Download Plant Tissues

PLANT TISSUES
Biology Department
PLANT TISSUES

Tissues can be classified into :

Meristematic tissues

Permanent tissues
I . MERISTEMATIC TISSUES

They are usually called meristems.
They are young tissues of the embryo or the
mature plant which are responsible for its growth
and development since their cells have the
ability to divide.
 The cells are :
 small
 thin-walled
 usually no central vacuole
 no specialized features.

MERISTEMATIC TISSUES



Meristematic tissue is located in:
Primary meristems: near tips of roots and stems. This
is called apical meristems.
Secondary meristems: in vascular cambium and the
cork (cortical) cambium.
Fig. Root tip
MERISTEMATIC TISSUE
ROOT TIP
Islamic University -Gaza
Department
Biology
II. PERMANENT TISSUES:


Are derived from meristeims. They are known as mature
tissues.
During their development, mature tissues gradually
change morphologically and physiologically and
become specialized for specific function in the plant
body. Such are termed tissue differentiation.
PERMANENT TISSUES:
Tissues are further
arranged to form tissue
systems :
Dermal
tissue
consists of epidermis
which may later be
replaced by periderm
or exoderm.
Ground
tissue
Contains of three
types of tissues:
parenchyma
collenchyma
sclerenchyma.
Vascular
tissue
xylem and
phloem.
II.A.1 DERMAL TISSUES:
EpidermisLocations: in the outermost layer of the primary plant body covering leaves,
1.
floral parts, fruits, seeds, stems and roots (until they undergo secondary growth).
Characteristics:
1. These cells essentially tabular but differences in size
2. Cells are closely fitted together.
3. In surface view, the cells may be isodiametric or elongated.
4. The cell has a central vacuole and thin peripheral cytoplasm.

The epidermis in generally is only one cell layer thick and forms
when protoderm cells derived from the apical meristems
differentiate.
Functions: are diverse including desiccation resistance, gas
exchange, and protection against herbivores and pathogens.
Cell types of the epidermis
 Pavement cells fit tightly together and secrete a waterrepellent cuticle that reduces water loss and pathogen
invasion.
 Guard cells form stomata, (pores for gas exchange).
They are generally kidney shaped cells (in Dicot
epidermal tissue )in surface view, rich in cytoplasm and
with prominent nucleus and contain chloroplast.
(in monocot epidermal tissue dample shape cells)
 The epidermis of leaves often contains trichomes,
various types of hairs.

Epidermis
CUTICLE
HAIRS
II.A.2 GROUND TISSUES : FOUND BETWEEN
EPIDERMIS AND VASCULAR TISSUE

Parenchyma- is the main ground tissue
•Aerenchyma - Parenchyma tissue with extensive connected air
spaces.
•Chlorenchyma - Parenchyma cells full of chloroplasts.
Locations:

•
•
•
In the primary plant body they occur as continuous masses in :
The cortex of roots & stems
Piths of stems and roots, and leaf mesophyll.
They may also occur as vertical strands of cells in vascular
tissues and also as horizontal strands (rays) in secondary
vascular tissues.
PARENCHYMA
Characteristics:



living at maturity and may become meristematically active
large thin walled.
They are generally polyhedral in shape. Tend to have
large vacuoles and many contain various secretions.
Cell Wall: primary or primary and secondary( may be
lignified, suberized or cutinized).
Functions: performs several functions such as storage,
respiration, photosynthesis, assimilation, those of xylem and
phloem are connected with the conduction of food and water.
PARENCHYMA
Islamic University -Gaza
Department
Biology
2-COLLENCHYMA
:
Locations: at the periphery of the primary stem, petiole and in the outer
part of the cortex.
Characteristics:
1. Composed of elongated collenchymal cells which are living at maturity.
2. They are similar to parenchymal cells except that they have much
thicker cell walls.
3. The thickening of the walls may be in the angles where cells are joined
together or on the tangential walls or on the walls around the intercellular
spaces.
Cell Wall: primary only, highly hemicellulosic and pectic, not lignified.
Functions: they provide support, largely for the primary plant body.
COLLENCHYMA
Islamic University -Gaza
Department
Biology
3. SCLERENCHYMA

It is a simple tissue formed of:
Fibers- long slender cells which occur in vascular
bundles (xylem fibers) and phloem, ground tissues epidermis
or bundle sheath.
 They provide support and some storage.





