Mass transport Plants Flashcards
What is transpiration?
Loss of water from the leaves via open stomata
How does water move through the leaf?
mesophyll cells have evaporation due to heat energy from the sun, water moves down a water potential gradient from cells to air spaces.
Lowers the water potential of mesophyll, so water moves by osmosis from adjacent mesophyll stomata open and allow water from high to low water potential gradient.
Sets up a water potential gradient across the leaf to Xylem.
What is the cohesion-tension theory?
Water drawn up the Xylem due to cohesive hydrogen bonding between molecules, adhering to Xylem walls as well due to hydrogen bonding. Water is pulled up as a continuous column producing negative pressure called tension.
How does water move up the xylem?
Water from Xylem enter mesophyll due to the lower water potential.
Water drawn up this island because of the cohesive forces hydrogen bonding.
Between water molecules
create tension negative pressure adhesion to walls.
Water pulled up as a column which creates the continuous negative pressure called tension.
What is the evidence for the cohesion-tension theory?
during the day high transpiration low diameter of tree trunk due to negative pressure
when Xylem are broken air leaks out not water showing tension not pressure
when air enters xylem they become blocked as it breaks the continuous column
How would you use a potometer to measure water uptake?
cut shoot at slant so no air in stem
assemble apparatus underwater, seal with Vaseline
dry leaves
no air bubbles
close the tap
allow time for plants to equilibrate
time how long it takes for meniscus remove Xmm.
Reset with syringe
How are xylem vessels adapted for their function?
no end walls so continuous flow
no cytoplasm easier flow
lignin for support and water retention spiral structure flexible
pits in walls so lateral movements bypass blockages
narrow tubes capillarity
What is the job of the phloem?
Transport sugars sucrose from source to sink, shoots to roots, sieve tubes transport the sugars, companion cells transport sugars in and out of the sieve cells.
Can you explain the mass flow hypothesis for the mechanism of translocation in plants?
Companion cells use ATP to actively transport protons out of cell into tissue.
Electrochemical gradient established protons and sucrose actively transport the row code transport protein into companion cell against concentration gradient.
Sucrose moves through plasmodesmata that connect companion cells and sieve tube elements, active loading.
Sucrose lowers water potential of sieve tube
Osmosis in from Xylem
High hydrostatic pressure forces water down phloem
Sucrose diffusers and downloads into sink (root cells) higher water potential osmosis out into Xylem lower hydrostatic pressure creating a pressure gradient
Can you explain the use of tracers and ringing experiments to investigate transport in plants?
Ring of woody bark removed which removes phloem.
Bulge forms above ring high concentration of sugars than below (evidence for downward flow of sugars).
Aphids Pierce phloem SAP flows quicker at top than bottom (pressure gradient).
Radioactive tracer carbon 14 to track movement of organics down the phloem.
ATP metabolic inhibitor stops translocation shows active transport involved.
