Important ACT Science Vocabulary Terms

Getting to know the type of ACT Science Vocabulary Terms that the ACT exam expects you to know can help you score higher and make you feel more comfortable with the format of the Science section (for many students the hardest section in the exam). 

Most of these ACT Science vocabulary and definitions I gathered from the Barron's ACT Math and Science Workbook, which gives good vocabulary lists and appendices related to Math and Science. I also recommend Michael Cerro's For the Love of ACT Science for a great book that specifically focuses on raising the ACT Science score.

ACT Science Vocabulary: Practice Set #1

PDF of ACT Science Vocabulary

  1. absolute zero: lowest-possible temperature, approximately -273 degrees
  2. acceleration:  the rate of change of velocity
  3. acid: compound with a pH less than 7
  4. alloy: a substance composed of two or more metals (synonym: amalgam)
  5. aerobic respiration:  The breakdown of glucose in the body of an animal to supply muscles with oxygen 
  6. alkalinity:  Having a pH greater than 7 ( contrast with basic, which meaning having PH less than 7) 
  7. antigen:  A substance such as a toxin or enzyme that is capable of eliciting an immune response 
  8. asteroids:  Small celestial bodies that revolve around the sun
  9. barometer: an instrument used to measure atmospheric pressure
  10. biomass:  Total mass of all living matter within a given area 
  11. boiling point: the temperature at which additional thermal energy causes a substance to change from liquid to vapor
  12. carbohydrate: an organic compound like sugar or starch that contains carbon, hydrogen, and oxygen at a ratio 1:2:1; also the main source of energy for humans
  13. carcinogen: cancer-causing agent
  14. catalyst: a substance that speeds up a chemical reaction without being changed by the reaction
  15. chlorophyll: the main pigment in plants that captures light energy during photosynthesis
  16. compound: a substance composed of two or more chemically bonded elements
  17. compressibility:  The ease at which pressure can alter the volume of matter
  18. conductor: a material that allows heat or electricity to flow through it with minimal resistance
  19. control: a sample in which no variables are tested, thus serving as a basis for comparison
  20. control variable: a variable that stays constant in an experiment, allowing the effect of another variable to be measured
  21. diffusion time:  The time that it takes for material to spread from one area to another
  22. ecological succession: a sequence of changes in the plant or animal life of a region or habitat
  23. ecology: The field of science that concentrates on relationships between organism and their environments 
  24. electron: a negatively charged fundamental atomic particle
  25. emulsion:  A state in which one liquid is suspended in another because the liquids will not dissolve in one another

ACT Science Vocabulary: Practice Set #2

  1. erosion: wearing away, typically by running water or wind
  2. evaporation: the changing of liquid into gas
  3. equilibrium: a state of balance
  4. experimental Variables: Elements of an experiment that are changed (distinguished from constants), which are held the same in order to produce significant results
  5. fahrenheit: A temperature scale in which the boiling point of what is 212 degrees and the freezing point is 32 degrees 
  6. fermentation: The chemical process of breaking down an organic substance into simpler substances, such as a fermentation of sugar to alcohol 
  7. friction: the force resistant to motion
  8. habitat: the area of the ecosystem where a plant or animal naturally lives
  9. herbivore: an animal that eats only plants
  10. hormone: a chemical substance secreted by a gland of the body that affects change on other parts of the body
  11. humidity: the amount of water vapor in the air
  12. Hydrogen bonding:  The chemical bonding of hydrogen atom with another electronegative atom 
  13. Indigenous:  Native to or naturally existing in a certain area
  14. Intracellular:  Fluid in cells
  15. infrared radiation: electromagnetic waves whose wavelength is longer than that of visible light
  16. insulator: a substance that blocks the flow of heat or electricity
  17. ion: a molecule or atom that has become charged by either gaining or losing an electron
  18. isotope: a type of element with the same number of protons per atom but different number of neutrons
  19. kinetic energy: the energy of an object in motion
  20. lipid: An oily or waxy organic compound that cannot be dissolved in water
  21. lithosphere: A substance (such as air) that possesses the quality of indefinite expansion
  22. manometer
  23. melting point: the temperature at which a substance changes from solid to liquid state
  24. molecular weight:  The weight of all the atoms in a molecule
  25. neutron: an atomic particle that has no charge

PDF of ACT Science Vocabulary

Note: While vocabulary is important,learning how to approach the Science section and manage your time well is equally important (like those in For the Love of ACT Science). If you haven't already done so, supplement the ACT Science vocabulary with my timing tips for this section.

ACT Science: Practice Set #3

  1. organic matter:  matter that is derived from living or formerly living organisms
  2. osmosis: the movement of liquid through a membrane
  3. parasite: an organism that invades another organism and feed off that organism
  4. pH: a scale from 1-14; represents the acidity or alkalinity of a solution; low values are acidic, 7 is neutral, high values is alkaline
  5. photosynthesis: the process in which plants use the sun's energy to convert carbon dioxide and water into glucose
  6. pigmentation: coloration
  7. proteinA compound that consist of amino acids and plays various structural, mechanical and nutritional roles within the organism 
  8. proton: a positively charged atomic particle
  9. radioactive decayA natural process by which an atom of a radioactive isotope spontaneously decays into another element 
  10. specific gravityThe ratio of the weight of one substance to the weight of another substance 
  11. starch: a complex carbohydrate found in many vegetables
  12. ultraviolet radiation: electromagnetic waves with wavelength shorter than that of visible light
  13. vapor: the gaseous for of liquid
  14. velocity: speed of motion
  15. viscosity: a liquid resistant to flow
  16. wavelength: the distance between repeating crests of a wave

PDF ACT Science Vocabulary

Don't Forget About ACT Math

Some students struggle specifically in the Math and Science sections (the more English and History types). So if a student is strong in the English and Reading sections, Princeton's Review Math and Science Workout can be a great book for targeting those areas.


ACT Science Vocabulary: Important Tips

Note: The ACT Science vocabulary lists include words that the ACT test expects you to know and typically will not define them for you. The ACT exam does not test more specific terminology, such as "male-to-female body mass ratio", and often defines these more specific terms in the text or table and figure notes in the passages. 

Make Flashcards

Important: Don't just read over the ACT Science Vocabulary list below. Get out a pen and create a flashcard for each term that you are not familiar with. Also, remember, the ACT Science does not expect you to know the exact definition as much as the general concept and the context the terms is used in the passages. So, grab a pencil and start creating those flashcards!

Note: The makers of the ACT do not expect you to know very specific science terminology, and the test makers frequently define specific scientific terms. If you see an unfamiliar term in the question, check to see if the term is defined in the text paragraphs.

More ACT Science Tips

The ACT Science vocabulary can be challenging for many students. The test seems to throw words at you that maybe you have never seen or, even if you have, do not really remember them. So refreshing your vocabulary can really help a student feel more comfortable with the terminology in the ACT Science section. But don't forget to review general ACT Science test-taking strategies as well.

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