absorption & transpiration of water

  • Created by: ben
  • Created on: 01-05-13 10:34

movement of water through roots

Uptake of Water by Roots Hairs
 -- all water need to be absorbed due to the loss from transpiration.
-- they are efficient exchange surface becasue:
       ~they have a large surface are due to there being a lot of them & being very long.
       ~they have a thin cell surface therefore there is a short difusion pathway.
-- they are surrounded by soil consiting of a lot of water and mineral.
-- the soil has a high water potential compared to the root hairs.
-- therefore water moves in via osmosis.
-- water is then absorbed in the root hair cells in 2 way; apoplastic & symplastic pathway.

Apoplastic Pathway
-- water drawn into endodermal cells pulling more water into the cells due to cohesive properties of water.

-- this causes tension that draws water along the cell walls of the root hair cells.

Symplastic Pathway
-- takes places in the cytoplsm to osmosis.
-- water pases between each cells via plasmodesma that contains cytoplasm.
-- the following cells always has a lower water potential so water is drawn in via osmosis.

Passage of Water into the Xylem
-- the casparian ***** (a waterproof band) prevents further movement of water
-- water is forced into the xylem.
-- this is done due to salts and minerals being actively transported into the xylem causing a water potential gradient the water moves through via osmosis.
-- ^^ this is the root pressure ^^

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