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Every Concept on the ACT Science Section

Below is a list of every topic that you can possibly see on the science section of the ACT. Even though these topics appear, there are only about 2-3 questions on the entire ACT science section that you need to have prior knowledge for and you cannot just rely on the information in the graphs, charts, and passages.
With that being said, it is still beneficial to be knowledgeable about these topics because it will help you understand the passages better. For instance, if there is a passage that explains how the genes of a certain species mutate, then understanding the definition of words such as “genes”, “mutation”, “DNA”, “allele”, “chromosome”, etc. will help you understand the passage better.
If any of these topics are unfamiliar to you, I encourage you to type the word into google to review the definition and understand some of the basic concepts associated with the word. For some of the more complicated terms, I included the hyperlink to the definition so you can learn more about that concept! There is no need to do in depth research and study endlessly about one topic. Just knowing the definition and how it can be used in a research study is sufficient.

List of Topics on the ACT Science Section


  • classifications: Domain, Kingdom, Phylum, Class, Order, Suborder, Animal Families, Genus, Species
  • human anatomical systems: skeletal, muscular, nervous, endocrine, cardiovascular, lymphatic, respiratory, digestive, urinary, and the reproductive system
  • eukaryotic and prokaryotic organisms: eukaryotic cells have a membrane-bound nucleus and prokaryotic cells do not. (knowing their parts – ribosomes, mitochondria, etc – would also be helpful)
  • photosynthesis: how plants transform light into energy
  • pollination: transferring pollen grains from the male anther of a flower to the female stigma
  • metamorphosis stages: changing from egg, larva, pupa, and adult.
  • genetics (allele, genes, chromosomes, X and Y chromosomes)
  • proteins: large, complex molecules that play many critical roles in the body
  • DNA: double-stranded helix held together by weak hydrogen bonds between purine-pyrimidine nucleotide base pairs: adenine (A) paired with thymine (T), and guanine (G) paired with cytosine (C).
  • RNA: RNA is most often single-stranded unlike DNA
  • genotype: unique sequence of DNA
  • phenotype: detectable expression of this genotype
  • osmosis: movement of liquid through a semipermeable memberane
  • dominant traits: the inheritance of traits that are typically passed vertically from parent to child
  • recessive traits: the alleles of the trait-causing gene are the same, and both (recessive) alleles must be present to express the trait
  • also know about the process of crossing over of dominant and recessive alleles
  • mitosis and meiosis: Mitosis results in two identical daughter cells, whereas meiosis results in four sex cells. (mainly know the differences between then)
  • cellular division phases: prophase, prometaphase, metaphase, anaphase, and telophase


  • understanding (and balancing) chemical equations and reactions: shows the starting compound(s)—the reactants—on the left and the final compound(s)—the products—on the right, separated by an arrow.
  • atom: particle of matter that uniquely defines a chemical element
  • nucleus: a positively charge center of an atom
  • ion: an atom or molecule with a charge
  • molecule: a group of atoms bonded together
  • solute: the minor competent of a solution
  • solvent: the substance that dissolves the solute
  • solution: a mixture of a solute and solvent
  • reactant: starting materials in a reaction
  • product: ending product of a reaction
  • solubility: degree that a substance dissolves
  • states of mater: solid, liquid, gas:
  • pH: acidity of a solution
  • acid: a molecule or ion capable of donating a proton
  • base: a molecule or ion capable of accepting a proton and can neutralize a acid
  • viscosity: the thickness of a substance
  • condensation: change of state from gas to liquid
  • evaporation: change of state to liquid to gas
  • electrons: negatively charged particle
  • protons: positively charged particle
  • neutrons: neutral particle
  • atomic number: number of protons in the nucleus
  • atomic mass: total mass in an atom
  • molar mass: ratio of mass in the substance to moles in the substance
  • isotopes: members of a family of an element that all have the same number of protons but different numbers of neutrons
  • solid, liquid, gas and melting, boiling, freezing points (very generally speaking; not specific to any particular substance, except maybe water)
  • important elements: e.g. water is H20


  • velocity: speed in a given direction (can be positive or negative)
  • acceleration: increase in speed
  • polarity: an entity contains two distinct and opposite poles that can either attract or repel each other
  • buoyancy: tenancy to float in fluid
  • waves: oscillation of something
  • amplitude: maximum displacement from the top to the bottom of the wave
  • frequency: the amount of waves in a certain time
  • wavelength: the distance between two corresponding points on a wave
  • charges: the amount of protons or elections that cause polarity; like charges attract; opposite charges repel
  • circuits (capacitor, resistor): a system that includes a capacity, resistor, inductors, diodes and much more that lets electricity flow.
  • amperes: unit of electric current often abbreviated as amps
  • volts: the pressure from an electrical circuit that pushes the electrons to make the electricity flow
  • convection: process of heat transfer through air or water
  • conduction: process of heat transfer from a hotter area of one surface to a colder part of the surface
  • radiation: emission or transmission of energy in the form of waves or particles through space or through a material medium
  • kinetic energy: energy due to motion
  • potential energy: energy due to an object being held in potion
  • gravitational potential energy: energy due to a change in position when presented to a gravitational field
  • mechanical energy: sum of potential energy and kinetic energy
  • density: Unit of measurement to identify how much mass per volume. The formula is D=M/V otherwise known as Density = Mass / Volume.

Earth and Space

  • metamorphism: state change. (typically in rocks) due to temperature, pressure, or chemicals
  • layers of earth: the crust, the mantle and the core
  • erosion: the gradual distraction of something by wind, water, or other natural agents.
  • altitude: hight or vertical measurement
  • air resistance: drag or force in opposite direction due to air
  • orbit: curved path around a star, moon, or planet
  • terrestrial planet/gas giants: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

Other Science Terms

  • independent variable: a variable (often denoted by x ) whose variation does not depend on that of another.
  • dependent variable: a variable that changes based on changes of the independent variable
  • control: anything that is held constant in a research study
  • hypothesis: a proposed explanation
  • endothermic: accompanied by the absorption of heat or an animal capable of regulating either own heat
  • exothermic: accompanied by the release of heat
  • ectothermic: animals that are unable to regulate their own internal body temperature
  • matter: material in the universe to form objects
  • mass: a measurement of how much matter is in an object

All in all, if you study all these terms and know them well, then you will have an easier time understanding the passages on the Science portion of the ACT Exam. If you don’t understand any of the terms, you can research them more on google or reach out to a tutor to help you understand them further. 

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