3.3)Transport in plants Flashcards
why do plants need a specialised transport system?
-larger plants have a smaller sa:vol ratio
-transport water and minerals from roots to leaves
-transport sugars from leaves to rest of the plant
why is diffusion alone not efficient for plants?
-not very active = respiration rate is low = oxygen can diffuse
BUT
-water cannot be absorbed by air (by diffusion)
-sugars can’t be absorbed by soil (by diffusion)
what are the 2 types of vascular tissue and what do they carry?
xylem tissue = water and soluble mineral ions
phloem tissue = assimilates (e.g. sucrose sugar)
what isn’t carried in plant vascular tissue that is in animals?
respiratory gases
what are dicotyledonous plants?
plants that have 2 seed leaves and a branching pattern of veins
what tissue do vascular bundles contain?
-collenchyma & sclerenchyma=provide support and strength to the plant
-xylem = water
-phloem = assimilates
where is the vascular bundle found in a young root and what shape is it?
-core of young root
-x shaped = arrangement provides strength to withstand pulling forces that roots are exposed to
what surrounds the vascular bundle (young root)?
-sheath of endodermis cells = allows water to enter xylem
what is the significance of pericycle cells and where are they found (young root)?
-inside the endodermis
-able to divide and differentiate into any type of cell = grow and repair damaged tissue
where are the vascular bundles found in the stem?
outer edge of the stem
how do the vascular bundles differ in woody plants and non-woody plants (in the stem)?
non-woody = bundles are separate and discrete
woody = separate in young stems but continuous rings in older stems
what is the significance of the complete rings of vascular tissue under barks of trees?
the arrangement provides strength and flexibility to withstand bending forces exerted by wind onto stems nd branches
what is found between the xylem and phloem (in stems)?
layer of cambium (meristem cells) = divide to produce xylem and phloem cells
where are the vascular bundles found in the leaf?
form the midrib and veins of the leaf
what is the function of companion cells?
to load sucrose into the sieve tubes
what are sieve tube elements?
make up tubes in the phloem tissue
what are the 3 main structures of the xylem?
vessels = carry water nd dissolved minerals
fibres = support the plant
living parenchyma cells = act as packing tissue that separate nd support vessels
where is lignin found in the xylem nd what does it do?
-found in walls
-is waterproof = kills the cell = end walls nd cell contents decay
what are found in areas where lignification is incomplete in the xylem?
bordered pits = allow movement of water between adjacent vessels
how are xylem adapted to carry water nd mineral ions from roots to leaves?
-made from dead cells = form continuous columns from roots to leaves
-tubes are narrow = don’t break easily nd capillary action is effective
-bordered pits = water move sideways to adjacent vessels
-lignin deposited n spiral/annular/reticular patterns = xylem can stretch = stem/branch bends
why is the flow of water not impeded in the xylem?
-no cross walls
-no cell contents
-thick lignin layer prevents walls from collapsing
how do sieve tube elements help to carry assimilates up/down the phloem?
-lined up end to end to form sieve tubes
-no nucleus, little cytoplasm = lots of space for mass flow of assimilates
-sieve plate cross walls (at ends of tube) = assimilates travel through holes to next sieve tube element
what do companion cells have many of and what are they needed for?
-many mitochondria = ATP for active processes = load assimilates into sieve tubes
what are the 3 pathways taken by water?
Apoplast
Symplast
Vacuolar
describe the apoplast pathway
-water moves by osmosis
-through spaces between cell walls
describe the symplast pathway
-water enters cytoplasm through plasma membrane
-leaves through plasmodesmata to next cell
describe the vacuolar pathway
-water passes through cytoplasm nd vacuoles
-leaves through plasmodesmata to next cell
what is water potential?
-the tendency of water molecules to move from one place to another
-water moves DOWN water potential grad. (high—>low)
what is the water potential in the cytoplasm?
contains mineral ions nd sugars (solutes) = more (-)ive water potential that pure water
what happens when a plant cell is placed in pure water?
-water potential in pure water is 0
-water potential in cytoplasm is (-)ive
-water moves down water potential grad.
-water will move into the cell = turgid
what happens once the cell is full of water?
water inside the cell exerts P. on cell wall = P. potential build up = inflow of water reduced
what happens when a plant cell is placed in a salt solution?
-water potential in cytoplasm in (-)ive
-water potential n salt solution is more (–)ive!!
-water moves down water potential grad.
-water moves out of cell
= flaccid
what is plasmolysis?
when the plasma membrane loses contact with the cell wall due to water loss in cytoplasm nd vacuole
what is a potometer used for?
measure the rate of water uptake as a leafy stem respires
what is transpiration?
