water transport

Question 1

list the roles of water

Answer 1

tugor pressure
cell expansion
cooling
transport of minerals and assimilates
photosynthesis

Question 2

role of water in turgor pressure

Answer 2

provides hydrostatic skeleton, due to osmosis, to support the stem and leaves

Question 3

role of water in cell expansion

Answer 3

turgor drive cell expansion, force enables plant roots to force through concrete

Question 4

role of water in cooling

Answer 4

loss of water by evaporation, help plants cool

Question 5

role of water in transport of minerals and asssimilates

Answer 5

mineral ions and products of photosynthesis are transported in aqueous solutions

Question 6

role of water in photosynthesis

Answer 6

is a raw material

Question 7

what are root hair cells

Answer 7

exchange surfaces in plants, water is taken into body of plant from soil
specialised epidermal cell, near growing root tip
long, thin extension from root hair cell

Question 8

adaptations of root hair cells

Answer 8

microscopic size - penetrate easily between soil particles

large SA:V - thousands of root hair growing on each growing root tip

thin surface layer - diffusion and osmosis can take place quickly

concentration of solute in cytoplasm maintain a water potential gradient between soil water and cell

Question 9

movement of water into root hair cells

Answer 9

soil water, low concentration of dissolved minerals, high water potential
root hair cell, cytoplasm + vacuolar sap, high concentration of dissolved minerals, water potential lower

water move into root hair cell by osmosis

Question 10

three pathways movement of water from root hair to xylem

Answer 10

apoplast
symplast
vacuolar

Question 11

what is the apoplast pathway

Answer 11

movement of water though apoplast (cell wall and intercellular spaces)

water fills spaces between lose, open network of fibres in cellulose cell wall

as water mol move into xylem, more water mol are pulled through apoplast behind due to cohesive forces between water mol, creates tension

continuous flow of water through open structure of cellulose wall, little to no resistance, mass flow

Question 12

what is the symplast pathway

Answer 12

water moves through symplast (continuous cytoplasm of living cells connected by plasmodesmata) by osmosis

cytoplasm of root hair cell becomes more dilute as water moves through

root hair cell has higher water potential than next cell, move to next cell by osmosis

process continues till water reaches xylem

water potential of cytoplasm falls when water leaves root hair cell

maintains steep water potential gradient, ensure as much water continue to move into cell from soil

Question 13

what is the vacuolar pathway

Answer 13

same as symplast, but water is not confined to cytoplasm
able to travel through vacuoles
slower than symplast

Question 14

how does water move into xylem

Answer 14

via apoplast, symplast, vacuolar pathways till endodermis

Question 15

what is the endodermis

Answer 15

layer of cells surrounding the vascular tissue of the roots

recognised by casparian strip

Question 16

what is the casparian strip

Answer 16

band of waxy material called suberin, runs around each of endodermal cells to form a waterproof layer

Question 17

where can water in apoplast pathway go no further

Answer 17

casparian strip

Question 18

what happens to water in apoplast pathway wen casparian strip is reached

Answer 18

forced into cytoplasm of cell, join water in symplast

Question 19

why is it important that water is diverted to the cytoplasm

Answer 19

ensures water must pass through selectively permeable cell surface membrane, any potentially toxic solutes in soil water are prevented from reaching living tissues (no carrier protein to admit them)

Question 20

what happens to water once inside vascular bundle

Answer 20

returns to apoplast pathway, enter xylem itself, move up plant

solute concentration in endodermal cell low / high in xylem
water move into xylem by osmosis
movement of ions into xylem, active transport, cause water to move in by osmosis, result in root pressure

Question 21

what is root pressure

Answer 21

water move into medulla, pressure in root medulla build up, force water into xylem, pushing water up xylem

root pressure give water a push up xylem
push water up a few meters, cannot account for water getting to top
not the major factor in movement of water up root to leave , transpiration is

Question 22

what are the evidence for active transport

Answer 22

root pressure increases with temperature, evidence for dependence on active transport + chemical reactions

cyanide, affects mitochondria, reduce root pressure

levels of oxygen/respiratory substrate falls, root pressure falls

xylem sap may exude from cut end of stems at certain times,guttation

Question 23

what is guttation

Answer 23

loss of water from leaves when root pressure is high

transpiration stop at nightime, high soil moisture, root water potential low, water accumulate in plant, root pressure increase