AP Environmental Science Unit 1 Vocabulary

A comprehensive collection of vocabulary flashcards covering key concepts from AP Environmental Science Unit 1 (The Living World: Ecosystems), including biogeochemical cycles, terrestrial and aquatic biomes, trophic levels, productivity formulas, and ecological structure.

Biogeochemical Cycle

The self-regulating pathways by which chemical molecules rotate through living (biotic) and non-living (abiotic) systems.

Reservoir

A location or temporary storage pool (such as atmosphere, ocean, or ice caps) where water or nutrients sit for varying amounts of time.

Source

A process or reservoir that releases more nutrients or matter into the environment than it accumulates.

Sink

A process or reservoir that absorbs and stores more nutrients or matter than it releases.

Flux

The movement of matter between pools or reservoirs in a biogeochemical cycle.

Carbon Cycle

The movement of carbon atoms through biotic processes (photosynthesis, respiration) and abiotic reservoirs (atmosphere, oceans, sedimentary rocks).

Photosynthesis

The process by which autotrophs pull carbon from the atmosphere ($CO_2$) to create chemical energy ($C_6H_{12}O_6$), acting as a critical short-term carbon sink.

Cellular Respiration

The process by which living organisms break down organic glucose, releasing $CO_2$ back into the atmosphere as a short-term carbon source.

Decomposition

The breaking down of dead organic matter by microorganisms, returning carbon to the soil or releasing $CO_2$ through microbial respiration.

Sedimentation & Burial

A long-term geological sink where dead organic material is trapped under heat and pressure, turning over millions of years into limestone rock or fossil fuels.

Combustion

The burning of organic material (biomass or fossil fuels) that rapidly converts long-term stored carbon into atmospheric $CO_2$.

Nitrogen Fixation

The step where unusable atmospheric nitrogen ($N_2$) is converted into biologically accessible forms like ammonia ($NH_3 / NH_4^+$) by specialized bacteria (like Rhizobium in legume roots) or lightning.

Nitrification

The process where soil bacteria convert toxic ammonia ($NH_4^+$) first into nitrites ($NO_2^-$) and then into highly usable nitrates ($NO_3^-$).

Assimilation

The process where plants absorb nitrates or ammonium through their roots and synthesize them into organic proteins and nucleic acids.

Ammonification (Mineralization)

The process where decomposers break down dead tissue and animal waste, converting organic nitrogen back into inorganic ammonia ($NH_4^+$).

Denitrification

The process where anaerobic soil bacteria convert nitrates ($NO_3^-$) back into $N_2$ gas, returning it to the atmosphere.

Phosphorus Cycle

The slow movement of phosphorus through rocks, water, soil, and organisms, which lacks an atmospheric gas phase entirely.

Weathering

The mechanical or chemical breakdown of rocks that releases phosphate ions ($PO_4^{3-}$) into the soil and waterways.

Limiting Nutrient

A resource that is in short supply and constrains the growth of an entire organism or population, with phosphorus typically serving this role in freshwater systems.

Algal Bloom

A rapid explosion of algae populations caused by excess nutrient runoff (nitrogen/phosphorus) entering water bodies.

Hypoxia

A condition of severely low oxygen levels in water bodies caused when massive algal blooms die and decompose.

Dead Zone

An area created by hypoxia where aquatic life suffocates due to severely depleted oxygen levels.

Hydrologic Cycle

The continuous cycle of water powered by solar energy moving through the biosphere.

Evaporation

The transformation of liquid water into atmospheric water vapor due to heat from the sun.

Transpiration

The evaporation of water directly out of the stomata (microscopic pores) of plant leaves.

Evapotranspiration

The combined amount of water leaving an ecosystem via evaporation from the soil plus transpiration from plants.

Infiltration

The initial entry of surface water downward into the top layers of soil.

Percolation

The deep movement of water through sub-soil and rock layers down into groundwater aquifers.

Runoff

Water from precipitation that flows over the landscape rather than sinking into the ground, often carrying sediments and nutrients into local waterways.

