N. B. The cell membrane (plasma membrane) surrounds the cytoplasm of a cell and physically separates the intracellular components from the extra cellular environment, thereby serving a function similar to that



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Cell wall

A cell wall is a fairly rigid layer surrounds a cell and located external to the cell membrane, which provides the cell with structural support and protection. The cell wall also prevents overexpansion when water enters the cell. They are found in plants, bacteria, archaea, fungus, and algae.

Animals and most protists do not have cell walls.

In plants a cell wall plays mostly a mechanical support role rather than a role as a selective boundary

N.B. The cell membrane (plasma membrane) surrounds the cytoplasm of a cell and physically separates the intracellular components from the extra cellular environment, thereby serving a function similar to that of the skin

THE PLANT CELL WALL

In plants the cell wall is constructed from different materials dependent upon the species. During the differentiation of the cell, the original cell wall may undergo various chemical modification, which change its physical properties. In plants, the cell wall is constructed primarily from a carbohydrate polymer called cellulose

(in bacteria the cell wall is peptidoglycan. Fungi possess cell walls of chitin. Algae typically possess walls constructed of glycoproteins )

The principal modifications are the deposition of ; Further cellulose, Hemi-cellulose, Lignin, Cutin, Suberin, Mucilage, and Chitin

CELLULOSIC CELL WALL

Cellulose is the most abounded carbohydrates; it form 50% or more of all the carbon in plants.

The cellulose molecules is an insoluble un-branched polysaccharide consisting of about 10,000 glucose unites .

Color reaction of cellulose: i-Gives a blue color with chlor-zinc-iodine

ii-Dissolved in ammoniacal solution of copper oxide

iii-Give no color with phloroglucinol & HCL

HEMI – CELLULOSIC WALL

Group of polysaccharides that are more soluble than cellulose

They are vary in there chemical composition from one species of plant to another

Cellulose fibers are cement together by a matrix of Hemi-cellulose

Color reaction of Hemi-cellulose:

i-Blue color with iodine

ii-Insoluble in ammoniacal solution of copper oxide

LIGNIFIED CELL WALL

Composing as much as 35% of the dry weight of the secondary cell wall

Extremely complex polymer composed of complex molecule derived from certain amino acid (named phenyl-propanoid )

Strengthening material which formed the cell wall of tracheids, vessels, fibers and sclereids of vascular plants

Color reaction of lignin:

i-Phloroglucinol & HCL stains lignified walls pink or red ii-Acid aniline sulphate stains lignified walls bright yellow iii-Chlor-Zinc-iodine stains lignified walls yellow

SUBERIZED CELL WALL

Suberin is waterproof material, formed from highly polymerized fatty acids called suberic acid

Found in cork cells and endodermal cells

CUTINIZED CELLWALL

Cutin form a secondary deposit on primary cellulosic wall

Leaves are covered with a deposit of cutin which may show characteristic papillae

Color reaction for both suberin & cutin:

i-Yellow to brown color with Chlor-zinc-iodine

ii-Red color with Sudan III

iii-Strong solution of potash stains suberin and cutin yellow

vi-Dilute tincture of alkanna stains the walls red

MUCILAGINOUS CELL WALL

The cellulosic cell wall, in this case, is transformed into a gelatinous mass of carbohydrate in nature, namely gum or mucilage

Mucilaginous walls are found in the epidermal cells and center of the pith in the gum yielding species of some plants

Chemically, mucilage is a complex molecules of sugars e.g. glucose, arabinose and xylose

With ironic acid combined with metals

Color reaction: i- Yellow color or granular precipitation with lead subacetate

CHITINOUS CELL WALL

Chemically chitin is formed from a complex unites of N-acetyl gloucosamine joined by glycoside bonds

Chitin forms the major part of The cell wall of insects and many fungi, e.g. Ergot

Color reaction of chitin:

Chitin, when heated with 50% of KOH at 160-170 degree for one hour it is converted to Chitosan , which gives violet color when treated with 5% iodine solution then with 1% sulphuric acid

ERGASTIC CELL CONTENT

Plants and other photosynthetic organisms convert Carbon dioxide into billions of tons of organic molecules

Chemical energy stored in these molecules and fuels the metabolic reactions that produced either food-storage products or by-products of metabolism include: Carbohydrates, proteins, fixed oil and fats, alkaloids, glycosides, gums mucilage, volatile oil and resins, tannins, Calcium oxalate,

These by-products of the plant cell metabolism, being nonliving they are referred to as ergastic

STARCH

Starch is the typical form of carbohydrate used for energy storage in plants and formed in special cells called chloroplasts



It is a polymer of glucose unites occurs in two forms of different size: Amylose (un-branched glucose units) and Amylopectin (branched chain)

Starch occurs in almost all organs of plants; it is found most abundantly in roots and rhizomes

