Download Phloem TOJ

Grab a whiteboard and pen and write what you see!
What are we going to do today?
 Describe
the structure of the Phloem
 Explain the mass flow theory for translocation
of sugars
 Apply knowledge of techniques to study
transport in plants and translocation to
interpret investigation results
Phloem is a tissue which
transports biological
molecules in flowering
plants.
 It consists of living cells
called sieve tube elements,
which form a long channel.
 The sieve tube elements
are separated from each
other by sieve plates,
which allow the movement
of substances from element
to element.

Minerals
Amino acids
Hormones
Sucrose
Why would the plant transport carbohydrates in the form of
sucrose?
The exact mechanism for translocation within the phloem is
still under debate and study, but the most widely accepted
theory currently in the ‘mass (or pressure) flow theory’.
Create your own card sort!
1.
2.
3.
4.
Write down how mass flow theory works
Separate out into separate statements
Cut out your statements and mix them up.
Give to your neighbour to try!
Have a go at Q9.1
You have 5 minutes!
 Evidence
for water movement in xylem and sugar
movement in phloem.
 Woody
stems have an outer protective layer of
bark, with a ring of phloem inside and a ring of
xylem inside that.
 Outer
layers of bark and phloem are removed from
a section of stem.
Stem above missing tissue ring swells with liquid rich in
sugars.
 Non-photosynthetic tissues below the ring wither and die.

Conclusions
 Sugars of phloem accumulate above ring as they are
unable to move down the stem.
 Sugars don’t pass below the ring so tissues die.
Phloem, rather than xylem, is responsible for the
translocation of sugars in the plant.
 Radioactive
carbon isotope 14C is used to make 14CO2.
 The 14C is incorporated into the sugars produced during
photosynthesis.
 Autoradiography allows tracking of these sugars.
Radioactive areas correspond to areas of phloem, not xylem.