-the loss of water vapour from aerial parts (parts above soil) of plant
-mostly though stomata in leaves
why is transpiration limited on the surface of the leaf?
waxy cuticle
why does transpiration occur more during the day?
-stomata open to release water vapour
-stomata open mostly during day for gas exchange as there is sufficient sunlight for photosynthesis
describe the typical transpiration pathway
into leaf through xylem –> (osmosis) spongy mesophyll –> evaporates from spongy m. cell wall –> (diffusion) out of leaf through open stomata
what does transpiration trigger?
water lost through transpiration is replaced by transpiration stream = draws more water up the stem
why is transpiration important?
-transports useful minerals up plant
-maintains cell turgidity
-supplies water = growth, elongation nd photosynthesis
-supplies water = evaporates = cool plant (on hot day)
how does light intensity affect rate of transpiration (ROT)?
light = stomata open to allow gas exchange for photosynthesis = ROT inc.
how does temp affect ROT?
high temp = water molecules have more KE = more leave the stomata = ROT inc
high temp = decreases water vapour potential in air = more rapid diffusion ut of leaf
how does humidity affect ROT?
higher humidity in the air = less steep water vapour potential grad. = ROT decreases
how does wind affect ROT?
air moving outside of leaf = water vapour carried away = maintain steep water vapour potential grad. = high ROT
how does water availability affect ROT?
little water in the soil = water lost by transpiration can’t be replaced = stomata close = ROT decreases
what precautions are taken when using a potometer?
-vaseline around edges of apparatus to prevent air bubbles
-ensure shoot is healthy
-cut stem under water = prevent water entering xylem
-cut stem at angle = provide large SA in contact w water
-dry the leaves
what is adhesion?
attraction between water molecules and walls of the xylem vessels (carbohydrate molecules)
what is cohesion?
attraction between water molecules nd other water molecules
what are terrestrial plants?
plants that live on land
why is access to no water a problem for terrestrial plants?
-stomata remains open during the day for gas exchange (CO2 for photosynthesis)
-open stomata=water loss via transpiration
what are terrestrial plants adapted for?
-reduce water loss
-replace water lost
what are the structural and behavioural adaptations of terrestrial plants to reduce water loss?
-waxy cuticle= reduce water loss via evaporation in epidermis
-stomata under the leaf= reduce evaporation=not in direct sunlight
-stomata closed at night= no light for photosynthesis
-deciduous plants lose leaves in winter= ground frozen= less water available + temp too low for photosynthesis
what are xerophytes?
plants that live in arid (dry) conditions
what are some examples of xerophytes?
-cacti
-conifers
-marram grass
cacti is a succulent, what does this mean?
store water in its stem
what are some adaptations of cacti?
-ribbed/fluted stem= expand when water is available
-spines (instead of leaves)= reduce S.A= reduce water loss
-green stem= photosynthesis
-widespread roots= take up water when available
what are some adaptation of other xerophytes?
-small leaf S.A
-sunken stomata
-stomatal hairs
-closing stomata (when water is low)
-rolled leaves
-extensive root systems
-reduced # of stomata
-thick waxy cuticle
-leaf loss
how does a small leaf S.A affect water loss?
reduced S.A for evaporation
how does a sunken stomata affect water loss?
maintain humid air around stomata=reduce water potential gradient
how do stomatal hairs affect water loss?
maintain humid air around stomata=reduce water potential gradient=reduce evaporation
how does closing the stomata when there is less availability of water affect water loss?
reduce water loss=reduce the need to uptake water
how does rolled leaves affect water loss?
reduce the effect of wind=reduce water potential gradient=reduce evaporation
how do extensive root systems affect water loss?
-maximise water uptake=increase chances of contact with water
-shallow + wide=absorb rainfall
how does a reduce number of stomata affect water loss?
reduce the amount of places water can evaporate from
how does a thick waxy cuticle affect water loss?
waterproof leaves and stem=reduce evaporation
how does leaf loss affect water loss?
prevent water loss through the leaves
what are hydrophytes?
plants that live in water
(submerged, surface or at the edge of bodies of water)
why do hydrophytes need adaptations?
to help them cope with growing in water or permanently saturated soil
what are some examples of hydrophytes?
-water lilies
-duckweed
-bulrushes
why is it important for the leaves of hydrophytes to be kept in the sunlight?
receive enough sunlight for photosynthesis
what is a problem for hydrophytes?
waterlogging= water unable to drain away
what are the adaptations of hydrophytes?
-very thin or no waxy cuticle
-many + always open stomata
-reduced structure
-wide + flat leaves
-small roots
-large S.A of stem and roots
-air sacs
why do hydrophytes have a thin or no waxy cuticle?
