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Transcript of 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
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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)