PLANT TRANSPORT Flashcards
2 transport systems of plants
Phloem (transports products of photosynthesis from the leaves to the rest of the plant) and Xylem (moving water and mineral ions from the roots to the aerial parts of the plant)
2 types of flowering plants
xylemmonocytelodonous
dicotyledonous
monocytelodonous
plants w long, narrow leaves
dicotyledonous
plants w stalks
petiole
stalk
components of xylem tissue
vessel elements/ tracheids
sclerenchyma fibres
parernchyma cells
xylem vessel elements
hollow, dead cells arranged end-to-end with a large lumen and lignified cell walls, aiding in the mass flow of water
lignin function
impermeable to water, preventing leakage
strong, providing strength to the vessel and preventing collapse under negative pressure
pits function
(original plasmodesmata in living cells) allow lateral movement of water between vessels
tracheids
narrower, dead and hollow cells which are tapered at the end.
have pits within walls
mineral ions transported by xylem
magnesium (Mg 2+) used in photosynthesis for chlorophyll
nitrate (NO3-) required for synthesis of organic compounds
root hairs
have large sa for osmosis and ion active transport
found just behind root tip.
How does water enter the root hair cell?
osmosis, down a water potential gradient
moves from root hairs to cortex to xylem over gradient
why does the cytoplasm and cell sap have a lower water potential?
as they have larger quantities of inorganic ions and dissolved organic molecules pumped in via active transport)
symplast pathway
the movement of water through the cytoplasm and vacuoles via plasmodesmata
apoplast pathway
the flow of water through the cell walls of the plant without entering the cells themselves (due to cohesive properties of water
suberin
waterproof substance in the cell walls of the endodermis
casparian strip
impermeable barrier caused by lining of suberin, forcing water to move via the apoplast way
passage cells
cells without suberin lining, of which the symplast pathway can occur
transpiration stream
movement of water up the plant, due to the cohesive properties of water.
transpiration
the loss of water vapour from a plant to its environment via diffusion down a water potential gradient via stomata in the leaves as a consequence of gas exchange
why are internal spaces in the leaf moist?
they act as a gas exchange surface
cohesion
the attraction of water molecules to one another due to hydrogen bonding
adhesion
the attraction of water molecules to other surfaces due to cellulose in the xylem walls
transpiration pull
removal of water from the top of the xylem vessels creates tension on the columns of water in the xylem, pulling it up via cohesion.
COHESION TENSION THEORY
transpiration stream
the mass flow of water up the xylem from the roots to the leaves
Is the cohesion tension theory active or passive?
passive
air lock
when air gets into the xylem columns, preventing the upward movement
root pressure
active transport of solutes into the root xylem vessels, lowering water potential, meaning water moves into the xylem vessels via osmosis, increasing hydrostatic pressure in the xylem vessel.
capillary action
the movement of fluid up a narrow tube
aids transport, w cellulose and lignin helping adhesion.
factors affecting transpiration rate
humidity wind speed temp light intensity drought
humidity effect on transpiration
low humidity, steeper gradient, faster transpiration
wind speed effect on transpiration
wind removes humidity, therefore increasing gradient.
temp effect on transpiration
higher temps increase the KE of water molecules so that rate of transpiration increases.
drought effect on transpiration
releases stress hormones such as ABA which close stomata, preventing transpiration so as to reduce water loss.
xerophytic adaptations
rolled leaves (produced by hinge cells) stomata (in sunken pits) thick waxy cuticle trichomes multiple layers of epidermal cells spines as leaves water storage in stems root systems (shallow or deep)
phloem components
sieve tube elements
companion cells
parenchyma
fibres
sieve tube elements
elongated living cells joined end to end with certain organelles missing and a cellulose cell wall (no lignin)
separated by sieve plates w pores which can be blocked
do sieve tube elements have lignin
NO
callose
a carbohydrate which blocks sieve tube plates when they are damaged
companion cells
living cells w normal organelles, connected to sieve tube elements via plasmodesmata, acting together as a metabolically active unit.
difference between xylem and phloem vessel elements
xylem are dead while phloem are alive
xylem cell walls are lignified while phloem are not
xylem have no cell contents while sieve tubes have a cytoplasm
xylem vessels have no end walls while phloem have sieve plates
xylem withstand high negative pressure while phloem withstands high positive pressure
translocation
the mass flow of organic solutes in the phloem from source to sinks.
which way does translocation occur?
both direction as technically whole plant is a sink
how does sucrose get into the phloem?
companion cells actively load sucrose into the phloem with a cotransporter protein.
Hydrogen ions are actively pumped out of companion cells into its cell wall with ATP before diffusing back into the companion cell down a concentration gradient.
sucrose then diffuses into the sieve tube elements via the plasmodesmata linking the cells before moving across the leaf in the apoplastic pathway.
process of phloem mass flow
organic solutes are actively loaded into phloem from source, decreasing water potential of sap, meaning water moves into sieve tube elements via osmosis, increasing hydrostatic pressure.
transport of solute particles from source to sink
solute is actively transported into sieve elements, decreasing water potential, meaning water moves into the sieve elements due to low water potential.
at sink, solute particles are actively transported out of sieve elements, producing a high water potential which causes water to leave, reducing hydrostatic pressure in the phloem.
why is the hydrostatic pressure gradient needed?
causes sap to flow from high to low pressure with solutes, creating a mass flow.
sucrose will be converted into other substances to maintain a concentration gradient.
vascular bundles in dicotyledonous plants
located in a ring towards the outer edge of the stem
monocotyledonous plant vascular bundles location
scattered randomly around stem
mechanisms of phloem
active transport to load sugar into the phloem tissue
and osmosis to follow sugar into the phloem
