ACT Science Practice Questions with Answers

Concept Explanation

ACT Science practice questions are designed to evaluate your ability to interpret, analyze, and evaluate scientific data presented in passages, tables, and graphs. Unlike a traditional biology or chemistry test that requires rote memorization of facts, this section of the ACT Prep curriculum focuses on scientific reasoning and data literacy. You are given 35 minutes to answer 40 questions, which are typically divided into three categories: Data Representation (graphs and tables), Research Summaries (descriptions of experiments), and Conflicting Viewpoints (different hypotheses on a single phenomenon).

To succeed, you must be comfortable with the scientific method, which includes identifying independent and dependent variables, understanding controls, and predicting trends. Most information is provided within the text or visuals, but a basic understanding of general science concepts from Khan Academy or high school courses is helpful. The test rewards students who can quickly locate specific data points and recognize the relationship between variables, such as direct or inverse proportions. Utilizing an AI Question Generator can help you simulate the specific pressure and formatting of these varied passage types.

Solved Examples

1. Example 1: Interpreting a Line Graph
   A graph shows the solubility of Salt X in water from $0^\circ \text{C}$ to $100^\circ \text{C}$. At $20^\circ \text{C}$, the solubility is $30 \text{g}/100 \text{g}$ of water. At $80^\circ \text{C}$, the solubility is $70 \text{g}/100 \text{g}$ of water. What is the relationship between temperature and solubility?
   Solution:
   1. Identify the variables: Temperature is on the x-axis, and Solubility is on the y-axis.
   2. Observe the change: As temperature increases from 20 to 80, solubility increases from 30 to 70.
   3. Conclude: Since both variables move in the same direction, there is a direct relationship.
2. Example 2: Identifying Variables
   In a study, identical plants were grown in different concentrations of nitrogen fertilizer ($0\%$, $5\%$, and $10\%$) to measure their height after 30 days. What is the independent variable?
   Solution:
   1. Recall the definition: The independent variable is the factor changed by the researcher.
   2. Identify the change: The researcher is intentionally varying the nitrogen concentration.
   3. Conclude: The independent variable is the concentration of nitrogen fertilizer.
3. Example 3: Extrapolating Data
   A table shows that a gas exerts a pressure of $1.0 \text{ atm}$ at $300 \text{ K}$ and $2.0 \text{ atm}$ at $600 \text{ K}$. If the trend is linear, what is the predicted pressure at $900 \text{ K}$?
   Solution:
   1. Determine the rate of change: For every increase of $300 \text{ K}$, the pressure increases by $1.0 \text{ atm}$.
   2. Apply the rate: Add $1.0 \text{ atm}$ to the last known value ($2.0 \text{ atm}$).
   3. Result: $2.0 + 1.0 = 3.0 \text{ atm}$.

Practice Questions

1. A researcher finds that as the depth of a lake increases, the concentration of dissolved oxygen decreases. Based on this, which of the following would likely be the oxygen concentration at the deepest point of the lake compared to the surface?

2. In a chemical reaction, the rate of reaction doubles for every $10^\circ \text{C}$ increase in temperature. If the rate is $R$ at $20^\circ \text{C}$, what is the rate at $40^\circ \text{C}$?

3. Scientist 1 argues that global warming is caused primarily by solar activity. Scientist 2 argues it is caused by greenhouse gas emissions. Which piece of evidence would most strongly support Scientist 2 over Scientist 1?

4. According to a data table, Substance A has a boiling point of $50^\circ \text{C}$, Substance B has $75^\circ \text{C}$, and Substance C has $100^\circ \text{C}$. If a mixture of these substances is heated to $80^\circ \text{C}$, which substance(s) will have turned into gas?

5. An experiment tests the effect of different light wavelengths on photosynthesis by measuring oxygen bubbles produced. If the control group is kept in the dark, what is the purpose of this control?

6. If Figure 1 shows a downward-sloping curve representing the relationship between Volume and Pressure for a gas, what happens to volume as pressure is halved?

7. A student believes that the mass of a pendulum bob affects its period (time for one swing). In an experiment to test this, what variable must be kept constant?

8. Looking at a graph of pH levels in a stream over 24 hours, the pH drops significantly at night. If photosynthesis (which consumes $\text{CO}_2$, an acidic gas) stops at night, does this support the observation?

9. Study 1 uses a sample size of 10 mice, while Study 2 uses 1,000 mice. Which study's results are generally considered more reliable in scientific research?

10. Based on the trend where density decreases as temperature increases for a specific metal, would the metal occupy more or less space at $500^\circ \text{C}$ than at $100^\circ \text{C}$?

Answers & Explanations

1. The oxygen concentration will be at its lowest point. Since the relationship is inverse (as depth increases, oxygen decreases), the maximum depth correlates with the minimum oxygen levels.
2. $4R$. From $20^\circ \text{C}$ to $30^\circ \text{C}$, the rate doubles to $2R$. From $30^\circ \text{C}$ to $40^\circ \text{C}$, it doubles again: $2 \times 2R = 4R$.
3. Data showing stable solar output alongside rising temperatures. This would invalidate Scientist 1's claim that solar activity is the driver, leaving greenhouse gases as the likely cause.
4. Substances A and B. Since $80^\circ \text{C}$ is higher than their respective boiling points ($50^\circ \text{C}$ and $75^\circ \text{C}$), they will have evaporated.
5. To establish a baseline. The dark control shows the rate of oxygen production (or lack thereof) without the influence of light, allowing researchers to ensure the bubbles in other groups are actually caused by light.
6. The volume doubles. In an inverse relationship (as shown by a downward curve for gas laws), halving one variable results in doubling the other.
7. The length of the pendulum string. To isolate the effect of mass, all other factors like string length and release angle must remain the same. This is a core concept often seen in ACT Reading Practice passages that involve scientific descriptions.
8. Yes. If $\text{CO}_2$ is acidic and is no longer being consumed at night, $\text{CO}_2$ levels will rise, making the water more acidic and lowering the pH.
9. Study 2. Larger sample sizes reduce the impact of outliers and provide a more accurate representation of the population.
10. More space. If density ($\text{mass}/ \text{volume}$) decreases, and the mass remains the same, the volume must increase. Therefore, the metal expands.

1. Which of the following best describes an "independent variable" in a science experiment?

• AThe factor that is measured by the researcher
• BThe factor that remains constant throughout the study
• CThe factor that is intentionally changed or manipulated
• DThe group that does not receive the experimental treatment

Frequently Asked Questions

Do I need to be a genius in biology or chemistry for ACT Science?

No, the section primarily tests your ability to read graphs and follow the logic of experiments rather than advanced scientific knowledge. Most of the answers are found directly in the provided passages and figures.

How many questions are on the ACT Science section?

There are 40 multiple-choice questions that you must complete within a 35-minute time limit. This requires a pace of about 52 seconds per question, including reading time.

What is the most common type of passage?

Data Representation and Research Summaries make up the bulk of the test. You will usually see 2-3 passages of each, plus one Conflicting Viewpoints passage per exam.

Can I use a calculator on the Science section?

Calculators are not permitted on the ACT Science section, though they are allowed on the Math section. Any math required in Science will involve basic arithmetic or estimation based on visual data.

How can I improve my speed on this section?

Focus on looking at the questions first before reading the entire passage. Often, a question will point you to a specific figure or table, allowing you to find the answer without reading the introductory text. Using an AI Exam Simulator can also help you build the necessary stamina.