Question

question 15
read the following scenario and answer the question(s) below.
mercury is a heavy metal that occurs naturally in minerals and rocks. release of mercury from natural sources has been relatively constant over time. however, anthropogenic release of mercury has increased significantly in recent years primarily due to increased fossil fuel mining and combustion. mercury that is released into the air eventually ends up in soils or surface water. once in water, microbes convert mercury into methyl mercury, which is absorbed quickly and concentrated in the tissues of predatory fish such as shark and swordfish. large fish typically concentrate more mercury than small fish. people who eat fish with high methyl mercury concentrations (e.g., more than 2 parts per million) may exhibit tremors, deafness, muscle dysfunction, and attention deficits. pregnant women and children are especially sensitive to methyl mercurys toxic effects. learning disabilities and developmental delays are common in children who have been exposed to significant levels of methyl mercury.
pregnant women and children are warned not to eat certain kinds of fish that have high mercury content. why do some fish tend to have higher mercury levels than other fish?
some species of fish live in areas that are more contaminated with methyl mercury. the species of fish living in those areas should be avoided.
fish that are high in the food chain eat prey that already have biomagnified levels of methyl mercury, thus further biomagnifying the pollutant.
fish that are high in the food chain eat prey that already have biomagnified levels of methyl mercury, thus further biomagnifying the pollutant.
some fish tend to thrive in habitats near factories that release high levels of mercury.
the high levels of mercury are an adaptation to avoid predation by humans.

Explanation:

Step1: Understand biomagnification

Biomagnification is the process where the concentration of a pollutant (like methyl - mercury) increases as it moves up the food chain.

Step2: Analyze each option

• Option A: Just living in areas with methyl - mercury does not explain why some fish (larger ones) have higher levels. Smaller fish also live in those areas.
• Option B: Fish that are high in the food chain eat prey that already have biomagnified levels of methyl - mercury. Since they are at a higher trophic level, they consume multiple prey items, each contributing to the accumulation of methyl - mercury in their bodies. For example, if a small fish has \(x\) amount of methyl - mercury, a larger fish that eats 10 of those small fish will have a higher concentration (assuming no excretion) than the small fish.
• Option C: Fish that are high in the food chain do not "further biomagnify" the pollutant in the sense of a chemical transformation. Biomagnification is about accumulation through consumption, not a new process of magnification by the fish itself.
• Option D: There is no indication that high mercury levels are an adaptation to avoid predation by humans. The text focuses on the biological process of biomagnification.

Answer:

B. Fish that are high in the food chain eat prey that already have biomagnified levels of methyl - mercury, thus further biomagnifying the pollutant.