3.1.2 The living world — AQA GCSE Geography revision notes

3.1.2.1Ecosystems

Ecosystems exist at a range of scales and involve the interaction between biotic and abiotic components.

• Biotic components are the living parts — plants, animals, bacteria and fungi. • Abiotic components are the non-living parts — climate, water, soil, rock and light.

You need an example of a small scale UK ecosystem to illustrate the concept of interrelationships within a natural system. A hedgerow, a pond and a woodland are the usual choices; use whichever your school studied. What the example has to demonstrate is the vocabulary below, applied to something real.

Producer: An organism that makes its own food using sunlight — a green plant.
Consumer: An organism that eats other organisms. Primary consumers eat producers; secondary consumers eat primary consumers.
Decomposer: An organism such as a bacterium or fungus that breaks down dead material, returning nutrients to the soil.
Food chain: A single line showing what eats what, from producer upwards.
Food web: Many food chains joined together, showing that most organisms eat and are eaten by several others.
Nutrient cycling: The movement of nutrients between the soil, plants, animals and litter, driven by decomposers.

The balance between components, and the impact on the ecosystem of changing one component, is the idea this section is really testing. Because everything is connected, a change to one part spreads through the rest.

The reasoning to reproduce: if one species is removed, whatever ate it loses a food source and declines, while whatever it ate is no longer controlled and increases. That increase then affects the next link, and so on. A food web makes this visible in a way a single food chain cannot — which is why the specification asks for both.

Worked example

In a UK pond, a disease kills most of the frogs. Explain the likely effects on the rest of the ecosystem.

Identify what frogs eat: insects, including pond insect larvae.
With fewer frogs, fewer insects are eaten, so the insect population increases.
More insects means more grazing on pond plants, so plant numbers may fall.
Identify what eats frogs: herons and other predators, which lose a food source.
Those predators decline, or switch to eating fish instead — so the effect spreads to a part of the web that had no direct link to frogs.
Finish with the general point the question is testing.

Answer: Insects increase because a predator has gone, plants are grazed more heavily, and herons decline or switch prey. Because the components are interdependent, changing one component causes changes throughout the ecosystem, not just to the species directly connected to it.

An overview of the distribution and characteristics of large scale natural global ecosystems. The main global ecosystems, or biomes, run in broad bands by latitude, and their positions follow directly from global atmospheric circulation in 3.1.1.3:

• Tropical rainforest — on and near the equator, where air rises and rainfall is heavy all year. • Tropical grassland (savanna) — just beyond the rainforest, with a distinct wet and dry season. • Hot desert — at about 30° north and south, where air sinks and there is little rain. • Temperate grassland and temperate deciduous forest — in the mid-latitudes, with four distinct seasons. • Boreal (coniferous) forest — a broad band across the far north, cold with short summers. • Tundra and polar — nearest the poles, extremely cold with very little precipitation.

Common mistake

Deserts are not where they are because they are near the equator — the equator is the wettest place on Earth. They sit at about 30° because that is where air sinks. Tying the biome map back to the pressure belts turns a list into an explanation.

The specification names the *type* of case study, never the place — your school chose which. The worked example below is one in common use; if your school taught a different one, use theirs and keep the same structure, because the structure is what the marks are for.

Figure: A small scale UK ecosystem: Epping Forest, Essex and north-east London

	Detail
What it is	Around 2,400 hectares of ancient deciduous woodland on the edge of London, much of it beech, oak and hornbeam that was traditionally pollarded
Producers	Trees, shrubs such as holly and bramble, and ground plants including bluebells and ferns; they photosynthesise and form the base of every food chain in the wood
Consumers	Caterpillars and other insects feed on the leaves; blue tits and woodpeckers feed on the insects; sparrowhawks and foxes are top predators; deer and grey squirrels browse the vegetation
Decomposers	Fungi, bacteria and invertebrates break down leaf litter and dead wood, returning nutrients to the soil for the trees to take up again
Interrelationships	Autumn leaf fall feeds the decomposers, whose released nutrients feed the trees. The layered structure — canopy, understorey, shrub layer and ground layer — lets different amounts of light through, and each layer supports different species
Human impacts and management	Millions of visitors a year cause trampling and soil compaction; deer numbers, litter and the loss of traditional pollarding all shift the balance. Management includes fencing, path maintenance and a return to pollarding

This example is used to show interrelationships, so revise it as a set of links: change one part — remove the decomposers, or lose a tree layer — and follow the effect through the rest.

