Science — CBSE Class 10 board question

(a) Organisms of the first trophic level (autotrophs/producers) are important because they fix solar energy and convert it into chemical energy (food), making it available for all heterotrophs. Without them, no energy would enter the food chain.

(b) Energy flow is unidirectional because energy captured by autotrophs does not revert to the solar input, and energy passed to herbivores does not return to autotrophs. As energy moves through trophic levels, it is lost as heat and cannot be reused by the previous level.

Source: Chapter 13, Section 13.1.1 Food Chains and Webs

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• (a) The key point examiners want: producers fix solar energy → make it available to consumers. The word "autotrophs" scores marks.
• (b) Use the exact textbook language: "does not revert back" and "no longer available to the previous level." Also mention energy lost as heat — this explains why it's unidirectional.
• Keep both answers concise; this is a 1-mark each sub-question.