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About This Drill
ACT Science: Research Summaries (Drill 4) is a Science practice drill covering Research Summaries. It contains 5 original questions created by Brian Stewart, a Barron's test prep author with over 20 years of tutoring experience.
ACT Research Summaries questions test analysis of experimental design and interpretation of results across multiple studies. This drill presents three experiments on natural selection in peppered moth populations, requiring identification of variables, comparison of results, and evaluation of a simulation model.
Questions & Explanations
Experiments 1–3
The peppered moth (
Biston betularia) exists in two color morphs: light (typica), which is pale and speckled, and dark (carbonaria), which is nearly black. Birds are the primary predator, and moths that blend into their resting surface are less likely to be eaten. Researchers conducted three studies to investigate how environmental conditions affect the survival and frequency of each morph.
Experiment 1 -- Predation Survival Rates
Equal numbers of light and dark moths were released in two woodland sites. After one week of exposure to bird predation, the percentage of released moths still surviving was recorded for each morph at each site. Polluted woodland had dark, soot-covered tree bark; unpolluted woodland had light, lichen-covered bark.
Table 1. Survival Rate by Morph and Environment
| Environment | Moth Morph | % Surviving |
|---|
| Polluted | Light | 13.7 |
| Polluted | Dark | 48.6 |
| Unpolluted | Light | 47.2 |
| Unpolluted | Dark | 17.5 |
Experiment 2 -- Population Survey
Researchers surveyed moth populations at 10 industrial cities and 10 rural areas across the United Kingdom and recorded the percentage of dark morphs at each location.
Table 2. Percentage of Dark Morphs by Location Type
| Location Type | Mean % Dark Morphs | Range (%) |
|---|
| Industrial cities | 68.5 | 63–74 |
| Rural areas | 7.4 | 4–11 |
Experiment 3 -- Allele Frequency Over Generations
A computer model simulated changes in the frequency of the dark allele in a polluted environment over five generations, starting from an initial frequency of 0.30. The model applied a selection coefficient of 0.35 against the light morph each generation.
Table 3. Dark Allele Frequency Over Time (Polluted Environment)
| Generation | Dark Allele Frequency |
|---|
| 0 | 0.300 |
| 1 | 0.397 |
| 2 | 0.504 |
| 3 | 0.609 |
| 4 | 0.706 |
| 5 | 0.787 |
Question 1. According to Table 1, in the polluted woodland, approximately how much greater was the survival rate of dark moths than light moths?
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A) 13 percentage points
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B) 29 percentage points
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C) 35 percentage points ✓
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D) 48 percentage points
Explanation: From Table 1 in the polluted woodland: dark moths had a survival rate of 48.6% and light moths had a survival rate of 13.7%. The difference is 48.6 − 13.7 = 34.9 percentage points, which is closest to 35. Dark moths survived at a much higher rate because their coloration matches the soot-darkened bark, making them harder for predatory birds to spot. Light moths were more visible and were taken at a much higher rate.
Experiment 1
The peppered moth (
Biston betularia) exists in two color morphs: light (typica), which is pale and speckled, and dark (carbonaria), which is nearly black. Birds are the primary predator, and moths that blend into their resting surface are less likely to be eaten. Researchers conducted three studies to investigate how environmental conditions affect the survival and frequency of each morph.
Experiment 1 -- Predation Survival Rates
Equal numbers of light and dark moths were released in two woodland sites. After one week of exposure to bird predation, the percentage of released moths still surviving was recorded for each morph at each site. Polluted woodland had dark, soot-covered tree bark; unpolluted woodland had light, lichen-covered bark.
Table 1. Survival Rate by Morph and Environment
| Environment | Moth Morph | % Surviving |
|---|
| Polluted | Light | 13.7 |
| Polluted | Dark | 48.6 |
| Unpolluted | Light | 47.2 |
| Unpolluted | Dark | 17.5 |
Question 2. In Experiment 1, what was the independent variable?
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A) The percentage of moths surviving
-
B) The type of woodland environment (polluted vs. unpolluted) ✓
-
C) The number of birds in each woodland
-
D) The duration of the experiment
Explanation: The independent variable is the factor deliberately manipulated by the researchers -- in this case, the type of woodland environment (polluted vs. unpolluted). The researchers chose which site each group of moths was released into. The percentage of moths surviving is the dependent variable (what was measured as a result). The number of birds and duration of the experiment were controlled variables -- held constant to prevent them from confounding the results.
Experiments 1 and 2
The peppered moth (
Biston betularia) exists in two color morphs: light (typica), which is pale and speckled, and dark (carbonaria), which is nearly black. Birds are the primary predator, and moths that blend into their resting surface are less likely to be eaten. Researchers conducted three studies to investigate how environmental conditions affect the survival and frequency of each morph.
Experiment 1 -- Predation Survival Rates
Equal numbers of light and dark moths were released in two woodland sites. After one week of exposure to bird predation, the percentage of released moths still surviving was recorded for each morph at each site.
