Transport in plants Flashcards
how do plants lose water vapor
from leaves by transpiration
why do plants lose water vapor from transpiration
- stomata have to be open for gas exchange
- water vapor diffuse out of the stomata during gas exchange
what do plants living on land need to be adapted to do
- reduce the loss of water
- replace the water lost
give general adaptations land plants have to save water loss
- waxy cuticle
- stomata on under-surface of leaves
- stomata closed at night
- deciduous plants
terrestrial plants
plants that live on land
waxy cuticle
reduces water loss due to evaporation through the epidermis
stomata on under surface of leaf
reduces evaporation due to direct heating from the sun
stomata closed at night
no light for photosynthesis
deciduous plants
plants that lose their leaves in winter
why are deciduous plants adapted to reduce water loss
- they lose their leaves in winter
- ground may be frozen at this time
- so temperatures could be too low for photosynthesis
xerophytes
plants that have been adapted to live in very dry habitats where there is little access to water
give examples of where xerophytes could help found
- cold icy conditions where all water is frozen and inaccessible
- hot dry desert
- sand dune environments
xerophytes - adaptations
- rolled leaves
- hairy leaves
- sunken stomata
- reduced surface area of leaves
- dense spongy mesophyll layer
- reduced stomata
- thick waxy cuticle
- root adaptations
- lead loss
- succulent tissues
- avoiding problems
rolled leaves
- reduce surface area for evaporation
- traps a layer of water vapor, creating a higher water potential outside the stomata
- reducing water potential gradient
- reducing evaporation of water from leaf
hairy leaves
- traps a layer of water vapor
- creates a higher water potential outside the stomata
- reducing water vapor potential gradient
- reducing evaporation of water of the leaf
sunken stomata
- pit like
- traps layer of water vapor (as it isn’t taken away from the wind as easily )
- creating a higher water vapor potential outside the stomata
- reducing water vapor potential gradient
- reducing evaporation of water from leaf
reduced surface area of leaves
- e.g needle leaves
- reduces surface area of leaf
- less evaporation of water vapor
dense spongy mesophyll layer
smaller surface area for evaporation
reduced number of stomata
- closed during the day to prevent water vapor escaping
- reduces evaporation
thick waxy cuticle
- waterproof
- prevents water leaving through evaporation
root adaptations
- long deep roots to take up water
- high solute concentration in root hair cells
why do root hair cells have a high solute concentration
- to reduce water potential inside the roots
- so more water is drawn in through osmosis
leaf loss
- losing leaves when water isn’t available
- trunks and branches of plant may turn green instead for photosynthesis
succulent tissues
- succulent plants store water in a specialised parenchyma tissue in their stem and roots
- this gives them a swollen, fleshy appearance
- so water can be stored in plentiful supply when in drought
avoiding problems
- plants may lose leaves and become dormant, or die completely, leaving seeds behind to germinate and grow rapidly when rain falls again
- others survive as storage organs
- some plants withstand the dehydration and recover
how is a cacti adapted
- thick waxy layer on epidermis - reducing water loss by evaporation (layer is waterproof)
- have spines instead of leaves - reducing SA for water loss
- close their stomata at hottest times of day when transpiration rates are highest
why are sand dunes such harsh conditions for plant growth
- dry, salty conditions with little water
- little shade to reduce evaporation
- water vapor can be swept away from wind easily
what grows on sand dunes
marram grass
marram grass - adaptations
- has stomata that are sunk in pits, so they are sheltered from wind
- layer of hairs on epidermis
- roll their leaves in hot or windy conditions
- thick waxy layer of epidermis
what do the hairs on the epidermis of marram grass help to do ?
