•  The process of transpiration is basically water evaporating from the surface of a plant.
• in order for this to happen water has to turn into gas which is only possible through heat which is provided by the sun.
• the sunlight is then absorbed by the structure of the leaves. The light energy from the sun turns into heat energy therefore the liquid water turns into gas
• The evaporation is through the stomatal pores.
• When sunlight is shone on the leaves not all of it is taken in by the chloroplasts. It is also taken in by other cell structures which generate some heat.  
• The water is transported uo through the xylem and moved through the spongy musifiles
• Just above the stomatal pore and in the middle of the spongy musifiles is where the conversion from liquid to gas takes place.
• The gas then diffuses through the stamatal pores at a steep diffusion gradient.

Summary:

• Sunlight warms leaf
• Liquid water is turned to gas
• Gas is diffused through stamatal pores