transport in plants🌱🌿 Flashcards
how are guard cells adapted
- thick inner wall, thin outer wall
- when cells swell the outer wall is able to bend
- opens stomata
use cohesion tension theory to explain how water moves up xylem from roots to leaves
- evaporation at leaf
- creates tension in xylem
- H2O molecules are cohesive
- columb pulled up by tension
difference between transpiration and transpiration stream
transpiration- evaporation of water at the leaves
transpiration stream- movement of water up xylem vessels from roots to leaves
what in xylem vessels allows water to pass into adjacent vessels
pits
what are the gaps in cell walls between companion cells and sieve tube elements called
plasmodesmata
what is source and sink
source- site where sucrose is loaded onto phloem
sink- site where sucrose is unloaded from phloem
when bark is removed, phloem is also removed. explain why when whole ring of bark is removed, the tree trunk swells above the cut
- sugars cannot pass the cut
- water potential decreases (bc sugars stay)
- water moves into cells
Explain the significance of the relationship between rate of diffusion and the surface area to volume ratio for large plants.
- low sa:v ratio
- diffusion too slow to meet oxygen demands
- need exchange surface area
- need transport system
function of pits
- allows water to move between vessels
- to bypass blockage
- supply water to other tissues
adaptations of sieve tubes for mass flow
- no nucleus
- pores in sieve plates
- elements joined end to end
how are assimilates loaded onto phloem
- active transport of h+ ions out of companion cells
- creates h+ ion concentration gradient
- facilitated diffusion of h+ ions back into companion cells
- sucrose moves in with h+ ions by cotransport
- sucrose diffuses through plasmodesmata into sieve tube element
why do flowers survive longer when stems cut and immediately put into water
air bubbles in xylem removed to restore continuous column of water
how does transpiration contribute to the mechanism of water transport up the stem
in leaf
- water loss from leaf replaced via apoplast and symplast pathways
- down wp gradient
- lost water replaced by water from xylem
in xylem
- loss of water creates low hydrostatic pressure in leaf
- water moves down pressure gradient
- under tension
- by mass flow
- cohesion
how to make sure potometer is set up correctly
- make sure shoot healthy
- assemble apparatus underwater
- cut end of shoot
- check so no air bubbles
- apparatus water tight
- dry leaves
explain why potometer gives estimate of transpiration
- potometer measures water uptake
- not all water is lost
adaptations that reduce water loss in leaf
- waxy cuticle is waterproof and impermeable
- stomata close during day which reduces diffusion
- fewer stomata reduces diffusion
- sunken stomata trap water vapour
does phloem form vessels
no lol
in cross section of xylem, what is the hole in the middle
vessel lumen
precaution when using potometer
keep temp constant as it affects rate of transpiration
how to ensure estimate of leaf area is accurate
flatten leaves
describe how new xylem cells are produced
- produced in meristem
- differentiation
describe apoplast pathway
- water movement through cell wall
- continuous flow of water through open structure of cellulose cell wall
- casparian strip in endodermis is waterproof and forces water to enter symplast pathway
describe symplast pathway
-through cytoplasm and plasmodesmata of cells
evidence for role of active transport in root pressure
- cyanide stops mitochondria from producing ATP, when it is applied to roots then root pressure disappears
- as temp increases root pressure increases suggesting chemical reactions involved
- low oxygen or glucose then root pressure falls
evidence for cohesion tension
- when transpiration is at its highest during the day, tension in xylem is at its highest
- when xylem vessel is broken, eg stem cut, air is pulled up stem and water does not leak
- also then the plant can no longer move water up stem as continuous stream has been broken
adaptations of xerophytes
- thick waxy cuticle
- sunken stomata
- reduced number of stomata
- reduced leaves
- hairy leaves
- curled leaves
- roots that spread deep and wide
adaptations of hydrophytes
- thin or no waxy cuticle
- many always open stomata on upper surface
- reduced structure to plant as water supports it
- wide flat leaves to capture as much light
- small roots as water diffuses directly into stem
- air sacs to float
evidence that translocation is an active process
-microscopy to see adaptations of companion cells
-if mitochondria inhibited by poison then translocation stops
-much faster than diffusion suggesting active
-
xylem vs phloem
- x water and ions p assimilates
- x up p up and down
- x from root p from source
- x to leave p to sink
- x transpiration p translocation
- x dead p alive
- x thick cell wall p thin cell wall
- x xylem vessels p sieve tube elements and companion cells
