B2.2.6 - Factors Affecting Transpiration

Question 1

What can you use to measure the rate of transpiration?

Answer 1

A potometer

Question 2

Describe the process of using a potometer.

Answer 2

Take an air bubble into the capillary tube.
As water moves up into the shoot and evaporates in the leaves, the air bubble moves towards the plant.
Measure how fast the bubble travels.

Question 3

What is the equation you use for the air bubble in the potometer to calculate the rate of transpiration?

Answer 3

Rate of reaction = distance travelled / time taken

Question 4

What affects the rate of transpiration?

Answer 4

Light intensity
Temperature
Humidity
Air movement

Question 5

Why does anything that increases the rate of photosynthesis increase the rate of transpiration?

Answer 5

Because during photosynthesis the stomata opens to let carbon dioxide diffuse in, while letting the water evaporate

Question 6

Why does light intensity increase the rate of transpiration?

Answer 6

It causes more water to evaporate and more stomata to open.

Question 7

When does transpiration reach its maximum rate for light?

Answer 7

When all stomata are open

Question 8

Why does temperature increase the rate of transpiration?

Answer 8

Water evaporation occurs quicker

Diffusion of water vapour our of the leaf is quicker

Question 9

Why does air movement increase the rate of transpiration?

Answer 9

When air moves over the surface of a leaf, it moves evaporated water molecules away from the leaf, so if it was quicker the water would be further so the concentration gradient will be bigger and so the rate of diffusion will have increased.

Question 10

Why does humidity affect the rate of transpiration?

Answer 10

Humidity is the amount of water in the air, so if the humidity is low in the air, there will be no water molecules so the concentration gradient will be strong, increasing the rate of water vapour diffusion.