2.3.2 Transpiration

Question 1

Transpiration

Answer 1

• The loss of water vapour by diffusion from the leaves of plants through the stomata when they are opened to allow gas exchange for photosynthesis

Question 2

Transpiration stream

Answer 2

The movement of water through plant rooots to the leaves as a result of water loss by evaporation from the surface of leaves

Question 3

Movement of water in plants (7p)

Answer 3

1) Water absorbed in the roots by osmosis into the root hair cell
2) Water moves from the root hair cell to the xylem by osmosis
3) Water moves up the xylem
4) Water moves into the leaves from the xylem
5) Water evaporates from the spongey mesophyll to be replaced by more water
6) Air spaces in leaf fill with water vapour
7) Water vapour diffuses through the stomata into the outside air

Question 4

Factors effecting rate of transpiration (6p)

Answer 4

• Higher light intensity
• Higher CO2 concentration
• Higher temperature
• Dry conditions (low humidity)
• Windy conditions
• More leaves

Question 5

Higher light intensity/ higher CO2 concentration (factors effecting rate of transpiration)

Answer 5

• More stomata open for photosynthesis to occur so more water can be evaporated

Question 6

Higher temperature (factors effecting rate of transpiration)

Answer 6

• Particles have greater kinetic energy so more water evaporates

Question 7

Dry conditions/ low humidity (factors effecting rate of transpiration)

Answer 7

Steeper diffusion gradient, so water vapour diffuses out of leaves faster

Question 8

Windy conditions (factors effecting rate of transpiration)

Answer 8

Removes the evaporated water, maintaining diffusion gradient

Question 9

More leaves (factors effecting rate of transpiration)

Answer 9

Larger surface area

Question 10

What causes a plant to wilt?

Answer 10

If transpiration occurs faster because there is less water

Question 11

Ways to reduce water loss by controlling transpiration (7p)

Answer 11

• Waxy cuticle
• Location of stomata
• Guard cells
• Wilting
• Stress response
• Hairy leaves
• Rolled leaves

Question 12

Waxy cuticles (Ways to reduce water loss)

Answer 12

• Prevent uncontrolled water loss

Question 13

Location of stomata (Ways to reduce water loss)

Answer 13

• Underside of leaf to protect it from direct sunlight and energy from the sun

Question 14

Guard cells (Ways to reduce water loss)

Answer 14

Controls the opening and closing of the stomata on the leaf

Question 15

Wilting (Ways to reduce water loss) (2p)

Answer 15

• When all leaves collapse and hang down
• This reduces the surface area available for water loss by evaporation

Question 16

Stress response (Ways to reduce water loss)

Answer 16

• Close stomata

Question 17

Hairy leaves (Ways to reduce water loss)

Answer 17

• Tiny hairs can trap a layer of air close to the leaf surface, educing transpiration

Question 18

Rolled leaves (Ways to reduce water loss) (2p)

Answer 18

• Helps to reduce the effect of the wind and slows the rate of water loss
• Rolling leaves shelters stomata from the wind

Question 19

Situations where the guard cells would close the stomata (3p)

Answer 19

• Lack of sunlight
• Flat concentration gradient of CO2
• Lack of water to reduce water loss

Question 20

What causes the guard cell to change shape and open the stomata (3p)

Answer 20

• Chloroplast so photosynthesis occurs
• Glucose is made to decrease the concentration of water in the leaf
• Osmosis occurs into the guard cell making it turgid