Science (086) — AI-generated practice question

Unidirectional flow of energy means that energy moves in one direction only — from the Sun to producers, then to herbivores, then to carnivores — and cannot return to a previous trophic level. The energy captured by autotrophs does not revert to solar input, and energy passed to herbivores does not come back to autotrophs. At each level, energy is lost as heat and cannot be reused.

Difference from matter: Minerals and other matter are recycled in an ecosystem. Decomposers break down dead organisms into simple inorganic substances that go back into the soil and are reused by plants. Thus, matter moves in a cycle, while energy flows in a single direction and is progressively lost.

Source: Chapter 13, Section 13.1.1 — Food Chains and Webs; Section 13.1 — Ecosystem Components

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• The key contrast examiners look for is unidirectional (one-way, non-recyclable) energy vs cyclic (recyclable) matter/minerals.
• Mention that energy is lost as heat at each trophic level — this is why it cannot be returned.
• Decomposers are the link that explains why matter can be cycled but energy cannot.
• Avoid writing "energy is recycled" — that is a common error that costs marks.