In an ecosystem, flow of energy declines as it passes from lower to higher trophic level. This is explained by the following:

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Correct — B, Second law of thermodynamics. Energy flow through an ecosystem is unidirectional, and no energy transformation is ever 100% efficient: at every trophic transfer, a large share of the energy is lost as heat, chiefly through respiration, rather than being passed on as usable biomass. This progressive loss of usable energy at each step — the reason flow declines from lower to higher trophic levels — is a direct consequence of the second law of thermodynamics (entropy increases; some energy always dissipates as unusable heat).

Why the other options are wrong — (a) The first law (conservation of energy) only says total energy is neither created nor destroyed — it explains the overall energy balance, not why the USABLE energy specifically shrinks at every trophic transfer; that decline is a second-law (entropy/heat-loss) phenomenon.  (c) Newton's second law (F = ma) relates force, mass and acceleration in mechanics — it has no bearing on energy transfer efficiency in an ecosystem.  (d) Newton's third law describes equal-and-opposite paired forces between interacting bodies — irrelevant to trophic energy flow.

Concept: Energy flows through an ecosystem only in one direction — from producers to successive consumer levels — and is never fully passed on: at every trophic transfer a large fraction (commonly cited as roughly 80-90%) is lost as heat, mainly through respiration, so only a small share becomes new biomass at the next level. This step-by-step loss of usable energy is a direct application of the second law of thermodynamics: no energy conversion is completely efficient, and some energy is always dissipated as heat rather than remaining available to do biological work.

State PCS 2023 Q8 — Environment & Ecology PYQ with Answer

State PCS 2023 Q8 — Environment & Ecology PYQ with Answer