3.1.2.2Tropical rainforests

Tropical rainforest ecosystems have a range of distinctive characteristics.

The physical characteristics: hot all year, at about 27 °C, with over 2000 mm of rain and no dry season; soils that are surprisingly thin and infertile; and a dense, layered structure of vegetation.

The layers, the adaptations each one explains, and why the soil is poor despite the lush forest.

The interdependence of climate, water, soils, plants, animals and people is what makes the rainforest a system rather than a place. Each part depends on the others:

• The hot, wet climate allows rapid plant growth all year. • Dense vegetation intercepts rainfall and releases water vapour by transpiration, which forms clouds and produces more rain — the forest generates much of its own rainfall. • Rapid growth means rapid leaf fall, and the heat and moisture make decomposition very fast, so nutrients are recycled quickly. • Almost all nutrients are stored in the biomass rather than the soil, and heavy rain leaches what little is in the soil. • Animals depend on the plants for food and habitat, and many plants depend on animals for pollination and seed dispersal. • People have traditionally lived in the forest, using it for food, shelter and medicine.

The consequence that matters for the rest of this section: remove the trees and you remove the nutrient store and the rainfall mechanism at the same time.

How plants and animals adapt to the physical conditions:

Plants • Drip tips on leaves let heavy rain run off quickly, so leaves do not rot. • Waxy leaf surfaces resist the constant moisture. • Buttress roots spread wide to support tall trees in thin soil. • Lianas climb existing trees to reach the light rather than growing their own thick trunk. • Epiphytes grow on branches high up, taking moisture from the air.

Animals • Many live in the canopy, where the food is — with strong limbs, gripping tails or the ability to glide between trees. • Camouflage and bright warning colours are both common, because visibility is poor and competition is intense. • Some are nocturnal, avoiding competition and the daytime heat.

Issues related to biodiversity. Tropical rainforests contain a very high proportion of the world's species, in part because the climate is stable and productive all year.

Why that matters: species are lost as habitat is cleared, and many have never been recorded, so their potential value — including for medicines — is lost with them. Species are often highly specialised to a narrow niche, so they cannot simply move elsewhere when their habitat goes.

Deforestation has economic and environmental impacts. Changing rates of deforestation: the rate has varied over time and between countries, and in some places has slowed in recent years while continuing elsewhere. Where a question gives you rate data, describe the trend from the figures rather than asserting a general direction.

You need a case study of a tropical rainforest to illustrate the causes and impacts of deforestation. The specification names what it must cover, so use your own case study and check it against this list:

Figure: What your rainforest case study must cover

Causes of deforestation	Impacts of deforestation
Subsistence farming — clearing land to grow food for a family	Economic development — jobs, exports and income from timber, minerals and farmland
Commercial farming — cattle ranching and large plantations	Soil erosion — with no tree roots or canopy, heavy rain washes the thin soil away
Logging — felling trees for hardwood timber	Contribution to climate change — carbon released by burning, and less carbon dioxide absorbed
Road building — opening up the interior to further clearance
Mineral extraction — mining for ores and precious metals
Energy development — flooding valleys for hydroelectric dams
Settlement and population growth — land cleared for housing

Note that economic development sits under impacts, not causes: deforestation brings real benefits, which is precisely why it is difficult to stop.

Tropical rainforests need to be managed to be sustainable.

The value of tropical rainforests to people and the environment: they are a source of timber, food, medicines and other resources; they support the livelihoods of indigenous people; they attract tourists; they hold enormous biodiversity; they store carbon and so slow climate change; they regulate the water cycle and maintain rainfall; and their roots protect the soil.

