SEM III Record

Annonaceae – Annona squamosa (Custurd apple)

Habit :  small sized tree  

Vegetative characters

Root system : tap root, branched

Stem : Aerial, erect , woody and branched.

Leaves : simple, alternate, petiolate, entire and reticulate venation.

Floral characters

Inflorescence : Solitary cyme in the axils of  leaves.

Flower : Bracteate, pedicellate, complete, bisexual, actinomorphic, trimerous and hypogynous.

Calyx :  Sepals 3, free / united at base, valvate aestivation.

Corolla :  petals 3, free, valvate aestivation.

The thalamus forms a large convex structure above the perianth, on which essential organs are spirally arranged.

Androecium :  Stamens numerous, arranged spirally on the thalamus, filament short and thick, adnate and extrose.

Gynoecium : Carpels many, spirally arranged on the receptacle, apocarpus, ovary superior, unilocular, one ovule in the ovary in parietal placentation.

Fruit :  Aggregate of berries.

Floral formulae :

Capparidaceae  – Cleome viscosa

Habit :  small herb

Vegetative characters

Root system : tap root, branched

Stem : Aerial, erect , herbacious and  branched

Leaves : simple, alternate, trifoliate, stipulate, petiolate,  and reticulate venation.

Floral characters

Inflorescence : Solitary cyme in the axils of  leaves.

Flower : Bracteate, pedicellate, complete, bisexual, actinomorphic, tetramerous and hypogynous.

Calyx :  Sepals 4, free (polysepalous), valvate aestivation.

Corolla :  petals 4, free (polypetalous), valvate aestivation.

Androecium :  Stamens numerous, anthers bithecous, basifixed and introrse.

Gynoecium : Carpels 2, syncarpus, ovary superior, a stalk is elongated between androecium and gynoecium in the form of Gynophore, unilocular, many  ovules in the ovary arranged in parietal placentation.

Fruit :  Capsule

Rutaceae – Citrus aurantium  (lemon)

Habit :  small sized tree  

Vegetative characters

Root system : tap root, branched

Stem : Aerial, erect , woody and branched.

Leaves :  unipinnately compound, alternate, petiole modified into wing, entire,  gland dotted and reticulate venation.

Floral characters

Inflorescence : Solitary cyme in the axils of  leaves.

Flower : Bracteate, pedicellate, complete, bisexual, actinomorphic, pentamerous and hypogynous. A nectar secreting disc is present at the base of the ovary.

Calyx :  Sepals 5,  united , valvate/ imbricate aestivation.

Corolla :  petals 5, free, valvate / imbricate aestivation.

Androecium :  Stamens numerous, united to form several bundles ( polydelphous condition). Anthers bithecous, basifixed and introrse.

Gynoecium :  It is raised on a nectar secreting disc. It is pentacarpous, syncarpous and the ovary is superior,  multilocular, 1 - many  ovules in the ovary in axile placentation.

Fruit :  Hesperidium

Floral formulae :

Fabaceae – Tephrosia purpurea 

Habit :  Annual herb  

Vegetative characters

Root system : tap root, branched and bears  root  nodules.

Stem :  Aerial, erect , herbacious and branched.

Leaves :  alternate, petiolate, pinnately compound,  leaf base pulvinous  and reticulate venation.

Floral characters

Inflorescence : Simple raceme.

Flower : Bracteate, pedicellate, complete, bisexual, zygomorphic, pentamerous and hypogynous/ perigynous.

Calyx :  Sepals 5, gamosepalous, valvate aestivation.

Corolla :  petals 5, free, Papilionaceous. The posterior odd petal is larger in size known as standard / vexillum, which encloses the wings/ alea. This wing petals in turn encloses the anterior petals keel/ carina, in turn which encloses essential organs. This type of aestivation is known as descending imbricate aestivation.

Androecium :  Stamens 10, arranged in 2 bundles of (9) +1, diadelphous condition, anthers dithecous,  and introrse.

Gynoecium : monocarpellary,  ovary superior, unilocular, many ovules  marginal placentation.

Fruit :  Legume/ pod  splitting along dorsal and ventral sutures.

Floral formulae : 

Caesalpinaceae – Caesalpina pulcherrima 

Habit :  mall sized tree / shrub 

Vegetative characters

Root system : tap root, branched.

Stem :  Aerial, erect , woody  and branched.

Leaves :  alternate, petiolate, bipinnately compound,  leaf base pulvinous  and reticulate venation.

Floral characters

Inflorescence : Simple raceme ( Corymb)

Flower : Bracteate, pedicellate, complete, bisexual, zygomorphic, pentamerous and hypogynous.

Calyx :  Sepals 5, polysepalous, valvate aestivation.

Corolla :  petals 5, free, Polypetalous. The posterior odd petal is smaller in size. The aestivation is known as ascending imbricate aestivation.

Androecium :  Stamens 10, arranged in 2 bundles of 5 +5,  anthers dithecous,  and introrse.

Gynoecium : monocarpellary,  ovary superior, unilocular, many ovules  marginal placentation.

Fruit :  Legume/ pod  splitting along dorsal and ventral sutures.

Floral formulae :

Mimosoideae – Acacia nilotica 

Habit :  Perennial tree. 

Vegetative characters

Root system : tap root, branched.

Stem :  Aerial, erect , hard woody  and branched.

Leaves :  alternate, petiolate, bipinnately compound,  leaf base pulvinous, stipules modified into thorns  and reticulate venation.

Floral characters

Inflorescence : Flowers are grouped in globose heads ( racemose).

Flower : Bracteate, sessile, complete, bisexual, actinomorphic, pentamerous and hypogynous/ perigynous.

Calyx :  Sepals 5, gamosepalous, valvate aestivation.

Corolla :  petals 5, united, gamopetalous, valvate aestivation.

Androecium :  Stamens numerous,  free, long, exserted filaments,  anthers dithecous,  and introrse.

Gynoecium : monocarpellary,  ovary superior, unilocular, many ovules  marginal placentation.

Fruit :  Lomentum.

Cucurbitaceae – Coccinia cordifolia 

Habit :  annual climber  

Vegetative characters

Root system : tap root, branched.

Stem :  Aerial, weak , herbaceous,  branched, hairy and pentangular.

