transport in plants Flashcards
how are guard cells adapted for their role
unevenly thickened cell wall
can change shape
has chloroplast to provide atp
cohesion tension theory
when evaporation occurs at the top of the plant it creates tension in the xylem so water molecules stick together and are pulled up by tension
what do companion cells contain
contain many mitochondria
plasmodesmata between companion cell and sieve tube
many ribosomes
transpiration vs transpiration stream
transpiration is the loss of water vapour from the leaves
transpiration stream is the movement of water from the roots to the leaves
xerophytic features
thick waxy cuticle
leaf is folded which reduces surface area
hairs trap water vapour which increases water potential outside of the leaf which decreases the water potential gradient
stomata are sunken into pits
how do sieve tubes enable mass flow to occur
no nucleus/few organelles
pores in end walls
thin layer of cytoplasm
transpiration contribution to mechanism of water movement
water loss is replaced
via symplast and apoplast pathways
down the water potential gradient
in xylem-
loss of water creates a low hydrostatic pressure
water moves from a high pressure to a low pressure down the pressure gradient under tension by mass flow
cohesion pulls water molecules up
source and sink meaning
source is where assimilates are loaded onto the phloem
sink is where assimilates are unloaded from phloem
why is lignin essential
provides strength
prevents xylem from collapsing as transpiration produces pressure
waterproofs cell wall
improves adhesion of water
what do pits do
pits allow water to move in and out between vessels to supply water to other tissues
how to use potometer
make apparatus water tight-so no air enters
dry leaves
cut plant under water with a slant so no air enters shoots
measure distance air bubble travels
dont allow air bubble to move too far so it doesnt enter the xylem
place open end in water so no new air bubble introduced
keep shoot still to avoid breaking water column
calculate volume of water uptake
make sure conditions eg temp are constant
translocation and transpiration meaning
movement of assimilates from the source to the sink
movement of water vapour out of the leaf
why should you cut the stem before placing in water
to remove air bubbles and blockage in xylem and to restore continous column of water
mass flow
assimilates enter the sieve tube and lower the water potential
water enter the sieve tube by osmosis and increases the hydrostatic pressure.
assimilates move from high to low hydrostatic pressure down the concentration gradient.
mass flow in general
shortens the diffusion pathway and moves substances quickly