- trap moist air around stomata
- reducing water potential gradient
- slowing transpiration
hydrophytes
plants which live in water, partially submerged
hydrophytes - examples - live IN water
- water - lillies
- watercress
- duckweed
hydrophytes - examples - live ON water
- iris
- bulrush
if plants live IN the water, why is it important that their leaves float
- so they are near the surface of the water to get the light needed for photosynthesis
hydrophytes - adaptations
- very thin waxy cuticle, or none at all
- stomata found on upper surface of leaf
- stomata open most of the time
- reduced supporting tissues/structures
- wide, flat leaves
- small roots
- large surface area of stems/roots under water
- specialised air sacs
- aerenchyma tissue
wide, flat leaves
- Large SA = more photosynthesis
phneumatophore
- roots that grow out of the water to aid with gas exchange
- increases photosynthesis
stomata
- lots of stomata which will be open most of the time on upper surface
- increases rate of gas exchange
waxy cuticle
- thin or none at all
- water loss does not need to be prevented
root system
- short root system
- so they don’t become damaged by currents
- plant can meet its needs due to living in water
reduced structure to plant
- water supports the leaves and flowers
- no need for strong supporting structures
air sacs
- enables leaves to float on the water surface
aerenchyma
- plant tissue with air sacs
- allowing buoyancy
- forms low resistance pathway for the movement of substances, e.g oxygen to tissues below water
- route for waste gases to leave
- allows oxygen to diffuse through plant to all respiring cells
how do some hydrophytes prevent their roots becoming water logged
- they may have special roots which grow upwards in the air, allowing them to take in oxygen which is then passed down into submerged parts
transpiration
the loss of water vapour from leaves
what is the issue with hydrophytes and normal transpiration
- water cannot evaporate into water or high humidity air
- if water can’t leave transpiration stream stops
what happens when transpiration stream stops
plant cannot transport mineral ions up the leaves
what do hydrophytes have to help them transpire
hydathodes
hydathodes
specialised structures on the tips or margins of plant leaves which release water droplets which then evaporate from the leaf surface
xylem vessels
- transport system in plants
- transports water and minerals from roots to all other parts
phloem vessels
- transport system in plants
- transports sugars (sucrose) and amino acids made in leaves to all other plant parts
what do the transport systems in plants do
move substances between leaves, stems and roots
why is transport in plants important
plants have :
- high metabolic demands
- size
- surface area
high metabolic demands - plant needs
- many internal and underground parts of the plants can’t photosynthesise so need oxygen and glucose transported to them and waste products of cell metabolism removed
- hormones made in 1 part of the plant need taking to another where they’re used
- mineral ions absorbed by roots need to be transported to all cells to make proteins
size - plants
- plants continue to grow throughout their whole lives and become larger
- so need effective transport systems to move substances both up and down from the root tips to the tops of leaves and stems
- photosynthesis only happens in the leaves, products must be transported
surface area - plant needs
- size and complexity of multicellular plants mean that stems, trunks and roots - when considered give plants a small SA:V ratio
- plants can’t rely solely on diffusion to supply everything they need
dicotyledonous plant
- plants that make 2 cotyledons in their seeds
cotyledons
- organs that act as food stores for the developing embryo plant
- form the first leaves when the seed germinates
herbaceous dicotyledons
- soft tissues
- short life cycles
- e.g leaves, stems
woody dicotyledons
- hard lignified tissue
- long life cycle
what are xylem and phloem tissues arranged into
vascular bundles
where do gases diffuse in and out of the plant
stomata
root hair cells
transpiration stream
movement of water up a plant
transpiration
evaporation of water vapor from the stomata
water moves along water potential gradient - what is this
water moves from areas of high water potential to low water potential
where does water START when being transported in plants
root hair cells
where does water LEAVE the plants after being transported
stomata as water vapor
transpiration stream
movement of water up the plant
transpiration
evaporation of water vapor from the stomata
how do mineral ions move into the root hair cells
facilitated diffusion
active transport
what does the mineral ions do to the water potential when it moves into root hair cells
lower it
how does water move from the soil into the root hair cell
osmosis
due to water potential gradient
how are root hair cells adapted to suit their function
- large surface area to volume ratio for absorption of water and dissolved mineral ions