Leaves :  Simple leaves, alternate, petiolate, palmately lobed  and reticulate venation.

Floral characters

Inflorescence :  Axillary solitary. Plants are dioecious, bearing male and female flowers on the same twig.

Male Flower :  Bracteate, pedicellate, in complete, unisexual, actinomorphic, pentamerous and epigynous.	Female Flower :  Bracteate, pedicellate, in complete, unisexual, actinomorphic, pentamerous and epigynous.
Calyx :  Sepals 5, gamosepalous, valvate aestivation.	Calyx :  Sepals 5, gamosepalous, valvate aestivation.
Corolla :  petals 5, gamopetalous, united to form a tube valvate aestivation.	Corolla :  petals 5, gamopetalous, united to form a tube valvate aestivation.
Androecium :  Stamens 5, arranged in 3 bundles of (2) + (2) +1, in which the filaments and anthers are fused to form Synandrous condition.	Androecium :  Absent
Gynoecium :  Absent	Gynoecium :  tricarpellary, unilocular, ovary inferior, parietal placentation.

Fruit :  Fleshy fruit  Pepo

Floral formulae : 

Apiaceae – Coriandrum sativum 

Habit :  annual herb  

Vegetative characters

Root system : tap root, branched.

Stem :  Aerial, erect , herbaceous with hollow internodes, emits aromatic smell due to presence of essential oils.

Leaves :  alternate, petiolate, decompound,  sheathing leaf base  and reticulate venation.

Floral characters

Inflorescence : Simple umbel.

Flower : Bracteate, pedicellate, complete, bisexual, actinomorphic, pentamerous and epigynous.

Calyx :  Sepals 5, free, polysepalous, valvate aestivation.

Corolla :  petals 5, free, alternating with sepals. Petals are inflexed in buds. Valvate/ imbricate aestivation.

Androecium :  Stamens 5, alternating with petals,  anthers dithecous,  and introrse.

Gynoecium : Bicarpellary,  syncarpous with bilocular inferior ovary. Each carpel contains a single pendulous ovule on axile  placentation. A disc is present on the ovary called stylopodium, on which 2 styles arises.

Fruit :  Cremocarp splitting  into 2 one seeded mericarps attached to a stalk called Corphophore.

Floral formulae :

                                            Asclepiadaceae – Calotropis gigantia 

Habit :  perennial  shrub  

Vegetative characters

Root system : tap root, branched and bears  root stock.

Stem :  Aerial, erect , branched and woody  in lower portions, all parts of plant contains latex.

Leaves :  simple leaves, sessile, opposite decussate, entire margin, both the surfaces of leaves have waxy coating,   and reticulate venation.

Floral characters

Inflorescence :  cymose inflorescence ( dichasial cyme ).

Flower : Bracteate, pedicellate, complete, bisexual, actinomorphic, pentamerous and hypogynous

Calyx :  Sepals 5, free, polysepalous, quincuncial aestivation.

Corolla :  petals 5, gamopetalous, outgrowths of the petal bases  unites to form a crown like structure known as corollary corona, which attracts the insects, twisted aestivation.

Androecium :  Stamens 5, epipetalous,anthers are attached to the angles of pentangular disc the Gynostegium, each anther have group of pollen the pollinium. Two pollinia, one each from adjacent anthers are united together by a thread like retinacula, 2 retinacula are attached to a glandular Corpusculum. The pollinia with retinacula and corpusculum together are known as Translator.

Gynoecium : Bicarpellary,  carpels are free below, styles are united at apices, stigma forms a pentangular disc Gynostegium,  ovary superior, ovary of each carpel is unilocular, many ovules in each locule are  in  marginal placentation.

Fruit :  the fruit is a pair of follicles. Sees with tufts of silky hairs called coma.

Floral formulae :

Lamiaceae – Ocimum  tenuiflorum ( syn. Ocimum sanctum ) 

Habit :  annual herb  

Vegetative characters

Root system : tap root, branched .

Stem :  Aerial, erect , herbaceous, quadrangular, aromatic and branched.

Leaves :  simple,  petiolate,  opposite decussate, covered with epidermal glandular hairs secreting volatile oils  and reticulate venation.

Floral characters

Inflorescence : Special inflorescence (thyrsus).

Flower : Bracteate, pedicellate, complete, bisexual, zygomorphic, pentamerous and hypogynous.

Calyx :  Sepals 5,  gamosepalous,  bilipped, 1+4 arrangement  and valvate aestivation.

Corolla :  petals 5, gamopetalous, 2 – lipped (bilipped), the posterior upperlip is 4 fid and  the anterior lower lip is 1 fid and longer than the upper lip. The aestivation is  valvate aestivation.

Androecium :  Stamens 4, epipetalous, didynamous, filaments free, anthers dithecous,  and introrse.

Gynoecium : bicarpellary, syncarpous ovary superior, bilocular but becomes quadrilocular due to formation of false septum. 1 ovule  in each locule  axile placentation. Style gynobasic, stigma bifid, hypogynous.

Fruit : .Schizocarp, breaking into 4- nutlets / achenes.

Floral formulae :

Amaranthaceae – Achyranthes aspera 

Habit :  perennial herb  

Vegetative characters

Root system : tap root, branched.

Stem :  Aerial, erect , herbacious and branched.

Leaves :  simple leaves, opposite decussate, entire  and reticulate venation.

Floral characters

Inflorescence : Simple spike.

Flower : Bracteate, sessile, complete, bisexual, actinomorphic, pentamerous and hypogynous.

Perianth :   tepals 5, free, scaly,  membranous and colourless imbricate aestivation.

Androecium :  Stamens 5, opposite to tepals, monadelphous, equal number of staminodes alternating with the anthers. Stamiondes fimbriated. anthers dithecous,  and introrse.

Gynoecium : bicarpellary, syncarpous, ovary superior, unilocular with one ovule in basal placentation.

Fruit :  usually a utricle..

Floral formulae :

                                       Euphorbiaceae – Croton bonplandianum 

Habit :  annual herb  

Vegetative characters

Root system : tap root, branched.

Stem :  Aerial, erect , herbacious and branched.

Leaves :  simple leaves, alternate, but whorled below the inflorescence,  and reticulate venation.

Floral characters

Inflorescence : Simple raceme. Base of the inflorescence contains female flowers, male flowers are present at the apex.

