transpiration stream Flashcards
describe the route that water takes to get into the xylem
-route hair cells maximise SA
-symplast/vacuolar pathway through cytoplasm (osmosis)
-apoplast through cell walls (mass flow)
-apoplast blocked by casparian strip
-carrier protiens pump mineral ions from cytoplasm into xylem
-lowers water potential in xylem
-water moves from cortex into xylem
what does the casparian strip block
the apoplast pathway
what is the advantage of the casparian strip blocking the apoplast pathway
-water and mineral ions have to pass into the cytoplasm
-transporter proteins pump minerals from cytoplasm to medulla
-makes medulla lower water potential
-water moves into xylem by osmosis
what does water move up the xylem by
mass flow
what are the 3 processes that help move water up the stem
-capillary action
-transpiration pull
-root pressure
how does capillary action help move water up stem
-xylem vessels very narrow
-more narrow = water travels further up
-forces of cohesion and adhesion can pull water up the sides of the vessel in a continuous column
cohesion vs adhesion
-cohesion is attraction between water molecules (hydrogen bonds)
-adhesion is attraction between water molecules and wall of xylem vessel
how does transpiration pull help move water up stem
-loss of water creates low hydrostatic pressure in top
-and creates tension in the column of water
-water molecules move down the pressure gradient by mass flow
why do xylem need to be strengthened with lignin
-prevents vessel from collapsing under tension
what is the tension in the transpiration pull created by
-cohesion and adhesion properties of water
-continuous loss of water through evaporation from the plant’s leaves
what is transpiration
the loss of water vapour from the upper parts of the plant
why does the casparian strip block the apoplast pathway
-to ensure water must past through symplast pathway
how does root pressure help move water up stem
-endodermis moves minerals into the xylem/medulla
-draws water in by osmosis
-increase hydrostatic pressure and pushes column of water up xylem
-root pressure pushes water a few metres up stem
(cannot account for water getting to top of tall trees)
what does endodermis move minerals by
by active transport
what does cohesion of water molecules enable
-enables water to move by mass flow
-pulled upwards by tension from above
where does water evaporate from
-the cell surface
how does water move out from the top of the xylem to the air
-osmosis moves water across from leaf
-diffusion out of leaf
