plant tissue system

8/11/2019 plant tissue system

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TISSUES


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DEFINITION

A group of cells similar in structure

that work together to perform a

particular function are called tissues. The tissues are of different types depending

on the functions of the organism, they are

mainly of two categories PLANT TISSUES andANIMAL TISSUES.


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PLANT TISSUES

Plants perform functions which are different fromanimals and also their structure is different , hencethey have tissues which are different from animals.They are further classified into many sub

categories which is shown in the table below: Meristems

Simple (Ground) Tissue:frequently the site of storage, sometimessupport

Vascular Tissue: conduction of water and materials used in synthesis

Dermal Tissue:protection and interface with the environment

Secretory Tissue: protection against herbivores and pathogens andattraction of pollinators


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Primary and Secondary Growth


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Your growth

infant child You, today


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Plant Growth

1styearall primary growth

Primary growthplant growth that produces

an increase in length and new structures


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Secondary growthplant growth that produces

an increase in diameter in existing plant parts in

the second and any subsequent growing seasons

2nd

yearonly secondary growth, in blue, isshown below


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2ndyear primary (in green) and secondary (in

blue) growth


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3rdyears growth, showing

both primary (black) and

secondary (red) growth


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Woody dicot stem cross section showing

growth rings


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Apparent increase in limb height on many trees

is due to loss of lower limbs


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MERISTEMATIC TISSUEMeristems: - Permanent regions of active cell division

- (undifferentiated plant tissue)

= plant stem cells

The main characteristic of this tissue is

that it is responsible for the growth ofplants.

The cells of this tissue continuously

divide and later differentiate ( i.e. getconverted ) into permanent tissue.


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Characteristics of the cells/ tissue

The cells are made of thin & elastic cell wallmade of cellulose.

The cells may be round , oval, polygonal or

rectangular in shape.

They are compact, having no intercellular

space.

There is a large nucleus and abundantcytoplasm.

The protoplasm contains very few or no

vacuoles at all.


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Tissue occurs at specific regions of the plant body

This is so because in plant

body growth occurs only at

these regions.

Hence , on the basis of this

there are 3 types of

meristem :

1. APICAL MERISTEM

2. INTERCALARY MERISTEM

3. LATERAL MERISTEM


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APICAL MERISTEM

As the name suggeststhis tissue is present atthe apex of the main& lateral shoots and

roots.

This tissue gives theplant body a lineargrowth.

Primary Meristems

Protoderm

Ground Meristem

Procambium


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LATERAL MERISTEM

This tissue lies on the sides of

the plant body.

It lies under the bark of the

plant in form of cork

cambium.

Produce tissues that increase

the girth of roots and stems

(Involved in Secondary Growth)


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INTERCALARY MERISTEM

This tissue is present at the base of the

nodes, internodes, leaves etc.They are also present in between the

permanent tissue.

They give the plant growth in length.


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Name Location Function

Apicalmeristems

Growing tips(Apex) of roots

and stems

Elongation

Lateralmeristems

(Cambium)

Beneath thebark, in vascular

bundles of dicot

stems

Increase indiameter

Intercalary

meristems

Base of the

leaves /

internode

Increase of

length


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PERMANENT TISSUE

These tissues arise from the meristematictissue.

The cells of this tissue gradually loose their

power to divide and acquire a definiteshape, size and function.

These tissues may be living or dead.

There are 2 types of permanent tissues1. Simple permanent tissue

2. Complex permanent tissue.


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SIMPLE PERMANENT TISSUE

This tissue comprises of same type of cells

which perform the same function and all arise

from the same origin. There are three

categories of simple permanent tissues:Parenchyma, Collenchyma, & Sclerenchyma.


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THE THREE SIMPLE PERMANENT

TISSUES


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PARENCHYMA Characteristics:

a) The cells are living.

b) The cells are thin walled.

c) There may or may not beintercellular spaces.

d) They are the mostunspecialized cells.

e) No depositions are seen,the cell wall consists only ofcellulose.

f) There is a prominentnucleus, cytoplasm &vacuoles.


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There are some special types of parenchymatissues :

Storage parenchyma : The cells enlarge to storenutrients & water.

Aerenchyma : Air cavities are present in theparenchyma tissue to provide buoyancy to theaquatic plants.

Chlorenchyma : These parenchyma cells havepresence of chlorophyll & hence can perform thefunction of photosynthesis.

Parenchyma tissue is found generally in all parts ofthe plant body. It forms the Ground tissue inleaves, stem, roots & fruits etc.


