AP Environmental Science 3-Day Cram Plan

You have three days until the AP Environmental Science exam. This is not the time to master all nine units from scratch — it's time to drill the highest-frequency topics that account for 70% of the points and lock in the FRQ patterns the College Board reuses.

This plan assumes ~4 focused hours per day. Finish every section in the checklist; if you're short on time, shorten the practice sets, not the topic coverage.

Day 1: Ecosystems, Biogeochemical Cycles & Population Dynamics (4 hrs)

The first 25-30 multiple-choice questions lean heavily on these foundations. These are core to everything in APES.

What to review (90 min)

Ecosystems & Energy Flow (Units 1–2)

• Biogeochemical cycles: carbon (atmosphere ↔ biosphere ↔ hydrosphere, fossil fuels), nitrogen (atmospheric N₂ → nitrates via bacteria, eutrophication return), phosphorus (weathering of rock → soil → water → sediment), water (evapotranspiration, infiltration, runoff).
• Energy flow: trophic levels, the 10% rule ($\text{Energy}_{\text{trophic level}} = \text{Energy}_{\text{previous level}} \times 0.1$), net primary productivity (NPP).
• Food webs vs. food chains: decomposers, bioaccumulation, biomagnification (concentration up the food chain).
• Ecosystem services: pollination, water filtration, nutrient cycling.

Population Dynamics (Unit 3)

• Growth models: exponential ($N_t = N_0 e^{rt}$), logistic ($N_t = \frac{K}{1 + (\frac{K-N_0}{N_0})e^{-rt}}$ or $\frac{dN}{dt} = rN(1 - \frac{N}{K})$).
• $r$ selection vs $K$ selection: rabbits vs. elephants, boom-and-bust vs. slow-and-steady.
• Demographic transition: Stage 1 (high birth/death), Stage 2 (high birth, low death), Stage 3 (low birth, low death), Stage 4 (low birth, low death), Stage 5 (aging population).
• Carrying capacity, density-dependent vs. density-independent factors.

💡 Highest leverage: Biogeochemical cycles appear on nearly every exam. Memorize the four main cycles and be able to identify human disruption (fossil fuels, fertilizers, deforestation).

What to practice (2.5 hrs)

• 25 mixed multiple-choice questions (half on cycles & ecosystems, half on population growth).
• 1 FRQ on a scenario involving population projections or ecosystem energy flow.
• Sketch the nitrogen cycle and label anthropogenic inputs.

Day 2: Earth Systems, Energy Resources & Consumption (4 hrs)

These topics account for 20-25% of exam points and are easier to gain points on than pollution (which is more detailed).

What to review (90 min)

Earth Systems & Resources (Units 4–5)

• Plate tectonics: convergent/divergent/transform boundaries, volcanoes, earthquakes, mining/mineral extraction impacts.
• Soil formation: weathering, O/A/B/C horizons, soil fertility, erosion, salinization.
• Atmosphere & weather: greenhouse gases (CO₂, CH₄, N₂O), ozone layer (CFC link), Coriolis effect, jet streams, inversion layers.
• Water systems: watersheds, eutrophication (nitrate/phosphate runoff), thermal stratification, aquifers.
• Agriculture & land use: monoculture, irrigation (salinization, aquifer depletion), deforestation, desertification, urbanization.

Energy Resources (Unit 6)

• Fossil fuels: coal/oil/natural gas formation, extraction, combustion emissions (CO₂, SOₓ, NOₓ, particulates).
• Renewable energy: solar (efficiency ~15-20%), wind (capacity factor ~25-40%), hydro (impacts: methane from reservoirs, ecosystem disruption), geothermal (limited geography).
• Nuclear: fission reactor, half-life, waste disposal, carbon-low but upfront cost.
• Energy efficiency: SEER rating, LED vs. incandescent, building insulation, R-values.

⚠️ FRQ trap: When comparing energy sources, don't just say "solar is clean." Quantify: lifecycle CO₂ (grams per kWh), land use (acres/MW), water consumption. Feasibility matters: solar in Alaska is not practical.

