This mini-lesson covers Eduqas Theme 3, Key Idea 3.1 — How Ecosystems Function: the world's biomes and how they link to climate zones, two contrasting biomes (tropical rainforest and hot semi-arid grassland / savanna), how the parts of an ecosystem are interdependent, nutrient cycles, food webs, biodiversity, and one small-scale UK ecosystem and its management.
Work through each screen, answer the questions as you go (multiple-choice, short-answer and games) and collect ⭐ stars. Press Start when you're ready.
3.1 What is an ecosystem?
Ecosystems, biomes & biotic vs abiotic
An ecosystem is a community of living things (plants and animals) together with the non-living environment they live in, and the way they all interact.
Biotic parts — the living components: plants, animals, insects, fungi and micro-organisms.
Abiotic parts — the non-living components: climate (temperature, rainfall, sunlight), soil, water and rock.
A biome is a very large, global-scale ecosystem (e.g. tropical rainforest, savanna, hot desert) defined mainly by its climate.
Key idea: ecosystems come in all sizes — from a single pond up to a whole biome. The living (biotic) and non-living (abiotic) parts are all linked, so a change to one affects the others.
Biomes & climate zones
Why biomes sit in latitude belts
Biomes are arranged in rough belts around the globe because climate changes with latitude — and climate is driven by global patterns of air pressure and rainfall.
At the equator, intense sun heats the air, which rises — this is a belt of low pressure giving heavy rain all year, so tropical rainforest grows.
Near 30° N and S, that air has cooled and sinks as dry high pressure, giving hot deserts and, at their edges, hot semi-arid grassland (savanna).
Quick check
Biomes and climate
?Tropical rainforest is found in a belt along the equator. Which climate feature best explains why?
Contrasting biome 1
Tropical rainforest
The tropical rainforest is hot and wet all year (typically around 26–28°C with over 2,000 mm of rain a year). This constant warmth and moisture supports the most biodiverse biome on Earth, arranged in distinct layers:
Sunlight is caught by the dense canopy, so little reaches the dark forest floor. Nutrients are held mostly in the living plants (biomass), not the soil.
Key idea: because it is hot and wet all year, dead leaves rot very quickly and nutrients are taken straight back up by the trees — so nutrient cycling is rapid and most nutrients are stored in the biomass, leaving the soil surprisingly poor.
Contrasting biome 2
Hot semi-arid grassland (savanna)
The savanna, or hot semi-arid grassland, lies between the rainforest and the hot deserts. Its climate has a distinct wet season and dry season, so the plants and animals must survive long periods of drought:
Vegetation — mostly grasses with scattered, drought-resistant trees such as the acacia (small waxy leaves, long roots to reach deep water).
Animals — large grazing herds (e.g. zebra, wildebeest) that migrate to follow the rains, and predators that follow them.
Adaptations — grasses grow fast in the wet season then die back and survive underground in the dry season; many plants can regrow after fire, which is common on the dry grassland.
Contrast: the rainforest is hot and wet all year and stores nutrients in its biomass; the savanna has seasonal drought, so life is adapted to survive the dry season and to bounce back with the rains.
Energy & food webs
Food chains, food webs & trophic levels
Energy enters an ecosystem as sunlight and flows through it along food chains. Each feeding stage is a trophic level:
Producers (green plants) make food from sunlight; primary consumers (herbivores) eat them; secondary and tertiary consumers (carnivores) eat other consumers. A food web is many food chains linked together.Match it
Match the trophic level to an example
Tap a trophic level on the left, then tap its correct example on the right.
Quick check
Which trophic level?
?In the chain grass → zebra → lion, what is the zebra?
Nutrient cycle
Nutrient stores & flows (Gersmehl)
Nutrients (like nitrogen) cycle between three stores: biomass (living plants and animals), litter (dead leaves on the ground) and soil. They move between the stores in flows:
Plants take up nutrients from the soil into biomass; dead leaves fall as litter; decomposers break litter down, returning nutrients to the soil. Rain adds nutrients; leaching removes them.Explain it
Your turn — rainforest nutrients
✎The tropical rainforest is lush, yet its soil is surprisingly poor in nutrients. Explain why. Use the words hot and wet, decompose, biomass and uptake.