Male flower : present at the apex of inflorescence, Bracteate, pedicellate, incomplete, unisexual, actinomorphic, pentamerous and hypogynous.	Female flower : present at the base of inflorescence, Bracteate, pedicellate, incomplete, unisexual, actinomorphic, pentamerous and hypogynous.
Perianth  :  arranges in 2 whorls of 5+5, free,  valvate aestivation.	Perianth  :  arranged  in 1 whorl of 5, free,  valvate aestivation.
Androecium :  Stamens 15, arranged spirally  anthers dithecous,  and introrse.	Androecium :  absent .
Gynoecium :  absent	Gynoecium :  tricarpellary, syncarpous, trilocular, superior ovary, one pendulous ovary in each locule with axile placentation. The styles are three, each style is bifid.

Fruit :  3 chambered  schizocarpic capsule .

                                                    Orchidaceae – Vanda roxburghii

Habit :  Epiphytic  herb  

Vegetative characters

Root system :  Adventitious roots, 2 types, attaching roots and velamen roots.

Stem :  Aerial, erect , herbacious and monopodial.

Leaves :  simple leaves,  alternate,  entire  and  parallel venation.

Floral characters

Inflorescence : Simple spike, look like a raceme.

Flower : Bracteate, pedicellate, complete, bisexual, zygomorphic, trimerous and epigynous.

Perianth :   tepals  in 2 whorls of 3+3, free, fleshy. Outer whorl green and inner whorl is petaloid, of these posterior tepal is highly modified into labellum. The labellum shifts from anterior to posterior side by resupination.scaly,  membranous and colourless imbricate aestivation.

Androecium :  Stamen 1, monoandrous, present at the tip of the column, present at anterior side  anthers dithecous,  and introrse. pollen grains are aggregated into pollinia. The pollinia connected to a sticky thread called Caudicle. Caudicles end in a disc shaped Viscidin.

Gynoecium : tricarpellary, syncarpous, ovary inferior, unilocular with many ovules on 3 parietal placentae. The column has 2 fertile stigmas and a specialised sterile stigma modified as rostellum.

Fruit :  A capsule.

Floral formulae :

 

                                Poaceae – Oryza sativa

Habit :  annual herb  

Vegetative characters

Root system : adventitious root, branched.

Stem :  Aerial, erect , herbacious and .

Leaves :  simple leaves, alternate with sheathing leafbase, entire  and parallel venation.

Floral characters

Inflorescence :  Panicle of  spikelets. Each spikelet consists of very short axis (rachilla) which bears 2 rows of bracts. The lowest row of bracts known as sterile glumes, followed by  fertile glume lemma ends with stiff awn. A membranous structure present between fertile glume and rachilla known as Palea. Lemma and palea bears one flower.

Flower : small, inconspicuous,  complete, bisexual, zygomorphic, trimerous and hypogynous.

Perianth :   highly modified , reduced into 2 hyaline structures lodicules.

Androecium :  Stamens 6, arranged in 2 whorls of 3+3, alternating with lodicules. Filaments are free and delicate, versatile, anthers dithecous,  and introrse.

Gynoecium : monocarpellary, syncarpous, ovary superior, unilocular with one ovule in basal placentation. Two styles with feathery stigmas

Fruit :  one seeded caryopsis.

Floral formulae :

TULASI

Scientific name: Ocimum tenuiflorum L. (Ocimum sanctum L.) 

Family: Lamiaceae

Common names:Sacredbasil

Useful parts:fresh and dried leaves 

Morphological Characters: Aromatic herbs; stems and branches woody, pubescent, leaves simple, opposite, 

aromatic, ovate, flowers small purplish in terminal thyrses. 

• Medicinal Value: Cough, Cold, earache, Fever, bronchitis, malaria, diarrhea, dysentery, skin disease, arthritis, 

eye diseases, insect bites etc. 

• Active Principles: Contain 0.7% volatile oil comprising about 71% eugenol and 20% methyl eugenol. 

PIPPALU (Piper longum)

Scientific name: Piper longum

Family: Piperaceae

Vernacular name: Piplamul,Pippali, Pippallu

Useful parts: Root and Fruits are generally used.

MORPHOLOGY: 

• Leaves: They are dark in colour, ovate or heart shaped, they are about 2 to 3 inches in length.

• Flowers: The plant bears flowers during rainy season, male and female flowers both are borne on 

different plants.

• Fruits: Fruits are ovoid in shape , orange and yellowish in colour, and they grow in early winters , 

drupes are about 1 inch in diameter. 

• Spikes: Once when ripened, spikes turn red in colour.

• Root: Perrineal woody root.

CHEMICAL CONSTITUENTS
• Volatile Oil
• Resin
• Piperin
• Piperlongumine
• Piperlatin
• Brachyamide A
• Brachyamide B
• Sterols
Medicinal properties and uses:
1. Both piplamul (root & stem bases) and fruits are used for diseases of respiratory tract like
cough, bronchitis, asthama, cold etc.
2. It is also used as analgestic when applied locally for muscular pain and inflammation
3. Internally it is used as a sedative, carminative and general tonic

KARAKAYA

Scientific name: Terminalia chebula Retz.

Family: Combretaceae 

Common names:karaka,Hirda,Harda

Useful parts: dried mature fruits,small fruits,

Morphological Characters: Moderate sized tree; bark smooth and pale yellow when young; corky and 

grayish black when aged; peeling in flakes. Leaves simple, opposite, broadly oblong; flowers small, pale 

yellow in terminal and axillary spikes. Fruits ovoid, greenish to brownish, smooth when young; brownish 

black, rough and ribbed or angled when dry.

• Medicinal Uses: The fruit is the one of the ingredient in the a well known Ayurveda drug “Triphala” . Helps 

in indigestion, weight loss, urinary disorders, blood purifier, cardiac attacks, nervous disorders, general 

debility and cough etc.

• Active Principles: Fruit contains 20-50 % of Hydrolysable tannins : phenolic carboxylic acid like gallic acid, 

ellagic acid, and chebulic acid. 

Kalabanda (Aloe vera)

Scientific name: Aloe vera (L.) Burm.f.

