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Uptake and Transport of Water and Ions in Plants - Coggle Diagram
Uptake and Transport of
Water and Ions in Plants
Uptake of Water INTO
& ACROSS Roots
STEPS
water enters root hairs by osmosis
from soil
passes across root cortex
into xylem tissue
up xylem vessels in stem to leaf
Why these
steps occur?
root hairs well adapted for
absorbing water and mineral ions
thin walls - short diffusion pathway
shape - large SA/V ratio
water passes down wp gradient from H in soil
to low in root hair by
osmosis
water in soil very weak solution mineral
salts = higher water potential
root hair vacuole strong solution of sugars
& other dissolved substances = low wp
water passes across cortex + enters
xylem tissue in centre of root
wp in xylem lower than in root hairs
Apoplast
Pathway
water passes through
cell walls of cortex cells
cell walls made of cellulose fibrils
parallel arrangement of microfibrils
allow water easily between layers
as water seeps through,
cohesive forces
pull more water along apoplast
most water moves via this
route as limited resistance
Symplast
Pathway
water passes through
cytoplasm of cortex cells
gradient in wp across cortex
as route hair cells takes in water,
water p
less negative
+ is higher
than adjacent cell
water moves via
osmosis
down
wp gradient via
plasmodesmata
Most water moves via apoplast way until it
becomes blocked...
cell wall impregnated with waxy
material (
suberin
) -
CASPARIAN STRIP
suberin waterproof so CS stops
water passing through
only way water can pass across endodermis
is move into protoplast + join water in is via
symplast
pathway through cytoplasm
under
metabolic control
(impurities removed
at this point as cannot pass through c.membrane
endodermal cells
pump ions
into xylem vessels by
active transport
xylem vessels lowers wp so by osmosis H2O moves INTO xylem
creates
root pressure force
that helps move water up the plant
cohesive forces pull water from endodermis to xy
once enters stele - bulk water returns
apoplast
water out of pits of xylem into cells
Uptake of Ions INTO
& ACROSS Roots
similar to
uptake of water
main uptake through root hairs
via
facilitated diffusion/active transport
depends on concentration gradient
Transport of Water UP
the Root + Stem in Xylem
Negative Pressure
(tension)
created as water
evaporates
out of stomata of leaf
responsible of pulling water
up the column as
mass flow
in order to work, there must be
a
continuous unbroken column water
through xylem - TRANSPIRATION STREAM
Cohesion
when molecules of a substance
attracted to each other
magnitude of this force depends on:
mass of the particles
distance apart
HYDROGEN bonding increases
cohesive forces
effect of large cohesion =
water molecules pulled inwards
towards each other allowing to be
sucked up xylem in continuous column
happens as water at top
of column evaporates out of leaf
Adhesion
weakest
large adhesive force between
WALL
of
XYLEM
+
WATER
within
when molecules attracted to ones of a different type - CAPILLARITY
magnitude of this force depends on:
width of diameter
(smaller diameter, higher it rises)
COHESION-TENSION
THEORY
water lost from leaves during
transpiration
moves from saturated air inside leaf to drier air outside by
evaporation
TRANSPIRATION STREAM
As water molecules removed
from xylem, more water molecules
move up to replace them
D: mechanism of water moving through
plant, involving tension + cohesive forces
transpiration is pulling water column
in xylem upwards and gravity pull downwards
so water column
stretched
+
under tension
EVIDENCE
1.Diameter of Tress reducing during daylight
during day - transpiration rate highest
water evaporation fast so fast pull into plant
tension much greater
pull
walls of xylem inwards
reducing diameter of tree
(most obvi woody plants as more xylem)
2.
Air gaps in water column of xylem
means water below cant be pulled up
cut flowers kept out of water for long time
air enters xylem column
placing flowers in water not make a difference
as water column already broken
flowers will wilt
Movement of Water
ACROSS Leaf
midrib divides into number of
veins that distribute across
the leaf
water enters leaf via
vascular bundle
found
in
midrib
water passes from veins
to surrounding cells for:
photosynthesis
providing turgor
lost in transpiration
Transpiration
water evaporates from walls of spongey mesophyll into air spaces - becomes saturated
water diffuses from region high wp (air spaces)
to low wp (outside air)
as water evaporates out, more drawn in to replace it
sets up water potential gradient
water passes from
xylem to spongey mesophyll
via
APOPLAST or SYMPLAST