Use a potometer to measure water uptake/rate of transpiration
Potometer:
cut shoot underwater and attach to apparatus underwater. This keeps cohesion intact
shut screw clip and remove potometer from water
Dry the leaves
allow time to acclimatise
calculate distance air bubble moves per minute
Cohesion-tension theory:
In the leaf most of the water evaporates from the surface of the spongy mesophyll cells into the air spaces and passes out of the leaf via the stomata as water vapour into the atmosphere (transpiration) creating tension
As water molecules leave the xylem in the leaf, they pull up the molecules behind them (transpiration pull) It occurs because molecules have large cohesive forces between them. Molecules form adhesive forces with the hydrophilic lignin lining of the xylem vessels
water is pulled up the xylem in one continuous stream called the transpiration stream
