ACT Science Key Terms

101 Key Terms that are important to know for the science section of the ACT

Absolute zero

the lowest possible temperature. It is 0 Kelvin or approximately -273 degrees Celsius.

Abundant

something which is plentiful or exists in large quantities.

Acceleration

rate of change of velocity, often expressed in m/s2.

Acid

a molecule capable of donating a positively-charged hydrogen ion, or capable of forming a covalent bond by donating an electron pair.

Adhere

to stick completely on a surface.

Aerobic respiration

the process of glucose breakdown in the body of an animal for supplying muscles with oxygen.

Altitude

the vertical distance between an object and the ground or sea level; any object on the ground or sea level is said to have 0 altitude.

Analyze

to examine something in detail (such as phenomena, the result of an experiment, data collected from a survey, etc.).

Anecdote

a story told by someone based on his/her past experiences.

Anticipate

to predict an event or a result based on current events or past experiences.

Assert

to state a fact or belief with authority and confidence; to make others believe in one’s authority.

Burgeon

for something to grow or increase rapidly.

Attribute

a feature or property which is regarded as a part of something or someone.

Characteristic

something which is commonly a feature or a quality of a person, place, or a thing.

Carbohydrate

an organic compound containing carbon, hydrogen, and oxygen at a ratio of 1:2:1. For example, sugars and starches are the main sources of energy for living beings.

Catalyst

a substance which speeds up a chemical reaction but does not change the outcomes of the reaction.

Chlorophyll

the green pigment present in plants which captures light energy for photosynthesis.

Coherent

logical and consistent with the preceding arguments, theories, or policies.

Correspond

to agree or correlate with; to communicate by exchanging messages.

Combustion

a high-temperature reaction involving a fuel and an oxidant (usually oxygen), commonly associated with the process of burning.

Compose

to be a part of or to make up something; to write or create a work of literature, art, science, etc.

Compressibility

a measure of the amount of effort it would take to reduce the volume of the matter by applying pressure. Lower compressibility would indicate more effort is required to reduce the volume.

Conduction and conductivity

conduction is the transmission of energy like heat or electricity. Conductivity is an attribute of a material specifying its efficiency in transferring that energy.

Conductor

a material which offers minimum resistance to the flow of heat or electricity.

Contour

the outline which represents the bounding shape of an object or form; to mold something into a specific shape.

Consecutive

something which is followed in an unbroken or continuous sequence.

Contradict

to assert the opposite or to deny the truth of a statement.

Correlate

to have a mutual relationship or connection between two or more things.

Critical

expressing harsh or disapproving comments or judgments about something; analyzing a work of science, literature, music, etc.; describing a situation or a problem which can be potentially disastrous.

Decelerate

to slow down, or to reduce the speed (or velocity) of a moving body.

Deposition

a substance that is naturally deposited somewhere.

Determine

to find the exact cause and explanation of an event, phenomena, result (in an experiment), etc.

Diffusion time

the amount of time it takes for molecules or atoms of a material to spread from an area of high concentration to an area of lower concentration.

Distinguish

to treat something or recognize it as different.

Dissoluble

something which can be dissolved into another liquid or aqueous solution.

Ecology

the field of science which is concerned with relationships between organisms and their environments.

Efficient

to be able to accomplish a task or a purpose without wasting resources (such as time, energy, money, etc.).

Electron

a fundamental part of an atom. It is negatively charged.

Emit

to discharge, generally used in the context of heat, light, radiation, etc.

Emerge

to become obvious, more prominent, or important.

Emulsion

a state where one liquid is suspended in another but the two liquids would not dissolve in one another.

Engage

to make someone or something involved in an event, conversation, or discussion; to participate or get involved in something; to keep someone’s interest.

Equilibrium

a state where all the constituents of a system (such as reactants in a chemical reaction) are in balance.

Erode or Erosion

the process of air or water flow removing soil, rock, or material from one location and transporting them to another location.

Evolve

to develop something gradually; to develop something from a simpler form to more complex forms.

Exhibit

to make property or a skill visible or apparent.

Fermentation

the chemical process of breaking something down into simpler substances. For example, when sugar is fermented into alcohol.

Friction

a force acting between two solid surfaces where the relative motion of the surfaces is resisted.

