Vegetative Structure and Function

8/3/2019 Vegetative Structure and Function

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ROOTS Origin of the Root

Hypocotyl portion of theembryo axis located below thecotyledonary node that giverise at its tip to the radicle

Radicle - lowermost porion of

the embryonic axis of a seed.Responsible for theproduction of the primaryroot

Primary Root from the maintrunk or from the hypocotyl

Secondary roots arise fromthe primary root

Adventitious roots fromstems, leaves and other partsof plants

Developed from structures otherthan the hypocotyl or primary

root.


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Types of Root System

Taproot System

Characteristic of dicots

Primary roots continue to growand send out lateral smaller roots

Fibrous or Diffuse Root System Characteristic of monocots

Primary root stops growing and

numerous adventitious rootsgrow and develop from the baseof the stem and take the place of

the primary root.


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Functions of the Roots

Anchorage-locate

Absorption- extracts

Storage- store and hoard

Conduction-transport


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Structure of Roots

Root tip

Root cap

Composed of elongatedcolumella cells that later

develop into peripheral cells

meristem

Senses light and pressure

exerted by soil particles

Secretes slimy substancemucigel, that aid in

protection, lubrication, water

and nutrient absorption


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Quiscent center Located just behind the root cap

Composed of 500-1000 inactivecells arrested in G1 phase

Divides only once in 15-20 days Unaffected by radiation and

other extreme environmental

con t ons Functions as reservoir to

replace damaged cells ofmeristem

Reorganizes patterns of primarygrowth in roots


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Subapical region Zone of

cellulardivision

Zone of

cellular

elongation

Zone ofcellular

maturation


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Zone of cellular division

Dome-shaped apical meristem

surrounding the quiscent center

Located 0.5-1.5 mm behind the root

itp

ompose o ense y un eren a ecytoplasmic cells

Divides every 12-36 hours

Produces almost 20,000 new cells perday


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Zone of cellular elongation

4-15 mm behind the root tip

Long vacuolated cells

Process of differentiation starts


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Zone of cellular maturation

Process of differentiation

complted

10-50 mm behind root tip

on-e ongate , mature ce s Presence of many ephemeral

root hairs


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Mature region

Epidermis

Cortex

Stele


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Epidermis

Covers root except root cap

Usually one cell thick; lacks stomata

Lacks a cuticle or have a thin layer cuticle


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Cortex

Interior to epidermis

Occupies largest cross-sectional area of root

Consists of 3 concentriclayers

ypo erm s protect roots Parenchyma tissue stores

energy reserves

Endodermis lined withCasparian strips, whichdiverts water and dissolvedminerals into cytoplasm of

endodermal cells


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Stele Includes all tissues inside

the cortex

Pericycle produces branchroot

Vascular tissue x lem and

phloem form in laternatingstrands interior to thepericycle

Most dicots have solid coreof xylem

Most monocots have

parenchymatous pith


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STEMS

Origin of Stems

Epicotyl

Portion of the embryo axis in the seed

Short cylindrical structure bearing a small mass meristematic

tissue and frequently a pair or more of tiny leaves at its tip

Immature shoot that later becomes the stem


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Kinds of Stem As to location

Aerial or epiterranean - above surface

Underground or subterranean-beneath soil

Rhizome horizontal direction bearsmost of the feature of t ical stem

e.g. ginger Corn arise from base of an aerial

shoot covered with dry leaves e.g.taro (gabi)

Bulb stem of bulb is in the form or

reduced, flattened disc e.g onion


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Functions of Stem Store materials

parenchymal cells

Support leaves- turgor

pressure

Transport water andsolutes betwwen roots

and leaves vascular

system

Produce carbohydrates -

chlorophyll


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External Structure of Stem Node leaves and buds arise

Internode- between 2successive nodes

Lenticel- tiny raised pores on

for gas exchange

Scar- remnant mark from leaf,bundle, bud, fruit, flower,

twig Bud immature shoot,

largely meristematic


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Internal Structure of

Stem

Epidermal tissue

Transparent cells

surrounding stem

ne ce t c t at o tenbears trichomes

in dicot trees, modified into

bark as plant grows older


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Vascular tissue

Embedded in the ground tissue

Composed of xylem and phloem occurred in

vascular bundles Phloem for the transport of food from the leaves down

to the roots and other parts of the plant, and xylem for

the transport of water from the roots up to the leaves.


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Vascular bundles are arranged differently in differentrou s of lants

Monocots have vascular bundles embeddedthroughout the ground tissue, where phloemoriented outward and xylem inward

Most dicots have a single ring of vascular bundlesembedded in the ground tissue

Many non-flowering plants and few dicots haveconcentric cylinders of xylem and phloem


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Ground tissue In dicots, the parenchymatous ground tissue is

composed of cortex and pith

Because monocots have vascular bundles

throughout their ground tissue, their stems do

not ave cortex or pit


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LEAVES

Origin of Leaves

Leaf primordia

Outgrowths of the apicalmeristem in terminal and

lateral buds

its position in the bud

determines the relative

position of leaves on the

stem the first pair of leaves are

produced during the

development of the seedling


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Leaf Morphology

Petiole stalk of the leaf that

connects the leaf blade to thenode of the stem

Blade broad, flat,photosynthetic portion of a

leaf divided into: Veins vascular tissues within

a leaf located on both sides ofe m r

Midrib narrow, thickenedstructure which is acontinuation of the petiole andextends through the center of

the blade to the opposite end;the major vein in a leaf thatdivides the blade into twohalves


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Stipule small paired

leaf-like structures atthe base of the leaf

stalk found on cetrtain

plants

Leaf sheath the base

of the leaf blade thatcompletely encircles

the portion of the

internodal segment ofthe stem, present

among grasses


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Leaf Anatomy

Upper and lower Epidermis Transparent, not pigmented

Coated with waxy material, cuticle

Cells are modified in the form of hairs and glandular cells

Presence of chloroplast-containing guard cells (small

opening is called stoma)


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Mesophyll

oca e e ween ep erma ayers

Made up of parenchymatous, photosynthetic tissues

Consists of 2 distinct types:

Palisade layer- vertically elongated comunar cells arrangedbelow the upper epidermis

Spongy layer irregular parenchymatous cells with manyintercellular spaces (called stomata chambers) arranged

above the lower epidermis


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Vascular bundles

Consists of primary xylem and primary phloem surroundedby a bundle sheath

Also conatin sclerenchymatous fibers or collenchyma cells

No vascular cambium Xylem composed of vessel elements located toward the

upper epidermis

Phloem- composed of sieve tubes, members and

companion cells located toward the lower epidermis

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Vegetative Structure and Function