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ACT Science Practice Questions with Answers & Explanations

Passage 1: Biology Graph

A student measured the height of a sunflower plant over 5 weeks.

Week Height (cm)
1 12
2 18
3 27
4 35
5 42
Question 1: Which week showed the greatest increase in plant height?
A. Week 1–2
B. Week 2–3
C. Week 3–4
D. Week 4–5

Correct Answer: B. Week 2–3

Explanation

Calculate the growth during each interval:

  • Week 1→2 = 18 − 12 = 6 cm
  • Week 2→3 = 27 − 18 = 9 cm
  • Week 3→4 = 35 − 27 = 8 cm
  • Week 4→5 = 42 − 35 = 7 cm

The largest increase is 9 cm between Weeks 2 and 3.

Tip: Always compare the differences between values rather than the values themselves.

Passage 2: Chemistry Table

A scientist dissolved different amounts of salt in water.

Salt (g) Dissolved?
10 Yes
20 Yes
30 Yes
40 No
Question 2: Based on the table, what is the maximum amount of salt that completely dissolved?
A. 10 g
B. 20 g
C. 30 g
D. 40 g

Correct Answer: C. 30 g

Explanation

The highest amount marked "Yes" is 30 g.

40 g did not dissolve completely.

Tip: Read exactly what the question asks. The maximum dissolved amount is not necessarily the highest amount tested.

Passage 3: Physics Graph

A car traveled at different speeds.

Time (s) Speed (m/s)
0 0
2 4
4 8
6 12
8 16
Question 3: The data suggest the car:
A. Is slowing down
B. Maintains constant speed
C. Accelerates at a constant rate
D. Stops after 8 seconds

Correct Answer: C. Accelerates at a constant rate

Explanation

Every 2 seconds, speed increases by 4 m/s.

A constant increase in speed indicates constant acceleration.

Tip: Look for patterns in changes between values.

Passage 4: Experimental Design

A scientist wants to determine whether fertilizer affects plant growth.

Group A receives fertilizer.

Group B receives no fertilizer.

Both groups receive equal sunlight and water.

Question 4: What is the independent variable?
A. Plant height
B. Sunlight
C. Water
D. Fertilizer

Correct Answer: D. Fertilizer

Explanation

The independent variable is the factor deliberately changed by the scientist.

Only fertilizer differs between the groups.

Tip: Independent variable = changed by scientist.
Dependent variable = measured outcome.

Passage 5: Environmental Science Table

Researchers measured fish populations.

Year Fish Population
2020 500
2021 450
2022 400
2023 350
Question 5: What trend is shown?
A. Increasing population
B. Constant population
C. Decreasing population
D. Random changes

Correct Answer: C. Decreasing population

Explanation

Each year the population becomes smaller.

500 → 450 → 400 → 350

This shows a steady decrease.

Tip: Look for overall patterns rather than focusing on one value.

Passage 6: Biology Experiment

Students tested how light intensity affects photosynthesis.

Light Intensity Oxygen Produced
Low 5
Medium 10
High 15
Question 6: Which conclusion is best supported?
A. Photosynthesis decreases with more light
B. Photosynthesis increases with more light
C. Light has no effect
D. Oxygen prevents photosynthesis

Correct Answer: B. Photosynthesis increases with more light

Explanation

As light intensity increases, oxygen production increases.

Since oxygen production indicates photosynthesis rate, photosynthesis increased.

Tip: Identify whether variables move in the same direction or opposite directions.

Passage 7: Chemistry Graph

A substance was heated.

Temperature (°C) Time (min)
20 0
40 2
60 4
80 6
100 8
Question 7: What would most likely be the temperature after 10 minutes?
A. 110°C
B. 120°C
C. 130°C
D. 140°C

Correct Answer: B. 120°C

Explanation

Temperature increases 20°C every 2 minutes.

From 8 to 10 minutes:

100°C + 20°C = 120°C

Tip: ACT often asks students to extend trends beyond the provided data.

Passage 8: Earth Science Table

A scientist measured rainfall.

Month Rainfall (cm)
January 4
February 6
March 8
April 10
Question 8: Which month had twice the rainfall of January?
A. February
B. March
C. April
D. None

Correct Answer: B. March

Explanation

January rainfall = 4 cm

Twice 4 cm = 8 cm

March rainfall = 8 cm

Tip: Simple calculations frequently appear in ACT Science.

Passage 9: Conflicting Viewpoints

Scientist 1 states that increased carbon dioxide causes global temperatures to rise.

Scientist 2 states that changes in solar activity are the main cause of temperature changes.

Question 9: Which statement describes a disagreement?
A. Earth has an atmosphere.
B. Temperature changes occur.
C. The main cause of temperature changes.
D. Carbon dioxide exists.

Correct Answer: C. The main cause of temperature changes.

Explanation

Both scientists discuss temperature changes.

They disagree about what causes those changes.

Tip: In conflicting viewpoints passages, focus on what the scientists disagree about.