Family: Xanthorrhoeaceae (Liliaceae; Aloaceae) 

Common names:Musabhar,musambaram

Useful parts: leaves 

Morphological Characters: Main stem reduced, underground, roots fibrous; leaves cauline, rosette, fleshy, 

thick, margins spiny, flowers brick red to pale yellow in terminal racemes.

• Medicinal Uses: Skin diseases itching, inflammation, diabetes burnings, bowel diseases, fever etc., and 

cosmetics.

• Active Principles: Amino acids, anthroquinones, phenolic compounds, Saponins, salicylic acids, and sterols

Turmeric

Scientific name: Curcuma longa 

Family: Zingiberacae

Vernacular name: Haldi, Pasupu, Halada

 Useful parts: Dried rhizome 

Chemical properties:

Turmeric contain yellow colouring matter called Curcumin of which three analogs have been detected they are 

Curcumin I( diferuloyl methane)-

Cucumin II( Caffeoyl feruloyl methane), 

Curcumin III(dicaffeoyl methane)

Medicinal properties:

1. Turmeric is used as a colouring agent and condimentincurrypowders.It has also been used to stimulate biliary secretion and treat gall stones.

2. Curcuma rhizomes are extensively used in ayurvedic,unani amd chinese traditional 

medicines as a stmachic,uretic andanodyne for biliary calculus and menstrual pains

3. It iis a common house-hold remedyor cough and cols externally,it is used uin form of a cream to improve complexion.

4. Anti-inflammatory activity of curcumirin well is established

ASHWAGANDHA

Scientific name: Withania somnifera (L.) Dunal

Family: Solanaceae 

Common names: Ashwagandha; Indian ginseng, Winter cherry

Morphological Characters: Under shrubs, roots tuberous, stems and branches grayish pubescent, leaves 

simple , opposite, ovate, flowers small, greenish in axillary cymes or clusters. Fruits berries, enclosed with 

persistent calyx, bright orange when ripe.

• Ethnomedicinal uses: Ashwagandha is taken for strength, rejuvenation, digestion, improve sexual desires, 

insomnia, nervous disorders-arthritis, rheumatism, cough, ulcers, diabetes, leprosy, intestinal infections, 

bronchitis, asthma, impotence and a suppressant in HIV/AIDS patients etc.

AMLA
Scientific name: Phyllanthus emblica L.(Emblica officinalis Gaertn.)
Family: Phyllanthaceae (Euphorbiaceae)
Common names: Amla; Usiri; Indian goose berry
Morphological characters: small to medium sized tree; bark grayish feeling in flakes; leaves simple closely set along
the branchlets and appears like compound leaves; flowers small, pale yellow, clusters in leaf axils, fruits berry ,
yellowish green, globose, grooved.
Ethnomedicinal uses: The fruit is the one of the ingredient in the well known ayurvedic drug “Triphala”. Used to
revitalizing potency and the digestive system, rejuvenating longevity, treat constipation , reduce fever, purify the
blood, reduce cough, alleviate asthma, strengthen the heart, benefit the eyes, stimulate hair growth, diabetes and
cancer, weight loss etc.. Raw fruits are rich in vitamin “C” eaten and used for making pickle.

SARPAGANDHA
Scientific name: Rauvolfia serpentina (L.) Benth. ex Kurz
Family: Apocynaceae (Apocynaceae includes Asclepiadaceae)
Common names: Sarpagandha; Snake root
Morphological Characters: Under shrubs; roots tuberous, stems and branches with milky latex; leaves
simple, whorled, oblong lanceolate; flowers white with red calyx on terminal umbels; fruits berries two
lobed, ripen bluish.
• Ethnomedicinal Uses: High Blood Pressure: This herb is considered to be effective in lowering blood
pressure and fever.
• It also helps in stimulating uterine contractions at the time of delivery.
• Insanity: Popularly known as pagal-ki-dawa (Medicine for the mentally upset),
• Insomnia: This herb has sedative properties, so it is very useful in relieving insomnia.

Centella asiatica
Family: Apiaceae
Common Name: Asiatic Pennywort Saraswathi Aaku

• Morphological  Characters : Prostrate, faintly aromatic, creeper herb

Brahmi
Scientific name: Bacopa monnieri (L.) Wettst.
Family: Plantaginaceae (Scrophulariaceae)
Common names: Brahmi, Saraswathi
Morphological characters: Prostrate herbs, growing near marshy habitats, stems prostrate, succulent, rooting
at nodes, leaves simple, opposite, fleshy; flowers violet in leaf axils. Fruit capsule.
Ethnomedicinal uses: Brahmi is useful for improving mental clarity, confidence and memory recall.
• Brahmi is also used for the treatment of epilepsy, insomnia, asthma and rheumatism, arthritis, hair loss,
fever, constipation etc.
• Studies have also shown Brahmi to possess anticancer activity.

Bacteria

Bacteria are small, microscopic, unicellular organisms that exhibit a great diversity in habitat, morphology, nutrition, metabolism and reproduction. The term bacterium was first used by Ehrenberg which comes from a Greek word bacterion which means little rod or stick. The study of bacteria is known as bacteriology.

A Dutch man, Anton van Leeuwenhoek, was the first to discover the bacteria in 1675, but he thought them to be animalcules. For about two centuries, thereafter, the bacteria did not receive much scientific attention. Later Louis Pasteur in 1864 and Robert Koch in 1876 reported that these microorganisms could cause disease.

Louis Pasteur declared that all putrefaction (decomposition of organic substances) is due to action of microorganisms. He also established that fermentation is also caused by microorganisms and developed the method of preservation of liquids (milk, wine etc) called the pasteurisation. Heating of liquids upto less than 100^o C temperature to kill the microorganisms is called the pasteurisation.

Robert Koch showed that anthrax disease is transmitted through spores. Koch proposed that all bacterial disease must follow some set conditions: i) that the organisms must be present in the lesions of the disease, ii) that it must be possible to grow these organisms in pure cultures outside the host body, iii) that the culture should be able to produce the typical symptoms of the disease, iv) that the same organism must invariably be present in the disease caused by the inoculum.

General Characters of Bacteria:

1. They are omnipresent, found in all possible habitats, which can support life.

2. They are unicellular and morphologically least complex of all living organisms.

3. Cell is prokaryotic – a well organised nucleus is absent.  Membrane bound cell organelles like endoplasmic reticulum, Golgi bodies, Mitochondria etc are absent.