Primary Productivity

The total rate at which solar energy is captured and converted into organic compounds via photosynthesis in a given area over time.

Gross Primary Productivity (GPP)

The total amount of solar energy captured by producers via photosynthesis before any energy is used for survival.

Net Primary Productivity (NPP)

The remaining energy stored by producers after accounting for the energy they consume through cellular respiration, determined by the formula $\text{NPP} = \text{GPP} - \text{Respiration}$.

Biomass

The total mass of all dry organic matter within a specific trophic level or designated area.

Trophic Levels

The successive, hierarchical levels of an ecosystem where organisms obtain energy based on what they eat.

Producers (Autotrophs)

Organisms at the base of the food chain that make their own food using sunlight (photosynthesis) or chemical energy (chemosynthesis).

Consumers (Heterotrophs)

Organisms that cannot produce their own energy and must eat other living things, divided into primary, secondary, and tertiary consumers.

Decomposers

Organisms like bacteria and fungi that secrete enzymes to chemically break down and recycle organic elements back into the ecosystem.

Detritivores

Organisms like earthworms and woodlice that physically consume and break down dead organic matter.

The 10% Rule

The principle stating that only about $10\%$ of the usable energy at one trophic level successfully transfers up to the next level.

First Law of Thermodynamics

The principle stating that energy cannot be created or destroyed, only changed in form.

Second Law of Thermodynamics

The law stating that as energy is transferred, its quality degrades and entropy increases, resulting in $90\%$ of energy being lost as low-quality metabolic heat between trophic levels.

Food Chain

A linear sequence showing a single, direct path of energy and consumption transfers through an ecosystem.

Food Web

A highly complex, realistic model of interconnected food chains that illustrates multiple pathways of matter and energy transfers between species.

Trophic Cascade

A chain reaction triggered by the addition or removal of a top predator, which alters the balance of lower trophic levels and can collapse an entire ecosystem structure.

Ecology

The study of relationships between organisms and their environment.

Species

A group of organisms capable of reproducing with one another and producing fertile offspring.

Population

All individuals of the same species living in the same area.

Community

All populations of different species living and interacting in an area, representing living organisms only.

Ecosystem

A community of organisms together with the nonliving environment with which they interact.

Biome

A large ecological region characterized primarily by climate and dominant vegetation.

Biosphere

All parts of Earth where life exists, representing the sum of all ecosystems.

Biotic Factor

A living or once-living component of an ecosystem, such as plants, animals, fungi, and bacteria.

Abiotic Factor

A nonliving component of an ecosystem, such as temperature, sunlight, water, soil, salinity, and nutrients.

Niche

The ecological role of a species, including the resources it uses and its interactions with other organisms and the environment.

Terrestrial Biome

A major land-based ecosystem characterized by temperature, precipitation, and dominant vegetation.

Climatogram

A graph showing average monthly temperature and precipitation for a location.

Permafrost

Permanently frozen soil beneath the surface, characteristic of the tundra biome.

Leaching

The movement of dissolved nutrients downward through soil due to water.

Disturbance

An event such as a fire, flood, drought, or storm that changes an ecosystem.

Littoral Zone

Shallow area near the shore of a lake or pond where sunlight reaches the bottom and rooted plants can grow.

Limnetic Zone

Open, sunlit surface water away from the shore in a lake or pond.

Profundal Zone

Deep water in a lake or pond receiving little or no sunlight.

Benthic Zone

The bottom surface and sediments of an aquatic ecosystem.

Wetland

An area where soil is saturated or covered by water for at least part of the year, providing water filtration, flood control, groundwater recharge, wildlife habitat, and carbon storage.

Estuary

A coastal area where freshwater from rivers mixes with saltwater from the ocean, serving as a shallow, nutrient-rich, and well-lit nursery habitat.

Coral Bleaching

The loss of symbiotic algae from coral due to stress, often caused by unusually warm water.

Photic Zone

The upper layer of an aquatic ecosystem receiving enough sunlight for photosynthesis.

Aphotic Zone

The region of an aquatic ecosystem receiving insufficient sunlight for photosynthesis.