TASC Environmental Science Level 3 cheat sheet

Environmental Science

• Matter cycles through ecosystems; energy flows directionally. Biogeochemical cycles (carbon, nitrogen, phosphorus, water) recycle atoms, while energy from the sun is lost as heat at each trophic transfer.

• The 10% rule: roughly 10% of energy at one trophic level transfers to the next; the remainder is lost as heat through respiration. This limits food chains to about four to five levels.

• Primary productivity is the rate at which producers convert solar energy into biomass. Gross primary productivity (GPP) minus respiration equals net primary productivity (NPP), the energy available to consumers.

• Population growth: exponential growth follows N(t) = N0·e^(rt); logistic growth adds a carrying capacity K, slowing growth as N approaches K. r-strategists favor rapid reproduction; K-strategists favor few, well-cared offspring.

• Carrying capacity (K) is the maximum population an environment sustains given available resources. Overshoot causes dieback; sustainable yield keeps harvest at or below the population's regeneration rate.

• The greenhouse effect: greenhouse gases (CO2, CH4, N2O, water vapor) absorb outgoing infrared radiation and re-emit it, warming the surface. Enhanced greenhouse warming results from human emission increases.

• Air pollution standards: primary pollutants are emitted directly (CO, SO2, NOx, particulates); secondary pollutants form in the atmosphere (ozone, smog). Photochemical smog forms when NOx and VOCs react under sunlight.

• Water quality indicators include dissolved oxygen (DO), biological oxygen demand (BOD), pH, turbidity, and nutrient levels. High BOD signals organic pollution because microbes consume oxygen while decomposing waste.

• Rock cycle and soil: weathering breaks rock into parent material; soil horizons (O, A, E, B, C, R) develop over time. Soil texture (sand, silt, clay proportions) governs water retention and fertility.