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transport in plants, doubt - where did protons come from? - Coggle Diagram
transport in plants
mass flow hypothesis
movement of fluid in cell down a pressure or temperature gradient
always fluids
eg -
blood circulation is a mass flow
transport of water/sap in xylem/phloem
is a mass flow
not the same as diffusion
diffusion is movement of ions, molecules down conc. gradient
but this is pressure or temp grandient
within
the medium is diffusion
mass flow is
by
the medium - the whole medium is flowing
when in xylem
water potential gradient in soil and air
creates pressure gradient
so transport is passive - no need of extra energy
long and continuous xylem
while phloem is not continuous - sieve plate creates pressure gradient - so needs energy
when it assimilates
in phloem - energy used
active transport
accepted theory
german plant physiologist Ernst Munch (1930)
or called Munch pressure hypothesis
cell membrane of companion cells is folded for surface area
lots of mitochondria
also has many proton pumps and sucrose pumps
one molecule in one direction
uniport
two in same direction
symport
2 in 2 directions -
antiport
facilitated diffusion
pump - meaning energy is needed - atp energy
build up of protons in the cell
when many protons
try to move out, but it can't use the same pathway
uses a symport
move fm outersurface to cell wall
along with this, sucrose moves out
all that energy was used to create a pressure gradient, and then so that sucrose can move out with it
now sucrose is in, uses the symplast pathway
1 more item...
because it came in from that pathway
why a specialised transport is needed?
slow diffusion because the distance is large
but when passing through a column of liquid, it is faster
herbacious dicotyledons
assimilation
called assimilates
substances absorbed become part of the cells
doubt - where did protons come from?