Model answer
Because the climate is hot and wet all year, dead leaves that fall to the floor decompose (rot) very quickly.
The released nutrients are almost immediately taken back up by plant roots (rapid uptake), so they do not build up in the soil.
This means most nutrients are stored in the living biomass (the plants and trees), leaving the soil itself thin and nutrient-poor.
Interdependence
Everything is interdependent
In an ecosystem the climate, soils, vegetation, animals and humans all depend on one another. Change one part and there are knock-on effects right through the system:
Climate controls which plants grow; plants feed the animals and shelter the soil; soil quality affects the plants; and humans depend on and change the whole web.
Worked example: if the rainforest trees are cleared, the soil is exposed to heavy rain and nutrients are washed away (leached); with no leaves falling the nutrient cycle breaks; animals lose their food and shelter; and the local climate becomes drier. One change ripples through the whole ecosystem.
Sort it
Producer or consumer?
Tap whether each organism is a producer or a consumer.
Biodiversity
Biodiversity: the variety of life
Biodiversity means the range of different species living in an ecosystem. Warm, wet, stable environments tend to have the highest biodiversity:
The tropical rainforest holds around half of all the world's plant and animal species, making it the most biodiverse biome; the drier savanna and desert support far fewer species.
Why it matters: high biodiversity makes an ecosystem more resilient — if one species is lost, others can fill its role. Losing biodiversity (e.g. through deforestation) makes the whole system less stable.
Explain it
Your turn — surviving the savanna
✎Explain two ways plants and animals are adapted to survive the savanna's climate. Use the words dry season, roots, migrate and fire.
Model answer
To survive the long dry season, trees like the acacia have long roots to reach deep water and small waxy leaves to cut water loss; grasses die back above ground but survive from their roots.
Many grasses and trees can regrow quickly after fire, which is common on the dry grassland.
Grazing animals such as wildebeest and zebra migrate to follow the rains and fresh grass when their area dries out.
A UK ecosystem
A small-scale UK ecosystem: a freshwater pond
You also study one small-scale UK ecosystem. A freshwater pond is a good example — a self-contained system with its own producers, consumers and decomposers:
Producers (algae, pondweed) → primary consumers (water insects, tadpoles, water snails) → secondary consumers (small fish, frogs) → top predators (herons). Decomposers recycle dead material on the pond bed.
Biotic & abiotic: the pond's abiotic factors (water depth, temperature, oxygen and light) control which biotic species can live there — showing the same interdependence at a tiny, local scale.
Quick check
Nutrient stores
?In the tropical rainforest, which nutrient store is the largest?
Sort it
Rainforest or savanna?
Tap a feature, then tap the biome it belongs to.
🌳 Tropical Rainforest
🌾 Savanna (hot semi-arid grassland)
Using & managing the pond
How the UK pond is used & managed
People use and value a pond ecosystem — for wildlife, education and recreation — but it faces threats that have to be managed:
Pollution & nutrient run-off — fertiliser or rubbish washing in can trigger algal blooms that use up the oxygen and kill fish.
Silting & overgrowth — a pond naturally fills with sediment and vegetation, which can eventually turn it into dry land.
Invasive species — non-native plants can crowd out the native pondweeds and reduce biodiversity.
Management: conservation groups (e.g. Wildlife Trusts) manage ponds by clearing excess vegetation, occasionally de-silting, keeping fertiliser buffer strips around the edge, and removing invasive species — keeping the ecosystem healthy and biodiverse while people still enjoy it.
Quick check
Interdependence in action
?A large area of rainforest is cleared for farming. Which chain of effects best shows interdependence?
Quick check
Contrasting the two biomes
?Which statement best describes how the savanna's climate differs from the tropical rainforest's?
Recap
The key ideas to know
Ecosystem: living (biotic) + non-living (abiotic) parts, all interacting. A biome is a global-scale ecosystem set by climate.