IB ESS SL flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Open system

A system that exchanges both matter and energy across its boundaries with the surroundings; a forest or a lake is an example, unlike a closed system which exchanges only energy.

Negative feedback

A mechanism in which a change triggers a response that counteracts the original change, returning the system toward equilibrium; predator-prey regulation and temperature homeostasis are examples.

Tipping point

A threshold beyond which a system shifts irreversibly into a different stable state, such as permafrost collapse or Amazon dieback, after which recovery requires far greater effort.

Precautionary principle

The rule that lack of full scientific certainty should not delay action to prevent serious or irreversible environmental harm, shifting the burden of proof onto the proponent of an activity.

Net primary productivity

The energy or biomass fixed by producers that remains after their own respiration is subtracted; NPP equals gross primary productivity minus respiration, and it sets the energy available to consumers.

Trophic level

The feeding position an organism occupies in a food chain, such as producer, primary consumer or secondary consumer; energy transfer between levels is typically about ten percent.

Keystone species

A species whose influence on community structure is disproportionately large relative to its abundance; removing it causes major changes, as when sea otter loss triggers kelp deforestation.

Ecological succession

The progressive change in community composition over time; primary succession starts on bare substrate with pioneer species, while secondary succession follows disturbance where soil remains.

Simpson's reciprocal index

A measure of species diversity calculated as one divided by the sum of the squared proportional abundances of each species; higher values indicate greater richness and evenness.

In-situ conservation

Protection of species and habitats within their natural environment, using protected areas such as national parks and reserves, allowing ecological processes and interactions to continue.

Ex-situ conservation

Maintenance of species outside their natural habitat in zoos, aquaria, botanic gardens or seed banks; used as a backup but limited by small population size and loss of ecological context.

Edge effect

The altered conditions along the boundary of a habitat fragment, where light, wind and predation differ from the interior, reducing effective habitat area and favouring generalist species.

Eutrophication

Nutrient enrichment of water, usually by nitrates and phosphates, causing algal blooms whose decomposition depletes dissolved oxygen and can produce fish kills and dead zones.

Maximum sustainable yield

The largest harvest that can be taken from a population indefinitely without reducing its ability to regenerate; it corresponds roughly to the population size at half carrying capacity.

Aquifer

An underground layer of permeable rock or sediment that stores and transmits groundwater; abstraction faster than recharge lowers the water table and can cause subsidence or saltwater intrusion.

Biochemical oxygen demand

The amount of dissolved oxygen consumed by microorganisms decomposing organic matter in a water sample over a set period; high BOD indicates organic pollution and low oxygen availability.

Soil texture triangle

A classification diagram that assigns a soil name from the percentages of sand, silt and clay it contains; loam, a balanced mixture, generally offers the best fertility and drainage.

Leaching

The downward movement of dissolved nutrients through soil by percolating water, removing soluble ions from topsoil and depositing them in lower horizons or groundwater.

Salinisation

Accumulation of soluble salts in topsoil, typically from irrigation in arid regions where evaporation exceeds precipitation, reducing crop yields and eventually rendering land unusable.

Food security

A condition in which all people have reliable physical and economic access to sufficient, safe and nutritious food; it depends on availability, access, utilisation and stability.

Tropospheric ozone

A secondary pollutant formed when nitrogen oxides react with volatile organic compounds in sunlight; it damages lungs and crops and is a key component of photochemical smog.

Temperature inversion

A layer of warm air above cooler surface air that suppresses vertical mixing, trapping pollutants near the ground and concentrating smog, often in valleys or during winter anticyclones.

Global warming potential

A measure of how much energy a greenhouse gas traps over a set period compared with the same mass of carbon dioxide, allowing different gases to be compared on a common scale.

Acid deposition

The fallout of sulfuric and nitric acids formed when sulfur dioxide and nitrogen oxides react with water vapour; it acidifies soils and lakes and damages forests and stone buildings.

Radiative forcing

The change in the Earth's energy balance, measured in watts per square metre, caused by a factor such as greenhouse gases, aerosols or albedo change; positive values warm the climate.

Ice-albedo feedback

A positive feedback in which warming melts reflective ice, exposing darker ocean or land that absorbs more solar radiation, causing further warming and more melting.

Mitigation versus adaptation

Mitigation reduces the causes of climate change by cutting emissions or enhancing sinks; adaptation reduces vulnerability to impacts through measures such as sea defences and drought-resistant crops.

Energy security

Reliable, affordable and uninterrupted access to energy supplies; it depends on diversity of sources, domestic availability and resilience of transmission and import infrastructure.

Demographic transition model

A four-stage description of population change: high birth and death rates, then falling death rates and rapid growth, then falling birth rates, ending in low stable rates.

Population momentum

Continued population growth after fertility falls to replacement level, caused by a large cohort of young people now entering reproductive age; it can persist for decades.

IPAT equation

A model expressing environmental impact as the product of population size, affluence (consumption per person) and technology (impact per unit of consumption), used to analyse drivers.

Ecological footprint

The area of biologically productive land and water required to supply a population's resources and absorb its wastes, expressed in global hectares and compared with available biocapacity.

Waste hierarchy

A ranked preference for waste management: prevention first, then reuse, recycling, energy recovery and finally disposal; the ranking reflects the relative environmental burden of each option.