Question
Why is only 10% of energy transferred from one trophic level to the next? Explain Lindeman’s 10% Law with an example and state its significance in determining food chain length.
Solution — Step by Step
At every trophic level, an organism takes in food energy but uses most of it just to stay alive — respiration, movement, maintaining body temperature, reproduction. This metabolic work releases energy as heat, which is permanently lost to the environment.
Not all of a plant gets consumed by a herbivore. Roots, bark, tough cellulose — a large fraction is never ingested. What is ingested isn’t fully digested either; some exits as faeces. So the energy available to the next level is already a small fraction before metabolism even begins.
Raymond Lindeman (1942) quantified this: on average, only about 10% of the energy stored at one trophic level is transferred to and stored as biomass at the next trophic level. The remaining ~90% is lost as heat (respiration), undigested waste, or simply never eaten.
Say a grassland fixes 1000 J of solar energy into plant biomass (producers).
| Trophic Level | Energy Available |
|---|---|
| Producers (grass) | 1000 J |
| Primary consumers (grasshoppers) | 100 J |
| Secondary consumers (frogs) | 10 J |
| Tertiary consumers (snakes) | 1 J |
By the time we reach a top predator, almost nothing is left. This is why food chains rarely exceed 4–5 trophic levels.
The rule tells us that the total biomass supportable at each level drops by 90% with each step. A given ecosystem can support far more herbivores than carnivores, and far more plants than herbivores — energy flow dictates population size at every level.
Why This Works
The fundamental reason is thermodynamics. The second law states that every energy conversion generates heat that cannot be recaptured by biological systems. When a grasshopper oxidises glucose in its muscles, that energy becomes body heat — permanently unavailable to the frog that eats it.
The 10% figure is an ecological average, not a strict law. Actual transfer efficiencies vary: warm-blooded (endothermic) animals like birds and mammals lose far more to thermoregulation, so their efficiencies can be as low as 1–2%. Cold-blooded animals like fish or insects are more efficient, sometimes reaching 15–20%.
For NEET and CBSE boards, the clean 10% number is what you work with. The underlying principle — energy is dissipated at every step — is the concept worth owning.
Alternative Method — Energy Pyramid Approach
Instead of tracing a single chain, draw an Ecological Pyramid of Energy. Each bar represents the total energy (in kcal/m²/year) flowing through that trophic level.
For a standard NCERT-style problem with 10% efficiency:
So if a snake population requires 10 J, the frogs below must have had 100 J, the grasshoppers 1000 J, the grass 10,000 J. Work backwards from the top predator’s requirement — this is the reverse calculation NEET loves to ask.
NEET frequently asks: “How much energy must producers fix to support 1 kcal at the 4th trophic level?” Work backwards: 1 → 10 → 100 → 1000 kcal. The answer is 1000 kcal at the producer level. One multiplication step per trophic level.
Common Mistake
Students often write “90% energy is lost because it is used by the organism for its life processes.” This is only partially correct. Energy is lost through three routes: respiration (heat), undigested matter (faeces), and uneaten biomass. Writing only “respiration” costs you a mark in NEET and CBSE long-answer questions. Always mention all three.
A second trap: confusing energy transfer with energy storage. The 10% rule is about how much energy becomes stored biomass at the next level — not how much energy the organism receives as food. Some CBSE papers ask specifically about “assimilation efficiency” vs “transfer efficiency”; keep those distinct.
Quick Recap
- Lindeman’s 10% Law: only 10% of energy at one trophic level becomes biomass at the next
- ~90% lost via heat (respiration), faeces, and uneaten material
- Limits food chains to 4–5 levels — beyond that, energy is negligible
- Reverse calculation trick: multiply by 10 for each step you move down the chain
This concept carries good weightage in NEET (Chapter 14, Ecosystem) — expect one direct question and sometimes a data-based question using the energy pyramid. The calculation type is always straightforward once you own the 10× rule.