Biological magnification refers to the increase in concentration of a substance as it moves up the food chain.

• A. The increase in concentration of a substance as it moves up the food chain
• B. The decrease in concentration of a substance as it moves up the food chain
• C. The processing of biological samples through magnets
• D. The genetic modification of organisms

Answer: (A)

Biomagnification happens when a substance becomes more concentrated in organisms at higher levels of the food chain because toxins accumulate in tissues and are not easily excreted. As predators eat many prey items, they accumulate the toxins from all those prey, so the concentration increases at each step up the chain. This is why the statement describing an increase in concentration as you move up the food chain matches what happens with certain pollutants like fat‑soluble pesticides.

The other ideas don’t fit: a decrease in concentration up the chain is the opposite of biomagnification, and processing samples with magnets or genetically modifying organisms aren’t related to how contaminants accumulate through feeding relationships.