xylem and transpiration - lqc 2b

Question 1

xylem function

Answer 1

transports water and mineral ions, structural/mechanical support

Question 2

lignin and cellulose microfibrils in walls function

Answer 2

for strength to prevent vessel collapsing

Question 3

lignin in walls function

Answer 3

to make the vessel waterproof

Question 4

large cross-sectional area function

Answer 4

allows a larger volume of water to be transported

Question 5

pits in walls function

Answer 5

allow lateral/sideways movement of water between xylem vessels

Question 6

no end walls function

Answer 6

forms a continuous, dead hollow tube with no cell cytoplasm- reduces resistance/obstruction to water flow

Question 7

lignin in rings or spirals function

Answer 7

to allow stretching/flexibility as the plant grows

Question 8

water transport in a plant from the roots to the leaves

Answer 8

· water evaporates from the surface of the leaf cells into the air spaces and exits the leaf by the process of transpiration (water vapour diffuses out of the leaves though stomata , down a diffusion gradient)
· this creates a low hydrostatic pressure in leaves which draws water out of the xylem vessels by osmosis
· a continuous column of water molecules (transpiration stream) is pulled, under tension, up the xylem by capillary action
· due to cohesion - hydrogen bonding between polar water molecules in xylem
· and adhesion - hydrogen bonding between water and cellulose in the xylem walls
· water moves into roots by osmosis – creating a high hydrostatic pressure
· water moves along a hydrostatic pressure gradient, from high pressure in roots to low pressure in leaves, by mass flow