3.1.2 The Living World — Topic Overview

The living world examines ecosystems — the relationships between organisms and their physical environment — and focuses on two contrasting global ecosystems.

What is an ecosystem?

An ecosystem is a community of living organisms interacting with each other and with their non-living (abiotic) environment. Key components:

• Producers (plants): convert sunlight to energy via photosynthesis
• Consumers (animals): eat producers or other consumers
• Decomposers (bacteria/fungi): break down dead matter; recycle nutrients
• Nutrient cycles and energy flows link all components

Small-scale ecosystems (a pond, a hedgerow) illustrate the same principles as large-scale biomes.

Global ecosystems / biomes

A biome is a large-scale ecosystem characterised by climate and dominant vegetation. Key biomes:

• Tropical rainforest (TRF): hot, wet climate; high biodiversity; nutrient cycle in litter layer
• Temperate deciduous forest: seasonal; four seasons
• Tropical grassland / savanna: wet and dry seasons; fire-adapted
• Hot desert: very low rainfall; extreme temperatures; adapted plants and animals
• Cold environments (tundra, polar): extreme cold; permafrost; fragile ecosystems

Tropical rainforests in depth

TRFs receive >2000 mm rainfall annually; average temperature ~27 °C. Biodiversity is extraordinarily high (over 50 % of species on 6 % of land). Key features: stratification (emergent, canopy, understorey, shrub, ground layers); nutrient cycle (nutrients held in biomass, not soil); interdependence.

Deforestation (logging, farming, mining) destroys TRFs at rate of millions of hectares per year. Consequences: biodiversity loss, soil erosion, carbon release, disrupted water cycle. Sustainable management: eco-tourism, selective logging, debt-for-nature swaps.

Hot deserts in depth

Very low precipitation (<250 mm/year), extreme heat (day/night range). Plant adaptations: succulents (store water), deep/wide roots, waxy cuticles. Animal adaptations: nocturnal, concentrated urine. Desertification — spread of desert conditions into semi-arid areas (due to climate change + human activity).

Exam focus

• Know the TRF and hot desert case studies (AQA specifies: Malaysia/Amazon for TRF; Sahara/Middle East for hot desert)
• Explain adaptations using specific examples
• Evaluate management strategies for TRF conservation