Ecosystems and biomes: how ecosystems work (food chains and webs, nutrient cycling, energy flows), the distribution and characteristics of the global biomes, and the structure and adaptations of one biome such as the tropical rainforest.

What this dot point is asking

This is part of Eduqas GCSE Geography A (C111) Theme 5, Weather, Climate and Ecosystems, a core theme in Component 2. Eduqas expects you to know how ecosystems work (food chains and webs, nutrient cycling, energy flows), the distribution and characteristics of the global biomes, and the structure and adaptations of one biome, usually the tropical rainforest.

How ecosystems work

Energy and matter move through the ecosystem.

• Food chains and webs: producers (green plants) capture the Sun's energy by photosynthesis; consumers eat plants or other animals; decomposers break down the dead. A food web shows the many linked food chains in an ecosystem.
• Energy flow: energy enters as sunlight and passes along the chain, but about 90 percent is lost at each step (as heat and movement), so there are fewer top predators than plants.
• Nutrient cycling: nutrients are stored in the biomass (living things), the litter (dead material on the ground) and the soil, and cycle between them as plants grow, die and are broken down by decomposers.

The global biomes

A biome is a very large-scale ecosystem, defined mainly by climate.

• Tropical rainforest: hot and wet all year, near the Equator; the most biodiverse biome.
• Tropical grassland (savanna): hot with a wet and a dry season.
• Hot desert: very dry, with extreme temperatures.
• Temperate deciduous forest: mild with four seasons (much of the UK and Europe).
• Coniferous forest (taiga): cold winters, cool summers.
• Tundra: very cold, with frozen ground (permafrost), near the poles.

Their distribution follows latitude and climate: temperature falls and seasons change from the Equator to the poles, setting which biome grows where.

The tropical rainforest: structure and adaptations

The tropical rainforest is the usual biome studied in detail. It is hot (about 27 degrees Celsius) and wet (over 2000 mm of rain) all year, with no real seasons, so growth is continuous.

It has a layered structure:

• Emergents: the tallest trees, poking above the rest.
• Canopy: a continuous layer of treetops that catches most of the light.
• Under-canopy: smaller trees in the shade.
• Shrub and ground layers: little light reaches here, so few plants grow.

Adaptations fit the hot, wet, competitive, low-light environment.

• Plants: drip-tip leaves shed heavy rain; buttress roots support tall trees in thin soil; lianas climb trees to reach light; epiphytes grow on branches high up.
• Animals: many live in the canopy where the food is, with strong limbs and tails for climbing, camouflage, and nocturnal or specialised habits to reduce competition.

Try this

Q1. Define an ecosystem. [2 marks]

• Cue. A community of living organisms interacting with each other and with their non-living environment in a particular area.

Q2. Explain one way a rainforest plant is adapted to heavy rainfall. [4 marks]

• Cue. Drip-tip leaves have a pointed end that channels heavy rain off quickly, stopping water pooling and rotting the leaf.