Biosphere
Ecosystems and energy flow
The biosphere is the zone of life. In ecosystems, producers (plants) capture solar energy, consumers eat, and decomposers recycle nutrients. Energy flows one way through food chains and webs, while matter cycles (carbon, nitrogen, water). Biodiversity increases with habitat variety, warmth and moisture, and is greatest in tropical rainforests.
Biomes
Major biomes include tropical rainforest, savanna, desert, Mediterranean shrubland, temperate forest, steppe, taiga and tundra. Each is defined by climate, especially temperature and precipitation, and by characteristic vegetation and soils. Altitudinal zonation mirrors latitudinal change: climbing a mountain resembles travelling toward the poles.
Human impact and conservation
Deforestation, desertification, habitat fragmentation, pollution and climate change threaten biodiversity. Conservation tools include protected areas, national parks, biosphere reserves and international agreements. Know the difference between a national park (protection plus limited public access) and a strict reserve (minimal human use).
Traps
Don't confuse a food chain (linear) with a food web (interconnected); remember energy is lost at each trophic level, so top predators are few; and note that tundra and taiga differ sharply in temperature and tree cover.
Worked example
A question asks why tropical rainforests have high biodiversity but poor soils. Rapid decomposition and heavy rain leach nutrients from soils, while abundant warmth and moisture support many species; nutrients are stored mainly in living biomass.