7–10% of the AP exam. 13 key topics. 4 common errors analyzed.
Unit 8 (Aquatic and Terrestrial Pollution) addresses environmental systems and human impacts. FRQs in this unit typically ask you to identify problems, propose specific solutions, and explain environmental consequences.
These are the most frequently penalized mistakes on AP exam FRQs and MCQs. Review each before your next practice session.
Conflating bioaccumulation and biomagnification: bioaccumulation refers to the buildup of a toxin in the tissues of a single organism over its lifetime; biomagnification refers to the progressive increase in toxin concentration at each successive trophic level — both concepts are frequently tested and must be distinguished precisely
Describing eutrophication as the algal bloom itself rather than as the process: excess nutrients (nitrogen, phosphorus) stimulate algal growth; when algae die, bacterial decomposition consumes dissolved oxygen, creating hypoxic conditions that kill aquatic organisms — students must trace the full causal chain
Confusing primary sewage treatment (physical settling of solids) with secondary treatment (biological decomposition of dissolved organic matter by microbes) and tertiary treatment (chemical or filtration removal of remaining nutrients and pathogens)
Misinterpreting LD50: students sometimes state that a lower LD50 means a substance is less toxic, when the opposite is true — LD50 is the dose lethal to 50% of a test population, so a lower value indicates higher toxicity
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