Lesson 8 of 11 · 9 min
Trophic levels and the 10 per cent law
NCERT §12.4
Ma'am hands out ten biscuits to the first student in a line, who must pass one on and keep or drop the rest. By the fourth student there are no biscuits left to share.
The lesson in notes
In short
An organism's trophic level is its place in the food chain, based on its source of food.
Producers form the first trophic level, herbivores (primary consumers) the second and carnivores (secondary consumers) the third.
The amount of energy decreases at each successive trophic level.
When any organism dies it becomes detritus, dead biomass that is an energy source for decomposers.
The standing crop is the mass of living material at a trophic level at a given time, measured as biomass or as number per unit area.
Biomass is given as fresh or dry weight; dry weight is the more accurate measure.
The 10 per cent law: each trophic level receives just a tenth of the energy held by the level below it.
This limits the number of levels in a grazing food chain: producer, herbivore, primary carnivore, secondary carnivore.