03-The Dead Parts of Cell

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THE DEAD PARTS OF CELL

3rd

meeting

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BASE COMPETENCE

THE STUDENTS UNDERSTAND STRUCTURE

AND FUNCTION OF THE PLANT CELL PARTS

INDICATOR

The students can identify many dead partsof cell from the picture of plant cell

The students can mention the function of

many dead parts of cell

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THE DEAD PARTS OF CELL

CONSIST OF:

VACUOLESERGASTIC SUBSTANCES

CELL WALL

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VACUOLES

• Occupy more than 90% of the volume of most matureplant cells

• Vacuoles surrounded by a membrane called tonoplast 

• It contains various organic and inorganic substances,

such as sugars, proteins, organic acids, phosphatides,tannins, flavonoid pigments and calcium oxalate

• Some substances in the vacuole may occur in solid formand may even be crystalline

• In meristematic cells possess many minute vacuoles

• In mature cells the vacuoles enlarge form large centralvacuole

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INITIATION OF VACUOLES

• From pre-existing vacuoles which multiply byfission, and after cell division each daughtercell receive a number of vacuoles

• By a de novo process, by attraction of waterto a certain localized region in the cytoplasmand the formation of membrane around it

•

From Golghi vesicles• By dilatation of ER cisternae or vesicles

derived from the ER

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THE FUNCTION OF VACUOLES

The function of vacuoles are regulation thewater and solute content of the cell, i.e. inosmoregulation, in storage and in digestion

Vacuoles contain digestive enzymes thatcapable of breaking down the cytoplasmiccomponent and metabolites

The hydrolytic activity of vacuoles resemblesthat of lissomes of animal cells

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ERGASTIC SUBSTANCES

Reserve and waste materials produced bythe cell are called ergastic substances 

The kind of ergastic substances, consistof:

1. Starch

2. Proteins

3. Oil, fats and waxes

4. Crystals and silica bodies

5. Tannins

6. Pigmentation7

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STARCH

a carbohydrate composed of long chainmolecules.

It appears in the form of grains

Starch grains are first form in chloroplasts

In the other case the starch is broken downand moves as sugar to storage tissueswhere it is resynthesized in amyloplast

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STARCH

• Starch grains commonlyshow layering around apoint termed hillum

•The hillum may becentrally situated or it maybe eccentric

•The layer termed lamella•In the starch grains of

cereals the number oflayer corresponds to thenumber of days duringwhich the grain growths

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PROTEINS

Amorphous protein is found in theoutermost endosperm layer, the aleuronlayer, of the caryopsis of cereals

Protein in the form of cuboidal crystalloid

is found in the cells of the peripheralparenchyma of potato tuber and in the fruitparenchyma of Capsicum  

Crystalline and amorphous protein arefound together in aleurone grains in theendosperms and embryos of many seeds

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Endosperm of seed

Zea mays 

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OIL, FATS AND WAXES

Oil and fats are important reserve materialsin plants

Most commonly present in seeds and fruits

Fats and oils may be produced by elaioplastor spherosomes

Lipid compounds others than fats, oils andwaxes

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CHRYSTALLS AND SILICA BODIES

Crystals ofvarious formsare often present

in plant cells The most

common crystalsare those ofcalcium oxalate,which appear indifferent forms

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TANNINS

They are a heterogeneous group of phenolderivates

In microscopically section they usually appears asgranular masses or bodies colored yellow, red or

brown Tannin can be found in leaves, periderm, vascular

tissue, unripe fruits, seed coats, and in tissues ofpathogenic growth

Tannins may be found in the vacuoles or in theform of droplet in the cytoplasm

Tannins are used commercially especially in theindustry of the tanning of animal skins to obtain

leather 14

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PIGMENTATION

The plant pigment usually found in theplastids and in the vacuoles

The green color is due to chlorophyll whichis found in the chloroplasts

Carotenoids is the yellow to red pigments,are also found but they are masked by thechlorophyll, they become noticeable whenthere is a little or no chlorophyll

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PIGMENTATION

Flavonoids, generally present in vacuoles ,water soluble, they found in flowers and fruits

Anthocyanins, give red, pink, lilac and bluecolor

In acid solution the color varies from orange-red to lilac

In basic solutions blue-colouredanthocyanins are form

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CELL WALL

The present of a wall in plant celldistinguishes them from animal cells

The cell wall growth when in contact with theprotoplast but out side of it

The cell wall consist of cellulose micro fibrils

The matrix of cell wall consist mainly ofpectin substances and hemicelluloses

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THE LAYER OF CELL WALL

Secondary wall

Primary wall

Middle lamella

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THE STRUCTURE OF CELL WALL

•The chain likecellulosemolecules are

regularly arrangein bundles.•Each bundle,which form anelementary fibril,consist of about40 molecules

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THE GROWTH OF CELL WALL

The growth of cell wall is a accomplished byintussusception or by apposition

According to Frey-Wyssling and Stecher (1951),suggested that the primary cell wall grows in a way thathas been termed mosaic growth . The fibrillar texture incertain wall areas become loosened as a result of turgorpressure and afterwards mended by deposition of newmicro fibrils in the gaps

Another theory termed multinet growth (Houwink and 

Ruelofsen, 1954). According to this theory the thickeningof the primary wall is brought about by the separation ofthe crossed microfibrils and alteration in their orientationin the earliest formed lamellae , from being almosttransverse to almost longitudinal

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NOKTAH (PIT)

Certain portion of the cell wall that remainthin even as the secondary wall is formed,called noktah or pit

The pits are apparently areas through whichsubstances pass from cell to cell

Generally each pit has a complementary pit

exactly opposite it in the wall of theneighboring cell

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SURFACE OF PITS

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