SAT Subject Biology Practice Question 364: Answer and Explanation

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Question: 364

14. 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

What is the most likely explanation for the shift in the percentage of

A. The white moths no longer blended with the color of the tree bark and, thus, were selected for.
B. The black moths blended better with the color of the tree bark and, thus, were selected for.
C. The black moths blended better with the color of the tree bark and, thus, were selected against.
D. The white moths blended better with the color of the tree bark and, thus, were selected against.
E. The black moths did not blend with the color of the tree bark and, thus, were selected against.

Correct Answer: B

Explanation:

B Because the percentage of black moths is increasing, they must be selected for. This eliminates C and E. Because the percentage of white moths is decreasing, they must be selected against, eliminating choice A. Choice D is wrong because white moths would not blend better against dark tree bark.

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