AP Environmental Science (APES) is unique among AP sciences because it explicitly connects biological, chemical, physical, and social systems to environmental problems and their policy solutions. The exam tests both content knowledge and the ability to apply scientific reasoning to real environmental scenarios — and it includes math calculations on every exam.
Unit 1: The Living World — Ecosystems
Energy flow: producers (autotrophs) → primary consumers → secondary → tertiary consumers. Only ~10% of energy transfers between trophic levels (10% rule). Food chains vs. food webs. Biogeochemical cycles: carbon cycle (photosynthesis/respiration, combustion, ocean absorption), nitrogen cycle (fixation by Rhizobium bacteria and lightning, nitrification, denitrification), phosphorus cycle (no atmospheric phase — weathering and runoff), water cycle (evapotranspiration, infiltration, runoff). Know what disrupts each cycle and the environmental consequences.
Units 2–3: Biodiversity and Populations
Biodiversity: species richness, genetic diversity, ecosystem diversity. Island biogeography (species equilibrium = immigration rate – extinction rate; larger islands and proximity to mainland → more species). Ecosystem services (provisioning, regulating, cultural, supporting). Population dynamics: r-selected vs. K-selected species, logistic growth (S-curve) vs. exponential growth (J-curve), carrying capacity, age structure diagrams. Human population: demographic transition model, total fertility rate, doubling time (Rule of 70: doubling time ≈ 70/growth rate %).
Units 4–5: Earth Systems and Land Use
Plate tectonics: earthquakes, volcanoes, tsunamis, and soil formation via weathering. Soil horizons (O, A, B, C, R) and properties (texture, porosity, permeability). Soil degradation: erosion, salinization, desertification. Agriculture: irrigation methods (drip vs. flood vs. spray efficiency), soil erosion from conventional tillage, pesticide treadmill, GMOs. Forestry: clear-cutting vs. selective cutting vs. shelterwood method. Fishing: maximum sustainable yield, bycatch, overfishing indicators.
Units 6–7: Energy Resources and Pollution
Fossil fuels: coal, oil, natural gas — extraction methods, energy return on energy investment (EROEI), and pollution profiles. Nuclear energy: fission, half-life calculations, radioactive waste storage. Renewable energy: solar (PV vs. concentrating), wind, hydropower, geothermal, tidal. Energy efficiency. Air pollution: primary vs. secondary pollutants, photochemical smog formation (VOCs + NOx + UV), acid deposition (SO₂ → H₂SO₄, NOx → HNO₃), particulate matter (PM2.5), indoor air pollution. Clean Air Act, NAAQS, cap-and-trade.
Units 8–9: Aquatic Pollution and Global Change
Water pollution: point vs. nonpoint sources, eutrophication (nutrient runoff → algal bloom → oxygen depletion → dead zones), biochemical oxygen demand (BOD), heavy metal contamination (bioaccumulation, biomagnification — PCBs, mercury, DDT). Safe Drinking Water Act, Clean Water Act. Climate change: enhanced greenhouse effect, forcing agents (CO₂, CH₄, N₂O, water vapor), feedback loops (ice-albedo, permafrost methane, water vapor), effects (sea level rise, extreme weather, coral bleaching). Stratospheric ozone depletion: CFCs → chlorine radical chain reaction, Montreal Protocol. IPCC, Paris Agreement.
Math You Must Know
APES requires calculations on the FRQ section. Key formulas: Rule of 70 for doubling time, unit conversion (especially energy units — BTU, kilowatt-hour, joule), percent change, and energy calculations (watts = joules/second). Know how to read and interpret graphs showing population growth, resource consumption, or pollution concentration over time.
AP Environmental Science Practice Questions · APES Practice Test · All AP Courses
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