Transpiration
Exam-ready definition
The loss of water vapour from the leaves of a plant, mainly through the stomata, as water evaporates from the surfaces of mesophyll cells.
How this is marked
Two details earn marks: water vapour (not liquid water) and through stomata. Factor questions (temperature, humidity, wind speed) want explanations in terms of evaporation rate and diffusion gradients, not just 'it gets faster'.
In an exam answer
Explaining water loss on a hot day: 'Water evaporates from the mesophyll cell surfaces and the water vapour diffuses out through the open stomata. This is transpiration.'
Full topic guide: Transport in animals
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