module 3 - 9.2 water transport Flashcards
what is osmosis?
net movement of water of molecules from high to low water potential
what does lysis mean?
to burst
what is water potential?
concentration of air spaces water diffuses out of
what happens if the water potential inside the cell is low?
water moves IN by osmosis
- cell becomes turgid (contents push on cell walls)
what would be the reason for water being low inside the cell?
if there’s a higher salt concentration
what happens if the water potential inside the cell is high?
water moves OUT by osmosis
what would be the reason for water being low outside the cell?
if there’s a low salt concentration
what does cell sap contain?
dissolved minerals
what happens in low external water potential?
- water moves out the cell
- cell is plasmolysed
- plants can survive this for short periods - they can shrink the cell membrane away from cell water
where does water move? (differences in water potential)
high WP (e.g. -800kPa) to low WP (e.g. -1500kPa)
what are root hair cells?
- specialised exchange surfaces for uptake of water & mineral ions
- maximise surface area in contact with soil (absorb more water)
where are water and mineral ions contained?
within small air spaces in soil
what happens when roots make contact with the soil?
water moves into the roots via osmosis
why does osmosis occur when roots make contact with the soil?
because there’s a higher concentration gradient of solutes in the plant than in the soil
what is the symplast pathway?
- water moving through cytoplasm (living spaces)
- changing cells through the plasmodesmata
- each cell further away from roots has lower WP so water’s drawn up plant
- largely passive
what is the vacuolar pathway?
water moving through living spaces in cytoplasm AS WELL AS vacuoles
what is the apoplast pathway?
- water moving and through intracellular spaces (staying in cell walls)
- cohesive and tension forces acting on cell walls pulls water up
what is the order of speed of the pathways?
fastest - apoplast pathway
middle - symplast pathway
slowest - vacuolar pathway
what is the casparian strip?
- located in the endodermis
- is an impermeable layer of suberin - a waxy material
- forces all water in apoplast pathway into symplast pathway
what 3 processes (caused by changes in concentration and attractions pull) water up xylem?
- root pressure (active process)
- transpiration pull (cohesion-tension theory)
- capillary action
what evidence is there for active transport in root pressure to do with the effects of cyanide?
cyanide stops mitochondria working, so root pressure decreases
what evidence is there for active transport in root pressure to do with the effects of temperature?
root pressure increases as temp increases and decreases as temp decreases (suggests enzyme controlled reaction)
what evidence is there for active transport in root pressure to do with the reactant availability?
if oxygen or respiratory substrate levels drop, root pressure decreases
what evidence is there for active transport in root pressure to do with guttation?
sap and water will move out of cut stem cells, suggesting they’re actively pumped out (not drawn by transpiration)