Passage 10: Multiple Data Representation

Table 1

Fertilizer Growth (cm)
A 10
B 15

Table 2

Fertilizer Cost ($)
A 5
B 12
Question 10: Which fertilizer produced more growth per dollar?
A. Fertilizer A
B. Fertilizer B
C. Both equal
D. Cannot determine

Correct Answer: A. Fertilizer A

Explanation

Fertilizer A:

10 ÷ 5 = 2 cm per dollar

Fertilizer B:

15 ÷ 12 = 1.25 cm per dollar

Fertilizer A provides more growth for each dollar spent.

Tip: Some ACT questions require combining information from multiple tables before calculating the answer.

Passage 11: Population Growth Study

Researchers recorded the number of rabbits living in a field.

Year Rabbits
2020 50
2021 65
2022 80
2023 95
2024 110
Question 11: How many more rabbits were present in 2024 than in 2020?
A. 50
B. 55
C. 60
D. 65

Correct Answer: C. 60

Explanation

2024 population = 110

2020 population = 50

110 − 50 = 60

Therefore, there were 60 more rabbits.

Tip: When comparing years, subtract the earlier value from the later value.
Question 12: If the trend continues, approximately how many rabbits would be expected in 2025?
A. 115
B. 120
C. 125
D. 130

Correct Answer: C. 125

Explanation

Population increases by 15 rabbits each year:

  • 50 → 65 (+15)
  • 65 → 80 (+15)
  • 80 → 95 (+15)
  • 95 → 110 (+15)

110 + 15 = 125

Tip: When data show a consistent pattern, extend that pattern to make predictions.

Passage 12: Enzyme Activity Experiment

Scientists measured enzyme activity at different temperatures.

Temperature (°C) Activity Rate
10 5
20 12
30 18
40 25
50 17
Question 13: At which temperature was enzyme activity greatest?
A. 20°C
B. 30°C
C. 40°C
D. 50°C

Correct Answer: C. 40°C

Explanation

The highest activity value is 25.

This occurs at 40°C.

Tip: Look for the highest value in the data table rather than assuming the highest temperature gives the highest result.
Question 14: The data suggest that enzyme activity:
A. Always increases with temperature
B. Increases then decreases
C. Always decreases with temperature
D. Remains constant

Correct Answer: B. Increases then decreases

Explanation

Activity rises from 5 to 25 as temperature increases from 10°C to 40°C.

At 50°C activity drops to 17.

This shows activity increases and then decreases.

Tip: Many biological processes have an optimum point rather than increasing forever.

Passage 13: Chemistry Reaction Study

Students mixed acid and metal and measured hydrogen gas produced.

Metal Mass (g) Hydrogen Gas (mL)
1 10
2 20
3 30
4 40
Question 15: What relationship exists between metal mass and hydrogen gas production?
A. Negative relationship
B. No relationship
C. Direct relationship
D. Random relationship

Correct Answer: C. Direct relationship

Explanation

As metal mass increases, gas production also increases.

Both variables move in the same direction.

Tip: When two variables increase together, a direct relationship exists.
Question 16: How much hydrogen gas would likely be produced by 5 g of metal?
A. 45 mL
B. 50 mL
C. 55 mL
D. 60 mL

Correct Answer: B. 50 mL

Explanation

Each additional gram produces 10 mL more gas.

5 g × 10 mL/g = 50 mL

Tip: Identify the pattern before making predictions.

Passage 14: Physics Investigation

A ball was dropped from different heights.

Height (m) Time to Reach Ground (s)
2 0.6
4 0.9
6 1.1
8 1.3
Question 17: As drop height increases, the time to reach the ground:
A. Decreases
B. Remains constant
C. Increases
D. Cannot be determined

Correct Answer: C. Increases

Explanation

Higher drop heights correspond to longer fall times.

2 m → 0.6 s

8 m → 1.3 s

Therefore, fall time increases.

Tip: Read both columns together to determine trends.
Question 18: Which height produced the longest fall time?
A. 2 m
B. 4 m
C. 6 m
D. 8 m

Correct Answer: D. 8 m

Explanation

The greatest fall time is 1.3 seconds.

This occurred from 8 meters.

Tip: Many ACT questions simply ask you to locate the largest or smallest value.

Passage 15: Earth Science Data

Researchers measured atmospheric carbon dioxide.

Year CO₂ (ppm)
2018 408
2019 411
2020 414
2021 417
2022 420
Question 19: What trend is shown?
A. CO₂ levels are decreasing
B. CO₂ levels are increasing
C. CO₂ levels are constant
D. CO₂ levels fluctuate randomly

Correct Answer: B. CO₂ levels are increasing

Explanation

The values steadily rise from 408 ppm to 420 ppm.

This indicates a consistent increase.

Tip: Trend questions are among the most common ACT Science questions.
Question 20: If the pattern continues, what CO₂ level would be expected in 2023?
A. 421 ppm
B. 422 ppm
C. 423 ppm
D. 425 ppm

Correct Answer: C. 423 ppm

Explanation

The increase is approximately 3 ppm each year:

408 → 411 → 414 → 417 → 420

420 + 3 = 423

Tip: Identify the average yearly change when predicting future values.