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Functions of parenchyma :

a) To store materials such as starch, proteins,hormones etc and waste products such as gum,tannin, resin etc.

b) Parenchyma cells perform the metabolicactivities of the plant.

c) Forms the packaging tissue between thespecialized tissue.

d) By providing turgidity , they provide mechanicalstrength.

e) Chlorenchyma helps in performingphotosynthesis.


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COLLENCHYMA


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Characteristics:

a) It has cells which aresomewhat elongated.

b) The cell walls are thinexcept at the angularregion ( where the cellsjoin). The thickenings are

caused due to depositionof cellulose or pectin.

c) There is no or lessintercellular space.

d) The cells are living, havedistinct nucleus & denseprotoplasm.

e) They often containchlorophyll.

Functions :

a) Providing mechanicalstrength is the primary

function.b) Provide flexibility.

c) Photosynthesis, as theycontain chlorophyll.

They are present belowthe epidermis in dicotstems and leaves. They

absent in dicot rootsand all parts ofmonocot plants.


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SCLERENCHYMA


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Cells with thick, tough, secondary walls

Normally impregnated with lignin.

< Flexible & stronger than collenchyma

Fx = mechanical (support ) & food storage.

2 TYPES OF CELLS (based on cell-shape) Sclerids - Stone Cells

Fibers - Contain Lumen


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Scleroids

Found in

nut shells

the hard part of seeds

flexible floating leafblades of water plants.


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Sclerenchyma fibres

Elongated & thick-walled with flattened

ends.

E.g. Fibres from flax

and hemp are used to

make fabric and rope.

The fibres also store

food like starch forthe plant


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Simple permanent tissue

Parenchyma Collenchyma Sclerenchyma

Location Soft parts of

plat

Cortexof root,

ground

tissues in

stem,

mesophyll of

leaves

Below the

epidermisof dicot

stem and

petiole

(Absent in

monocot)

In stem around

vascular bundle,roots, veins of

leaves, hard

covering of seeds

and nuts

N C ll i di i Th ll Th ll l


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Nature Cells are isodiametric

i.e. equally expanded on

all sides

They may be oval,

round, polygonal or

elongated Nucleus is present and

hence living

The cell walls are thin

and made of cellulose

Cytoplasm is dense with

a single large vacuole

Intercellular spaces may

be present

May contain

chlorophyll. Parenchyma

which contain

chlorophyll are called

chlorenchyma.

The cells are

elongated and are

circular, oval or

polygonal in

cross-section

Cell wall isunevenly

thickened with

cellulose at the

corners against

the intercellular

spaces

Nucleus is

present and hence

the tissue is living

Vacuoles are

small

Intercellular

spaces are

generally absent

If they contain

chlorophyll they

are known aschlorenchyma

The cells are long,

narrow, thick and

lignified, usually pointed

at both ends

The cell wall is evenly

thickened with lignin andsometimes is so thick that

the cell cavity or lumen

is absent

Nucleus is absent and

hence the tissue is made

up of dead cells

They have simple, often

oblique pits in the walls

The middle lamella i.e.

the wall between

adjacent cells is

conspicuous


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Function

Store and

assimilate food

Give mechanical

strength by

maintaining

turgidity

Prepare food if

chlorophyll is

present

Store waste

products like tanin,

gum, crystals and

resins

Provide mechanical

support to the stem

Allows easy bending

in various parts of the

plant without actually

breaking it

Gives mechanical

support to the

plant by giving

rigidity, flexibility

and elasticity to

the plant body.


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Meristematic tissue Permanent tissue

Cells devide repeatedly Cells are derived from

meristematic tissue &

normally do not devide

Undifferentiated Fully differentiate

Small Variable in shape and

size

Intercellular spacesgenerally absent

Intercellular spaces arepresent

Vacuole absent Large vacuoles in mature

cells


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Complex Tissue

Complex tissues since they include 2 or morekinds of cells. cells.All these co-ordinate toperform a common function. Complex tissuestransport water,mineral salts(nutrients) & food

material to various parts of plant body.

Xylem

Phloem

Xylem & phloem are both conducting tissues &also known as vasculartissues; together both ofthem constitute vascular bundles.


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Xylem

similar to straws

dead at functional maturity vesselscomposed of vessel elements (cells); uniform

tubes, open at both ends, relatively large diameter, may berelatively short

tracheidstapered at both ends, numerous pits ratherthan large openings between adjacent cells

conducts water and minerals upwards

Functions-

i. The main function of xylem is to carry water & mineralssalts upward from the root to different parts of shoots.

ii. Since walls of tracheids, vessels & sclerenchyma ofxylem are lignified, they give mechanical strength to theplant body.


