2.54 Transpiration

• for evaporation to occur: water (liquid) ---->  water vapour (gas).     and for this to occur you need heat. to get this heat we use sunlight

• water is delivered in from leaf by xylem, and from there it moves through the spongy mesophyll layer and then to just above the stomatal pore. 

• then the gas water vapour diffuses through the stomatal pore through a fairly steep diffusion gradient,  as the water vapour inside the stomatal pore is at 100% humidity and outside the leaf the humidity is less than that and the distance between them is only one cell thick.