Question

The type of organism likely to suffer the most from the effects of biological magnification is

Answer 1

Answer: a tertiary consumer (or higher level consumer); or, "apex predator".
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The higher up an organism is in the food chain (i.e, the higher the trophic level), the more likely the organism is likely to suffer the most from the effects of "biomagnification" (biological magnification; accumulation of toxins).