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B3.1.13 (HL)—Oxygen dissociation curves

Oxygen dissociation curves show how adult haemoglobin, foetal haemoglobin and myoglobin differ in percentage saturation, oxygen affinity and oxygen release.

Syllabus
First assessment 2025
Objective
B3.1.13
Level
HL

Exam analysis

Chance of appearing4%of analysed past papers
Latest appearanceMay 2025
Most common paperPaper3
Typical marks1–6

Common command terms

  • Explain
  • Discuss
  • State
  • Identify
  • Describe

Scoring notes

Common mistake
Reversing graph axes or failing to label partial pressure of oxygen and percentage saturation correctly.

Recent exam appearances

May 2025Paper1B ["HL"] · TZ21(b)[ 2 ]B3.1.13 (HL)—Oxygen dissociation curves
May 2025Paper1B ["HL"] · TZ21(a)[ 1 ]B3.1.13 (HL)—Oxygen dissociation curves
May 2023Paper3 ["HL"] · TZ123(c)[ 1 ]B3.1.13 (HL)—Oxygen dissociation curves
May 2019Paper3 ["HL"] · TZ223[ 6 ]B3.1.13 (HL)—Oxygen dissociation curves
May 2017Paper3 ["HL"] · TZ121(b)[ 2 ]B3.1.13 (HL)—Oxygen dissociation curves
Practice this objective

Coverage 2012–2025 · Updated 15 Jul 2026

Concept essentials

  • Adult haemoglobin shows a sigmoid oxygen dissociation curve because of cooperative binding.
  • Higher oxygen partial pressure increases haemoglobin saturation until the curve plateaus.
  • Foetal haemoglobin is left-shifted because it has greater oxygen affinity than adult haemoglobin.
  • Myoglobin has very high oxygen affinity and a curve further left than foetal haemoglobin.
ConceptIB Biology HL