The rate of transpiration can be investigated by measuring the volume of water absorbed.

Volume of water absorbed

A potometer can be used to measure the volume of water absorbed. Usually a leafy shoot is used instead of a single leaf.

A simple potometer comprises:

• a container of water
• a capillary tube
• rubber tubing to connect the capillary tube to the stem of the leafy shoot
• a scale to measure the distance travelled by a bubble in the capillary tube

The faster the bubble moves, the greater the rate of water uptake - and so the greater the rate of transpiration. You can vary the conditions to investigate the effect of:

• changing temperature
• humidity
• wind speed (for example, with a hair dryer)
• light intensity