transport in plants Flashcards
why do multicellular plants need transport systems?
big, high metabolic rate, low SA:VOL ratio so they need this to move substances to and from individual cells quickly
what does the xylem tissue transport?
water and mineral ions in solution, move up the plant from the roots to the leaves
what does the phloem tissue transport?
sugars both up and down the plant
how are xylem vessels adapted for transporting water and mineral ions?
long tube like structures
no end walls water passes easily
dead cells so no cytoplasm
walls thickened with woody substance called lignin which supports the vessel and stops it from collapsing inwards
how are phloem tissues adapted for transporting solutes
sieve tube elements - living cells joined end to end to form sieve tubes, no nucleus
companion cells- for each sieve tube element as the lack of nucleus and other organelles means they cant survive on their own. they provide energy for active transport of solutes
where does water enter a plant?
through its root hair cells
what is the symplast pathway?
goes through the living parts of the cell, the cytoplasm.
what is the apoplast pathway?
goes through the non living parts of the cell, cell walls. mass flow (high hydrostatic pressure to low hydrostatic pressure)
how does adhesion help move water through a plant?
water molecules are attracted to the walls of the xylem vessels, this helps water to rise up through the xylem vessels
how does tension and cohesion help move water through a plant?
water evaporates from leaves at the top of the xylem (transpiration)
this creates a tension (suction) which pulls more water into the leaf
water molecules are cohesive (stick together), so when some are pulled into the leaf others follow. this means a whole column of water in the xylem from the leaves down to the roots, moves upwards
water enters the stem through the root cortex cells
what is transpiration?
its the evaporation of water from a plants surface, the leaves
what is transpiration a result of?
gas exchange
plant opens stomata to let CO2 in for photosynthesis, this lets water out at the same time as higher conc inside than out
what are 4 main factors that affect transpiration rate?
light (stomata opens when it gets light)
temperature (warmer water molecules have more energy so evaporate from cells inside leaf faster)
humidity (the lower the humidity , faster rate. air around plant dry, water potential gradient increased between leaf and air )
wind ( windier, the faster rate as lots of air movement blows away water molecules from around the stomata which increases the water potential gradient
what is used to estimate transpiration rate?
potometer
where are xerophytic plants adapted to live in?
in dry climates
what are 2 examples xerophytes
cacti and marram grass
how is marram grass adapted to live in dry climates and reduce water loss?
has stomata sunken in pits so sheltered from the wind reducing transpiration rate
layers of hairs on epidermis which traps moist air round the stomata reducing transpiration rate
in windy and hot condition, it rolls up its leaves reducing exposed surface area and trapping moist air
how is cacti adapted to live in dry climates and reduce water loss?
thick waxy layer on the epidermis, reducing water loss by evaporation as the layer is water proof (marram grass also)
spines instead of leaves to reduce surface area for water loss
close their stomata at hottest times of day when transpiration rates are the highest
where are hydrophytes plants adapted to live in?
water
what is an example of hydrophilic (hydrophytes) plants?
water lilies’
how are hydrophytes adapted to live in water and cope with low oxygen levels ?
air spaces - help the plants float, can act as a store for oxygen
stomata - usually only present on the upper surface of floating leaves helping to maximise gas exchange
have flexible leaves and stems. these plants are supported by water around them so dont need rigid stems for support, flexibility helps prevent damage by water currents.
what is translocation?
it is the movement of dissolved substances/assimilates (sucrose, amino acids) to where they are needed in a plant - source to sink
what is the mass flow hypothesis?
active transport is used to actively load the solutes into the sieve tubes of the phloem at the source (leaves)
this lowers the water potential inside the sieve tube so water moves in via osmosis from xylem and companion cells
this creates a high pressure inside the sieve tubes at the source end of the phloem
at the sink end, solutes are removed from the phloem to be used up. this increases water potential inside the sieve tubes so water leaves via osmosis.
this lowers the pressure inside the sieve tubes
the result is a pressure gradient from the source to the sink end. the gradient pushes solutes along the sieve tubes to where they are needed
what is a SOURCE?
where the substance is made
what is a SINK?
where its used up
describe the process of active loading?
in companion cell, ATP is used to transport hydrogen ions out of cell into surrounding tissue cells
a concentration gradient is set up more H+ outside than in companion cell
an H+ ion binds to co transporter protein in companion cell membrane and re enters the cell.
a sucrose molecule binds to the co transport protein at the same time. the movement of the H+ ion is used to move sucrose molecule into cell against its conc gradient.
sucrose molecules are then transported out of companion cells and into sieve tubes by the same process
