transpiration

Question 1

what is transpiration pull

Answer 1

water that has evaporated from leaves is replaced by water coming up the xylem. water molecules are attached to each other by cohesion. Ad molecules are lost of the top the whole column is pulled up. the pull from above creates adhesion in the column of water. xylem vessels are strengthened by lignin preventing the vessel from collapsing

Question 2

how does light intensity effect transpiration

Answer 2

in light stomata open for an exchange. Higher light = increased transpiration rate

Question 3

how does temperature effect transpiration

Answer 3

-higher temp= increased transpiration rate
-increase the rate of evaporation increases the rate of diffusion through the stomata as H2O molecules have more kinetic energy and decreases the water vapour potential in the air

Question 4

how does relative humidity effect transpiration

Answer 4

higher humidity will decrease the rate of water loss. this is because there is smaller water vapour potential gradient between air spaces in leaf and outside

Question 5

how does wind effect transpiration

Answer 5

air moving outside the leaf will carry away water vapour that has just diffused out of the leaf. high water vapour potential gradient

Question 6

how does water availability effect transpiration

Answer 6

if there’s little water in soil then the plant cannot replace the water that is lost. the stomata will close and the leaves will wilt

Question 7

what happens when the stomata is turgid (open)

Answer 7

-water moves into the vacuoles by osmosis
-outer wall is more flexible than the inner wall so cell bends and opens the stoma

Question 8

what happens when the stomata is flaccid (closed)

Answer 8

-water moves out of the vacuoles by osmosis
-outer wall is more flexible than the inner wall, so the cell bends back and closes the stoma

Question 9

what is the pathway by most water entering the leaf

Answer 9

-water enters the xylem and moves by osmosis into the cells of the spongy mesophyll. it may also pass along the cell walls via the apoplast pathway
-water evaporates from the cell wall of the spongy mesophyll
-water vapour moves by diffusion out of the leaf via stomata

Question 10

what does the water pathway in a plant rely on

Answer 10

-difference in concentration of water vapour molecules compared with the outside
-this is known as the water vapour potential gradient
-there must be a higher water vapour potential inside the leaf than outside

Question 11

how does root pressure transport water

Answer 11

-the action of the endodermis transporting mineral ions into the medulla and xylem by active transport
-this creates a -ve water potential. water moves into medulla and xylem by osmosis
-pressure in the root medulla builds up and forces water into the xylem, pushing water up the xylem

Question 12

how does capillary action transport water

Answer 12

-adhesion between the water molecules and xylem vessels takes place
-as vessels are narrow forces of attraction can pull the water up the sides of the vessel

Question 13

what created the transpiration pull that helps water move up through the xylem

Answer 13

evaporation of water at leaves