9.2 Transport of water in multicellular plants Flashcards
How are root hair cells adapted for exchange?
microscopic size= easily penetrate between soil particles
large surface area to volume ratio
thin surface layer= shorter diffusion distance
Conc of solutes in cytoplasm of root hair cells maintains a water potential gradient
Symplast pathway
water moves through symplast (continuous cytoplasms of living plant cells that are connected via plasmodesmata)
–> root hair cells have higher water potential than next cell= water moves from one root hair cell to the next cell via osmosis until xylem is reached
Apoplast pathway
water moves through apoplast (cell walls and intercellular spaces)
–> water fills spaces between loose, open network of fibres in cellulose cell wall
What happens as water moves into the xylem (apoplast)
more water molecules are pulled through apoplast behind them through cohesive forces
Pull from water moving into xylem and up plant creates a tension meaning there is a continuous flow of water through the open structure of cellulose walls (little resistance)
Movement of water into the xylem
water continues till it reaches the endodermis in both pathways
–> water in apoplast pathway can not go any further and is forced into cytoplasm, joining symplast pathway
What does water from the apoplast pass through before getting to the endodermis?
water must pass through selectively permeable cell surface memberanes
–> excludes any potentially toxic solutes in soil water
Casparian strip function?
bad of waxy material called suberin that runs around each of the endodermal cells forming a water proof layer
–> regulate water and mineral uptake by the roots.
What happens to water once it enters the vascular bundle
it returns to the apoplast pathway to enter xylem
Root pressure: what is it
active pumping of minerals into the xylem to produce movement of water via osmosis
