Why this matters now
These fundamentals underpin all environment questions — food chains, trophic levels, the 10% energy law and ecological pyramids are direct Prelims favourites.
The ecosystem and its components
An ecosystem is a community of living organisms interacting with their non-living environment. It has abiotic components (sunlight, water, air, soil, temperature) and biotic components: producers (green plants — autotrophs), consumers (herbivores, carnivores) and decomposers (bacteria, fungi that recycle nutrients).
Food chains, food webs and trophic levels
Energy flows through a food chain — producer → herbivore → carnivore — and interlinked chains form a food web. Each feeding stage is a trophic level. Energy transfer is one-way and inefficient: only about 10% of energy passes to the next level (the 10% law), which is why food chains are short.
Ecological pyramids
Ecological pyramids represent the relationship between trophic levels by number, biomass or energy. The pyramid of energy is always upright; pyramids of number and biomass can sometimes be inverted (e.g. in some aquatic ecosystems).
Nutrient cycles
While energy flows through and is lost, nutrients cycle repeatedly through biogeochemical cycles (carbon, nitrogen, phosphorus, water). Decomposers return nutrients to the soil/water, sustaining the system. This balance of energy flow and nutrient cycling keeps ecosystems functioning.
UPSC angle
Know the components (producers/consumers/decomposers), food chain vs web, the 10% law, and that the energy pyramid is always upright (number/biomass can invert). Distinguish energy flow (one-way) from nutrient cycling (recycled).
Frequently asked questions
What is an ecosystem?
A community of living organisms interacting with their non-living (abiotic) environment as a functional unit.
What is the 10% law?
Only about 10% of the energy at one trophic level is transferred to the next, so energy is rapidly lost up a food chain.
What is the difference between a food chain and a food web?
A food chain is a single linear sequence of who eats whom; a food web is the network of many interconnected food chains.
Which ecological pyramid is always upright?
The pyramid of energy is always upright; pyramids of number and biomass can sometimes be inverted.