Everything Life Sciences Grade 10

Figure 6.18: Transpiration vs humidity.

Wind

When water is lost from the leaf it forms a thin layer outside the leaf. This reduces the water

potential between the leaf and the atmosphere outside. Thus when there is wind, this layer

is blown away, thus maintaining the water potential gradient across the leaf.

Figure 6.19: Wind speed vs transpiration.

Measuring the rate of transpiration DUMMY

To measure the rate of transpiration we use a piece of equipment called apotometer.A po-

tometer measures how factors such as light, temperature, humidity, light intensity and wind

will affect the rate of transpiration. The main type of potometer is the ’bubble’ potometer

shown in Figure 6.20. The potometer can measure the amount of water lost from a leafy

shoot by monitoring the following variables:

• the change in the mass of the leaf shoot.


• the rate that the air bubble moves along the narrow tube as the leafy shoot sucks up
  water to replace the water lost by the transpiration of the plant.

As the leafy twig transpires, the air bubble moves to the left. The quicker the air bubble

moves, the faster the leafy twig is transpiring.

172 6.3. Transpiration