Ecosystem

The pyramid of energy is always upright for any ecosystem because energy flow obeys the laws of thermodynamics, and a substantial fraction is lost as heat during respiration at each trophic transfer. Consequently each higher trophic level can never contain more energy than the level below it, so the pyramid cannot be inverted. The pyramid of biomass can be inverted, for instance in an aquatic ecosystem where small, fast-reproducing phytoplankton support a larger standing biomass of zooplankton at a given moment, so it is not always upright. The pyramid of numbers can also be inverted, as in a single large tree supporting many herbivorous insects and even more parasites. A pyramid of decomposers is not a standard category of ecological pyramid in the NCERT scheme. As described in NCERT Class 12, Chapter 14 (Ecosystem), energy pyramids are always upright while biomass and number pyramids may be upright or inverted. A key limitation of all ecological pyramids is that they do not accommodate a food web, and they assume each organism belongs to a single trophic level, which is rarely true in nature. Plausibility check: since no trophic level can create energy and each loses some as heat, an upright energy pyramid is thermodynamically inevitable, confirming the answer.