Your FREE AP Environmental Science Flashcards 2026 – 200+ Cards

Only about 10% of the energy at one trophic level is passed to the next; the rest (~90%) is lost as heat through cellular respiration.

A feeding position in a food chain: producers, primary consumers, secondary consumers, etc. Energy decreases at each higher level.

An organism that makes its own food, usually by photosynthesis (plants, algae); the base of the food chain.

A herbivore that eats producers (the second trophic level).

A carnivore that eats primary consumers (the third trophic level).

An organism (bacteria, fungi) that breaks down dead matter and recycles nutrients back into the ecosystem.

A network of interconnected food chains showing all the feeding relationships in a community.

The total rate at which producers capture and store energy through photosynthesis.

GPP minus the energy producers use for their own respiration; the energy available to consumers.

A species with a disproportionately large effect on its community; removing it dramatically changes the ecosystem (e.g., sea otters).

The movement of an element through the living and nonliving parts of an ecosystem (carbon, nitrogen, phosphorus, water).

Photosynthesis removes CO₂ from the air; respiration, decomposition, and combustion return it. Oceans, soils, and fossil fuels are reservoirs.

Conversion of inert N₂ gas into ammonia (NH₃/NH₄⁺) usable by organisms — done by bacteria, lightning, and the Haber-Bosch process.

The bacterial conversion of ammonium (NH₄⁺) to nitrite (NO₂⁻) and then nitrate (NO₃⁻), the form plants use most easily.

The bacterial conversion of nitrate (NO₃⁻) back into N₂ gas, returning nitrogen to the atmosphere.

Moves phosphorus through rock, soil, and water with NO atmospheric (gas) phase; phosphorus often limits aquatic plant growth.

The nutrient in shortest supply that caps growth; nitrogen often limits land plants, phosphorus often limits aquatic ones.

Water moves through evaporation, transpiration, condensation, precipitation, runoff, and infiltration into aquifers.

Process where producers use sunlight, CO₂, and water to make glucose and release oxygen; it stores energy and removes CO₂.

Process where organisms break down glucose with oxygen to release energy, returning CO₂ to the atmosphere.

A diagram showing energy decreasing at each higher trophic level, with producers at the wide base.

A large region defined by its climate and characteristic plant and animal communities (e.g., tundra, desert, rainforest).

The variety of life at three levels — genetic, species, and ecosystem diversity. Higher diversity = more resilience.

The number of different species in a community.

How balanced the populations of different species are in a community.

The variety of genes within a species; greater diversity helps a species adapt to change and resist disease.

Free benefits ecosystems provide: pollination, water filtration, flood control, climate regulation, and food.

The gradual, predictable change in a community over time after a disturbance, ending in a climax community.

Succession that begins on bare rock with no soil (after a glacier or lava flow); pioneer species are lichens and mosses.

Succession that rebuilds on existing soil after a disturbance (fire, abandoned farm); much faster than primary.

The first organisms to colonize a disturbed area (lichens, mosses, fast-growing weeds), which begin building soil.

A relatively stable, mature community in equilibrium with the local climate at the end of succession.

The ability of an ecosystem to recover after a disturbance; higher biodiversity generally increases resilience.

A species whose health reflects the condition of its environment (e.g., amphibians for water quality).

A species with a narrow niche and specific requirements (e.g., the panda); vulnerable to environmental change.

A species with a broad niche that can use many resources (e.g., raccoons); adaptable to change.

The role a species plays in its ecosystem — what it eats, where it lives, and how it interacts with others.

The theory that larger islands closer to the mainland support more species than small, remote ones.

A period when a large fraction of Earth's species go extinct over a short geologic time; Earth has had five.

A symbiotic relationship in which both species benefit (e.g., bees and flowers).

A relationship in which one species benefits and the other is unaffected (e.g., barnacles on a whale).

A relationship in which one species (the parasite) benefits at the host's expense.

An interaction where one organism hunts and eats another; their populations rise and fall in linked cycles.

The range of conditions (temperature, pH, salinity) an organism can survive; outside it, the organism cannot live.

The maximum population size an environment can support indefinitely given its resources.

J-shaped growth that occurs with unlimited resources; the population grows by a constant percent each interval.

S-shaped growth that slows as a population nears its carrying capacity and limiting factors increase.

A limiting factor that intensifies as population density rises: food shortage, disease, predation, competition.

A limiting factor that affects a population regardless of its density: weather, natural disasters, climate.

