Made of
dead cells
joined end to
end with no
end walls
between
them and a
hole down
the middle.
Carry water and
minerals from the roots
to the stem and leaves
in the transpiration
stream.
Phloem
Made of columns of
living cells with small
holes in the ends to
allow substances to
flow through.
Transport food
substances (mainly
dissolved sugars) made
in the leaves to growing
regions (e.g. new shoots)
and storage organs (e.g.
root tubers) of the plant.
Transportation goes
in both directions.
Transpiration
Caused by the
evaporation and
diffusion of water
from inside the
leaves.
This creates a slight
shortage of water in the
leaf, and so more water is
drawn up from the rest of
the plant through the
xylem vessels to replace
it.
This in turn means
that more water is
drawn up from the
roots and so there's
a constant
transpiration stream
of water through
the plant.
Transpiration is just a side-effect of the
way that plants are adapted for
photosynthesis. They have to have
stomata in them so that gases can be
exchanged easily.
Because there's more water
inside the plant than in the air
outside, the water escapes
from the leaves via the stomata
because of osmosis.