2.54) Transpiration

Recall that transpiration is the evaporation of water from the surface of a plant.

• In order for liquid water to evaporate into water vapour, we need the HEAT energy from sunlight which was absorbed by the chloroplasts and other cells in the leaves. (Sunlight travels as ultraviolet rays, pass through particles, and turned into long infrared rays which gives off heat.)
• Water from the roots moves up the stem and into the leaves.
• Water moves from xylem into the spongy mesophyll layer of the leaf. (It is here that the changing of water from liquid to gas takes place.)
• Sunlight absorbed gives the heat energy and turn liquid water into gas water vapour.
• Air in the leaf is full of water with 100% humidity. It is therefore denser than the outer environment. (Air outside has mostly 70% humidity.)
• The water vapour then diffuses out of the leaves from the stomata. (Diffusion is the movement of particles from area with greater concentration to area with lesser concentration.)