Download Sugar and Water Movement in Plants

Sugar and Water Movement in
Plants
Water Movement
• Water is moved up
from the roots of the
plants, up the stem
and out the leaves by
the Transpiration-Pull
Theory (CohesionTension Pull theory).
Water Movement
•
The theory is based on the
three key properties of water:
1)
Cohesion: the ability of water
molecules to stick together
2)
Adhesion: the ability of water
molecules to stick to the
sides of hollow tubes.
3)
The high surface tension of
water.
Water Movement
• Water molecules are
absorbed into the
roots through the
process of osmosis.
• Here water is forced
through the
endodermis into the
xylem, but only if the
xylem has room for it.
Water Movement
• At the leaves, water is
being used in
photosynthesis or it is
evaporated out of the leaf
through the stomata (a
process known as
transpiration)
• Due to the cohesion of
water molecules, as one
is pulled out of the
stomata or used in the
leaf, another takes its
place.
Water Movement
• Due to adhesion, the
water is able to stick
to the sides of the
xylem tubes and not
slide back down
towards the root.
Water Movement
• This occurs
throughout the entire
length of xylem in the
plant!
• Due to these
properties, water can
be pulled against the
force of gravity
upwards of hundreds
of feet!
Water Movement
• As water is being
pulled up through the
stem, more water is
forced through the
endodermis of the
root to replace water
lost at the leaves, so
there is a continual
flow of water through
the plant.
Sugar Movement
Sugar Movement
1. Glucose is created
at the leaf (The
Source) during
photosynthesis.
Glucose is changed
into the disaccharide
sucrose in order to
be transported in the
plant.
Sugar Movement
2. This sucrose is
actively transported
(uses energy) into
the phloem cells in
the leaf.
3. There is a high
concentration of
sugar (sucrose) in
the phloem at the
source.
Sugar Movement
4. Because there is so
much sugar in the
phloem, some water
moves in from the xylem
to try and balance out
the concentration.
5. This creates a high
amount of pressure in
the phloem near the
source.
Sugar Movement
6. Meanwhile sugar is being actively
transported into the root or any other
storage area in the plant (The Sink).
7. Sinks have lots of sugar (usually joined
together to form starch).
8. The phloem cells around a sink have low
amounts of sugar and therefore water will
leave them and cause them to have a
low amount of pressure.
Sugar Movement
Sugar Movement
9. Due to the difference in pressure in the phloem cells at
the Source and the Sink, sugar will be forced down the
phloem along this pressure gradient.
Sugar Movement
• This process is known as the PressureFlow Theory, which still has yet to be
proven.
• It was suggested by Ernst Munch, a
German plant physiologist, in 1926.