4.4 Flashcards
xylem
water and disolved mineral ions
from roots to leaves
one way transport
dead cells
cell walls with lignin
hollow
pits
dead
phloem
living tissues
sucrose
from leaves (where produced) to where it is needed
mass flow
translocation
no lignin
no pits
companion cells and sieve plates
cambium
layer of unspecialised cells that divide, giving rise to more specialised cell that in turn form both the xylem and the phloem
formation of the xylem
starts as living tissue
first xylem to form is protoxylem - streches and grows because the walls are not fully lignified
cellulose microfibrilis withstands the pressure of compression
as the cells age increasing amount of lignin is joined to the cell wall
the cells then become inpermeable to water and die
this lignified xyem is a metaxylem
the end walls mostly break down so the xylem is a hollow tube
xylem support
pays important role in larger plants.
as the plants age more xylem is lignified to increase support
support in small plants
non woody
turgid parenchyma cells
sclerenchyma
collenchyma
evidence of the xylem
dye can be seen moving through a plant
parenchyma
thin walls of cellulose
collenchyma
cell walls with thickened areas of additional cellulose
sclerencyma
have lignified cell walls
2 types - sclereids and fiber (long and thin) cells
support
symplast pathway
water moves down concentration gradient from hair to the xylem through cytoplasm of cells
moves through plasmodesmata gaps in cellulose walls
living
slower
osmosis
apoplast pathway
water is pulled in by the attraction between water across adjacent cell walls from root hair to xylem
up to half of cell wall can be filled with water
water moves across cells walls until it reaches the endodermis which contains the waterproof layer called the casparian strip - then enter cytoplasm
non living
faster
diffusion
translocation
movment of substances arount plants
passive process in xylem
active in phloem
transpiration
loss of water vapour from the surface of the plant
xylem movments
xylem proved by josef using porous pot
transpiration
water lost from leaves
lower water potential
cohesion - water polat
adhesion of water to xylem
transpiration
light
stoma open in light and closed in dark
so rate increase with light intesity untill all stoma open
transpiration
temp
temp increases evaporation
increases amount of water vapour before saturation
increase conc gradient
so increased rate
eventualy there will be a limiting factor
transpiration
wind
reduces shell of air
increases conc gradient
increased rate
transpiration
humidity
lowers rate as reduced conc gradient
translocation
phloem transports assimilate
mass transport system
- sap is the transport medium
guttation
when transpiration rates are low and drops of water are forced out of the leaves
sources
site of sugar production
sinks
where sugar is used or stored
phloem loading
1.sympast pathway - sucrose moves by diffusion down a conc gradient into companion cells through cytoplasm and into seive cells then water moves by osmosis into seive tube causing positive hydro static pressure - passive
2.apoplast pathway - moves by diffusion down a conc gradient through cell wall to companion cell across membranes by active transport producing a high conc in the cytoplasm of companion cells , passes into seive tubes through plasmodesmata. water then moves due to os producing positive hydrostatic presssure
unloading
into sink cells by diffusion then sucrose moves rapidly into the other cells maintaing the diffusion gradient
evidence for transclocation
use radioactivity (carbon 14) to measure where glucose goes
limitations of mass flow model
- dosent take active loading of sucrose in to phloem seive cells into account, this changes the conc gradient, rate of osmosis and even direction
-translocation is continous
-water can move in at any point - return route of water is xylem
- pressure flow is better
transport through the phloem
moves as a solution
sucrose actively pumped into phloem at the source
sucrose moves out the phloem into the sink tissues
and moves to a region of lower hydrostatic pressure
stomata
guard cells become larger
inner wall is less flexible than the outer
minteral ions into plant
active transport through carrier proteins in the cytoplasm root cells
gas exhange in roots
CO2 out
O2 in
gas exchange surface in woody plant
lenticel
slowest conditions for water uptake
cold, humid and dark
low wijnd speed
movement of sugards
sugars pumped in phloen so water enters
pressure in phloem increases
sugars converted to starch in root cells
increase in water potential so water moves out
aerenchyma
when parenchyma is modified to create tissues with air spaces for buoyancy or aeration of tissues,
