B3.1 Gas exchange
Gas exchange links animal ventilation, alveolar diffusion, leaf stomata, transpiration and haemoglobin affinity to oxygen supply and carbon dioxide removal.
- Syllabus
- First assessment 2025
- Topic
- B3.1
- Level
- HL
What you’ll learn
13 learning objectivesChoose one objective for a focused lesson, or study the complete topic.
Exam analysis
An aggregate view of how the complete B3.1 Gas exchange appears across past papers.
Chance of appearing45%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper3
Most tested objectives
- B3.1.9—Transpiration22 questions
- B3.1.5—Lung ventilation11 questions
- B3.1.12 (HL)—Bohr shift10 questions
Common question formats
- Process explanation
- Definition or recall
- Graph interpretation
- Diagram interpretation
- Calculation
- Experimental design
- Comparison
Exam question appearances
November 2025Paper1A ["HL"] · TZ123[ 1 ]B3.1.12 (HL)—Bohr shift
May 2025Paper2 ["HL"] · TZ36(b)[ 2 ]B3.1.7—Leaf gas exchange adaptations
May 2025Paper2 ["HL"] · TZ36(a)[ 2 ]B3.1.7—Leaf gas exchange adaptations
May 2025Paper2 ["HL"] · TZ34(d)[ 2 ]B3.1.5—Lung ventilation
May 2025Paper1A ["HL"] · TZ325[ 1 ]B3.1.12 (HL)—Bohr shift
Practice this topic
10 original exam-style questions based on the patterns above.
Coverage 2012–2025 · Updated 15 Jul 2026