If 20 J of energy is trapped at producer level, then how much energy will be available to peacock as food in the following chain? plant → mice → snake → peacock

Ten Percent Law

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NCERT Class 12 · Ecosystem · 1 NEET question

Energy is not infinite. It is a finite, decaying resource as it moves up the trophic levels. If you think 100% of energy transfers, you have already failed the NEET Biology paper.

The idea

Lindeman’s Ten Percent Law states that only 10% of the energy available at one trophic level is transferred to the next. The remaining 90% is lost as heat during respiration or used for metabolic activities. This thermodynamic limitation strictly restricts the number of trophic levels in any ecosystem. Consequently, food chains rarely exceed four or five levels.

Why it matters

Energy is lost as heat during metabolic processes at each transfer, limiting the number of steps in a food chain.

NEET lens

NEET focuses on the calculation of energy availability at specific trophic levels. Memorize that 90% is lost as heat, not stored. Expect a numerical problem where you must divide by 10 for each successive level. Do not confuse this with the 10% rule of ecological efficiency; stay strictly within NCERT parameters.

Clinical significance

In human nutrition, this law explains why primary producers (plants) support a larger population than secondary consumers. When this energy flow is disrupted, as seen in biomagnification of toxins like Mercury or DDT, the higher trophic levels suffer severe neurological and reproductive failure. Energy scarcity at the top leads to ecosystem collapse.

Introduction

Only about 10 per cent of the energy is transferred to each trophic level from the lower trophic level. This is Lindeman's 10 per cent law.

Core concept

Energy flow is unidirectional, from the sun to producers and then to consumers. At each step, much energy is lost as heat (respiration) and used for life processes; only about 10 per cent is stored in the next level. Example calculation: if 20 J of energy is trapped at the producer level, a primary consumer gets 2 J, a secondary consumer 0.2 J, and a tertiary consumer 0.02 J. Because of this loss, the number of trophic levels in a grazing food chain is restricted — generally to four or five.

Go deeper

The 10 per cent law explains why pyramids of energy are always upright and why top carnivores are few in number.

From Class 10

When a cow eats grass, most of the grass's energy is used up or lost as heat. Only a small part is stored in the cow's body.