4. Most of the bacteria have heterotrophic mode of nutrition i.e., they obtain their food directly from external source. They may live as saphrophytes, parasities or symbionts. Some bacteria are autotrophic, as they possess bacteriochlorophyll, the photosynthetic pigment.

5. Binary fission is the most common method of reproduction.

6. True sexual reproduction is absent. However, recombination of genetic material occurs by conjugation, transformation and transduction.

Occurrence and Distribution:

Bacteria are among the most numerous of all living organisms being present in almost very conceivable environment. There are about 2,000 known species.

Bacteria are ubiquitous organisms and occur in all natural habitats. They occur in abundance in both fresh waters of rivers, ponds, reservoirs and lakes and alo in saline waters of Oceans and Seas. They are found in all soil and above the earth.

Some thrive well in hot water springs (75^oC) and can also survive below freezing point in the Atlantic ice. Similarly, their tolerance to hydrogen concentration ranges from pH near to 0 to pH 11.

Many species of bacteria are free-living, and others are symbiotic, parasitic or saphrophytic. They are found within and upon the bodies of plants and animals. They flourish well on our skin, mouth and intestine.

The features which contribute to their universal distribution are:

1. Extremely simple structure

2. Small size, cell division occur rapidly.

3. Resistance of vegetative cells to adverse environmental factors

4. Formation of highly resistant endospores

5. Diversity of their modes of nutrition.

Size:

Bacteria are very small microscopic, unicellular organisms. The size of bacteria varies from 0.2µ (1 micron = 0.0001mm) in diameter and less than 2-10 microns in length.

Thiomargarita namibienxsis and Epulopischum fishelsoni are upto ½ a millimetre long and are visible to the unaided eye.

Forms or Shapes of Bacteria:

The bacteria vary in their shape which is usually constant for each species and helps in their identification.

I. Coccus Bacteria

Spherical or ellipsoidal bacteria are called cocci bacteria. Almost all coccal forms lack flagella (non-motile). The spherical cells may occur singly but often tend to stick together and occur in pairs, chains etc. On the basis of arrangement of cells in a cluster, the cocci are classified into the following six groups:

1. Monococcus: single spherical shaped cells. E.g., Micrococcus luteus

2. Diplococcus: a pair of spherical shaped cells (result when cocci divide and remain together to form pairs) e.g., Neisseria, Diplococcus pneumonia

3. Streptococcus: Cocci cells occur in long chains. Result when cells adhere after repeated divisions in one plane. E.g., Streptococcus lactis (milk bacterium).

4. Staphylococcus: Irregular group of many spherical bacteria arranged in bunches(grapes like). Result when cocci divide in radom planes. E.g., Staphylococcus albus (causes abscesses, wound infections).

5. Sarcinia: cuboidal arrangement of eight cocci cells. Results when cocci cells divide regularly in three planes. E.g., Sarcinae lutea

II. Bacillus Bacteria

This is the probably the most common form of bacteria. These are rod-shaped or hyhens (-) like bacteria are called the bacillus bacteria. Some are motile and some non-motile.

Based on the number of cells and their arrangement bacillus are classified into following :

1. Monobacillus: single rod shaped cells. E.g., Pseudomonas, Clostridium.

2. Diplobacillus:a pair of rod shaped cells. E.g. Corynebacterium diphtheria, Yersinia pestis (plague bacterium)

3. Streptobacillus: chain of bacillus bacteria appearing like straws. E.g., Bacillus tuberculosis, Lactobacillus.

III. Helical Bacteria : the helical forms are of two types – vibrioid and spirillum..

1. Vibrioid: rod shaped bacteria are slightly curved and look like a comma. A vibrio bears a single flagellum at its tip. E.g., Vibrio cholearae

2. Spirillum: the bacteria having the body twisted spirally or into helix. The spirilla forms usually bear two or more flagella at one or both poles. They occur as single cells or in short chains but do not form colonies. E.g., Spirillum volutans.

IV. Filamentous Bacteria:

Some bacteria are filamentous and branched. E.g., Beggiatoa, Thiothrix.

V. Pleomorphic Bacteria:

Some bacteria are able to change shape and size temporarily in response to changes in the environment. For example, Acetobacter, a group of vinegar bacteria occus as small rods, long rods, ellipsoids or a chain of small rods. Such bacteria are called pleomorphic.

Staining of Bacteria:       

Physician Christian Gram, in 1884 devised a differential staining procedure for identification of bacteria called the Gram staining.

A thin smear of bacterial cell is prepared on a glass slide. To the smear, Crystal Violet solution is applied for 30 seconds – step I. The slide is then rinsed in clean water. Then an Iodine solution is applied for 30 seconds – step II. This, inturn, is rinsed off with clean water.

Examination of the smear with the microscope reveals that all the bacteria have taken the purple colour. The next step in the staining procedure is to apply 95% Ethyl alcohol to the smear until the all the except the thickest layers of the smear have ceased to give off the dye.

Examination of the smear at this stage reveals that many of the bacteria still retain the original purple colour, whereas from others it has been washed off.

The bacteria that retain the original purple stain are called gram-positive bacteria. Those which loss the purple colour and become decolourised are called gram-negative bacteria.

The decolourised gram-negative bacteria are nearly invisible. To study their details counter stains like eosine or safranine are added to the smear.

Structure of Bacterial Cell

Bacteria are unicellular organisms. The ultra structure of bacteria is a typical example for the prokaryotic cell that lacks membrane bound nucleus and other cell organelles.

Like other living plant cells, the bacterial cell comprises of a cell wall and protoplast. Structurally, bacterial cell consists of following components:

1. Structures external to cell wall – flagella, fimbriae, pilli, capsule or slime layer

2. The cell Wall

3. Structures internal to cell wall – cell membrane, mesosomes, ribosomes, nucleoid

4. Special cell structures – storage granules, gas vacuoles, carboxysomes, magnetosomes, endospore

Structures External to Cell Wall

Slime layer:

The gelatinous layer present on the outer surface of the cell wall. It is secreted by the cell protoplast. The slime diffuses through the cell wall and deposits in form of a thin, extracellular, viscous layer external to the cell wall.

It is usually composed of polysaccharides or polypeptides or both. When it is made up of only polysaccharides, which forms a viscous layer and loosely attached to the cell wall, it is called Slime layer.

