Summary
Summary AQA ALEVEL BIOLOGY NOTES ON THE PHLOEM
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- AQA
ALEVEL NOTES ON THE PHLOEM ADJUSTED TO THE AQA SPECIFICATION AND MADE FROM MARKSCHEMES
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🎋Phloem
Translocation the
→ is process by which
organic molecules and some mineral ions are transported from one
part
of another
a
plant to .
Structure of a Phloem %/
"E - E a s e , -
¥
Phloem made up of
is sieve tube elements
long thin
arranged
'
structures
-
end to end .
Longitudinal
sieve plate with pore holes)
""
.
phloem 's end walls are perforated (
pierced with to form sieve plates .
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§
" " " "" "" "" " "
" " """" " "" "° "" "" """ " " " "° " "" " "
" " "" " "" "
companion cell
what are sources and sinks ?
nucleus of
companion cell
→ Sources the sites of of ( where
are
production photosynthesis )
sugars occurs
cytoplasm of
companion cell " "" " "" " "" "
"" "" " "" " "" " " "" """ .
www..ua . .
" "" " " "" """"
sieve tube element
"
" Transverse lumen
Ions view
Inorganic
:
Organic Molecules :
cytoplasm of sieve cellulose cell
tube element .
Potassium ( Kt ) ions .
Sucrose wall
Chloride J
-
( C1 ions Amino sieve pore
•
acids
⑤ É::•
.
}
Phosphate )
-
LP04
-
ions
sieve plate
"
)
Magnesium (
Mg ions
•
:*
companion cell
Mechanism of Translocation
with nucleus
÷÷÷÷÷ . sieve tube
element
The of fast
rate is be explained by diffusion
'
movement too to
.
cytoplasm
The flow
theory
this
mass explains mechanism
-
.
I Transfer of sucrose into sieve elements from photosynthesis ing tissue
a) Sucrose is manufactured from of
the
products photosynthesis in cells with chloroplasts
b) Sucrose diffuses by facilitated diffusion from photosynthesis ing cells into
companion cells
ions ( Ht ) ATP
c)
Hydrogen are
actively transported from
companion cells into the spaces within cell walls
using .
d) LH
"
) then diffuse down through tube
Hydrogen ions a concentration gradient carrier proteins into sieve elements .
e) Sucrose molecules transported Ht
by transport
are
along ions co -
.
2 Mass flow of sucrose through sieve tube elements
a) When sieve tubes tubes have potential 4
sucrose enters the ,
the sieve a more
negative water .
from ( with into
b) Water moves the
xylem a less
negative water potential ) the sieve tubes
by osmosis ,
creating a
high
hydrostatic pressure within them .
c) At sinks, sucrose is used
up during respiration or converted to search for
storage .
d) These cells have low content from
a so sucrose is
actively transported into them the tubes
lowering their water
'
. . sucrose sieve
potential .
e) Water into these cells from the tubes
by osmosis , the hydrostatic of
lowering
i. pressure
moves
respiring sieve
the sieve tubes .
i.
High hydrostatic pressure at source and low
hydrostatic pressure
at sink .
i. Mass flow of sucrose solution is caused
by hydrostatic pressure down the sieve tubes .
3 Transfer of from the tube elements into sink cells
sucrose sieve
storage or
The is
sucrose
actively transported by companion cells out of the sieve tubes and into the sink cells
-
.
,
?⃝
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