- thin walls
what does the water need to travel through before getting to the xylem
cell to cell across cortex of root
what are the 2 different pathways water can use to to move from cortex cell to cortex cell towards the xylem
apoplastic pathway
synplastic pathway
apoplast pathway
- movement of water through cell walls and intercellular spaces
- water fills spaces between the loos open network of fibres into the cell wall
- as water moves into the xylem more water molecules are pulled into the apoplast behind them due to cohesion
how is a continuous flow of water caused in the apoplast pathway
- pull from water moving into xylem (cohesive forces)
- causes tension
- continuous flow through the open structure of cellulose cell wall causes little to no resistance
symplast pathway
-water moves through cell membrane and cytoplasm of cells
- root hair cell has higher wp than the next cell along
- caused by water diffusing in from soil
- causing cytoplasm to be more dilute
- so water moves in from the root hair cell into the next door cell by osmosis
when does the symplast pathway continue until
xylem is reached
in the symplast pathway how is as much water drawn up as possible
- as water laves root hair cell by osmosi wp drops
- this maintains a steep concentation gradient
- ensures as much water is drawn up as possible
water molecules continue to move across the cortex using both pathways until what is reached
endodermis of root
what does the endodermis have which occurs a problem
a strip of water proof material in their walls
- forms a casparian strip
due to the casparian strip what pathway is blocked
apoplast
what does the water that has been using the apoplast pathway due when it gets blocked by the casparian strip
- use the symplast route
- this slows down flow of water slightly
- gives plant control over which mineral ions to pass through
2 types of transport vessels
- xylem
- phloem
how are xylem and phloem arranged
in vascular bundles
vascular bundle arrangement in stem
- around the edge
- for support
how are vascular bundles arranged in the roots
- in the middle
- helps plant withstand tugging strains
- which results as stems and leaves are blown in the wind
how are vascular bundles arranged in leaves
- midrib of dicot leaf is main vein
- carries vascular tissue through organ
- supports structure
- small branching veins through leaf for transport and support
xylem - structure
- non living tissue
- made up of mostly dead cells
xylem vessels
- long hollow structures made of columns of cells fusing together end to end
xylem fibres
- long cells with lignified secondary walls providing mechanical strength
lignin - xylem
- laid in walls of xylem vessels
- as rings, spirals or solid tubes
- there are some unlignified areas called bordered pits
bordered pits
where water leaves the xylem into other cells of the plant
phloem - structure
- living tissue
main supporting elements of phloem
- sieve tube elements
- made up of many cells joined end to end
- forms a long hollow structure
when cells walls become perforated in the phloem what forms
- sieve plates
sieve plates
- allow phloem contents through
there are large pores in the cell walls of phloem - what does this cause
- vacuolar membrane
- nucleus
- other organelles
all break down
what is closely linked to sieve tube elements
- companion cells
what links sieve tube elements and companion cells
- plasmodesmata
companion cells features
- have all of their organelles
companion cell role
- act as a life support system for sieve tube cells
- as these have lost most of their normal functions
other phloem structures for support
- fibres and sclerids
- sclerids (cells w thick walls)
water role in plants - turgor pressure
- provides a hydrostatic skelton
- supports the stems and leaves
water role in plants- turgor drives cell expansion
- force which enabled plant roots to force their way through tarmac and concrete
water role in plants - evaporation
keeps plant cool
water role in plants - transport
mineral ions and products of photosynthesis are transported in aqueous solutions
water role in plants - raw material
for photosynthesis
root hair cells adaptations
- microscopic size
- large sa:v ratio
- thin surface
- concentration of solutes in cytoplasm
root hair cells - microscopic size
can penetrate easily between soil particles
root hair cells - sa:v ratio
- there are lots of them also
- so can happen quickly
root hair cells - thin surface layer
diffusion and osmosis happens quickly
root hair cells - concentration of solutes in cytoplasm of root hair cells
maintains a water potential gradient between soil water and the cell
root hair cell function
- optimize water movement into the root
how does water move into the root hair cells
- by osmosis
- due to low concentration of dissolved material and has high water potential
- cytoplasm and vascular sap of root hair cell has lots of solvent so has a low water potential
apoplast pathway
