IB ESS SL key terms

A set of interconnected parts that work together as a whole, with inputs, outputs, stores and flows of energy or matter, and boundaries chosen by whoever is studying it.

A circular process in which a change in a store causes a further change that either amplifies the original change (positive feedback) or reduces it (negative feedback), affecting how stable a system is.

A feature or behaviour that appears when parts of a system interact but cannot be predicted from studying the parts alone, such as the stability of a food web.

A threshold beyond which a system changes rapidly and often irreversibly into a different state, because positive feedbacks take over once the threshold is crossed.

The ability of a system to absorb disturbance and reorganise while keeping the same basic structure and functions, so it keeps supplying the same goods and services.

A measure of how dispersed or disordered energy is. In any energy transfer some energy becomes less useful, so ecosystems need a constant input of high-quality energy to stay organised.

The area of biologically productive land and water needed to supply a population with the resources it uses and to absorb the wastes it produces, usually expressed in global hectares per person.

Development that meets the needs of people today without reducing the ability of future generations to meet their own needs, balancing social, economic and environmental objectives.

The stocks of natural resources and ecosystem processes that yield a flow of useful goods and services, such as forests, soils, fisheries and the atmosphere's capacity to absorb waste.

The benefits people obtain from ecosystems, grouped as provisioning (food, water, timber), regulating (climate, flood control), supporting (nutrient cycling, soil formation) and cultural (recreation, identity).

The position an organism occupies in a food chain, defined by how many energy-transfer steps separate it from the original energy source, such as producer, primary consumer or secondary consumer.

The rate at which biomass is produced. Gross primary productivity is the total energy captured by producers; net primary productivity is what remains after their respiration and is available to consumers.

The increase in concentration of a persistent, fat-soluble pollutant at each successive trophic level, so top predators accumulate doses far higher than those in the surrounding environment.

The build-up of a substance inside an organism's body over its lifetime, because the rate of intake exceeds the rate at which the substance is broken down or excreted.

The maximum population size of a species that a given environment can support indefinitely, given the food, water, space and other resources available and the wastes produced.

The resource or condition that is in shortest supply relative to need and therefore controls the growth, distribution or abundance of a population or the rate of a process.

A species whose effect on its community is much larger than its abundance suggests; removing it causes major changes to the structure of the ecosystem, as with sea otters and kelp forests.

A region with exceptionally high numbers of endemic species that has already lost a large proportion of its original habitat, so it is a priority for conservation funding and protection.

A species found naturally in one restricted area and nowhere else, which makes it especially vulnerable to habitat loss, invasive species and other local disturbances.

Protecting species and habitats where they naturally occur, for example through national parks, marine protected areas and habitat corridors, so ecological processes continue intact.

Protecting species outside their natural habitat, such as in seed banks, zoos or botanic gardens, useful as a backup but unable to preserve the full range of ecosystem interactions.

Nutrient enrichment of a water body, usually by nitrates and phosphates, causing algal blooms; when these decay, oxygen is used up and fish and other animals may die.

The amount of dissolved oxygen consumed by microorganisms breaking down organic matter in a water sample over a set period, used as an indicator of organic pollution.

A condition in which dissolved oxygen in water falls so low that most animal life cannot survive, often creating a dead zone below nutrient-enriched coastal waters.

The cloudiness of water caused by suspended particles such as silt, clay or algae, which reduces light penetration and can smother aquatic plants and animals.

The build-up of soluble salts in soil or water, often from irrigation with salty water and high evaporation, which reduces soil fertility and can make land unfit for crops.

The removal of the fertile top layer of soil by wind or water, usually accelerated by removing vegetation, overgrazing or poor cultivation, which reduces productivity and can silt up rivers.

The relative proportions of sand, silt and clay particles in a soil, which determine how well it holds water and nutrients and how easily air moves through it.

The downward movement of dissolved nutrients and minerals through soil with percolating water, removing them from the root zone and potentially polluting groundwater.

The degradation of dryland ecosystems into desert-like conditions through a combination of drought, overgrazing, deforestation and poor irrigation, reducing their capacity to support people.

Growing a single crop species over a large area, which raises efficiency but reduces genetic and habitat diversity and increases vulnerability to pests and disease.

The state in which all people have reliable physical and economic access to enough safe, nutritious food to meet their dietary needs for an active, healthy life.

The proportion of incoming solar radiation reflected by a surface; bright surfaces such as snow and ice have high albedo, dark surfaces such as ocean and forest have low albedo.

The warming of the lower atmosphere as gases such as carbon dioxide, methane and water vapour absorb outgoing infrared radiation and re-emit it towards the Earth's surface.

The change in the balance between incoming and outgoing energy at the top of the atmosphere caused by a factor such as a greenhouse gas or aerosol, measured in watts per square metre.

The total greenhouse gas emissions, expressed as carbon dioxide equivalent, caused directly or indirectly by a person, organisation, product or activity over a defined period.

Action that reduces the causes of climate change, such as cutting greenhouse gas emissions, improving energy efficiency or increasing carbon sinks, as opposed to adapting to its effects.

Adjustment to actual or expected climate effects that reduces harm or exploits opportunities, for example flood defences, drought-resistant crops or early-warning systems.