Science
3 free practice tests · 40 questions · 40min · No sign-up required
About This Section
The ACT Science section tests your ability to interpret data, evaluate experimental designs, and analyze competing scientific viewpoints. It does not require advanced science knowledge — it is fundamentally a reasoning and data interpretation test. On the enhanced ACT (2025+), Science is an optional section and is not included in the composite score, but many colleges still consider the Science score.
What's Covered
- Data Representation — reading and interpreting graphs, tables, and charts; identifying trends and relationships in data
- Research Summaries — understanding experimental design, identifying variables, evaluating methods, and predicting outcomes based on study results
- Conflicting Viewpoints — comparing two or more scientific hypotheses or theories, identifying the evidence each relies on, and determining which evidence supports which viewpoint
For the official section description, see the official ACT exam structure page.
Study Tips
- You do not need to memorize scientific facts. The ACT Science section tests your ability to read data and reason about experiments, not recall biology or chemistry knowledge.
- For data interpretation questions, look at axis labels, units, and trends before reading the answer choices. Identify whether relationships are positive, negative, or nonlinear.
- For conflicting viewpoints, read each viewpoint carefully and note where they agree and disagree. Questions will often ask you to identify which evidence supports which theory.
- Pace yourself: with 40 questions in 40 minutes, you have about 60 seconds per question. Spend time understanding the data presentation before jumping to questions.
- Watch for extrapolation questions that ask you to predict beyond the data. Follow the established trend, but note that trends may change outside the measured range.
How to Register
Register at act.org. The ACT without writing costs $68; with the optional writing section, $93. The enhanced ACT (2025+) includes English, Reading, and Math as required sections, with Science and Writing as optional. Scores are reported on a 1–36 scale for each section and as a composite.
About Our Practice Tests
All questions are original and written to match the difficulty, format, and topic coverage of the real exam based on official exam descriptions. We offer two modes: Practice Mode gives you instant feedback and explanations after each question, and Test Mode simulates the real exam with a timer and no feedback until you submit. Both modes are completely free with no account required.
Sample Practice Questions
Review these sample questions to get a feel for the exam. For the full interactive experience, use the Practice Tests above.
- A) As temperature increases, the percentage of bleached coral decreases.
- B) As temperature increases, the percentage of bleached coral increases proportionally.
- C) Temperature has no effect on coral bleaching.
- D) The relationship is random and unpredictable.
View Answer & Explanation
Correct Answer:
B) As temperature increases, the percentage of bleached coral increases proportionally.
Explanation:
The data clearly show that as temperature increases (Reef A: 1.5°C with 15% bleached; Reef B: 2.0°C with 35% bleached; Reef C: 2.5°C with 65% bleached), bleaching percentage increases proportionally.
- A) Algae overgrowth in the ocean.
- B) Corals expelling symbiotic algae from their tissues.
- C) A decrease in ocean pH.
- D) Increased ocean salinity.
View Answer & Explanation
Correct Answer:
B) Corals expelling symbiotic algae from their tissues.
Explanation:
The passage explicitly states that coral bleaching 'occurs when corals expel the symbiotic algae living in their tissues.' This is the immediate cause, though it is triggered by temperature.
- A) 75%
- B) 85%
- C) 95%
- D) 100%
View Answer & Explanation
Correct Answer:
C) 95%
Explanation:
The data show an accelerating trend: from 1.5°C to 2.0°C, bleaching increased by 20 percentage points; from 2.0°C to 2.5°C, it increased by 30 percentage points. Continuing this accelerating pattern, the next 0.5°C increase would add approximately 30 or more percentage points, putting the estimate near 95%.
- A) Blue light (450 nm)
- B) Green light (550 nm)
- C) Red light (650 nm)
- D) Violet light (380 nm)
View Answer & Explanation
Correct Answer:
C) Red light (650 nm)
Explanation:
According to the data table, red light at 650 nm produces 9.1 units of oxygen per minute, the highest value in the table.
- A) Green light is not actually part of the light spectrum.
- B) Plants do not contain chlorophyll that absorbs green light.
- C) Chlorophyll absorbs red and blue light most effectively, not green light.
- D) Green light is too weak to drive photosynthesis.
View Answer & Explanation
Correct Answer:
C) Chlorophyll absorbs red and blue light most effectively, not green light.
Explanation:
Chlorophyll absorbs blue and red light wavelengths most efficiently and reflects green light, which is why green light is less effective for photosynthesis but visible to our eyes.