Biogeography and ecosystems
Biogeography and ecosystems
This domain tests ecosystem structure, energy and nutrient flow, soil formation, biome distribution and biodiversity conservation, with the Sundarbans mangrove as the standard West Bengal case.
Core rules
- Ecosystem = biotic community plus abiotic environment, linked by energy flow (one-way) and nutrient cycling (closed loops).
- Trophic levels: producers → primary consumers → secondary consumers → decomposers. Roughly 10% of energy transfers between levels (Lindeman's law), so biomass and energy pyramids are upright; only a pyramid of numbers can invert (many insects on one tree).
- Soil formation depends on parent material, climate, organisms, relief and time; a mature profile shows O, A, B, C and R horizons.
- India's biodiversity hotspots within the syllabus region: Himalaya, Indo-Burma, Western Ghats–Sri Lanka, and Sundaland (Nicobar). A hotspot needs high endemism plus serious habitat loss.
- Mangrove adaptations: stilt and pneumatophore roots for aeration in waterlogged mud, viviparous germination, salt-excreting or salt-accumulating leaves, leathery cuticle.
Worked example
If producers fix 20 000 kcal, how much reaches the tertiary consumer under the 10% law? Reasoning: producer → primary consumer = 2000 kcal → secondary = 200 kcal → tertiary = 20 kcal. Only about 0.1% of the original energy survives three transfers, which is why food chains rarely exceed four or five links and why top carnivores need large territories.
Traps that cost marks
Writing that energy cycles and nutrients flow one way (it is the reverse); quoting 10% as a fixed measured value rather than an ecological average; listing the Sundarbans as a tropical rainforest; saying any forest is a biodiversity hotspot; forgetting decomposers as a trophic level.