AP Environmental Science cheat sheet

Gross primary productivity (GPP) is total energy captured by photosynthesis; net primary productivity (NPP) = GPP − respiration of producers.

Trophic levels transfer roughly 10% of energy to the next level (range ~5–20%); biomass pyramids can invert in aquatic systems where producers turn over fast.

Biogeochemical cycles: carbon and nitrogen have atmospheric reservoirs; phosphorus and potassium cycle mainly through rock and soil with no gas phase.

Nitrogen fixation (bacteria, lightning) converts N2 to ammonia; nitrification makes nitrate; denitrification returns N2 to the atmosphere.

Eutrophication sequence: nutrient input → algal bloom → decomposition consumes O2 → hypoxia → fish kills.

Primary succession begins on bare substrate (lava, glacial till); secondary succession begins where soil remains after disturbance.

Keystone species exert outsized influence relative to abundance; removing one triggers disproportionate community change.

Productivity is limited by the single scarcest nutrient (Liebig's law of the minimum); open ocean is often nitrogen- or iron-limited, fresh water often phosphorus-limited.

Residence time = reservoir size ÷ flux in or out; large atmospheric reservoirs with slow flux have long residence times.

Species richness counts species present; species evenness describes relative abundance - high evenness raises diversity at equal richness.

Island biogeography: larger islands and islands nearer the mainland support more species and lower extinction rates.

Ecosystem services split into provisioning (food, timber), regulating (climate, water), cultural (recreation), and supporting (nutrient cycling).

Generalist species tolerate wide conditions and are favored in disturbed or fragmented habitat; specialists decline first.

Bottleneck and founder effects reduce genetic diversity and raise extinction risk in small populations.

Edge effects increase along fragmented boundaries, favoring edge-tolerant species and harming interior specialists.

Biodiversity hotspots combine high endemism with high habitat loss; they are conservation priorities.

Inbreeding depression lowers fitness; genetic rescue via immigration of unrelated individuals can restore diversity.

Exponential growth: dN/dt = rN; population grows without limit only when resources are unlimited.

Logistic growth: dN/dt = rN(K − N)/K; growth is fastest at N = K/2 and zero at carrying capacity K.

Doubling time ≈ 70 ÷ percent growth rate (Rule of 70).

Total fertility rate (TFR) near 2.1 gives replacement-level population in the absence of migration.

Age-structure pyramids: broad base predicts rapid growth; narrow base predicts decline; column shape indicates stability.

Type I survivorship has high early survival (large mammals); Type III has heavy early mortality (many fish, insects).

Density-dependent factors (disease, competition, predation) intensify with crowding; density-independent factors (fire, drought, storms) act regardless of density.

r-selected species: many small offspring, little parental care, early maturity; K-selected species: few large offspring, high parental care.

Earth's interior layers: crust, mantle, outer core (liquid, generates magnetic field), inner core (solid).

Plate boundaries: divergent (seafloor spreading, ridges), convergent (subduction, volcanoes, trenches), transform (strike-slip earthquakes).

Rock types: igneous (cooled magma), sedimentary (compacted deposits, holds fossils), metamorphic (heat and pressure).

Soil horizons: O (organic litter), A (topsoil, humus), E (leached), B (subsoil accumulation), C (weathered parent material), R (bedrock).

Porosity is total void space; permeability is the rate fluid moves through it - clay has high porosity but low permeability.

El Niño: weakened trade winds, warm eastern Pacific water, altered global precipitation; La Niña is the opposite phase.

Hadley, Ferrel, and polar cells drive prevailing winds and climate bands; Coriolis deflection is right in the Northern Hemisphere, left in the Southern.

Insolation is most intense near the equator; seasonal variation results from axial tilt, not distance from the Sun.

Clear-cutting removes all trees at once, raising erosion and nutrient loss; selective cutting removes fewer trees and disturbs less.

The Green Revolution raised yields through high-yield varieties, irrigation, fertilizer, and pesticides, with costs of salinization and water depletion.

