Trophic levels: producers, consumers and decomposers
Every organism in a feeding relationship sits at a trophic level — a feeding level, counted from the start of the food chain.
The levels
| Trophic level | Name | What it does | Example |
|---|---|---|---|
| 1 | Producer | Makes its own food by photosynthesis; traps light energy | Grass, oak tree, phytoplankton |
| 2 | Primary consumer | Eats the producer — a herbivore | Rabbit, caterpillar, zooplankton |
| 3 | Secondary consumer | Eats the primary consumer — usually a carnivore | Stoat, blue tit, small fish |
| 4 | Tertiary consumer | Eats the secondary consumer | Fox, hawk, tuna |
Decomposers (bacteria and fungi) feed on dead organisms and waste (faeces, urine, fallen leaves). They break down these materials and release mineral ions, such as nitrates, back into the soil where plants can absorb them. Decomposers are not usually given a number — they act on every trophic level.
How to work out a trophic level
Count the arrows from the producer, don't guess from the animal's size or how fierce it looks.
grass → grasshopper → frog → snake → hawk
- grass = producer
- grasshopper = primary consumer (it eats the producer)
- frog = secondary consumer
- snake = tertiary consumer
- hawk = quaternary consumer (just say "fourth trophic level" if unsure)
The same species can occupy different trophic levels in different chains within a food web. A fox eating a rabbit is a secondary consumer; a fox eating blackberries is a primary consumer.
Words that get confused
| Term | Meaning |
|---|---|
| Population | All the organisms of one species in an area |
| Community | All the populations of all species living in an area |
| Ecosystem | The community plus the non-living (abiotic) parts of the habitat |
A question asking about the community wants only living organisms; a question about the ecosystem also allows soil, water, light and temperature.
Common mistake: writing "secondary consumer" for the herbivore. A primary consumer is the first consumer, i.e. the animal that eats the plant — it is not the first animal to be eaten. Examiners report this swap every series.
Examiner tip. Two confusions cost marks here repeatedly: (1) primary vs secondary consumer — always count arrows from the producer rather than relying on memory; (2) community vs ecosystem — 'community' is living organisms only, 'ecosystem' includes the physical environment. Read the stem word carefully before answering.