Medium ACT Scientific Method Practice Questions

Concept Explanation

The scientific method on the ACT refers to the systematic process of conducting experiments, identifying variables, and evaluating the validity of experimental designs. Success on this section requires you to distinguish between independent variables (the factors changed by the scientist), dependent variables (the results being measured), and control variables (factors kept constant to ensure a fair test). You must also understand the role of a control group, which provides a baseline for comparison. This fundamental framework is essential for navigating the ACT Prep landscape, as it allows you to predict how changes in a procedure will influence the data collected. Most ACT experimental design practice questions will ask you to identify which factor was manipulated or why a specific step was necessary to maintain the integrity of the study.

Solved Examples

Review these examples to see how scientific method principles are applied to ACT-style scenarios.

1. Identifying Variables: A student wants to see how different concentrations of salt affect the boiling point of water. She boils 500 mL of water with 0g, 10g, 20g, and 30g of salt and records the temperature at which boiling begins.
   Solution:
   1. Identify the independent variable: The amount of salt added (0g, 10g, 20g, 30g).
   2. Identify the dependent variable: The boiling point temperature.
   3. Identify the control variables: The volume of water (500 mL) and the type of container used.
2. Understanding Control Groups: In a study on plant growth, Group A receives 10 hours of sunlight and 100 mL of water daily. Group B receives 0 hours of sunlight and 100 mL of water daily. Group B is the control group for the variable of sunlight.
   Solution:
   1. The scientist is testing the effect of sunlight.
   2. To see the effect, you need a baseline where the variable is absent.
   3. Group B serves as that baseline (0 hours) to show how the plant grows without any sunlight at all.
3. Hypothesis Testing: A researcher hypothesizes that $\text{Pressure} (P)$ is inversely proportional to $\text{Volume} (V)$ at a constant temperature. If the volume is doubled, what should happen to the pressure according to the hypothesis?
   Solution:
   1. The relationship is $P \propto \frac{1}{V}$.
   2. If $V$ becomes $2V$, then $P$ becomes $\frac{1}{2}P$.
   3. The pressure should decrease by half.

Practice Questions

Test your knowledge with these Medium ACT Scientific Method Practice Questions. Be sure to pay close attention to the experimental setup described in each prompt.

1. A biologist tests the effect of temperature on the enzyme activity of amylase. She keeps the pH at 7.0 and the enzyme concentration at 5% for all trials. What is the independent variable in this experiment?
2. In a study regarding the friction of different surfaces, a block is pulled across wood, ice, and sandpaper. The force required to move the block is measured in Newtons (N). Which of the following is a controlled variable (constant) in this study?
   • The type of surface
   • The force measured
   • The mass of the block
   • The coefficient of friction
3. A student adds varying amounts of fertilizer to four identical pots of marigolds. Pot 1 receives 0g, Pot 2 receives 2g, Pot 3 receives 4g, and Pot 4 receives 6g. Why did the student include Pot 1 in the experiment?

4. Researchers are measuring the rate of photosynthesis by counting oxygen bubbles produced by an aquatic plant under different colors of light. If the researchers want to ensure the results are due only to light color, they must keep which of the following constant?
   • The number of bubbles
   • The color of the light
   • The distance between the light source and the plant
   • The rate of photosynthesis
5. An experimenter believes that increasing the acidity of soil will decrease the number of earthworms present. This statement is best described as a(n):
   • Observation
   • Conclusion
   • Hypothesis
   • Theory
6. If a scientist repeats an experiment ten times and gets the same results each time, the experiment is said to have high:
   • Reliability
   • Accuracy
   • Variable count
   • Sensitivity
7. A scientist conducts an experiment where the amount of sunlight is increased for a group of plants, while the amount of water is decreased. Why is this an ineffective experimental design?
8. In a chemical reaction study, the temperature is increased by $10^\circ \text{C}$ every 5 minutes. The scientist records the time it takes for a color change to occur. What is the dependent variable?

Answers & Explanations

1. Temperature. The independent variable is the factor the scientist changes. Since she is testing the effect of temperature, she will vary the temperature while keeping other factors like pH and concentration the same.
2. The mass of the block. To ensure the test is fair, the mass of the block must remain constant so that the only factor affecting the force is the change in surface type.
3. To serve as a control group. Pot 1 (0g of fertilizer) provides a baseline to show how much the marigolds grow naturally without any fertilizer, allowing the student to see the actual impact of the fertilizer in the other pots.
4. The distance between the light source and the plant. Light intensity changes with distance. If the distance varies between trials, the researchers won't know if the results were caused by the color of the light or the intensity of the light.
5. Hypothesis. A hypothesis is a testable prediction about the relationship between two variables (soil acidity and earthworm count).
6. Reliability. Reliability refers to the consistency of results when an experiment is repeated under the same conditions.
7. Too many independent variables. A valid experiment should only change one independent variable at a time. By changing both sunlight and water, the scientist cannot determine which factor caused the change in plant growth.
8. The time it takes for a color change to occur. The dependent variable is the outcome being measured or observed in response to the changes made to the independent variable (temperature).

1. Which of the following best defines a dependent variable in a scientific experiment?

• AThe factor that is intentionally changed by the researcher
• BThe factor that is measured or observed as a result
• CThe factor that remains constant throughout all trials
• DThe group that does not receive the experimental treatment

Frequently Asked Questions

What is the difference between a control group and a control variable?

A control group is a set of subjects that does not receive the experimental treatment to provide a baseline, while control variables are specific conditions kept the same for every subject in the experiment.

How do I identify the independent variable on an ACT graph?

The independent variable is almost always plotted on the x-axis (horizontal axis), while the dependent variable is plotted on the y-axis (vertical axis).

What makes an experiment "valid" on the ACT Science section?

An experiment is considered valid if it tests the hypothesis accurately by controlling all variables except for the one being studied and using a sufficiently large sample size.

Can there be more than one dependent variable?

Yes, a scientist can measure multiple outcomes from a single change, such as measuring both the height and the leaf count of a plant after changing the fertilizer type.

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

If a hypothesis is refuted, it means the data collected during the experiment did not support the predicted outcome, requiring the scientist to revise their ideas. You can practice more with the AI Question Generator to see how different data sets support or refute claims.