What is true about ecosystem ?

Question

UnlockIAS · Accepted Answer

Correct — C, 'Producers are more than primary consumers.' Energy enters an ecosystem only through the producers, and at every feeding step most of it is lost as heat in respiration — as a rule of thumb only about 10% passes to the next trophic level (Lindeman's ten per cent law). The producer level therefore has to form the broad base of the ecological pyramid: it captures and holds far more energy, and in the great majority of ecosystems more biomass and more individuals, than the herbivores it feeds. That upward tapering is the standard structure of an ecosystem, which makes (c) the statement that is generally true.

Why the other options are wrong — (a) The exact opposite is true. Primary consumers are the herbivores — they feed directly on producers and on nothing else, so no trophic level is more dependent on producers than this one.  (b) Not the general rule — producers normally outnumber the herbivores they support. Numbers can be inverted in special cases (a single large tree feeding thousands of insects, or a parasitic food chain), but as a blanket statement about ecosystems it is wrong, and the energy pyramid is never inverted.  (d) Wrong on both counts. Energy dwindles as it moves up the chain, so higher consumer levels are the fewest in number and the smallest in total biomass, not the largest. Body size also does not track trophic position — the blue whale, among the biggest animals alive, feeds near the base of the chain on krill.

Concept: An ecosystem is organised into trophic levels: producers (green plants and other autotrophs) fix solar energy, primary consumers (herbivores) eat them, secondary and tertiary consumers eat the level below, and decomposers return nutrients to the soil. Energy flow is one-way and lossy, so the quantity available shrinks sharply at each step; nutrients, by contrast, cycle. Ecological pyramids — of numbers, of biomass and of energy — are simply pictures of this trophic structure.

State PCS 2019 Q20 — Environment & Ecology PYQ with Answer

State PCS 2019 Q20 — Environment & Ecology PYQ with Answer