What to practice (2.5 hrs)

• 20 mixed multiple-choice questions on earth systems and energy.
• 1 FRQ on energy efficiency or renewable feasibility (e.g., "A town wants to reduce coal reliance by 50%. Propose a realistic mix and justify trade-offs").
• Calculate percent change in carbon footprint using $\frac{\text{new} - \text{old}}{\text{old}} \times 100$.

Day 3: Pollution, Climate Change & Full FRQ Practice (4 hrs)

What to review (90 min)

Atmospheric & Aquatic Pollution (Units 7–8)

• Criteria air pollutants: CO (incomplete combustion), NO₂/NOₓ (acid rain, respiratory), SO₂ (acid rain, coal), O₃ (photochemical smog), particulates (PM2.5, lung damage), Pb (banned in US but still a concern).
• Photochemical smog: NOₓ + VOCs + UV → ground-level O₃. London smog (sulfurous) vs. LA smog (photochemical).
• Acid rain: SO₂ + NO₂ → H₂SO₄ + HNO₃. pH < 5.6 defined as acid. Effects: lakes (fish), forests, structures.
• Eutrophication: excess N/P → algae bloom → hypoxia ("dead zone"). Mississippi River example.
• Water pollution: point source (factory pipe) vs. nonpoint (runoff, atmospheric deposition). Bioaccumulation & biomagnification.
• Solid & hazardous waste: landfill leachate, incineration (ash toxins), nuclear waste (half-life concern), e-waste (heavy metals).

Global Change & Climate (Unit 9)

• Ozone depletion: CFCs → Cl radicals → O₃ destruction. Montreal Protocol success story.
• Climate change drivers: CO₂ (fossil fuels, deforestation), CH₄ (rice paddies, livestock, wetlands, landfills), N₂O (agriculture), radiative forcing.
• Climate effects: sea-level rise (thermal expansion + melting ice), ocean acidification ($\text{CO}_2 + \text{H}_2\text{O} \rightarrow \text{H}^+ + \text{HCO}_3^-$, lowering pH), species migration/extinction, drought/flooding.
• Mitigation vs. adaptation: carbon sequestration, renewable transition vs. coastal engineering, crop breeding.
• Invasive species & conservation: island biogeography (extinction risk), genetic diversity, protected areas.

🎯 Most commonly missed on FRQs: Confusing climate forcing factors (what causes warming) with climate effects (what results). CO₂ is a driver; sea-level rise is an effect.

What to practice (2.5 hrs — timed full FRQ set)

• 1 full Design-an-Investigation FRQ on water quality or air pollution.
• 1 full Problem-Solving FRQ on mitigation strategies (e.g., propose CO₂ reduction in a city; identify economic/social/environmental trade-offs).
• 20 mixed multiple-choice (calculator + concept), strictly timed.

FRQ format reminder

The three FRQ types:

1. Design an Investigation: ID hypothesis, independent/dependent variables, control, predict outcomes.
2. Analyze Problem & Propose Solution: given a scenario (e.g., mercury in fish), propose mitigation and identify trade-offs.
3. Quantitative Analysis: math with dimensional analysis, percent change, energy unit conversion (J ↔ kJ ↔ kWh).

Before bed

Read our last-minute-review. Get 8 hours of sleep — your brain needs it to consolidate biogeochemical cycles and distinguish climate drivers from effects.

What this 3-day plan skips

You will not fully relearn island biogeography or detailed mineral extraction in 3 days. Skim the formulas, do 1-2 example problems, and accept you may lose 2-3 points. Spend the saved time mastering cycles, energy, and pollution instead.

Common point-leaks

• Forgetting units on energy calculations (J vs. kJ vs. kWh).
• Confusing source vs. effect of climate change (CO₂ is a source, warming is an effect).
• Missing the "10% rule" on energy flow questions.
• Not identifying both the problem and the solution in two-part FRQs.
• Writing "renewable energy" without specifying which type or feasibility constraints.

Ready to start?

Open the AP Environmental Science topic library → and start with whichever Day 1 topic you feel weakest on. Work through 3-5 problems per topic. You've got this.