Irrigation waterlogging and salinization accumulate salts in topsoil; drip irrigation reduces both.

Soil erosion control: contour plowing, terracing, windbreaks (shelterbelts), no-till, and cover crops.

Integrated pest management combines biological, cultural, and limited chemical controls to reduce resistance pressure.

Urban sprawl increases impervious surface, which raises runoff volume and carries more pollutants to streams.

Tragedy of the commons: shared open-access resources are depleted unless regulated by privatization, quotas, or community rules.

Aquaculture and CAFOs concentrate waste; manure lagoons can leak nutrients and pathogens into groundwater.

Energy sources: renewable (solar, wind, hydro, geothermal, biomass) versus nonrenewable (coal, oil, natural gas, nuclear fuel).

Coal combustion emits the most CO2 and SO2 per unit energy; natural gas emits the least CO2 of the fossil fuels.

Net energy = energy returned − energy invested; higher ratios mean greater usable surplus.

Photovoltaic cells convert sunlight directly to electricity; solar thermal concentrates heat to drive turbines.

Wind power scales with the cube of wind speed; hydro requires elevation drop and disrupts fish migration.

Nuclear fission splits U-235; wastes stay hazardous for thousands of years, and plants need cooling water.

Combustion of fossil fuels converts stored chemical energy to heat, then mechanical, then electrical energy, with losses at each step.

Cogeneration (combined heat and power) reuses waste heat and raises overall efficiency.

Primary pollutants are emitted directly (CO, NOx, SO2, particulates); secondary pollutants form in the atmosphere (ozone, PANs, sulfuric acid).

Photochemical smog forms when NOx and volatile organic compounds react in sunlight, peaking in warm, sunny, low-wind conditions.

Industrial smog (gray smog) comes from coal combustion: SO2, particulates, and sulfuric acid.

Thermal inversion traps cool air under warm air, concentrating pollutants near the surface.

Acid deposition forms when SO2 and NOx convert to sulfuric and nitric acids; it acidifies lakes and mobilizes soil aluminum.

Stratospheric ozone is destroyed by CFCs releasing chlorine radicals; the Montreal Protocol phased out those compounds.

Indoor air pollution from biomass burning and radon is often a larger exposure risk than outdoor pollution.

Catalytic converters reduce CO, NOx, and hydrocarbons; scrubbers remove SO2 from smokestack gases.

Biomagnification concentrates fat-soluble, persistent toxins (e.g., methylmercury, DDT) at higher trophic levels.

Point-source pollution enters at a single identifiable location (pipe, outfall); nonpoint source is diffuse (runoff).

Dead zones form where nutrient-driven algal blooms decay and deplete dissolved oxygen below about 2 mg/L.

Wastewater treatment: primary (settling), secondary (biological digestion), tertiary (nutrient and pathogen removal).

Hazardous waste disposal options include secure landfills, incineration, and bioremediation; Superfund addresses abandoned sites.

LD50 is the dose killing 50% of a test population; lower LD50 means greater acute toxicity.

Endocrine disruptors mimic or block hormones at low doses, producing effects not predicted by high-dose testing.

Sanitary landfills require clay and synthetic liners plus leachate collection to protect groundwater.

Greenhouse gases: CO2, CH4, N2O, water vapor, and CFCs; methane has far higher warming potential per molecule than CO2 over 20 years.

The greenhouse effect is natural and necessary; the enhanced effect results from rising greenhouse gas concentrations.

Positive feedbacks amplify warming: permafrost thaw releasing methane, and reduced ice albedo.

Ocean acidification follows CO2 dissolving to form carbonic acid, lowering pH and hindering calcification in corals and shellfish.

Sea level rises from thermal expansion of water plus melting land ice; melting sea ice does not raise sea level.

Ozone depletion and climate change are separate problems: ozone absorbs UV, while greenhouse gases trap infrared.

Range shifts move species poleward and upslope as temperatures rise, disrupting phenology and migration timing.

Mitigation reduces emissions (renewables, efficiency); adaptation adjusts to impacts (sea walls, drought-resistant crops).