Table 1. Survival Rate by Morph and Environment
| Environment | Moth Morph | % Surviving |
|---|
| Polluted | Light | 13.7 |
| Polluted | Dark | 48.6 |
| Unpolluted | Light | 47.2 |
| Unpolluted | Dark | 17.5 |
Experiment 2 -- Population Survey
Researchers surveyed moth populations at 10 industrial cities and 10 rural areas across the United Kingdom.
Table 2. Percentage of Dark Morphs by Location Type
| Location Type | Mean % Dark Morphs | Range (%) |
|---|
| Industrial cities | 68.5 | 63–74 |
| Rural areas | 7.4 | 4–11 |
Question 3. The results of Experiment 2 are best explained by which conclusion from Experiment 1?
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A) Dark moths survive at a higher rate than light moths regardless of environment
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B) In polluted environments, dark moths survive at a much higher rate, so over many generations dark morphs become more common ✓
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C) Light moths survive better in all environments, explaining why rural areas still have some light moths
-
D) Bird predation rates are higher in cities than in rural areas
Explanation: Table 2 shows dark morphs are far more common in industrial cities (mean 68.5%) than in rural areas (mean 7.4%). Experiment 1 provides the mechanism: in polluted woodland, dark moths survive at 48.6% vs. 13.7% for light moths -- a huge survival advantage. Over many generations of differential survival and reproduction, dark moths accumulate in industrial areas while light moths remain dominant in rural areas where their coloration provides camouflage. Option A is wrong -- Table 1 shows dark moths have a lower survival rate than light moths in unpolluted environments.
Experiment 3
The peppered moth (
Biston betularia) exists in two color morphs: light (typica), which is pale and speckled, and dark (carbonaria), which is nearly black. Birds are the primary predator, and moths that blend into their resting surface are less likely to be eaten. Researchers conducted three studies to investigate how environmental conditions affect the survival and frequency of each morph.
Experiment 3 -- Allele Frequency Over Generations
A computer model simulated changes in the frequency of the dark allele in a polluted environment over five generations, starting from an initial frequency of 0.30. The model applied a selection coefficient of 0.35 against the light morph each generation.
Table 3. Dark Allele Frequency Over Time (Polluted Environment)
| Generation | Dark Allele Frequency |
|---|
| 0 | 0.300 |
| 1 | 0.397 |
| 2 | 0.504 |
| 3 | 0.609 |
| 4 | 0.706 |
| 5 | 0.787 |
Question 4. Suppose the model in Experiment 3 were run in an unpolluted environment instead of a polluted one, with the selection coefficient of 0.35 now applied against the dark morph. Starting from the same initial dark allele frequency of 0.30, what would most likely happen to the dark allele frequency over the five generations?
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A) It would increase at the same rate as in Table 3
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B) It would remain constant at 0.300
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C) It would decrease, because dark morphs are now at a survival disadvantage ✓
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D) It would increase more rapidly, because unpolluted environments favor all moths equally
Explanation: In Table 3, the dark allele increases because selection acts against the light morph in a polluted environment. If the same selection pressure (s = 0.35) were instead applied against the dark morph -- as happens in unpolluted woodland where light coloration provides camouflage -- then dark moths would survive at a lower rate and reproduce less. The dark allele frequency would decrease over successive generations. This mirrors the real-world observation that dark moths declined in UK populations after the Clean Air Acts of the 1950s–1970s reduced industrial pollution and tree bark lightened again.
Experiment 1
The peppered moth (
Biston betularia) exists in two color morphs: light (typica), which is pale and speckled, and dark (carbonaria), which is nearly black. Birds are the primary predator, and moths that blend into their resting surface are less likely to be eaten. Researchers conducted three studies to investigate how environmental conditions affect the survival and frequency of each morph.
Experiment 1 -- Predation Survival Rates
Equal numbers of light and dark moths were released in two woodland sites. After one week of exposure to bird predation, the percentage of released moths still surviving was recorded for each morph at each site. Polluted woodland had dark, soot-covered tree bark; unpolluted woodland had light, lichen-covered bark.
Question 5. In Experiment 1, the researchers released equal numbers of light and dark moths at each site. What was the most likely reason for this design choice?
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A) To ensure that survival rates could be directly compared between the two morphs without a numerical bias from unequal starting populations ✓
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B) To maximize the total number of moths surviving at the end of the experiment
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C) To ensure that birds could not distinguish between the two morphs
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D) To reflect the natural morph ratio found in wild peppered moth populations
Explanation: Starting with equal numbers of each morph is a controlled design choice that ensures a fair comparison. If, say, 200 dark moths and 50 light moths were released, the survival percentages could be influenced by the different starting numbers (e.g., birds might deplete a smaller starting group more quickly regardless of coloration). By starting with equal numbers, any difference in the percentage surviving can be attributed to the morph's relative camouflage -- not to unequal initial counts. This is an application of controlling variables: keeping starting conditions equal so that the independent variable (morph coloration) is the only meaningful difference between groups.