Species with many small offspring, little parental care, and short lives (insects, weeds); boom-and-bust populations.

Species with few large offspring, high parental care, and long lives (elephants, oaks); stable near carrying capacity.

Most individuals survive to old age then die quickly (humans, large mammals).

Most individuals die young in huge numbers; few survive to adulthood (fish, insects, plants).

Growth rate = (births − deaths + immigration − emigration). For a simple rate: (births − deaths) ÷ 10 per 1,000.

Doubling time (years) ≈ 70 ÷ the percent growth rate. A 2% growth rate doubles in about 35 years.

A four-stage model of how birth and death rates fall as a country develops.

The average number of children a woman has in her lifetime; about 2.1 is replacement level in developed nations.

The TFR (~2.1) at which a population exactly replaces itself, leading to stable size over time.

A graph of a population by age and sex; a wide base predicts rapid growth, a narrow base predicts decline.

The number of infant deaths per 1,000 live births; a key indicator of a country's development.

The time it takes a population to double in size, estimated with the rule of 70.

Anything that restricts the size of a population, such as food, water, space, or predators.

A sharp drop in numbers after a population overshoots its carrying capacity.

The maximum reproductive rate of a population under ideal conditions.

Immigration is individuals moving INTO a population; emigration is individuals moving OUT. Both change population size.

Continued population growth after fertility falls to replacement level, because of a large young population.

The movement of Earth's crustal plates, which causes earthquakes, volcanoes, and mountain-building at boundaries.

A layer in a soil profile, from O (organic litter) and A (topsoil) at the top down to C and bedrock.

The proportion of sand, silt, and clay in soil; it controls water and nutrient holding. Loam is best for farming.

A balanced mix of sand, silt, and clay that holds water and nutrients well — ideal agricultural soil.

The lowest atmospheric layer where weather occurs and most air mass and water vapor are found.

The atmospheric layer above the troposphere that contains the protective ozone layer.

A global circulation cell where air rises at the equator (wet) and sinks around 30° latitude (dry, where deserts form).

The deflection of moving air and water by Earth's rotation, which shapes global wind belts and ocean currents.

A periodic warming of the eastern Pacific that weakens trade winds, suppresses upwelling, and shifts global weather.

The cool phase of ENSO with stronger trade winds and cooler eastern Pacific water — the opposite of El Niño.

The rise of cold, nutrient-rich water from the deep ocean to the surface, supporting productive fisheries.

An underground layer of permeable rock or sediment that stores and transmits groundwater.

The land area that drains into a particular river, lake, or other body of water.

The fraction of sunlight a surface reflects; ice and snow are high (reflective), dark land and ocean are low (absorbent).

Long-term natural variations in Earth's orbit and tilt that drive ice ages — a natural, not human, climate driver.

The physical and chemical breakdown of rock at Earth's surface, the first step in soil formation.

The transport of weathered soil and rock by water, wind, or ice; worsened by removing vegetation.

The buildup of salts in soil from irrigation in dry climates, which reduces crop productivity.

How easily water and air move through soil or rock; sandy soil is highly permeable, clay is not.

The global ocean conveyor belt driven by differences in water temperature and salinity (density).

The dry region on the leeward side of a mountain, where descending air has lost its moisture.

Ground shaking from plate movement; the Richter (or moment magnitude) scale measures its energy.

The overuse of a shared, unregulated resource because individuals benefit while the cost of depletion is shared by all.

The 20th-century increase in crop yields through fertilizer, irrigation, pesticides, and high-yield seed varieties.

Plowing across a slope along its contour lines to reduce soil erosion and water runoff.

Planting without plowing, which keeps soil and moisture in place and stores carbon.

Alternating the crops grown in a field to restore soil nitrogen and break pest cycles.

Combining biological, mechanical, and limited chemical controls to manage pests with less pesticide.

Growing a single crop over a large area; efficient but vulnerable to pests and hard on soil.

Letting livestock eat vegetation faster than it regrows, leading to soil erosion and desertification.

The degradation of once-productive land into desert, often from overgrazing, deforestation, or drought.

Concentrated Animal Feeding Operation; raises many animals in a small area and generates large amounts of waste.

Harvesting a renewable resource no faster than it can replenish itself.

Removing surface layers to reach a shallow deposit; cheaper but highly destructive to the land.

A form of surface mining that blasts off mountain tops to reach coal, burying streams with debris.

