SAT Subject Biology Practice Question 142: Answer and Explanation

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Question: 142

12. A grassy field experiences an increase in growth in an area where phosphorus has been added. However, no such growth occurs in a second area to which nitrogen has been added. Which is a limiting nutrient for this ecosystem?

A. Nitrogen, because addition of this nutrient did not affect plant growth
B. Phosphorus, because addition of this nutrient did not affect plant growth
C. Nitrogen, because addition of this nutrient resulted in increased plant growth
D. Phosphorus, because addition of this nutrient resulted in increased plant growth
E. Both nitrogen and phosphorus, because addition of one nutrient increased plant growth

Correct Answer: D

Explanation:

Phosphorus is a limiting nutrient, as evidenced by the fact that when phosphorus was added, plant growth increased. Nitrogen is not a limiting nutrient; addition of nitrogen has no effect on vegetation.

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