transpiration DEFINITELY IN EXAM

Question 1

define transpiration

Answer 1

the evaporation of water from the surface of leaves

transpiration starts with the evaporation of water from cells inside the leaf

Question 2

explain the process of the transpiration stream

Answer 2

transpiration starts with the evaporation of water from cells inside the leaf

• the water diffuses through the air spaces in the spongy mesophyll and out of the leaf through the stomata
• water passes from the xylem into the leaf to replace the water that has been lost
• water is drawn into the root hair cells and up the xylem vessels to the leaf

Question 3

what substance does transpiration bring to the leaf? and what is this substance required for?

Answer 3

transpiration brings water to the leaf which is required for photosynthesis (carbon dioxide + water –> glucose + oxygen)

Question 4

expect from water what else does the transpiration stream transport?

Answer 4

the transpiration stream (transports water as well) also transports dissolved mineral ions such as magnesium

Question 5

what does the evaporation of water from the leaf allow?

Answer 5

evaporation of water from the leaf allows the leaf to cool down (especially in warmer weather)

Question 6

4 conditions for greater rate of transpiration

Answer 6

higher temperature = greater rate of transpiration
( this is because evaporation is faster when temperatures are higher)

dry conditions = greater rate of transpiration
( there is more evaporation under dry conditions)

increased wind intensity = greater rate of transpiration
(wind removes any water vapour allowing more water to evaporate)

increased light intensity = increased rate of transpiration
( high light intensity increases the rate of photosynthesis as the stomata are now open to allow carbon dioxide to enter, once the stomata are open water vapour can now pass out of the leaf)

Question 7

explain how stomata work

Answer 7

• stomata are surrounded by 2 guard cells
• when the light intensity is high guard cells swell and change their shape
• this causes the stomata to open
• carbon dioxide can now diffuse into the leaf and can be used during photosynthesis
• under hot conditions the plant closes it’s stomata to reduce water loss by transpiration (that means the plant cannot photosynthesise)