How to Solve: ACT Science – Research Summaries (Experimental Design, Variables, Control)

How to Solve: ACT Science – Research Summaries (Experimental Design, Variables, Control)

Introduction

"Mastering Research Summaries on the ACT Science section can boost your score by 2–4 points—enough to turn a ‘good’ score into a ‘great’ one for college admissions. These questions test whether you can read real experiments like a scientist, not just memorize facts."

WHAT YOU NEED TO KNOW FIRST

1. Basic graph/table reading – You must extract data points quickly.
2. Difference between independent and dependent variables – If you mix these up, you’ll miss easy points.
3. What a control group is – Without it, experiments can’t prove cause-and-effect.

KEY TERMS & FORMULAS

No formulas needed – This is about reading comprehension, not math.

STEP-BY-STEP METHOD

Step 1: Identify the Independent Variable (IV)

• Action: Underline the one thing the scientist changes in the experiment.
• Where to look: Usually in the first paragraph or table headers.
• Example: "Scientists tested how different light colors affect plant growth." → IV = light color

Step 2: Identify the Dependent Variable (DV)

• Action: Circle what the scientist measures at the end.
• Where to look: In the results (tables/graphs) or the last paragraph.
• Example: "They recorded plant height after 2 weeks." → DV = plant height

Step 3: Find the Control Group (if any)

• Action: Look for the group that does NOT get the IV.
• Where to look: Often labeled as "no treatment" or "baseline."
• Example: "One group received no fertilizer." → Control = no fertilizer group

Step 4: List Controlled Variables (Constants)

• Action: Note what’s kept the same across all groups.
• Where to look: Phrases like "all other conditions were identical."
• Example: "All plants received the same amount of water." → Constant = water amount

Step 5: Match the Hypothesis to the Data

• Action: Check if the results support or reject the hypothesis.
• Where to look: The hypothesis is usually stated early; results are in tables/graphs.
• Example: "Hypothesis: Blue light increases growth." → If blue light plants grew tallest, the hypothesis is supported.

Step 6: Answer the Question

• Action: Use the IV, DV, and control to eliminate wrong answers.
• Key rule: If the question asks about cause, the answer must involve the IV.

WORKED EXAMPLES

Example 1 – Basic

Passage: "Scientists tested how different amounts of fertilizer affect tomato plant height. Group A received 0g, Group B received 5g, and Group C received 10g. All plants were given the same water and sunlight. After 4 weeks, plant heights were measured."

Question: What is the independent variable? Answer Choices: A) Tomato plant height B) Amount of fertilizer C) Amount of water D) Sunlight exposure

Step-by-Step: 1. IV = What the scientist changes → Amount of fertilizer (0g, 5g, 10g). 2. DV = What’s measured → Tomato plant height. 3. Control Group = Group A (0g fertilizer). 4. Constants = Water and sunlight (same for all). 5. Answer: B) Amount of fertilizer

What we did and why: We identified the IV (what’s changed) and DV (what’s measured). The control group helps compare results, and constants ensure a fair test.

Example 2 – Medium

Passage: "A study tested how caffeine affects reaction time. Group 1 drank 0mg, Group 2 drank 50mg, and Group 3 drank 100mg. All participants were the same age and had no prior caffeine. Reaction time was measured in milliseconds."

Question: Which group is the control group? Answer Choices: A) Group 1 B) Group 2 C) Group 3 D) All groups

Step-by-Step: 1. IV = Caffeine amount (0mg, 50mg, 100mg). 2. DV = Reaction time (measured in ms). 3. Control Group = Group 1 (0mg caffeine = no treatment). 4. Constants = Age, no prior caffeine. 5. Answer: A) Group 1

What we did and why: The control group does not receive the IV (caffeine). This lets scientists compare how caffeine affects reaction time.

Example 3 – Exam-Style

Passage: "A researcher studied how sleep duration affects test scores. Students were divided into 3 groups: 4 hours, 6 hours, and 8 hours of sleep. All students took the same test. The 8-hour group scored highest, while the 4-hour group scored lowest."

Question: Which of the following is a controlled variable? Answer Choices: A) Sleep duration B) Test scores C) The test itself D) Number of students

Step-by-Step: 1. IV = Sleep duration (4h, 6h, 8h). 2. DV = Test scores. 3. Control Group = None (no "no sleep" group). 4. Constants = The test itself (same for all). 5. Answer: C) The test itself

What we did and why: Controlled variables are kept the same to ensure fairness. The test must be identical for all groups to measure sleep’s effect.

COMMON MISTAKES

EXAM TRAPS

1-MINUTE RECAP

"Here’s the fast version for test day: 1. Find the IV – What’s being changed? Underline it. 2. Find the DV – What’s being measured? Circle it. 3. Spot the control group – Who got no treatment? 4. List constants – What’s kept the same? 5. Match the hypothesis – Do the results support it? 6. Answer the question – Use the IV/DV to eliminate wrong choices.

Remember: The ACT Science section is about reading experiments, not memorizing facts. If you get stuck, go back to the passage—every answer is there!