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Xylem


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Phloem

alive at functional maturity

consist of sieve tube members and companion cells

Sieve tube memberscylindrical, conduct organic

molecules up and down through plant

Companion cellsregulate activity of sieve tubemembers

Functions-phloem transport photosynthetically prepared

food materials from the leaves to the storage organs &later from storage organs to the growing regions of the

plant body.


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Phloem


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Xylem

Phloem


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Dicot Stem


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Epidermis

Cork (or phellem)

Epidermis


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ORK

As plants grow older,the outer protective tissue undergoescertain changes.A strip of secondary meristem,called phellogenor cork cambium replaces epidermis of stem.

Cork cambium is a simple tissue having only one type of cells.Thecells of cork cambium are rectangular & their protoplasts are

vacuolated & contain tannins & chloroplasts. Cork cambium gives off new cells on its both sides,thus,forming

cork on the outer side & the secondary cortex or phelloderm onthe inner side.

The layer of cells which is cut by cork cambium on the outer side

ultimately becomes several layered thick cork or the bark oftrees.


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Cells of cork are dead & compactly arranged withoutintercellular spaces.

The walls of cork cells are heavily thickened bydeposition of an organic substance, called suberin.

Suberin makes these cells impermeable to water &gases. The cork cells do not contain protoplasm but are

filled with resin or tannins. In case of onion bulb too, in the skin of onion the cell

walls become thick & water proof due to addition ofsuberin.

Cork is protective in function.

Cork cells prevent desiccation,infection & mechanicalinjury.


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Dermal Tissue

Epidermiscovers primary growth, single

layer of cells; often secretes cutin (lipid)

forming cuticle (reduces transpiration and

protection from pathogens)

Peridermcovers secondary growth,

many cell layers; becomes impregnated

with lipids (suberin)


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Epidermis (cont.)

Root hairs - single cell extensions from the

epidermis near root tips

greatly increase surface area in contact with

soil and thereby enhance water and mineral

absorption


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Stomata

openings in epidermis

surrounded by Guard Cells that regulate

opening

Stomata from a epidermal peel of Commelina communis by Dr. J. Weyers


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Stomate

Guard Cells


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Lenticels

regions of loosely packed cells in the periderm

promote gas exchange with tissues below


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Secretory Tissue

produce a variety of products

nectar in flowers

oils in citrus and mints

latex

resins

opium mucilagee.g. for trapping insects

Reproductive shoot (flower)


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Apical bud

Node

Internode

Apicalbud

Shoot

systemVegetative

shoot

Leaf

Blade

Petiole

Axillary

bud

Stem

Taproot

Lateral

branch

roots

Root

system

Roots


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Roots

Roots are multicellular organs with important

functions:

Anchoring the plant

Absorbing minerals and water

Storing organic nutrients


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A taprootsystem consists of one main vertical root

that gives rise to lateral roots, or branch roots

Adventitious roots arise from stems or leaves

Seedless vascular plants and monocots have a

fibrous root system characterized by thin lateral

roots with no main root


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In most plants, absorption of water and minerals

occurs near the root hairs, where vast numbers of

tiny root hairs increase the surface area

Many plants have modified roots

Stems


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Stems

A stemis an organ consisting of

An alternating system of nodes, the points at which

leaves are attached

Internodes, the stem segments between nodes


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An axillary bud is a structure that has the potential

to form a lateral shoot, or branch

An apical bud, or terminal bud, is located near the

shoot tip and causes elongation of a young shoot

Apical dominance helps to maintain dormancy in

most non-apical buds

Many plants have modified stems

Leaves


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The leaf is the main photosynthetic organ of most

vascular plants

Leaves generally consist of a flattened blade and a

stalk called the petiole, which joins the leaf to a

node of the stem

Plant Tissue Systems


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Plant Tissue Systems

Cells of a plant organized into THREE tissue

systems:

a) Dermal Tissue System

(Epidermis)

a) Ground Tissue System

b) Vascular Tissue System

D l Ti S


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Dermal Tissue SystemIn nonwoody plants, the dermal tissue system consists of

the epidermis Epidermis - Single layer of tightly packed cells (one or

more)

Covers and protects entire body ("skin" of the plant)

Secretes a waxy coating called cuticleto help retain water(adaptation)

