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

This section requires you to judge whether the information you are given is valid, make conclusions and predictions based on that information, and determine whether explanation for scientific phenomena are actually backed by new findings. In this guide, we'll break down the different question types that may come up under this category, tips and tricks to help you answer questions in this category, and go through a few examples! Let's dive 🌊 right in! 

**When you take the ACT Science section, 25-35% of the questions will fall under the Evaluation of Models, Inferences, and Experimental Results (EMI) category. **

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

The EMI category contains the following question types: evaluation of models, making inferences based on models and data, and determining the results of experiments.

📍 Evaluation of Models

• • A "model" in this context (not a runway model 💃!) is a representation of a concept or phenomena in the real world. For example, an Evaluation of Models question might ask you various questions about contrasting viewpoints regarding Bohr's model of an atom or the billiard ball model of gases.
• • When answering questions that ask you to evaluate a scientific model, don't skim👀the paragraphs describing the model! It is tempting to skim these sections since they tend to be larger, but often understanding the small differences and details in a model when you read about them the first time will help you answer questions quicker, as you won't have to go back and reread the relevant passages! 📌 Inferences
• • Inference questions will ask you to draw conclusions based on information given to you; this information may be in the passage 📜 or in charts/graphs 📉.
• • For inference questions, annotating the passage as you go will be vital! This is because inference questions often require you to synthesize large amounts of information before making a conclusion, so marking up the passage by highlighting main ideas, writing short phrases that summarize viewpoints, and underlining key words will help you recall the gist of what you read and making conclusions much faster⚡.  📊 Experimental Results
• • Experimental results questions ask directly about the results of an experiment outlined in one of the ACT Science passages. Normally, these questions will ask you what the results of an experiment were or if the results support a given viewpoint/hypothesis.
• • When answering an experimental results question, look directly at the graphics and charts mentioned by the question and its possible answer choices. For example, if a question asks "A chemist claimed that in Experiment 2, the pH of the sample solution was greater at a value of 0.1 mL of titrant added than at a value of 1.9 mL of titrant added. Do the results of Experiment 2 support this claim?", go directly to the results chart for Experiment 2! A big part of doing well on the ACT Science section is using your time well and not focusing on unnecessary information/rereading information you already know, so when the question directly points out an experiment ⚗️or graphic to focus on, use that to your advantage!

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🪄 Tips and Tricks

1. • Skim the questions first but read 🔍 the passage carefully! The most efficient way to answer ACT Science questions about models and results is to first skim the questions before reading the passage(s). That way, you know what to look for! For instance, if you notice four questions mention Figure 3, find the parts of the passage relevant to Figure 3 to get context, and then direct your attention to the figure. Make sure to read carefully, otherwise you might miss crucial information for correctly interpreting the models and results presented!
2. • Pay special attention to the experimental design 📈(if there is one). Experimental design has to do with how the experiment is structured; this includes the measured and calculated variables, relationships between variables, as well as experimental and control conditions. Many EMI questions will ask you to draw conclusions about hypothetical situations based on the variables/conditions you are given, so make sure you understand what variables are being measured, how they relate to one another, and the different conditions before trying to draw conclusions!
3. • Note if contrasting viewpoints 📢 are being presented. EMI questions may also ask you to categorize which viewpoint best supports a given situation or phenomenon, so it is important to note what the various viewpoints are in a passage. In fact, it may be helpful to write a quick one sentence summary next to each viewpoint so you don't have to reread entire passages when questions reference specific viewpoints/hypotheses.
4. • Take time to understand figures 📊 provided to you. Results and models are often presented in the form of visual figures, so take your time when interpreting them! It is extremely easy to misinterpret or misread a figure if you are in a hurry, so if a question references a specific model/figure, refer back to areas in the text with relevant information so you don't miss anything!

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✏️ 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 ever-green 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: Notice that we are given three hypotheses, all with different perspectives on how butterflies store lipids. When presented with a question like this one, we should summarize all three viewpoints while reading. Example summaries for each of the hypotheses may look like this:

H1 = store lipids for migration and overwintering

H2 = store lipids for migration only

H3 = store lipids for overwintering only

With the information in a condensed form like this, the answer is easier to identify; Hypothesis 1 is the only one that mentions butterflies storing lipids for two separate periods, and a quick reference to the text confirms that, according to that hypothesis, butterflies store lipids before migration and before overwintering. Therefore, 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—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 refers to the results of Experiments 1 and 2, so we look a the tables displaying the results for each experiment. After reading the descriptors above each table, we can see that the tables display the colors of different indicators in solutions of various pHs. Looking at the row for curcumin, we can see that the color is consistently yellow in where the pH ranges from 1 to 7. As soon as the pH changes to 8 (first column of Table 2), the color shifts to orange, but then from pH 9 and onwards, the color is red. This means that the transitioning range will be around pH 8, as that is when the indicator is an intermediate between its two other colors (yellow and red). Looking at the answer choices, we see that answer C is the most centered around a pH of 8, so that is the correct answer.

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🎉 Conclusion

When it comes to the ACT, the trick lies in knowing what details to pay attention to. The more you practice using the tips above on Evaluation of Models, Inferences, and Experimental Results questions, the better you'll get at them. You've got this! ✊