Under certain conditions of growth, the slime accumulates in form of a well-defined, thick , persistent  layer, firmly attached to the cell wall. It is called the sheath or capsule. E.g., Streptococcus pneumonia, Bacillus anthracis.

The sheath protects the bacteria against dessication and antibodies. The encapsulated pathogenic bacteria can with stand phagocytosis.

Some bacteria produce diffuse slime which spreads into the environment and encloses bacterial colonies. This is known as loose slime.

The bacterial cell with a capsule normally does not bear flagella.

Functions:

Provides protection under unfavourable conditions.

Function in the storage of food substances, and as storage site for the disposal of waste material.

Helps bacterium in attaching to various surfaces in order to survive in its natural environment such as streams, roots, teeth and tissues.

Flagella:

Mobility is universal among the spirillum bacteria, common among the bacillus bacteria but lacking or rare in coccal forms.

The motile bacteria have small whip or hair-like appendages called the flagella. They are about 120A⁰ – 150A⁰ thick and 4 0r 5 µ long. They are cytoplasmic in nature. Each flagellum arises within the cytoplasmic membrane and passes out through the cell wall.

Structure

Bacterial flagellum is composed of three parts – basal body, the hook and the filament.

The outermost, long, hair-like, cylindrical, hollow structure of the flagellum is called filament or shaft. It has a constant diameter of 120-200A⁰. It is made up of globular proteins, the flagellin.

The flagellum is composed of several chains of flagellin subunits forming a hollow cylindrical thread. Unlike the Eukaryotes, the filaments are not covered by a membrane or sheath.

Hook is short, curved, thicker segment of the flagellum. It is made up of a single type of protein. It connect the basal bodies to the filament of the flagellum. It passes out through the cell wall.

The basal body attaches the flagellum to the cell wall and plasma membrane. It is composed of a small central rod inserted into a series of rings. In Gram negative bacteria two pairs of rings, the proximal ring and the distal ring, are connected by a central rod.

The outer pair of rings i.e., L-ring (Lipopolysaccharide ring) and P- ring (Peptidoglycon ring) are attached to respective polysaccharide and  peptidoglycan layers of the cell wall. The inner pair of rings i.e., M-ring (Membrane ring) and S-ring (Super membrane ring) are attached with the cell membrane.

In Gram positive bacteria only inner pair of rings are present. The S ring is attached to the peptidoglycan layer and M-ring is attached to the cell membrane.

Flagellation:

The number, position and arrangement of flagella varies with the species. The flagella may be restricted to one or both ends of the bacterium cell (polar flagellation) or may be distributed uniformly all over the body surface (non-polar flagellation).

On the basis of number and arrangement of flagella, bacteria are classified into the following types:

Polar Flagellatoin:

This type of flagellation is found in bacilli and spirillum bacteria. They are all gram-negative. Polar flagellation are following types:

I. Monontrichous: bacteria with a single flagellum located at one end or pole. All Vibrios are monotrichous. Eg., V.cholerae

II. Amphitrichous: bacteria with one flagellum at each pole or end of the cell.

III. Cephalotrichous : two or more flagella at one pole of the bacterium cell. Eg., Pseudomonas fluorescenes. The flagellum shows more than two curves.

IV. Lophotrichous: Bacteria with two or more flagella at both the poles of the cell. Eg., Spirillum volutans.

Non-Polar Flagellation:

Flagella are found all over the cell surface. It is of one type only.

Peritrichous: bacterial cell with flagella evenly distributed all over the cell surface. Eg., Bacillus tylphosus, Proteus vulgaris.

Atrichous: all bacteria which lack flagella are called atrichous. Eg., Diptheria bacilli, Lactobacillus.

Pili:

Minute, straight, hair-like, non-flagellar appendages found on the cell wall of many gram negative bacteria. They are rigid and composed of a protein called pilin. They may be several microns long but are smaller in diameter around 30-50 A⁰.

There may be 100-400 pilli distributed over the surface of the bacterium cell.

The structures which are shorter than the pili are called the fimbriea.

Function:

Some pili are used for the attachment.

Pathogenic bacteria use them to identify and to attach their host cells.

F or sex pili are involved in the transfer of the DNA during bacterial conjugation.

Cell Wall:

Enveloping the protoplast of bacterial cell, there is a thin, firm cell wall. It gives rigidity and shape to bacterial cell.

The bacterial cell wall is composed of  4 layers. The outer most layer is L₄, it is wavy and electron dense. Within this is a lighter layer called the L₃. Next is the inner dense layer – L₂ made up of mucopeptide. The inner most layer is the L₁.

The most important component of bacterial cell wall is peptidoglycon or murein (mucopeptide or muramic acid, Gr. Murus=wall). This polymer is made up of chains of alternating molecule of N-acetyl glucosamine (NAG) and N-acetyl muramic acid (NAM). NAG and NAM are linked by 1, 4, β-glycosidic bonds.

The cell wall of Gram +ve bacteria (Clostridium, Bacillus) is thick, homogenous, mainly consists of peptidoglycon (90%). The remainder being made up of proteins, polysaccharides and teichoic acid. Lipid content is very less in Gram +ve bacteria. The cell wall of Gram +ve bacteria is more sensitive to pencillin.

The cell wall of Gram –ve bacteria is chemically more complex and heterogenous. Peptidoglycan comprises up to 10% of the cell wall. The outer layer that surrounds peptidoglycan is two layered and consists of phospholipids, proteins and lipopolysaccharide mixture. Gram –ve bacteria possess more lipid. Teichoic acid is absent. The cell wall is less sensitive to pencillin.

The protoplast:

Within the cell wall is the living liquid called the protoplast. The protoplast is a clear water or slightly viscous substance.

It is differentiated into the cell or cytoplasmic membrane, cytoplasm and chromatin or nuclear body.

Cell or Cytoplasmic or Plasma Membrane:

At the surface of protoplast is a differentiated, delicate, fine membrane known as cell membrane or cytoplasmic membrane. It is about 75A⁰ thick. It lies close to the cell wall. Chemically it consists of phospholilpids with proteins and polysaccharides.

