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Chapter 36
Plant Form
Parts of Vascular Plants (fig.36.1)
• Consists of root and shoot systems
• Both grow at their tips – shoot and root apices
• Root system anchors and provides nutrition to the
soil by penetrating into the soil to absorb water and
ions
• Shoot system consists of stems and their leaves
• Leaves, flowers, fruits and seeds are formed on the
shoot
• Stems serve as scaffold for positioning leaves
(arrangement, size and other features of leaves)
decides a plant’s production of food
Parts of vegetative shoot
• Consists of internode, node, leaf and axillary buds.
• Nodes are regions where leaves are attached to
stems (figure – 36.22)
• Region between two nodes - internodes
• An axillary bud is a lateral shoot apex that allows the
plant to branch or replace the main shoot. Develop in
axils (region between stem and leaf).
• Reproductive phase produces flowers or floral shoots
• A vegetative axillary bud has capacity to reiterate the
development of primary shoot
What are the three tissues present in roots, shoots
and leaves?
• Dermal, ground and vascular tissues systems
• Dermal tissue – epidermis is the outer protective
covering. Coated with layer of wax (desert
succulents)
• Ground tissue – function in storage, photosynthesis
and secretion (support and protection of the plant)
• Vascular tissue- conducts fluids and dissolved
substances throughout plant body. Xylem – conducts
water and dissolved minerals and phloem –
conducts a solution containing nutrients like
sucrose
Apical and lateral meristems fig.-36.5
• Apical meristems- elongation of shoot and root apices
(primary stem and root) because of repeated cell
divisions
• Apical meristem – three primary meristems –
protoderm forms epidermis, procambium
produces primary xylem and phloem, and ground
meristem forms ground tissue
• Lateral meristems- produce an increase in root and
shoot diameter (girth)
• Two lateral meristems are Cork cambium-produces
outer bark of tree and vascular cambiumproduces secondary vascular tissues
• Older roots and shoots – secondary tissues –
secondary plant body
Dermal tissue
• Epidermis is covered
with fatty cutin (cuticle)
• Specialized cells
occurring in epidermis –
stomata guarded by
guard cells, trichomes
and root hairs
• Guard cells flanking
stomata regulate in
passage of water and
gases
stomata
Guard cells
Trichomes and Root hairs
• Trichomes are cellular or multicellular hairlike
growth of epidermis. It keeps leaves cool and
reduces evaporation.
• Some trichomes are glandular secreting
substances that deter herbivores (figure 36.8)
• Root hairs are extensions of root epidermis
that help roots in absorption of water and
minerals (figure 36.10).
Ground tissue
• Thin walled,
spherical
parenchyma cells
(apple)
• Function in storage,
photosynthesis and
secretion
• Parenchymal cells
containing
chloroplasts are
called Chlorenchyma
Collenchyma
• Collenchymal cells –
support and
protection
• Present in celeryallow plant organs to
bend without breaking
them
Sclerenchyma
• Sclerenchyma have thick
cell walls-provide support
and protection
• Secondary cell walls have
lignin
• Fibers are long, slender
cells and grouped together
• Sclereids (single or in
groups) – gritty nature of
pears
What are the four zones in roots? (fig. 36.14)
• Developing roots are divided into four zones
• Root cap is composed of inner columella cells and
outer lateral root cap cells. Protects the roots during
their extension across abrasive soil particles
• Zone of cell division
• Zone of elongation – roots lengthen due to activity
of primary meristem (longer and wider)
• Zone of maturation- Cells differentiate.
• Cortex differentiates to form endodermis, casparian
strips has suberin produced in bands, all tissues
internal to endodermis form stele (ground meristem)
Stems: support for above-ground organs
• Stems support plants against gravity
• The apical shoot meristem produces stem
tissues, leaf primordia and bud primordia
that develops into shoots, leaves, and flowers
• Arrangement of leaves – phyllotaxy –
exposure of leaves to sun
• Regions where stipules fall off – leaf scars
with tiny bundle scars where vascular
connections were present (deciduous trees)
Vascular tissue arrangement in stems
• Vascular bundles in monocots stems are
scattered throughout ground tissue and in
dicots stems the bundles are arranged in a ring
(figure 32.23)
• Parenchymal cells located in centre of stem –
Pith
• Modified stems and roots serve different
specialized functions of storage and
reproduction
What are lenticels?
• In woody trees, cork
cambium produces suberin
impregnated cork cells
(outside) and phelloderm
(inside).
• Cork
cambium+cork+phelloderm
= periderm
• Lenticels are unsuberized
cells of cork cambium –
gaseous exchange
Lenticels
Leaves are main photosynthetic organs
• Two basic types of leaves – microphylls and
megaphylls
• Microphyll is a leaf with one vein branching and
megaphyll has several veins
• Vein consists of xylem and phloem (vascular
bundles) and are distributed throughout the leaf blade
• Simple leaves have undivided blades
• Compound leaves – blades are divided into leaflets
(Pinnately and palmately arranged leaves – figure
36.31)
• Dicots have reticulate or netted veins whereas
monocots have parallel veins (figure 36.30)
Structure of leaf
• Leaves have upper and lower epidermis with
numerous stomata flanked by guard cells.
• Palisade mesophyll - parenchyma is present
below upper epidermis – barrel shaped to
cylindrical chlorenchyma cells
• Spongy mesophyll present between palisade
mesophyll and lower epidermis – many
interconnected air spaces with stomata – help
in gas exchange and passage of water from
leaves
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