Fuse

(verb) to join different objects together; (noun) a safety device used in electrical equipment which breaks the circuit in case more current than desired is drawn into the circuit.

Gauge

(verb) to estimate or measure a property (such as volume, amount, etc.); (noun) a device which measures a certain property of something.

Given

information which is specified or stated.

Habitat

an area where an organism naturally lives in the ecosystem.

Herbivore

an animal that survives by exclusively eating plants.

Humidity

the measurement representing the amount of water vapor present in the air.

Hypothesis

a tentative theory which has not been verified or proven, but tries to explain certain facts or phenomena.

Imminent

an event which is close to happening; something which is about to happen in a short period.

Incendiary

something which causes conflicting arguments; a device which is designed to cause and propagate fires.

Incremental

a quantity which is gradually increasing with discrete additions regularly.

Indigenous

something which naturally exists in a certain area or is native to that area.

Infer

to deduce a conclusion not explicitly written in the given evidence and information.

Infrared radiation

Electromagnetic waves with wavelengths longer than those of visible light (0.7 microns).

Impervious

something which is immune to any change from another thing (specific or in general).

Insoluble

something which cannot be dissolved into another liquid or aqueous solution.

Insulator

the opposite of conductor, a substance which resists the transfer of heat or electricity through it.

Interval

a deterministic period between two activities or instants.

Ion

a molecule or an atom which has a positive or negative charge due to losing or gaining one or more electrons

Kinetic energy

the energy of the motion of an object.

Latter

the second statement stated of the two previous statements.

Mass

a measure determined by the amount of matter or energy present in a body, it is the measure of a body’s resistance to acceleration.

Neutron

a fundamental part of an atom which has no charge.

Notion

a belief about something, an impulse, or desire.

Obsolete

something which is no longer of any use, or has a viable replacement which is easier to obtain or function.

Organic matter

carbon-based compounds found within natural environments and beings.

Osmosis

the process of liquid moving through a semipermeable membrane from a less concentrated solution to a more concentrated solution.

Omit

to exclude some information intentionally or forgetfully; to fail or neglect to do something.

Precipitation

phenomena of any form of water falling to the ground (in the form of rain, mist, snow, etc.).

Parasite

an organism which uses another organism as a host and feeds off the host for survival.

pH

a scale from 1-14 which specifies the concentration of hydrogen ions in an aqueous solution. It represents the alkalinity or acidity of that solution. A pH value of 7 is neutral, lower is acidic, and higher is alkaline.

Photosynthesis

a process used by plants to convert carbon dioxide and water into glucose, using energy from sunlight.

Precede

an event which occurs before another event in time; something which comes before another thing regarding their positions.

Principle

something which forms the foundation of a system or behavior.

Proficient

to be well versed and skilled in using a tool or thing.

Prolong

to increase the duration or the physical space of an event or object.

Proportionality

the relationship between two distinct quantities or amounts. In “directly proportional” quantities, an increase of one quantity causes the increase of the other quantity. In “indirectly proportional” quantities, increase of one quantity causes the decrease of the other quantity.

Protein

a compound made up of amino acids which plays several roles in forming the structural components of the body (such as muscles, hair, etc.) within an organism.

Proton

a fundamental part of the atom which is positively charged.

Radioactive decay

a naturally occurring process by which an atom spontaneously decays into another atom of a different element.

Redundant

information which is no longer needed or is of use, usually because it has been stated or deduced earlier.

Relevant

information which is related or appropriate to the subject or holds some value or interest to the subject being discussed.

Residual

remaining parts after an activity has been done to an object, or something which was left over.

Solution

a mixture of two or more substances which is homogeneous (has a uniform mixture and composition).

Specific gravity

the ratio of the weight of one substance to the weight of a different substance.

Starch

a complex carbohydrate which forms the energy supply within many vegetables.

Substrate

a substance which is acted upon by an enzyme; a layer which is underneath another layer.

Trial

testing the performance or result of an experiment.

Uniform

something which always shows the same form or manner without variation.

Variable

a factor which is meant to be changed in an experiment to determine the effects it has on the experiment.

Vapor

liquid in gaseous state.

Velocity

the speed and direction of an object’s motion.

Viscosity

the tendency of a liquid to resist flow. More viscous liquids flow more slowly than less viscous ones.