Ecosystem
A community of living organisms interacting with each other and with their nonliving environment within a defined area.
Energy FlowTrophic level
A position in a food chain — producer, primary consumer, secondary consumer, tertiary consumer, or decomposer.
Energy FlowProducer (autotroph)
An organism that converts solar (or chemical) energy into chemical energy through photosynthesis or chemosynthesis. Forms the base of every food chain.
Energy FlowConsumer (heterotroph)
An organism that obtains energy by eating other organisms. Primary consumers eat producers; secondary consumers eat primary consumers, and so on.
Energy FlowDecomposer
An organism (like fungi or bacteria) that breaks down dead organic matter, releasing nutrients back into the ecosystem for producers to reuse.
Energy Flow10% rule
The generalization that only about 10% of the energy at one trophic level is transferred to the next; the rest is lost as heat through cellular respiration.
Energy FlowGross primary productivity (GPP)
The total rate at which producers convert solar energy into chemical energy through photosynthesis.
Energy FlowNet primary productivity (NPP)
GPP minus the energy producers use for their own respiration. This is the energy actually available to consumers.
Energy FlowFood web
A network of interconnected food chains showing the many feeding relationships in an ecosystem, rather than a single linear path.
Energy FlowBiome
A large geographic region defined by characteristic climate, vegetation, and animal life. Examples: tundra, taiga, desert, tropical rainforest.
BiomesTundra
The coldest biome, with permafrost, low precipitation, and low biodiversity. Found at high latitudes and elevations.
BiomesTaiga (boreal forest)
A cold biome dominated by coniferous evergreen trees, with long winters and short growing seasons; located south of the tundra.
BiomesTropical rainforest
A biome with high temperature and very high year-round precipitation, producing the highest biodiversity of any biome but nutrient-poor soil.
BiomesDesert
A biome defined by very low precipitation (under 25 cm/year); can be hot or cold. Organisms are adapted to conserve water.
BiomesEstuary
A highly productive ecosystem where a freshwater river meets the salty ocean, creating a nutrient-rich, brackish-water habitat.
BiomesWetland
Land saturated with water (fresh, salt, or brackish) that supports water-tolerant vegetation; includes marshes, swamps, and bogs.
BiomesBiogeochemical cycle
The movement of a chemical element through living organisms (the "bio") and the physical environment — rock, water, atmosphere (the "geo" and "chemical").
CyclesCarbon cycle
The movement of carbon among the atmosphere, oceans, land, and organisms via photosynthesis, respiration, decomposition, and combustion.
CyclesCarbon sink
A reservoir (like a forest or ocean) that absorbs more carbon than it releases, reducing atmospheric CO2.
CyclesNitrogen fixation
The conversion of atmospheric nitrogen gas (N2) into a usable form like ammonia (NH3), carried out by nitrogen-fixing bacteria.
CyclesNitrification
The conversion of ammonia into nitrite and then nitrate by nitrifying bacteria — nitrate is the form most plants absorb.
CyclesDenitrification
The conversion of nitrate back into nitrogen gas by denitrifying bacteria, completing the nitrogen cycle.
CyclesPhosphorus cycle
The movement of phosphorus through rock weathering, soil, and water — unlike carbon and nitrogen, phosphorus has no significant atmospheric gas phase.
CyclesEutrophication
Excess nutrients (especially N and P) entering water causing algal blooms; decomposition of the algae depletes dissolved oxygen and kills aquatic life.
CyclesLimiting nutrient
The nutrient in shortest supply relative to demand, which restricts growth. Phosphorus typically limits freshwater systems; nitrogen typically limits marine systems.
Cycles