Tunneling underground to reach deep deposits; costlier and more dangerous than surface mining.

Restoring land after mining by regrading, replacing topsoil, and replanting vegetation.

Catching fish faster than populations can reproduce, leading to collapse; managed with catch limits.

Farming fish and shellfish; boosts food supply but can pollute water and spread disease.

Removing all trees in an area at once; cheap but causes erosion and habitat loss.

The spread of low-density development outward from a city, consuming farmland and increasing car dependence.

The amount of productive land and water needed to supply a person's resources and absorb their waste.

Solutions to the tragedy of the commons: government quotas/regulation or assigning private ownership.

A vegetated zone along a waterway that filters runoff and reduces fertilizer and sediment pollution.

Energy from finite stocks formed over millions of years: coal, oil, natural gas, and nuclear fuel.

Energy from sources that replenish on a human timescale: solar, wind, hydro, geothermal, and biomass.

Coal, oil, and natural gas formed from buried ancient organisms; burning them releases CO₂ and pollutants.

The dirtiest fossil fuel; abundant and cheap but releases the most CO₂, SO₂, mercury, and particulates.

The cleanest-burning fossil fuel; releases less CO₂ than coal but leaks methane, a potent greenhouse gas.

Splitting uranium-235 atoms to release heat that boils water to spin a turbine; no CO₂ but radioactive waste.

Rods in a nuclear reactor that absorb neutrons to slow or stop the fission chain reaction.

Overheating that melts a reactor core and can release radiation (e.g., Chernobyl, Fukushima).

Converting sunlight directly into electricity with solar cells; clean but intermittent.

Using turbines to convert wind into electricity; clean and renewable but intermittent and location-dependent.

Generating electricity from flowing water, usually behind a dam; reliable but disrupts rivers and fish.

Using Earth's internal heat to generate electricity or heat buildings; steady and clean but location-limited.

Burning organic material (wood, crops, waste) for energy; renewable but releases CO₂ and air pollutants.

Reducing energy use through efficiency and behavior; the cheapest and cleanest 'source' of energy.

Getting more useful output from each unit of energy input (e.g., LED bulbs, hybrid cars).

Capturing waste heat from electricity generation to use for heating, raising overall efficiency.

A device that produces electricity from hydrogen and oxygen, emitting only water; clean but costly.

A market policy that sets a pollution limit and lets companies buy and sell emission allowances.

The usable energy from a source after subtracting the energy needed to produce it.

Unconventional fossil fuels that are energy- and water-intensive to extract and process.

Injecting high-pressure fluid to crack rock and release natural gas or oil; can contaminate groundwater.

Large dams provide renewable power and flood control but flood habitat, displace people, and block fish.

A pollutant emitted directly into the air (CO, SO₂, NOₓ, particulates, VOCs).

A pollutant that forms in the atmosphere from reactions of primary pollutants (e.g., ground-level ozone).

A brownish haze of ground-level ozone formed when sunlight reacts with NOₓ and VOCs on hot, sunny days.

A harmful secondary pollutant in smog that damages lungs and crops — 'bad' ozone, nearby.

A layer of warm air over cooler air near the ground that traps pollutants and worsens smog.

Tiny solid or liquid particles in the air (soot, dust); PM2.5 lodges deep in the lungs and harms health.

Precipitation acidified by sulfuric and nitric acids formed when SO₂ and NOₓ react with water in the air.

A pollutant from burning coal that contributes to acid rain and respiratory problems.

Pollutants from combustion that form smog and acid rain and contribute to ground-level ozone.

A colorless, odorless gas from incomplete combustion that binds hemoglobin and reduces oxygen delivery.

Carbon compounds that evaporate easily (from fuels, paints, solvents) and help form photochemical smog.

The U.S. law that regulates air pollutants and sets National Ambient Air Quality Standards.

A smokestack device that removes SO₂ and particulates from exhaust gases before they reach the air.

A device on cars that converts CO, NOₓ, and VOCs in exhaust into less harmful gases.

A device that uses an electric charge to remove particulates from smokestack exhaust.

A naturally occurring radioactive gas that seeps into buildings from soil; a leading cause of indoor lung cancer.

A fibrous mineral once used as insulation; inhaling its fibers causes lung disease and cancer.

Health problems linked to poor indoor air quality in a building, from VOCs, mold, and poor ventilation.

Smog from burning coal and oil, high in sulfur dioxide and particulates; common in industrial cities.

