provides a hydrostatic skeleton to support the stems and leaves
turgor also drives cell expansion how is this useful
it is the force that enables plant roots to force their way through tarmac and concrete
how does the loss of water by evaporation help plants
keeps plants cool
where is water taken into the plant
root hair cells
how are root hairs adapted as exchange surfaces
microscopic size means they can penetrate easily between soil particles
millions of microscopic hairs with large SA:VOL ratio
each hair has a thin surface layer so diffusion and osmosis can happen quickly
concentration of solutes in the cytoplasm of root hair cell maintains a water potential gradient between the water in the soil and the cell
why does soil water have a very high water potential
because it has very low concentration of dissolved minerals
how does water move into the root hair cell by osmosis
because water in the soil had a high water potential where as inside the root hair cell theres a low water potential so water moves into the cells as water moves from an area of high water potential to an area of low water potential
which two pathways does water move from roots to xylem
symplast pathway
apoplast pathway
how does water move through the symplast route
water moves continuously through the cytoplasm of adjacent cells through the plasmodesmata
root hair cell has a higher water potential than the next cell along so water moves into the next cell by osmosis and this continues until the xylem is reached
how does water move through the apoplast route
water moves through the cellulose cell walls (fibres with water filled spaces)
as water moves into the xylem more water is pulled through continuously due to the cohesive forces between water molecules
the continuous flow of water and the cohesive forces creates tension which means there a continuous flow of water through the cell wall
what is the endodermis
layer of cells surrounding the vascular tissue (xylem and phloem) of the roots
what is the casparian strip
band of waxy material called suberin that runs around each of the endodermal cells forming a waterproof layer
when and why does the apoplast pathway stop and join the sympoplast pathway
both pathways travel across the roots until it reaches the endodermis
here the apoplast pathway joins the sympoplast pathway due to the effect of the casparian strip
water must pass selectively permeable cell surface membranes so this excludes any potentially toxic solutes in the soil water from reaching living tissues as membranes have no carrier proteins to admit them
how does water move into the xylem
the solute concentration in the cytoplasm of the endodermal cells is relatively dilute compared to the cells in the xylem
also endodermal cells move mineral ions into the xylem by active transport
so the water potential is much lower in xylem than in the endodermal cells
as a result water moves by osmosis from endodermal cells into the xylem
what happens once inside the vascular bundle
water returns the apoplast pathway to enter the xylem and move up the plant
what results in root pressure
active pumping of minerals into the xylem to produce the movement of water
what does root pressure do
gives water a push up the xylem but under most circumstances it is not a major factor