Question
What is the difference between a food chain and a food web? Give one example each from a forest ecosystem and a pond ecosystem. What happens to energy at each trophic level?
(NCERT Class 10 — Our Environment)
Solution — Step by Step
A food chain is a single linear pathway showing who eats whom:
Producer → Primary Consumer → Secondary Consumer → Tertiary Consumer
A food web is a network of interconnected food chains in an ecosystem. It shows that most organisms eat (and are eaten by) multiple species.
Food chain: Grass → Deer → Tiger
Food web connections: Grass is also eaten by rabbits and insects. Rabbits are eaten by snakes and eagles. Deer are eaten by tigers and leopards. Snakes are eaten by eagles. These interconnections form a web.
Food chain: Algae → Small fish → Big fish → Crane
Food web connections: Algae are eaten by tadpoles, water fleas, and small fish. Tadpoles are eaten by small fish and water snakes. Small fish are eaten by big fish, cranes, and kingfishers. Multiple pathways = food web.
At each trophic level, only 10% of the energy is passed to the next level. The rest is lost as heat through respiration.
This is the 10% law (given by Lindeman). It explains why food chains rarely have more than 4-5 trophic levels — there is simply not enough energy left.
Why This Works
Energy enters the ecosystem through producers (photosynthesis). At each step, organisms use most of the energy for their own life processes, and only a fraction gets stored in their body (available to the next level).
Food webs are more stable than single food chains. If one species disappears, other pathways can compensate. In a single food chain, removing one link breaks the entire chain. This is why biodiversity matters — more connections mean a more resilient ecosystem.
Alternative Method
You can also describe trophic levels using a pyramid of energy — a bar diagram where each level is smaller than the one below. This visual representation makes the 10% law very clear and is often asked in CBSE diagrams.
For NEET, remember the distinction: pyramid of energy is always upright (energy always decreases). But pyramid of biomass can be inverted in aquatic ecosystems (small algae support large fish biomass at any instant). This is a common MCQ trap.
Common Mistake
Students often confuse the 10% law with “10% of food is eaten.” The 10% law says 10% of ENERGY is transferred to the next trophic level — not 10% of the organisms or 10% of the food. The rest is used in respiration, lost as heat, or goes to decomposers. Be precise with your wording in board answers.