Question

acid precipitation that results from the burning of fossil fuels disrupts the nutrient cycles in an environment. some of these disruptions greatly affect the organisms that live in an ecosystem. for example, bacteria that play important roles in the nitrogen cycle cannot tolerate a decrease in the ph of soil due to acid precipitation. which statement explains how an ecosystem is likely to be affected by this disruption of the nitrogen cycle?
a animal populations in the ecosystem will find other sources of nitrogen and change very little.
b the sizes of plant populations in the ecosystem will decline due to lack of soil nitrogen.
c there will be little effect because there is plenty of free nitrogen in the atmosphere.
d new kinds of plants will begin to grow in the ecosystem and restart the nitrogen cycle.

Explanation:

To solve this, we analyze each option:

• Option A: Animals relying on other nitrogen sources is unlikely as acid precipitation disrupts the nitrogen cycle and affects all organisms, so A is incorrect.
• Option B: Bacteria involved in the nitrogen cycle (like nitrogen - fixing bacteria) are sensitive to pH changes. Acid precipitation lowers soil pH, harming these bacteria. With fewer nitrogen - fixing bacteria, soil nitrogen decreases, leading to a decline in plant populations (since plants need nitrogen). This explains the disruption.
• Option C: The atmosphere has free nitrogen, but most organisms can't use it directly. The nitrogen cycle relies on soil - based processes (like nitrogen fixation by bacteria in soil). So the abundance of atmospheric nitrogen doesn't mean little effect on the nitrogen cycle, making C incorrect.
• Option D: New plants growing and restarting the cycle is not a direct result of acid precipitation disrupting the nitrogen cycle. Acid precipitation harms the existing cycle, and new plants would still need the nitrogen cycle to function properly, so D is incorrect.

Answer:

B. The sizes of plant populations in the ecosystem will decline due to lack of soil nitrogen.