Strategies used to manage the rainforest sustainably:

Figure: Sustainable management strategies

Strategy	How it works	Limitation
Selective logging and replanting	Only mature trees are felled and new ones planted, so the forest structure survives	Slower and more expensive than clear felling
Conservation and education	National parks and reserves protect areas; education builds local support	Needs money to police, and reserves can be logged illegally
Ecotourism	Small-scale tourism gives local people an income from the forest standing rather than cleared	Only supports limited numbers of people, and tourists themselves have an impact
International agreements about the use of tropical hardwoods	Restrict trade in illegally logged timber and certify sustainable sources	Only work if countries sign and enforce them
Debt reduction	Wealthier countries cancel debt in return for a commitment to protect forest	Depends on the receiving government honouring the agreement

Common mistake

Sustainable management does not mean stopping all use of the forest. It means using it in a way that meets present needs without preventing future generations from meeting theirs — which is why selective logging and ecotourism count, and why a strategy that leaves local people with no income tends to fail.

Figure: A tropical rainforest: deforestation in the Amazon, Brazil

Cause or impact	Detail
Scale	The Amazon covers around 5.5 million square kilometres, roughly 60% of it in Brazil. Rates of clearance have risen and fallen with government policy and commodity prices rather than steadily
Cause: farming	Cattle ranching is the single largest cause of clearance; soya is also grown on cleared land, mostly for animal feed and export
Cause: logging	Valuable hardwoods such as mahogany are felled, and the access roads cut for logging open the interior to further clearance
Cause: mineral extraction	Iron ore at Carajás, along with gold and bauxite; mining clears land directly and pollutes rivers, gold working with mercury
Cause: energy and roads	Hydroelectric dams such as Belo Monte flood large areas of forest; the Trans-Amazonian Highway opened the interior to settlement
Cause: settlement	Government resettlement schemes moved landless families into the forest, who cleared plots to farm
Environmental impacts	Loss of biodiversity, including species not yet recorded; exposed soils erode quickly under heavy rain and lose fertility within a few years; less transpiration means less rainfall; carbon stored in the trees is released, adding to global warming
Economic and social impacts	Jobs, exports and tax revenue from ranching, timber and mining, plus roads and settlements; against that, indigenous peoples lose the land they depend on, and violent conflict over land is common

Deforestation questions almost always ask you to weigh economic development against environmental cost, so revise the last two rows together rather than learning the causes alone.

Tropical rainforest: an ecosystem that is hot all year at about 27 °C with over 2000 mm of rain and no dry season, with thin infertile soils and a dense layered structure

3.1.2.3Hot deserts

Optional route — study this OR Cold environments, whichever your school teaches.

In this section you study Ecosystems and Tropical rainforests, and then one from Hot deserts or Cold environments. Check which your school covers before revising this — you only need one.

Hot desert ecosystems have a range of distinctive characteristics. The physical characteristics: under 250 mm of rain a year, falling unpredictably; very hot days, often over 40 °C, but cold nights because there is no cloud to trap heat; sparse vegetation; and thin, sandy or stony soils with little organic matter.

The interdependence of climate, water, soils, plants, animals and people. Water is the limiting factor and everything follows from it: little rain means sparse vegetation, sparse vegetation means little leaf litter, little litter means soils with almost no nutrients, and poor soils in turn limit plant growth further. People have traditionally survived by moving — nomadic herding — or by settling where water is available at an oasis or a river.

How plants and animals adapt to the physical conditions:

Plants • Very long tap roots reaching deep groundwater, or wide shallow roots catching brief rainfall. • Thick fleshy stems storing water, as in cacti. • Spines or tiny waxy leaves, reducing water loss and deterring animals. • Short life cycles — some seeds germinate, flower and set seed within days of rain.

Animals • Nocturnal habits, sheltering underground through the heat of the day. • Getting most of their water from food rather than drinking. • Large ears or thin bodies to lose heat, or the ability to store fat in one place rather than insulating the whole body.

Issues related to biodiversity: biodiversity is low compared with a rainforest, because conditions are so harsh, and species are highly specialised — so they are vulnerable if conditions change or habitat is lost.

Development of hot desert environments creates opportunities and challenges. You need a case study of a hot desert covering both:

Figure: What your hot desert case study must cover

Development opportunities	Challenges of developing
Mineral extraction — ores and metals close to the surface and easily seen	Extreme temperatures — dangerous to work in and hard on machinery
Energy — abundant sunshine for solar power, and oil and gas in some deserts	Water supply — very little available, and what there is may be deep underground
Farming — highly productive where irrigation water can be supplied	Inaccessibility — vast distances, few roads, expensive to build infrastructure
Tourism — dramatic scenery, reliable sunshine and adventure activities

Areas on the fringe of hot deserts are at risk of desertification — the process by which land becomes so degraded that it turns into desert.

