cellular organisation in plant

7/29/2019 Cellular Organisation in Plant

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CELLULAR ORGANISATION

PLANT


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Least specialized plant

cells

Thin and somewhat

flexible cell walls

Living at maturity

Carry on most of the

plant's metabolic

functions

Generally have a largecentral vacuole

Most parenchyma cells

have the ability to

differentiate into other

cell types under specialconditions

During repair and

replacement of organs

after injury

PARENCHYMA CELLS


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The cells of parenchyma are large, thin-walled,

and usually have a large central vacuole. They

are often partially separated from each otherand are usually stuffed with plastids.

In areas not exposed to light, colorless plastids

predominate and food storage is the main

function. The cells of the white potato are

parenchyma cells.

Where light is present, e.g., in

leaves, chloroplasts predominate

and photosynthesis is the main function.
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/Chloroplasts.htmlhttp://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/P.htmlhttp://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/P.htmlhttp://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/Chloroplasts.html


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COLLENCHYMA CELLS

Thicker primary cells walls (usually with uneven thickness)

Living at maturity

Role in support of herbaceous plants

Example - the "strings" of celery


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Collenchyma cells have thick walls that

are especially thick at their corners.

These cells provide mechanical support

for the plant.

They are most often found in areas that

are growing rapidly and need to be

strengthened.

The petiole ("stalk") of leaves is usually

reinforced with collenchyma


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SCLERENCHYMA CELLS

Thick secondary cell walls

Dead at functional maturity

Cannot increase in length - occur in

parts of the plant which have quit

growing in length

Two types - fibers and schlerids

Fibers - long, slender cells with a

more or less regular secondary cell

wall

Example - hemp fibers for

making ropeSchlerids - shorter cells with an

irregular shape

Example - stone cells in pears

and hard nut and seed shells
http://www.uic.edu/classes/bios/bios100/labs/schlerenchyma.jpghttp://www.uic.edu/classes/bios/bios100/labs/schlerids.jpghttp://www.uic.edu/classes/bios/bios100/labs/schlerids.jpghttp://www.uic.edu/classes/bios/bios100/labs/schlerenchyma.jpg


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The walls of these cells are very thick and built up in

a uniform layer around the entire margin of the cell.

Often, the cell dies after its cell wall is fully formed.

Sclerenchyma cells are usually found associated with

other cells types and give them mechanical support.

Sclerenchyma is found in stems and also in leaf

veins.

Sclerenchyma also makes up the hard outer

covering of seeds and nuts.


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EPIDERMAL CELLS

Protective tissue covers

the surface of leaves and

the living cells of roots

and stems.Its cells are flattened with

their top and bottom

surfaces parallel.

The upper and

lower epidermis of the

leafare examples of

protective tissue


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TISSUES


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EPIDERMAL TISSUES

Generally a single layer of cellsThe "skin" of the plant

Primarily parenchyma cells

Main role is protection of the plant


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MERISTEM TISSUES

The main function of meristematic tissue is mitosis. The cellsare small, thin-walled, with no central vacuole and no

specialised features.

Meristematic tissue is located in

-the apical meristems at the growing points of roots and

stems.

-the secondary meristems (lateral buds) at the nodes of stems

(where branching occurs), and in some plants,

-a ring of meristematic tissue, called the cambium, that isfound within the mature stem.

The cells produced in the meristems soon become

differentiated into one or another of several types.


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Apical meristems

located at the tips of roots and shoots

supply cells for the plant to increase in length (grow up for

shoots and down for roots)

growth in this direction is known as primary growth

primary growth found in herbaceous and woody plants

primary growth found in monocots and dicots

Lateral meristemslocated near the periphery of the plant,

usually in a cylinder

supply cells for the plant to increase in girth

growth in this direction is known as secondary growth

found in all woody and some herbaceous plants

lateral meristems and secondary growth found only in

dicots


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GROUND TISSUES

Makes up the bulk of the plant

Predominately parenchyma,

but collenchyma and

schlerenchyma cells are found

Diverse functions including

photosynthesis, storage,

and support


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VASCULAR TISSUES

Involved in thetransport of water,

ions, minerals, and

food

Also has a secondary

role in support

Composed of xylem,

phloem, parenchyma,

schlerenchyma


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VASCULAR TISSUES

XYLEM

Thick secondary cell walls, oftendeposited unevenly in a coil-likepattern so that they may stretch

Dead at functionally maturity. Involved in conduct of water and

ions in the plant

Two types - tracheids and vessels

Tracheids - long, slender cellsconnected to each other bypits. Found in all vascular plants

Vessels - shorter, larger diametercells with completely perforatedcell wall ends. Found only inAngiosperms

PHOLOEM

Involved in transport of sucrose,other organic compounds, and someions

Living at functional maturity

Protoplast may lack organelles andnucleus, though

Endwalls connect to each other viasieve-plates

Two types of cells in the phloem -sieve-tube members and companioncells

Sieve-tube members - actual conduitfor sucrose transport

Companion cells - has a nucleus thatmay also control the sieve-tubeelement and may aid in sucroseloading
http://www.uic.edu/classes/bios/bios100/labs/trachei1.gifhttp://www.uic.edu/classes/bios/bios100/labs/vessel3.gifhttp://www.uic.edu/classes/bios/bios100/labs/vessel3.gifhttp://www.uic.edu/classes/bios/bios100/labs/trachei1.gif


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ORGAN

LEAF

FLOWER

STEM

ROOT

FRUIT


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SYSTEM

Root System

Underground (usually)

Anchor the plant in the soil

Absorb water and nutrients

Conduct water andnutrients

Food Storage

Shoot System

Above ground (usually)

Elevates the plant above thesoil

Many functions including: photosynthesis

reproduction & dispersal

food and water conduction

Note: the shoot system

includes the leaves and thereproductive organs,although these will becovered in more detailseparately


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The shoot system includes organs such

asleaves, buds, stems, flowers,

and fruits and usually it develops above

ground.The functions of the shoot

system includePhotosynthesis,

Reproduction,

Storage,

Transport,

Hormone production.

The root system includes roots as well

as modified stem structures such

as tubers andrhizomes and usually it

developsunderground.The functions of

the root system include

Anchorage,Absorption,

Storage,

Transport,

Production of certain hormones
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cellular organisation in plant

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