Assertion (A) : The energy which passes to the herbivores does not come back to autotrophs.
Reason (R) : The flow of energy in a food chain is unidirectional.
Generated by claude-sonnet-4-6 · 2026-06-15 06:45 · grounding rag
Model Answer
(a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of (A).
The flow of energy in a food chain is unidirectional; energy passed to herbivores does not return to autotrophs, which directly explains the Assertion.
Source: Chapter 13, Section 13.1.1 (Energy flow diagram, Fig. 13.4)
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Explanation
- The textbook explicitly states both facts together: "the flow of energy is unidirectional" and "the energy which passes to the herbivores does not come back to autotrophs" — making R the direct cause/explanation of A.
- This rules out option (b). Since both statements are true and R correctly explains A, option (a) is the only correct choice.
- Key phrase to remember: energy moves progressively through trophic levels and is "no longer available to the previous level."