- movement of water through the cell walls and intercellular spaces
- water fills spaces between the loose open network of fibres into the cell wall
what does the cytoplasm and vascular sap of the root hair cells contain
- lots of solvents
- mineral ions
- sugars
- amino acids
when in the root hair what are the 2 routes water moves across into the xylem by
- symplast pathway
- apoplast pathway
what happens as water moves into the xylem in the apoplast pathway
- more water moved in due to cohesive forces
- causes continuous flow
- cause if little to no resistance
benefits of apoplast pathway
- faster
- no organelles or cell obstructions in the way
symplast route
- water moves through continuous cytoplasm of living plant cells that is connected through plasmodesmata by osmosis
how does water move through symplast route
- root hair cell has a higher water potential than next cell along
- water moves from root hair cell into next cell by osmosis
- happens across route until xylem is reached
- steep gradient kept as water leaves root hair cell by osmosis water potential of cytoplasm falls again so maximum water drawn up
water is moved across the root until what is reached
endodermis
endodermis
layer of cells which surrounds xylem and phloem
what runs around the endodermal cells
casparian strip
waterproof strip of waxy material
what does the casparian strip prevent
- movement of water through cell walls (apoplast route)
- so water is forced into cytoplasm
what does the water in the apoplast route need to cross to enter the symplast pathway
- selectively permeable cell surface membrane
- excludes toxic solutes from water reaching living tissues
how do endodermal cells move mineral ions into the xylem
active transport
what does moving mineral ions from endodermal cells into water do
- lower wp of xylem making it lower than wp of endodermal cells
- create root pressure
- increase rate of water moving into xylem by osmosis down wp gradient from endodermis into symplast pathway
once inside the symplast pathway what pathway can water return to
- apoplast pathway so it can enter the xylem and move up plant
- aided by root pressure
evidence for active transport in root pressure
- poisons which affect mitochondria when applied to root cells root pressure stops
- root pressure increased with a rise in temperature and falls with a decrease in temperature
- if levels of oxygen or respiratory substrates fall root pressure falls
- when other methods like transpiration of water transport are low xylem zap can still be exuded from leaf tips = guttation
transpiration
water vapor loss from leaves and stems of the plant cells by evaporation via the stomata
how is gas exchange controlled
stomata opening and closing
stomata activity day
mainly open
allows oxygen and carbon dioxide in and out of the
water vapor is lost by diffusion
stomata activity night
mainly closed
prevents excessive water loss
demands for co2 is low but o2 still needed
transpiration stream
- water enters roots by osmosis
- transported up xylem until leaves are reached
- moves by osmosis across membranes and by diffusion along apoplast pathway from xylem
- evaporates from freely permeable cellulose cell walls of mesophyll cells into air spaces
- water moves out of leaves through stomata down a diffusion gradient
cohesion tension theory
theory that the transpiration stream is the main driving force for water movement up from the roots to the leaves
transpiration stream def
movement of water through a plant until it’s lost by evaporation through the leaves
transpiration pull
- caused a tension in the xylem which helps love water across roots from soil
evidence for cohesion tension theory
- changes in tree diameter
- breaking a xylem vessel
changes in tree diameter
- transpiration is at its highest tension in xylem vessels are too
- when transpiration is lower at night so is tension in xylem vessels so tree diameter increases
breaking a xylem vessel
- when you cut flower stems to put in water air draws into the xylem instead of water leaking out
- so a plant can’t move water up the stem as the continuous stream of water held by cohesion is broken
benefits of transpiration
- delivers water and mineral ions to fells
- evaporation cools leaves down and prevents heat damage
limitations of transpiration
- water availability is often limited
- in high intensity light rate of photosynthesis is very fast so stomata must be open to supply carbon dioxide but the plant can lose a lot of water and in some cases lose so much so supply can’t meet demand
translocation
transport of organic compounds usually in the form of sucrose
why is sucrose transported instead of glucose
- glucose is more reactive and may be broken down in transport
- sucrose has more energy storage
- efficient energy transfer
- removes risk of in between reactions
where does transport occur in translocation
source to sink
source
plant regions which produce assimilated by photosynthesis or from storage materials
e.g leaves, storage organs, fruit, seeds, tuber