-do not need to conserve water
-water loss is not an issue
why do hydrophytes have many always open stomatas?
-maximise gas exchange
-no risk of becoming turgid (always water available)
-guards cells are inactive
-plants with floating leaves=stomata on top of the leaf
why do hydrophytes have a reduced structure?
the water support the leaves and the flowers
why do hydrophytes have wide and flat leaves?
capture as much light as possible
why do hydrophytes have small roots?
water can diffuse directly into the stem and leaf tissue= less need for roots to uptake
why do hydrophytes have a large S.A of stems and roots?
-maximise area for oxygen to diffuse
-oxygen to diffuse
why do hydrophytes have air sacs?
allow the leaves and flowers to float
how do hydrophytes transpire?
-they cannot transpire= transpiration stream stops + mineral ions are not transported
-have specialised structures= HYDATHODES
-found at the tip or margins of the leaf
-release water droplets= evaporate from the leaf surface
what do leaves of a plant produce large amounts of ?
glucose
what is glucose used for in plants?
respiration
when transporting glucose what is it transported into?
sucrose
what happens when sucrose reaches the cell?
-converted back to glucose=respiration
-converted to starch=storage
-used to make AA + other essential compounds
define translocation
transport of assimilates around a plant via the phloem
what are assimilates?
substances made by the plant using substances absorbed by the environment
what are some examples of assimilates?
-sugars
-AA
where are the assimilates transported to?
in the phloem from the sources to the sink
what is the source?
part of plant that loads assimilates into the sieve tubes
what are the sinks?
part of plant that removes assimilates from the sieve tubes
what are the main sources of assimilates?
-green leaves + stems
-storage organs
-food stores
-early spring roots
how are green leaves and stems sources of assimilates?
glucose made in leaves=converted to sucrose=loaded into sieve tube elements
what are some examples of storage organs ?
-tubers
-roots
-meristems
where are food stores found?
seeds when plants germinate
why are early spring roots assimilate sources?
source=energy stored as starch is converted to sucrose=moved to other plants of the plant=enable growth
what 2 components of phloem tissue are concerned with transport?
-sieve tube elements
-companion cells
what are the steps of active loading of assimilates at the source?
1)H+ ions actively pumped out of the companion cells via proton pumps=require ATP
2)ATP–>ADP
3)H+ conc. inside companion cell decreases
4)H+ ions diffuse back into cell=special cotransporter proteins
5)movement of H+ ions into companion cell is ONLY allowed if accompanied by sucrose=SECONDARY ACTIVE TRANSPORT
6)active transport of H+ out of the cell=sucrose moves against conc. gradient
7)movement of sucrose into cell=conc. increase
8)sucrose move into sieve tube via plasmodesmata=high conc. (companion cell) –> low conc. (STE)
9)water potential in sieve tube element decreases
10)water move from high water potential (companion cell) –> low water potential (STE) = osmosis
11)movement of water and sucrose=turgor pressure=mass flow of assimilates in phloem
12)assimilates flow from high turgor pressure to low turgor pressure=down pressure gradient
13)diff in turgor pressure=movement of water by mass flow
14)assimilates can move either up or down=depending on position of source
what type of process is assimilate loading?
active
what type of process is assimilate unloading?
passive
describe the steps of phloem unloading?
1)sugar move into sink= low water potential
2)water follows= from high water potential (STE) –> low water potential (sink) –> OSMOSIS
3)uses sugar for various things=converted into something else
4)help maintain the conc. gradient between STE and sink
what are the main sinks in a plant?
-roots
-meristems
-parts of plant that are laying down food stores
summarise the steps of translocation?
1)sucrose actively loaded into STE =reduce water potential
2)water follow by osmosis= increases hydrostatic pressure in STE
3)sap move down sieve tube= high hydrostatic pressure (source) –> lower hydrostatic pressure (sink)
4)sucrose removed from sieve tube = increase water potential
5)water move out of sieve tube= reduce hydrostatic pressure
what is the evidence supporting translocation?
1) phloem is cut= organic molecules exuded
2)flow of sugars in phloem is 10,000X faster than diffusion=active process
3)plants provided with radioactive CO2 at their roots, show radioactive carbon in phloem= supports mass flow
4)mitochondria is poisoned=inhibits production of ATP=translocation stops
5)sucrose conc. is higher in leaves than roots
6)ring of bark removed from woody stem=bulge forms above ring=build up of fluid=more sugar above bulge than below=evidence for downward flow (leaves to roots)
7)increasing the sucrose in the leaf= increase the sucrose in the phloem
8)downward flow occurs at daylight=photosynthesis – but not at night= higher respiration at night + lack of photosynthesis = no longer a conc. gradient
