Trophic levels are formed by -
- (a)Plants only
- (b)Carnivorous animals only
- (c)Organisms linked in food chain
- (d)Animals only
Correct — C, Organisms linked in food chain. A trophic level is a feeding step in a food chain; it is defined by an organism’s position in the flow of food and energy. All organisms sharing the same feeding position — producers, herbivores, carnivores, decomposers — occupy the same trophic level. Since trophic levels arise from organisms linked together in a food chain, option (c) is correct.
- (a)Plants only — Plants (producers) form just the first trophic level. Trophic levels also include herbivores, carnivores and decomposers, so ‘plants only’ is incomplete.
- (b)Carnivorous animals only — Carnivores occupy only the higher trophic levels (secondary/tertiary consumers). They alone cannot form all trophic levels, which begin with producers.
- (d)Animals only — This excludes producers (green plants/phytoplankton) and decomposers, which are essential trophic levels — the first level is made of producers, not animals.
In an ecosystem, energy flows from the Sun through producers to a series of consumers. Each feeding step is a trophic level: producers (1st), primary consumers/herbivores (2nd), secondary consumers (3rd), tertiary consumers (4th), with decomposers acting on all levels. Organisms linked in this feeding sequence — the food chain (and interlinked food webs) — constitute the trophic levels.
The three wrong options each pick just one group (plants, carnivores, or animals). The correct idea is broader: a trophic level is about feeding position within a food chain, so it is formed by the organisms linked together in that chain, whatever their type.
- A trophic level = a feeding step in a food chain, based on the source of an organism’s food/energy.
- Sequence: producers → primary consumers (herbivores) → secondary/tertiary consumers (carnivores).
- Energy transfer between successive trophic levels averages only about 10% (Lindeman’s ‘ten per cent’ law).
- Decomposers (bacteria, fungi) recycle nutrients from every trophic level.
- 1st level — Producers (green plants, phytoplankton)
- 2nd level — Primary consumers (herbivores)
- 3rd level — Secondary consumers (carnivores)
- 4th level — Tertiary consumers (top carnivores)
- Across all — Decomposers recycle nutrients
Trophic levels are formed by organisms at each feeding step of the food chain — option (c).
- Equating a trophic level with only plants or only animals — it is a feeding position, not a taxonomic group
- Forgetting decomposers as a functional part of the trophic structure
UPSC/UPPSC ask to define a trophic level, arrange a correct food-chain sequence, or reason about energy loss between levels.
With reference to food chains in ecosystems, consider the following statements: 1. A food chain illustrates the order in which a chain of organisms feed upon each other. 2. Food chains are found within the populations of a species. 3. A food chain illustrates the numbers of each organism which are eaten by others. Which of the statements given above is/are correct?
- (a) 1 only
- (b) 1 and 2 only
- (c) 1, 2 and 3
- (d) None
Answer(a) 1 only
Same concept — a food chain is the sequence in which organisms feed on one another (linking different species); trophic levels are the feeding steps within it.
Which one of the following is the correct sequence of a food chain?
- (a) Diatoms-Crustaceans-Herrings
- (b) Crustaceans-Diatoms-Herrings
- (c) Diatoms-Herrings-Crustaceans
- (d) Crustaceans-Herrings-Diatoms
Answer(a) Diatoms-Crustaceans-Herrings
Same concept applied — ordering producers → primary consumers → secondary consumers is exactly arranging organisms by trophic level in a food chain.
- practice — not a real PYQ
In a food chain, roughly what percentage of energy is transferred from one trophic level to the next?
- (a)1%
- (b)10%
- (c)50%
- (d)90%
Answer(b) 10% — Lindeman’s ten-per-cent law of energy transfer between trophic levels.
- practice — not a real PYQ
Which of the following occupies the first trophic level in an ecosystem?
- (a)Herbivores
- (b)Carnivores
- (c)Green plants (producers)
- (d)Decomposers
Answer(c) Green plants (producers) — they capture solar energy and form the base trophic level.