AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.
(B) Unidirectional — energy flows from autotrophs to consumers and is not reversed
The flow of energy is unidirectional. Energy captured by autotrophs does not revert to solar input, and energy passed to herbivores does not return to autotrophs.
The textbook explicitly states: "the flow of energy is unidirectional" — energy moves from producers → primary consumers → secondary consumers → tertiary consumers and is never reversed. At each step, energy is also lost as heat, so it cannot cycle back. This is a frequently tested concept; remember it contrasts with the cycling of matter (which does cycle), making option B the only correct choice.