Causes of desertification: • Climate change — less rainfall and higher temperatures dry the soil. • Population growth — more people needing food and fuel from the same land. • Removal of fuel wood — trees cut for cooking fuel, leaving soil unprotected. • Overgrazing — too many animals strip the vegetation cover. • Over-cultivation — growing crops continuously exhausts the soil's nutrients. • Soil erosion — with no plant cover, wind and rain remove the topsoil.

Notice that the last is partly a consequence of the others, which is why desertification accelerates once it begins.

Figure: Strategies to reduce the risk of desertification

Strategy	How it works
Water management	Drip irrigation delivers water straight to the roots with little evaporation; small dams store seasonal rain
Soil management	Leaving fields fallow to recover, rotating crops, and adding manure to restore nutrients
Tree planting	Roots bind the soil and the canopy shelters it from wind and heavy rain; trees also provide fuel wood so existing trees are spared
Use of appropriate technology	Simple, cheap, locally repairable methods such as stone lines along contours to slow runoff, and efficient stoves that need less wood

Appropriate technology is favoured because it can be built and maintained by local people with local materials, so it keeps working after any outside project ends.

Figure: A hot desert: the Western Desert, south-west USA

	Detail
Where	The arid south-west of the United States, covering parts of Arizona, California, Nevada, Utah and New Mexico
Opportunity: mineral extraction	Copper is mined in Arizona, along with uranium, lead and coal, bringing employment and export income
Opportunity: energy	Very high sunshine totals make large solar installations viable, and the Hoover Dam on the Colorado generates hydroelectric power
Opportunity: farming	Irrigation with water from the Colorado River supports fruit, vegetables and cattle, particularly in the Imperial and Coachella valleys
Opportunity: tourism	The Grand Canyon, Lake Mead and Las Vegas draw millions of visitors, supporting hotels, transport and services
Challenge: extreme temperatures	Summer temperatures above 40°C limit outdoor work, raise the cost of cooling, and put workers and visitors at risk of heat exhaustion
Challenge: water supply	The Colorado is over-allocated between several states and Mexico, and farming competes with fast-growing cities for the same limited supply
Challenge: inaccessibility	Great distances between settlements, few roads and extreme heat make construction, transport and maintenance expensive

You need hot deserts OR cold environments, not both — check which your school taught before revising this section.

3.1.2.4Cold environments

Optional route — study this OR Hot deserts, whichever your school teaches.

Cold environments — polar and tundra — have a range of distinctive characteristics. The physical characteristics: very low temperatures, below freezing for much of the year; low precipitation, mostly as snow, so they are technically deserts; permafrost, ground that stays frozen all year; a very short growing season; and thin soils that are waterlogged in summer because meltwater cannot drain through the frozen ground beneath.

The interdependence of climate, permafrost, soils, plants, animals and people. Permafrost is the component that makes this system distinctive. The cold keeps the ground frozen; frozen ground stops water draining, so the surface is boggy in summer; waterlogged, cold soil means decomposition is extremely slow, so nutrients are locked up in undecayed material; poor nutrients and a short growing season mean only low, slow-growing plants survive; and those plants support a small number of specialised animals. People have lived here by hunting and herding, moving with the animals.

How plants and animals adapt to the physical conditions:

Plants • Low, ground-hugging growth, staying out of the wind and using the warmth near the ground. • Shallow roots, because they cannot penetrate permafrost. • Small, waxy or hairy leaves reducing water loss, since liquid water is scarce. • Very rapid flowering and seed-setting to fit the short growing season.

Animals • Thick fur or feathers, and a layer of blubber, for insulation. • Small ears and compact bodies, reducing surface area and so heat loss. • White winter coats for camouflage. • Hibernation or migration to avoid the worst of the winter.

Issues related to biodiversity: biodiversity is low, and food chains are short and simple — so removing one species has a disproportionate effect. Growth is so slow that damage takes decades to repair, which is the heart of the word fragile.

