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
