transport in plants Flashcards
what do xylem and phloem make up ?
vascular system in a plant
where are xylem / phloem in root ?
center to provide support
xylem in middle
where are xylem / phloem in stem ?
near outside to reduce bending
xylem in middle
where are xylem / phloem in leaf ?
make up network of veins which supports the leaves
xylem on outer surface
describe the tubes of the xylem
long tube structure with no cell walls
describe cells of xylem
dead, so no cytoplasm
describe xylem walls
thickened with lignin, which helps support xylem and prevents collapsing (amount of lignin increases as gets older)
how does water / ions move in / out of xylem ?
small pits in walls where there’s no lignin
what are sieve tube elements ?
- living cells that form phloem
- joined end to end to form tubes
- holes in end walls to allow solute to pass
what are companion cells ?
- carry out living function for both themselves and sieve element (like provide energy for active transport)
how does water move up a plant against gravity ?
adhesion, cohesion and tension
name the two examples of xerophytes
cacti / marram grass
what is a xerophyte ?
plant adapted to live in dry climates
name the adaptations of marram grass
- stomata in sunken pits to shelter from wind (micro climate)
- hairs on epidermis which traps moist air around stomata
- rolls leaves (micro climate)
name adaptation both cacti / marram grass have
thick waxy cuticle on epidermis to reduce water loss by evaporation as layer is waterproof
name the adaptations of cacti
- spines instead of leaves (less SA)
- close stomata at hottest times of day
name a hydrophyte
water lily
name adaptions of a hydrophyte
- air spaces help plant float (more light) and store oxygen
- stomata on upper surface of leaves
- flexible as don’t have to support their own weight (flexibility prevents damage from currents)
what are assimilates ?
dissolved substances (transported in translocation)
where does translocation move substances from / to ?
sources to sinks
what is a source ?
where assimilates are made
what is a sink ?
where assimilates are used / converted for storage
what are sugars transported as in translocation ?
why ?
sucrose, as it is both soluble and metabolically inactive
what is the symplast pathway ?
water passes through cytoplasm and plasmodesmata (osmosis)
what is the apoplast pathway ?
water passes through cell walls (diffusion), until reaches endodermis, where Casparian strip blocks water so must go symplast pathway
why is symplast pathway useful ?
passes through cell membrane so can control which substances pass
why is apoplast pathway the main pathway ?
has the least resistance
outline the the route water takes from roots
roots – xylem – leaves – transpiration
outline the process of mas flow in phloem
- solutes actively loaded into sieve tubes
- water moves in
- increase in hydrostatic pressure
- at sink end, solutes actively unloaded
- pressure decreases
- pressure gradient formed
outline the process of active loading in phloem
- ATP used to actively transport H+ ions out of companion cell
- conc gradient set up
- H+ binds to co-transporter protein, which binds to sucrose
- H+ moves back into companion cell
- same process used to move sucrose to sieve element
