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Summary AQA ALEVEL BIOLOGY NOTES ON THE XYLEM
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- AQA
ALEVEL NOTES ON THE XYLEM ADJUSTED TO THE AQA SPECIFICATION AND MADE FROM MARKSCHEMES
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XylemWhat is transpiration ?
→
Transpiration is the
process of water movement
through a
plant and its evaporation from aerial parts , such
as leaves ,
stems and flowers .
The for transpiration is supplied by the Sun hence it is
passive process
energy
-
,
a .
How does water out stomata ?
move
through the
The of
humidity atmosphere less that of
•
the is than air spaces next to the stomata .
There potential from the
gradient through
'
. . is a water air
spaces the stomata to the air .
i. If diffuse of air the air
stomata are open, water vapour molecules out the spaces into
surrounding
. .
Explain how water leaf
moves
through the
from
water is lost
mesophyll cells
by evaporation from their cell walls to the air spaces of the leaf
-
.
Water lost is replaced by water from the cell walls the
cytoplasm
the
xylem via
•
reaching mesophyll cells or
.
The cytoplasmic route of water movement
1)
Mesophyll cells lose water to the air spaces by evaporation
due to heat supplied by the sun
2) These cells now have a lower water
potential and so water
enters osmosis from neighbouring
by cells
3) of from lowers their water
Loss water
neighbouring cells
potential .
4) These cells from their
,
in turn , take in water neighbours
by osmosis .
WEEK
How water Moves
-
up the
E E -wa x- k- o.c a
Xylem : cohesion -
tension
theory
% ,
Water
plant force of gravity from roots
against to
•
moves the
up a ,
leaves .
This be explained the combined action of cohesion
by
•
can
and tension .
1) water evaporates from
mesophyll cells due to
heat from the sun
leading to transpiration .
molecules form bonds between
2) Water
hydrogen one
another hence tend to stick together .
This is
cohesion .
3) Water forms a continuous , unbroken column across
cells and down
the
mesophyll the
xylem .
from
4) As water evaporates the
mesophyll cells in
the leaf into the air spaces beneath the stomata ,
more molecules of water are drawn up behind it
due to cohesion .
5) Transpiration pull occurs in which a column of water
is pulled up the
xylem as a result of transpiration .
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