ACT Scientific Method Practice Questions with Answers

Concept Explanation

The ACT scientific method consists of the systematic steps researchers use to investigate phenomena, including identifying variables, forming hypotheses, and interpreting experimental designs. On the ACT Science section, you are not required to memorize specific scientific facts, but you must understand how a study is structured. This involves distinguishing between the independent variable (the factor changed by the researcher), the dependent variable (the factor being measured), and controlled variables (factors kept constant to ensure a fair test). You must also be able to identify the control group, which serves as a baseline for comparison by not receiving the experimental treatment. Success on these questions requires analyzing how changes in one variable affect another and determining if a specific hypothesis is supported or refuted by the data provided in tables or figures. For comprehensive strategies across all sections, check out our ACT Prep hub.

Solved Examples

Understanding these concepts in practice is easier when you break down the experimental setup step-by-step.

1. Identifying Variables: A student wants to see if the amount of sunlight affects the height of pea plants. She places 10 plants in full sun and 10 plants in the shade, keeping the soil and water amount the same for all. What is the independent variable?
   1. Identify what the researcher is intentionally changing: the amount of sunlight.
   2. Identify what is being measured: the height of the plants (dependent variable).
   3. Identify the constants: soil and water.
   4. Conclusion: The independent variable is the amount of sunlight.
2. Hypothesis Testing: A scientist hypothesizes that as the temperature of a gas increases, its volume will also increase. A table shows that at $273 \text{ K}$, volume is $22.4 \text{ L}$, and at $373 \text{ K}$, volume is $30.6 \text{ L}$. Does the data support the hypothesis?
   1. Compare the initial and final temperatures: $273 \text{ K} \rightarrow 373 \text{ K}$ (Increase).
   2. Compare the initial and final volumes: $22.4 \text{ L} \rightarrow 30.6 \text{ L}$ (Increase).
   3. Check if the trend matches the hypothesis: Both increased.
   4. Conclusion: Yes, the data supports the hypothesis.
3. Experimental Design: In a study of a new fertilizer, Group A receives the fertilizer and Group B receives plain water. Why is Group B necessary?
   1. Determine if there is a group that does not receive the "treatment."
   2. Recognize that Group B is the control group.
   3. Recall the purpose of a control: to provide a baseline to ensure the results are caused by the fertilizer and not other factors.
   4. Conclusion: Group B acts as a control to compare the natural growth of the plants.

Practice Questions

Test your knowledge of the ACT scientific method with the following questions. If you find the logic-based reasoning of science challenging, you might also want to improve your literal comprehension through ACT Reading Practice Practice Questions.

1. A researcher tests how different concentrations of salt ($0\%$, $5\%$, and $10\%$) affect the boiling point of water. Each trial uses $500 \text{ mL}$ of distilled water. What is the dependent variable in this experiment?
2. In a study regarding the effect of pH on enzyme activity, a scientist keeps the temperature at a constant $37^{\circ} \text{C}$. What role does temperature play in this experimental design?
3. A student believes that seeds will germinate faster in acidic soil. She plants seeds in soil with a pH of 4, 5, 6, and 7. The seeds in pH 7 soil germinate in 3 days, while seeds in pH 4 soil germinate in 6 days. Does this support her hypothesis?

4. A chemist performs an experiment where the pressure of a gas is varied while the volume is measured. If the resulting graph shows a downward slope as pressure increases, what is the relationship between pressure and volume?
5. Identify the control group: A study investigates the effect of caffeine on heart rate. Group 1 is given $100 \text{ mg}$ of caffeine, Group 2 is given $200 \text{ mg}$, and Group 3 is given a sugar pill with no caffeine.
6. Which of the following would most likely increase the reliability of an experiment: reducing the number of trials or increasing the number of trials?
7. A scientist conducts a study on the scientific method to observe how different light wavelengths affect photosynthesis. If the rate of oxygen production is measured, what does this oxygen production represent?
8. In an experiment measuring the friction of different surfaces, a block is pulled across wood, ice, and sandpaper. The same force is used to pull the block each time. Is the force an independent or controlled variable?
9. Suppose an experiment finds that $y = 2x + 5$. If $x$ is the independent variable, what happens to $y$ as $x$ increases?
10. A researcher wants to test if a specific metal corrodes faster in saltwater than in freshwater. What should be kept constant to ensure valid results?

Answers & Explanations

1. Boiling point of water: The dependent variable is the outcome being measured. Since the researcher is looking for the effect of salt on the boiling point, the boiling point is the result.
2. Controlled variable (Constant): Because the temperature is kept the same ($37^{\circ} \text{C}$) throughout all trials to prevent it from influencing the results, it is a control.
3. No: The hypothesis stated seeds would germinate faster (less time) in acidic soil (lower pH). However, the data showed pH 7 (neutral) took 3 days while pH 4 (acidic) took 6 days. The seeds actually germinated slower in acidic soil.
4. Inversely proportional: A downward slope indicates that as one variable (pressure) increases, the other variable (volume) decreases.
5. Group 3: The control group is the group that does not receive the active treatment (caffeine) being tested.
6. Increasing the number of trials: More trials help account for anomalies and ensure that the results are consistent and not due to chance.
7. The dependent variable: The rate of oxygen production is the measurable response to the change in light wavelength.
8. Controlled variable: Since the force is the "same each time," it is not being changed to see an effect, but rather held steady to ensure a fair comparison between surfaces.
9. y increases: According to the linear equation $y = 2x + 5$, the positive coefficient of $x$ means there is a direct relationship where $y$ grows as $x$ grows.
10. Temperature, metal type, and surface area: To isolate the effect of the water type, all other environmental and material factors must remain the same.

1. In a scientific experiment, which variable is the one that the scientist purposefully changes?

• ADependent variable
• BIndependent variable
• CControlled variable
• DControl group

Frequently Asked Questions

What is the difference between an independent and dependent variable?

The independent variable is the factor you change or control in an experiment to test its effects. The dependent variable is the variable being tested and measured, which changes in response to the independent variable.

How do I identify the control group on the ACT Science section?

Look for the trial or group where the treatment is absent or kept at a "normal" or "zero" level. This group serves as the standard for comparison against the experimental groups.

What does it mean if a hypothesis is "refuted"?

A hypothesis is refuted when the experimental data consistently contradicts the prediction made by the researcher. On the ACT, this often involves seeing a trend in a table that is the opposite of what the scientist expected.

Can an experiment have more than one independent variable?

While complex studies exist, a valid basic experiment should only have one independent variable at a time. This ensures that any observed changes in the dependent variable can be attributed solely to that single factor.

How do I determine if a relationship is direct or inverse?

A relationship is direct if both variables increase or decrease together. It is an inverse relationship if one variable increases while the other decreases, often shown as a downward-sloping line on a graph.