8.3: Transpiration
The Loss of Water Vapour from Leaves
📖 SYLLABUS DEFINITION:
Transpiration: The loss of water vapour from plant leaves by evaporation of water at the surfaces of the mesophyll cells followed by diffusion of water vapour through the stomata.
The Two-Step Process
Step 1: Evaporation
Water on the surface of mesophyll cells turns into water vapour (gas). This happens in the air spaces inside the leaf.
Step 2: Diffusion
Water vapour moves from high concentration (inside leaf) to low concentration (outside) through the stomata.
Interactive Leaf Cross-Section
🔥 Higher Temperature = More kinetic energy → Faster evaporation → More water vapour → Faster diffusion out
⚠️ EXAMINER TRAP:
NEVER say "water evaporates from the stomata." Water evaporates from mesophyll cells into air spaces, then water vapour diffuses through stomata. Two separate processes!
🎯 FINAL EXAM TIPS:
- 1.Never say "water evaporates from stomata" - it evaporates from mesophyll cells!
- 2.Always use specific terms: "diffusion" not "movement", "concentration gradient" not "difference"
- 3.For factor questions, explain the mechanism: How does it affect evaporation/diffusion?
- 4.Remember: Transpiration = Evaporation (liquid → gas) + Diffusion (through stomata)
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