Passage 16: Plant Growth Under Different Light Conditions

Researchers grew identical plants under three light conditions.

Day Low Light (cm) Medium Light (cm) High Light (cm)
0 5 5 5
5 7 9 11
10 9 13 17
15 11 16 22
Question 21: After 15 days, which group had the tallest plants?
A. Low Light
B. Medium Light
C. High Light
D. All were equal

Correct Answer: C. High Light

Explanation

At Day 15:

  • Low Light = 11 cm
  • Medium Light = 16 cm
  • High Light = 22 cm

The tallest plants were grown under High Light conditions.

Tip: When comparing groups, make sure you compare values from the same row or time point.
Question 22: How much growth occurred in the High Light group from Day 0 to Day 15?
A. 15 cm
B. 16 cm
C. 17 cm
D. 22 cm

Correct Answer: C. 17 cm

Explanation

Initial height = 5 cm

Final height = 22 cm

Growth = 22 − 5 = 17 cm

Tip: Growth is usually calculated as final value minus initial value.
Question 23: Which statement is best supported by the data?
A. More light decreases growth.
B. Light intensity has no effect.
C. Greater light intensity is associated with greater growth.
D. Plants cannot grow in low light.

Correct Answer: C. Greater light intensity is associated with greater growth.

Explanation

Plants exposed to higher light levels consistently showed greater heights.

This suggests a positive relationship between light intensity and growth.

Tip: Choose conclusions directly supported by the data rather than assumptions.

Passage 17: Water Temperature and Fish Activity

Scientists measured fish activity at different water temperatures.

Temperature (°C) Activity Score
5 8
10 15
15 24
20 30
25 28
Question 24: At which temperature was fish activity highest?
A. 15°C
B. 20°C
C. 25°C
D. 30°C

Correct Answer: B. 20°C

Explanation

The highest activity score is 30.

This occurs at 20°C.

Tip: Look for the maximum value in the table.
Question 25: The data suggest fish activity:
A. Constantly increases with temperature
B. Constantly decreases with temperature
C. Increases then slightly decreases
D. Is unrelated to temperature

Correct Answer: C. Increases then slightly decreases

Explanation

Activity increases from 8 to 30 between 5°C and 20°C.

At 25°C activity drops slightly to 28.

Tip: Many biological systems have an optimum condition where performance peaks.

Passage 18: Experimental Design

A scientist tests whether fertilizer affects tomato production.
Three groups of plants receive:

  • Group A: No fertilizer
  • Group B: 10 g fertilizer
  • Group C: 20 g fertilizer

All plants receive equal water, sunlight, and soil.

Question 26: What is the dependent variable?
A. Fertilizer amount
B. Water supplied
C. Tomato production
D. Sunlight

Correct Answer: C. Tomato production

Explanation

The dependent variable is what the scientist measures.

The goal is to determine how fertilizer affects tomato production.

Tip: Ask yourself: “What result is being measured?”
Question 27: Why are water and sunlight kept constant?
A. To increase growth
B. To eliminate other possible causes
C. To reduce fertilizer effects
D. To decrease tomato production

Correct Answer: B. To eliminate other possible causes

Explanation

Scientists control variables so that differences can be attributed to the independent variable.

In this experiment, fertilizer should be the only major difference.

Tip: Controlled variables improve the reliability of conclusions.

Passage 19: Atmospheric Pressure Data

Altitude (m) Pressure (kPa)
0 101
1000 89
2000 79
3000 70
Question 28: What relationship exists between altitude and pressure?
A. Direct relationship
B. No relationship
C. Inverse relationship
D. Random relationship

Correct Answer: C. Inverse relationship

Explanation

As altitude increases:

  • Pressure decreases.

One variable goes up while the other goes down.

Tip: An inverse relationship means variables move in opposite directions.
Question 29: Based on the trend, atmospheric pressure at 4000 m would most likely be:
A. 60 kPa
B. 70 kPa
C. 80 kPa
D. 100 kPa

Correct Answer: A. 60 kPa

Explanation

Pressure drops approximately:

  • 101 → 89 (-12)
  • 89 → 79 (-10)
  • 79 → 70 (-9)

A value near 60 kPa is the most reasonable prediction.

Tip: Predictions do not need to be exact. Choose the answer most consistent with the trend.

Passage 20: Conflicting Viewpoints

Two students discuss dinosaur extinction.
Student 1: A large asteroid impact caused rapid environmental changes that led to dinosaur extinction.

Student 2: Long-term volcanic eruptions caused climate changes that led to dinosaur extinction.

Question 30: The students disagree primarily about:
A. Dinosaurs once existed
B. Extinction occurred
C. The cause of extinction
D. Environmental changes occurred

Correct Answer: C. The cause of extinction

Explanation

Both students agree that dinosaurs became extinct.

They disagree about what caused the extinction:

  • Student 1: Asteroid impact
  • Student 2: Volcanic eruptions
Tip: In conflicting-viewpoint passages, identify the specific point of disagreement rather than general topics both sides discuss.

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