Transport in plants

Transport in plants
Two groups of flowering plants
• Monocotyledons
• Dicotyledons
Plants need transport systems
• Water does not enter plants through the leaves.
• Water and dissolved mineral nutrients enter
through the roots and has to be transported to
the leaves.
• Sugar is made in green parts of the plant exposed
to sunlight by photosynthesis.
• Sugar needs to be transported to root cells and
non photosynthesizing parts of the plant where it
is needed for energy.
Xylem and phloem
• Water is transported up the plant in xylem
• Sugar is transported up or down the plant in
phloem
Vascular tissue in roots
• In the roots of
dicotyledons the vascular
tissue is found in the
centre – called the stele.
• The xylem forms a cross
shape (or similar) in the
centre with the phloem in
bundles between the
arms of the cross
• This is surrounded by a
ring of tissue called the
endodermis
Vascular tissue in stems
• There is a ring of vascular
bundles around the stem
just underneath the surface.
• The phloem is on the outer
side of each vascular bundle
and the xylem on the inner
side.
• The two are separated by a
layer of dividing tissue
called the cambium.
• Annual division and growth
by the cambium forms the
rings found in woody
trunks.
Vascular tissue in leaves
• Vascular bundles form
the veins in plant leaves
• Xylem appears above
the phloem
Structure of xylem
• As xylem vessels form the cells
make lignin and deposit it in the
cell walls in patterns of rings,
spirals or reticulate (broken
rings).
• Lignin strengthens the cell walls
making them waterproof but this
also kills the cells.
• The end walls breakdown forming
hollow tubes able to withstand
strong tensile forces.
• Small pits in the cell walls enable
water to move sideways between
xylem vessels