Biology · Class 12 · Chapter 12
Ecosystem
11 lessons 78 min 2 simulations
This chapter treats the ecosystem as a working unit of nature. It covers terrestrial, aquatic and man-made ecosystems, their structure (species composition and stratification), the pond as a model, primary and secondary productivity with GPP − R = NPP, the steps of decomposition, one-way energy flow from the sun, grazing and detritus food chains and food webs, trophic levels with the 10 per cent law, and pyramids of number, biomass and energy with their exceptions and limits.
What the exam asks
NEET asks for GPP − R = NPP and the biosphere's NPP figures (about 170 billion tons, oceans 55 billion tons), the order and meaning of fragmentation, leaching, catabolism, humification and mineralisation, what speeds or slows decomposition, the PAR figures (under 50 per cent of sunlight; plants capture 2-10 per cent of PAR), GFC versus DFC, trophic level numbering, the 10 per cent law, and which pyramids can be inverted: number for a tree, biomass in the sea, energy never. Marks are lost by calling decomposers primary consumers, by saying the energy pyramid can be inverted, and by counting the sparrow at a single trophic level.
Lessons
11 lessons · 78 min
1Ecosystem: meaning and typesNCERT §12 (introduction)5 min2Structure and functionNCERT §12.15 min3The pond ecosystemNCERT §12.16 min4ProductivityNCERT §12.26 min5DecompositionNCERT §12.36 min6Energy flowNCERT §12.46 min7Food chains and food websNCERT §12.46 min8Trophic levels and the 10 per cent lawNCERT §12.49 min 1 sim9Ecological pyramidsNCERT §12.510 min 1 sim10Limits of trophic levels and pyramidsNCERT §12.56 min11Chapter reviewMust-know facts, traps and formulas13 min