3.3 Transpiration

Question 1

1. is humidity in the air more or less than the air spaces next to the stomata?

Answer 1

less

Question 2

2. so what do the water molecules do (if the stomata are open) as humidity is less outside?

Answer 2

diffuse out airspaces into surrounding air

Question 3

3. water lost from the airspaces is replaced by what?

Answer 3

water evaporating from cell walls of surrounding mesophyll cells

Question 4

4. water lost by evaporation from cell walls is replaced by water from where?

Answer 4

the xylem by either the symplastic or apoplastic pathway

Question 5

5. when water evaporates from mesophyll cells does it do?

Answer 5

lowers water potential of that cell

Question 6

6. what then happens to the mesophyll cells after water has evaporated and kPa is lowered?

Answer 6

more water moves in to the mesophyll cell by osmosis from neighbouring cells

Question 7

7. what does the water potential gradient then do?

Answer 7

pulls water from the xylem across the leaf mesophyll into the air

Question 8

what is the model of water moving xylem -> leaf in a continuous stream called?

Answer 8

cohesion tension theory

Question 9

why is water cohesive?

Answer 9

due to the hydrogen bonding between water molecules as water is a polar molecule

Question 10

water is also adhesive what does this help it do?

Answer 10

reacts with lignin in walls of xylem to help it keep moving in a continuous stream

Question 11

what is the purpose of stomata opening?

Answer 11

to allow diffusion of gases into and out the leaves

control water loss

Question 12

what is the opening and closing of stomata controlled by?

Answer 12

guard cells

Question 13

during the day what does the plant need to take in for photosynthesis?

Answer 13

carbon dioxide

Question 14

at night when no oxygen is being produced the plant needs to take in oxygen for what?

Answer 14

cellular respiration

Question 15

what is transpiration?

Answer 15

the loss/evaporation of water from the leaves and stem of a plant

Question 16

what is a transpiration stream?

Answer 16

• water entering roots by osmosis
• transported up the xylem
• cohesion tension theory
• movement across leaves by osmosis
• evaporation from mesophyll cells into air spaces
• out stomata

Question 17

does the transpiration pull use energy?

Answer 17

no

Question 18

how is water pulled up to the leaves?

Answer 18

by its cohesive and adhesive nature