Pollutants inside buildings (radon, CO, VOCs, mold, asbestos), often a greater health risk than outdoor air.

Unwanted or harmful sound that can cause hearing loss and stress in humans and disrupt wildlife.

A toxic metal once in gasoline and paint that harms the nervous system, especially in children.

Nutrient enrichment of water (nitrogen, phosphorus) that triggers algal blooms; decay then depletes oxygen.

Human-accelerated eutrophication from fertilizer runoff, sewage, and detergents.

An area of water with too little dissolved oxygen to support most life, caused by eutrophication.

Pollution from a single identifiable source, such as a factory discharge pipe — easier to regulate.

Diffuse pollution from many sources, such as farm and street runoff — harder to control.

The amount of oxygen decomposers use to break down organic waste in water; high BOD starves water of oxygen.

The buildup of a persistent toxin in one organism's tissues over its lifetime.

The increase in a toxin's concentration at each higher trophic level, so top predators carry the most.

A persistent pesticide that biomagnified up food chains and thinned the eggshells of birds of prey like eagles.

A toxic metal from coal burning and mining that biomagnifies in fish and harms the nervous system.

A long-lasting, fat-soluble toxic chemical (DDT, PCBs) that biomagnifies and resists breakdown.

A graph showing how the harmful effect of a substance increases with the dose received.

The dose of a toxin that is lethal to 50% of a test population; a standard measure of toxicity.

A lined and covered site for solid waste, designed to protect groundwater from leachate.

Liquid that drains through a landfill, picking up contaminants that can pollute groundwater.

Burning solid waste to reduce its volume and generate energy; releases air pollutants and ash.

The waste hierarchy: reduce consumption first, then reuse, then recycle before disposal.

The first stage that physically removes solids from wastewater by screening and settling.

The biological stage that uses bacteria to break down dissolved organic waste in wastewater.

The release of heated water (often from power plants) that lowers dissolved oxygen and harms aquatic life.

Oil coats organisms and feathers, smothers habitats, and is hard to clean; harms birds, mammals, and fisheries.

The U.S. law that regulates pollutant discharges into surface waters and sets water-quality standards.

Natural warming when greenhouse gases (CO₂, methane, water vapor, nitrous oxide) absorb and re-emit Earth's infrared heat.

The extra warming caused by human emissions of greenhouse gases above natural levels.

The most abundant human-released greenhouse gas, mainly from burning fossil fuels and deforestation.

A greenhouse gas that traps far more heat per molecule than CO₂ but is less abundant; from livestock, landfills, and gas leaks.

The long-term rise in Earth's average surface temperature driven by the enhanced greenhouse effect.

Long-term shifts in temperature and weather patterns, largely driven by human greenhouse-gas emissions.

The drop in ocean pH as CO₂ dissolves to form carbonic acid, harming coral and shell-building organisms.

The rise in ocean levels from melting land ice and the thermal expansion of warming seawater.

A change that amplifies itself; melting ice lowers albedo, absorbing more heat and melting more ice.

As reflective ice melts it exposes dark land/ocean, which absorbs more heat and accelerates warming.

Thinning of the stratospheric ozone layer by chlorine from CFCs, letting more harmful UV reach the surface.

Chemicals once used in refrigerants and aerosols that release ozone-destroying chlorine in the stratosphere.

The 1987 treaty that phased out CFCs and is allowing the ozone layer to slowly recover — a major success.

Stratospheric ozone protects life from UV ('good up high'); ground-level ozone is a pollutant ('bad nearby').

A non-native species that spreads rapidly and harms an ecosystem, often lacking natural predators (zebra mussels, kudzu).

The drivers of biodiversity loss: Habitat destruction, Invasive species, Pollution, Population, Climate change, Overexploitation.

Breaking a large habitat into smaller, isolated patches, which reduces biodiversity and species movement.

A species at serious risk of extinction throughout all or much of its range.

The U.S. law that protects threatened and endangered species and their critical habitat.

A threshold beyond which a system shifts abruptly and often irreversibly to a new state (e.g., a dying coral reef).

International agreements to reduce greenhouse-gas emissions and limit global warming.

The total greenhouse gases produced by a person, product, or activity, expressed as CO₂ equivalent.

Capturing and storing atmospheric CO₂ in forests, soils, oceans, or underground to slow warming.

Clearing forests removes a carbon sink and releases stored carbon, worsening global warming.