ACT Science: Evaluation of Models, Inferences, & Experimental Results

🧐 Evaluation of Models, Inferences, & Experimental Results Question Types

On the ACT Science section, 25-35% of the questions fall under the Evaluation of Models, Inferences, and Experimental Results (EMI) category. These questions ask you to judge whether given information is valid, draw conclusions and predictions from data, and determine whether new findings actually support a proposed explanation.

The EMI category breaks down into three question types: evaluation of models, making inferences based on models and data, and determining experimental results.

📍 Evaluation of Models

A model in this context is a simplified representation of a concept or phenomenon in the real world. For example, you might see questions about contrasting viewpoints regarding Bohr's model of an atom or the billiard ball model of gases.

When answering these questions, don't skim the paragraphs describing the model. These sections tend to be long, which makes skimming tempting, but the small differences and details between competing models are exactly what the questions test. Understanding those details on your first read-through saves you from going back and rereading later.

📌 Inferences

Inference questions ask you to draw conclusions based on information in the passage or in charts and graphs. They often require you to synthesize information from multiple parts of the passage before arriving at a conclusion.

Annotating as you read is critical here. Highlight main ideas, write short phrases that summarize viewpoints, and underline key terms. These markups help you recall the gist of what you read so you can form conclusions much faster.

📊 Experimental Results

Experimental results questions ask directly about the outcomes of an experiment described in the passage. Typically, they'll ask what the results were or whether the results support a given hypothesis.

When answering these, go straight to the graphics and charts the question references. For example, if a question asks "Do the results of Experiment 2 support the claim that pH was greater at 0.1 mL of titrant than at 1.9 mL?", go directly to the results chart for Experiment 2. A big part of doing well on ACT Science is not wasting time on information the question doesn't ask about. When a question points you to a specific experiment or figure, use that direction to your advantage.

🪄 Tips and Tricks

1. Skim the questions first, then read the passage carefully. Before diving into the passage, glance at the questions so you know what to look for. If four questions mention Figure 3, find the parts of the passage relevant to Figure 3 for context, then focus on the figure itself. But don't rush through the reading; missing a detail can lead to misinterpreting the models and results.

2. Pay special attention to experimental design. This includes which variables are measured or calculated, how variables relate to one another, and what the experimental vs. control conditions are. Many EMI questions ask you to predict what would happen in a hypothetical situation based on these variables and conditions. Make sure you understand the setup before trying to draw conclusions.

3. Note when contrasting viewpoints are presented. EMI questions may ask which viewpoint best supports a given situation or phenomenon. Write a quick one-sentence summary next to each viewpoint as you read. This keeps you from rereading entire passages when a question references a specific hypothesis.

4. Take time to understand figures. Results and models are often presented as visual figures, and it's easy to misread a graph or table when you're rushing. If a question references a specific figure, check the axis labels, units, and any relevant text before answering.

✏️ Example Questions

ACT Practice Test 2017: Question 8

In the fall, monarch butterflies (Danaus plexippus) in eastern North America migrate to Mexico, where they overwinter in high-altitude forests of oyamel fir (an evergreen conifer). The butterflies store (accumulate) body lipids to use as a source of energy at a later time. Consider the following 3 hypotheses pertaining to when the butterflies store lipids and when the energy from the stored lipids is used, with respect to migration and overwintering.

Hypothesis 1

Monarch butterflies require energy from stored lipids for migration and during the overwintering period. The butterflies first store lipids before they begin their migration. During migration, as stored lipids are converted to energy, lipid mass continuously decreases. When the butterflies reach the overwintering sites, ending their migration, they must store lipids again before beginning the overwintering period.

Hypothesis 2

Monarch butterflies require energy from stored lipids for migration but not during the overwintering period. The butterflies store lipids before they begin their migration. During migration, as stored lipids are converted to energy, lipid mass continuously decreases. Because energy from stored lipids is not required during the overwintering period, the butterflies do not store lipids while at the overwintering sites.

Hypothesis 3

Monarch butterflies require energy from stored lipids during the overwintering period but not for migration. The butterflies do not store lipids before they begin their migration. Instead, lipids are stored during migration; therefore, lipid mass continuously increases from the beginning of migration until the end of migration. The butterflies arrive at the overwintering sites with enough lipids to provide themselves with energy during the overwintering period, so they do not store lipids while at the overwintering sites.

Which hypothesis, if any, asserts that monarch butterflies store lipids during 2 distinct periods?

F. Hypothesis 1

G. Hypothesis 2

H. Hypothesis 3

J. None of the hypotheses

Correct Answer: F

Explanation: You're given three hypotheses with different perspectives on how butterflies store lipids. The fastest approach is to summarize each viewpoint as you read:

• H1 = store lipids before migration AND before overwintering (two distinct periods)
• H2 = store lipids before migration only (one period)
• H3 = store lipids during migration only (one period)

With these summaries, the answer becomes clear. Hypothesis 1 is the only one describing two separate storage periods: once before migration and once before overwintering. The answer is F.

ACT Practice Test 2017: Question 29

A typical acid-base indicator is a compound that will be one color over a certain lower pH range but will be a different color over a certain higher pH range. In the small range between these pH ranges, the transition range, the indicator's color will be an intermediate of its other 2 colors.

Students studied 5 acid-base indicators using colorless aqueous solutions of different pH and a well plate (a plate containing a matrix of round depressions, or wells, that can hold small volumes of liquid).

Experiment 1

The students added a pH = 0 solution to 5 wells in the first column of the well plate, then added a pH = 1 solution to the 5 wells in the next column, and so on, up to pH = 7. Next, they added a drop of a given indicator (in solution) to each of the wells in a row, and then repeated this process, adding a different indicator to each row. The color of the resulting solution in each well was then recorded in Table 1 (B = blue, G = green, O = orange, P = purple, R = red, Y = yellow).

Image Courtesy of Question 29, ACT Practice Test 2017

Experiment 2

Experiment 1 was repeated with solutions that had a pH of 8 or greater (see Table 2).

Image Courtesy of Question 29, ACT Practice Test 2017

Based on the results of Experiments 1 and 2, which of the following is a possible transition range for curcumin?

A. pH = 3.9 to pH = 7.3

B. pH = 4.2 to pH = 6.6

C. pH = 7.4 to pH = 8.6

D. pH = 8.4 to pH = 9.5

Correct Answer: C

Explanation: The question points you to the results tables, so go straight there. Here's how to work through it:

1. Find the curcumin row in Table 1. The color is consistently yellow from pH 0 through pH 7.
2. Find the curcumin row in Table 2. At pH 8, the color shifts to orange, and from pH 9 onward, the color is red.
3. Recall that the transition range is where the indicator shows an intermediate color between its two main colors. Curcumin's two main colors are yellow (low pH) and red (high pH), and orange appears at pH 8. So the transition range is around pH 8.
4. Check the answer choices. Answer C (pH 7.4 to pH 8.6) is the only range centered around pH 8. The answer is C.

🎉 Conclusion

With EMI questions, the trick is knowing what details to pay attention to and where to find them quickly. Summarize viewpoints as you read, go directly to referenced figures, and understand the experimental setup before drawing conclusions. The more you practice applying these strategies, the faster and more accurate you'll get.