Transporation

Question 1

What is transpiration?

Answer 1

The loss of water vapour from a plant’s surface, usually via stomata in leaves/stems

Question 2

Where does transpiration take place?

Answer 2

In the plants leaves

Mainly on the lower surface

Question 3

Explain the transpiration stream

Answer 3

1. Transpiration- water vapour is lost (lower WP)
2. More water is pulled up through xylem vessels in the stem to replace loss (down WP gradient)
3. More water is absorbed into the roots via root hair cells, via osmosis from the soil

Question 4

In the transpiration stream, why is water replaced?

Detailed chemistry of water etc

Answer 4

H2O molecules are stuck together by bonds (cohesion)

This means when water moves up the stem it is followed by more water (ie replaced)

Question 5

What do stomata do?

Answer 5

Allow the uptake of CO2 for photosynthesis.

When they open water evaporates from spongy mesophyll and diffuses out of leaf (down WP gradient)

Question 6

What factors increase transpiration?

Answer 6

High temperature
High wind speed
Low humidity
High light intensity

Question 7

How does high temperature affect transpiration?

Answer 7

Increases evaporation rate

More water vapour - increases WP gradient - faster diffusion of water vapour out of air spaces

Question 8

How does high wind speed affect transpiration?

Answer 8

Wind moves moist air layer away from leafs surface - increases WP gradient - speed up water loss

Question 9

How does low humidity affect transpiration?

Answer 9

Drier air increases WP gradient between leaf + air - faster diffusion

Question 10

How does high light intensity affect transpiration?

Answer 10

Stomata open to allow CO2 in for photosynthesis, also allowing more water vapour to escape