C4.2.18—Carbon sinks and sources
Carbon sinks and sources explains how energy flow, matter cycling or carbon transfer is represented, measured or limited within ecosystems.
- Syllabus
- First assessment 2025
- Objective
- C4.2.18
- Level
- HL
Exam analysis
Chance of appearing4%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper1
Typical marks1–2
Common command terms
- Identify
- Explain
- Describe
Scoring notes
- Common mistake
- Reversing photosynthesis and respiration arrows in carbon-cycle diagrams.
Recent exam appearances
November 2025Paper2 ["HL"] · TZ14(b)[ 2 ]C4.2.18—Carbon sinks and sources
May 2025Paper1A ["HL"] · TZ237[ 1 ]C4.2.18—Carbon sinks and sources
May 2018Paper1 ["HL"] · TZ224[ 1 ]C4.2.18—Carbon sinks and sources
November 2017Paper2 ["HL"] · TZ08(c)[ 4 ]C4.2.18—Carbon sinks and sources
November 2016Paper1 ["HL"] · TZ015[ 1 ]C4.2.18—Carbon sinks and sources
Practice this objective
Coverage 2016–2025 · Updated 16 Jul 2026
Concept essentials
- Carbon sinks and sources must be linked to the correct source, store, transfer or loss process.
- The evidence for carbon sinks and sources depends on distinguishing energy flow from matter cycling.
- Carbon sinks and sources is clearer when arrows, units and trophic positions match the biological process.
- Data or diagrams for carbon sinks and sources need interpretation as ecosystem transfer evidence.