Biology · Ecosystems · NEET
It is the 10 percent law, not the 1 percent law. Only about 10 percent of energy moves to the next trophic level. NEET 2026 gave a trap statement saying "transfer of energy follows the 1% law" and it was marked WRONG. The 1 percent (actually 2-10 percent) figure is about how much PAR plants capture from sunlight, not about transfer between levels. Do not mix the two.
The 10 percent law was given by Raymond Lindeman in 1942. He studied energy flow in a lake and found roughly 10 percent of energy passes from one trophic level to the next. For NEET you should remember both the name Lindeman and the value 10 percent.
About 90 percent is lost at each step. Most is lost as heat during respiration. Some energy is used for movement, growth, and daily activities, and some is never eaten (dead parts, not all prey is caught). Because energy leaves as heat, it cannot be reused, which is why energy flow is unidirectional.
The 10 percent law is about ENERGY transfer between trophic levels. It is not a strict rule for biomass or number. Biomass and number pyramids can even be inverted, but the pyramid of energy is always upright because of this energy loss. So in a numerical, apply 10 percent to energy values (kcal), not blindly to grams.
The energy available to the next level is taken from the NPP (net primary productivity) of the level below, and it becomes the GPP of the next level. So NPP of one level x 10% = energy entering (GPP of) the next level. NEET 2024 tested exactly this: NPP of level 1 = 100x, so GPP of level 2 = 10x, and GPP of level 3 = 1x. Watch which level the question asks for.
In an ecosystem, if the Net Primary Productivity (NPP) of the first trophic level is 100x kcal m⁻² yr⁻¹, what would be the GPP (Gross Primary Productivity) of the third trophic level of the same ecosystem?
Which of the following statements are correct? (a) Energy flow from producers to consumers is unidirectional; (b) Energy pyramid can never be inverted; (c) Transfer of energy follows the 1% law.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is the rule that only about 10 percent of the energy present at one trophic level is passed to the next higher trophic level, while roughly 90 percent is lost, mainly as heat.
At each level, organisms use most energy for respiration, movement, and body upkeep, and much escapes as heat. Not all food is eaten or digested either. So only a small fraction, about 10 percent, is stored and available to the next level.
Since energy drops to one-tenth at each step, after 4 to 5 levels very little energy is left to support any organisms. That is why food chains usually have only 3 to 5 trophic levels.
No, it is an average approximation. Actual transfer efficiency varies from about 5 to 20 percent in real ecosystems, but for NEET you use the standard 10 percent value.
Multiply by 1/10 for each step you move up the food chain. If producer energy is 1000 units, the herbivore level gets 100, the next gets 10, and so on. Always check which trophic level the question asks about.