Starch gives blue to violet color with iodine solution

The common types found in powder drugs are: i-Maize starch ii-Potato starch iii-wheat starch iv-Rice starch

PROTEINS

Portions are the most common cell components, developed in the cell as macromolecules. It is composed of amino acids (nitrogenous organic substances)

Proteins are involved in all aspects of plant cell metabolism

It stored in the plant cell in the form of aleurone grains which well seen in oily seeds e.g. caster seed and linseed

Aleurone grain consists of a mass of protein surrounded by a thin membrane, embedded in the ground protein are a rounded bodies (globoids) and angular bodies (crystalloid)

All proteins are insoluble in organic solvents and precipitated by salts of heavy metals and by tannic acid

Proteins gives red color with Millon’s reagent, yellow color with picric acid and violet color with 20% NaOH and copper sulphate solution

FIXED OIL AND FATS

They are reserved food materials, occurs in the plant in the form of glyceryl (esters of fatty acids with glycerin)

They are greasy, non volatile, viscous liquid, semisolids or solids

Insoluble in water, soluble in ether, chloroform and petroleum ether

Hydrolyzed by aqueous alkalis, giving salt of fatty acid (soap) and glycerin

Fixed oil & fats stained red with tincture alkanna & sudan III also stained brown to black with 1% osomic acid

ALKALOIDS

Alkaloids are basic nitrogenous compounds, contain 1 or more nitrogen atoms usually in heterocyclic ring

Alkaloids usually have a physiological action on man or other animals e.g. nicotine in tobacco

Tests for alkaloids: i- With Mayer’s reagent (potassium mercuric iodide) gives cream PPT

ii- With Wagner’s reagent (iodine/KI) gives brown PPT iii- With Dragendorff’s reagent ( potassium bismuth iodide) gives reddish PPT iv-With solution of tannic acid gives dirty white PPT v-With saturated solution of picric acid gives yellow PPT

GLYCOSIDES

Glycoside is an organic compound of plant origin consisting of a sugar part linked to non-sugar which known as aglycone

Glycoside can be hydrolyzed either by acids or enzymes emulsin to give chemically different aglycone

These differences is the bases of the chemical classification of glycosides into:



  1. Phenolic glycosides found in uva ursi leaves 2-Antheracene glycosides found in senna leaves 3-Flavonoid glycosides found in buchu leaves 4-Cyanogenetic glycosides Found in bitter almond 5-Thio glycosides found in muster seeds 6-Cardiac glycosides found in digitalis leaves 7-Saponin glycosides found in quillaia bark

GUMS AND MUCILAGE

Gums and mucilage are polysaccharide complexes formed from sugar & uronic acid and frequently combined with metals

They are insoluble in alcohol but dissolve or swell in water e.g. gum tragacanth

Specific color reactions are: 1-Mucilage of senna & buchu leaves stained red with Ruthenium red reagent

2-Muciage of squill stained red with alkaline solution of corallin soda

VOLATILE OIL AND RESIN

Volatile oils occur as droplets inside the cell, they are soluble in alcohol but sparingly soluble in water

Resin may be found alone as irregular masses in the cell or may be associated with volatile

oils in the form of oleoresins or associated with gum to form gumresins

They stain slowly with dilute tincture of alkanna or with iodine solution

TANNINS

Tannins are widely distributed in the plants and occur in the cell sap, they are soluble in water and in alcohol



Tannins classified into two groups:

1-Hydeolysable tannins (Pyrogallol tannins) These group hydrolysable by acids or enzymes, give blue color with ferric chloride and present in clove, galls, bearberry leaves and pomegranate bark

2-Condensied tannins )(catechol tannins These group include all other tannins which resist hydrolysis with acid and enzymes, give green color with ferric chloride and present in tea, hamamelis leaves, cinnamon and cinchona bark

CALCIUM OXALATE

Very common cell content in the plant kingdom

It is formed in the cell as a result of the reaction of calcium salts absorbed from the soil and oxalic acid produced in the plant as a result of the metabolic process

Since the formed calcium oxalate is insoluble in water and in the mild acid cell-sap, it is deposited in crystalline form

Calcium oxalate crystals are insoluble in water, alcohol or acetic acid but dissolves in HCL with out effervescence (distinction from calcium carbonate). The crystals decomposed with 20% sulphuric acid with formation of needle-shaped crystals of calcium sulphate

FORMS OF CRYSTALS

Different forms of calcium oxalate afford a valuable aid in the differentiation of drug even in the powder forms i-Prisms crystals as in quillaia, cascara, and frangula barck ii-Cluster crystals as in senna leaf iii-Acicular or needle- shape as in Ipecacuanha root crystals iv-Sandy crystals as in cinchona barck v-Sphaero-crystal






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