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About This Drill
ACT Science: Data Representation (Drill 2) is a Science practice drill covering Data Representation. It contains 5 original questions created by Brian Stewart, a Barron's test prep author with over 20 years of tutoring experience.
ACT Data Representation questions require accurate reading and comparison of experimental figures. This drill uses graphs of pepsin and trypsin activity across temperature and pH ranges, asking you to identify optima, compare enzymes, and assess the validity of a student's conclusion.
Questions & Explanations
Figures 1 and 2
Researchers studied how temperature and pH affect the activity of two human digestive enzymes, pepsin (secreted in the stomach) and trypsin (secreted in the small intestine). Enzyme activity was measured as the rate of substrate breakdown in micromoles per minute (μmol/min). In Experiment 1, each enzyme was tested at six temperatures (10°C, 20°C, 30°C, 37°C, 50°C, and 60°C) at its respective optimal pH. In Experiment 2, each enzyme was tested at six pH levels (pH 1, 2, 4, 7, 8, and 10) at 37°C. Results are shown in Figures 1 and 2.
Figure 1. Enzyme Activity vs. Temperature
Activity (μmol/min)
Temperature (°C)
0
20
40
60
80
100
10
20
30
37
50
60
Pepsin
Trypsin
Figure 2. Enzyme Activity vs. pH
Activity (μmol/min)
pH
0
20
40
60
80
100
1
2
4
7
8
10
Pepsin
Trypsin
Question 1. According to Figure 1, at which temperature was pepsin activity the highest?
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A) 20°C
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B) 30°C
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C) 37°C ✓
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D) 50°C
Explanation: In Figure 1, the pepsin line (blue) reaches its peak of 100 μmol/min at 37°C, normal human body temperature. Activity rises steadily from 10°C to 37°C, then drops sharply at higher temperatures as the enzyme begins to denature. This is characteristic of human digestive enzymes, which are optimized for the body's internal temperature.
Figure 2
Researchers studied how temperature and pH affect the activity of two human digestive enzymes, pepsin (secreted in the stomach) and trypsin (secreted in the small intestine). Enzyme activity was measured as the rate of substrate breakdown in micromoles per minute (μmol/min). In Experiment 1, each enzyme was tested at six temperatures (10°C, 20°C, 30°C, 37°C, 50°C, and 60°C) at its respective optimal pH. In Experiment 2, each enzyme was tested at six pH levels (pH 1, 2, 4, 7, 8, and 10) at 37°C. Results are shown in Figures 1 and 2.
Figure 2. Enzyme Activity vs. pH
Activity (μmol/min)
pH
0
20
40
60
80
100
1
2
4
7
8
10
Pepsin
Trypsin
Question 2. According to Figure 2, what is the optimal pH for trypsin?
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A) pH 2
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B) pH 4
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C) pH 7
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D) pH 8 ✓
Explanation: In Figure 2, the trypsin line (red) peaks at pH 8, where activity reaches approximately 100 μmol/min. This matches trypsin's role in the small intestine, which has a slightly alkaline environment (pH 7.5–8.5). Activity is nearly zero at acidic pH values (1–4), which makes biological sense: trypsin is inactive in the acidic stomach but highly functional once it reaches the alkaline small intestine.
Figure 1
Researchers studied how temperature and pH affect the activity of two human digestive enzymes, pepsin (secreted in the stomach) and trypsin (secreted in the small intestine). Enzyme activity was measured as the rate of substrate breakdown in micromoles per minute (μmol/min). In Experiment 1, each enzyme was tested at six temperatures (10°C, 20°C, 30°C, 37°C, 50°C, and 60°C) at its respective optimal pH. In Experiment 2, each enzyme was tested at six pH levels (pH 1, 2, 4, 7, 8, and 10) at 37°C. Results are shown in Figures 1 and 2.
Figure 1. Enzyme Activity vs. Temperature
Activity (μmol/min)
Temperature (°C)
0
20
40
60
80
100
10
20
30
37
50
60
Pepsin
Trypsin
Question 3. Based on Figure 1, which of the following best describes pepsin activity from 37°C to 60°C?
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A) It increased steadily
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B) It remained constant
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C) It increased then decreased
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D) It decreased steadily ✓
Explanation: In Figure 1, pepsin (blue line) peaks at 37°C. From 37°C to 50°C activity drops to about 40 μmol/min, then falls further to about 5 μmol/min at 60°C, a steady decrease throughout. Temperatures above 37°C progressively disrupt the hydrogen bonds and other interactions that maintain the enzyme's three-dimensional shape, a process called denaturation, which reduces catalytic activity.
Figure 2
Researchers studied how temperature and pH affect the activity of two human digestive enzymes, pepsin (secreted in the stomach) and trypsin (secreted in the small intestine). Enzyme activity was measured as the rate of substrate breakdown in micromoles per minute (μmol/min). In Experiment 1, each enzyme was tested at six temperatures (10°C, 20°C, 30°C, 37°C, 50°C, and 60°C) at its respective optimal pH. In Experiment 2, each enzyme was tested at six pH levels (pH 1, 2, 4, 7, 8, and 10) at 37°C. Results are shown in Figures 1 and 2.
Figure 2. Enzyme Activity vs. pH
Activity (μmol/min)
pH
0
20
40
60
80
100
1
2
4
7
8
10
Pepsin
Trypsin
Question 4. At pH 4, approximately how much greater was pepsin activity than trypsin activity, according to Figure 2?
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A) 10 μmol/min
-
B) 30 μmol/min
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C) 40 μmol/min ✓
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D) 60 μmol/min
Explanation: At pH 4 in Figure 2, pepsin (blue) is at approximately 60 μmol/min while trypsin (red) is at approximately 20 μmol/min. The difference is 60 − 20 = 40 μmol/min. pH 4 is moderately acidic, closer to pepsin's optimum of pH 2 than to trypsin's optimum of pH 8, which is why pepsin remains substantially more active at this pH.
Figure 1
Researchers studied how temperature and pH affect the activity of two human digestive enzymes, pepsin (secreted in the stomach) and trypsin (secreted in the small intestine). Enzyme activity was measured as the rate of substrate breakdown in micromoles per minute (μmol/min). In Experiment 1, each enzyme was tested at six temperatures (10°C, 20°C, 30°C, 37°C, 50°C, and 60°C) at its respective optimal pH. In Experiment 2, each enzyme was tested at six pH levels (pH 1, 2, 4, 7, 8, and 10) at 37°C. Results are shown in Figures 1 and 2.
Figure 1. Enzyme Activity vs. Temperature
Activity (μmol/min)
Temperature (°C)
0
20
40
60
80
100
10
20
30
37
50
60
Pepsin
Trypsin
Question 5. A student claims that at 60°C, both enzymes have lost most of their activity compared to their respective peaks. Is this claim supported by Figure 1?
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A) Yes; both enzymes show activity below 20 μmol/min at 60°C ✓
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B) Yes; pepsin drops to near zero but trypsin retains about half its peak activity at 60°C
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C) No; trypsin activity is still near its peak at 60°C
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D) No; both enzymes show increased activity at 60°C compared to 37°C
Explanation: At 60°C in Figure 1, both pepsin and trypsin have dropped to approximately 5–10 μmol/min, well below their shared peak of 100 μmol/min at 37°C. Both values fall below the 20 μmol/min gridline, supporting the claim. Temperatures well above 37°C disrupt the non-covalent interactions that maintain each enzyme's three-dimensional shape, causing denaturation and steep loss of catalytic activity in both cases.