Transport in plants Flashcards
why do plants need transport systems
.they have low SA:VOL ratio
.diffusion is too slow to meet metabolic needs
.substance must be moved over long distances
what are the two main transport systems in a plant
xylem and phloem
what is the role of the xylem
.transports water and mineral ions
.provides structual support
how is the xylem tissue adapted
.elongated
.hollow tubes
.no end walls
.lack organelles
.wall thickened with lignin for support
.pits to allow movement of water and ions in and out of vessels
role of phloem
transports sugars and amino acids
adaptations of sieve tube elements
.connected end to end
.have sieve plates with pores to allow flow of sugars and amino acids
.lack nuclei and most organelles
.thin layer of cyto
adaptation of companion cells
.connected to sieve tube elements through pores
.cyto contains large nucleus
.many mito to release energy for active transport through sieve tube elements
.many ribosomes for protein synthesis
xylem and phloem in the root
.xylem forms a cross in the middle
.phloem are in the corners of the cross
xylem and phloem in the stem
.xylem in the inside
.phloem on the outside
xylem and phloem in the leaf
.xylem on the top
.phloem on the bottom
what is transpiration
evaporation of water from plants as a side effect of gas exchange
why does transpiration occur
.water evaporates from mesophyll cells
.stomata open so they can absorb CO2 for photo
.this provides a pathway for water vapour loss through the stomata
.water vapour moves down water potential gradient from the air spaces in the leaf into the atmosphere
how does light effect transpiration rate
.high light intensity = stomata open for maximum CO2 absorption for photo
how does temp effect transpiration rate
.high temp = evaportation of water faster due to higher kinetic energy
how does humidity effect transpiration rate
.low humidity increases water vapour gradient between leaf and atomosphere
how does wind speed effect transpiration rate
high wind speed = increase water vapour gradient between leaf and atmosphere
how to use a photometer
.cut the shoot underwater at a slant to increase SA for water uptake
.assemble photometer with shoot submerged in water
.keep capillary tube end of photometer submerged
.check that apparatus is airtight
.dry leaves
.leave time for shoot to acclimatise
.shut the tap and record the position of the air bubble
.measure dist move by air bubble and time taken
how to calculate rate of transpiration
.calculate area of capillart tube = pi r^2
.times the area by distance moved = volume of water uptake
.divide by time taken
how does water move through plants
.enters plants root hair cells via osmosis
.moves through the cytoplasm or cell walls towards xylem
.xylem transports water from roots to leaves
what is the apoplast pathway
.water moves through spaces in the cell walls and between cells
what is the symplast pathway
.water moves from cell to cell through cytoplasm and plasmodesmata
what does the casparian strip do
forces water molecules to take the symplast pathway to go to the xylem
how does water travel upwards through the xylem
.cohesion = H-bonds causes water to stick together and move as one column
adhesion = H-bonds between water molecules and cellulose in xylem vessel walls pulls water upwards
.transpiration pull = from evaportaion of water at leaves
leaf structure
.upper epidermis with waxy cuticle- reduces water loss from the surface
.palisade mesophyll cells- carry out photo
.spongy mesophyll cells- carry out photo
.stomata
.lower epidermis
what are the adaptation of leaf for gas exchange
.air spaces =
.network for gases to quicly diffuse in and out and access photosynthesising cells
.mesophyll cells =
.provides large SA for gases to diffuse
.stomata =
.open up allowing inward diffusion of CO2 and outward diffusion of O2
.close to minimise water loss
how do plants limit water loss
.waxy cuticle = waterproof
.guard cells = close stomata
what are xerophytes
.plants that are adapted to live in dry enviroments
adaptations of xerophytes
.thick waxy cuticle = reduces water loss
.rolling of leaves = encloses stomata to reduce air flow and evporation of water
.hairs = trap moist air
.sunken stomata in pits = reduce air flow and transpiration
.needle like leaves = reduce SA
translocation steps
.at soruce, sucrose is actively loaded into sieve tube elements from companion cells
.this decreases water potential in sieve tube elements
.water enter sieve tube elements from xylem and companion cells via osmosis
.this increases hydrostatic pressure in sieve tube elements at the source
.at sink, solutes are actively removed from sieve tube elements
.this increases water potential in sieve tube elements in sink
.water leaves phloem by osmosis decreasing hydrostatic pressure at the sink
.this creates a pressure gradient, pushing solutes from source to sink
how does active loading into the phloem work at the source
.hydrogen ions are actively transported out of companion cells into source cells
.H+ is co-transported along the concentration gradient back into companion cells with surcrose
.sucrose then diffuses along concentration gradient through plasemodesmata from companion cells to sieve tube elements
