B3.1.12 (HL)—Bohr shift
The Bohr shift links high carbon dioxide, lower blood pH and reduced haemoglobin oxygen affinity, increasing oxygen release in active tissues.
- Syllabus
- First assessment 2025
- Objective
- B3.1.12
- Level
- HL
Exam analysis
Chance of appearing8%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper3
Typical marks1–6
Common command terms
- Explain
- Draw
Scoring notes
- Common mistake
- Drawing or describing the Bohr shift in the wrong direction when carbon dioxide increases.
Recent exam appearances
November 2025Paper1A ["HL"] · TZ123[ 1 ]B3.1.12 (HL)—Bohr shift
May 2025Paper1A ["HL"] · TZ325[ 1 ]B3.1.12 (HL)—Bohr shift
November 2024Paper3 ["HL"] · TZ021(d)[ 3 ]B3.1.12 (HL)—Bohr shift
November 2020Paper3 ["HL"] · TZ023(a)[ 3 ]B3.1.12 (HL)—Bohr shift
May 2019Paper3 ["HL"] · TZ124(b)[ 6 ]B3.1.12 (HL)—Bohr shift
Practice this objective
Coverage 2014–2025 · Updated 15 Jul 2026
Concept essentials
- Respiring tissues produce carbon dioxide, which lowers blood pH.
- Lower pH reduces haemoglobin affinity for oxygen.
- The Bohr shift moves the oxygen dissociation curve to the right.
- At a given oxygen partial pressure, more oxygen is released to active tissues.
- The Bohr effect helps match oxygen delivery to tissue respiration rate.