You are viewing a free preview of this lesson.
Subscribe to unlock all 10 lessons in this course and every other course on LearningBro.
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.
Epping Forest is the largest public open space in the London area, covering approximately 24 km² (2,400 hectares) across the boundary of Greater London and Essex, about 19 km north-east of central London. It is a fragment of ancient temperate deciduous forest that has existed for at least 1,000 years, and is protected as a Site of Special Scientific Interest (SSSI) and a Special Area of Conservation (SAC). It is the AQA-recommended example for a small-scale UK ecosystem.
Biotic components: Epping Forest contains over 55,000 ancient trees, including beech, hornbeam, oak, silver birch, holly and rowan. It supports 177 species of birds (including tawny owls, great spotted woodpeckers, nuthatches and green woodpeckers), 38 species of mammals (including fallow deer, muntjac deer, grey squirrels, foxes, bats, weasels and badgers), 33 species of butterflies, and over 1,400 species of fungi. Beech trees form the canopy; holly and hornbeam occupy the under-canopy; bracken, bluebells and wood anemones grow on the forest floor. Decomposers — fungi, bacteria, earthworms, woodlice — break down leaf litter and return nutrients to the soil.
Abiotic components: the climate is temperate maritime, with mild summers (averaging 17-20°C) and cool winters (2-5°C), annual rainfall of 600-700 mm spread across the year, and well-defined seasons. Soils are brown earths — fertile, well-drained, and rich in organic matter from autumn leaf fall. Light levels vary dramatically through the year: in summer the canopy casts deep shade, while in spring (before leaves emerge) abundant ground-level light allows bluebells to flower.
Interdependence in Epping Forest: a clear example of cause-and-effect chains can be seen in the case of oak trees and weevils. Oaks produce acorns that feed grey squirrels, jays, and mice; the weevil larvae that feed inside acorns are eaten by blue tits, which nest in tree cavities and feed their chicks on caterpillars that feed on oak leaves. Fungi such as the honey fungus decompose fallen wood, releasing nutrients that are absorbed by tree roots — a mutualistic relationship with mycorrhizae that boosts tree health. If oaks declined (for example through disease such as acute oak decline), the knock-on effects would ripple through the entire community: squirrels, jays, blue tits, weevils, deer (which browse oak saplings), and fungi (which specialise in oak wood) would all be affected, ultimately reshaping the structure of the ecosystem.
Management: Epping Forest is managed by the City of London Corporation under the Epping Forest Act 1878, which preserves it as common land for public access. Traditional practices including pollarding (cutting trees above grazing height to produce new growth) have shaped much of the forest. Challenges include air pollution from the M11 and M25 motorways, increasing visitor pressure (millions per year), climate change affecting native species, and invasive species such as muntjac deer and grey squirrels competing with natives.
A common misconception is that an ecosystem is the same as a habitat. They are related but not identical. A habitat is the physical place where an organism lives (e.g. the canopy of a beech tree, or a pond). An ecosystem is the whole system of living organisms plus their non-living environment, including all the biotic and abiotic interactions. Every ecosystem contains many habitats; every habitat exists within an ecosystem. Another misconception is that all green plants are producers. While this is usually true, some plants (such as the dodder, a parasitic plant found in Epping Forest margins) are not producers because they obtain energy by parasitising other plants rather than through photosynthesis. Precise vocabulary matters — examiners will penalise imprecise use of "ecosystem" versus "habitat."
Question: "The abiotic components of an ecosystem are more important than the biotic components." Assess this statement. (9 marks)
Grade 3-4 response (basic): Abiotic things like water and sunlight are important. Biotic things are plants and animals. Both are important but I think plants and animals are more important because they are alive. (Vague, no case study, no balanced argument, simple reasoning — Level 1, around 2-3 marks.)
Grade 5-6 response (clear): The abiotic components of an ecosystem include climate, soil and water, while biotic components are the living plants, animals and decomposers. In Epping Forest, the brown earth soil and the temperate climate allow beech and oak trees to grow. The trees then support birds, deer and fungi. However, without the sun and water there would be no plants, so I think the abiotic components are more important because they come first in the chain. (Clear, named case study, some reasoning — Level 2, around 5-6 marks.)
Grade 7-9 response (detailed, evaluative): The importance of abiotic versus biotic components in an ecosystem depends on how "important" is defined, and a balanced analysis suggests neither can function without the other. In favour of the statement, abiotic components are foundational — without sunlight (averaging 1,500 hours per year in Epping Forest), rainfall (600-700 mm annually), temperature (temperate maritime climate), and soil (fertile brown earth), no biotic life would exist. Producers such as beech and oak in Epping Forest depend directly on these abiotic conditions for photosynthesis, and any significant abiotic change — such as acute drought or soil degradation — rapidly collapses the entire biotic community. Against the statement, biotic components themselves actively shape the abiotic environment through interdependence: decomposers such as honey fungi return nutrients to the soil, earthworms aerate the ground, transpiration from Epping's 55,000 ancient trees moderates local humidity and temperature, and leaf fall in autumn builds the very fertile brown earth soil that supports the next generation. In tropical rainforests, trees generate around 50% of their own rainfall through evapotranspiration — without the biotic, the abiotic would change dramatically. Furthermore, ecosystem services (pollination by bees, pest control by birds, seed dispersal by squirrels) all depend on biotic relationships, without which the ecosystem loses function even when abiotic conditions are ideal. Overall, I partially disagree: abiotic components may provide the initial conditions for life, but ecosystems are defined by the dynamic interaction between biotic and abiotic — neither is more important than the other, because the two have co-evolved over centuries in places like Epping Forest. (Specific case study detail, technical vocabulary, balanced evaluation, nuanced conclusion — Level 3, around 8-9 marks.)
The Grade 7-9 response distinguishes itself through specific Epping Forest statistics (1,500 hours sunlight, 55,000 ancient trees, 600-700 mm rainfall), two-sided argument, technical vocabulary (evapotranspiration, ecosystem services, interdependence), and a nuanced justified conclusion that rejects the simple hierarchy.
This content is aligned with the AQA GCSE Geography (8035) specification, Paper 1: Living with the physical environment — The living world. For the most accurate and up-to-date information, please refer to the official AQA specification document.