Plant Review Video
• Watch this video to review plant taxonomy
•
http://www.youtube.com/watch?feature=player_embedded&v=h9oDTMXM7M8
Structure of Dicotyledon Stem
IB Assessment Statement
• Draw and Label plan diagram to show the
distribution of tissue in the stem and leaf of a
dicotyledonous plant.
What is a Dicotyledon?
• Dicotyledons: a type of flowering plant with
two embryo leaves (2 cotyledons)
Function of Stem
• Stems connect the
leaves, roots, and
flowers of plants and
transport material
between them using
xylem and phloem.
• Stems provide support.
How do stems provide support?
• Cells absorb water and high pressure develops
inside the cell. This is cell turgor and it makes
cell almost rigid.
• Some cells develop thickened cellulose walls
which strengthens the plant
• Cell Walls in the xylem tissue are both
thickened and lignified making them very
strong. Xylem provides support especially in
woody stems.
Tissues in the Dicotyledon Stem
• Epidermis: surface of the
stem made of a number
of layers often with a
waxy cuticle to reduce
waterloss.
• Cortex Tissue: Forming a
cylinder of tissue around
the outer edge of the
stem. Often contains cells
with secondary thickening
in the cell walls which
provides additional
support.
Tissues in the Dicotyledon Stem
• Vascular bundle: contains
xylem, phloem and
cambium tissue.
• Xylem: a longitudinal set of
tubes that conduct water
from the roots upward
through the stem to the
leaves. CELLS are DEAD!
• Phloem (sieve elements)
transports sap through the
plant tissue in a number of
possible directions. CELLS
are alive!
Tissues in the Dicotyledon Stem
• Vascular cambium is a
type of lateral meristem
that forms a vertical
cylinder in the stem.
The cambium produces
the secondary xylem
and phloem through
cell division in the
vertical plane.
Tissues in the Dicotyledon Stem
• In the centre of the
stem can be found the
pith tissue composed of
thin walled cells called
parenchyma. In some
plants this section can
degenerate to leave a
hollow stem.
Real Photo
Growth and Development of Stems
• Plants grow is restricted
to 'embryonic' regions
called meristems. Having
specific regions for
growth and development
(restricted to just the
meristematic tissue),
contrasts with animals in
which growth takes place
throughout the whole
organism.
IB Assessment Statements
• State that Dicotyledonous plants have apical
and lateral meristems
• Compare growth due to apical and lateral
meristems in dicotyledonous plants.
Two type of Meristem Tissue
• In dicotyledons there are two types of
meristem tissue:
1. Apical Meristem Tissue -2. Lateral Meristem
Two type of Meristem Tissue
Apical Meristem Tissue -at the tops of roots and
shoots allows them to
elongate (get longer)
Two type of Meristem Tissue
Lateral Meristem , also
called cambium -- located
in the cambium in the
vascular bundles, makes
roots and shoots thicker,
with extra xylem and
phloem tissue
Types of Cambium (lateral meristem)
growth
• Primary Growth
vascular cambrium for
vascular tissue with no
thickening
Types of Cambium (lateral meristem)
growth
• Secondary Growth -thickens cell wall with
cellulose and lignin
– 1. Vascular cambium
that produces secondary
xylem and phloem
– 2. Cork cambium
produces some of the
bark layer of a stem.
Lateral Meristem (secondary growth)
Lateral Meristem (secondary growth)
Lateral Meristem (secondary growth)
Animation on Secondary Growth
• http://bcs.whfreeman.com/thelifewire/conten
t/chp35/35020.html