3.3 Transport in Plants

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3.3 Transport in Plants
Plants need a transport system to:
Move water and minerals from the roots up to the leaves
Move sugars from the leaves to the rest of the plant
The Vascular Tissues
Water and soluble mineral ions travel upwards in the xylem tissue
Assimilates such as sugars travel in both directions in the phloem tissues
In a dicotyledonous plant (one that has two seed leaves) the xylem and phloem are present in the
vascular bundle along with other types of tissue such as collenchyma and sclerenchyma.
^ Transverse section of a root ^
Meristem ­ a layer of dividing cells, also called the pericycle
Cambium ­ the layer of meristem that divide to produce new xylem and phloem cells
^ Vascular bundle in a leaf ^

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Xylem
Long cell with thick lignified walls
The lignin waterproofs the walls of the
xylem and causes the cell to die
The end walls of the xylem cells then
decay and the contents leaves the cells
It is them a tube with no end walls called a
xylem vessel
Lignin strengthens the vessel walls and
prevents collapse when water levels are low
The spiralling patterns of lignin allow
flexibility to the stems and branches of the plant
In some place the lignin is not complete…read more

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Apoplast Symplast Vacuolar
Water passes through the Water enters the cell cytoplasm This is similar to the
spaces in between the cell through the plasma membrane symplast pathway in that
walls and in between the and through the plasmodesmata the water passes through
cells without passing from one cell to the next. the cells but it is not
through any plasma confined to the cytoplasm
membranes or into the or the cells and it is able to
cytoplasm at all.…read more

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Water availability ­ if water is less available the plant will preserve the water by closing the
stomata
Measuring Transpiration rate:
The main route of water loss from
a plant is through the stomata of
the leaf.
It is not easy to measure the rate
at which water vapour is lost from
the leaves.…read more

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This is the pressure when the endodermis actively moves water and minerals into the medulla
with no way to go back. This pressure forces the water and minerals up into the xylem. It can push
water up a few metres but cannot account solely for water getting to the top of tall trees.
Transpiration pull
The loss of water by evaporation from the leaves must be replaces by water from the xylem.…read more

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Leaf is rolled longitudinally so that air is available. gaseous exchange.
is trapped inside. This air becomes
humid which reduces water loss from The leaves are The leaf stem has many large
the leaf. The leaf can roll more tightly reduced to spines air spaces. This helps with
in arid conditions.…read more

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The concentration of H+ ions outside the cell increases and a gradient is formed.
3. The hydrogen ions diffuse back into the cell with sucrose through facilitated diffusion. This
is known as cotransport.
4. The cotransport required ATP to move the H + ions out of the cell and to let the sucrose
enter the cell against its concentration gradient.
5.…read more

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