9.2 water transport in multicellular plants Flashcards
what is turgor pressure?
hydrostatic pressure - provides a hydrostatic skeleton to support the stems and leaves.
what keeps plant cool?
the loss of water by evaporation
what are transported in aqueous solutions?
mineral ions and the products of photosynthesis
what cells are the exchange surface in plants where water is taken into the body?
root hair cells
what are root hair cells?
a long thin extension from a root hair cell, a specialised epidermal cell found near the growing root tip
how are root hair cells adapted as exchange surfaces.
- microscopic (penetrate easily in between soil particles)
- hair has a large SA:V ratio
- hair has a thin surface layer (diffusion and osmosis can happen quickly)
- concentrations of solutes in its cytoplasm maintains the water potential gradient
how does water move into the root hair cell by osmosis.
soil water has a low concentration of dissolved minerals (high water potential)
howevere the cytoplasm and vacuolar sap of root hair cell contains many solvent (low water potential)
how does water move across the root to the xylem?
either the symplast pathway or the apoplast pathway
what is the symplast pathway
water moves through the symplast by osmosis
root hair cell has a higher water potenital than the next cell
water diffsues in from the soil, cytoplasm is now more dilute
so water now moves from the root hair cell into the next cell osmosis
what is the symplast
continuous cytoplasm of the living plant cells that is connected through the plasmodesmata
what is the apoplast pathway
water moves through the apoplast
water fills the spaces between the open network of fibres in the cellulose cell wall
as water is moving into the xylem, more water is pulled through the apoplast behind due to the cohesive forces between water
this creates a tension which means there is a continuous flow of water through the open structure of the cell wall, no resistance
what is the apoplast/
the cell walls and the intercellular spaces
where does water reach before the xylem during either pathway?
endodermis
what is the endodermis?
layer of cells surrounding the vascular tissue (xylem and phloem) of the roots
why is the endodermis noticeable in the roots?
because of the casparian strip
what is the casparian strip?
a band of waxy material called suberin that runs around each of the endodermal cells forming a waterproof layer
what happens to the water in the apoplast pathway once it reaches the casparian strip?
can go no further and is forced into the cytoplasm of the cell, joining the water to the symplast pathway
why does water in the apoplast pathway stop at the casparian strip?
water must pass through the selective permeable cell surface membrane, which stops any toxic solutes reaching living tissues
how do endodermal cells move mineral ions into the xylem?
active transportw
why do endodermal cells move mineral ions into the xylem by active transport?
the solute concentration in the cytoplasm of the endodermal cells is dilute compared to the cells in the xylem
what has the lower water potential, endodermal cells or xylem cells?
xylem cells, as they have the higher solute concentration
what happens when the water reaches inside the vascular bundle?
water returns to the apoplast pathway to enter the xylem itself and move up the plant
what leads to root pressure?
active pumping of minerals into the xylem to produce movement of water by osmosis
what is root pressure?
gives water a push up the xylem, but under most circumstances it is not the major factor in the movement of water up from the roots to the leaves
what evidence is there that active transport is used to get water from the endodermis to the xylem?
- root pressure increases with a rise in temperature and falls with a fall in temperature (chemical reactions must be involved)
- if levels of oxygen falls, so does root pressure
- some poisons affect the mitochondrias production ATP, if it applied to root cells so there is no energy supply, root pressure disappears