Specialized Epidermis - Example: epidermal hairs to trapor poison insects

Ex: root hairs

In woody plants, protective tissues called peridermreplace the epidermis in older regions of stems and roots

Trichomesare outgrowths of the shoot epidermis and canhelp with insect defense


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V l i S


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Vascular Tissue System Responsible for transporting water, mineral

nutrients, and organic molecules betweenroots and shoots

Located in the centres of roots

In stems, arranged in strands called vascular

bundles

Monocots Dicots

- Long tissue strands calledvascular bundles scattered

through stems

-Long tissue strands calledvascular bundles arranged in

rings within stem, to form a

cylinder shape

T t f l ti


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Two types of vascular tissue:

1)Xylemtransports water and dissolved

minerals UPWARD2)Phloemtransports food made in leaves

DOWNWARD to roots and to other parts of

shoot system


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The vascular tissue of a stem or root is

collectively called the stele In angiosperms the stele of the root is a solid

central vascular cylinder

The stele of stems and leaves is divided intovascular bundles, strands of xylem and

phloem

Ground Tissue System


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Ground Tissue System Filling spaces between the dermal and vascular tissues. Ground

tissue internal to the vascular tissue is pith; ground tissueexternal to the vascular tissue is cortex

Ground tissue includes cells specialized for storage,

photosynthesis, and support (Responsible for metabolic

functions)

Consists of:

Parenchyma cells (majority) and Pith

Collenchyma cells

Sclerenchyma cells

Ground Tissue:


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Ground Tissue:

Parenchyma

Living ground tissue that makes up the bulk of the plantbody Have thin and flexible primary walls

Lack secondary walls

Are the least specialized

Perform the most metabolic functions

Retain the ability to divide and differentiate

Parenchyma not only sounds cool to say, it does cool

things like:- Photosynthesis

- Storage of nutrients, carbs and H2O

- heals wounds and regenerates plant parts


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..and Pith

Pith is the tissue in the center of roots and

stems

Contains spongy parenchyma and also

functions to store nutrients and carbs andwater


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Ground Tissue: Collenchyma

- is also made of living cells

- Strengthens the plant

- Supports the plants primary growth regions

They have thicker and uneven cell walls

They lack secondary walls

These cells provide flexible support withoutrestraining growth


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Sclerenchyma

Have you ever eaten a pear and found thatparts of it were really gritty to chew?

You were chewing sclerenchyma!

What is it? Ground tissue whose mature cellsare dead, have thick walls composed of

celluloseeven when dead, they performtheir function! This is good for hardness ofnuts and cactus spines.


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Sclerenchyma cellsare rigid because of thick

secondary walls strengthened with lignin

They are dead at functional maturity

There are two types:

Sclereids are short and irregular in shape and havethick lignified secondary walls

Fibers are long and slender and arranged in

threads


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Perforationplate

Vesselelement

Vessel elements, withperforated end walls

Tracheids

Pits

Tracheids and vessels(colorized SEM)

Vessel Tracheids 100 m

Water-Conducting Cells of the Xylem


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Water-Conducting Cells of the Xylem

The two types of water-conducting cells, tracheids

and vessel elements, are dead at maturity

Tracheids are found in the xylem of all vascular

plants

Vessel elements are common to most angiospermsand a few gymnosperms

Vessel elements align end to end to form long

micropipes called vessels

3 mSieve-tube elements:longitudinal view (LM)


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Sieve-tube element (left)and companion cell:cross section (TEM)

Sieve plate

Companioncells

Sieve-tubeelements

Plasmodesma

Sieveplate

Nucleus ofcompanioncells

Sieve-tube elements:longitudinal view Sieve plate with pores (SEM)

10 m

30 m


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Sugar-Conducting Cells of the

Phloem Sieve-tube elements are alive at functional

maturity, though they lack organelles

Sieve plates are the porous end walls that allowfluid to flow between cells along the sieve tube

Each sieve-tube element has a companion cell

whose nucleus and ribosomes serve both cells

Plant Growth


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Plant Growth

Pl t G th


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Plant Growth

Plants can go throughtwo different types of

growth

Primary Growth-

elongates the axis of a

plant (growth in length)

Secondary Growth-

increases the girth of aplant (growth in width)

Plant Growth


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Plant Growth

Plant growth occurs at specific tissues called meristems

Apical Meristem: are located at the tips of roots and shoots

and at the axillary buds of shoots. These extend the length

of the shoot or root

Lateral Meristems: These extend the girth of a stem or root,

a process called secondary growth

Intercalary Meristems


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Intercalary Meristems

Why grass grows upward after it is mowed.

