SAT Subject Biology Practice Question 366: Answer and Explanation

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Question: 366

16. In 1910, a small town on the East Coast of the United States relied primarily on agriculture to support its economy. In the mid-1930s, a steel mill was built, and the economy shifted from being agriculturally supported to being industrially supported. The steel mill released a lot of smog and soot into the air, which collected on the bark of trees in a wooded area near the outskirts of town. Over a period of ten years the bark gradually darkened, then maintained a constant dark color.

A variety of animals and insects lived in the wooded area. In particular, a certain species of moth served as the primary food source for a population of birds. The moths lay their eggs in the bark of the trees and, thus, must spend a fair amount of time sitting on the tree trunks. Table 1 presents data on the moth population.

Table 1

Birds track their prey visually, whereas bats rely on sonar to locate

A. 95% white, 5% black
B. 80% white, 20% black
C. 50% white, 50% black
D. 20% white, 80% black
E. 5% white, 90% black

Correct Answer: C

Explanation:

C The reason the percentage of black moths increased was because they were no longer visible against the now darkened bark of the trees. Because the white moths were more easily seen by the birds, their numbers declined. However, because bats rely on sonar to locate prey instead of vision, darker coloring would not give the moths any advantage, and the population percentages would stay at the point they were at when the birds were replaced by bats, a fifty-fifty split.

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