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An ecosystem is a community of living organisms (plants, animals, microorganisms) interacting with each other and with their non-living environment (soil, water, climate). Understanding ecosystems is the foundation of the entire Living World topic for AQA GCSE Geography. This lesson covers what ecosystems are, how they function, and introduces the concept of global-scale biomes.
An ecosystem can be as small as a pond or a hedgerow, or as vast as the Amazon rainforest. Every ecosystem has two fundamental components:
| Component | Definition | Examples |
|---|---|---|
| Biotic | The living parts of the ecosystem | Plants, animals, fungi, bacteria |
| Abiotic | The non-living, physical parts of the ecosystem | Climate, soil, water, light, temperature |
These two components are constantly interacting. For example, the amount of rainfall (abiotic) determines which plants (biotic) can grow in an area, and those plants in turn provide food and shelter for animals (biotic).
Exam Tip: A common exam question asks you to define the terms biotic and abiotic with examples. Make sure you can give at least two examples of each without hesitation.
Before going further, you need to be completely comfortable with these terms:
| Term | Definition |
|---|---|
| Ecosystem | A community of living organisms interacting with each other and their physical environment |
| Habitat | The natural home or environment of an organism |
| Producer | An organism that makes its own food through photosynthesis (e.g. grass, trees, algae) |
| Consumer | An organism that gets its energy by eating other organisms |
| Decomposer | An organism that breaks down dead organic matter, returning nutrients to the soil (e.g. fungi, bacteria) |
| Food chain | A linear sequence showing the transfer of energy from one organism to another |
| Food web | A network of interconnected food chains showing the complex feeding relationships in an ecosystem |
| Trophic level | The position an organism occupies in a food chain (e.g. producer = level 1, primary consumer = level 2) |
The most important concept in ecosystem geography is interdependence. This means that all the living and non-living components of an ecosystem are linked together. If one component changes, it has a knock-on effect on the others.
Imagine a simple grassland ecosystem. If the grass dies due to drought:
This is why ecosystems are described as being in a state of dynamic equilibrium — they are constantly adjusting and balancing, but a significant change can throw the whole system off.
Exam Tip: When writing about interdependence, always use a chain of reasoning. Show how one change leads to another, then another. Examiners love to see connected thinking, not just isolated facts.
Ecosystems exist at different scales:
| Scale | Description | Example |
|---|---|---|
| Small-scale (local) | A single habitat within a limited area | A pond, a hedgerow, a rock pool |
| Large-scale (global) | Vast areas with distinct climate, vegetation, and animal communities | Tropical rainforest, hot desert, tundra |
Large-scale ecosystems are called biomes. The distribution of biomes across the world is determined primarily by climate — especially temperature and rainfall.
The world's major biomes are distributed in broad bands roughly following lines of latitude. This is because latitude affects how much solar energy a place receives, which in turn determines temperature and precipitation.
| Biome | Location | Climate | Key Features |
|---|---|---|---|
| Tropical rainforest | Near the Equator (0-5°N/S) | Hot and wet all year (25-30°C, 2000mm+ rain) | Dense vegetation, highest biodiversity |
| Hot desert | Around 30°N and 30°S (tropics of Cancer/Capricorn) | Very hot and dry (<250mm rain per year) | Sparse vegetation, extreme temperatures |
| Tropical grassland (savanna) | Between tropics and deserts (5-15°N/S) | Hot with distinct wet and dry seasons | Grassland with scattered trees |
| Temperate deciduous forest | 40-60°N/S | Warm summers, cool winters, moderate rain | Trees that lose leaves in winter |
| Temperate grassland | Continental interiors 40-60°N/S | Hot summers, cold winters, low-moderate rain | Prairie and steppe grasses |
| Boreal forest (taiga) | 50-70°N | Long cold winters, short warm summers | Coniferous trees (pine, spruce) |
| Tundra | Above 65°N and at high altitudes | Extremely cold, very low precipitation | Mosses, lichens, permafrost |
| Polar | North and South Poles | Permanently below freezing | Ice sheets, virtually no vegetation |
Exam Tip: You do not need to memorise every biome in detail for AQA, but you must know the global distribution pattern and be able to explain why biomes are distributed the way they are. The key factor is latitude and its effect on temperature and rainfall.
AQA may ask about a small-scale UK ecosystem. A freshwater pond is a good example to know:
Producers: Algae, pondweed, water lilies — these photosynthesise using sunlight filtered through the water.
Primary consumers: Water fleas, tadpoles, pond snails — these feed on the plants and algae.
Secondary consumers: Dragonfly larvae, small fish (sticklebacks) — these feed on the primary consumers.
Tertiary consumers: Herons, pike — top predators in the pond ecosystem.
Decomposers: Bacteria and fungi break down dead organisms at the bottom of the pond, releasing nutrients back into the water and mud.
Ecosystems provide ecosystem services — benefits to humans including:
When ecosystems are damaged or destroyed, these services are lost, and the consequences can be severe for both the environment and human populations.
Exam Tip: Be prepared for a 6-mark question asking you to explain how an ecosystem works. Structure your answer around: components (biotic/abiotic), interdependence, and an example showing how a change in one part affects the whole system.