Sclereids- variable in shape, often branched, may occur singly or in groups in
ground tissues throughout the plant.
They make up the seed coats of seeds
shells of nuts, stones of drupes, and give the pear its gritty texture.
Their function is primarily for protection.
SCLERENCHYMA
Characteristics:
1. Composed of thick- walled lignified sclerenchymal cells which are
non-living and lack protoplasts at maturity.
Cell Wall: Thick, lignified secondary cell walls.
Functions: enables the plant to resist stresses of stretching, being,
weight and pressure without damage of other thin- walled cells.
Both collenchyma and sclerenchyma are mechanical
tissues of support.
SCLERENCHYMA (SCLEREIDS)
STONE CELLS IN PEARS
Islamic University -Gaza
Department
Biology
SCLERENCHYMA (FIBERS)
II.A.3 VASCULAR TISSUES:





include the xylem and phloem.
They are presents in the vascular plants.
Xylemis the principle of water conducting tissues in
vascular plants.
It may also act as a mechanical support to
different plant organs.
PRIMARY XYLEM:




is the xylem formed during primary growth from
procambium.
It includes protoxylem and metaxylem.
Metaxylem develops after the protoxylem but before
secondary xylem.
It is distinguished by wider vessels and tracheids
SECONDARY XYLEM:
is the xylem formed during secondary growth from
vascular cambium.
XYLEM :
Xylem is a complex tissue formed from of:

Vascular elements:
Tracheids are non- living elongated cell with tapering ends long and thin.
 They occur in seedless vascular plants, gymenosperms and some
primitive angiosperms.
Vessels are more complex than tracheid.
 The vessel is formed of a series of longitudinal expanded cells
while the tracheid is unicellular.
 Their wall is more thickened than tracheid.
 Vessels in contrast to tracheids are perforated at points of contact
with other vessels.
XYLEM :




Xylem fibers:- are derived from tracheids by an increase
in wall thickness, decrease in length
Xylem parenchyma:are alive cells.
Their walls may be thin or lignified.
2. PHLOEM:
is the principle food conducting tissue of the vascular plants.
It is a complex tissues formed from of:


Sieve elements- there are two types of sieve elements:
1.
Sieve cells –

are commonly long and slender with tapering ends.
Have sieve areas on their walls.
They occur in most seedless vascular plants and in gymnosperms.


2. Sieve tube members –




have large pores on sieve plates, usually on end walls.
Sieve tube members are stacked end to end to form sieve tubes.
They are the sugar-conducting cells of the phloem in angiosperms.
Sap flows between sieve tube members through sieve plate pores (modified
plasmodesmata).
.
Both sieve and sieve tube members do not contain
a nucleus and possess thin cellulose cell walls



Companion cells- are highly specialized parenchyma cells (the companium
cell retains its nucleus). They live only as long as the associated sieve tube
member is living.
Parenchyma cells and fibers- are associated with storage of food.
Fibers and sclerids- are common in phloem.
Epiderms
collenchyma
Parenchyma
Scelerenchyma
Fibers
Phloem
Xylem
Activities:
For identification of plant tissues by prepared slides:
Materials:
 Compound light microscope.
 Prepared slides.
1. Mention the meiotic figure you observed in slide for onion root tip
A: --------------------------------.
B: --------------------------------.
C: --------------------------------.
D: --------------------------------.
E: --------------------------------.
2. Examine prepared slide and draw ……….
Parenchyma
Chollenchyma
Sclereids in fruits
3. Label the figure.
A: --------------------------------.
B: --------------------------------.
C: --------------------------------.
D: --------------------------------.
E: --------------------------------.
F: --------------------------------.
4. Describe the differences between parenchyma, collenchyma, sclerenchyma,
with drawing?