B3.1.9—Transpiration
Transpiration is water loss from leaves, driven by evaporation and diffusion through stomata and altered by humidity, temperature, wind and light.
- Syllabus
- First assessment 2025
- Objective
- B3.1.9
- Level
- HL
Exam analysis
Chance of appearing15%of analysed past papers
Latest appearanceMay 2025
Most common paperPaper3
Typical marks1–2
Common command terms
- Explain
- Outline
- Suggest
- Define
- Compare
Scoring notes
- Common mistake
- Assuming a potometer directly measures water lost rather than estimating it from water uptake.
Recent exam appearances
May 2025Paper1A ["HL"] · TZ124[ 1 ]B3.1.9—Transpiration
November 2024Paper2 ["HL"] · TZ01(i)[ 2 ]B3.1.9—Transpiration
November 2024Paper2 ["HL"] · TZ01(d)[ 2 ]B3.1.9—Transpiration
November 2023Paper1 ["HL"] · TZ228[ 1 ]B3.1.9—Transpiration
May 2023Paper3 ["HL"] · TZ13(d)[ 2 ]B3.1.9—Transpiration
Practice this objective
Coverage 2012–2025 · Updated 15 Jul 2026
Concept essentials
- Transpiration involves evaporation from leaf surfaces followed by diffusion through stomata.
- Low humidity, higher temperature and wind usually increase the rate of transpiration.
- Light can increase transpiration by promoting stomatal opening for photosynthesis.
- Potometers estimate water uptake over time as an indirect measure of transpiration.
- Drought can reduce transpiration when stomata close to conserve water.