AP Environmental Science Last-Minute Review (Night Before)

The exam is tomorrow. This is not the time to learn new content — it's time to skim, consolidate, and rest. Spend 45 minutes on this page, then close your notes and sleep 8 hours.

The Four Biogeochemical Cycles (Memorize These)

Carbon Cycle

Atmosphere (CO₂) ↔ Biosphere ↔ Hydrosphere ↔ Lithosphere (fossil fuels, rocks)

Biotic: Photosynthesis (CO₂ → glucose), respiration (glucose → CO₂).
Abiotic: Atmospheric CO₂ dissolves in water; ocean surface ↔ deep ocean (slow).
Anthropogenic disruption: Fossil fuel combustion, deforestation (reduces carbon sink), cement production.
Effect: Excess atmospheric CO₂ → enhanced greenhouse effect → warming, ocean acidification.

Nitrogen Cycle

Atmosphere (N₂) ↔ Soil (NO₃⁻, NH₄⁺) ↔ Organisms

Fixation: Lightning or bacteria (Rhizobium) convert N₂ → NO₃⁻/NH₄⁺.
Nitrification: Bacteria oxidize NH₄⁺ → NO₃⁻ in soil.
Assimilation: Plants absorb NO₃⁻; animals eat plants.
Denitrification: Bacteria reduce NO₃⁻ → N₂ (returns to atmosphere).
Anthropogenic disruption: Synthetic fertilizer (Haber-Bosch process), livestock waste, fossil fuel combustion (NOₓ emissions).
Effect: Excess N in runoff → eutrophication → hypoxia ("dead zones"), algal blooms.

Phosphorus Cycle

Rock/Soil ↔ Water ↔ Organisms (No atmospheric component)

Weathering: Rock breakdown releases phosphate (PO₄³⁻) into soil.
Uptake: Plants absorb phosphate; animals consume plants.
Excretion & decay: Organisms release P back to soil/water.
Sedimentation: Phosphate settles to ocean floor (slow return to lithosphere via geological uplift).
Anthropogenic disruption: Phosphate mining, synthetic fertilizer, detergents, animal waste.
Effect: Excess P in water → eutrophication (same as excess N).

Water Cycle

Evaporation ↔ Transpiration ↔ Condensation ↔ Precipitation ↔ Infiltration ↔ Groundwater ↔ Runoff

Evaporation: Water from surface → atmosphere.
Transpiration: Water from plant leaves → atmosphere.
Condensation: Water vapor → clouds (cooling).
Precipitation: Rain/snow from clouds.
Infiltration: Water into soil → groundwater (aquifers).
Runoff: Water over land surface → rivers/streams → ocean.
Anthropogenic disruption: Dams (alter flow), deforestation (increase runoff, decrease infiltration), urban paving (reduce infiltration), irrigation (aquifer depletion).

💡 Cycle focus: Draw each one. Label: atmosphere, soil, water, organisms, human inputs. Revisit if any is fuzzy.

Energy Formulas (Know Cold)

Formula	Use
$10\% \text{ rule}$	Energy at each trophic level ≈ 10% of previous level. 100 kJ grass → 10 kJ herbivore → 1 kJ carnivore.
$N_t = N_0 e^{rt}$	Exponential growth. $r$ = intrinsic rate, $t$ = time.
$\frac{dN}{dt} = rN(1 - \frac{N}{K})$	Logistic growth. Inflection at $N = K/2$ .
Doubling time	$t = \frac{\ln(2)}{r} \approx \frac{0.693}{r}$ .
Percent change	$\frac{\text{new} - \text{old}}{\text{old}} \times 100\%$ .
Energy conversions	1 kWh = 3.6 MJ; 1 BTU ≈ 1,055 J; 1 gallon = 3.785 L.

Criteria Air Pollutants Reference

Pollutant	Source	Health/Environmental Effect
CO (carbon monoxide)	Incomplete combustion (cars, furnaces)	Binds hemoglobin; reduces O₂ to brain/heart. Lethal at high levels.
NO₂ (nitrogen dioxide)	Car exhaust, power plants	Respiratory damage; component of photochemical smog; contributes to acid rain.
SO₂ (sulfur dioxide)	Coal combustion, smelters	Respiratory irritation; precursor to acid rain (forms H₂SO₄).
O₃ (ground-level ozone)	Photochemical smog: NOₓ + VOCs + UV	Respiratory damage, reduced crop yields. (Note: stratospheric O₃ is protective.)
PM2.5 (particulate matter)	Combustion, dust, sea salt	Lodges in lungs; cardiovascular & respiratory disease.
Pb (lead)	Old paint, old pipes, leaded gas (rare now in US)	Neurological damage (especially children), reduced IQ, organ damage.

⚠️ Don't confuse: Ground-level O₃ (bad, photochemical smog) vs. stratospheric O₃ (good, UV shield). CFC → depletes stratospheric O₃ → more UV → skin cancer risk.

