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C1.2.4—Cell respiration system

Cell respiration releases energy from organic compounds in controlled enzyme-catalysed stages, transferring that energy into ATP, supporting usable cellular work and measurable biological activity.

Syllabus
First assessment 2025
Objective
C1.2.4
Level
HL

Exam analysis

Chance of appearing5%of analysed past papers
Latest appearanceMay 2025
Most common paperPaper2
Typical marks1–3

Common command terms

  • Identify
  • Outline
  • Distinguish
  • Suggest
  • Explain
  • Define
  • Compare
  • Describe

Recent exam appearances

May 2025Paper1A ["HL"] · TZ17[ 1 ]C1.2.4—Cell respiration system
November 2023Paper2 ["HL"] · TZ21(h)[ 3 ]C1.2.4—Cell respiration system
November 2023Paper2 ["HL"] · TZ21(g)[ 2 ]C1.2.4—Cell respiration system
November 2018Paper1 ["HL"] · TZ010[ 1 ]C1.2.4—Cell respiration system
May 2018Paper2 ["HL"] · TZ21(c)[ 2 ]C1.2.4—Cell respiration system
Practice this objective

Coverage 2013–2025 · Updated 15 Jul 2026

Concept essentials

  • Cell respiration releases energy from organic compounds to form ATP.
  • Glycolysis is part of cellular respiration and occurs before mitochondrial stages.
  • Aerobic respiration uses oxygen and produces carbon dioxide, water and high ATP yield.
  • Oxidation involves electron loss, oxygen gain or hydrogen loss.
ConceptIB Biology HL