Development of cold environments creates opportunities and challenges. You need a case study of a cold environment covering both:

Figure: What your cold environment case study must cover

Development opportunities	Challenges of developing
Mineral extraction — large reserves of ores and metals	Extreme temperature — dangerous for workers, and machinery fails in the cold
Energy — oil and gas reserves, and hydroelectric potential	Inaccessibility — few roads, long distances, supply only possible by air or by sea in season
Fishing — rich fishing grounds in cold seas	Provision of buildings and infrastructure — heat from buildings melts permafrost, so structures must be raised on piles to stop them sinking
Tourism — wilderness scenery and wildlife

The permafrost problem is the one most specific to cold environments, and worth naming: heated buildings thaw the ground beneath them and then subside.

Cold environments are at risk from economic development.

The value of cold environments as wilderness areas, and why these fragile environments should be protected: they are among the last places on Earth largely unaltered by people; they support species found nowhere else; they hold scientific evidence about past climate in their ice; the permafrost stores large amounts of carbon that would be released if it thawed; and they are of great cultural importance to indigenous people. They are fragile because growth and recovery are so slow that damage lasts for decades.

Strategies used to balance the needs of economic development and conservation:

• Use of technology — building on piles so heat does not thaw the permafrost, insulating and elevating pipelines, and directional drilling that reaches a wide area from one small site. • Role of governments — laws limiting where development can take place, and requiring environmental impact assessments before permission is given. • International agreements — treaties that restrict activity and set aside protected areas. • Conservation groups — campaigning, monitoring and putting pressure on companies and governments.

The word balance in that heading is doing real work: the specification is not asking whether development should happen, but how it can happen with least damage.

Figure: A cold environment: Svalbard, Norway

	Detail
Where	An Arctic archipelago around 800 km north of mainland Norway; the main settlement, Longyearbyen, has around 2,000 residents
Opportunity: mineral extraction	Coal mining has been the traditional industry and provided most local employment for decades
Opportunity: fishing	The Barents Sea is among the richest fishing grounds in the world, supporting cod, herring and haddock
Opportunity: tourism	Around 70,000 visitors a year come for glaciers, wildlife and the polar landscape, supporting hotels, guides and cruise services
Opportunity: research	The university centre and the Global Seed Vault bring scientists, students and investment
Challenge: extreme temperature	Winter temperatures average around −15°C and fall far lower, with several months of continuous darkness
Challenge: building on permafrost	Heat escaping from buildings thaws the ground and causes subsidence, so buildings and the pipes serving them are raised on stilts driven into the permafrost
Challenge: inaccessibility	There are almost no roads between settlements; access is by boat, snowmobile or aircraft, which makes everything expensive
Why it needs protecting	The ecosystem recovers very slowly, so vehicle tracks scar the ground for decades and spilt oil persists

The specification pairs development opportunities with the challenges of the environment, so learn them as two halves of one answer rather than as separate lists.

Permafrost: ground that stays frozen through the year, characteristic of cold polar and tundra environments
Cold environment: a polar or tundra ecosystem with very low temperatures, low precipitation mostly as snow, and permafrost

Before you practise

Study Ecosystems and Tropical rainforests, plus ONE of Hot deserts or Cold environments — check which your school teaches.
Biotic components are living, abiotic are non-living; producers, consumers and decomposers link through food chains and webs, with nutrients cycled by decomposers.
Changing one component affects the whole ecosystem, because the parts are interdependent.
Global biomes run in bands by latitude, and their positions follow from the pressure belts: rainforest at the equator, hot desert at about 30°.
Rainforest: hot and wet all year, layered structure, thin infertile soil because nutrients are held in the biomass and recycled fast.
Rainforest adaptations: drip tips, waxy leaves, buttress roots, lianas; animals mostly in the canopy.
Deforestation causes: subsistence and commercial farming, logging, road building, mineral extraction, energy development, settlement, population growth.
Deforestation impacts: economic development, soil erosion, contribution to climate change.
Sustainable management: selective logging and replanting, conservation and education, ecotourism, international hardwood agreements, debt reduction.
Hot deserts: under 250 mm rain, hot days and cold nights; desertification is caused by climate change, population growth, fuel wood removal, overgrazing, over-cultivation and soil erosion.
Cold environments: permafrost is the key component; buildings must be raised on piles or they thaw the ground and sink.
For every case study, use the one your school taught — but check it covers every bullet the specification lists.

Now practise it

Reading is the easy half. Answer questions on 3.1.2 The living world and find out which parts you actually know.

Written questions Multiple choice