ACT Science — the outside knowledge it still assumes: density, pH, units, cells, genetics and energy

The ACT Science section is mostly about reading data and judging experiments, but not entirely. ACT says that advanced knowledge is not required, yet background knowledge from general, introductory science courses may be needed to answer some of the questions, across biology, chemistry, Earth and space science and physics. Those few questions are cheap points for a student who has the basic facts ready and costly ones for a student who has forgotten them, because no amount of figure reading supplies a fact the passage takes for granted.

This material collects the core facts at the level of a first year of high-school science and asks you to apply each one to a short experimental setting, the way the section does. In the twelve quiz questions you decide which sample floats by computing densities, compare two solutions two pH units apart, explain why a thermometer stops rising while ice melts, recognize power from the unit joules per second, compute a speed with the right unit, identify isotopes from proton and neutron counts, explain a carbon dioxide level that falls in light and rises in darkness, predict the offspring of a Tt × tt cross, count chromosomes after meiosis, apply the ten percent rule along a food chain, predict which potato slice gains mass by osmosis, and separate an astronaut's mass from the same astronaut's weight on the Moon.

Each explanation states the fact, applies it step by step and names the misconception behind each wrong option: treating the pH scale as linear, doubling where a probability should be halved, stopping one level too early in a food chain, or confusing mass with weight.

The 28 flashcards are a compact review list: density and floating, the pH scale, phase changes and the energy they absorb or release, the newton, joule, watt and pascal, speed, atomic number, isotopes and mass number, photosynthesis and cellular respiration in words, dominant alleles and the two common crosses, mitosis and meiosis, energy transfer in food chains, osmosis, the three rock types, the phases of the Moon, and mass versus weight. Going through them a few times before test day is enough; the point is quick recall, not depth.

This material offers a quiz and flashcards. It is independent practice based on ACT's public description of the ACT Science section, and nothing here is produced or endorsed by ACT.

• Apply density, the pH scale and phase-change energy to simple laboratory results
• Recognize SI units of force, energy, power and pressure and compute a speed with its unit
• Use atomic number, isotopes and mass number correctly
• Explain photosynthesis and respiration results, predict simple genetic crosses and count chromosomes after meiosis
• Apply the ten percent energy rule, the direction of osmosis and the difference between mass and weight

Practice material written by Zestly, based on ACT's published description of the ACT Science section (reporting categories Interpretation of Data, Scientific Investigation, and Evaluating Scientific Arguments and Models with Evidence; act.org, retrieved September 2026). All data sets, figures and questions are original.