hmm1414 chapter 5 part 2

8/9/2019 HMM1414 Chapter 5 Part 2

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HMM/SCM1414-Biology 1

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Cells displaced from meristem,

derivatives, continue to divide for sometime until the cells they produce

differentiate within developing tissues.

Pattern of plant growth depends

on the location of meristems.

Two major types of meristems

(i) Apical Meristem Located at tips ofroots & in buds of shoots

Supply cells for plant to grow in length.

This elongation, primary growth, enablesroots to extend through soil and shoots to

increase their exposure to light and CO2. In herbaceous plants, primary growth

produces almost all of plant body.

(ii) Lateral Meristems(Cambium)

Add thickness to woody plants, a processcalled secondary growth (progressivethickening of roots and shoots where

primary growth has ceased.)

Two lateral meristems: vascularcambium and cork cambium.

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Vascular cambium adds layers of vascular

tissue called secondary xylem (wood) and

secondary phloem.

Cork cambium replaces epidermis with

periderm, which is thicker and tougher.

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5.6.2 PLANT CELL TYPESThree Tissue Systems:1. Dermal - epidermis,2. Vascular-Xylem + Phleom , and3. Ground- Parenchyma,collenchyma

(See Figure 35.8, Campbell, page 717)

Each system is continuous throughout

plant body.

(1) Dermal Tissue Outer covering.

In non-woody plants, it is a single layer of

tightly packed cells, orepidermis thatcovers and protects all young parts ofplant.

Epidermis has other specialized

characteristics consistent with function of

organ it covers.

Example:

Root hairs - extensions of epidermalcells near root tips.

Cuticle waxy coating secreted byepidermis of leaves and most stems -

helps aerial parts of plant retain water.

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In woody plants, protective tissues called

periderm replace epidermis in olderregions of stems and roots.

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(2) Vascular Tissue Continuous throughout plant - involved in

transport of materials between roots andshoots.

The two types of vascular tissues:

(i) Xylem Conveys water and dissolved

minerals upward from roots into

shoots.

(ii) Phloem Transports food (organic nutrients)

made in mature leaves to roots; to

non-photosynthetic parts of shoot

system; and to sites of growth, such

as developing leaves and fruits.

Vascular tissue of a root or stem is called

the stele. In angiosperms, stele of root forms a

solid central vascular cylinder. The stele of stems and leaves is divided

into vascular bundles, strandsconsisting of xylem and phloem.

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(3) Ground Tissue Tissue that is neither dermal nor vascular

tissue. In eudicot stems, ground tissue divided

into pith, internal to vascular tissue, andcortex, external to the vascular tissue.

Functions - photosynthesis, storage, and

support.

Example, the cortex of a eudicot stem

has both fleshy storage cells and thick-

walled support cells.

Some major types of plant cells:

(See Figure 35.8, Campbell, page 718 719)

(a) Parenchyma(b) Collenchyma(c) Sclerenchyma(d)Water-conducting cells of the xylem(e) Sugar-conducting cells of thephloem

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(a) Parenchyma Primary wall relatively thin and

flexible Most lack secondary wall.

Protoplast usually has large central

vacuole.

Often depicted as typical plant cells

because they generally are the least

specialized, but there are exceptions.

For example, highly specialized sieve-

tube members of phloem are parenchyma

cells.

Perform most of metabolic functions of

plant, synthesizing and storing various

organic products.

For example, photosynthesis occurs

within chloroplasts of parenchyma cells

in leaf.

Some parenchyma cells in stems and

roots have colorless plastids that store

starch.

Fleshy tissue of most fruit is composed of

parenchyma cells.

Most parenchyma cells retain

ability to divide and differentiate into other

cell types under special conditions, such as

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repair & replacement of organs after injury

to plant.

Possible to regenerate entire plant from

single parenchyma cell in lab.

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/groundtsa.jpg

(b) Collenchyma Thicker primary walls than parenchyma

cells.

Walls unevenly thickened.

Grouped into strands or cylinders,

collenchyma cells help support youngparts of plant shoot.

Young stems and petioles often have

strands of collenchyma just below

epidermis, providing support without

restraining growth.

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Mature collenchyma cells are living and

flexible and elongate with stems and

leaves they support.

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/groundtsb.jpg

(c) Sclerenchyma Have thick secondary walls usually

strengthened by lignin and function as

supporting elements of plant.

Much more rigid than collenchyma cells.

Unlike parenchyma cells, they cannot

elongate. Occur in plant regions that have stopped

lengthening.

Many are dead at maturity, but they

produce rigid secondary cells walls before

protoplast dies.

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In parts of plant that are still elongating,

secondary walls are deposited in a spiral

or ring pattern, enabling the cell wall to

stretch like a spring as the cell grows.

Two types: fibers and sclereids -

specialized entirely for support.

(i) Fibers Long, slender, and tapered, and

usually occur in groups. Hemp fibers are used for making rope;

those from flax are woven into linen.

(ii) Sclereids (Stone cells) Irregular in shape and shorter than

fibers.

Very thick, lignified secondary walls. Gives hardness to nutshells and seed

coats and gritty texture to pear fruits.

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Sclerenchyma fibers

Stone cells or sclereids

http://www2.volstate.edu/msd/BIO/1020/lab10planttissues.htm

(d) Xylem Water-conducting elements of xylem,tracheids and vessel elements, areelongated cells that are dead at maturity.

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Thickened wall

Pit
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Thickened cell walls remain as a

nonliving conduit (tube) through which

water can flow.

