ACT Science Passage Practice Questions with Answers

Forty questions must be completed in just 35 minutes during the science portion of the ACT exam. An ACT science passage practice questions set is a specialized study tool designed to mimic the data representation, research summaries, and conflicting viewpoints found on the actual test. Success on this section depends less on memorizing the periodic table and more on your ability to interpret trends, identify variables, and evaluate experimental designs under pressure. By working through a variety of ACT Prep materials, you can train your brain to filter out technical jargon and focus on the underlying data.

Concept Explanation

An ACT science passage is a structured presentation of scientific information followed by a series of multiple-choice questions. These passages typically fall into three categories: Data Representation (graphs and tables), Research Summaries (descriptions of one or more related experiments), and Conflicting Viewpoints (two or more alternative hypotheses). The core objective is to test your scientific literacy and analytical skills rather than prior knowledge. You will be expected to perform tasks such as interpolating values between data points, identifying independent and dependent variables, and determining how a change in one experimental condition affects the outcome. Understanding the scientific method is crucial, as many questions ask you to predict the results of a hypothetical additional trial. While the content covers biology, chemistry, physics, and earth sciences, the answers are almost always contained within the text, charts, or figures provided. To improve your speed, it is often helpful to practice with ACT Reading Practice to build the stamina needed for dense text analysis.

Solved Examples

Example 1: Data Interpretation
A table shows the boiling point of four different liquids at sea level: Liquid A (56°C), Liquid B (78°C), Liquid C (100°C), and Liquid D (125°C). If a researcher heats a mixture of these liquids to 90°C, which liquids will have reached their boiling point?

1. Identify the target temperature: 90°C.
2. Compare the boiling points of each liquid to the target: Liquid A (56 < 90), Liquid B (78 < 90), Liquid C (100 > 90), Liquid D (125 > 90).
3. Select the liquids where the boiling point is less than or equal to the target.
4. The correct answer is Liquids A and B.

Example 2: Identifying Variables
In an experiment, plants were grown in different concentrations of CO2 to measure their growth rate. Group 1 received 300 ppm, Group 2 received 600 ppm, and Group 3 received 900 ppm. All other factors like light and water were kept constant. What is the independent variable?

1. Recall that the independent variable is the factor changed by the scientist.
2. Look at what varied between the groups: the CO2 concentration.
3. Note that growth rate is the result being measured (dependent variable).
4. The correct answer is the concentration of CO2.

Example 3: Conflicting Viewpoints
Scientist 1 argues that global warming is caused primarily by solar activity. Scientist 2 argues it is caused by greenhouse gas emissions. Which of the following findings would support Scientist 2 but NOT Scientist 1?

1. Identify Scientist 2's claim: Greenhouse gases are the cause.
2. Evaluate a finding: "Atmospheric CO2 levels have reached record highs while solar radiation has remained constant."
3. Determine if this fits: This supports the greenhouse gas theory while contradicting the solar activity theory.
4. The correct answer is the finding regarding CO2 levels and constant solar radiation.

Practice Questions

Passage I: Solubility and Temperature
A student measured the solubility of Potassium Nitrate ($KNO_3$) in 100g of water at various temperatures. The data is as follows: 20°C (32g), 40°C (64g), 60°C (110g), 80°C (169g).

1. Based on the data, what is the most likely solubility of $KNO_3$ at 50°C?

2. If a student attempts to dissolve 120g of $KNO_3$ in 100g of water at 60°C, will the solution be saturated or unsaturated?

3. As the temperature of the water increases, what happens to the solubility of the salt?

Passage II: Pendulum Motion
A physics student conducts an experiment to see how the length of a string affects the period of a pendulum. Trial 1: length = 0.5m, period = 1.4s. Trial 2: length = 1.0m, period = 2.0s. Trial 3: length = 2.0m, period = 2.8s.

4. What is the dependent variable in this experiment?

5. If the student uses a string length of 1.5m, the period would most likely be between which two values?

6. According to the data, doubling the length of the string results in the period being multiplied by approximately what factor?

Passage III: Soil pH and Plant Growth
Two scientists discuss the growth of Hydrangea macrophylla. Scientist A claims that soil pH only affects flower color. Scientist B claims that soil pH affects both flower color and the overall height of the plant.

7. To test Scientist B’s claim, what additional data must be recorded besides flower color and pH?

8. If an experiment shows that plants in pH 5.0 and pH 7.0 both grow to exactly 45cm, does this support Scientist B?

Answers & Explanations

1. 87g (approx): 50°C is exactly halfway between 40°C (64g) and 60°C (110g). To find the likely solubility, you look for a value between 64 and 110. While the trend isn't perfectly linear, a value around 87g represents the midpoint trend.
2. Saturated: At 60°C, the maximum amount of $KNO_3$ that can dissolve is 110g. Since 120g is more than the maximum capacity, 10g will remain undissolved, making the solution saturated.
3. Increases: The data shows a direct relationship; as the temperature values go up (20, 40, 60, 80), the solubility values also go up (32, 64, 110, 169).
4. The period: The dependent variable is the outcome being measured, which in this case is the time it takes for one swing (the period).
5. 2.0s and 2.8s: Since 1.5m is between the lengths used in Trial 2 (1.0m) and Trial 3 (2.0m), the resulting period must fall between those two corresponding periods.
6. 1.4: Comparing Trial 1 (0.5m, 1.4s) to Trial 2 (1.0m, 2.0s), the length doubled. $\frac{2.0}{1.4} \approx 1.42$. This is consistent with the physics formula $T = 2\pi\sqrt{\frac{L}{g}}$, where period $T$ is proportional to $\sqrt{L}$.
7. Plant height: Scientist B specifically mentions that height is affected. Therefore, to verify or refute this, the height of the plants at different pH levels must be measured.
8. No: Scientist B claims pH affects height. If the height remains the same (45cm) despite different pH levels, the data contradicts Scientist B's hypothesis.

1. In an ACT science passage, what is the primary purpose of a control group?

• ATo provide a baseline for comparison
• BTo ensure the experiment finishes quickly
• CTo increase the complexity of the data
• DTo prove the hypothesis is correct

Frequently Asked Questions

Do I need to be an expert in biology or chemistry for the ACT Science section?

No, you do not need to be an expert because the test focuses on your ability to read and interpret scientific data rather than your recall of specific facts. Most of the information needed to answer the questions is provided directly in the passage or figures.

How much time should I spend on each passage?

Since there are usually 6 or 7 passages and only 35 minutes, you should aim to spend about 5 to 6 minutes per passage. Using an AI Exam Simulator can help you practice this pacing under realistic conditions.

What is the difference between an independent and a dependent variable?

The independent variable is the condition that the researcher intentionally changes or manipulates, while the dependent variable is the result or response that is measured. For more practice on technical nuances, check out ACT Subject Verb Agreement Practice to ensure your writing about these variables is grammatically correct.

How can I improve my speed on the science section?

Focus on the visuals first; often, you can answer questions by looking at the graphs and tables without reading the entire introductory text. You can also use tools like the Retrieval Challenge to sharpen your data-finding skills.

Are there any outside facts I should know?

While 90-95% of the information is in the passage, a few questions may require basic knowledge of concepts like the pH scale, freezing/boiling points of water, or basic genetics (DNA/RNA). Familiarizing yourself with these via Khan Academy Science can provide a helpful safety net.