This AP Environmental Science course reference brings together the major ideas students need for APES review, classwork, and exam preparation. It connects living systems, Earth systems, human impacts, and sustainability in one clear study sheet. Students need this cheat sheet because APES questions often combine science concepts, data interpretation, and real-world environmental decisions.
Key Facts
- The rule of 10 states that about 10 percent of energy is transferred from one trophic level to the next, while most energy is lost as heat.
- Population growth can be modeled by r = (births + immigration) - (deaths + emigration), where r is the change in population size.
- The ecological footprint measures the amount of biologically productive land and water needed to support a person, population, or activity.
- Primary productivity measures the rate at which producers convert solar energy into chemical energy, with NPP = GPP - respiration.
- Half-life is the time required for half of a radioactive substance to decay, and remaining amount = original amount x (1/2)^number of half-lives.
- Percent change = ((new value - old value) / old value) x 100, and it is commonly used to compare environmental data over time.
- Carbon dioxide, methane, nitrous oxide, and water vapor are greenhouse gases that trap outgoing infrared radiation and warm Earth’s surface.
- Sustainability means using resources at a rate that meets current needs without reducing the ability of future generations to meet their needs.
Vocabulary
- Ecosystem
- An ecosystem is a community of living organisms interacting with each other and with the nonliving environment.
- Biodiversity
- Biodiversity is the variety of life in an area, including genetic, species, and ecosystem diversity.
- Carrying Capacity
- Carrying capacity is the maximum population size an environment can support over time with available resources.
- Watershed
- A watershed is an area of land where all water drains into the same river, lake, or other body of water.
- Eutrophication
- Eutrophication is the enrichment of water by nutrients that can cause algal blooms and low dissolved oxygen.
- Renewable Resource
- A renewable resource is a natural resource that can be replenished on a human time scale if managed sustainably.
Common Mistakes to Avoid
- Confusing energy flow with matter cycling is wrong because energy moves one way through ecosystems while matter is recycled through biogeochemical cycles.
- Using the 10 percent rule as an exact value is wrong because it is an average estimate and real energy transfer efficiency can vary by ecosystem.
- Forgetting units in APES calculations is wrong because environmental data often requires units such as ppm, kWh, hectares, metric tons, or percent.
- Assuming renewable always means pollution-free is wrong because renewable energy and resources can still have land use, habitat, mining, or waste impacts.
- Mixing up weather and climate is wrong because weather describes short-term atmospheric conditions while climate describes long-term patterns over decades.
Practice Questions
- 1 A forest has a gross primary productivity of 2400 kcal/m2/year and plant respiration of 900 kcal/m2/year. What is the net primary productivity?
- 2 A town used 80,000 kWh of electricity last year and 92,000 kWh this year. What is the percent increase in electricity use?
- 3 A radioactive isotope has an original mass of 64 grams and a half-life of 10 years. How much remains after 30 years?
- 4 Explain why protecting biodiversity can make ecosystems more stable and resilient after a disturbance.
Understanding AP Environmental Science Course Reference
Environmental systems are connected by feedbacks. A feedback happens when a change causes effects that influence the original change. Negative feedback tends to keep a system within a stable range.
For example, plants take in carbon dioxide as they grow, which can reduce some carbon dioxide in the air. Positive feedback increases a change. Melting sea ice exposes darker ocean water, which absorbs more sunlight and leads to further warming.
Students should practice identifying the starting change, each link in the chain, and whether the final effect strengthens or weakens that change. Many climate, forest, and water questions depend on this reasoning.
Matter moves through ecosystems differently from energy. Atoms such as carbon, nitrogen, phosphorus, and water are reused through air, soil, rocks, organisms, and water bodies. Human activity can speed up or redirect these cycles.
Burning coal, oil, and gas moves carbon from long term underground storage into the atmosphere. Fertilizer adds reactive nitrogen and phosphorus to farm fields. Rain can carry excess nutrients into lakes or coastal water, causing algal blooms.
When algae die, decomposers use oxygen while breaking them down. Low oxygen can kill fish and create dead zones. The important skill is tracing a substance from its source to its environmental effect.
Population patterns require more than memorizing a growth model. A population may grow rapidly when resources are abundant, then slow as food, space, disease, predation, or waste become limiting. Carrying capacity is not a fixed number.
A drought can lower it for deer in a forest. Better sanitation or farming methods can raise it for people. Age structure diagrams give clues about future growth.
A wide base usually shows many young people who may increase the population as they reach reproductive age. In real communities, population change affects housing, water demand, transport, food production, and habitat loss. When reading graphs, check the units, time scale, and whether the graph shows a total, a rate, or a percentage.
Environmental decisions involve tradeoffs, evidence, and uncertainty. A solar farm can reduce emissions from electricity generation, though it may use land and affect local species. A dam can provide water storage and power, though it can change river flow, sediment movement, and fish migration.
Good analysis compares short term benefits with long term costs, then identifies who receives each outcome. Data questions often include misleading visual choices, such as a graph axis that starts above zero or two variables that change together without proof that one caused the other. Pay close attention to controls in experiments, sample size, repeated trials, and natural variation.
Percent change is useful for comparing places with different starting values, but a large percentage can come from a very small original amount. Clear environmental reasoning always connects a claim to specific evidence and explains the mechanism behind it.