Both have secondary walls interrupted bypits, thinner regions where only primarywalls are present.

(i) Tracheids Long, thin cells with tapered ends.Water moves from cell to cell mainly

through pits. Because their secondary walls are

hardened with lignin, tracheids function

in support as well as transport.

(ii) Vessel elements

Generally wider, shorter, thinner walled,

and less tapered than tracheids.

Aligned end to end, forming long

micropipes orxylem vessels. Ends are perforated, enabling water to

flow freely.

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Tracheids Vessel elements


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http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPLANTANAT.html

Other xylem cells: fibers & parenchyma

not conductive.

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Pit

Perforationplate
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPLANTANAT.htmlhttp://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPLANTANAT.html


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(e) Phloem Sucrose, other organic compounds, and

some mineral ions move through tubesformed by chains of cells called sieve-tube members. Alive at maturity, although cell lacks

nucleus, ribosomes, and vacuole.

End walls (sieve plates) have pores thatfacilitate flow of fluid between cells.

Each sieve-tube member has non-

conducting nucleated companion cell,connected to sieve-tube member by

numerous plasmodesmata.

Nucleus and ribosomes of companion cell

serve both that cell and adjacent sieve-

tube member.

In some plants, companion cells in leaves

help load sugar into sieve-tube members,

which transport sugars to other parts of

plant.

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http://io.uwinnipeg.ca/~simmons/2153/lb1pg6.htm

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5.6.3 STRUCTURE OF EUDICOT &MONOCOT STEMS, ROOTS ANDLEAVES

(1) Tissue Organization of Stems In gymnosperms and most eudicots,

vascular tissue consists of vascular

bundles arranged in a ring

In most monocot stems, vascular bundles

are scattered throughout ground tissue.

(a) Structure of eudicot stem

Epidermis (dermal tissue):

Outer surface covered with cuticle.

May be perforated with stomata.

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Cortex (ground tissue)

Several layers of collenchyma cells

immediately below epidermis

Parenchyma cells below collenchyma

cells.

Vascular bundles

Arranged in a ring.

Xylem towards inner side, and phloem

towards outside. Xylem and phloem separated by

cambium.

Pith (ground tissue)

Made up of living parenchyma cells.

Secondary growth

Woody dicot plants undergo

secondary growth, an increase in girth of

stems.

Cambium divides, forming secondary

xylem (wood) on inside and secondary

phloem (inner bark) on outside.

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(b) Structure of monocotyledonous stem

Epidermis (dermal tissue):


May be perforated with stomata.

Does not have distinct area of cortex.

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Vascular bundles

Not arranged in a circle/ring but are

scattered throughout ground tissues.

Does not possess lateral meristems

(cambium) that give rise to secondary

growth.

Monocot does not produce wood.

(2) Tissue Organization of Roots In roots of typical gymnosperms and

eudicots, as well as some monocots, the

stele is a vascular cylinder consisting of a

lobed core of xylem with phloem between

lobes.

Stele of many monocot roots is a vascular

cylinder with a core of parenchyma

surrounded by a ring of alternating xylem

and phloem.

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(a) Internal structure of eudicot root

http://sps.k12.ar.us/massengale/plant_structure_bi1.htm

Epidermis

No cuticle.

Have root hairs. Cortex

Contains thin-walled parenchyma

cells.

Endodermis

One layer of cells. Each cell has a

special bandlike region, called a

Casparian strip. Pericycle

One layer of cells.

Surrounds vascular bundle.

Vascular cylinder

Xylem arranged like a star in

transverse section with several spokes.

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Phloem located in between spokes

of xylem.

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(b) Internal structure of monocot root

Epidermis

No cuticle.

Have root hairs.

Cortex

Contains thin-walled parenchyma

cells.

Endodermis

One layer of cells.

Pericycle

One layer of cells.

Surrounds vascular bundle.

Vascular cylinder

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Xylem does not arrange like a star in

transverse section.X AND P ARRANGED

ALTERNATELY

Phloem and xylem are in separate

alternating bundles arranged around

central pith.

Pith consists of parenchyma cells.

(3) Tissue Organization of Leaves Epidermis in leaves is interrupted by

stomata, which allow CO2 exchange

between air and photosynthetic cells in a

leaf.

Ground tissue in a leaf is sandwiched

between upper and lower epidermis.

Vascular tissue of each leaf is continuous

with vascular tissue of stem.

(a) Internal structure of eudicot leaf

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http://home.earthlink.net/~dayvdanls/plant_structure.html

Epidermis

On upper and lower surface.


Lower epidermis perforated by

stomata.

Palisade mesophyll.

Very little air spaces between

palisade cells.

Cells contain chloroplast performs

most of the photosynthesis.

Spongy mesophyll

Loosely arranged allows CO2 to

diffuse easily.

Cells contain fewer chloroplasts.

Vascular bundles

Xylem and phloem surrounded by

bundle sheath.

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Xylem and phloem in leaves form in

strands called veins.

Most dicots have netted venation.

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(b) Internal structure ofmonocotyledonous leaf

Epidermis

On upper and lower surface.


Lower epidermis perforated by

stomata.

Although most monocots have both

palisade and spongy mesophylls, some

monocots lack distinct regions of palisadeand spongy mesophylls.

Vascular bundles

Leaves of most monocots have

parallel venation.

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http://www.cbu.edu/~seisen/LeafStructure.htm
http://www.cbu.edu/~seisen/LeafStructure.htmhttp://www.cbu.edu/~seisen/LeafStructure.htm

hmm1414 chapter 5 part 2

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