Component 3.2 - Transpiration

Question 1

What is a harmful aspect of transpiration?

Answer 1

Water loss

Question 2

What are the useful aspects of transpiration?

Answer 2

1) water uptake
2) water distribution
3) ion distribution
4) evaporative cooling

Question 3

What factors does transpiration rate depend on?

Answer 3

Genetic factors e.g distribution ad size of stomata

Environmental factors e.g temperature, humidity and air movement - affect the water potential gradient between water vapour in leaf and atmosphere

Light intensity

Question 4

How does temperature increase effect transpiration rate ?

Answer 4

It increases the kinetic energy of water molecules, meaning they move faster and accelerates their rate of evaporation. The higher temperature causes the water molecules to diffuse away from the leaf more quickly, reducing the water potential around the leaf.

Question 5

How does high humidity effect transpiration rate ?

Answer 5

Transpiration leaves a layer of saturated air at the surface of leaves surface. The higher the humidity the smaller the difference in water potential and therefore water will not diffuse down a concentration gradient as quickly so transpiration rate will decrease.

Question 6

What does an increase in air movement do to the transpiration rate?

Answer 6

The faster the movement of the surrounding air the faster the concentric shells of water vapour get blown away. This increases the water potential gradient between the inside and the outside of the leaf meaning transpiration rate increases.

Question 7

How does a higher light intensity effect the transpiration rate?

Answer 7

As light intensity this increases the width of which the stomata open, increasing the rate of transpiration. So stomata tend to open the widest in the middle of the day increasing transpiration rate.

Question 8

What do you have to make sure you do when you set up a potometer?

Answer 8

Cut the leafy shoot/assemble the equipment under water - to make sure no air bubbles enter the xylem as this could block transportation stream

Seal joints with Vaseline to make sure no air enters the equipment

Dry leaves to remove and water from around the leaf which would reduce transpiration rate