Question
Why is the energy transfer from one trophic level to the next only about 10%? Where does the remaining 90% go?
Solution — Step by Step
Lindeman’s 10% Law (1942) states that only about 10% of the energy available at one trophic level is transferred to the next trophic level. The remaining ~90% is lost at each step.
If producers (plants) capture 10,000 kJ of energy from sunlight:
- Herbivores (primary consumers) get ~1,000 kJ
- Carnivores (secondary consumers) get ~100 kJ
- Tertiary consumers get ~10 kJ
Reason 1 — Respiration: The majority of energy in an organism is used in cellular respiration to fuel metabolism, movement, growth, and reproduction. Heat is generated and lost to the environment. This energy cannot be passed on.
Reason 2 — Incomplete consumption: Not everything at one trophic level gets eaten. Dead organisms (leaves, fallen trees, dead animals) are consumed by decomposers, not the next trophic level. Some is simply not eaten.
Reason 3 — Indigestible material: Much of what is consumed cannot be digested — bones, hair, cellulose (in plant cell walls), chitin (in insect exoskeletons). This passes out as faeces and is broken down by decomposers, not transferred up the food chain.
Reason 4 — Excretion: Waste products (urine) contain energy-rich compounds that are excreted rather than used for growth.
A herbivore eating 100 kJ of plant material:
- Respiration: ~60 kJ lost as heat
- Indigestible material (faeces): ~20 kJ (to decomposers)
- Excretion (urine): ~5 kJ (to decomposers)
- Actual body tissue (available to next level): ~10-15 kJ
So roughly 10% becomes biomass available for the next consumer.
Because only 10% transfers per level, food chains in nature are short (usually 4-5 trophic levels). Beyond that, there is too little energy to sustain a population.
This is also why eating plants directly (vegetarian diet) is more energy-efficient than eating animals that ate plants — you capture 10 times more food energy per unit of land.
Why This Works
Energy transfer is fundamentally limited by thermodynamics. The second law of thermodynamics says energy transformations are never 100% efficient — some energy is always dissipated as heat. Living organisms are no exception. Their metabolic activities (maintaining body temperature, moving, pumping ions, building molecules) all generate heat that escapes the food chain permanently.
Alternative Method — Ecological Pyramid Perspective
An energy pyramid quantifies this. Each level of the pyramid represents the total energy at that trophic level. The pyramid narrows sharply because each level has ~10% of the energy below it. This is why there is far more plant biomass than herbivore biomass, and far more herbivore biomass than carnivore biomass in any ecosystem.
Common Mistake
Students often say “90% of energy is lost in respiration.” While respiration is the biggest single drain, the 90% loss is distributed across respiration (~60%), excretion/faeces (~20-25%), and incomplete consumption (~10-15%). CBSE often asks for multiple reasons — listing only respiration will cost marks.
The 10% is an approximation — actual efficiency varies from 5% to 20% depending on the ecosystem and organisms involved. Warm-blooded animals (mammals, birds) spend more energy on thermoregulation, so their efficiency is lower. Cold-blooded animals (fish, insects) are more efficient (up to 20%) because they don’t spend energy maintaining body temperature.