This topic summary covers Knowledge Organiser within Transpiration for GCSE Biology. Transpiration process, stomatal control, factors affecting rate, plant adaptations, measuring transpiration, and practical investigations It is section 18 of 20 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 18 of 20
Practice
20 questions
Recall
25 flashcards
Knowledge Organiser
Key Terms
- Transpiration — water evaporation through stomata
- Transpiration stream — water pathway from root to leaf
- Stomata — pores in leaf epidermis
- Guard cells — control stomatal opening
- Potometer — measures water uptake rate
- Xerophyte — adapted to dry conditions
- Wilting — loss of cell turgor due to water deficit
- Boundary layer — humid air layer at leaf surface
Factors — THAW
- Temperature up → transpiration up (more kinetic energy)
- Humidity down → transpiration up (steeper gradient)
- Air movement up → transpiration up (removes boundary layer)
- Wavelength/light up → stomata open → transpiration up
- All four act by changing the concentration gradient or the area of the stomatal pore
Must-Know Facts
- 99% of water absorbed is lost by transpiration
- Stomata are mainly for CO₂ in / O₂ out — water loss is a trade-off
- Potometer measures uptake, NOT transpiration directly
- Cut shoot underwater — prevents air locks in xylem
- Guard cells open by K⁺ in → osmosis → turgid → pore opens
- Marram grass: rolled leaf, sunken stomata, hairs in grooves
Xerophyte Adaptations
- Thick waxy cuticle — reduces cuticular evaporation
- Sunken stomata — humid air trapped in pit
- Rolled leaves (marram grass) — encloses humid air
- Hairs in grooves — trap water vapour near stomata
- Reduced leaf area — less surface for evaporation
- CAM photosynthesis — stomata open at night only (Higher)