Biosphere: Soils, Biomes and Biodiversity
Biosphere: Soils, Biomes and Biodiversity
This domain tests soil formation and profiles, major soil types, world biomes and biodiversity conservation. Expect factor-based explanations and matching of soils or biomes to regions.
Core rules and concepts
- Soil forms from parent material, climate, relief, organisms and time. These controls explain texture, depth, fertility and acidity.
- A soil profile has horizons: O (organic litter), A (topsoil), E (leached), B (accumulation), C (weathered parent material) and R (bedrock).
- Indian soil types include alluvial (fertile, plains), black/regur (clayey, moisture-retentive, Deccan), red (crystalline rocks), laterite (heavy leaching), desert and mountain soils.
- Biomes are large ecological units: tropical rainforest, savanna, desert, temperate grassland, taiga and tundra, each with characteristic climate and vegetation.
- Biodiversity is the variety of genes, species and ecosystems. India is megadiverse; the Western Ghats, Himalaya, Indo-Burma and Sundaland (Nicobar) are global hotspots.
Worked example
Why do laterite soils form on the Western Ghats? Reasoning: high rainfall leaches silica and bases, leaving iron and aluminium oxides. The result is acidic, low-fertility soil that hardens when exposed. This links climate (heavy rain) to a soil process (leaching) and to a land-use limitation, which is the chain examiners reward.
Traps
Alluvial soil is not the same as black soil. Red soil colour comes from iron oxides, not from lava. A biodiversity hotspot must have high endemism and habitat loss, not just many species. Do not reverse the A and B horizons.