plant transport Flashcards
definition of xerophyte
Plant ADAPTED TO reduce water loss so it can survive in VERY ARID conditions
Why is transpiration unavoidable during the day
The stomata are open for photosynthesis
Oxygen has to be removed
stomata is an easy route for water to be lost
How do most plants reduce water lost
Waxy cuticle
Xerophytes adaptations for surviving in arid conditions
1.Small leaves,
How is sucrose loaded into the phloem
Companiion cells use ATP to actively tranport Hydrogen ions out into surrounding tissues
Diffusion gradient produced and hydrogen ions diffuse back into companion cell, through COTRANSPORTER PROTEINS
tHESE PROTEINS allow hydrogen to bring sucrose molecules into the companion cells
As concentration of sucrose builds up they diffuse into SIEVE TUBE ELEMETNS THROUGH PLASMODESMATA
Definition of translocaion
The transport of assimilates throughout the plant in the phloem tissue
Definiton of source and sink
Source loads sucrose into the phloem
Sink Unloads sucrose from the phloem
WHy does the bark swell when it has been cut
Area above the bark acts as a sink where sugar collects, and cell division occurs
How do we know phloem is used
If radioactively labelled CO2 is used in photosynthesis the labelled carbon appears in phloem
Ringing a tree to remove phloem results n sugars collecting above the ring
Aphid feeding on stem, mouthparts are taking food from phloem
How do we know that trasnlocation is an active process
COmpanion cells have many mitochondria
MEtabollic poisons inhibits formation of ATP
How do we know translocation uses this mechanism
pH of companion cell is higher than surrounding cells
Higher concentration of sucrose in source than sink
Evidence against the mechanism of translocation
not all solutes in phloem sap flow at the same rate
role of sieve plates is unclear
WHat is meant by active loading
using atp to transport sucrose
compare translocation with transpiration
Translocation is an active process that loads sugars from the source to the sink
Decreasing the water potential, Water enters via osmosis and increases the hydrostatic pressure
TRANSPIRATION- driven by the evaporation of water from leaf
this reduces the hydrostatic pressue in the top of the plant, creating a pressure gradient, pulls the water up aided by cohesion
WHy do companion cells have a higher PH compared to surrounding cells
Hydrogen ions pumped out of companion cells, leaves
fewer hydrogen ions
Hgher PH
Possible function of sieve plates
COuld be used to block the flow of sugars if phloem is cut and sugars lost
8 Physical and Environmental factors that affect water loss
Physical:
Number of leaves
Number and size of stomata
Presence of cuticle
Environmental Light temperature humidity air movement/ wind water availibility- little water in soil, means it can't replace water loast via evaportaation
How can a potometer be used to measure water uptake
Potometer measures water uptake by a leafy shoot
water uptake is measured by the movement of the meniscus along a capillary tube
The volume = cross sectional area x distance moved
Precaustions taken when using a potometer
Set up underwater, ensure no extra air bubbles get into system
Joints must be air tight and water tight
Potometer and shoot must be left to climatise before readings start
Two adaptations of the sieve tubes that allow mass flow to occur
elements joined end to end to form a column
Little cytoplasm to reduce resitance to cell sap
WHy might flower survive longer if the ends cut off immediately before put into water
Air in xylem
restores continuous column
Suggest why a potmoter gives only an estimate of water uptake
It measure the water uptake
not all water is lost
some used for photosynthesis
describe the role of the Casparian strip
Cells with a waterprood strip in the endodermis
block the apoplast pathways
force water to take a symplastic route to pass through plasma memranes, so ions entry can be controlled
Definition of turgid and plasmolysis
Turgid means full of water
Plasmolysis means the cells contents have shrunk enough to pull the membrane away from the cell wall
