planttissuesandorgans

8/13/2019 planttissuesandorgans

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PLANT TISSUES AND

ORGANS


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Plant Cell Types (Support andStorage)

Parenchyma cellsare the mostnumerous type of cell in youngplants.

Parenchyma cells usually havethin walls and large centralvacuoles.

The photosynthetic cells inleaves are parenchyma cellsfilled with chloroplasts. Thesecells are called mesophyll cells.

Some parenchyma cells storelipids or starch (potatoes).

Other parenchyma cells serve

as packing material and play avital role in supporting the stemespecially in nonwoody stems.


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Collenchyma cellsaresupporting cells that laydown primary cell wallsthat are thick in thecorners.

Collenchyma cellsprovide support to leafpetioles, nonwoodystems, and growingorgans.

These cell typescompose the cortex andpith tissues of the rootand stems.


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Sclerenchyma cells

are the mainsupporting cells of aplant. They have a

thick secondary cellwall that contains asubstance calledlignin, a componentof wood. Therefore

they are found inwoody plants.


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There are two types ofsclerenchyma cells:

elongated fibers andvariously shapedsclereids.

Fibers often organizeinto bundles. (They are

common components ofxylem.)

Sclereids may packtogether very densely.(Sclereids are found infruits such as pears andthis give them theirgritty texture.) Theyare often referred to asstone cells.


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Plant Cell Types Vascular (Transport)

Xylem The xylem conducts water

from roots to above groundplant parts. It containsconducting cells calledtracheary elements.

Tracheids are evolutionarilymore ancient trachearyelements found ingymnosperms.

Both tracheary elements

and tracheidsundergoapoptosis(die) and do theirjobs as empty cells (onlythe cell walls remain).


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Tracheids and vessel elements: Waterconducting cells

Vessel elementsare thewater pipeline systemin flowering plants, alsoformed from dead cells.

Flowering plants haveboth tracheids and vesselelements.

Vessel elements aregenerally larger in

diameter than tracheidsand are laid down end-to-end to form hollowtubes.


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Sieve-tube members: Food onductingCells

Phloem

Cells of the phloem arealive when they do their

job, unlike those of thexylem.

The characteristic cell of thephloem is the sieve tubemember.

Cells of the phloem are

arranged end-to-end andform long sieve tubes,which transportcarbohydrates and othermaterials.


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The plasmodesmata in sievetube members enlarge as

they mature, resulting inend walls that look likesieves.

At functional maturity, asieve tube is filled withsieve tube sap (water,

sugars, and other solutes).

The sieve tube membershave adjacent companioncells.

Companion cellsretain alltheir organelles and mayregulate the performance ofand support the sieve tubemembers.


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Plant Tissues

A tissue is an organization of cells that work togetheras a functional unit.

Parenchyma cells make up parenchyma tissue,which is a simple tissue.

Xylem and phloem are complex tissues; they arecomposed of a number of different cell types.

Tissues are grouped into tissue systems that extendthroughout the body of the plant to form the variousorgans of the plant.

There are three plant tissue systems: vascular,dermal, and ground.


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Plant Tissues


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THREE TISSUE SYSTEMS IN

PLANTVascular Tissue The vascular tissue system

includes the xylem andphloem; it is the conductiveor plumbing system of theplant.

Thephloem transportscarbohydrates from sites of

production (sources such as

leaves) to sites of utilizationfor energy or where it isbeing stored (sinks)elsewhere in the plant.


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Vascular Tissue

Thexylem distributes water

and mineral ions taken upby the roots to the stem

and leaves.


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Dermal Tissue The dermal tissue system is

the outer covering of theplant.

All parts of the young plantbody are covered by anepidermis, which is a singlelayer or multiple layers of

cells. The epidermis contains

epidermal cells and otherspecialized cells such asguard cells.

The shoot epidermis

secretes a layer of wax-covered cutin, the cuticle,which helps retard waterloss from stems and leaves.


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Ground Tissue

The ground tissuesystem makes up therest of a plant andconsists primarily ofparenchyma tissue.

Ground tissue functionsprimarily in storage,support, photosynthesis,and the production ofdefensive and attractant

substances (oils andtoxins).


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Meristems generate cells for

new organs(Plant Stem Cells) In plants the growth of roots and stems is

indeterminate and is generated from specific regions ofactive cell division.

The localized regions of cell division in plants, calledmeristems, are forever embryonic. They have theability to produce new cells indefinitely.

The cells of meristematic tissues are analogous to thestems cells found in animals.

When a meristem cell divides, one daughter celldevelops into another meristem cell, and the otherdifferentiates into a more specialized cell. Themeristem gives rise to all plant cell and tissue types.


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There are two types of meristems:

Apical meristems give rise to the primary plant body,

which is the entire body of many plants. Lateral meristems give rise to the secondary plant

body. The stems and roots of some plants form wood and become

thick; it is the lateral meristems that give rise to the tissuesresponsible for this thickening.