This is all we will say about intercalary meristems.

intercalary meristem

These are regions of growth situated between two regions

of mature (non-growing) tissue


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Primary Tissuesresult from primary growth

which are derived from apical meristems.

Primary Plant Growth and Development


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I t ti ll t d i i t h


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In mature tissues, cells are arrested in interphase

P i th i d t f


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Primary growth is a product of

Cell division

Cell elongation

E di ith ll/ti diff ti ti t ti


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Ending with cell/tissue differentiation-maturation


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In primary growth, cell division isnt entirely restricted to the

apical meristem proper. Cell division continues in the derived

immature tissues behind the apical meristem. These tissues are

called the primary meristematic tissues.

Protodermmatures to form the epidermis

Ground Meristemmatures to form the ground tissue

Procambiummatures to form the vascular tissue


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Protoderm ProcambiumGround Meristem

EpidermisGround Tissue Vascular Tissue

Undifferentiated Cells of Apical Meristem

P i G th i R t


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Primary Growth- in Roots

In roots, primary growthoccurs in 3 different zones

Zone of Cell Division (contains

root apical meristem) Zone of Elongation

Zone of Maturation

Simpler than in the shoot as there are no nodes or internodesAlways includes a root cap. The apical meristem of the root

encompasses some of the area of the root cap

Zone of Cell Division


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Zone of Cell Division

Lots of mitosisoccurring in the cells

here

Contains the newestcells (newly divided)

Zone of Elongation


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Zone of Elongation

Cells get longer topush the root tip into

the soil

Cells start developingtheir specialized

functions

Zone of Maturation


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Zone of Maturation

Cells become fullyspecialized

Considered mature

cells

Primary Meristematic

Meristems in a Root Tip


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Meristems in a Root Tip

Protoderm = outer layer of cells

Procambium = inner core of cells

Ground Meristem = everything else

Root Cap


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Root Cap

Root cap protectsthe root apical

meristem as root

pushes throughthe soil

Like a helmet for

the root cells

Primary Growth Stems


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Primary Growth- Stems

Is more complex because itgenerates both leaf and stem tissue

along with the axillary buds at the

internodes.

Growth occurs at the shoot apical

meristems

Shoot apical meristems are located

at the tips of buds Plants grow from the top, not the

bottom of the stem

Gross Morphology

Apical Meristem


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Gross Morphologyof the Shoot

Apical meristems of the Shoot


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p

are more complex than that of the

root.

L f P i di


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Leaf Primordium

Three primary meristmatic tissues


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Protoderm

b


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Procambium

G d M i t


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Ground Meristem

Gross MorphologyV

ascular Strands


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Gross MorphologyVascular Strands

Gross Morphology


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Leaf Traces

Gross Morphology

f


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Gross MorphologyLeaf Gaps

Secondary Growth


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Secondary Growth

Growth in width of stems and roots Degree of secondary growth varies

some plants barely have any, others

have extensive secondary growth.

Results in the formation of wood

and bark

Results from activity in the lateral

meristems Vascular Cambium

Cork Cambium

Primary growth in stems


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Shoot tip (shootapical meristemand young leaves)

Lateral meristems:

Axillary budmeristem

Vascular cambium

Cork cambium

Root apicalmeristems

Primary growth in stems

Epidermis

Cortex

Primary phloem

Primary xylem

Pith

Secondary growth in stems

Periderm

Corkcambium

Cortex

Primaryphloem

Secondaryphloem

Pith

Primaryxylem

Secondaryxylem

Vascular cambium

Primary and secondary growthin a two year old stem

(a)


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in a two-year-old stem

Epidermis

Cortex

Primaryphloem

Vascularcambium

Primaryxylem

Pith

Periderm(mainly corkcambiaand cork)

Primaryphloem

Secondary

phloemVascularcambium

Secondaryxylem

Primaryxylem

Pith

Pith

Primary xylem

Vascular cambium

Primary phloem

Epidermis

Cortex

Vascularray

Primaryxylem

Secondary xylem

Vascular cambium

Secondary phloem

Primary phloem

First cork cambium Cork

SecondaryXylem (twoyears ofproduction)

Vascular cambium

Secondary phloem

Most recentcork cambium Cork

Bark

Layers ofperiderm

Secondary phloem

Vascular cambium

Secondary xylem

Bark

Cork

Late wood

Early wood

Corkcambium Periderm

Vascular ray Growth ring

Cross section of a three-year-old Tilia(linden) stem (LM)

