Key Terms: Ecosystems & Processes (AQA A Level Geography): Revision Note

Nature of ecosystems - key terms

Abiotic factors – Non-living components of an ecosystem such as sunlight, temperature, soil, water, and wind.

Autotrophs (Producers) – Organisms that produce their own food from inorganic materials, mainly through photosynthesis.

Biomass – The total mass of living material in a given area or volume; also a store of energy within ecosystems.

Biotic factors – The living components of an ecosystem, including plants, animals, and microorganisms.

Community – All the different populations of organisms that live together in a particular area and interact with one another.

Consumers – Organisms that cannot produce their own food and must consume other organisms for energy (heterotrophs).

Decomposers – Organisms such as bacteria and fungi that break down dead matter, recycling nutrients back into the ecosystem.

Detritivores – Animals that feed on fragments of dead and decaying organic matter, aiding decomposition.

Ecosystem – A community of interacting living organisms and their physical environment.

Food chain – A linear sequence showing the transfer of energy and nutrients from one organism to another.

Food web – A complex network of interconnected food chains showing the feeding relationships in an ecosystem.

Interdependence – The reliance of living organisms on each other for survival, such as for food, shelter, and reproduction.

Open system – An ecosystem that exchanges both energy and matter with its surroundings.

Photosynthesis – The process by which green plants use sunlight to synthesise food from carbon dioxide and water.

Respiration – The process by which organisms break down glucose to release energy for cellular processes.

Trophic level – Each step in a food chain or web, representing a level of feeding (e.g. producer, primary consumer).

Nutrient cycling - key terms

Biomass store – Nutrients stored in living organisms within an ecosystem.

Decomposition – The breakdown of organic matter into simpler substances by bacteria, fungi, and detritivores.

Gersmehl diagram – A circular model used to show nutrient flows and stores within an ecosystem (biomass, litter, soil).

Inputs – Nutrients added to the ecosystem via precipitation and weathering of rock.

Litter store – Accumulation of dead plant and animal material on the ground.

Leaching – The loss of nutrients from soil due to rainwater washing them away.

Mineral nutrients – Essential elements such as nitrogen, phosphorus, potassium, and sulphur required by organisms for growth and metabolism.

Nutrient cycle – The continuous movement of nutrients through the biotic and abiotic components of an ecosystem.

Outputs – Nutrients lost from the ecosystem, often through runoff or leaching.

Soil store – Nutrients stored in the soil, made available through weathering, decomposition, and litterfall.

Transfers – Movements of nutrients between stores, such as from litter to soil via decomposition.

Terrestrial ecosystems - key terms

Biome – A large-scale ecological area defined by its climate, soil, flora, and fauna (e.g. rainforest, desert, tundra).

Desert – A biome with low precipitation (less than 250mm/year) and sparse vegetation; includes hot and cold deserts.

Forest – A terrestrial ecosystem dominated by trees and a variety of plants and animals; includes tropical, temperate, and boreal types.

Grassland – An ecosystem where grasses are the dominant vegetation; includes tropical savannas and temperate grasslands.

Latitude – A geographical factor influencing climate and therefore the type of biome found in a region.

Soil – The top layer of the Earth’s surface that supports plant life, influenced by climate, geology, and organic matter.

Temperature – A key factor determining the type of vegetation and organisms that can thrive in a given area.

Topography – The shape and features of land surfaces that influence drainage, exposure, and vegetation patterns.

Tundra – A cold biome with limited vegetation, found in polar and high-altitude regions.

Changing ecosystems - key terms

Climate change – Long-term shifts in global or regional climate patterns, significantly impacting ecosystems and species distributions.

Deforestation – The removal of trees and forested areas, often leading to habitat loss, reduced biodiversity, and ecosystem degradation.

Desertification – The process by which fertile land becomes desert due to drought, deforestation, or inappropriate agriculture.

Ecological collapse – A drastic reduction in the carrying capacity of an ecosystem, often due to rapid environmental change.

El Niño – A natural climate pattern that disrupts weather globally, often bringing floods or droughts that affect ecosystems.

Human exploitation – Activities such as agriculture, urbanisation, pollution, and resource extraction that alter ecosystems.

Invasive species – Non-native species introduced by human activity that disrupt ecosystems and outcompete native species.

Natural change – Environmental shifts that occur without human influence, such as volcanic eruptions or glacial cycles.

Plagioclimax – A stable ecosystem maintained by human activity or interference, preventing it from reaching its climatic climax.

Positive feedback loop – A cycle in which change reinforces itself, such as increased wildfires releasing more CO₂, which increases warming and further fires.

Restoration – Conservation efforts aimed at returning ecosystems to their natural state or improving biodiversity and function.

Seasonal shifts – Regular changes in climate and daylight that influence growing seasons and animal behaviour.

Succession – The natural and gradual process of change in the species composition of an ecosystem over time.