Ecosystem

Ecosystem is a compact but high-yield ecology chapter — a consistently well-represented NEET chapter (productivity, the ten per cent law and ecological pyramids are perennial favourites) and a common CBSE 2- or 3-mark question on energy flow or decomposition. It treats the ecosystem as a functional unit and works through its four processes: productivity (primary production, gross versus net primary productivity with GPP - R = NPP, and secondary productivity), decomposition (detritus and the steps of fragmentation, leaching, catabolism, humification and mineralisation), energy flow (the sun, PAR, the unidirectional flow obeying the laws of thermodynamics, producers and consumers, trophic levels and the ten per cent law), and the food chains, food webs and ecological pyramids that arise from it. The chapter rewards precise recall of the definitions and numbers — the GPP/NPP relationship, that plants capture only 2-10 per cent of PAR, the ten per cent transfer law, and why the pyramid of energy is always upright while the pyramid of biomass in the sea is inverted. Master the energy-flow diagram and the three pyramids and most of the marks are secure.