxis General Science key terms

A testable, tentative explanation for an observation or a proposed answer to a scientific question, stated clearly enough that evidence could support or contradict it.

The factor in an experiment that the researcher deliberately changes or selects, so that its effect on the measured outcome can be observed.

The comparison group in an experiment that does not receive the treatment being tested, used to show what would happen without it.

A broad, well-supported explanation for a body of evidence that has survived repeated testing and can generate new predictions; far stronger than a guess or hunch.

The process in which independent experts examine a study's methods, data, and reasoning before publication, helping catch errors and weak or unsupported evidence.

A simplified representation, whether physical, mathematical, or computational, used to describe, explain, or predict aspects of a real system too complex to study directly.

A cyclical approach to solving practical problems: define the need, brainstorm solutions, build and test a prototype, then evaluate results and redesign as needed.

The smallest unit of an element that keeps that element's chemical properties, made of protons and neutrons in a nucleus surrounded by electrons.

A bond formed when one atom transfers electrons to another, creating oppositely charged ions that then attract each other, as in table salt.

A bond formed when two atoms share one or more pairs of electrons, typical of molecules such as water and carbon dioxide.

The amount of mass packed into a given volume, calculated as mass divided by volume; it helps explain why some objects float and others sink.

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

The rate at which velocity changes, including speeding up, slowing down, or changing direction, measured in meters per second squared.

The energy an object has because of its motion; it increases with the object's mass and with the square of its speed.

The principle that energy cannot be created or destroyed, only transferred or transformed between forms, so the total in a closed system stays constant.

The flow of electric charge through a material, usually electrons moving in a wire, measured in amperes and driven by a voltage difference.

The distance between two matching points on consecutive waves, such as crest to crest; together with frequency it determines a wave's color or pitch.

The full range of electromagnetic radiation, ordered from long radio waves through microwaves, infrared, visible light, and ultraviolet to short X-rays and gamma rays.

A scale from 0 to 14 describing how acidic or basic a solution is, based on hydrogen ion concentration, with 7 considered neutral.

The time required for half of the atoms in a radioactive sample to decay into other elements; this value is fixed for each isotope.

The thin, flexible barrier surrounding a cell that controls what enters and leaves, built mainly from a double layer of phospholipids with embedded proteins.

The movement of water across a selectively permeable membrane from an area of higher water concentration to an area of lower water concentration, requiring no added energy.

The process by which plants, algae, and some bacteria use light energy to convert carbon dioxide and water into glucose and release oxygen.

The set of reactions in cells that break down glucose to release usable energy, using oxygen in most organisms and producing carbon dioxide and water.

A double-stranded molecule that stores genetic instructions using four bases, found in the cells of all living organisms and copied when cells divide.

A segment of DNA that carries the instructions for building a particular protein or influencing a trait, and is passed from parents to offspring.

Cell division that halves the chromosome number to produce gametes, generating genetically varied sex cells for sexual reproduction.

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

The ability of an organism to keep internal conditions such as temperature and blood chemistry within a stable, workable range despite changes outside.

A protein that speeds up a specific chemical reaction in living things by lowering the energy needed, without being consumed by the reaction.

A diagram showing how energy and matter move through an ecosystem as organisms eat and are eaten, linking several overlapping food chains.

The theory that Earth's rigid outer shell is broken into plates that move over the mantle, causing earthquakes, volcanoes, and mountain building at their boundaries.

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

The continuous movement of water among oceans, atmosphere, and land through evaporation, condensation, precipitation, runoff, and storage in ice and groundwater.

The breakdown of rocks and minerals at Earth's surface by water, ice, wind, plants, and chemical reactions, producing sediment without carrying it away.

The warming of a planet's surface as certain atmospheric gases trap heat radiating from the surface, keeping Earth warm enough for liquid water.

The roughly 23.5-degree slant of Earth's rotation axis, which stays pointed in nearly the same direction and produces the seasons as Earth orbits the Sun.

Regular rises and falls of ocean water caused mainly by the Moon's gravity pulling differently on different parts of Earth, with the Sun adding its effect.

The model that a solar system forms from a rotating cloud of gas and dust that collapses, flattens into a disk, and clumps into a star and planets.

Determining the order in which past events occurred by applying principles such as superposition and cross-cutting relationships, without assigning numerical ages in years.