It is a selective permeable membrane which controls the passage of dissolved substances in an out of the cell. The cytoplasmic membrane also contains enzymes involved in enzymes and synthesis of capsule and cell wall material. It is also the site of ATP synthesis and the centre for control of flagellar motility.

Mesosomes

The plasma membrane of bacteria, at certain places, forms infoldings to form vesicle or tubular structures called the mesosomes. The term mesosomes was coined by Fitzjames. They increase the surface area of the membrane. They have respiratory enzymes, but they are not analogous to mitochondria. During division, they play a role in the DNA replication, septa formation, cell wall synthesis and spore formation.

Cytoplasm:

The bacterial cytoplasm is a complex mixtures composed of 70-80% of water and proteins, carbohydrates, lipids, inorganic ions. Organic matter is in the colloidal state.

The cytoplasm shows no streaming movement and contain no vacuoles. Cytoplasm is dense and transparent.

Bacterial cytoplasm contains nucleoid, plasmid, and ribosomes. Other membrane bound cell organelles like mitochondria, Endoplasmic reticulum, Golgi bodies are absent. Although a well organised chloroplast is absent, the photosynthetic bacteria have chromatophores.

The non-living inclusions are the storage granules of volutin, glycogen, lipid globules, poly-β-hydroxybutyrate (PHB).

Ribosomes:

In electron micrographs the bacterial cytoplasm is granular and contains numerous, minute, nearly spherical, hollow bodies called the ribosomes. They are composed of rRNA and proteins. Their number varies from 10,000 to 15,000 in a cell, which account upto 30% of total dry weight of the cell.

Bacterial ribosomes are of 70S type and is made up of two sub-units – 50S and 30S. Ribosomes are functional only when the two subunits are together. The association and dissociation of two subunits of ribosomes depends on the concentration of Mg²⁺ ions.

The 50S subunit has one molecule of 23S rRNA (3200 nucleotides), one molecule of 5S rRNA (120 nucleotides) and 34 different proteins. 30s subunit contains one molecule of 16s rRNA (1600 nucleotides) and 23 different proteins.

The ribosomes lie free in the cytoplasm but sometimes they occur in small groups called polyribosomes held by a strand of messenger RNA.

The ribosomes are sites for protein synthesis. Several antibiotic like streptomycin, neomycin and tetracycline inhibit protein synthesis on the ribosomes.

Nucleoid:

Area in the bacterial cytoplasm where the genetic material or DNA is present is called as nucleoid or genophore. Usually it is centrally located in bacterial cells and is equivalent to the nucleus in eukaryotes. However, it lacks nuclear membrane and nucleoli.

The shape of the nucleoid varies, often it is irregular, sometimes spherical or oval but elongated. The nucleoid is composed of about 60% DNA, 30% RNA and 10% proteins.

The DNA is single, long, circular, double stranded approximately 5X10⁹ base pairs and molecular weight of about 3X10⁹ daltons. The nucleoid can be stained with Feulgen stains.

Plasmids:

In addition to the nucleoid, bacterial cytoplasm normally contains one or more molecules of circular, double stranded DNA. Small, circular, self replicating and double stranded DNA molecule present in bacterial cell, in addition to nucleoid are called as plasmids. Lederberg coined the term plasmid.

They replicate autonomously, and inherited by both the daughter cells during the cell division. Some plasmids get integrated  into the bacterial DNA or chromosome. They are called episomes by Jacob Schaeffer and Wollman.

The number of plasmids ranges from one to hundred or more per bacterial cell. A plasmid contains 5-100 genes that govern several biological functions. Plasmids are not essential for the growth and survival of the bacterial cell, but they confer special characteristics like drug resistance, toxigenecity to the bacteria.

On the basis of functions, plasmids are divided into several types:-

i. F-factor (fertility) plasmids,

ii. R-factor (Resistance) plasmids

iii. col-factor (calicinogeny) plasmids

iv. Virulance plasmids conferring pathogenecity to mammals

v. Ti- plasmids of Agrobacterium tumifacines

vi. Ri-plasmids (root inducing) if Agrobacterium rhizogenes

Plasma Membrane

The cell has a different internal milieu from that of its external environment. This difference is maintained throughout the life of the cell by the thin surface membrane, the plasmalemma or plasma membrane. It controls the entrance and exit of molecules and ions.

The limiting membrane of the cell organelles like Golgi complex, endoplasmic reticulum, nuclear membrane etc., is known as cell membrane. The cell membrane and plasma membrane are collectively known as biological membranes.

Cell membranes may be defined as the membranes that serve as boundary of cytoplasm or organelles, exerts selective influence on the molecules and ions entering or leaving the cell or organelles, help in controlling intracellular melieu and influence the cell or organelle behaviour.

In some eukaryotic cells the different membrane systems make up as much as 80 percent of the total dry cell mass. Membranes serve not only as barriers separating aqueous compartments with different solute composition but also as the structural base to which certain enzymes and transport systems are firmly bound. They are very thin (about 8 nm) and flexible.

Composition of membrane:

The cell membrane mainly consists of proteins and lipid or lipoproteins. In certain cases polysaccharides, sialic acid, RNA and DNA have also been found. The ratio of protein to lipid varies from 1:0.8 to 1:4 and it depends, on the type of membrane, type of cell and type of organism.

All these chemical components are held together in a thin film – like pliable sheet of about 75A⁰ thickness, in three concentric layers. The middle layer is about 35A⁰ and outer layer on either side are 20 A⁰ thick.

Lipids:

The amount of lipids found in the membrane varies from 30 percent (mitochondria) to 70 percent of the total dry matter of cell membrane.

The most common lipids found in the membrane are phospholipids, glycolipids and sterols. All of them are amphipathic i.e., they have both hydrophilic and hydrophobic portions within a molecule.

The major proportion of membrane phospholipids is represented by phosphatidylcholine, phosphatidylethanolamine and sphingomylein. Glycolipids contain a sugar (glucose or galactose) in addition to fatty acids and sphingosine. The examples of sterols are cholesterols present in animal tissues, phytosterols present in plant cells and ergosterol present in ergot and  yeast.

Membrane Proteins:

Proteins represent the main component of most biological membranes. They play an important role, not only in the structure of the membrane, but also as carriers or channels, serving for transport, they may also be involved in regulatory or ligand-recognition properties. Numerous enzymes, antigens, and various kinds of receptor molecules are present in plasma membranes.