Apical meristems are located at the tips of roots and stemsand in buds.

Shoot apical meristems supply the cells that extend stems andbranches.

Root apical meristems supply the cells that extend roots. Apical meristems are responsible for primary growth, which

leads to elongation and organ formation.


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Location of Meristematic Tissues


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Primary Growth of Root

Root CapThimble-likecovering which protects thedelicate apical meristem

Produced from cells derivedfrom the root apical

meristem

Secretes polysaccharideslime that lubricates the soil

Constantly sloughed off andreplaced


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Apical MeristemRegion ofrapid cell division of

undifferentiated cells Most cell division is directed

away from the root cap

Quiescent CenterPopulations of cells in apical

meristem which reproducemuch more slowly thanother meristematic cells

Resistant to radiation andchemical damage

Possibly a reserve which

can be called into action ifthe apical meristembecomes damaged


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The Zone of Cell Division- Primary Meristems

Three areas just above theapical meristem thatcontinue to divide for sometime

Protoderm- outermostprimary meristem -

produces cells which willbecome dermal tissue

Ground meristem-central primary meristem -produces cells which willbecome ground tissue

Procambium- innermostprimary meristem -produces cells which willbecome vascular tissue


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The Zone of ElongationCells elongate up to tentimes their original length

This growth pushes the rootfurther downward into the

soil

The Zone of MaturationRegion of the root wherecompletely functional cellsare found


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The leaf

vein

stalk

lamina

midrib
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The Leaf Cross-section

Midrib - extension of

the stalk into the leaf

Vein Branch-off fromthe midrib

Lamina - the blade

of the leaf

Stalk - attaches the

leaf to the stem

midrib

vein

lamina


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Waxy Cuticle & Epidermis The waxy cu t ic leis a thin layer

atop the epidermis.

Its function is to reduce the w ater

los tfrom the leaf.

In arid conditions this cuticle layer

can be quite thick.

Epidermis cel ls contain no

chloroplastsnot true of the

stoma cells.

They form layers on the upper and

lower surfaces of the leaf.

Their function is to prevent w ater

get t ing outand stopp ing

unwanted substances/organ isms

gett ing in.

cuticle

epidermis


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Palisade Mesophyll Layer

The pal isade mesoph yl l layer

is where most of the

photosynthes isoccurs in the

leaf.

The palisade cells contain a lotof chlorop laststo help them

perform this photosynthesis.

The palisade cells are closely

packed togetherto maximize

light absorption. In the leaf cross-section we can

see the palisade cells are only

found in the upper par t of the

leaf.


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Spongy Mesophyll Layer

The cells in the spongy mesophyl l

layerare not as closely packedas

the cells in the palisade mesophyll

layer. This creates air spacesinside

the leaf to enable gases to

move in and out.

There are not as many

chloroplastsin the spongy

mesophyll cells as there are inthe palisade mesophyll cells

but pho tosynthes is st i l l

occurs in the spongy

mesophy l l layer.


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Stomata There are holes found in leaves

called stoma

These holes allows gases to

di f fuse in and o ut of th e leaves

The stoma are formed by two

highly specia l ized epidermis

cel ls.

These cells, called guard c el ls, are

the only epidermis cells that contain

chloroplasts.

The stoma open and c lose

depending upon the requirements of

the plant.

It is through these stoma that water

leaves the leaf, the process that

powers t ranspirat ion.


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During photosynthesis

carbon dioxide diffuses inand oxygen diffuses out

When the stomata are

closed,often at night or in ahumid environment, this

stops gases diffusing in and

out of the leaf

Openstomata

Closestomata


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FLOWERS

A flower is were the reproductiveparts of the plant is held. Manyparts are inside of a flower. The

major parts are:

-Stamen -Stigma-Pistil -Filament-Ovary -Eggs-Pollen/Sperm -Anther


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Flowers

Flower Parts

Pistil

Female part of plant Containing:

Stigma

Style

Ovary


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The pistilis the term for all thefemale parts of a flower. Each pistilincludes an ovary(where the eggsare produced; the female

reproductive cells, a style(a tubeon top of the ovary), and a stigma(which the pollen sticks to during

fertilization).


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Stamen

Male reproductive part

Contains

Anther

Filament

The male parts of the flower

help fertilize the egg ofthe flower.

These parts are usually in aplace that can be easilymoved by insects andanimals.


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Sepals

Small green structureson the base of a flowerthat protect the flower

bud Petals

Highly colored part of theflower, may containperfume and/or nectarglands


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Parts of the Seed


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Testa -outer

covering of the seed;protects the embryo

Hilum - the scar onthe seedcoat; place

where the seed wasattached to theovary

Endosperm-the food

supply of the babyplant.

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