C4.2.10—Trophic levels
Trophic levels explains how energy flow, matter cycling, trophic transfer or carbon movement is represented, measured or limited within ecosystems.
- Syllabus
- First assessment 2025
- Objective
- C4.2.10
- Level
- HL
Exam analysis
Chance of appearing14%of analysed past papers
Latest appearanceMay 2025
Most common paperPaper1
Typical marks1
Common command terms
- Identify
- Explain
- Discuss
- Deduce
- Describe
- State
- Distinguish
- Suggest
Scoring notes
- Common mistake
- Reversing food-web arrows instead of showing energy transfer direction.
Recent exam appearances
May 2025Paper2 ["HL"] · TZ22(c)[ 1 ]C4.2.10—Trophic levels
November 2023Paper3 ["HL"] · TZ216(b)[ 1 ]C4.2.10—Trophic levels
May 2023Paper2 ["HL"] · TZ24(a)(ii)[ 2 ]C4.2.10—Trophic levels
May 2023Paper3 ["HL"] · TZ216(a)[ 1 ]C4.2.10—Trophic levels
May 2023Paper3 ["HL"] · TZ115(a)[ 1 ]C4.2.10—Trophic levels
Practice this objective
Coverage 2012–2025 · Updated 16 Jul 2026
Trophic levels describe feeding position
A trophic level classifies an organism by its feeding position in a particular food chain.
| Trophic level | Role | Example in grass → grasshopper → frog → snake |
|---|---|---|
| Producer | Synthesizes organic carbon from inorganic sources | Grass |
| Primary consumer | Feeds on producer | Grasshopper |
| Secondary consumer | Feeds on primary consumer | Frog |
| Tertiary consumer | Feeds on secondary consumer | Snake |
An omnivorous bird may be a primary consumer when eating seeds and a secondary consumer when eating herbivorous insects, so trophic level depends on the food chain.
Trophic level is not body size, intelligence or a permanent label for a species with a varied diet.
Trophic levels
Assessment in practice
1 marksHow it is assessed
This objective is assessed through structured response, commonly using Identify / Explain / Discuss.
Command terms
Identify / Explain / Discuss / Deduce / Describe / State / Distinguish / Suggest
What earns marks
Build the answer around this relationship: Trophic levels must be linked to the correct source, store, transfer or loss process.
Watch for
Reversing food-web arrows instead of showing energy transfer direction.
Representative question
Question 1
Explain, using an example of a food chain, how trophic levels can be deduced.
Energy and Matter
- Ecosystems are open systems: energy flows through them and leaves as heat, while matter is recycled and may enter or leave.
- Photoautotrophs capture light; chemoautotrophs oxidize inorganic substances. Both build biomass from inorganic carbon. Heterotrophs obtain organic carbon from other organisms.
- Food-web arrows show energy and biomass transfer. Energy decreases between trophic levels through respiration, heat, egestion, excretion and uneaten material, limiting chain length.
- Gross primary production minus producer respiration gives net primary production; secondary production is heterotroph biomass gain.
- Decomposers obtain energy from detritus and return inorganic nutrients to producers.
- Carbon-cycle diagrams distinguish stores and fluxes. Photosynthesis removes CO2; respiration, decomposition and combustion release it.
- A sink absorbs more carbon than it releases; a source does the reverse. The Keeling Curve shows a long-term atmospheric CO2 rise with seasonal oscillation.
Concept essentials
- Trophic levels must be linked to the correct source, store, transfer or loss process.
- The evidence for trophic levels depends on distinguishing energy flow from matter cycling.
- Trophic levels is clearer when arrows, units and trophic positions match the biological process.
- Data or diagrams for trophic levels need interpretation as ecosystem transfer evidence.