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C4.2.19—CO₂ release during combustion

CO₂ release during combustion explains how energy flow, matter cycling, trophic transfer or carbon movement is represented, measured or limited within ecosystems.

Syllabus
First assessment 2025
Objective
C4.2.19
Level
SL

Exam analysis

Chance of appearing2%of analysed past papers
Latest appearanceNovember 2023
Most common paperPaper1
Typical marks1

Common command terms

  • Calculate
  • Compare
  • Contrast
  • Identify
  • State

Scoring notes

Common mistake
Reversing photosynthesis and respiration arrows in carbon-cycle diagrams.

Recent exam appearances

November 2023Paper1 ["SL"] · TZ221[ 1 ]C4.2.19—CO₂ release during combustion
November 2023Paper1 ["SL"] · TZ121[ 1 ]C4.2.19—CO₂ release during combustion
November 2023Paper2 ["SL"] · TZ21(a)[ 1 ]C4.2.19—CO₂ release during combustion
Practice this objective

Coverage 2023–2023 · Updated 16 Jul 2026

Combustion transfers stored carbon to the atmosphere

Combustion transfers stored carbon to the atmosphere.

Burning an organic fuel oxidises its carbon and usually releases CO₂. The atmospheric increase depends on fuel carbon, oxidation completeness and subsequent uptake.

fuel carbon; oxidation; CO₂ output; incomplete combustion products; later sinks.

Burning methane produces CO₂ and water when complete, while limited oxygen also produces carbon monoxide and soot.

Combustion releases carbon; it does not create carbon atoms.

CO₂ release during combustion

Assessment in practice

1 marks
How it is assessed

This objective is assessed through multiple choice, commonly using Calculate / Compare / Contrast.

Command terms

Calculate / Compare / Contrast / Identify / State

What earns marks

Build the answer around this relationship: CO₂ release during combustion must be linked to the correct source, store, transfer or loss process.

Watch for

Reversing photosynthesis and respiration arrows in carbon-cycle diagrams.

Representative question

Question 1

[Maximum number: 1]

The graph shows how the worldwide use of fossil fuels has increased from 1800 to 2019.

How has the increased combustion of fossil fuels contributed significantly to global warming?

A

The heat released raises the temperature of the air.

B

Combustion causes ozone depletion, which enhances the greenhouse effect.

C

Carbon dioxide produced by combustion prevents radiation from the Sun reaching Earth.

D

The products of combustion absorb long wave radiation.

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

  • CO₂ release during combustion must be linked to the correct source, store, transfer or loss process.
  • The evidence for co₂ release during combustion depends on distinguishing energy flow from matter cycling.
  • CO₂ release during combustion is clearer when arrows, units and trophic positions match the biological process.
  • Data or diagrams for co₂ release during combustion need interpretation as ecosystem transfer evidence.
ConceptIB Biology SL