ACT, College admissions

Science (Optional)

Science is optional on the enhanced ACT and is not part of the composite score. Students who take it answer 40 questions in 40 minutes, exactly 60 seconds per question, and receive a separate 1 to 36 science score plus a STEM score that combines math and science. The section tests scientific reasoning applied to figures, tables, experiment descriptions, and competing explanations far more than it tests recalled science content, though comfort with basic biology, chemistry, physics, and earth science vocabulary helps.

Position: 4 of 5 sections
Questions: 40 questions
Time: 40 minutes
Topics covered: 3 topics in this guide

What is covered

Topics inside this section.

These topics describe the scope students most often review for this part of ACT. Treat them as a study checklist rather than an exhaustive list of what a single exam form can sample.

Interpretation of Data: Reading values, trends, and relationships from graphs, tables, and diagrams, interpolating and extrapolating, translating between representations, and comparing results across figures.
Scientific Investigation: Understanding experimental design: what was varied, what was held constant, why a control exists, what a described tool or procedure does, and how a study would change under a new condition.
Evaluation of Models, Inferences, and Experimental Results: Judging whether a hypothesis, model, or conclusion is supported by the evidence presented, and deciding which competing explanation new results would strengthen or undermine.

Study tips

How to practice Science.

Section-specific guidance that follows from how this material is usually tested.

Decide early whether science is part of your plan, since programs and scholarships differ on whether they want it, and then commit so your practice time is not split.
Work the figures before the prose on data-heavy passages, and go back to the text only for the questions that require it.
Passages that present competing explanations need genuine reading rather than data lookup, so budget extra minutes for them and consider taking them last.
At exactly 60 seconds per question, practice deciding fast which figure a question points to; locating the right data is most of the work.

Where this fits

Science (Optional) is 4 of 5 sections in the ACT guide. Use the full guide to balance it against everything else you have to review.

Back to the ACT guide Official exam information

Sample Science questions

Practice questions, not yet expert-reviewed

Original practice questions written to the published framework for this section. No expert has reviewed them, and they are not taken from any official exam. Try each one before you open the answer.

Question 1Foundational
In a controlled experiment, what is the name for the variable that the researcher deliberately changes?
1. AThe dependent variable
2. BThe independent variable
3. CThe control variable
4. DThe confounding variable
Show answer
Answer: B. The independent variable
The independent variable is set by the researcher, and the dependent variable is measured because it is expected to respond. Control variables are the conditions deliberately held constant so they cannot explain the result.
Key insight: You change the independent variable and measure the dependent one.
Question 2Foundational
True or false: in a trial testing a new fertilizer, the group of plants that receives no fertilizer serves as the control group.
1. ATrue
2. BFalse
Show answer
Answer: A. True
A control group is treated identically except for the variable being tested, so the unfertilized plants supply the baseline that the treated plants are compared against. Without that baseline, ordinary growth could be mistaken for an effect of the fertilizer.
Key insight: The control group is the comparison that makes an effect measurable.
Question 3Intermediate
A student measures a reaction rate at 10, 20, and 30 degrees Celsius, then estimates the rate at 25 degrees from those results. What is that kind of estimate called?
1. AExtrapolation
2. BInterpolation
3. CReplication
4. DCalibration
Show answer
Answer: B. Interpolation
The estimate falls between measured points, which is interpolation. Extrapolation estimates a value outside the measured range, such as the rate at 50 degrees, and carries far more uncertainty because the trend may not continue.
Key insight: Inside the data is interpolation; outside the data is extrapolation.
Question 4Intermediate
Two scientists explain a lake's summer oxygen decline differently: Scientist 1 blames decaying algae, and Scientist 2 blames warmer water holding less dissolved gas. Which finding would most support Scientist 2?
1. AOxygen falls by the same amount each summer in a nearby lake that has no algal blooms
2. BAlgal blooms are largest in the warmest years
3. CDead algae accumulate on the lake bottom every August
4. DFish deaths increase during algal blooms
Show answer
Answer: A. Oxygen falls by the same amount each summer in a nearby lake that has no algal blooms
A lake with no algae that shows the same decline isolates temperature as the cause, which is exactly Scientist 2's mechanism. The other findings all involve algae and would fit Scientist 1's explanation at least as well.
Key insight: Support one explanation by finding a case where the rival explanation's cause is absent.
Question 5Advanced
In a study, one group receives a treatment and another receives an inactive substitute, and neither the participants nor the researchers recording outcomes know who received which. What is this design called?
1. AA double-blind, placebo-controlled study
2. BA single-blind observational study
3. CA case study
4. DA cross-sectional survey
Show answer
Answer: A. A double-blind, placebo-controlled study
The inactive substitute is a placebo, and keeping both participants and outcome recorders unaware makes the design double blind, which guards against expectation effects on both sides. A single-blind design keeps only the participants unaware.
Key insight: Double blind means neither the participant nor the assessor knows the assignment.

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Science (Optional)