The different types of proteins present in membranes are:

i. Structural proteins: that form the backbone of the membrane and are strongly lipophilic in nature.

ii. Functional proteins: like enzymes that catalyse several physiological reactions (e.g., glucose 6 phosphatase found in membranes of endoplasmic reticulum and cytochrome oxidase present in mitochondria)

iii. Carrier proteins: that bring about the diffusion of substances across the membrane.

The proteins present in the plasma membrane are further differentiated into integral or intrinsic or integral proteins and peripheral or extrinsic proteins.

The intrinsic proteins make up 70 percent or more of the total membrane proteins. They are very tightly bound to the lipid portion and can be removed only by drastic procedures for isolation. The intrinsic proteins are highly insoluble in water solutions and are associated with lipids. These proteins may be attached to oligosaccharides , thus forming glycoproteins.

The peripheral or extrinsic proteins are loosely attached to the membrane surface, free of lipids and can easily be removed in soluble form by mild extraction procedures.

Structure of Plasma Membrane or Molecular models of Cell Membrane

Since substances soluble in lipid solvents penetrate the plasma membrane easily, in 1902 Overton postulated that the plasma membrane is composed of a thin layer of lipid.

Lipid Bilayer Model:

In 1925, E.Gorter and F.Grendel made the first proposal that the plasma membrane might contain a lipid bilayer. They extracted the lipids from human erythrocytes and concluded that the plasma membrane contained a bimolecular layer of lipids, or simply a lipid bilayer.

They also suggested that the polar groups of each molecular layer were directed towards the outside of the bilayer.

Later, it was found that some water soluble molecules could move across the cell surface and this resulted in the suggestion that the  plasma membrane was a mosaic of lipid and non-lipid substances.

Danielli – Davson Model:

In 1935, James Danielli and Hugh Davson studied the starfish egg membrane and proposed that the plasma membrane is made up of two layers of lipids sandwiched between two continuous layers of proteins.

According to this model, the protein and lipid molecule layers are electrostatically held together the former being the charged and the latter negatively charged. The lipophilic(hydrophobic) tails of fatty acids face one another in the centre and their hydrophilic heads face outwards.

They further envisioned the polar ends of the lipid molecules as being associated with a monomolecular layer of polar globular proteins. Each protein layer is found to be 20 A⁰ thick and lipd layers 35A⁰ thick, making the membrane 75 – 100 A⁰ thick.

This model cannot be applied to all membranes, as it reveals the definite proportion of lipids and proteins, which has not been found true. Moreover, recent studies reveal that proteins are found in form of particles and not as continuous layer.

Unit Membrane Concept:

It was proposed by Robertson . This concept was based on the study of the myelin sheath of a nerve fibre.

Robertson studied the structure of membrane with the help of electron microscope and found that all biological membranes show three layers (trilaminar) i.e., two outer layers  (electron dense) separated by a lighter middle layer. These correspond to two layers of proteins and a middle layer of phospholipids.

The molecular chains of lipids remain parallel to each other thus forming a bimolecular structure. The two chains remain linked by non-polar and hydrophobic inner ends of lipid molecules. Van der Waals forces bind the two lipid layers together.

The protein layer provides elasticity and mechanical resistance to plasma membrane. The unit membrane model is similar to Danielli-Davson model except that the protein layers at the exterior and interior are different. The outer surface has mucoproteins, while the inner surface has un-conjugated protein molecules are present. This shows the asymmetry of the protein surfaces on either side of the lipid bilayer.

Robertson provided evidence that the membranes of other cell organelles like endoplasmic reticulum, mitochondria, golgi complex have the unit membrane structure.

The Robertson’s unit membrane model was widely approved but remained unsatisfactory because it could not explain the dynamic nature and functional specificity of the membrane.

Fluid Mosaic Model

The most satisfactory model of membrane structure was postulated by S.J. Singer and G.L. Nicolson called the fluid-mosaic model.

This model postulates that the phospholipids of membranes are arranged in a bilayer to form a fluid, liquid-crystalline matrix or core. In this bilayer individual lipid molecules can move laterally, endowing the bilayer with fluidity, flexibility and a characteristically high electrical resistance and relative impermeability to highly polar molecules.

The fluid mosaic model postulates that that the membrane proteins are globular and are dispersed in the lipid bilayer. Thus, the proteins would form a mosaic like structure in the fluid phospholipid bilayer. In a way, these protein molecules resemble floating icebergs in the sea of lipids.

This mosaic is not fixed or static, since the proteins are free to diffuse laterally. Some of the proteins are partially embedded in the membrane, penetrating in the lipid layer (integral or intrinsic proteins) and some are superficially attached (peripheral or extrinsic proteins.

The important concepts of fluid mosaic model can be summarized as i) that biological membranes are quasi-fluid structures in which both the lipids and integral proteins are able to perform translational movements within the bilayer, ii) that the lipid and integral proteins are disposed in a kind of mosaic arrangement.

The fluid mosaic model accounts satisfactorily for many features and a properties of biological membranes. It provides for membranes with widely different protein content, varying thickness of different types of membranes, it account for the asymmetry of natural membranes, it accounts for the electrical properties and permeability of membranes.

The Micellar Model:

Many cell biologists suggested that membrane might consists of closely packed repeating units which are similar in structure.

In 1953, Hillier and Hoffman suggested that the membranes have a non-lamellar pattern, consisting of globular subunits known as micelles.

Each micelle is about 40-70A⁰ in diameter with a lipid core and a hydrophilic shell of polar groups. The protein components of the membrane form a monolayer on either side of the plane of lipid micelles.

The space between micelles represent water filled pore (4A⁰). These pores are lined partly by the polar groups of micelles and partly by the polar groups of associated proteins.

Functions of Biological Membranes

1. Membranes are living boundaries of the cytoplasm and cellular organelles. They form and continuous and unbroken sheets that divide the living matter into self-sustaining units to perform specialised functions.

2. Acts as a selectively permeable membrane- allowing appropriate substances into the cell and removing the inappropriate substances out of cell.

3. Allow the transport of metabolic essential substances

4. membranes have on their outer surface specific protein molecules acting as receptors, which unit with complementary substances or ligands providing external stimuli to the cell.

5. Perform different biochemical activities in the presence of enzymes.