FACT
Do you remember
that sucrose is made
up of glucose and
fructose
monosaccharides?
Plants transport
sucrose rather than
glucose because it is
less reactive and has
less of an effect on
the water potential.- fibres have walls all the same thickness, have no spirals or rings and they are pointed
at the end. If necessary, make a second slide if you did not find xylem.
- Move a good part to the centre and enlarge. Examine the secondary walls of these
cells.
Questions:- Describe the shape of xylem vessels.
- What secondary walls patterns do you see?
- Suggest the function of such secondary walls.
Phloem tissue DUMMY
Phloem tissue is the living tissue responsible for transporting organic nutrients produced
during photosynthesis (mainly as the carbohydratesucrose) to all parts of the plant where
these are required. The phloem tissue is made up of the following major types of cells:
- sieve elements: these are conducting cells which transport sucrose.
- parenchyma cells: which store food for transport in phloem.
- companion cells: are associated with parenchyma cells and control the activities of
sieve tube elements, since the latter have no nuclei. Companion cells are responsi-
ble for providing energy to the sieve elements to allow for the transport of sucrose.
Companion cells play an important role in loading sieve tubes with sucrose produced
during photosynthesis. Companion cells and sieve tube elements are connected via
connecting strands of cytoplasm called plasmodesmata. - fibres: unspecialised cells and supportive cells.
Diagram MicrographFigure 5.17: Longitudinal section: phloem
tissue transports nutrients throughout the
plant.Figure 5.18: Cross-section: the arrow indi-
cates the location of the phloem in the vas-
cular bundle.In the table below, the key structural features of the phloem are related to their function.
Chapter 5. Plant and animal tissues 129