Plant Tissues - PowerPoint Presentation

Slide1

Plant Tissues

Biology DepartmentSlide2

Plant Tissues

Tissues can be classified into

:

Meristematic

tissues

Permanent

tissuesSlide3

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.Slide4

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

tipSlide5

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Meristematic

Tissue

Root tipSlide6

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

.Slide7

Permanent tissues:

consists of epidermis which may later be replaced

by periderm

or

exoderm

.

Contains of

three types of tissues: parenchyma collenchyma sclerenchyma.

xylem and phloem. Slide8

II.A.1 Dermal tissues:

1

.

Epidermis

-

Locations:

in the outermost layer of the primary plant body covering leaves, 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

.Slide9

Cell types of the epidermis

Pavement cells

fit tightly together and secrete a water-repellent 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.Slide10

EpidermisSlide11

cuticleSlide12

hairsSlide13
Slide14

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.Slide15

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.Slide16

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ParenchymaSlide17

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.Slide18

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CollenchymaSlide19

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

.

 Slide20

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.Slide21

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Sclerenchyma (

Sclereids

)

stone cells in pearsSlide22
Slide23

Sclerenchyma (Fibers)Slide24

II.A.3 Vascular tissues:

include the xylem and phloem.

They

are presents in the vascular plants.

Xylem-

is

the principle of water conducting tissues in vascular plants.

It may also act as a mechanical support to different plant organs.Slide25

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 tracheidsSecondary xylem:

is

the xylem formed

during secondary growth

from

vascular cambium

.Slide26

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.

 Slide27
Slide28

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.

Xylem :Slide29

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

).

.

 Slide30

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.Both sieve and sieve tube members do not contain a nucleus and possess thin cellulose cell wallsSlide31

Epiderms

collenchyma

Parenchyma

Scelerenchyma

Fibers

Phloem

XylemSlide32
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Slide34
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