ACT Science: Compare Two Experiments and Spot Design Differences in Seconds

When ACT Science asks you to compare two experiments, create a simple four-box grid: top-left box list variables in experiment 1, top-right list variables in experiment 2, bottom-left list results/findings from experiment 1, bottom-right list results/findings from experiment 2. Scan left-to-right, top-to-bottom, and differences jump out immediately. This visual method eliminates rereading and prevents confusion because everything is mapped at a glance.

Example: Experiment 1 tests pH effect on enzyme activity using pH 5, 7, 9 and measures enzyme activity (units/min). Experiment 2 tests temperature effect on the same enzyme using 20°C, 40°C, 60°C and measures enzyme activity (units/min). The grid shows both measure the same outcome (enzyme activity) but vary different inputs (pH vs. temperature). The question asks "What is the independent variable in Experiment 2?" Your grid answer: temperature.

Trick 1: Both experiments measure the same outcome but change different variables. Students confuse which variable changed in which experiment. Trick 2: One experiment controls variables while the other doesn't. A well-designed experiment keeps everything constant except the independent variable. Trick 3: Experiments may use slightly different methods (one measures directly, one calculates). Don't assume identical procedures. Always read the methods section carefully and note exactly what is held constant and what is varied in each experiment.

When comparing experiments, ask: (1) What is measured? (Same or different?) (2) What is changed? (Same or different?) (3) What is held constant? These three questions map every comparison.

Experiment A: Test salt concentration (0%, 5%, 10%, 15%) on plant growth, measure height in cm after 30 days. Experiment B: Test fertilizer type (A, B, C, D) on plant growth, measure height in cm after 30 days. Grid: both measure height (same), Experiment A varies salt (independent), Experiment B varies fertilizer type (independent), both use 30-day period (control). Now answer: "Which variable is the independent variable in Experiment A?" Answer: salt concentration. "What is held constant in both experiments?" Answer: time period (30 days) and measurement method (height in cm). Complete the grid for each problem set before answering questions, ensuring you map all variables clearly.

This habit takes 30 seconds but eliminates confusion that costs most students 1-2 points.

Experiment comparison questions are straightforward if you organize the information visually. Most students lose points because they try to hold all details in their head while rereading. The four-box grid organizes everything and lets you answer questions in seconds without rereading.

On your next ACT Science practice test, use the four-box method for every comparison question. You will notice immediate improvement in speed and accuracy.