ACT Science Outside Knowledge Questions

While the ACT Science section is famously a test of data interpretation, a few questions on every exam require you to draw on basic scientific knowledge. These outside knowledge questions are rare—typically only 3 to 5 of the 40 total questions—but they are predictable and can be easy points if you're prepared. Understanding the foundational concepts they tests prevents you from being caught off guard and allows you to focus your mental energy on the more complex graph and passage analysis that defines the section.

Core Concepts: The Four High-Yield Science Disciplines

The outside knowledge tested falls squarely within standard introductory high school courses. You don't need advanced expertise, but a firm grasp of the following core areas is essential.

1. Biology Fundamentals

Biology questions frequently touch on genetics and cellular processes. You should be able to recall basic definitions and relationships without prompting from a passage.

• Genetics: Understand dominant and recessive alleles. Know that a phenotype is the observable trait (e.g., blue eyes) and the genotype is the genetic combination (e.g., Bb). Be familiar with basic Mendelian crosses using Punnett squares.
• Cell Biology: Know the core functions of major organelles. The mitochondria are the site of cellular respiration and ATP (energy) production. The nucleus houses DNA. The ribosomes synthesize proteins. Understand that photosynthesis occurs in plant chloroplasts, converting light energy, carbon dioxide, and water into glucose and oxygen.
• Ecosystem Basics: Know the direction of energy flow (from sun to producers to consumers) and that matter (like carbon or nitrogen) cycles. Understand that producers (plants, algae) form the base of the food web.

2. Chemistry Essentials

Chemistry outside knowledge questions often center on properties of matter and simple reactions.

• The pH Scale: This is a top-tested concept. Memorize that a pH of 7 is neutral, below 7 is acidic, and above 7 is basic (or alkaline). Understand that each whole number change represents a tenfold change in acidity/basicity. Common acids include vinegar (acetic acid) and lemon juice (citric acid). Common bases include soap and baking soda.
• States of Matter and Phase Changes: Know that adding heat energy can cause melting (solid to liquid), evaporation (liquid to gas), and sublimation (solid to gas). Removing heat energy causes condensation (gas to liquid) and freezing (liquid to solid).
• Basic Chemical Reactions: Recognize the general form of key reactions. Combustion typically involves a fuel reacting with oxygen to produce carbon dioxide and water. Acid-Base neutralization produces a salt and water. Understand that in a chemical reaction, atoms are rearranged, not created or destroyed (the Law of Conservation of Mass).

3. Physics Principles

Physics questions test fundamental relationships between forces, motion, and energy. You will not need to perform complex calculations.

• Forces and Motion: Know Newton's Three Laws conceptually. An object at rest stays at rest, and an object in motion stays in motion, unless acted upon by a net force (First Law). Force equals mass times acceleration ($F=ma$, Second Law). For every action, there is an equal and opposite reaction (Third Law).
• Energy: Understand the core forms: kinetic energy (energy of motion, $KE=\frac{1}{2}m{v}^2$) and potential energy (stored energy, often gravitational). Know the law of conservation of energy: energy cannot be created or destroyed, only transferred or transformed.
• Simple Circuits: Know that in a series circuit, the current is the same through all components, and voltages add. In a parallel circuit, the voltage is the same across all branches, and currents add. Understand that a switch must be closed for a circuit to be complete and for current to flow.

4. Earth and Space Science Basics

These questions draw from geology, astronomy, and meteorology.

• Rock Cycle: Know the three basic rock types. Igneous rocks form from cooled magma or lava. Sedimentary rocks form from compressed sediments. Metamorphic rocks form from existing rocks changed by heat and pressure.
• Water Cycle: Be able to identify processes: evaporation, condensation, precipitation, and runoff.
• Solar System Fundamentals: Know the order of planets from the sun (My Very Educated Mother Just Served Us Noodles: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune). Understand that seasons are caused by the tilt of Earth's axis, not its distance from the sun.

Common Pitfalls

Missing these questions is often avoidable. Watch out for these classic mistakes.

1. Misreading the Question Type: The biggest error is wasting time searching a data table for information that is simply a fact you need to know. If a question asks, "Based on the student's knowledge of biology..." or directly references a concept like pH without providing a defining graph, it is an outside knowledge question. Recognize it and answer from memory.
2. Overcomplicating Simple Facts: The ACT tests basic, foundational knowledge. Don't overthink or search for a trick. If a question asks what organelle is responsible for energy production, the answer is mitochondria—not a complex exception you learned in AP Bio.
3. Confusing Similar Terminology: Be precise. Don't mix up phenotype and genotype, speed and velocity, or weathering and erosion. A quick mental review of these high-yield term pairs before the test can save a point.
4. Forgetting Units and Scale: Remember the order of magnitude on the pH scale and the basic metric prefixes (kilo-, centi-, milli-). Knowing that a pH change from 5 to 3 is a 100x increase in acidity is the kind of recall that leads directly to a correct answer.

Summary

• Expect 3-5 Questions: Only a small subset of the ACT Science section requires prior knowledge, but these are guaranteed points.
• Focus on High-Yield Topics: Prioritize review of core concepts in biology (genetics, cell parts), chemistry (pH, states of matter), physics (Newton's Laws, energy), and earth science (rock cycle, water cycle).
• Recognize the Question Type: Identify outside knowledge questions by their direct reference to scientific facts not explained in the passage, saving you from fruitlessly re-reading data.
• Trust Your Foundation: The knowledge tested is introductory. Recall the simplest, most standard definition or relationship.
• Avoid Overthinking: The correct answer is usually the most straightforward application of a basic scientific principle you learned in your first-year courses.