B3.1.7—Leaf gas exchange adaptations
Leaf gas exchange occurs through stomata and internal air spaces, with guard cells balancing carbon dioxide uptake against water loss.
- Syllabus
- First assessment 2025
- Objective
- B3.1.7
- Level
- HL
Exam analysis
Chance of appearing4%of analysed past papers
Latest appearanceMay 2025
Most common paperPaper2
Typical marks1–2
Common command terms
- Identify
- Explain
Scoring notes
- Common mistake
- Calling any pore a stoma without identifying the guard-cell opening through the epidermis.
Recent exam appearances
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
November 2020Paper1 ["HL"] · TZ032[ 1 ]B3.1.7—Leaf gas exchange adaptations
November 2020Paper3 ["HL"] · TZ01(b)[ 1 ]B3.1.7—Leaf gas exchange adaptations
May 2013Paper1 ["HL"] · TZ232[ 1 ]B3.1.7—Leaf gas exchange adaptations
Practice this objective
Coverage 2012–2025 · Updated 15 Jul 2026
Concept essentials
- Stomata allow carbon dioxide, oxygen and water vapour to diffuse through the epidermis.
- Guard cells regulate stomatal opening by changing turgor.
- Spongy mesophyll air spaces provide internal diffusion routes.
- The upper epidermis and cuticle protect the leaf while allowing light entry.