(b)

0.5 mm

0.5mm


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Secondary xylem accumulates as wood, and

consists of tracheids, vessel elements (only inangiosperms), and fibers

Early wood, formed in the spring, has thin cell walls

to maximize water delivery Late wood, formed in late summer, has thick-walled

cells and contributes more to stem support

In temperate regions, the vascular cambium of

perennials is dormant through the winter


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As a tree or woody shrub ages, the older layers of

secondary xylem, the heartwood, no longertransport water and minerals

The outer layers, known as sapwood, still transport

materials through the xylem Older secondary phloem sloughs off and does not

accumulate

Vascular Cambium


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Divides into

Secondary Xylem On the side closer to the center of the stem/root

Secondary Phloem

On the side closer to the outside of the stem/root

As the vascular cambium divides, it continues to pusholder cells farther away.


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Vascular cambium Growth

Secondary

xylem

After one year

of growth

After two years

of growth

Secondary

phloem

Vascular

cambiumX X

X X

X

X

P P

P

P

C

C

C

C

C

C

C

Cork Cambium


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Cork Cambium

As the secondary phloemgrows, it breaks the outer layerof the stems and root(epidermis)

Secondary phloem on the veryoutside becomes corkcambium

Cork cambium grows into cork

Cork cells contain suberin to

protect from water loss,physical damage and harmfulsubstances.

Types of wood


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yp

Heartwood

Older secondary xylem

Cells get cloggedstop conducting water

Darker in color Sapwood

Newer secondary xylem

Still actively conductingwater (and minerals)

Lighter in color


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Growth

ring

Vascular

ray

Secondary

xylem

Heartwood

Sapwood

Bark

Vascular cambium

Secondary phloem

Layers of periderm

Annual Rings in Wood


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Annual Rings in Wood

The age of a tree can bedetermined by looking at thenumber of rings that it has.

Wood = secondary xylem

What forms the rings?

Spring: water most available, watertransport cells are large and have

thin walls Summer: less water available,

water transport cells have thickerwalls and are darker

Epidermis

Cortex Vascular cylinder


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GroundDermal

Key

to labels

Vascular

Root hair

Zone of

differentiation

Zone ofelongation

Zone of celldivision

Apical

meristem

Root cap

100 m

Epidermis

Cortex

Endodermis


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Vascular

cylinder

Pericycle

Core of

parenchyma

cells

Xylem

Phloem100 m

Root with xylem and phloem in the center

(typical of eudicots)

(a)

Root with parenchyma in the center (typical of

monocots)

(b)

100 m

Endodermis

Pericycle

Xylem

Phloem

50 m

Key

to labels

Dermal

Ground

Vascular

Lateral roots arise from within the pericycle, the


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Cortex

Emerging

lateral

root

Vascular

cylinder

100 m Epidermis

Lateral root

321

outermost cell layer in the vascular cylinder

Shoot apical meristem Leaf primordia


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Youngleaf

Developingvascular

strand

Axillary budmeristems

0.25 mm


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Phloem Xylem

Sclerenchyma

(fiber cells)Ground tissue

connecting

pith to cortex

Pith

Cortex

1 mm

Epidermis

Vascular

bundle

Cross section of stem with vascular bundles forming

a ring (typical of eudicots)

(a)

Key

to labels

Dermal

Ground

Vascular

Cross section of stem with scattered vascular bundles

(typical of monocots)

(b)

1 mm

Epidermis

Vascular

bundles

Ground

tissue

Tissue Organization of Leaves


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The epidermis in leaves is interrupted by stomata,

which allow CO2exchange between the air and thephotosynthetic cells in a leaf

Each stomatal pore is flanked by two guard cells,

which regulate its opening and closing The ground tissue in a leaf, called mesophyll, is

sandwiched between the upper and lower

epidermis

Guard


123/123

Key

to labels

Dermal

Ground

VascularCuticle Sclerenchyma

fibersStoma

Bundle-

sheath

cell

Xylem

Phloem

(a) Cutaway drawing of leaf tissues

Guard

cells

Vein

Cuticle

Lower

epidermis

Spongy

mesophyll

Palisade

mesophyll

Upper

epidermis

Guard

cells

Stomatal

pore

Surface view of a spiderwort

(Tradescantia) leaf (LM)

Epidermalcell

(b)

5

0m

100m

Vein Air spaces Guard cells

Cross section of a lilac

(Syringa)) leaf (LM)

(c)

plant tissue system

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