water transport Flashcards
list the roles of water
tugor pressure
cell expansion
cooling
transport of minerals and assimilates
photosynthesis
role of water in turgor pressure
provides hydrostatic skeleton, due to osmosis, to support the stem and leaves
role of water in cell expansion
turgor drive cell expansion, force enables plant roots to force through concrete
role of water in cooling
loss of water by evaporation, help plants cool
role of water in transport of minerals and asssimilates
mineral ions and products of photosynthesis are transported in aqueous solutions
role of water in photosynthesis
is a raw material
what are root hair cells
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
adaptations of root hair cells
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
movement of water into root hair cells
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
three pathways movement of water from root hair to xylem
apoplast
symplast
vacuolar
what is the apoplast pathway
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
what is the symplast pathway
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
what is the vacuolar pathway
same as symplast, but water is not confined to cytoplasm
able to travel through vacuoles
slower than symplast
how does water move into xylem
via apoplast, symplast, vacuolar pathways till endodermis
what is the endodermis
layer of cells surrounding the vascular tissue of the roots
recognised by casparian strip
what is the casparian strip
band of waxy material called suberin, runs around each of endodermal cells to form a waterproof layer
where can water in apoplast pathway go no further
casparian strip
what happens to water in apoplast pathway wen casparian strip is reached
forced into cytoplasm of cell, join water in symplast
why is it important that water is diverted to the cytoplasm
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)
what happens to water once inside vascular bundle
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
what is root pressure
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
what are the evidence for active transport
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
what is guttation
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
