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Dicotyledonous stem Main functions of the stem
Holds the leaves in a favourable position for the
absorption of sunlight needed during
photosynthesis.
Holds the flowers in a favourable position for
pollination.
Holds the fruit in a favourable position for the
distribution of seeds.
Transports water and mineral salts from the
roots to the rest of the plant.
Transports organic substances from the leaves
to the rest of the plant. External structure of a stem
Consists of nodes, internodes, apical/terminal bud
and axillary bud.
Nodes: where the leaves and side branches
develop.
Internodes : region between 2 nodes.
Apical/terminal bud: Occurs at the tip of the
stem. Has meristematic tissue that divides and
form new cells resulting in primary growth
(increase in length)
Axillary bud : occur in the axils between the
petiole and the stem (develop into lateral
branches or flowers) Internal structure of a
dicotyledonous stem
Consists of three
regions, namely:
Epidermis.
Cortex
Central cylinder Cross section of a dicotyledonous stem showing
tissues 1.Epidermis
Outer layer of the
stem.
Has a single layer of
thin -walled, brick -
shaped cells.
Can be modified to
form stomata.
Outer walls are
covered with
waterproof cuticle.
Multi -cellular hairy
outgrowths may occur. 2. Cortex
The region directly after the
epidermis.
Consists of 4 layers:
Collenchyma, chlorenchyma,
parenchyma and endodermis. 2.1 Collenchyma
Occurs under the epidermis.
Cell walls are thickened at the corner.
Small or no intercellular spaces. 2.2 Parenchyma
Thin -walled with
large intercellular
spaces .2.3
# Endodermis
Inner layer of the cortex
with brick -shaped cells.
Absent in some stem or
not easily distinguished.
Stores starch. 3. Central cylinder
Vascular tissue (xylem and phloem)
occurs in vascular bundles.
Are arranged in oval shape.
Xylem is on the inside.
Phloem is on the outside.
Schlerenchyma cap occurs on the
outside of the phloem and consists of
dead cells and thickened walls.
Phloem is under the schlerenchyma
cap
Cambium: meristematic tissue
between the xylem and the phloem
Pith: the central region of the stem. Functions of tissues in a
dicotyledonous stem
Epidermis: protects underlying tissues.
Cuticle: prevents loss of moisture.
Stomata: allows for gaseous exchange.
Collenchyma: Strengthens and keeps
the stem upright. Can have
chloroplasts for photosynthesis.
Parenchyma: stores organic
substances, intercellular spaces allow
for gaseous exchange
Endodermis: stores starch.
Schlerenchyma fibres: protects the
vascular bundles, strengthens and
supports the stem. January 2023
> Classwork no:
> External structure of a dicotyledonous stem
1. List 5 main functions of the stem.
2. Draw and label the external structure of a dicot stem.
3. Describe the 4 external parts of the stem. January 2023
> Homework no:2
> Internal structure of a dicotyledonous
1. Draw a cross section structure of a dicotyledonous stem and label
it.
2. List and describe the internal regions of a stem.
3. List 6 functions of tissues in a dicotyledonous stem. January 2023
Classwork no:
External structure of a dicotyledonous stem
Page 12 mind action series