Science — CBSE Class 10 board question

At each trophic level, only 10% of the energy is transferred to the next level; the remaining 90% is lost as heat and in metabolic processes. Since so little energy is available at each successive step, very little usable energy remains after three or four trophic levels. Therefore, food chains generally do not exceed four steps.

Source: Chapter 13, Section 13.1.1 — Food Chains and Webs

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• The key concept here is the 10% law of energy transfer — only 10% of food energy passes to the next trophic level.
• Examiners expect you to explicitly state that energy is lost as heat at each level and that after 3–4 levels, the remaining energy is too little to support another consumer level.
• Avoid vague answers like "not enough food" — use precise terms: energy, trophic level, 10%.
• This is a 2-mark question: one mark for the 10% energy transfer rule, one mark for linking it to the limitation on food chain length.