Climate Change: Drivers vs. Effects

Drivers (Causes of Warming)

Driver	Source	Radiative Forcing
CO₂	Fossil fuels, deforestation, cement (~55% of warming)	1.9 W/m²
CH₄	Livestock, rice paddies, wetlands, landfills, natural gas leaks (~16%)	0.5 W/m²
N₂O	Agriculture (fertilizer), manure (~6%)	0.2 W/m²

Effects (Results of Warming)

Effect	Mechanism	Consequence
Temperature rise	Increased atmospheric CO₂ & CH₄ trap more longwave radiation	Glacial melt, coral bleaching, range shifts.
Sea-level rise	Thermal expansion of water; ice sheet melt	Coastal flooding, island submersion, saltwater intrusion.
Ocean acidification	CO₂ + H₂O → H⁺ + HCO₃⁻ (pH ↓)	Shell/skeleton dissolution (pteropods, corals), reduced ocean productivity.
Species range shifts	Habitat becomes unsuitable; organisms migrate poleward/upslope	Extinction risk, altered predator-prey, invasive species.
Drought & flooding	Altered precipitation patterns; evaporation ↑	Crop failure, water scarcity, wildfires, floods.

🎯 Critical distinction: CO₂ causes warming (driver). Warming causes sea-level rise (effect). Don't mix them up in FRQs.

Top 10 Traps That Cost Real Points

Forgetting units on energy, population, or pollution calculations. Always write units (kWh, kg CO₂, fish, etc.).
Confusing climate driver and effect. "Climate change causes CO₂" is backwards. CO₂ is a driver of climate change.
Misapplying the 10% rule. It's about energy transfer, not biomass. 1000 kg of grass → 100 kg of herbivore (not 10 kg).
Missing tradeoffs on FRQ Type 2. Don't just list benefits; discuss environmental, economic, and social trade-offs.
Wrong growth model. Exponential: no carrying capacity, $N$ grows without bound. Logistic: carrying capacity $K$ , curve levels off. Match the scenario.
Not reading the FRQ fully. "Propose a solution" means say what, where, how much, and why. Not just "use solar energy."
Confusing point-source and nonpoint pollution. Point source: a pipe from a factory (easy to trace). Nonpoint: agricultural runoff, atmospheric deposition (diffuse, hard to trace).
Bioaccumulation vs. biomagnification. Bioaccumulation: one organism builds up a contaminant over time. Biomagnification: concentration increases up the food chain (predators have higher levels than prey).
Demographic transition stage confusion. Stage 2 (high birth rate, low death rate from medicine) = population explosion. Stage 4 (low birth, low death) = stable or shrinking. Don't flip them.
Ignoring the question's specific ask. "Design an investigation" needs hypothesis, IV, DV, control, and prediction. Miss one, lose points.

Skim the Units You're Weakest On

Weak on cycles? Draw the C, N, P, H cycles on a piece of paper right now. Label inputs and outputs. Burn the image in your head.

Weak on population math? Do one exponential problem: "Population is 2000, $r = 0.08$ , calculate after 10 years." Then one logistic: "Same $r$ and initial population, but $K = 10{,}000$ . At what population does growth rate peak?" (Answer: $K/2 = 5{,}000$ .)

Weak on FRQs? Read the FRQ practice guide → (10 min) and look at one worked example for each type.

Scoring Boundaries (Recent Years)

Out of 108 total points (50 MCQs + 3 FRQs × 10 ea. = 50 + 30 = 108 is not the exact formula; College Board rescales, but here's the ballpark):

5: ~70% of points (roughly 75+ raw)
4: ~58-70%
3: ~44-57%
2: ~32-43%
1: below ~32%

You only need ~64-65% to earn a 5. You can miss 35-40% of the exam and still top score. Don't panic if you don't know every detail.

Morning-of Checklist

☐ 8 hours of sleep (non-negotiable).
☐ Real breakfast: protein + slow carbs (eggs + oatmeal, not just sugar).
☐ 2 sharpened #2 pencils + blue/black pens.
☐ Photo ID + AP ID label sheet.
☐ Approved calculator + spare batteries (check batteries tonight).
☐ Water, light snack for the break.
☐ Arrive 30 min early.

During the Exam

Multiple Choice (Section I, 1.5 hrs):

Scan all 50 questions first (30 sec). Note which ones look familiar.
Start with easiest (usually cycles, simple definitions).
Mark & skip anything that takes >90 seconds on first pass. Come back if time.
Process of elimination: cross out obviously wrong answers first.
No second-guessing in final 10 minutes. Your first instinct is often right.

Free Response (Section II, 1.5 hrs for 3 FRQs):

Read all 3 FRQs (1 min). Mental note: which type is each (Design, Problem-Solve, Quantitative)?
Start with the one you're most confident on (usually builds momentum).
Write the setup before the answer. "I used $N_t = N_0 e^{rt}$ because the scenario specifies exponential growth." This earns partial credit if your arithmetic is off.
Always include units in final answer.
Don't leave anything blank. Partial credit on FRQs is generous.
Set up the integral/equation/calculation even if you run out of time.

One Last Thing

You've done the work. You know the cycles, the formulas, and the FRQ patterns. Trust your prep. The rubric wants to give you points — your job is to show your reasoning clearly enough that it can.

Breathe. Eat breakfast. Show up rested.

You've got this. 🎯

Need a full review? Skim the 3-Day Cram Plan → or drill FRQs →. Otherwise, close your laptop, rest, and see you on exam day.