SAT Subject Biology Practice Question 447: Answer and Explanation
17. Six pairs of bald eagles were released into the wild in Indiana. Four of the pairs of birds successfully nested and raised young. Two of the pairs nested near an industrial complex that released waste products (PCBs) into a nearby lake. These birds laid eggs, but the embryos failed to develop.
The eggshells of the embryos that failed to develop were tested and were found to contain more PCBs than the nearby plants and insects. This is due to
B. increased levels of PCBs in the lake
C. the resistance of the insects to PCBs
D. failure of the plants to take up PCBs
E. absorption of PCBs from the nesting site into the eggshell
Correct Answer: A
A Because the higher trophic levels feed on the lower trophic levels, toxins tend to accumulate in the higher trophic levels by a process called biomagnification. Eagles are top carnivores and would exhibit a lot of toxin accumulation, more so than plants or insects. Choice B may be true but doesn't answer the question-don't fall into the temptation trap. Choice C is not mentioned in the passage, and the plants do take up PCB (choice D is eliminated). The PCB in the eggs came from the eagles themselves, not from absorption.